Ecological Systems of the Galiuro Mountains
Safford Ranger District, Coronado National Forest,
Arizona
http://www.azfirescape.org/galiuro
Jim Malusa
School of Natural Resources and the Environment
University of Arizona
[email protected]
The following is a summary of the methods used in mapping the ecological systems of
Galiuros Mountains within the bounds of the Coronado National Forest. Because this
map is part of a larger effort to provide maps for landscape-wide planning in the
Coronado, I also provide a brief history detailing the evolution of our mapping in other
districts of the Coronado, from an emphasis on soils and landform in the Catalina and
Rincon Mountains, to an emphasis on existing vegetation in the Galiuro Mountains.
Background
The Coronado National Forest encompasses a dozen mountain ranges in southeastern
Arizona and southwestern New Mexico. In 2008, Cleland et al. began mapping the land
type associations of the Coronado and adjacent lands (Land Type Associations of
Southeastern Arizona, available at http://www.azfirescape.org/home/related_activities/).
This was a large-scale map covering almost 2 million acres, and subsequent efforts
focused on a smaller areas and finer scale.
For instance, in 2009 we mapped the land type associations and, where possible, the
smaller ecological land types, of the Catalina and Rincon Mountains. (Land Type
Associations capture repeatable patterns of soil complexes and plant communities, while
Ecological Land Types are based on finer scale topographic, geologic, soil, and plant
associations. See http://www.azfirescape.org/catalina/mapping_methods/). The study area
included a considerable expanse of alluvial fans and terraces outside the Coronado's
boundaries. In all, we mapped over 100 land type associations and 300 ecological land
types (http://www.azfirescape.org/catalina/landscape_types/).
Because the Coronado NF was considering landscape-scale treatments for restoring
sustainable, more natural fire regimes across entire mountain ranges, these units were
summarized into 30 ecological units, or 'ecounits', based primarily on potential vegetation
and landform. For example: Upper Sonoran desert on fans, terraces and weakly
consolidated pediments with limy soils. However, these ecounits were problematic when
applied to modeling exercises such as determining the Fire Regime Condition Class,
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because of the difficulty in cross-walking between the ecounits we used, and the ecounits
used by LandFire (http://LandFire.cr.usgs.gov/)
LandFire is a uniform system for landscape data nationally, and is created by
interpretation of data from remotely sensed 30-meter pixels. There are GIS layers for
both potential vegetation ('biophysical setting, or BpS) and existing vegetation (existing
vegetation type, or EVT). Each of these is named for the 'ecological systems' listed and
described on NatureServe (http://www.natureserve.org/explorer/index.htm/).
In 2010 our mapping efforts shifted to the Chiracahua, Dragoon, and Dos Cabezas
Mountains, where we mapped not the land type associations but the existing vegetation
using the accepted ecological systems names whenever possible
(http://www.azfirescape.org/chiricahua-dragoons-dos-cabezas). Of the 12 ecological
systems mapped, three of the ecological systems were not accepted names in the
NatureServe repository: (1) Madrean Oak/Conifer/Manzanita on Rocks, (2) Madrean
Pinyon-Mt.Mahogany on Limestone, and (3) Madrean Pinyon-Juniper-Oak Woodland.
The first two encompass elements of the Land Type Associations, in which
substrate/landform is paramount. The last, Madrean Pinyon-Juniper-Oak Woodland, is a
composite of three NatureServe ecological systems: PJ woodland, Juniper Savannah, and
Madrean Encinal. These were combined because of the time and money required to tease
them apart without adequate imagery (such imagery was thankfully available for the
Galiuros.) Mapping was done without the benefit of soils maps (most of the study area
was mountainous, and lacked soil surveys), but with geologic maps to delimit limestones
and associated sedimentary rocks. Available imagery, mostly 2006 NAIP, was fair but
not great. The resulting ecosystem map was based primarily on field observations and
photos during the summer of 2010, combined with data from other vegetation maps,
including:
Southwestern ReGAP Landcover
LandFire EVT (Existing Vegetation Type)
LandFire EVC (Existing Vegetation Cover)
USFS Mid-scale Dominance Units
Ecological Systems of the Galiuros
Overview of Study Area
Earlier mapping efforts in the Catalina, Rincon, Dos Cabeza, Chiricahua, and Dragoon
Mountains included both public and private lands, taking in a good deal of the alluvial
fans and valleys surrounding the mountains. For the Galiuros, we mapped only those
lands within the Coronado National Forest. The Coronado includes about 135,000 acres
of the Galiuro Mountains, within an area that runs about 27 miles from southeast to
northwest, and 8 to 10 miles wide. Elevations range from 7663 feet atop Bassett Peak, to
3500 feet at the mouth of Kielberg Canyon. Most of the Galiuros are built of rhyolite of
Tertiary age, block faulted into two roughly parallel ranges, the 'east divide' and 'west
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divide.' Both of these ranges hold peaks in excess of 7000 feet, with big conifers clinging
to the north slopes. However, much of the high country, as seen in this view from Bassett
Peak (below), is rock. The outstanding vegetation is border pinyon, typically 3 to 5 m
tall, with associated silverleaf oak, netleaf oak, and manzanita.
