Granite Outcrop Communities of the Piedmont Plateau in Georgia
Madeline P. Burbanck; Robert B. Platt
Ecology, Vol. 45, No. 2. (Apr., 1964), pp. 292-306.
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Mon Jun 11 16:06:20 2007
M . P. B U R B A K C K A N D R . B. PLATT
Ecology, V O ~45,
. NO. 2
GRANITE OUTCROP COMMUNITIES O F T H E PIEDMONT PLATEAU I N GEORGIA A N D ROBERT
MADELINE
P . BURBANCK
B. PLATT
Department of Biology, Emory University, Atlanta, Georgia
Abstract. Communities in depressions, occurring as islands surrounded by naturally
exposed granitic rock, were classified by the correlates of maximum soil depth and characteristic vegetation cover into: diamorpha communities, 2-6 cm; lichen-annual herb communities,
7-15 cm ; annual-perennial herb communities, 16-39 cm ; and herb-shrub communities, 40-50 cm.
The total flora of the 40 island communities included 76 species, but only 39 of these occurred
in five or more communities and were considered characteristic. The extreme environmental
conditions of high light intensity and low soil moisture content were indicated by the fact
that of the 20 plants present in over 50% of the communities, 18 were lichens, mosses, and
flowering annuals and only two were perennial flowering plants. The flora of the island
communities is distinct from that of border vegetation. Only three endemics are among the 39
characteristic plants. Seasonal aspects of the outcrop vegetation are striking. During the
winter months, hTovember through February, mosses and lichens are most conspicuous,
but seedlings of spring-blooming annuals are also present. From late February to May
there is a continuous succession of plants in flower, the majority of which complete their
life cycles before the hot dry months from May to August. In September the outcrops
are covered with the orange-yellow flowers of Vigzliera Porteri. Spring-flowering annuals
germinate in October at the time summer-flowering annuals are dying. The four types of
island communities described appear to represent stages in plant succession directly related to
edaphic conditions. Apparently the island con~munitieshave existed long enough in geologic
rime for an endemic flora to have evolved. The life of any one community, however, is
rneasured in hundreds rather than in thousands of years.
species are different, the types of plants and the
stages
of successiotl on exposed granite and acThis study is concerned with the characteristic
plant communities which occur on outcroppings cumulated gravel at Enchanted Rock, Texas, as
of granite gneisses and schists in the Atlanta area reported by Iihitehouse (1933), are similar to
of the Piedmont Plateau of Georgia, with em- conditions in Georgia. Winterringer and Vestal
phasis upon their seasonal aspects, the relative (1956) reported the presence and abundance of
abundance of their component species, and the plants on rock ledges in southern Illinois and discussed succession of plants on three types of rock
role of succession in their composition.
Granite and granite gneisses are present in a surfaces. Similar studies of granitic outcrops in
large part of this area (Watson 1902) and fre- the southeastertl United States have been made
quently occur as extensive areas of exposed rock. by Oosting and Anderson (1939) and Keever,
The best known is Stone Mocntain in DeKalb Oosting, and Anderson (1951) in North Carolina.
County, a massive granite monadnock which rises Harper (1939) reported species of plants from
to a height of 220 tn above the Piedmont Plateau granite outcrops in Chilton and Randolf Counties,
(1,686 ft above sea level, Herrmann 1954) about Alabama, areas similar both physically and florist15 miles east of Atlanta. East and southeast of ically to outcrops in DeKalb County, Georgia.
AIcVaugh ( 1943) studied the occurrence and
Stone Mountain are several lesser tnonadnocks
and small and large areas of flat or gently sloping origins of characteristic plants of the granitic flat
exposures of granite gneiss. Crustose lichens rocks of North Carolina, South Carolina, Georgia,
and mosses cover most of their exposed surfaces, and Alabama, but his floral lists were not comwhile in temporary pools, shallow soil pockets, plete and some of the generalizations on succescrevices, and on rubble heaps are plants which are sion on granite do not apply in the Georgia Piedcharacteristic of and often restricted to such out- mont. Numerous studies have been made over the
past 25 years on outcrops in the Atlanta area.
crops in this part of Georgia.
Studies of rock vegetation have been made The seasonal flora of Stone Mountain was studied
elsewhere in the United States. 111his study of by Smith (1938) and of Mount Panola by Matthe forests of Isle Royale, Lake Superior, Cooper thews (1941). Two papers by Baker (1945,
(1913) stressed the importance of crevice vegeta- 1956) reviewed the data accumulated by a number
tion and heath mats in early stages of establish- of life history studies, and summarizedd&e,,vegement of plant communities on rock. Although the tation of the local outcrops. More recently's&eral
Spring 1964
GRANITE OUTCROP COMMUNTTIES
papers habe appeared on the physiological ecology
of indhi ~1 species (Cotter 1958, Lammers 1958,
Cotter a d Platt 1959, Wiggs and Platt 1962)
and the effects of radiation on community structure (McCormick and Platt 1962). Lists of
mosses from Stone Mountain, Pine Mountain, and
Mount Arabia have been published by Schornherst
1945, Schnooberger 1945, Clebsch 1954, and
Breen and Purse11 1956.
This detailed analysis of the natural vegetation
of granite outcrop comtnunities near Atlanta was
undertaken to coordinate work on individual
species. Of the several kinds of outcrop cotnmunities, those which occur as relatively isolated
islands of vegetation surrounded by exposed, unquarried rock offer a unique opportunity for the
study of plant communities in geographically
separated but physically similar habitats. These
isolated plant communities may be divided into
two types. One consists of "solution pits with
intact rims" (Baker 1956) which retain water
long enough to limit vegetation to plants which
can survive submergence while rooted in shallow
soil, and the other consists of soil-filled depressions with eroded rims which only rarely contain standing water. Both types were studied.
1
Experimental areas selected were similar geographically, relatively undisturbed by quarrying,
ungrazed, and were neither tourist attractions nor
picnic spots. These factors ruled out Stone
Mountain, long popular for sight-seeing and now
a state park, extensively quarried Pine Mountain, and Mount Panola which is privately owned.
Of the other granite outcrops in the Atlanta
region, Mount Arabia and Rock Chapel Mountain
("Rock Mountain" on some maps) are the most
extensive and offer a variety of exposures. Two
miles west of Rock Chapel Mountain above Swift
Creek is another extensive area of exposed granite
formerly called the North Georgia Quarries
(Herrmann 1954) and more recently named
Mount Rollaway (Cotter and Platt 1959). The
greater part of the area has been quarried, but a
northeast-facing slope has a vegetation pattern
comparable to that of other undisturbed outcrops.
Mount Arabia, Rock Chapel Mountain, and
Mount Rollaway provide a variety of habitats,
namely : ( 1) mesophytic, usually forested areas
adjacent to the rock outcrops; ( 2 ) marginal communities (ecotones) between the forest area and
the cxposed rock; (3) exposed rock surfaces;
(4) natural depressions in the rock containing
soil; (5) rock crevices; and (6) rubble heaps.
The crevices vary in size from a crack in which a
293
tuft of grass survives to a deep fissure in which
a mature pine tree grows. The rubble heaps resulted from quarrying, and their flora varies depending upon the amount of soil present, the
source of the rubble, and its proximity to other
vegetation.
Attention was concentrated upon communities
in depressions containing soil (type 4 above) entirely surrounded by exposed rock and therefore
referred to as "island comtnunities." Many occur on Mount Arabia and Rock Chapel Mountain
but only a few on Mount Rollaway. Specific island communities on each of these three outcrops
were chosen to include (1) different elevations,
exposures, and habitats; ( 2 ) maximum number
of characteristic species; and ( 3 ) areas large
enough to support vegetation and yet small enough
to present the total aspect at a glance.
The island communities had certain physical
characteristics in common. The ~ l a n t s were
rooted in pockets of soil accumulated in depressions. All but three were located on a sloping
rather than a level part of the mait1 outcrop allowing precipitatiotlto run in and run off. T h e
soil was deepest toward the center of each depression and progressively shallower toward the periphery, or in some, deeper toward the upper
edge and shallower on the down-side. These soil
pockets were usually irregularly circular or elliptical with a maximum diameter of 9 m but more
often 5 tn or less. A portion of the community
usuallv occurred where the soil was shallow and
level with the surrounding rock. Opposite this
the rock might rise abruptly or gradually above
the soil pocket from a few to 20 or 30 crn or even
occasionallv to a meter. A t each side, the rock
sloped regularly or irregularly down to the level
area (Fig. 1, C, D ) : 111seven the soil level was
equal to or even slightly above the surrounding
rock (Fig. 2, A, B, C ) .
