Decadal shifts in grass and woody plant cover are driven by prolonged drying and modified by topo‐edaphic properties

Abstract

Woody plant encroachment and overall declines in perennial vegetation in dryland regions can alter ecosystem properties and indicate land degradation, but the causes of these shifts remain controversial. Determining how changes in the abundance and distribution of grass and woody plants are influenced by conditions that regulate water availability at a regional scale provides a baseline to compare how management actions alter the composition of these vegetation types at a more local scale and can be used to predict future shifts under climate change. Using a remote-sensing-based approach, we assessed the balance between grasses and woody plants and how climate and topo-edaphic conditions affected their abundances across the northern Sonoran Desert from 1989 to 2009. Despite widespread woody plant encroachment in this region over the last 150 years, we found that leguminous trees, including mesquite (Prosopis spp.), declined in cover in areas with prolonged drying conditions during the early 21st century. Creosote bush (Larrea tridentata) also had moderate decreases with prolonged drying but was buffered from changes on soils with low clay that promote infiltration and high available water capacity that allows for retention of water at depth. Perennial grasses have expanded and contracted over the last two decades in response to summer precipitation and were especially dynamic on shallow soils with high clay that have large fluctuations in water availability. Our results suggest that topo-edaphic properties can amplify or ameliorate climate-induced changes in woody plants and perennial grasses. Understanding these relationships has important implications for ecosystem function under climate change in the southwestern USA and can inform management efforts to regulate grass and woody plant abundances.

Interaction of seed dispersal and environmental filtering affects woody encroachment patterns in coastal grassland

“…, Munson et al. ). Woody encroachment may be favored when constraints for woody species growth are reduced, which vary by ecosystem (D'Odorico et al.…”

“…Woody encroachment into grassland communities has occurred on nearly every continent throughout the Americas, Australia, and Africa, within the past 150 yr (Hagenah et al 2009, Brantley and Young 2010, D'Odorico et al 2012, Anad on et al 2014. Mechanisms of woody encroachment are multi-faceted and can include factors that operate at global (i.e., climate warming), regional (i.e., rainfall, CO 2 , and temperature), or landscape scale, as well as shifts in disturbance regimes (i.e., fire frequency, introduction or removal of grazing and dispersing animals), or intrinsic properties of the system (Van Auken 2000, Knapp et al 2008, D'Odorico et al 2012, Munson et al 2016. Woody encroachment may be favored when constraints for woody species growth are reduced, which vary by ecosystem (D'Odorico et al 2012, Archer et al 2017.…”

Woody structure facilitates invasion of woody plants by providing perches for birds

“…Woody encroachment occurs in response to multifaceted and interacting anthropogenically influenced causes, including climate change (Sankaran et al., ; Eamus & Palmer, ; Munson et al. ), changes to nutrient cycles (Köchy & Wilson, ; Kraaij & Ward, ), fire suppression (Kraaij & Ward, ; Roques, O'Connor, & Watkinson, ), and overgrazing (Kraaij & Ward, ; Roques et al., ; Van Auken, ). Plant species responsible for woody encroachment generally decrease the diversity of grassland plant communities (Ratajczak, Nippert, & Collins, ) and alter abiotic conditions for native herbaceous and graminoid species (Jo, Fridley, & Frank, ; Siemann & Rogers, ).…”

Effects of Textural Layering on Water Regimes in Sandy Soils in a Desert-Oasis Ecotone, Northwestern China

“…The formation of textural layered soils is a complex process resulting from a number of factors, such as translocation via eluviation-illuviation, bioturbation, erosion, deposition, and artificial reclamation (Phillips, 2001;Alfnes, et al, 2004). Textural layered soils are ubiquitous in the natural world, in places like southwestern Australia (Tennant, et al, 1992), the southwestern United States (Munson, et al, 2016), and western Canada (Selim, 2011). In China, similar textural layered soils have been found in the wind-water erosion crisscross region of the Loess Plateau (Zhang, et al, 2017a), and in the desert-oasis ecotone of northwestern China (Zhou, et al, 2016).…”