COS 109-4
Post-fire recovery of biological soil crusts in the Great Basin: Cornerstone increased site resistance
The fire regime of the arid Great Basin is changing. Fires are burning at larger extents and with increased frequency due to more continuous fuel loads created by invasive annual grasses. Invasive annual grasses irreversibly alter hydrologic and nutrient cycles that promote plant recovery after fire. Biological soil crusts (BSCs) refer to mosses and lichens that live on the soil surface. BSCs maintain natural patterns of soil moisture and nutrient cycling and have been shown to hinder annual grass invasion, yet we do not know what influences BSC recovery following fire. We examined the distributions of BSCs across the Great Basin in relation to environmental factors and disturbances such as livestock grazing and fire, using a chronosequence approach and non-metric multidimensional scaling (NMS) ordinations. Surveyed fires burned once in recent history between 1990 and 2003. Fifteen fires and comparable unburned areas were surveyed between 2012 and 2013 for plant and BSC species abundance and composition. We develop a novel approach using functional traits related to energy acquisition, water regulation, dispersal capability and site / microsite specificity to compare post-fire recovery and assess the potential for BSCs to contribute to increased resistance to invasion by annual grasses across the Great Basin.
Results/Conclusions
NMS ordinations with three significant axes (p>0.05) demonstrated that species composition of BSCs varied along gradients of disturbance. A gradient of grazing intensity by livestock was apparent although the effect of time since fire was more variable by site. Moss species were a dominant component of BSCs at heavily grazed sites where as lichens increased in dominance with reduced grazing intensity. The effect of time since fire on species abundance was discernible at sites with low to moderate grazing intensities. The ability of BSCs to recover from fire was not only dependent on time since fire but showed interactions with fire intensity and site aridity. Site resistance to invasive annual grasses increased with increasing abundance of BSCs. Combinations of functional traits indicated intensity of past disturbances. The use of functional trait data reduced the influence of sites on ordinations and allowed for stronger relationships between BSCs and disturbance gradients. Results indicated that BSCs should be incorporated into monitoring protocols aimed at estimating site resistance to invasion following fire in the Great Basin. The use of functional traits is informative, can be readily applied by managers and will allow for future comparisons between the Great Basin and global steppe communities.