I am pursuing several projects to answer how ecohydrology of drylands affects ecosystem processes and composition of plant functional groups. Dryland ecosystems occupy 30% of the global land area and provide important ecosystem resources and services. Soil water dynamics are a critical factor for understanding water-limited ecosystems, which will likely respond differently to climate change than ecosystems in which water is not limiting. Changes in water balance likely will be pronounced in dry regions, which will be strongly affected by climate change.
Landscape-scale distribution of shrub steppe and coniferous forest
I focus on the combined impacts of climate change and disturbance regimes on ecotones of big sagebrush (Artemisia tridentata)-dominated ecosystems and coniferous forests in the semiarid western U.S. My simulation results suggested a northward and upslope movement of big sagebrush habitat suitability in response to climate change (Schlaepfer et al. 2012 Ecography). A further study revealed that climate change effects on the future ecosystem water balance increase non-linearly along a climatic gradient from snow-poor to snow-rich areas (Schlaepfer et al. 2012 Global Change Biol.). However, the potential for sagebrush to advance as coniferous forests retreat at the lower forest boundary is influenced by existing vegetation and disturbance regimes (Bradford et al. 2014 Ecosystems) and how environmental gradients influence the shape of this boundary.
Regional-scale patterns in semiarid vegetation dominated by shrubs
This project focuses on one of the most widespread semiarid ecosystem types in the western U.S. My results showed that soil water dynamics in these shrub vegetation types are characterized by a pronounced seasonal and soil-depth pattern, with a marked gradient across the geographic distribution (Schlaepfer et al. 2011 Ecohydrol.). These results suggested also that reducing the availability of deep soil water during summer dry periods, e.g. by reduced snowfall or earlier snowmelt, would potentially lead to large-scale shifts in the range of big sagebrush ecosystems in the future (Schlaepfer et al. 2012 Ecography). I am working on improving our spatially explicit understanding of these changes with three approaches: process-based predictions of how changes in climate means and climate variability will affect big sagebrush germination and seedling survival rates (Schlaepfer et al. 2014 Ecol. Model.); methodological advances of species distribution models (Bell et al. 2016 Ecol. Model.); development of a spatially-explicit, individual-plant based, competition and resource model to explore sensitivity of the shrub-dominated vegetation and habitat quality to disturbances and climate change.
Ecohydrological processes in global temperate dryland ecosystems
A third approach focuses on a global assessment of climate change impacts on the ecohydrology and functioning of temperate dryland ecosystems and services provided. My collaborators and I have assembled a workgroup that brings together 13 scientists from across the globe. Results from this workgroup will provide insights in important commonalities in ecohydrological dynamics, uncertainties in our understanding, and vulnerabilities to climate change of temperate dryland ecosystems worldwide. We are currently investigating how different precipitation seasonality patterns influence temporal and spatial dynamics of available soil water (Schlaepfer et al., in revision).
Albedo modification impact on global temperate dryland ecosystem water balance
Recently, substantial societal and scientific attention has highlighted important knowledge gaps about albedo modification, a potential strategy to counterbalance global warming caused by greenhouse gas emissions. Albedo modification, often implemented by augmenting stratospheric SO2, increases the amount of reflected solar radiation thereby having the potential to cool Earth within a few years. Despite huge potential and low cost, very little research has been done that explores how albedo modification will influence atmospheric processes and impact ecosystems. The few existing case studies suggest that albedo modification could lower temperatures, but also may decrease precipitation, with potentially large and unintended consequences for ecosystems, particularly in drylands, where water is often the most limiting resource. Our objective for this proposal is to investigate the ecohydrological consequences of changes in temperature and precipitation regimes caused by global albedo modification on global temperate drylands.
Invasive species provide insights into ecological, biogeographic and evolutionary processes. I contributed to the development of a well-cited, conceptual framework that considers how best to organize research in the field of invasion ecology (van Kleunen et al. 2010 Ecol. Lett.).
What determines invasiveness remains one of the most urgent questions in invasion ecology. Few studies have explicitly tested the role of ‘pre-adaptation’, that is, the formation of traits, before introduction that contributes to invasion success. I investigated pre-adaptation in populations of an abundant and widespread forb (Solidago gigantea, Asteraceae). I compared ploidy levels of native populations from across North America with invasive populations from Europe (Schlaepfer et al. 2008 J. Biogeogr.). Through experimental manipulations, I established that differences in rhizome development among ploidy levels were responsible for variation in the ability to spread to new areas (Schlaepfer et al. 2010, Oecologia). My results of a phylogeographic analysis suggested that the invasive potential of S. gigantea could be attributed to pre-adaptation in the native range before introduction (Schlaepfer et al. 2008 Mol. Ecol.). I continued to investigate the determinants of invasiveness with a large multi-species experiment. These results confirmed that traits leading to high plant performance in the native range contribute to pre-adaptation across a wide range of invasive species (Schlaepfer et al. 2010 New Phytol.; van Kleunen et al. 2011 J. Biogeogr.). Species traits that lead to pre-adaptation might be especially relevant for use in risk-assessment protocols before introduction.