Collaborative Proposal: Aeolian Processes: An Overlooked Driver of State Change in Drylands?

University Of California-Los Angeles, Los Angeles CA

Investigators

Abstract

The conversion of grassland to a desert with sparse shrubs, or desertification, is occurring in areas across the world. In many cases, desertification replaces plants that livestock and wildlife prefer to eat with shrubs that are difficult for them to digest. This problem therefore threatens the livelihood of farmers and ranchers while also jeopardizing wildlife habitat. Despite the widespread occurrence of desertification, the exact causes are difficult to pinpoint. Many scientists suggest that when grazing animals choose to eat grasses over shrubs, the shrubs take over. However, desertification has often been observed in areas without livestock, so there may be multiple causes for desertification. This research intends to discover if desertification in areas with low rainfall (which tend to be sandier) is due to sand being blown by the wind (sandblasting). Windblown sand can do two things that might cause desertification: 1) erode soil and decrease its fertility and 2) damage grass plants. Because grasses require richer soils and are more fragile than shrubs, shrubs may be at an advantage where there is more wind and soil fertility is lower. Through this research, undergraduate students and a postdoctoral researcher will be trained. Outreach to K-12 teachers and students will be conducted, and will include individuals from underrepresented groups. This research tests the following hypotheses: 1) leaf properties determine the effect of sandblasting on the plant's ability to regulate water loss and carbon uptake and to maintain an impermeable barrier to water loss during nighttime and dormant periods; 2) growth form, specifically plant height and exposure of growing points, determines vulnerability to sandblasting; 3) seedling water and nitrogen demands differ between grasses and shrubs, giving shrubs the advantage on wind-eroded soils; 4) vulnerability of new plants to sandblasting damage differs between grasses and shrubs and this vulnerability is related to soil nitrogen status; and 5) leaf and plant effects will lead to long-term changes in plant populations, culminating in a shift from grass to shrub dominance. Field experiments will be conducted on a wide range of grass and shrub growth forms. In one series of experiments, established plants will be placed in a wind tunnel that manipulates levels of sand blasting. In another, seedling establishment and growth will be quantified on sites with different soil surface characteristics associated with contrasting long-term levels of windborne transport. Results from these experiments will be integrated using models to quantitatively assess the role of these processes in driving desertification.