Figure 1. Photo Point 879. The view north over the East Divide of the Galiuros, from
7660 feet (2330 m) on Bassett Peak. Virtually the entire rocky habitat within view is
home to the Madrean Pinyon-Juniper Woodland, featuring border pinyon (Pinus
discolor), alligator juniper (Juniperus deppeana) silverleaf and netleaf oak (Quercus
hypoleucoides, Q. rugosa), and manzanita (Arctostaphylos pungens). Mountain
mahogany and beargrass were common associates. October 3, 2011.
The hallmark of the Galiuros is the large galley forests of pine and cypress that trace
Rattlesnake Canyon and Redfield Canyon to elevations all the way down to 4700 feet. In
the same drainages, Douglas fir is an important species above 5500 feet.
The far northern study area, in the Four Mile Creek watershed, is very different (see
figure 2 below). The bedrock geology is largely deeply eroded sedimentary rocks of
Pliocene to middle Miocene age. The climate is characterized by more winter
precipitation, at least relative to the southern end of the Galiuros. The vegetation is
single-needle pinyon, not border pinyon, along with scrub oak and single-seed juniper.
There are no Ponderosa or Chihuahuan pine, nor Douglas fir, despite elevations up to
6600 feet.
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Figure 2. In this view looking south over the Galiuros, the red polygon represents the
range of single-needle pinyon/juniper ecosystem, on the deeply eroded sedimentary rocks
of Pliocene to middle Miocene age. Further south, the majority of the Galiuros are built
of Tertiary volcanics.
Naming the Ecological Systems
For the Galiuros map, every named ecosystem corresponds to an ecosystem described by
NatureServe. This means that a pixel in a LandFire layer can be reassigned based on the
vegetation map generated in this project. Further, in the field you can use the vegetation
keys generated by the NatureServe Terrestrial Ecology Dept. (e.g., Field Key to
Ecological Systems and Target Alliances of LandFire Map Zones 25 and 26).
Eleven ecosystems were described, based on existing vegetation:
Sonoran Paloverde-Mixed Cacti Desert Scrub
Apacherian-Chihuahuan Semi-Desert Grassland
Apacherian-Chihuahuan Mesquite Upland Scrub
North American Warm Desert Riparian
Rocky Mountain Montane Riparian
Madrean Juniper Savannah
Great Basin Pinyon-Juniper Woodland
Mogollon Chaparral
Madrean Pinyon-Juniper Woodland
Madrean Encinal
Madrean Lower Montane Pine-Oak Forest and Woodland
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For some of these ecosystems, the NatureServe description and the observed vegetation
were happily congruent, as in the case of the Madrean Pinyon-Juniper Woodland. Other
ecosystems were more problematic. For instance, the northern study area, characterized
by single-needle pinyon, single-seed juniper, and scrub oak, was most similar to the Great
Basin Pinyon-Juniper Woodland, yet the NatureServe description reads: 'This ecological
system occurs on dry mountain ranges of the Great Basin region and eastern foothills of
the Sierra Nevada south in scattered locations throughout southern California'. There is
no mention of Arizona, but there is no other ecological system that approximates the
observed vegetation.
In other cases, the ecosystem is poorly defined in the NatureServe description. For
instance, the entry for Mogollon Chaparral merely mentions that the vegetation is
typically evergreen broadleafed shrubs such as scrub oak, mountain mahogany, and
manzanita. However, these species occur in a variety of settings, and the description
makes no mention of the cover values, only that there is 'moderate to dense' shrub cover.
