Agricultural sustainability

Feeding a growing world population while minimizing negative environmental externalities is a major global challenge. Agricultural technologies have raised global crop yields, yet increasing negative environmental impacts as a result of agricultural intensification are accumulating. In collaboration with ALUS Canada and the Food From Thought and Biodiversity Resilience Network research groups, I research farm management techniques to improve water quality, provide habitat for biodiversity, and create more resilient agricultural systems in the face of climate change.

  1. Context-dependent interactions and the regulation of species richness in freshwater fish
Farm in Western Wisconsin

Consequences of drought and invasion on ecosystem functioning

Vegetation feedbacks to ecosystem processes represent a major source of uncertainty in climate change scenarios. In Southern California’s historically shrub-dominated ecosystems, increasing drought severity and invasions by exotic species represent two major consequences of global change. Overall, this research showed that invasion increases ecosystem sensitivity to drought in both aboveground and belowground processes.

  1. Invasion and drought alter phenological sensitivity and synergistically lower ecosystem production
  2. Competition reverses the response of shrub seedling mortality and growth along a soil moisture gradient
  3. Drought in Southern California coastal sage scrub reduces herbaceous biomass of exotic species more than native species, but exotic growth recovers quickly when drought ends
  4. Foliar litter chemistry mediates susceptibility to UV degradation in two dominant species from a semi-arid ecosystem
  5. Direct and indirect effects of shifting rainfall on soil microbial respiration and enzyme activity in a semi-arid system
  6. Priority effects vary with species identity and origin in an experiment varying the timing of seed arrival
  7. Climate change and subsistence exchange in Southern California: was western sea-purslane a Channel Island trade good?
Rainfall exclusion shelters at the Santa Margarita Ecological Reserve

Is community change in response to nutrient addition predictable?

In collaboration with theNutrient Network, this work investigates the controls on ecosystem productivity and diversity worldwide. I am working with collaborators to understand how nutrient additions shape changes in species community composition.

  1. Belowground Biomass Response to Nutrient Enrichment Depends on Light Limitation Across Globally Distributed Grasslands
  2. Soil net nitrogen mineralisation across global grasslands
Field day at the Elliott Chaparral NutNet site

Warming and shrub encroachment affecting decomposition in an alpine ecosystem

Climate change is disproportionately impacting high elevation and high latitude regions. Hotter, dryer weather and shifting species ranges are obvious changes, but the influence on carbon loss via altered decomposition patterns is equally important. Our findings highlight how shifting species composition, through processes such as range expansions, can influence ecosystem responses to climate change.

  1. Warming and shrub encroachment decrease decomposition in arid alpine and subalpine ecosystems
Passive warming chambers at the White Mountain Research Station

Ecosystem consequences of grazing and nitrogen deposition

Serpentine grasslands have historically been more resistant to invasion by exotic species due to low fertility soils. Anthropogenic nitrogen deposition has made these systems more susceptible to invasion. Land managers often graze cattle in grasslands to reduce the impact of invasive species. This research looked at the dynamics of these two factors - N deposition and grazing - on soil microbial functionality.

  1. Response of soil microbial activity to grazing, nitrogen deposition, and exotic cover in a serpentine grassland
Coyote Ridge serpentine grassland, south of San Jose

Successional dynamics in restored prairie

As much as 90% of tallgrass prairie was converted to agriculture and urban areas since European settlement. Conversion of prairie to agriculture has had significant ecosystem consequences, including effects on soil C and nutrient pools - losses of 89% of original carbon and 75% of original nitrogen has been reported. This work found that diverse prairie restorations rapidly accumulate carbon as a result of fast turnover of annual and biennial early successional species.

  1. Rapid Accumulation of Soil Carbon and Nitrogen in a Prairie Restoration Chronosequence
Carelton Arb
A recently restored tallgrass prairie in the Carleton College Arboretum