I n general, evaporation is very rapid, and permanent pools of water are rare. In one island
community, Arabia no. 10, water reltlained during
all but the driest summer weather. and its flora
was distinct from that of other communities. I n
two communities, water accumulated at times at
one end, but the other end contained soil and
characteristic vegetation (Fig. 2, F ) . Water occasionally stood in the shallow parts of some other
communities.
Forty communities were selected and numbered
on the adjacent rock with aluminum paint, 17 on
Mount Arabia, 16 on Rock Chapel Mountain, and
7 on Mount Rollaway (Fig. 3 ) . Each of these
was visited five times in 1957, and supplementary
records made in 1958 and the fall of 1959. The
294
M . P. BURBASCK A N D R . B. PLATT
presence and the abundance of each species of
moss, lichen, and seed plant were recorded. These
records were timed to coincide with seasonal peaks
or lows of growth otl the outcrops: March 27April 2, spring-flowering plants; May 19-23, late
spring flowers ; July 2-10, xeric conditions ; October 8-10, fall aspect before frost; December 3-5,
winter aspect after frost. Abundance was based
primarily on area covered, not on numbers of
plants, since such diverse plants as lichens, mosses,
annual herbs, leafy perennials, and vines were
compared.
Ecology, Val. 45, No. 2
During July and August, size, depth of soil,
depression depth, and slope of adjacent rock were
measured, and notes taken on exposure, dominant
herbs, drainage pattern, and distance to neighboring communities. The outline of each community
was sketched on graph paper (scale of 1. in. =
1 m ) in the field and a planimeter used to calculate
the areas.
The life histories of characteristic outcrop
plants were compiled from data collected weekly.
A different outcrop was visited each week and
records were based on the outcrops as a whole, not
FIG.1. Island communities, Mount Arabia. Arrows indicate D i a ~ n o r p h azones. A. Diamorpha community
with plants in bud, April 10, 1962; B. Lichen-annual herb community no. 8, April 16, 1961 ; C. Early spring
aspect of lichen-annual herb community no. 2, March 24, 1961; D. Fall aspect of community no. 2 with V i g u iera in bloom and Dia+norpha dead, September 29, 1951 ; E. Arenaria and Senecio in bloom in an annualperennial herb community, April 10, 1962; F. Annual-perennial herb community dominated by S e ~ j & o with
last year's Andropogon and Viguiera stalks in center, April 10, 1962.
, "'t,
Spring 1964
G R A N I T E OUTCRl3~ C O M M U N I T I E S
just o n G t h eplants in the 40 communities. T h e
foll wing aspects of life cycles were recorded:
dor % v ( n ogreen parts evident), resumption of
growth, seed germination, flower production,
fruit production, and vegetative portion persistent.
3
Comwzunity types
O n the basis of maximum soil d e ~ t hcorrelated
with characteristic flora, island communities were
divided into four categories as follows : diamorpha,
lichen-annual herb, annual-perennial herb, and
herb-shrub.
Diamorpha cor~vvcunities.-Those communities
with the shallowest soil were designated diamorpha communities (Fig. l, A ) . The four in
this study, with maximum soil depths of 2, 4, 6,
and 9 cm respectively, supported only one
dicotyledonous plant, Diamorpha cymosa, and
that in great abundance during its growing season.
111one community the only additional plant was
a single clump of leafy lichens. T h e other three
contained well-established plants of Cladonia
leporina and Campylopus sp. T h e 9-cm depth
community included Cladonia car/oliniana associated with C . Zeporina, and a few plants of Viguiera
Porteri, which died before flowering. F o r approximately 18 weeks through the summer and
early fall after the Dia~eorphadies, these habitats
contain very few or no living plants.
Lichen-annual herb communities.-These communities were characterized by having a maximum
soil depth of 7-15 cm inclusive and a flora of
lichens, mosses, and annual herbs (Fig. 1, B, C,
D ) . Twelve species occurring in at least six of
the ten lichen-annual herb communities studied
and considered characteristic are : Cladonia
leporina, Cladonia caroliniana, Campylopus sp.,
Agrostis Elliottiana, Bulbostylis capillaris, Arenaria brez~ifolia,Crotonopsis elliptica, Diawaorplza
cymosa, Hypericum gentianoides, Linaria canadensis, R u m e x hastatulus, and Viguiera Porteri.
A few established plants of Senecio tomentosus
occurred in four of the lichen-annual herb communities and seedlings in a fifth, but this perennial
is more characteristic of soil pockets with soil
depths over 15 cm. Other species in two, three, or
four communities were Cladonia rangiferina, Cladonia spp., Ditrichum palliduwa, Bruchia Sullivanti, Polytriclzum commune, Juncus georgianus,
Panirum meridionale, Cyperus granitophilus,
Schoenolirion croceum, Krigia virginica, and Talinuwz teretifolium. Present in only one of the
nine were Cladonia grayi, Isopterygizbm micans,
295
Aristida dichoto~~ta,
Anzjhin~ttlzuspztsillus, Gnaphalium sp., and Opuntia humifusa.
Environmental conditions at the periphery of
the lichen-annual herb communities were similar
to those of diamorpha communities, there frequently being an outer zone of Diawzorpha only,
with a more diverse flora on the deeper soil (Fig.
1, B ) . In some lichen-annual herb communities,
Cladonia leporina and C. caroliniana occupied
almost the whole area with some Diamorpha at
the edges and Cawzpylopus and annual seed plants
scattered anlong the lichens. I n such communities
the gray of the lichens was a backdrop for the
white and green of Arenaria and Agrostis respectively in the spring, the gray-green Crotonopsis
and the brighter green, scale-leaved Hypericum
in the summer, both with inconspicuous flowers.
I n the fall the bright yellow-orange flowers of
Viguiera appeared. Yiguiera Porteri is very susceptible to drought, and it was not unusual for
seedlings to be common or abundant throughout
a lichen-annual herb community in late spring and
early summer but by flowering time there be
only a few or no living Viguiera plants. Thus in
contrast to seasonal diamorpha communities,
much of the area of each lichen-annual herb community was covered by persistent cladonias, supplemented by a year-round succession of annual
herbs.
Annual-perennial
herb
cowzz.ttzunities.-Soil
pockets with a maximum depth of from 14 to 39
cm support a mixed flora of lichens, mosses, annual and perennial herbs, and an occasional woody
plant and are called annual-perennial herb communities (Fig. 1, E. F ) . The flora of the annual-~erennialherb communities is the most diverse of any of the island communities. Most of
the species listed in Table I are represented. Not
all these species occurred in every annual-perennial herb community, however. The characteristic
plants of the shallower soils were usually present
at appropriate soil depths; occurrence of other
lichens, mosses, and herbs varied with the exception of Polvtrichum commune. Schoenolirion cvoceum, and Senecio tomentosus which were frequent and abundant in all annual-perennial herb
communities. P. comwzune was present in every
annual-perennial herb community but in only four
lichen-annual herb communities. This moss
covered over half the area of five annual-perennial
herb communities at Rock Chapel Mountain and
of three such communities at Mount Rollaway.
T h e narrow, dark green blades of Schoenolirion
leaves from a deeply buried corm were prominent
from November until they yellowed and dieti early
in June. Senecio towzentosus had green leaves all
296
&I. P. BURBASCK A N D R. B. PLATT
year, and the plants tended to form clumps near
the centers of the communities in the deepest and
moistest soil (Fig. 1, F ) .
Other plants that were characteristic of annualperennial herb communities but which did not
achieve any degree of aspect dominance were
Cladonia spp., Bruchia Sullivanti, Aulecomni.ttm
palustre, Isopterygi~~wzmicans, And7,opogon virginicus, Juncus geo~,gianus, Gnaphalium sp.,
Krigia virginica, Polygala curtissii, and Rumex
hastatulus. Sod lichens, Cladonia spp., were fre-
Ecology, Vol. 45, No. 2
cluently seen it1 annual-perennial herb communities
but not restricted to them. Although not present
in diamorpha communities and in only four lichenannual herb communities, the tiny moss, Bruchia
Sullivanti, grew at the edge of almost every annual-perennial herb community it1 a crust of soil
even shallower than that which normally sup~z
ported Diamorpha cymosa. A ~ ~ l a c o n z n i u palustre occurred as scattered clumps while Isopterygiuwz micans characteristically formed a flat mat
near the center of the communities under a shield-
FIG.2. Communities on Mt. Arabia, Rock Chapel Mt., and Mt. Rollaway. A. Dried Alzdropogolz stalks
prominent in winter aspect of herb-shrub community no. 15, Mt. Arabia, February 14, 1960; B. Fall aspect of
community no. 15, Mt. Arabia, September 29, 1961; C. Herb-shrub community no. 11, Rock Chapel, March 29,
1961; D. Midsummer dominance of Viguiera in herb-shrub community no. 2, Rock Chapel, July 29, 1960;
E. Large weather pool on top of Mt. Arabia, April 10, 1962; F. Polytrichuril and Juncus georgiat~ztsroo ed in
soil, and inifihianfhur present and blooming among rocky debris in temporary pool basin, in water rudp(pll
a 20" slope, community no. 6, Mt. Rollaway, March 25, 1960.
