Modeling seasonal vegetation phenology from hydroclimatic drivers for contrasting plant functional groups within drylands of the Southwestern USA

Abstract

In dryland ecosystems, vegetation within different plant functional groups exhibits distinct seasonal phenologies that are affected by the prevailing hydroclimatic forcing conditions. The seasonal variability of precipitation, atmospheric evaporative demand, and streamflow influences root-zone water availability to plants in water-limited environments. Increasing interannual variations in climate forcing of the local water balance and uncertainty regarding climate change projections have raised the potential for phenological shifts and changes to vegetation dynamics, posing risks to plant functional types across large areas, especially in drylands and within riparian ecosystems. Due to the complex interactions between climate, water availability, and seasonal plant water use, the timing and amplitude of phenological responses to specific hydroclimate forcing cannot be determined a priori, thus limiting efforts to dynamically predict vegetation greenness under future climate change. Here, we analyze two decades (1994-2021) of remote sensing data of soil adjusted vegetation index (SAVI) as well as contemporaneous hydroclimate data (precipitation, potential evapotranspiration, depth to groundwater, and air temperature), to identify and quantify the key hydroclimatic controls on the timing and amplitude of seasonal greenness. We focus on key phenological events across four different plant functional groups occupying distinct locations and rooting depths in dryland SE Arizona: xeric grasses and shrubs, xeric riparian terrace and hydric riparian floodplain trees. We find bimodal seasonal phenology curves for grass and shrubs that are strongly driven by contributions from spring and monsoonal precipitation, while canopy greenness in floodplain and terrace vegetation showed strong response to groundwater depth as well as antecedent available precipitation (P-PET) throughout reaches of perennial and intermediate streamflow permanence. The timings of spring green-up and autumn senescence were correlated with seasonal changes in air temperature for all plant functional groups. Based on these findings, we develop and test a simple, empirical phenology model, that predicts the timing and amplitude of greenness based on hydroclimate forcing. We demonstrate the feasibility of the model by exploring simple, plausible climate change scenarios, which may inform our understanding of phenological shifts in dryland plant communities and may ultimately improve our predictive capability of investigating and predicting climate-phenology interactions in the future.

Patterns, timing, and environmental drivers of secondary growth in two physiologically distinct Mediterranean alpine shrub species

“…Overall, we observed bimodal patterns of stem diameter changes in both alpine shrub species despite their physiological differences. This is consistent with the bimodal seasonal cycle observed in other shrub species in semi-arid environments, where this seasonal cycle has been attributed to seasonal interactions with temperature and precipitation (Warter et al 2023). However, these stem diameter changes did not always correspond to seasonal growth patterns but rather reflected differences in summer-heat-and winter-cold-induced droughts and corresponding dehydration and rehydration patterns (Albrecht et al 2023).…”

Assessing thermal ecology of herpetofauna across a heterogeneous microhabitat mosaic in a changing aridland riparian system

“…Sabino Canyon Recreation Area (SCRA) resides in the southern foothills of the Santa Catalina Mountains in Tucson, Arizona, USA (Lazaroff 1993). The regional climate is semi-arid desert with bimodal seasonal precipitation peaks in winter/spring and summer, abutted by dry periods (McMahan et al 2021, Warter et al 2023. Our study area occurred in lower SCRA, adjacent Sabino Creek.…”

“…This may in part be due to aridland lizards possessing greater flexibility to warming conditions (Goller et al 2014, Griffis-Kyle et al 2018. Desert riparian amphibians, such as H. arenicolor, may be more sensitive to their environment (Preest et al 1992, Snyder andHammerson 1993), especially as the region warms and dries (Archer and Predick 2008, Roby et al 2020, Warter et al 2023. Temporally, herpetofauna in the SCRA were as warm at mid-morning (i.e., 09:00 onward) than they were in early-afternoon (e.g., 12:00-13:00).…”

“…Climate change in aridland ecosystems, such as the southwestern United States, is predicted to bring increased temperature and aridity while stressing water availability via reduced precipitation, elevated evapotranspiration rates, and anthropogenic demand (Archer and Predick 2008, Roby et al 2020, Warter et al 2023. Riparian zones are important corridors of biodiversity (Naiman et al 1993), especially in aridland ecosystems (Free et al 2015).…”

Anthropogenic, environmental and temporal associations with vertebrate road mortality in a wildland–urban interface of a biodiverse desert ecoregion

“…Climate in many arid regions, such as the American Southwest, is predicted to become hotter and drier and with fluctuations towards extreme events [56,[119][120][121][122]. Increasing temperature and aridity can alter soil pH [66], plant phenology and productivity [123,124], and community compositions [30,125]. Small mammals may be better equipped for climate change than birds, for example, owing to their abilities to use microhabitat refuges to escape heat [93].…”