Landform Based Eco-Regional Mapping in Arid

Environments: Lessons from the Chihuahuan Desert

Michael N. DeMers, Daniel P. Dugas, Walter G. Whitford, and Janet Greenlee

Definition

Ecoregion: “recurring pattern of ecosystems associated with characteristic combinations of soil and landform that characterize that region.spatial coincidence of factorsmight involve “convergence” of evidenceoften hierarchical

Purpose

Develop a transferable method of rapid assessment of arid lands.

Goals: Method Characteristics

1. Triage-like decision tool for range managers

2. Technology light

3. Transferable to different arid regions

4. Effective

Method

Select undisturbed arid regionAssemble subject matter specialistsObtain hard copy of ETM7 imageryVisually classify the landformsConvert to vegetative classificationEvaluate classification

Chihuahuan Desert Study

Area: Armendaris

Ranch

Armendaris Ranch Study

Area

Polygon Mapping

Selected Study Area Landforms(after Peterson, 1981)

LF2 - Mountain slope LF13 - Depression

LF4 - Fan piedmont LF14 – Sedimentary bedrock hill

LF5 – Alluvial fan LF15 – Lava flow

LF8 – Fan skirt LF19 - Disturbed

LF9 – Lake plain LF20 – Aeolian terrain

LF10 – Alluvial flat LF22 - Bellana

LF12 - Playa LF23 – Inset fans

Methods of Geomorphology Classification

Modeled geomorphological units after hierarchical schemes for desert basin and range landforms

Obtained topographic characteristics using 1:15,000 scale, 20’ interval topographic sheets produced from digital files of 1:24,000 USGS sheets.

Designation of geomorphic units on 1:56,000 scale Landsat TM image plots. Band combinations of (5,4,1); (3,2,1); (7, 4, 1); band 1, PCA, etc. (visual interpretation)

Bedrock and sediment-shed mapping based on the geologic maps of Dane and Buchman (1965), Seager, et al. (1975), and Thompson (1992).

Obtain and Classify RS Data

Bands evaluated:

Rock types = TM 5 & 7.

Rock vs Veg = TM 1.

Combinations:

4, 5, 1

1, 3, 2

1, 4, 7

Principle Component Analysis Color Composite

Principle Component Analysis with Landform Polygons

Basic Geomorphi

c Unit Polygons

Variable Type LevelPH physiography: PH1 mountain

PH2 piedmontPH3 basin floor

LF landform: LF1 mountain canyonLF2 mountain slopeLF3 pedimentLF4 fan collarLF5 erosional fan remnantLF6 alluvial fan apronLF7 non-buried fan remnantLF8 alluvial plainLF9 playaLF10 hills of calcareous originLF11 hills and plateaus of igneous

originLF12 active dunesLF13 inactive dunesLF14 coppice dunesLF15 blowoutLF16 arroyo bottomLF17 other

2 montane slope4 fan piedmont5 alluvial fan8 fan skirt10 alluvial Flat12 playa13 depression14 sedimentary hills15 lava flows19 disturbed20 aeolian terrain22 balena23 inset fan

Vegetation Mapping

Verification

Random walk (with vehicle)GPS location plottedSpecies composition recorded9 initial communities identifiedCrosswalking field observations

with landforms yielded 3 additional categories

Plant Community Types I

V1 – Rock outcrop bedrock

3A – Desert grassland, shrub-mixed grass series

V2 – Rock outcrop 0 – Desert grassland, montane grassland

V3 - Steep piedmont slopes 3B - Desert grassland, threeawn series

V4 – Gently sloping piedmonts

0 – Desert grassland, gramma grass series

V5 – Fine textured basin drainage

0 – Desert grassland, closed basin playa alkalai sink-riparian

V6 – Run-on piedmont segments

0 – Desert grassland, tobosa series

Plant Community Types IIV7 – Upland rolling plains on piedmont

0/1A – Desert grassland grama grass series

V8 – Lava flows + aeolian deposits

4B – Desert grassland, shrub-mixed grass series

V9 – Basins with high gypsum soils

0 – Desert grassland, sacaton series / closed basin-playa-alkali sink riparian

V10 – Aeolian with coppice dunes

1C/2B - Chihuahuan Desert scrubland

V11 – Gentle lower piedmont interfluves with permanent livestock watering points

3C - Disturbed Chihuahuan Desert scrubland

V12 - Gently sloping lower piedmont erosional drainiges w/in 1.5 km of permanent livestock watering points

5C - Disturbed Chihuahuan Desert Scrubland

Composite Landform / Vegetation Polygons

Results

With few exceptions geomorphic map units also mark real vegetation boundaries

Triage mapping of vegetation using geomorphology/vegetation relationships is a useful and valid method

The geomorphology/vegetation relationships identified in the Armendaris Ranch study area are effectively being applied to compare potential (undisturbed) and disturbed rangeland conditions in the Jornada LTER.

What’s Next?

1. Create an appropriate methodology to quantitatively asses our accuracy (See Klimaszewski-Patterson)

2. Create a rule-based system to implement the “REAL” triage method of arid land evaluation

3. Export the methodology to a different arid rangeland region

Acknowledgements

Armendaris Ranch – general manager Mr. Tom Waddell

Mr. Dallas Bash from the Directorate of the Environment, U. S. Army, Fort Bliss, Texas – imagery.

This research was funded by National Aeronautics and Space Administration/Jet Propulsion Laboratory Grant (#1241945).