Shrub size modulates resource heterogeneity in a sagebrush-steppe ecosystem

Authors: LIN, LIN - Sichuan Agricultural University; VEBLEN, K - Utah State University; Monaco, Thomas

Submitted to: Western North American Naturalist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/8/2019
Publication Date: 4/1/2020
Citation: Lin, L., Veblen, K.E., Monaco, T.A. 2020. Shrub size modulates resource heterogeneity in a sagebrush-steppe ecosystem. Western North American Naturalist. 80(1):28-37. https://doi.org/10.3398/064.080.0104.
DOI: https://doi.org/10.3398/064.080.0104

Interpretive Summary: Shrubs create heterogeneity in resource availability, yet the influences of shrub age and size on these conditions in semiarid ecosystems is largely unknown. In order to inform restoration and conservation efforts, we assessed plant age-size relationships within an Artemisia tridentata stand in southern Idaho, USA and examined the dependence of two resources, soil water content (SWC) and light at the soil surface (photosynthetically active radiation; PAR), on size of individual plants in understory and interspace microsites. Results included a positive relationship between shrub age and size, a median age of 19 years old, and shrub sizes that varied by more than three orders of magnitude (i.e., 0.001 m3 - 1m3). Across this broad range in stand structure, PAR declined with increasing shrub volume more in understory than interspace microsites. Similarly, SWC declined with shrub volume, but understory and interspace microsites did not differ. These findings indicate that resource heterogeneity created by shrubs is size-dependent within this ecosystem and that variation in stand structure directly influenced resource heterogeneity between understory and interspace microsites. We suggest that routine monitoring of heterogeneity in stand structure could serve as a valuable indicator to assess site suitabiliy for restoration activities and make quantitative comparisons among sites to priortize conservation efforts.

Technical Abstract: Shrubs create heterogeneity in resource availability, yet the influences of shrub age and size on these conditions in semiarid ecosystems is largely unknown. In order to inform restoration and conservation efforts, we assessed plant age-size relationships within an Artemisia tridentata stand in southern Idaho, USA and examined the dependence of two resources, soil water content (SWC) and light at the soil surface (photosynthetically active radiation; PAR), on size of individual plants in understory and interspace microsites. Results included a positive relationship between shrub age and size, a median age of 19 years old, and shrub sizes that varied by more than three orders of magnitude (i.e., 0.001 m3 - 1 m3). Across this broad range in stand structure, PAR declined with increasing shrub volume more in understory than interspace microsites. Similarly, SWC declined with shrub volume, but understory and interspace microsites did not differ. These findings indicate that resource heterogeneity created by shrubs is size-dependent within this ecosystem and that variation in stand structure directly influenced resource heterogeneity between understory and interspace microsites. We suggest that routine monitoring of heterogeneity in stand struture could serve as a valuable indicator to assess site suitability for restoration activities and make quantitative comparisons among sites to prioritize conservation efforts.