A sequence of multi-year wet and dry periods provides opportunities for grass recovery and state change reversals

Authors: PETERS, DEBRA - US Department Of Agriculture (USDA); SAVOY, HEATHER - US Department Of Agriculture (USDA)

Submitted to: Ecological Monographs
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/17/2023
Publication Date: 8/3/2023
Citation: Peters, D.P., Savoy, H. 2023. A sequence of multi-year wet and dry periods provides opportunities for grass recovery and state change reversals. Ecological Monographs. Article ecm.1590. https://doi.org/10.1002/ecm.1590.
DOI: https://doi.org/10.1002/ecm.1590

Interpretive Summary: Multi-year periods (=4 y) of extreme rainfall are increasing in frequency as climate continues to change, yet there is little understanding how variability in land surface properties affect state changes in a sequence of these periods (dry to wet to dry). Dryland landscapes provide an opportunity to examine the importance of periods and land surface properties at multiple scales to either woody plant-dominance under persistent drought effects or a shift towards grass dominance and state change reversal if wet periods overwhelm subsequent dry periods. A 28-y record of rainfall containing a sequence of multi-year periods showed that distinguishing periods was important to relationships between perennial grass production and rainfall amount in a dry period following a wet period in shrublands. Number of consecutive wet years explained grass production in a wet period. For the other periods, land surface properties at the plant (initial herbaceous biomass), patch (erosion potential), and landscape scale (soil texture) increased R2 values by 3 to 5 times over relationships with rainfall alone. Legacies of a dry or wet period were asymmetric where the smallest grass and total production in all ecosystem types was found in a dry period preceding a wet period, and the largest production occurred either in the wet period or in a dry period following a wet period (grasslands). The decrease or increase in perennial grass production in each period coincided with changes in plant size distributions. For other herbaceous plants, production was primarily related to rainfall and initial biomass, soil texture or erosion potential. Production of dominant shrubs was similar for all periods within each ecosystem type, although the suite of important variables differed between periods. Identifying dry and wet periods, and the multi-scale processes governing responses is expected to be important in predicting future potential states with shifts towards grass dominance in degraded shrublands as the frequency of wet periods increases.

Technical Abstract: Multi-year periods (=4 y) of extreme rainfall are increasing in frequency as climate continues to change, yet there is little understanding how variability in land surface properties affect state changes in a sequence of these periods (dry to wet to dry). Dryland landscapes provide an opportunity to examine the importance of periods and land surface properties at multiple scales to either woody plant-dominance under persistent drought effects or a shift towards grass dominance and state change reversal if wet periods overwhelm subsequent dry periods. A 28-y record of rainfall containing a sequence of multi-year periods showed that distinguishing periods was important to relationships between perennial grass production and rainfall amount in a dry period following a wet period in shrublands. Number of consecutive wet years explained grass production in a wet period. For the other periods, land surface properties at the plant (initial herbaceous biomass), patch (erosion potential), and landscape scale (soil texture) increased R2 values by 3 to 5 times over relationships with rainfall alone. Legacies of a dry or wet period were asymmetric where the smallest grass and total production in all ecosystem types was found in a dry period preceding a wet period, and the largest production occurred either in the wet period or in a dry period following a wet period (grasslands). The decrease or increase in perennial grass production in each period coincided with changes in plant size distributions. For other herbaceous plants, production was primarily related to rainfall and initial biomass, soil texture or erosion potential. Production of dominant shrubs was similar for all periods within each ecosystem type, although the suite of important variables differed between periods. Identifying dry and wet periods, and the multi-scale processes governing responses is expected to be important in predicting future potential states with shifts towards grass dominance in degraded shrublands as the frequency of wet periods increases.