Mapping the Ecological Systems
No soils maps were available for the study area, which lay entirely within the bounds of
the National Forest. Bedrock geology maps from the Arizona Geology Survey served to
identify the rhyolite that characterizes most of the study area from the sedimentary rocks
in the northern study area. Field mapping was with eight days of hiking and one of
driving FS roads between May and October of 2011. A Garmin 550t GPS camera
recorded several hundred photo points; data on species composition and structure (height
and cover) were recorded for about 100 of these photo points. Even photo points without
vegetation notes proved valuable when drawing the boundaries of the ecosystems. For
instance, when trying to decide, whether a shrub on an aerial photo is a small juniper or a
large manzanita; in many cases, it's plain to see from the photo, because the camera not
only records the location, but the direction in which it is pointed. When viewed in
ArcGIS, an arrow on the screen indicates the location and direction of the photo.
I did not revisit the Redfield drainage in 2011, but instead used photographs and notes
from earlier trips in the Redfield watershed, some dating as far back as 1975. Georeferenced photos downloaded off Google Earth, after checking via landmarks to make
sure they were correctly positioned, supplemented these. Also useful was a 1985 map
from an unpublished report to the Nature Conservancy, "Vegetation Associations of the
Muleshoe Ranch Preserve," by L. Susan Anderson, Peter Warren, and Frank
Reichenbacher.
In addition, National Agriculture Imagery Program (NAIP) imagery from 2006, 2010,
and 2011 was available online, via both ArcGIS online, and Google Earth. The 2011
imagery was superb, as shown below in a view of Powers Garden, in which the cabin and
tack room are clearly shown.
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Figures 3 and 4.The remarkable recent imagery of the Galiuros can be appreciated in
this view of Powers Garden in June of 2011, with the watercourse of Rattlesnake Creek
to the right. The red arrow points to the fire pit outside the cabin. The May 2011 photo
below shows the same fire pit, to the far right near the bullet-scarred chair, with a red
bottle and plant press atop a plank bench that is only a foot wide, yet is clear in the
image above.
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This excellent imagery also benefited from a particularly dry spring in 2011, which
resulted in the oaks being scantily clad in reddish leaves that make them easy to
distinguish from the conifers. (Manzanita also appeared reddish, which made it difficult
to discern encinal from chaparral). Below is an example of how this was exploited to help
distinguish different ecosystems.
Figure 5. Two images of the same place, of about one square mile near Horse Mountain
Tank in the northern study area. The upper photo is from September, 2010, while the
lower is from June 2011. The lower photo shows that the dense vegetation near the
bottom of the images stays green; in other words: conifers, in this case, pinyon and
juniper.
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Imagery from November of 2011 (below) from the northern study area very clearly
showed the deciduous riparian vegetation, making it possible to map some areas, such as
upper Pipeline canyon, without having ever visited.
Figure 6. The swath of fall colors reveals a galley forest of deciduous riparian trees,
likely cottonwood, sycamore, and ash, at 5000 feet in Pipeline Canyon. This was
subsequently mapped as Warm Desert Riparian.
Comparing this Study to Other Mapping Efforts
This study was preceded by several others, all of which sought to describe the vegetation
of the Galiuros. These earlier efforts include USFS Potential Natural Vegetation Type
(PNVT, based on 24 Oct 2011 draft map), USFS Mid-scale Dominance Type, Southwest
Regional GAP Ecological System, Landfire Existing Vegetation Type, and Landfire
Biophysical Setting. All of these maps are remotely sensed raster data in 30 meter pixels,
and all have strengths and weaknesses. In an effort to show the correspondence – or lack
thereof – between this study and the previous maps, each of the ecosystem descriptions
that are part of this mapping package includes a quantitative comparison to other
mapping efforts.
In the example below, the Madrean Lower Montane Pine-Oak polygons created by this
study were used as a 'cookie-cutter' on the Landfire Existing Vegetation Type (EVT)
layer (see methods).
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Figure 7. In this view of the upper two miles of Rattlesnake Canyon, between 5500 and
6500 feet, Douglas fir, ponderosa, and cypress trace the watercourses and darken the
north-facing slopes. Pinyon-Juniper is on the relatively pale south-facing rocky slopes.
