Forest response and recovery following disturbance (Invited)
Abstract
Forest management and global climate change may modulate forest responses to disturbances such as drought, insect infestation or windthrow. Forest responses to drought and gypsy moth defoliation measured from 2005 to present in an oak/pine ecosystem in the Atlantic Coastal Plain (New Jersey Pinelands) show a relative conservatism of water use but longer lasting effects on carbon balance. While post-defoliation transpiration and evapotranspiration were similar to pre-defoliation levels, post-defoliation carbon fluxes have not returned to pre-disturbance levels even after five years of recovery due to a 25% reduction in basal area following tree mortality. Defoliation frequency also affects recovery with modeled carbon fluxes under various defoliation scenarios, showing pronounced reduction in productivity under frequent defoliation, but no effect if defoliation occurs at a rate of less than 15 years. Despite a relatively consistent seasonal water use through various disturbances, defoliation and drought affect water use differently. For example, canopy transpiration (EC) after defoliation and subsequent re-sprouting, was reduced by 25% compared to pre-defoliation levels, even though only half of the leaf area was replaced. However under severe drought conditions in 2006 and 2010, EC was only reduced by 8% and 18% respectively. Therefore, prolonged drought had a lesser effect on EC than reduced foliage or episodic defoliation, suggesting these trees have access to deeper soil moisture. These data also suggest that defoliation may make trees more sensitive to drought as evidenced by the higher reduction of Ec in 2010 compared to 2006 (pre-defoliation). Differential physiological responses of the various oak species as well as pitch pine may also create a species shift in an ecosystem that is also prone to fire. In this ecosystem, Quercus prinus showed consistently lower stomatal conductance, photosynthesis and maximum carboxylation rate compared to Quercus velutina, however both oak species displayed similar water and nutrient use efficiencies. Likewise, Pinus rigida, a predominant species in the Pinelands, showed comparable water - and nutrient use efficiencies to the oak species investigated signifying similar competitive strength in this ecosystem with respect to their physiologies. However, Q. velutina had higher mortality rates then Q. prinus suggesting a possible shift in oak species with more frequent defoliation events. Likewise, P. rigida may be released from competition if more oaks species face mortality due to gypsy moth defoliation occurrences. Therefore, forest functioning will likely be altered by re-occurring droughts, gypsy moth defoliation and windthrow, while the changes in energy partitioning will likely have impacts for regional climate in this forest ecosystem.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2013
- Bibcode:
- 2013AGUFM.B12C..03S
- Keywords:
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- 0439 BIOGEOSCIENCES Ecosystems;
- structure and dynamics;
- 0428 BIOGEOSCIENCES Carbon cycling