Spring 1964
GRANITE OUTCRI3~ C O M M U N I T I E S
297
ing o,over of herbaceous plants and occupied only area with shallow soil. Rather than a peripheral
a smhllrprcentage
of the total area. Juncus zone of Diafizorpha and lichens, masses of Polygeorgianus and Andropogon virginicus plants trichum frequently grew at the edges of the comtended to form discrete clumps, the Juncus near munities, and a larger proportion of the total
a moist edge of a community and associated with area was occupied by perennial plants than in the
Polytrichuvtt covrcvvcune (Fig. 2, F ) while the communities with shallower soil. Several sedges
Andropogon was usually near the center or where and grasses such as Carex comvl%unis,Scleria olithe soil was deepest (Fig. 1, F ) . T h e small, gantha, and Panicum species were more abundant
slender plants of the annual Krigia virginica were in the herb-shrub communities than in the few
showy ;Then in bloom, but this species, as well as annual-perennial herb communities in which they
Rumex hastatulus and Gnaphalium sp., are con- occurred. Two herbs recorded only from herbsidered weedy species and not typical of the out- shrub communities were Rhexia wzariana and
crop flora. seedlings of Gnaphaliuvlz are evident Ascyruut?,Hypericoides.
Special communities.-One aquatic and several
during winter months but decrease in number as
spring-flowering plants mature. Polygala curtissii disturbed habitats were also studied. Water-filled
is an annual which blooms during the summer solution pits, such as community no. 10 and others
and on into the fall, contributing scattered patches on top of Mount Arabia (Fig. 2, E), support a
of bright pink t o an otherwise rather colorless few species of aquatic plants, particularly the two
period. Additional plants which occurred in about endemics Isoetes vlzelanospora and Amphiantlzus
one-half the annual-perennial herb communities pusillus. T h e former is dominant and perennial,
were Ditrichum pallidufiz, Tradescantia olziensis, often carpeting the floor of these pits with its
bright green quill-like leaves, while the latter, an
and Talinutuz teretifoliuw.
There were six species which occurred in less annual with small submerged and floating leaves,
than half of the 20 annual-perennial herb com- is scattered throughout. Conditions in these pits
munities. T h e endemic sedge, Cyperus grani- are often severe, since the water may dry up for
toplzilus, grew as scattered tufts in the shallower long or short periods. When refilled by rain,
parts of eight; small cups of Cladonia grayi were however, the plants either begin growth anew or
identified in seven and may have been present in continue from the point where growth had ceased.
two others; seedlings and a few mature plants of There was water in community no. 10 at the time
Facelis retusa, were observed in six; Houstonia of each of the five floral surveys, but the absence
pusilla and Coreopsis grandifiora were present in of Amplzianthus on July 4 indicated an intervening
four but were more abundant on the outcrops in dry period.
Community no. 16 at Mount Arabia developed
other habitats; and isolated plants of Opuntia
in a disturbed area with soil and rubble from
humifusa occurred in four.
Herb-shrub eomvlzunities.-Five
communities quarrying operations. I t was selected to include
with a maximum soil deuth of 40-50 cm and with the endemic Oenothera fruticosa var. subglobosa.
small trees or stumps of trees in addition to herbs This species normally occurs as part of the
were called herb-shrub communities. Rock Chapel marginal or ecotone vegetation at the base of the
no. 2 contained a juniper stump 22 cm in diameter mountain where exposed rock alternates with
but no living woody plants (Fi,g. 2, D). T h e wooded areas, as well as in accumulations of soil
other four herb-shrub communities contained the and rubble. Although community no. 16 conwoody vine Smilax glauea and at least one small tained species typical of annual-perennial herb
tree, an Amelanchier arborea (3 m ) , Juniperus communities, there was also an unusually large
virginiana (3.8 m ) (Fig. 2, C ) , or a Prunus sero- number of species characteristic of the border
tina (1.8 and 2.5 m ) (Fig. 2, A , B ) . Other vegetation such as Coreopsis grandiflora, Geranwoody species present were Gelsevlziuvl%semper- ium carolinianufiz, Houstonia pusilla, Oenothera
virens, Parthenocissus quinquefolia, young Pinus fruticosa var. subglobosa, Parthenocissus quintaeda, Smilax Smallii, and Vaccinium ahoreum. quefolia, Portulaca Smallii, and Saxifraga virWith the exception of the woody species, the giniensis.
Community no. 14 on Mount Arabia may also
floral list of the herb-shrub communities was similar to that of the annual-perennial herb communi- have been affected by quarrying operations since
ties with a few additional species, but the relative its site contained loose rocks and rubble and was
abundance of the species was very different. located between an undisturbed slope and a partly
Physically these communities differed from the quarried area. T h e presence of Coreopsis, Houother types in that the soil was level with the sur- stonia, and Portulaca in addition to the usual isrounding rock o r slightly above it with very little land community species is further evidence that
298
M. P. BURBANCK A N D R. B. PLATT
such disturbed areas support a different flora than
do undisturbed communities.
Size of community and soil depth
Although communities were chosen not at random but with an approximate upper size limit, the
areas of individual communities varied from 1.3 to
56.9 sq. m (Fig. 3 ) . The maximum soil depth
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COMMUNITY DESIGNATION BY VEGETATION TYPE
FIG.3. Comparison of area with maximum soil depth
for 39 communities (numbered as in Table I ) grouped
according to vegetation type and arranged according to
increasing soil depth. A = Mt. Arabia, R = Mt. Rollaway, RC = Rock Chapel Mt.
ranged from 2 cm in a diamorpha community to
48 cm in an herb-shrub community. There was
not a close correlation between area and soil depth
for all communities (Fig. 3 ) , but the increase in
average maximum soil depth of community types
corresponded roughly with an increase in the
average area for each type :
Type of
community
Average
area (m2)
Diamorpha
2.8
Lichen-annual herb
5.5
Annual-perennial herb 12.4
Herb-shrub
25.5
Average maximum
soil depth (cm)
5.3
10.5
24.5
44.0
Presumably, as natural forces act on the underlying rock, disintegration does not proceed uniformly under the soil, but most rapidly a t the
deepest part of the concavity. Thus the increase
in diameter is probably not always proportional
t o the increase in soil depth.
Flora of island communities
Species recorded.-Presence
and abundance
records were kept for the 76 species listed in
Table I. As far as possible nomenclature follows
that of Gray's Manual of Botany (Fernald 1950).
Mushrooms, liverworts, and green algae were oc-
Ecology, Vol. 45, No. 2
casionally seen but are not included. Lichens and
mosses, however, are prominent and significant in
island communities, and since complete lists have
not been included in previous studies of the area,
a special effort was made to identify them. Those
most frequent, abundant, and readily recognized
are included in Table I.
I n addition to the five species of Cladorcia listed
(Table I ) , three lichens occasionally collected
from island communities were Cladonia subtenuis
(Des Abb.) Evans, Cladonia furcata (Huds.)
Schrad., and Cladonia sylvatica (L.) Hoffm. The
listing Cladonia spp. represents semicircular, compact, gray masses, usually 2-6 cm in diameter,
which occur on shallovr~soil near the edges of communities. T w o types were distinguished, those
whose surfaces are somewhat leafy with the tips
of the flakes spreading or recurved depending upon moisture conditions, and those which are more
compact with the upright flakes crowded closely
together as in the pile of a rug. Positive identification could not be made ( D r . Mason E. Hale,
private communication), but the specimens belonged to the group known as sod lichens and
some were probably Cladonia apodocarpa.
The listing Campylopus sp. includes the two
species C. introj'lexus and C. flexuosus. Originally it was not known that there were two species
present. Subsequent spot checks on all three
outcrops indicated that the two species intermingle
without showing dominance over each other and
both occupy the same ecological niche. Therefore,
Campylopus sp. is used with the assumption that
either or both of the species may have been
present.
