Current Research
Forest Response to Climate Change and Disturbances
Our research examines the effects of recent disturbances and changes in climate on tree recruitment and growth among western US conifer species using a combination of field observational studies, dendrochronology, and freely available national datasets.
Effects of changing climate on seed production and population viability of mast-seeding conifers
Mast seeding, or the highly synchronous and intermittent production of large seed crops, is a common life history strategy among many perennial plant species and may be particularly sensitive to changing climate. Our work is focused on: (1.) Quantifying the spatiotemporal patterns of cone production of western US conifer species to determine how total reproductive output and the degree of masting may be affected by changing climate; (2) Assessing how sensitive population dynamics are to changes in the magnitude and timing of cone production under different predicted climate scenarios.
Managing for Forest and Woodland Resilience to Global Change
Predicting tree invasions in South Africa using a nutrient stock analysis
Global vegetation models indicate that climate is a significant predictor of major vegetation types. However, vegetation models fail to predict extensive regions of the globe dominated by ‘open’ vegetation types such as savannas, grasslands and shrublands. The fynbos biome in the Cape Floristic Region of South Africa is an example of a region in which the realized woody biomass falls below the climatic potential, receiving sufficient mean annual precipitation and sufficiently high annual temperatures to support extensive closed canopy forest systems. The lack of more extensive woody forests in the fynbos region has long puzzled ecologists. The issue has recently been complicated by the extensive invasion of nonnative woody plants into areas previously devoid of significant woody biomass, demonstrating that some alien trees have the ability to thrive in an area normally devoid of forests. This leaves researchers asking what limits the growth of indigenous trees in fynbos shrublands?
In this project, we examine whether differences in nutrient requirements between invasive tree species and native tree and shrub species may partially explain recent invasion success in the fynbos biome. Tree wood contains significant concentrations of nutrients, and although these concentrations are lower than in leaves, when scaled by biomass the bulk of aboveground nutrients are associated with the wood. This nutrient investment in wood may constrain local native species from thriving in the nutrient poor fynbos soils. Preliminary sampling indicates that invasive tree species have wood with smaller concentrations of nutrients than that of indigenous species. Thus, we hypothesize that nutritionally “cheap” wood production enables nonnative trees to invade the native fynbos shrublands that were historically devoid of trees.
In this project, we examine whether differences in nutrient requirements between invasive tree species and native tree and shrub species may partially explain recent invasion success in the fynbos biome. Tree wood contains significant concentrations of nutrients, and although these concentrations are lower than in leaves, when scaled by biomass the bulk of aboveground nutrients are associated with the wood. This nutrient investment in wood may constrain local native species from thriving in the nutrient poor fynbos soils. Preliminary sampling indicates that invasive tree species have wood with smaller concentrations of nutrients than that of indigenous species. Thus, we hypothesize that nutritionally “cheap” wood production enables nonnative trees to invade the native fynbos shrublands that were historically devoid of trees.