Soils, hydrology and vegetation distribution on a saline landscape at Hailstone National Wildlife Refuge

Abstract

Landscape impacts from saline seep and human induced salinity are increasing across the western United States and are a major concern for global agricultural security (Gleick 1993). At Hailstone National Wildlife Refuge in south central Montana, refuge managers called for dewatering of a saline lake to reduce impacts to wildlife as a result of 80 years of exacerbated salinity. The dewatering has resulted in the rapid exposure of saturated and near-saturated sediments and a potential for wind driven salt mobilization. Prior to dewatering, salt tolerant vegetation was common on the lakeshore and tributaries and colonized in banded patterns. A study was initiated to understand abiotic conditions and species composition in these areas. Transects were established across the vegetated bands and plant species, percent canopy cover, richness, and diversity were sampled. Sample positions were categorized based on most common species. Abiotic conditions analyzed included landscape position, soil salinity and depth to saturation and soil nutrients for each sample point. Salicornia rubra dominated the lowest elevational position on the lakeshore, where prolonged saturation led to anaerobic conditions and the highest sodicity among all positions (electrical conductivity, EC = 34.5 dS/m, SAR= 33.6). Along the elevational gradient above the lake depression, there was gradual reduction of EC and increased depth to saturation. The most common plant species transitioned from Salicornia rubra to Suaeda calceoliformis and Distichlis spicata, and eventually to Poa pratensis in the upland position. Analyses showed that species type and distribution were sensitive to variations in landscape position, soil salinity, and saturation. A combination of these factors demonstrated correlation with plant species occurrence. This study provides evidence that abiotic conditions are an important determinant of vegetation banding across a salinity/saturation/elevation gradient at Hailstone National Wildlife Refuge. The data suggests that further understanding of soil salinity and soil moisture regimes on the exposed lakebed can be used in conjunction with a selection of adapted species to revegetate a saline lakebed.