Complete presence and abundance records were
not kept for five mosses (addendum to Table I )
because field identification was difficult. Pohlia
nutans (Hedw.) Lindb., reported here from
Mount Arabia, was first found south of Tennessee
in 1954 at Stone Mountain (Clebsch 1954). The
species Bruchia Sullivanti Aust., frequent on
Mount Arabia, Rock Chapel Mountain, and Mount
Rollaway, is also newly reported from granite
outcrops of Georgia.
Cuscuta was not seen in flower and fruit and
hence could not be identified to species. Seedlings
of Diodia and Gnaphalium never reached maturity
in island communities although Gnaplzaliz~~~z
pztrpureum L. was identified in border vegetation.
Panicutuz spp. represents several unidentified
species both annual and perennial.
Observations on the outcrops bear out the conclusion of McVaugh (1943) that Coreopsis saxicola Alexander probably is not "sufficie tly distinct" from Coreopsis gmndiflora Hk$&l~$?
be
S p r i n g 1964
299
GRANITE OUTCROP COMMUNITIES
TABL?I . Species recorded f r o m 40 island communities a n d t h e n u m b e r o f communities i n w h i c h t h e y occurred
11 3"-a
I l'.
I
Species
1
I
N u m b e r o f communities
M t.
Lichens Cladonia mistatella T u c k . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cladonia caroliniana T u c k . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cladonia leporina Fr . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cladonia grayi Merrill . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cladonia ranqiferina
(.L ..) W e b. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..
Cladoniaspp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mosses Polytrichum commune H e d w . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Bruchia Sullivanti A u s t . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ditrichum pallidum (Hedw.) H a m p e . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Campylopussp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Aulacomnium palustre ( W e b. & M o h r ) Schwaegr . . . . . . . . . . . . . . . . . . . . . . . . . Isopterygium micans (Sw.) B r o t h . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sphagnumsp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Fern allies
Isoetes melanospora Engelm .
Conifers
P i n u s T a e d a L. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Juniperus virginiana L . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Flowering plants-Monocotyledons Festuca octojlora W a l t . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Uniola laxa ( L . ) B S P . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Agrostis Elliottiana Schult . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Aristida dichotoma Michx . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Panicum lanuginosum Ell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Panicum meridionale Ashe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Panicum scoparium L a m . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Panicumspp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Andropogon virginicus L . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cyperus granitophilus M c V a u g h . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cyperus ovularis (Michx.) T o r r . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Bulbostylis capillaris ( L . ) C . B . Clarke . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Scleria oligantha Michx . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Carex communis Bailey . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Carex complanata T o r r . & H o o k . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Carex umbellata Schkuhr . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Commelina erecta L . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Tradescantia hirsuticaulis Small . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Tradescantia ohiensis R a f . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Juncus georgianus Coville . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A l l i u m Cuthbertii Small . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Erythronium americanum Ker . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Schoenolirion croceum (Michx.) A . G r a y . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . SmilaxglaucaWalt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Smilax Smallii Morong . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Flowering plants-Dicotyledons
Rumex hastatulus Baldw . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Portulaca Smallii P . W i l s o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
T a l i n u m teretifolium Pursh . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Arenaria brevifoolia N u t t . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Liriodendron Tulipifera L . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Diamorpha cymosa ( H u t t . ) Britton . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Saxifraga virginiensis Michx . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Amelanchier arborea ( M i c h x. f.) Fern . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Prunus serotina E h r h . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Geranium carolinianum L . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Polygala curtissii A . G r a y . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Crotonopsis elliptica W i l l d. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . AcerrubrumL. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Parthenocissus quinquefolia ( L . ) Planch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ascyrum Hypericoides L . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hypericum gentianoides ( L . ) B S P . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Opuntia humifusa R a f . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Rhexia mariana L . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . /
Rock
I
M t.
I
300
Ecology, V O ~45,
.
M . P. B U R B A K C K A N D R . B. PLATT
Table I.
NO.
2
(Continued)
I
Species
-
1
/
N u m b e r o f communities
Mt.
Arabia
(17)'
1
Rock
Mt.
Chapel M t . Rollaway
(16)
(7)
1
Total
Oenothera fruticosa L . var. subglobosa Small . . . . . . . . . . . . . . . . . . . . . . . . . . . . Vaccinium arboreum (Marsh.) N u t t . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Gelsemium sempervirens (L.) A i t . . . . . . , . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C u s c u t a s p. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Linaria canadensis ( L . ) D u m o n t . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Amphianthus pusillus T o r r . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Lindernia monticola Muhl.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Plantago virginica L . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Diodiasp. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Houstonia pusilla Schoepf.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . G n a p h a l i u m s p. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Facelis retusa ( L a m . ) Sch. Bip.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Viguiera Porteri (A. G r a y ) B l a k e . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . CoreopsisgrandiJEoraHogg . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Senecio Smallii B r i t t . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Senecio tomentosus Michx.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Krigia viryinica ( L . ) W i l l d . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Addendum-Presenc e or absence o n l y indicated Pleuridium subulatum ( H e d w . ) Lindb.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Dicranum condensatum H e d w . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Dicranum scoparium H e d w . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Weisia controversa H e d w . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Pohlia nutans ( H e d w . ) Lindb.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
x
x
-
x
x
I
1Number of experimental communiiies.
recognized as a separate species. Coreopsis, 2, E) and in a quarry pool at Mount Rollaway.
moreover, does not occur "in immense numbers Amplzianthus pusillz~sgrows in pools with Isoetes
on all the outcrops" ( McVaugh 1943). Tfiguicra, and also in certain conimunities on the sloping
not Coreopsis, is the plant which covers the granite sides of the outcrops m,hich contain water for days
outcrops of this area with yellow flowers in the or weeks. I11 &/larch 1960 there was no water
late summer and fall. Coreopsis is not abundant standing in community no. 6, Mount Rollaway,
in island communities but is more characteristic but plants of A?rzplziant/zus were in bloom among
the "rubble" (Fig. 2, F ; the outline of the temof disturbed areas and border vegetation.
Endemics.-Although
a high incidence of en- porary pool is indicated by the light area free of
deniisni on granite outcrops has been stressed by Parz~teliarosettes.).
Species distribzlfion and abundance.-The
disMcVaugh (1943) and Baker (1945, 1956), the
list of plants which occur in island cornniunities tribution of species on the three outcrops indicated
does not contain a large number of endemics. that there is a characteristic flora of the outcrops
McVaugh stated that more than a third of the 44 of this region rather than a flora peculiar to any
characteristic flat-rock species were endemic. Of one outcrop. T h e island communities had various
the 39 species recorded from at least five island exposures, but the environmental conditions on
communities, only three were endemics (Cyperzis these gentle slopes did not vary sufficiently to
g?,aniiop/?ilzw, Juncms geo~,gianus, and T/iguiera influence either the floral make-up or the type
po?*feri). Other endemics occasionally found of comniunity. Although 21 of the 76 plants
were Isoetes 17lclanosfiora, Awzplziantkiis pltsillus, listed in Table I were recorded from only one
Oenothera ft,ztticosa var. sz~bglobosa, and Portzt- outcrop, some were species with a very scattered
laca S17tallii. Ocnotlzera, Portulaca, and many of distribution; some were species characteristic of
the other ten endemics listed by McVaugh are disturbed areas; and some were species typical
characteristic of the vegetation bordering the ex- of the border vegetation. Splzagnztm sp., Uniola
posed rock rather than that of the island communi- laxa, Festzica octojlora, Isoetes 71zelanospora,
ties. Isoetes 71zelanospora and Azqlpkiantlzzts pusil- Lindernia ~qzonticola, and Rlzen-in i?rarinnn were
lzts are limited in distribution by special habitat recorded only from Mount Arabia, Jzcnipcrzts virrequirements. T h e former occurs in persistent, giniana only from Rock Chapel Moun in and
shallow pools on the top of Mount Arabia (Fig. Pimirun, scopnrizliil only from Mount 'AIllI{,way,
Spr111cI004
GRASITE
P L A N T S A N D TOT&,
N U M 2 F R OF C O M N J N I T ' E S
N NHICh EACH C C C U 7 j
IIAMOHPHC
CL iIr'.i
IEPCR'VL
CCMPILOPUS
40
38
38
v G~.
1 1 l.
FRb
37
OUTCROI' C C ) \ I ~ I U N I T I E S
ABUNDANCE
30 1
RATINGS
HYPERlCdM
35
CGROSTIS
'i.
