Functional convergence within forest and the role this plays in controlling the water fluxes through ecosystems

BUCCI SJ, SCHOLZ FG, MEINZER FC, GOLDSTEIN G

Australia

Conferencia; Canopy processes in a changing climate; 2010

IUFRO

Most lowland tropical forest and savanna ecosystems around the world are subjected to seasonal decreases in soil water potential. Several universal scaling relationships between leaf functional traits or between leaf traits and branch architectural traits across tree species tend to prevent water deficits and insure homeostasis in minimum YL and in total daily water loss per plant during the dry season. This isohydric behavior, depending on tree species and length of the dry period, can be the result of decline in total leaf surface area per tree, a strong stomatal control of evaporative losses, an increase in leaf-specific hydraulic conductivity and leaf hydraulic conductance, changes in water uptake patterns by roots, and an increase in the amount of water withdrawn from internal stem storage. These universal scaling relationships also include wood density and stem capacitance. Stems of most woody species operate far from the point of catastrophic dysfunction for cavitations, while leaves operate close to it and experience embolism on a daily basis, however differences exist depending on the type of forest ecosystem. All of these seasonal adjustments are important for maintaining YL above critical thresholds to reduce the rate of embolism formation in stems and help to avoid turgor loss in leaf tissues. This may be an advantage particularly in taller trees in which the cost of recovery from loss of hydraulic conductivity may be excessive in environments characterized by a long dry season, such as in dry forests and savannas. Using functional relationships across many different tree species, models were developed that allow predictions of effects of global climate change on structure and function of lowland tropical forests and savannas.