PARENT SESSION
Organized Oral Session 34: Incorporating ecological processes at many scales into biogeochemical and global climate change models
Organizer(s): WM Post, JS Olson, and C Peng
Wednesday, August 10, 1:30 PM - 5:00 PM, Meeting Room 510b, Level 5, Palais des congrès de Montréal

Contrasting short- and long-time scale effects of vegetation dynamics on water and carbon fluxes in water-limited ecosystems.

Williams, Christopher^{*,1, 2, 3}, Albertson, John^{1, 2}, ¹ Civil and Environmental Engineering, Durham, NC, USA² Nicholas School of the Environment and Earth Sciences, Durham, NC, USA³ Natural Resource Ecology Laboratory, Fort Collins, CO, USA

ABSTRACT- Though generally believed to influence land-atmosphere water and carbon fluxes, observations indicate that in some cases fluxes are insensitive to the magnitude and composition of vegetation cover. This apparent inconsistency may be resolved by contrasting fluxes over short- and long-time scales. To explore this contrast we employ a new model designed to simulate daily to decadal land surface water and carbon fluxes and vegetation dynamics for water-limited ecosystems. Two sets of numerical experiments were conducted, either with fixed (static) grass and wood covers, or allowing plant covers to adjust dynamically with production. Static simulations reveal that the direct effect of rainfall on soil moisture is more important than the prevailing grass and wood cover states in controlling annual transpiration and production. Dynamic simulations indicate sensitivity of daily fluxes to vegetation cover states during high soil water periods. However, depletion of finite soil water prevents an integrated effect from lasting over interstorm to annual time scales. Correspondingly, while seasonal vegetation dynamics enhance seasonality in fluxes, vegetation dynamics have only minor influence on annual transpiration and plant production. In fact, annual rainfall explains most (R > 0.85) of the temporal variation in annual water and carbon fluxes. Hence, despite alteration of daily and seasonal distributions of fluxes, for water-limited ecosystems, vegetation dynamics have little effect on annual transpiration and production.

Key words: water and carbon fluxes, water-limited vegetation dynamics, daily, seasonal, and annual time-scales, land cover