ARENARIC
34
CROTONOPSIS
32
'IA2OVl:,
C i K C . h AU:,
3 0
CLAOOPI,A i?
30
LINARIA
7- 9
POLYTRICHUM
i9
WLBOSTILIS
i
BRUCHIA
is
SOPTERYGIUM
25
RUMEX
25
SCHOENOLIRON
ii.
SLNECIO
?3
ShAPHALldM
22
KR,uIA
JUhCUI
I8
AULCCOMhlbM
8
JITRICHUM
7
FO-Y'>ALA
6
iU2GC?CuCY
4
CLLC;hlG
SQ:,Yl
Ii
TLLhLIM
2
CIPERdi
I'
TR;2FS'-il.T
C O n l E V S l ~
CCit "f , I i
8
OPUNTA
CL,I2Ohl;
RiU~~l'ERlNi,
PANIC: M M L Q : C O N A L E
7
FCCELI!
7
C A R i X CCMM,Il.lS
6
C L A D O N C CG S T C T E L L L
6
PINUS
6
LRISTISA
5
SMILAX ' b L i U i A
5
~
I . . 4
Coniparizon oi al~unrlanceand irecjuenc!- (numher of comn~unitiesin which each species occurred)
i~i
'cliar;~ctc.ri~tic
outcroll ~~lant.. Al~untlance ratings : I-rare ; 2-infrequent ; 3-con~n~on
; 4-abundant in a localixc.11 are;{ I ; ~ tlva,t oni.-~lua~.ter
of total area) : .;-abundant (bazccl on the greatest abundance attained in a
i.i\ c 11 c o i i i n i u ~ ~ i t tyl l ~ r ~ n1057'i.
g
11iit tlic,se ,sl)ccies \vpre seen in, o r lia\-e ljeen re- characteristic p l ; ~ ~ l tof
s island cominunjtics differ
~ j o r t dfrolli. similar 1ial)it:~tso n a t Icast o11e otlier markedly f r o m l r c \ - a u g h ' ~ list of characteristic
of the thrcc o u t c r o l ~ s . \\-eed!- plants \vlnicli Ivere illants of the flat rocks of southeastern L'nitetl
rccoi-tletl fro111 only one outcrop but \vliich ma!.
States i h l c \ v a u g l ~ 1913 1 . O n l y 13 species a r e
occur near roads o r tlist11rl)ed areas o ~ i:dl three connilion to l l c \ ~ a u g l i ' s list of 4 1 characteristic
outcrops a r e Lliutiicr anit1 Citsi.iita. Seetlli~igs of l ) l a ~ i t sa n d o u r list of 39 species. T h e species of
i1ri.i. ritl,i,iliii aiid 12ii-iotl~~~~clTro~l
T1i1ipiJ7
c i,a ~ e r c the island coniniwnities a p p e a r to form a flora disfount1 at niore t l i a ~ i one outcrop a s p a r t of tlic tinct from the total flora of granite outcrops.
I n a large n u m l ~ e rof island c o m ~ n u n i t i e s specica
,
I ~ o r t l r r 1-cgetation but recortletl from oiily on(.
isla~itlconlmtunity. O t h e r s similarly rccortletl a r e attained ail a b u ~ l d a n c erating of only r a r e o r in.i ~ii~-ln~ic.liic~i*
c71.71oi.c~ir. .'Yo.t-ifrc7~gc7 ~,ii~~jiriicrzsis-,
freciu(~11t( 1;ig. 4 ) ~ v h i c hsuggests that : ' ~ tloral
.\'(,ii(,(.io Siizallii, ant1 Ti.ncii~scc711tia1iii.sittic-tritlis. conil)o"tio~i tcntls to I)e cliverse rather t h a r ~,. -,..
'I'l~u.;, of tile 76 sl)ecies. only 1rather t h a ~ 21
i \\.eri. 11:itetl I)!- onc o r tn-o species, except in t h e s h a l l o n
Iiliiitc(1 to a single outcrop. Ilven these, Cai,c~.l. soil c o ~ n ~ n u n i t i e s . A fe\v species tlo 1)ccollle
c-oi~:pi~riiirtaatit1 .Srlci,ia oliija~flin from J I o u n t al111111:lalitin sollie c o n i m ~ i ~ i i t i c sp:irticularly
,
at
A\~-al)i;i.
C't!rr.r 1r11~l,c~llc7ttr
from l l o u ~ i tRolla~va!.. c?i-tai~lc,;isons o r t l t ' v ( ~ l o l ~ ~ i l e ~;t;lgc";
it;~l ( F i g . 2.
fro111 Tiocli Clnappl I)),a n d in general g r e a t a l ) u n d a ~ i c eis correlatctl
ant1 iT'(rizi(.itli! 1a~l!tiji~ios11111
l r e ) ~ i ~ ~ tIIIZIJ: ~ i ~wrll
i . liave ~viclerclistriI~~itic)~i.
\\.it11 high frequency. T h r e e spccics were cscep'I'lie 3') sl)ccies \vliicli occur in five o r niore oi tions to this ge~neralization. C t r ~ i l p ~ d o p s~pt ,s a n d
thi. 1 0 c o m m ~ i n i t i c~tiiclic.tla r e consideretl tyl1ic;il Cltrrlotlin spp. occurred a s scattered patchm i l l
g
\\.it11
( F i g . 4I .
'I'liey cc>nil)i-iqc.all(-tut 50C; of the tot:\\ shnllo~vsoil ~ v i t h o u tever l ~ e i ~ i"al~untlant"
flora. Of the 20 species present in more than half recl)ect to the total area of a c o ~ n n i u ~ ~ i I2iu(71.i(r
ty.
tli(> coliimu~iitiesonly tivo a r e perei~nialfloxvering c-ciiltrdc~.si.s, wit11 n-idesy~reatldistri1)ution on and
i t s . l'lic others a r c fon-cring a11nu;lls. mosses. off t h e granite outcrops, appenrecl u n a l ~ l eto com:111(1 l i c l i e ~ i .wliicli :ire \\-ell atlal)tetl to tlie xeric
petc. very successfully with island community
sllallo\v soil co~iclitiolistyl~icalof islnntl cc-~ni~iiuni- sl~ecies. tie. on gra~iitc'o1ltcrol)s.
Scnsorlal nspcct.c.-The
different seasonal as-
1 lie l i s t . ( ~ tlit.
~ i 20 ~iiobtt ' r c c l ~ ~ e ant1
~ i t (li tlie 30 pects of the vegetation of the granite outcroljs is
?.
Ecology, \-01.
AN11 K . B. I'LATT
45, KO. 2
SPRING FLOWERING PLANTS
very str~king. This part of Georgia has mild
ANNUALS
n i n t e r i , usually without snow. O n the outcrops,
I
I
1
I ire I
I
I
I
I
I
I
spring-blooming annuals germinate in the fall and
o\ er\?inter as low-growing seedlings. llosses
and lichens are the most conspicuous plants of the
island communities during the months of December, January, and February. During late Fehruary, hlarch, April, and May there is 3 profusion
of hloom (Fig. 1 , E ) . I n the shallow, peripheral
soil is the red-leaved, white-flowered Dia7ilorpha
PERENNIALS
cyvlosn. Interior to it a ring of dark green P o l y t~ir11111i1c o1117izlt~te
may occur, mixed with the delicate, ~vhite-flo\?eredArefluria brczifolia. I n the
center the taller, .ellow flowers of S c ~ t e c i oto71tcfitoszds rise aljove their broad, gray-green leaves.
mncus
Retneen the S c ~ z c c i oand the Arenaria or near the
periphery of island communities which do not ha1 e
complete rings of Dia71rorplza and Polyirichzti~lare
SUVVER FLOWERING PLANTS
the tiny seeclings of later hlootning annuals, inANNUALS
I
1
I _-x I
I
I
I
I
I
I no, I oat
termingled with the dead stalks of the previous
season ant1 tufts of the hright green grass, Agi+ostis Elliottiic~za I n tmany cotnmunities the quilled
green lea\ es and yellow racemes of Schoi~nolirion
crorelllil tlominate this zone for a hrief time in
April
Summer is the least favorable season. Drought
and high teml)eratures kill inany plants and cause
the mosses and lichens to look dried and ihrivPERENNIALS
elled. Yet there are always a feiv species l~looming
such as scattered plants of Hypcricltill gllizfiaizoidcs, antl \vliere moisture is sufficient, great
~iumhersof ieedlings of l/icjzticm occtlr ( F i g 2.
