PARENT SESSION
Oral Session # 70: Landscape Ecology.
Presiding: S Hannon
Thursday, August 7. 8:00 AM to 11:30 AM, SITCC Meeting Room 201.
Modeling vegetation community response to climate change and CO2 increases in the Chihuahuan Desert.
White, Joseph*,1, Gutzwiller, Kevin1, Barrow, Wylie2, Randall, Lori2, 1 Baylor University, Waco, TX2 U.S. Geological Survey, Lafayette, LA
ABSTRACT- Future climate changes coupled with increases in atmospheric CO2 may favor increased expansion and growth of woody shrubs in historically grass-dominated desert communities. We developed a spatially explicit mechanistic model to explore physiological and landscape processes associated with this potential conversion. The model predicts plant growth and allocation for different functional types; reproductive dispersal through varying pathways; and fire spread and effects. This model was applied to a region including Big Bend National Park to assess climate change and CO2 increases on community composition, above and belowground production, and fire frequency over the next 50 years. Average annual temperature for this area is expected to increase by 2 to 4°C with slight decreases in annual precipitation. Simulation results showed that potential future plant communities are dominated by woody shrub species as a combined effect of C3 photosynthesis physiology, greater drought tolerance, longer foliar retention and activity, and more reproductive output. Grasses decline in dominance because while their C4-type photosynthesis is enhanced with increased atmospheric CO2, their phenology is tightly coupled to soil moisture and precipitation which decrease with climate change. Overall primary productivity declines in the future scenario with a greater proportion of photosynthate allocated to belowground structures. Although fire fuels increase with climate change due to more shrub cover, fire frequency and return intervals decrease with less fine fuels contributed by grasses. In addition, reduced productivity decreases average vegetation canopy cover, leading to patchier fuel distributions and lower probability of fire spread. Spatial variation expressed in terms of both vegetation community and productivity decrease with climate change as increased shrub dominance and reduced fire frequencies result in a more homogeneous landscape.
Key words: carbon dioxide, fire, climate change, desert