Human activities are impacting the majority of the earth’s ecosystems, eroding provision of ecosystem services and biodiversity. Often many of these impacts – land-use change, climate change, invasive species, and altered nutrient and disturbance regimes – operate synergistically. There is large uncertainty about how policy and management should best respond to these complex and rapidly changing dynamics. Thus, a goal of our research is to apply understanding of community and ecosystem dynamics to reduce vulnerabilities and increase resilience and adaptation. Currently our research addresses three interrelated themes:


DYNAMICS. Ecosystem dynamics can be complex, non-linear and surprising. Threshold or abrupt changes in ecosystems are important to identify – before they occur, as there may be ways to avoid the transition, as well as afterwards, as they may fundamentally change restoration strategies. To tackle this challenge, we take a multifaceted approach, incorporating observational patterns, modeling and experimental approaches from the species to community to ecosystem levels of ecological organization.


MECHANISM. We combine field manipulations at both large and smaller scales with models to tease apart the underlying causal mechanisms that may buffer, accelerate and maintain ecosystem change. In particular, we are interested in feedbacks involving local plant-soil effects and landscape propagule pressure, as well as plant functional traits and functional diversity. Understanding these mechanisms is essential in order to predict how systems will respond – the extent of their resilience – in the face of restorative measures or further degradation.


APPLICATION. Predictions of ecosystem change and recovery are inextricably linked to restoration and conservation. Ecological science needs to be able to apply theory to practical challenges faced by conservation organizations and policy advocates. Thus, we try to collaborate with land managers and apply our work in management settings.

We are involved in a wide range of research projects, in settings that range from the alpine tundra in Colorado to the annual grasslands in California. Some current projects include:

• Community assembly and ecosystem change. What are the relative role of local resource competition and landscape level dispersal constraints influence coexistence and recovery dynamics? What is the influence of other interactions, such as plant-microbial and plant-herbivore interactions? Does resource partitioning of N forms and flowering time stabilize coexistence? How will environmental change, particularly increased levels of nitrogen deposition and changed snowpack, affect these interactions?


• Regime shifts, invasion and management. Can we use a multiple state framework to understand habitat conversion and widespread invasion? Do positive feedbacks mediated by species effects on litter and soil microbial processes contribute to invasion dynamics? How do differences in colonization rates between natives and exotics influence local interactions? Does grazing management influence the resilience and threshold dynamics in California rangelands?


• Restoration of ecosystem services and ecological resilience. What are the relationships among environment-functional trait mechanisms that can optimize multiple ecosystem services in complex landscapes? Do factors such as plant functional diversity and landscape heterogeneity increase ecological resilience to changed disturbance regimes or extreme climate events?



• Barriers to oak recruitment. Why are so few oaks able to recruit in oak woodlands? Is a demographic bottleneck to blame? How do seasonal grazing practices and interactions with annual grasses influence this bottleneck?


• Native recovery: Breaking the cycle of invasion. Following the removal of a problematic exotic, when does passive restoration of natives occur and when does an area get stuck in a vicious cycle of exotic replacement? Does the removal of the exotic have to reach some threshold reduction for sustainable restoration to occur? When can the application of ideas relating to novel ecosystems optimize biodiversity and ecosystem services?