D ) . By September, the T'igldicrtr. xvliich produces scattered floivers as earl! as June, is in full
._-----------------_______.
l~loom,the gray-green, 10- to 12-inch-high plants
of Croto~lop.ci.s are mature, and the tall green
------blatles of Aizdropogn~z h a l e replaced the golden
h r o ~ v nones so conspicuous during other seaion,
I
. 5.
Schematic reprewntation of life cycle. 11i
cl~aracteristic outcrop plants. (;reell \-egetati\.e part.;
(Fig. 2, A , R 1 .
ahove the ground a r e represented hy a solid ha,e line:
Graphic representation of the life c\cle, of dormancy hy a broken base line; time o i flowering 1)y
22 of tlie most fretluently occurring seetl p l a ~ l t t solid line a11oL.e base line; and time o i iruitilig hy wlid
f ~ o mtlie granite outcrops are presented it1 Fiq. 5, l i ~ l ea l ~ o ~floweritig
~ ~ ~ c r i d i ~ illas
l t u lt \~i o~
e
line. Pc~tzicu?~~
grouped according to time of flo~veritlgand annual flo\vering and fruiting periods per year.
or ~ x r e n n i a lhal~it T h e data for these life c!clei
represent com1)ined o b s e r ~ a t i o n s from all three ting-spritlg-floivering antluals are preparing to
outcrops ant1 from an! island cornmunit ieen
11100111 or are completing their life cycles.
One
F o r example, the height of 1)looming of Polygtrla e s c e ~ ~ t i owas
n summer-flo~veringHypcricttnz gclzcirrtissii \ \ a s in June ant1 J u l ~ .hut I)ecause of a titr~loidcs which germinated in Octol~er, overfew 1)lants which persi\tetl on ?IIount Arabia, Fig. ~ v i ~ ~ t e ras
e dtiny seedlings, and resumed growth
5 s h o ~ v sthe flowering time extentled ~ n t oearl!
[luring March. Flowers began appearing on
KO\e m l ~ e r
Hjlprr.ic-11i1~
~ ~ l a n in
t s A l q , and flowers antl fruit
T h e t1111e of germination of annual seedlings were produced until the plants diet1 in I1ecenil)er.
a t \\ell a i tinie of flowering of a~inuals antl 13y that time, the seeds ~jrotl~iceclthat summer
perennials separate the species 111to t \ \ o q r o t ~ l ~ s hat1 alreatly gern~inatetl mitl the seedlings ivere
T h e sumlller-floweri~ig species ger11iiii;lte after \Tell established. This life span of more than 12
the first of the e a r nhen the fall-germina- mo~itlisis in sharl) contrast to that of h'/tlho.stj~li.s
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Spring 1964
GRANITE OrTCROP COMMUKITIES
rapillaris, another summer-flowering plant ; 6
months (Fig. 5) is prohably longer than the life
span of any individual plant of this species g r o w
ing in the island communities and may represent
several generations. Young seedlings ivere obserled in Ma!, June, July, August, 0 c t o f ) e r . and
November
X period of drought late it1 June
k~lledmany plants before they had bloo111ed I n
.Augubt onl! a fev living mature specltnens \\ere
observed, but there were many young seedlings
which, it is presumed, completed their life cycles
11) Yovember
303
in succession. Dinnzorplza cywtosa has a metabolism peculiarly adapted to the extreme conditions
of high light intensity and low moisture and mineral content of the soil which exists in the shallow, soil-filled depressions on the granite outcrops (Raker 1956, Lammers 1958, Il'iggs and
Platt 1962). During the months of their growing
season, the plants maintain extensive root systems
and a low ground cover which aid in retaining
soil particles. Even after death the desiccated
plants niay intercept bits of \vindblo\vn and waterborne debris, but the midsummer loss of all moisture from the shallo~vsoil urevents conversion of
dead plant parts to humus as is usual in more
The ~ v o r d community has been used in this mesic conditions. I n writing of similar soil-filled
stutly to designate a group of plants liting in a depressions in exposed granite surfaces in North
restrictetl area, specifically, a soil-filled depres- Carolina, Oosting and Anderson ( 1939) state
sion st~rrounded1)y exposed rock. T h e classifica- that "Such dry depressions usually give no evition of the comtnunities is suggestive of sera1 dence of further successional development."
Although the shallolvest diamorpha comnlunistages in primary succession from the tlian~orpha
ties,
such as Mount Rolla~vayno. 2 ~ i t ha maxito the herb-shruh community. There are itldications that such a succession of vegetation does Inurn soil depth of 2 cm, show no evidence of succession, t h e number of species increases as
take place as the soil in the depression deepens
130th the deposition of organic and inorganic ma- maximum soil depth increases. A soil pocket
l l a have a
terial on the surfaces of the comniu~iitiesand the covered with red-leaied D i a ~ ~ ~ o r p niay
tlecom~>ositionof the underlying rock contribute. central area of gray-white lichens and white
If the soil I~ecomesdeeper and its water-holding Arctzat,ia blooms in the spring where the soil is
capacity increaies, the floristic composition of the 12 cm deep (Fig. 1, B 1 . Clndotiia lcporina, C .
carolitziatza, Cawlpyloplts sp., and Rltlbostylis cncommunity can change.
Present findings tend to support the contet~tion pillaris are the plants most frequently seen as "inSpecies of
of \\'interringer and lTestal (1956) that the con- vaders" of diamorpha communities
ventional secluence on rock surfaces of crustose Cladonia ant1 apparently particularly C . / F ~ o P ~ ~ z ( I .
lichens, foliose lichens, fruticose lichens, mosses. are adapted to survival on exposed, shallow soil
herbs. ~voodyplants, is not as important in plant 11y reason of a n ability to ahsorb and store moisiuccession as the accumulatiotl of soil through ture in their ftungal elements, obtain nutrients
physical agencies. The depressions ill the surfaces from their captive algae, and maintain a vegetative
of the granite outcrops are not nlerely the result year-round plant c m e r , thus avoiding a critical
of iucceeding generations of plants Depressions stage in their life cycle such as seed plants may
have I~eenformed by the eufol~ationof the rock, encounter. Observations of diamorpha and lich1)y erosion as n a t e r runs d o ~ v tthe
~ outcrops, and en-annual herb communities at hlount Aral)ia,
11) the intel-actions of wind. ~ v a t e r ,and rock par- Rock Chapel Alountain, and hIount Rollaway
titles which may result in a scouring and deepen- suggest that the establishment of colonies of
illy of shallow clepressio~ls. Regardless of the Cladonin lcporitza in island communities initiates
geologic processes which niay have heen responsi- a series of successional stages which correspond
1)le for their origins, there is a tendency for or- to the comn~unities listed earlier, i.e., lichen-anganic and inorganic materials to accumulate in nual herb ( F i g 1, C ) , annual-perennial her11
depressions. T h e growth of plants on such ac- (Fig. 1, F),and herh-shrub ( F i g . 2, B, C ) .
Once established. Cladonia lcporina influences
cunlulations of coarse and fine sand appears more
further
de~elopment. T h e exposed soil under the
iianificant than the lichens and moss on the adjacent exposed rock in the ultimate establishment much hranched lichen cover is a microenvironof a c l ~ m a \cover of seed plants on these ot~tcrop- ment more suitahle for germination of moss
pings of granite. Similarly, Whitehouse ( 1933) spores and spermatophyte seeds than is cornnotetl that iuccession was more rapid on acctumu- pletely bare and exposed soil or a seasonal dialatetl gral el than on exposed granite at Enchanted morpha community. Likelvise, the tangled mass of
Rock, Texas.
lichens is a barrier which intercepts debris the
It is tliffict~ltto e\.aluate tile role of Ditrl?zovplzrr deposition of which increases soil depth. T h e
depositetl tlel~rih 111:~)- incltitle sl)ores, seeds, and irl~~crica~zliirl,
,'lscy1.1~711 H y p c r i c o i d r s , aiid Iilir.ritr
l)l;lr~t 1);trth i ~ . l ~ i c ' e~lal)le
l~
est:tl)lisl~nlent of new ~lrnri~zrr
to occur. llToody vines can invatle such
members of tlie community. I\-ith tlie addition isla~ldcomnlunities, and if moisture conditions are
of Illosseh. 1)articularly Ctrlllpyloplis, and seed favorable for several consecutive years, seedlings
p l x ~ ~ t the
s , organic content and moisture-holding of P i ~ z l i s Tncdtr, J~inipcrlrs ~'irginitrnir...31iii.lnt1ZLY
a nd 1 7accinilclll trrcallacity of tlie sul)stratum is ~ n a r k e d l yiticreased, chicr nrborrn, P ~ I ~ T Zsc~,ofitla,
hut tl~iring1)eriods of tlrought, tlie soil of 1iche11- borclrlrt nlay sur\-ive.