Holdout Spring is in the upper right tributary. Image from June, 2010, NAIP.
Figure 8. Above: Same area as Figure 7, with the cross-hatched area showing the
Madrean Lower Montane Pine-Oak as mapped in this study.
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Figure 9. Above: The same area as in Figures 7 and 8, overlain with the LandFire
Existing Vegetation Type (EVT). Red is Madrean Lower Montane Pine-Oak, blue is
North American Warm Desert Riparian, dark green is Madrean Pinyon-Juniper, light
green is Madrean Encinal (oaks).
Figure 9 shows poor correspondence between the Madrean Pine-Oak as mapped in this
study (cross-hatched polygon), and Madrean Pine-Oak as mapped by LandFire EVT
(shown in red). A GIS analysis shows that within this study’s Madrean Pine-Oak
ecosystem, 29% of the EVT pixels were attributed as Madrean Encinal, 28% as Madrean
Pinyon-Juniper, 22% as Madrean Pine-Oak, and 12% as North American Warm Desert
Riparian Systems (which is Cottonwood-Willow, and not found in upper Rattlesnake).
Inexplicably, LandFire places much of the pine-oak on the south-facing slopes, which
typically hold pinyon-juniper.
This method of comparison can be misleading if the two GIS layers being compared
differ significantly in the number of total acres mapped as a particular ecosystem. For
example, let's compare the Madrean Pine-Oak as mapped in this study (cross-hatched
polygon) to the Madrean Pine-Oak as mapped by Southwest Regional GAP Ecological
System layer (see Figure 10, below). A GIS analysis shows that within this study’s
Madrean Pine-Oak ecosystem, 64% of the GAP map's Ecological Systems pixels were
attributed as Madrean Pine-Oak, a relatively high correspondence. But a closer look at
the data reveals that the GAP layer attributed 33,784 acres as pine-oak, far more than the
6842 acres mapped in this study. The 66% correspondence is no longer strong evidence
of similar results; with so much land mapped by the GAP layer as pine-oak, it's not
surprising there's considerable correspondence with the pine-oak mapped in this study.
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Figure 10. The same area as in Figures 7-9, overlain with the Southwest Regional GAP
Ecological System. Red is Madrean Lower Montane Pine-Oak, purple is Ponderosa Pine,
yellow is Mogollon Chaparral, and green is Madrean Pinyon-Juniper.
Still, the comparison gives an idea of the differences between the various vegetation
layers, and should be referred to when modeling fire behavior and Fire Regime Condition
Class. In particular, it always pays to check the correspondence between alternative
classification schemes when there is a vast difference in the number of acres mapped. For
instance, LandFire EVT mapped 17,067 acres of chaparral, compared to the 2612 acres
mapped in this study. (Chaparral, in the Landfire scheme, includes the Q. turbinella and
Cercocarpus montanus alliances). It’s hard to say why LandFire chaparral is so
abundant, but it does appear that, within the Galiuros, every pixel that LandFire attributes
as an Existing Vegetation Height (EVT) of either '0.5 to 1.0 meter shrub' or ‘1 to 3 meter
shrub’ is subsequently mapped as chaparral. (This is true regardless of the cover values;
even pixels with 10-20% cover are mapped as chaparral). When comparing the imagery
with the LandFire EVT of 0.5 to 3.0 m shrubs, it's clear that most of the pixels are on
very rocky areas with very low cover, or simply in areas of very low cover. LandFire is
certainly mapping something, but in this case it can hardly be considered chaparral.
Of course the ecosystem map offered here has its own share of shortcomings, particularly
when trying to map the often-similar juniper, oak, and pinyon ecosystems. These
problems are discussed in the ecosystem summaries, which provide plenty of photos to
help the reader understand the range of vegetation that we've tried to squeeze into eleven
neat ecosystems. Because nature often doesn't fit into our schemes, it's good to bear in
mind that the author has covered only a fraction of the Galiuros (see Figure 11, below),
and much of what is mapped was via binoculars and imagery. If you see a mistake, please
let us know at [email protected].
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Figure 11. Routes traveled by the author within the Galiuro Mountains. The heavy black
border encloses the Coronado National Forest. The Coronado includes about 135,000
acres of the Galiuro Mountains, within an area that runs about 27 miles from southeast
to northwest, and 8 to 10 miles wide.
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