Analysis of Soil and Vegetation Maps:
Accuracy and Utility for Describing Actual Habitats
There are four sources of landscape information from maps at
the project level a few miles on a side. Topogaphic maps, satellite maps, soil service
maps, and vegetation maps.
Comparing soil and vegetation maps at this scale is
complicated by inaccuracies of both map sources and the strange ambiguity of
aerial photography. Soil was mapped by
NRCS into 6 major soils. However, two of
the soils are described as compound soils, regions of undefined patches possibly
intergrading continuously into one another.
For example, Pyote-Maljamar soils (PU on soil map) have a layer of fine
sand everywhere, but there are unmapped bits and pieces of caliche at around 50
inches (Maljamar soils) in a matrix of deep sand (Pyote soils).
|
Soil map created using the NRCS Web Soil Survey showing major soil types. PT and PU are deep sands, BH and KO are shallower silty soils, and TF is intermediate. (PA and BA are extensions of PT and TF, respectively, in Eddy county.) |
Soil Profiles:
|
PT
|
PU
|
TF
|
BH
|
KO
|
Soil Name
|
Pyote
|
Pyote
|
Maljamar
|
Tunuco
|
Berino
|
Cacique
|
Kimbrough
|
0-10
|
A:
Loamy fine sand
|
A:
fine sand
|
A:
fine sand
|
A:
loamy fine sand
|
A:
fine sand
|
A:
fine sand
|
A:
gravelly loam
|
10-20
|
AC:
loamy fine sand
|
Btk:
sandy clay loam
|
Bt:
sandy clay loam
|
Bkm:
cemented material
|
20-30
|
Bkm:
cemented material
|
|
30-40
|
Bt:
Fine sandy loam
|
Bt:
fine sandy loam
|
Bt:
sandy clay loam
|
|
Bkm:
cemented material
|
40-50
|
|
50-60
|
Bkm:
cemented material
|
Type
|
Sandy eolian deposits
|
Sandy eolian deposits
|
Sandy eolian deposits
|
Sandy eolian deposits
|
Sandy eolian deposits over sandy
calcaereous alluvium
|
Calcaerous eolian deposits
|
Calcaerous alluvium and/or eolian
deposits
|
Selected Soil Properties
|
PT
|
PU
|
TF
|
BH
|
KO
|
Depth to restrictive layer
|
>200cm
|
127cm
|
43cm
|
>200cm
|
15cm
|
Calcium Carbonate (CaCO3)%
|
2%
|
2%
|
0%
|
17%
|
15%
|
% sand
|
75.8%
|
81.9%
|
78.6%
|
62.6%
|
43.0%
|
Ksat (inches/hour)
|
7.8
|
8.5
|
12.6
|
1.7
|
0.5
|
In this part of NM, depth to a restrictive soil layer
indicates the presence of caliche near the surface. These petrocalcic horizons are denoted Bkm on
the soil profile. KO has the shallowest
effective soil, followed by TF. Some
parts of BH appear quite shallow, but in the table the depth to a restrictive
layer is listed as greater than 200cm, possibly because some of the soil (i.e. the
Berino component) lacks a caliche layer. Caliche is composed of calcium
carbonate, so BH and KO are listed with the most calcium, and the least sand in
their profile.
Saturated hydraulic conductivity (Ksat) refers to the ease
with which pores in a saturated soil transmit water. The estimates are
expressed in inches/hour for ease of comparison to possible rainfall rates.
They are based on soil characteristics observed in the field, particularly
structure, porosity, and texture.
Restrictive soil layers and overall soil texture contribute
to the ability of a soil to drain water.
PT, PU, and TF are listed as very well drained soils because they can
all drain more than 7 inches of rain an hour, whereas BH and KO are
significantly less porous, draining only 1.7 and 0.5 inches of rain an hour,
respectively. Most of the water from
heavy rains probably runs off of these soil types, limiting the amount
available to grow plants.