annual her11 cotnmtmities may become completely
Parallelitlg the successional stages represented
drietl, liniiting this stage in successio~ito annuals, by types of communities, there are a l ~ p a r e ~ i t l y
lichens, ant1 drought-resistant mosses.
seral states lvithin the con~munities. T h e zones of
If tlie soil tleptli exceeds 15 cln, coml~leteclryi~iq platits, especially evidetit it1 annual-perennial herb
out of tlie soil is less likely and pere~inialsmay conimunities in the spring, correspo~idroughly to
iiivade the area. S r - l l o c n o l i r i o ~ r~-rocc7liil~\vliich tlie d i a ~ i i o r l ~ h alichen-annual
,
herb, and annualhas a deeply 1)urietl corm, and Scnccio t o l ~ ~ i ~ n t o sperennial
~~s
her11 comn~ut~ities.Given a co~ntiiunity
\vhich has a woody untlerground stelii and a tleep \\-it11 a centrally located population of S r n r c i o
\\-ith a zone of L ' l r c n a ~ i nbrr.7';s,
root system. are t\vo drought-resistant perennials t o i ~ c v z t o s ~ iringed
which are amollg tlie first to appear. X sure folia, lichens, and mosses, exterior to which is a
sign that tile annual-perennial stage ill succession pure stand of Dinl~zorphn i Fig. 1. E ) , tlie assumphas 1)cen reached is an extensive niat of the hair tion is that tile central portion of a sliallo~vdiacall moss, I'ol~'fi-ic-ll~riii._\lthough occasio~ially niorpha co~iimunitywas invaded first by lichens,
occurring as scattered patches in lichen-annual mosses, and a~inuals,and secondly, as soil conherb conliilullities, this moss is frequelit and often tinued to heconle deeper a t the center of the conia l ~ u n t l a ~ litn deeper soil conlniunities. I n the m u ~ l i t y S, r ~ l c r i oi~ivadedand colo~lizedthe deepest
sanie \Yay that species of C'ltrtlo~liashelter annual soil, displacing the second seral state ~vhichperseeclings, I'olytr-ir-l~lililappears to be a biotic factor sisted 011 soil intermediate in depth betwee11 that
i n t l ~ i c ~ ~ tin
i a linitiating tlie annual-perennial stage n e c e s s a y for S ~ v l r c i oa ~ l t ltlie very shallow periphof succession. C'orrelatetl with the greater depth eral soil on \vIiich only Ditrilloi.pho: r-y~llosacall
o i soil in this seral staqe a r e soil particles of a s ~ ~ r v i v e .T h e resultant zones are similar to tlie
Illore uniform size, increased capacity of ~ v a t e rre- zonatioll ~vliich occurs a r o u ~ i d a ~ n a r s h y , freslitention, :untl a c o ~ n l ~ l e t le~ l a n t cover tlistinctly ivater 11o11tl;in both instances.etlal)hic factors deia!,c~retl except in sliallo~vl)cril~heralsoil.
termine the floristic conipositio~l.
T h e increase in plant cover and diversity f o r
T h e :tl)ove description of st~ccessional zonation
each of tlie a l ~ o v esucceetli~igseral stages is ac- ill island conimunities is oversim~~lified. Decoml):~iietl by a corrcsl)onding ii1crc:ase i l l the pressions may deepen irregularly ant1 a perfect
o r g a ~ i i ccunteiit of tlie soil, and a tlecrcase ill l~atteriiof zones arranged as conce~itricrings is
acidity. Soils 2 cnl (lee11 llave an org:uiic content rare. T h e nu~iiber of zones ant1 their floristic
of al1o11t 37h and a p H of :tl)out 4.0: those 10 con~positio~i
varies from comnlunity to community
being
cm tlcc.1) :in organic contrnt of a l ~ o u t1'; ant1 a ant1 from season to season, there freclue~~tly
pH o i a l ~ o u t4.2 2 :111(1 tliosc over 15 ~ 1 1 1~ I c v ~;t11
)
niore t1i;ln three zones i ~ iaii~iual-~)erciiiiial
l~crl)
organic content of a l ~ o u tS? antl a 1113 o i nllout communities.
1.5. ( 1 )ctailed data \\.ill be publislied sul~seLTntler ~ ~ r e h e l lct l i ~ ~ i a t icontlitions,
c
tlie Iicr1,q"c11tly.
hhrtll) stage appears to Ile all etlnl~liicsull-cliniaz.
\\-it11 the increase in total vegetatio~i,it is as- T h e lack of ~ n o i s t ~ i r 11-liether
I~ec:l~ise
e,
of co~iil~eti~111iictl
tliat the soil in islantl com~iiunitiesgrntltial- tion. i~isufficient rainfall, or sliallo\v soils, liniit.;
ly 1)econies tleel~cr1)y tlel~osition of tlcl~ris,decay tlie occurrelice of tree species aiid shortelis tlie
of 1)l;lnt parts. :ui(I tlisintegration of the ~iiltler- lives of tlie fe\v trees \vhicli (lo beconie estal)lisl~ctl.
l!.i~lg rock. T h e thirtl seral staqe, an 1ierl)-~lirul) .As rece~itlyas 1916, small stantls of AY~'s.cabifloi.o.
co~iiniunit!-, i.q reaclietl \\-lien niasi~iitunsoil c l e ~ ) t l ~Jlr~iipri-11s;-ii,gi~lic~lia,
ant1 I'inlis Ttrrtltr g r e x on
is o\.ci- 10 cnl, t l ~ esoil level is eclual ~vitli o r S t o l ~ c 3Iou11taili (Cnn~l,l)ell lC121r \\-here I I ~ \ \ .
slightlj- :~l,o\.ct h r surface of tlie surrountling t-ocli there ni-e 110 trees. D r . I\-. 13. E:~l<er (p~-i\.:~tv
with little o r no margi~ial zone of shallo\v soil communicatio~i)of l<mor!- University stated tlint
(I;i:,.. 2. 13 I , antl the tlominants arc perennial these trccs (lied after a very tlr>- summer. I t i h
Iierl~sant1 \\-ootly plants. Yucli a community acts reaso~i;ll)lcto supl>osc tliat similar events have ocas :L s13011gc, holding \v:~ter \vliicli runs in ant1 :~1- curred on other granite outcrops.
l h e s c conimunities cannot I)e fully understootl
lo\vi~igonly a relatively smnll arno~llltto run o11t.
Conditions arc niesic enough for I?i.~flii,o~liiirii without placilig then1 in their geological IJerspec-
,
r .
Sprillg 1964
G R . \ S I T E O U T C R O P C'O.\1IRlUI;II'IE~ tive. T h e I'ietliiiont Plateau is comr>osed of a
great sliieltl of granite scliists a n d gneisscs, which
varies horizontally antl vertically in its resistance
to \\.eatliering. 1)ecp soils overlie the m o r e easily
\vcntlieretl materials, whereas the protlucts of deconil'osition \\-ash away a s fast a s they a r e formed
011 the more resistant areas, leaving tlie slightly
weatlierctl rocli e s l ~ o s e t l ,either a s lo\\- tlomcs o r
a s f a t rocks, often several hundred acres in e x tent. Stone l l o n u t a i n is a n extrusion of harder
granite into the granite schists a n d gneisses of the
plnteau (luring t h e P e r m i a n I'criod. S u l ~ s e q u e n t 1! the ,urrountling softer modified granites such
:I> those of l l o u n t Arabia. Rock Chapel h l o u n tain, ant1 1 I o u n t Rollaivay, ha\ e slonly ncathcrctl
a\va!. 1e:lving the m o r e resistant mass a s a nionatl~iocli standin:,. 200 m a1,ovc the surrounding
plaiii. A s erosion continues in geologic time, tlie
e x l ~ ~ s e tliartlcr
l,
lenses eventually disappear without ever hnving hat1 a complete cover of soil a n d
veqctation. lca\iny exposed the softer, soil-producinq strata. Concomitantly, atlditional harder
lenses a r e lleing uncoveretl in other areas. T h u , .
\vliile no one outcrop has persisted intlcfitiitelv.
collectively the outcrops ha\-c been prcscnt long
enough for the e v o l ~ ~ t i oof
i i tlie many species endeniic to them.
