Status of terrestrial vegetation and soils at Leslie Canyon National Wildlife Refuge

Hubbard, John; DeRango, Bethany; Hubbard, Tani; McIntyre, Cheryl; Studd, Sarah

Leslie Canyon National Wildlife Refuge (NWR) in southeastern Arizona was established to protect important habitat for endangered fish species in the Yaqui watershed. The immense diversity in flora and fauna in Leslie Canyon is a result of the refuge’s location in a transition area between major ecoregions. Management and protection of these unique natural resources requires an understanding of broad-scale changes in ecosystems over time. We implemented a terrestrial vegetation and soils monitoring program as a collaborative initiative between the U.S. Fish & Wildlife Service and the National Park Service to support effective management and protection of refuge natural resources. This report summarizes the first round of terrestrial vegetation and dynamic soils monitoring at Leslie Canyon NWR. We surveyed key terrestrial vegetation and dynamic soil functional attributes including vegetation community structure, lifeform abundance, status and trends of established exotic plants, early detection of previously unde-tected exotic plants, and indicators of soil dynamic function and erosion resistance: cover of mineral soil and the stability of surface soil aggregates. Permanent plots were established using stratification based on elevation and soil rock-fragment classes. We suggest management assessment points to aid interpretation of ecological infor-mation within a management context and serve as a potential early warning system. Terrestrial vegetation communities at Leslie Canyon NWR were comprised of three types based on surface soil rock content and exotic plant encroachment: ● Non-rocky (<35% surface soil rock fragments), mid-mountain (4,501–6,000 ft.) mariola/creosote bush shrublands ● Rocky (35-90% surface soil rock fragments), mid-mountain (4,501–6,000 ft.) mariola/Rio Grande saddle-bush/slim tridens shrub savannas ● Rocky (35-90% surface soil rock fragments), mid-mountain (4,501-6,000 ft.) Lehman lovegrass-dominated semi-desert grasslands The most striking differences in terrestrial vegetation at Leslie Canyon NWR appear to be driven by the varying distribution and dominance of the non-native invasive bunchgrass, Lehmann lovegrass (Eragrostis lehmanniana) on rocky sites. The northern part of the refuge has been extensively colonized by this grass and management assessment points related to exotic plant abundance and cover were consistently exceeded on these sites. Effec-tive control of this species will be vital in protecting native flora and fauna and depends on developing an under-standing of the root causes of this invasion. The powerful influence of upland erosion on hydrologic function, chemistry, morphology, nutrients, and biologi-cal processes suggest that managing upland areas is critical to successful management of aquatic resources in Leslie Creek. Our data indicate that soils at Leslie Canyon NWR are currently very well armored. Vegetative cover was relatively high and biological crust cover was within our assessment point limits. The majority of soil cover consisted of highly resistant materials such as gravel and rocks. Surface soil aggregate stability across the refuge was “moderately stable”. However, stability on exposed soils of rocky sites – a subset of locations that were not protected by vegetation canopies – ranged from “somewhat unstable” to “unstable”, although sampling issues greatly limited our sample size. As exposed bare soil is the weakest link in the soil “armor” mitigating erosion on a site, we recommend a targeted assessment of soil aggregate stability on rocky sites. Although species richness and taxonomic diversity were not very different between sampling sites, we were surprised at the overall floristic diversity of the refuge. We detected about 35% of the 509 known species (deter-mined in a companion flora effort) in terrestrial vegetation plots.

Status of terrestrial vegetation and soils at Leslie Canyon National Wildlife Refuge

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