Can trees help cities adapt to extreme heat events?

Urbanization results in cities having warmer temperatures than surrounding areas (i.e., urban heat island effect) which is anticipated to worsen as climate change progresses. A commonly proposed nature based solution to extreme heat is to increase urban canopy cover. Trees can help cities adapt to extreme heat by moving water from the ground to the atmosphere where it evaporates (or transpires) and creates a cooling latent heat fluxes that can reduce local temperatures. There are few studies, however, that quantify the response of tree transpiration to unique and heterogenous growth conditions trees experience in urban areas and how these growth conditions influence the response of urban trees to extreme temperatures (Winbourne et al. 2020). Using ground-based measurements of transpiration (e.g., sap flux sensors) with novel sensor design (Jones et al. 2020 Ecospheres) we are testing how tree transpiration responses to urbanization and extreme temperatures among tree species known to vary in their water use strategies.

To learn more click here to hear Winbourne discuss "Hot Days and Tree Transpiration" with Bioscience Talks podcast.

What are the spatial and temporal trends in biogenic carbon dioxide fluxes in urban areas?

Cities are responsible for ~70% of global anthropogenic carbon emissions and are where the majority of humans live on earth. Across the globe, cities are taking the lead on climate change action, making pledges to decarbonize their societies. Accurate measurements of carbon emissions in cities is necessary to guide policy decisions and monitor their efficacy. Historically urban areas have been considered concrete jungles with the influence of biology (plants and soils) on carbon fluxes being assumed as known, neutral or negligible. This has introduced biases of unknown magnitude into the measurement and modeling of carbon emissions in cities. Urbanization creates a suite of novel ecosystem conditions that can have important but poorly constrained impacts on ecosystem carbon balance (Winbourne et al. 2022). In the Winbourne lab we use empirical and modeling studies to investigate when, where, and how plants and soils influence urban carbon fluxes.

What regulates the availability of nitrogen in temperate and tropical forests?

Despite bathing in an atmosphere of nitrogen, this element remains one of the most common limiting nutrients to the growth of terrestrial plants. In the absences of anthropogenic fertilizers (or Haber-Bosch process) and lightening, only a select group of bacteria are able to convert the inert di-nitrogen in the atmosphere into inorganic forms of nitrogen essential to life on earth. Some plants have evolved symbiotic relationships with nitrogen fixing bacteria (such as plants in legume family) providing them a potential advantage when nitrogen is in short supply. Research in the Winbourne lab examines the drivers regulating the activity of biological nitrogen fixation in temperate and tropical forests by bacteria living in the soil or in symbiotic relationships with plants. Past research projects have examined the contribution of nitrogen from legumes during secondary tropical forest succession (Winbourne et al. 2018) and how we can improve our empirical estimates of this process (Winbourne et al. 2018).