Tliis tl!n;uiiic concept of continual change e m plinii/es t h e fact that ~e a r e vie\\-ing these communitics a t x specific moment, ant1 that evcli at
this moment, sliorter cycles of change :1re going
(111 \\.ithi11 tlie lax-gci- oncs of liuntlretls of thous:uitls of yeat-s in l(,ngtli.
I'cr11:1lv tlie ~ i i o s trapid erosional process is tlic
conti~it~;,lexfoliation of the csposcd rock caused
11v thc. formation of exiolintion sliclls which vary
111 tliicl,~lc.>sfrom several centimeters to 2 o r 3 111
antl \ a r j i l l tliametcr from a i e n to ;L huiltl~c~tl01iiiorc ~iic,tc~i-s
(Hol)son 1'158). IYintei- cold aiitl
s1uiiiiier hent help to loosen a n d fragnieiit t h e
u11l)er shells \\-liicli qrndually \\-eather away. T h i s
III-OCYSH~
ixfo1i;~tioii may destroy isla~ltl coiiililtmitics \vliicli li:l\.e t;llieii lluntlreds o i years to
tie\-clop.
I t is tliffic~lltto estimate the age o i island comiiitmitics. T n - o soil sxmples iron1 tlie bottom of a
comniunity at the to11 of l l o u n t ;li-al~~ix.
\vIiere
contlitio~is a r c niore s t a l ~ l r th:l~i 011 tlie slol)es,
!.icltletl c:lrl~oii-tlxtctl ~iixtcrial n l ~ o u t 670 !.ears
oltl. Ti1 terms of litmian ol)ser\-ation, this indicommunity. 1-egct:~tioiial changes in some islantl
coni~iiuniticsillav 1)e too slo\v for o l ) s e r \ a t i o ~ iof
all!. s~~ccessiconal
cllnnges in a 1ium:ln lifetitile.
H e n c e , tlie iilaiitl conimtmities have lleen periii:lneiitl! iiiarl\etl so tlint changes over 5. 10, 50,
30..
o r even sevcral hundred years m a y be observctl
o n a q ~ i a n t i t a t i \ eas n e l l a s a clualitative basis
T h i s provides for one of t h e tnost \aluahle ant1
also inost difficult kinds of ficltl studies, n a m c l ~ .
that of changes in o u r natural e n \ i r o n n ~ e n t
through time.
\Ye \\.is11 to thank I l r . hInso11 E . Hale. S m i t h i o ~ ~ i ; ~ n
Inititutio~i,ior the identification oi liclic~i<.Tlr. T.e\~ii E .
.L\nderson. Duke Univeriity, ior the itlcntificatio~i oi
mos>ca, Dr. 11-ilhur H . Duncan, University of Georgia,
ior h c l l ~ \\-ith the idc~itification of some oi the grasseb.
of the Geocliro~~onietric
and D r . S I e ~ ~ z Stuivcr
ic
12al~oratory. Yale University, for the radiocarbon dates, a i sul)portetl hy I S 1 2 grant G-19080. 11-c gratciully ; ~ c k ~ ~ o \ v l cdgc the assiita~iceo i Robert Pedigo, College of 11.illian1
and M a r y , in the collection o i tlic physical tlata, a~iti
thank John T. SIcGinnis for the photographi taken in
1962. T h i i \\ark \\.a\ .uliliorted in part I)y colitl-act
S o . A T (40-1 'I -2112 I\ it11 the Atornic Energy Corn~niasion.
Baker, W. B. 1915. Studies of the flora o i tile granite
O L I ~ C ~ O I I . ' ~f
Gcorgia. Etnory Univ. Quartel-ly 1 :
162-171.
. 1956. Sorne i~itcrestirigplants on tlie g r a ~ l i t c
outcrol), of Gcorgia. Gcorgia Mineral S c \ v . ~ I c t t c ~ .
9: 10-19.
Breen, R. S., and R. A. Pursell. 1956,. I f o r e mo>.cc
fro111 Stonc LIountain, Gcorgia, a n d vicinity. 1;1-yologist 59: 184-186.
Campbell, E. G. 1921. S o m e asnects o i Stonc LIountain a n d its vegetation. Proc. I n d i a n a ;\cad. Sci.
31: 91-100.
Clebsch, A. 1953. Rryological riotc on S t o ~ ~1Iou11e
tain, (;eorgia. Rryologi>t 57: -30.
Cooper, W. S. 1913. Tlie climax forest of Isle I<oy:ile.
l.ahc S u p r r i o r , ant1 its t l e v c l o l ~ n ~ e t ~11.
t . Tlie .uccez,io~l.. J:ota~i. (;;Iz. 55: 115-110.
Cotter, D. J. 1958. Studic. on the ecological liiv
hi.tory
oi P o ~ t i i l ( r c - c r .S'iiitrllii P . 11-ilson. 1'h.D.
T l ~ c q i . ~Eniory
.
Lni\er.ity. . i t l a ~ i t a , Ga. 93 11.
Cotter, D. J., and R . B. Platt. 1959. Studies on the n
Ecolopy
ecological life hiqtory of I J o i ~ t i ~ / t r c,C?itiillii.
4 0 : i15l-hOS.
Fernald, M. L. 1950. ( ; ~ - a y ' s111anual o i Ijotatly. 8th
etl. -4rne1-ican 1:ook C'o..
S70rk. 1632 11.
Harper, R. M. 10.30. ( i r a n i t e outcrop vegetation in
Alal~atila. Tot-I-ela 39: 153-1 59.
Herrmann, L. A. 1953. (;ei~logy of tile Stonc lIou11tain-1.ithonia d i > t ~ - i c t (;col.gi;i.
,
Geologic;il Survey
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PLANKTON A N D W A T E R CHEMISTRY I N T H E MONTREAL RIVER
LAKE-STREAM SYSTEM, SASKATCHEWAN1
.Ibstvact. T h e relations bet\veen dissolved solids, xvater exchange, and productivity were
studied in a lake-stream system. Detached epilithic algae composed the plankton of the upper
stream, but all other stations displayed a lentic plankton. Turbidity and unsuitable substrate
prevented the development of sessile algae on the hottom of the slow-flo~ving river sections
(lakes), but the macrophytes provided a surface for the development of these cornmunities.
T h e concentrations of total dissolved solids and those ions essential for photosynthesis and
algal nutrition decreased downstream coincident, in general, with a downstream increase of
phyto- and zooplankton numhers. T h e different rates of the decrease of these tfutrients in
the upper stream and lake-stream section a r e probably related to the greater populations of
autotrophic biota in the latter section. .Assuming that nutrients a r e being added to the system
throughout its course, then the downstream decrease indicates that the increasingly large
autotrophic populations a r e assimilating these nutrients a t a rate greater than they a r e being
added. Thus, the deciding factor regulating the accumulation o r removal of tiissolvcd nutrients
in a lake-stream system appears to be the degree of autotrophic enrichnient of the systeni.
Studies of the relationshil~s between dissolved
ions and related aquatic environn~entsusually concern either lakes or streams. Less attention has
been directed toward the nature of the exchange
of ions between lakes and streams or to the
effects of these euchanges upon the productivity
of a lake-stream system. Hynes (1960) suggests
that lakes may act as "fertility traps." removing
dissolved ions and depleting the supply of essential nutrients in the outlet stream. Alternatively, the ionic constituents mav increase downstream due to progressive accumulation from the
' T h i s work was supported by '.SF. Research Grant
G-12428 and is taken from a thesis submitted t o the
College of Graduate Studies, University of Saskatchewan,
in partial fulfillment of the requirements for the degree
of Doctor of Philosophy.
' Present address : Biology Laboratory, Hanford Laboratories. General Electric Company, Richland, IITashington.
drainage basin. Both theories have been advanced to explain data from studies of lake-stream
systems (Berg 1943, Reimers, Maciolek, and
Pister 1955. Hynes 1960). T h e principal factors
~vhichinfluence ionic changes are ( 1 ) the geological substrate and size of the drainage basin ; ( 2 )
the quality and quantity of the biota, especially the
producer organisms: ( 3 ) the size and degree of
eutrophication of the lakei : (4) the pli! 4cal characteristics of the stream; and ( 5 ) ion exchange
with the aquatic substrate.
T h e present study investigated the relationships
hetween the dissolved ions, water exchange, and
net plankton in the Montreal River and four
associated lakes.
DESCRIPTIONOF STUDYAREA
Geology
T h e drainage basin of the Ylontreal River is
situated immediately south of the Precambrian