Heterogeneity in the spatial structure of plants and soils is particularly important for desert ecosystems. In deserts, resources are greater beneath shrubs, creating a matrix of islands of fertility and bare interspaces. Shrub islands have been studied extensively in unburned areas in many ecosystems, but less is known about plant and soil heterogeneity related to shrub islands following wildfire. We investigated the correspondence between physical, chemical, and hydrological properties of shrub island (coppice) and interspace soil surfaces and the plant community in burned and unburned landscapes. Field studies were conducted during summer 2009 on the Snake River Plain of southeastern Idaho at three large natural wildfires and three unburned control sites. Soil chemical properties (total carbon, total nitrogen) were determined for samples collected from 0-1 cm depth in the field in late summer. Soil physical and hydrological properties (mechanical strength, volumetric water content, water infiltration rate) were measured on each soil surface in the field in late summer. Plant abundance and diversity on each soil surface were recorded from late spring through summer.
Results/Conclusions
Total carbon and total nitrogen were 2x greater for coppices than interspaces, and both were 1.3x greater in unburned than burned coppices. Mechanical strength was lower and infiltration rates were greater on coppices than interspaces in both burned and unburned areas, but surprisingly, volumetric water content was lower in coppices than in interspaces in both burned and unburned sites by 2% and 1%, respectively. Species richness and percent cover of forbs and grasses were greater on unburned coppices than interspaces; however, there was no difference in species richness or percent cover of forbs between burned coppices and interspaces. Percent cover of grasses was greater on burned coppices than interspaces in July, but was not different in May and June. In unburned sites, coppice and interspace soil surfaces differed in soil and vegetation characteristics; however, our data suggest that post-fire soils remain heterogeneous while the corresponding plant community is more homogenous. This indicates that other factors, in addition to soil heterogeneity, are influencing plant heterogeneity at this scale. Shortly following wildfire, plant communities appear homogeneous indicating alternative spatial patterns for rangeland management reseeding may not be necessary to increase plant cover, but long term post-fire studies are necessary.