Saturated hydraulic conductivity is considered in the design
of soil drainage systems and septic tank absorption fields. It probably has the
greatest impact on plant production of any soil parameter in SE NM.
|
Hydraulic conductivity is the rate at which a soil can absorb water. Red areas have the least ability to absorb rainfall, while blue areas have the greatest ability to absorb rainfall. Map created using NRCS Web Soil Survey. |
Vegetation Map
Vegetation Map Key and Attributes
Table 3. Vegetation Map Key and Attributes
Color
|
ReGAP
Community Name
|
Vegetation
Type
|
Dominant
Species
|
Accuracy
|
|
Great Plains Shortgrass Prairie
|
Grassland
|
Biennial wormwood, Russian thistle
|
Low – should be mapped as disturbed area
|
|
Mesquite Upland
|
Thornscrub
|
Mesquite, Catclaw Acacia, Mimosa, Yucca
|
High - mesquite dominant
|
|
Sandhill Shrubland
|
Shrub
|
Shinnery oak, Catclaw acacia, Giant dropseed
|
Medium – not all dune
|
N/A
|
Sandy Plains Semi-Desert Grassland
|
Grassland
|
Purple three-awn, Sand dropseed, Sand muhly
|
Low – not mapped
|
The GAP national land cover data, based on the NatureServe Ecological Systems Classification, are the foundation of the most detailed, consistent map of vegetative associations available for the United States. The soil map is interpolated based on soil pits and
vegetation patterns, so in a way it functions as a hand-drawn vegetation
map. Vegetation patterns have changed
from the time the soil survey was completed (1960’s?) to now. This GAP high-resolution vegetation map was
produced via satellite mapping and computer algorithms.
The prairies
of the southern Great Plains are also called the Llano Estacado, a region where
vast flat to rolling uplands are covered with blue grama grass. However, this
vegetation type is misclassified. GAP
maps roads and disturbed areas with low grass as shortgrass prairie (brown on
image) because these areas look similar to prairie in multispectral satellite
imagery. It maps the rest of the project
area as a fractal pattern of mesquite upland (mauve) patches and sandhill
shrubland (green) patches.
Mesquite has
spread throughout areas with deep sandy soils and now forms the default
vegetation community across much of the area. Mesquite can also invade sandhills
and desert washes and other coarse-textured soil areas. It is especially
invasive in grasslands such as Sandy Plains Semi-Desert Grasslands, Great
Plains Shortgrass Prairie, and Chihuahan Semi-Desert Grasslands.
Mesquite
grows best when soils are deep, lacking the caliche or clay pan that would
limit infiltration and storage of winter precipitation in deeper soils layers.
Mesquite and other deep-rooted shrubs exploit the deep soil moisture that is
unavailable to cacti or grasses.
The effects of major soil boundaries are evident: deep sand
(PT and PU) soils support more sandhill shrubland, whereas soils with shallow
restrictive horizons (BH and KO) tend to have more mesquite upland
patches. The vegetation map fails to
identify patches of Lehman lovegrass grasslands, or catclaw acacia shrublands,
but it does correctly identify shinnery oak areas as sandhill shrubland.
However, the map misses out on an important intermediate
community, sandy plains semi-desert grassland.
Sandy plains grasslands are actually the dominant community throughout
much of the project area. It is
distinguishable on the ground by the greater proportion of grass than shrubs on
sandy soils, often with Aristida purpurea, Muhlenbergia arenicola, and
especially Sporobolus flexuousus.
However, this community has been invaded by mesquite shrubs (some areas
of which have been recently killed with herbicides) so these grassland patches
can be difficult to distinguish from true shrublands.
Topo Map
A topo map shows that areas with accumulating sand are typically uplands, especially breaks in slope where winds drop eolian deposits. Eroding, exposed slopes reveal deeper, more-developed paleosoils, possibly
Pleistocene clays (Steve Hall, 2006
Geomorphology of Mescalero Sand Dunes).
On top of soil and geomorphic landscape-determined
vegetation patterns, local populations of invasive species have overlaid an
unpredictable pattern of monocultures of Lehman Lovegrass, Artemisia biennis,
and occasional plants of Salsola tragus around wellpads. Note that none of these invasive species are
NM state-listed noxious weeds. There are
also surprising areas of intact, diverse Chihuahuan grasslands with healthy
stands of black grama , muhly arenicola, and sporobolus cryptandrus. All of the sand dunes here, despite
presence of shinnery oak, and even some Artemisia filifolia, are coppice or hummock
dunes that formed around shrubs during historical time (Hall, 2006).
Conclusion
Unfortunately, there are no map sources of reliable data on habitats and vegetation communities at field- or project area-scale. Each source provides valuable clues along with misleading simplifications, errors, and obfuscations of actual on-the-ground conditions.
Appendix: Soil Properties Maps
Depth to a restrictive soil layer:
Percent sand:
Percent calcium carbonate: