Report 43
Management of Mountain Mahogany and
Wright's Silktassel to Increase Browse
Availabilitv for Big Game
J
Range Improvement Task Force
Agricultural Experiment Station
Cooperative Extension Service
u
4College of Agriculture and Home Economics
'hER~\
Management of Mountain Mahogany
and Wright's Silktassel
e
for Big Game
to Increase ~ r o w s~vailability
Jon C. Boreni, V.W. Howard, Jr., D.S. dasady2,and G. Morris Southward3
I
I
I
Mountain mahogany (Cercocarpus montanus) and
Wright's silktassel (Garrya wrightii) are important
browse species for deer (Odocoileus spp.) and elk
(Cenus elaphus) in pinyon-juniper (Pinus edulisJuniperus spp.) woodlands (Gordon and McClellan
1954). In New Mexico, lack of periodic fires has resulted in mountain mahogany and Wright's silktassel of
such heights that new leader growth is essentially inaccessible to big game.
Leaders that sprout following removal of tops of
mountain mahogany and Wright's silktassel may provide additional browse for deer and elk (Reynolds
1964).Top removal may also result in browse becoming
more accessible due to thereduction in tree height. Little
work has been done to determine if additional browse
for big game can be generated by removing mountain
mahogany and Wright's silktassel overstory. This study
was undertaken to determine if removing mountain
mahogany and Wright's silktassel top growth is a viable
means of increasing browse availability. Investigation
was also conducted to determine the amount of mountain mahogany and Wright's silktassel browse produced by complete pinyon-juniper overstory removal.
Methods
The study was conducted from September 1992
through September 1993. Two adjacent sites, each 1 ha,
in the Bear Mountain region of the Gila National Forest
were selected for study. The study areaoccurs within the
upper Sonoran zone typified by pinyon-juniper wood-
land (Lamb 1971). Climate is semi-arid, and precipitation during the study totaled 479 rnrn with a monthly
mean of 36.8 mrn (U.S. Dept. of Commerce 1992,
1993).
Trees were treated by removing the top portions with
a chain saw. After cutting, trees had a maximum height
of 1 m. The treatment was applied as complete or partial
removal of the overstory. Complete overstory removal
consisted of cutting all trees, including pinyon and
juniper, on the site. Partial removal consisted of only
cutting mountain mahogany and Wright's silktassel.
Ten randomly selected shrubs of each species in the
complete removal area and five of each species in the
partial removal area were selected for sampling. Pretreatment leader lengths were determined for each selected shrub by measuring the new growth of 10 randomly selected leaders up to 1 m from ground level. The
height restriction on pre-treatment measurements was
intended to concentrate sampling on areas of the shrubs
that are easily accessible to deer and elk. One year later,
post-treatment measurements were taken from randomly
selected leaders on all previously selected shrubs. Only
unbrowsed leaders were measured. Ten leader measurements from each sampled shrub were used in the analysis.
A matched-pair t-test was used to compare mean preand post-treatment leader lengths for both species. A
group comparison t-test was used to compare complete
and partial overstory removal mean leader lengths for
each species. A significance level of .a = 0.05 was used
for all comparisons.
I. Extension Wildlife Specialist, New Mexico State University
2. Professor and graduate assistant, respectively, Department of Fishery and Wildlife Sciences, New Mexico State University
3. Professor, Department of Experimental Statistics, New Mexico State University.
Results and Discussion
A profusion (> 100 on some shrubs) of leaders
sprouted from areas of the shrubs where previously
there had been very little growth. Post-treatment mean
leader lengths were significantly greater than pre-treat.merit mean leader lengths from both mountain mahogany (fig. 1) and Wright's silktassel (fig. 2). In
addition, mean leader lengths for both mountain.mahogany (fig. 1) and Wright's silktassel (fig. 2) were
significantly greater under partial removal than under
complete removal of pinyon and juniper.
These data suggest that the amount of browse available to big game can be increased by removing the tops
of mountain mahogany and Wright's silktassel. Cutting.
resulted in longer mean leader lengths for both species,
regardless of treatment type. Furthermore, all leader
growth that occurred after cutting was within easy reach
of browsers.
These data also suggest that complete overstory
removal did not produce greater amounts of browse
within small areas of similar size. Cutting individual
mountain mahogany and Wright's silktassel, ratherthan
patches of trees including pinyon and juniper, may have
several advantages. First, the amount of cover lost
through cutting will not be as extensive in the partial
removal area. Second, partial overstory removal of
mountain mahogany and Wright's silktassel will beless
labor intensive and less costly compared to complete
overstory removal. Hence, it is more efficient to only
remove the tops of mountain mahogany and Wright's
silktassel unless the pinyon and juniper tress can be
marketed for wood products. However, removal of
mum 1.
PI-+ and post-mzbmnt m u n luder kngths
of topped mounhln mahogany under -1
a
canpkta omrtm rsmoval In tha GI* H.tlwl
F a c r f New Medco. 1992-1993.
pinyon and juniper, as in a firewood harvest. and reduction of heights of mountain mahogany and Wright's
silktassel should increase the amount and availability of
browse from these plants.
'Ihe study design did not incorporate a comparison of
mean leader lengths between uncut control trees and cut
trees. We believe the lack of a control group does not'
invalidatetheresults. Removing theupper portion of the
trees drastically altered them not only physically, but
phyaicbgicall y as well. The observed increase in leader
production was so profound that we feel it cannot be
adequately explained simply by year-togear environmental variation. Year-to-year environmental variation
may have confounded the observed change in mean
leader lengths. However, we were mainly interested in
the change in browse availability rather than the actual
change in mean leader lengths.
Further investigation is also needed to determine if
mean leader length significantly differs from the total
number of leaders produced. Complete overstory removal may produce more total shoots of shorter average
length. Conversely, partial overstory removal may result in fewer shoots of longer average length. Total
browse production is undoubtedly a function of the
relationship between total leader length and the total
number of leaders.
Differences between complete and partial overstory
removal mean leader lengths may indeed be site specific.
On the other hand, the observed increase in available
browse following modification is probably reproducible
inother areas. We suggest an initial limited application of
partial overstory removal to areas under consideration to
determine if the desired results are obtainable.
2 hand port-hubmnt mun kader kngths
oflopped Wrlghrs sIllrt.lk1 under pu(kl O t
Gtk H.tlwl
cmpkm orcntay removal In
F m r f New Mexko. 1992-1995.
Acknowledgments
We would like to thank D. Smith and M. Remmenga
for their statistical assistance. Our work was make
possible by the U.S. Forest Serviceand McIntire-Stennis
funds.
Literature Cited
Gordon, L.S. and J. McClellan. 1954. Investigation of
game specieson the GilaNational Forest.New Mexico
Dept. of Game and Fish. Proj. W-61-R. 62pp.
Lamb, S.H. 1971. Woody plants of New Mexico and
their value to wildlife. New Mexico Dept. Game and
Fish Bull. 14. 80pp.
Reynolds, H.G. 1964. Elk and deer habitat use of a
pinyon-juniper woodland in southern New Mexico.
N. Am. Wildl. Nat. Res. Conf. Trans. 29:438-444.
U.S. Dept. of Commerce. 1992, 1993. New Mexico
climatological data. Natl. Oceanic and Atmos.
Admin., Natl. Climatic Data Center. 96:9-97:9.
Asheville, NC.
.