Impacts of Hurricane Frances on Florida scrub‐oak ecosystem processes: defoliation, net CO₂ exchange and interactions with elevated CO₂

Abstract

Hurricane disturbances have profound impacts on ecosystem structure and function, yet their effects on ecosystem CO 2 exchange have not been reported. In September 2004, our research site on a fire-regenerated scrub-oak ecosystem in central Florida was struck by Hurricane Frances with sustained winds of 113 km h À1 and wind gusts as high as 152 km h À1 . We quantified the hurricane damage on this ecosystem resulting from defoliation: we measured net ecosystem CO 2 exchange, the damage and recovery of leaf area, and determined whether growth in elevated carbon dioxide concentration in the atmosphere (C a ) altered this disturbance. The hurricane decreased leaf area index (LAI) by 21%, which was equal to 60% of seasonal variation in canopy growth during the previous 3 years, but stem damage was negligible. The reduction in LAI led to a 22% decline in gross primary production (GPP) and a 25% decline in ecosystem respiration (R e ). The compensatory declines in GPP and R e resulted in no significant change in net ecosystem production (NEP). Refoliation began within a month after the hurricane, although this period was out of phase with the regular foliation period, and recovered 20% of the defoliation loss within 2.5 months. Full recovery of LAI, ecosystem CO 2 assimilation, and ecosystem respiration did not occur until the next growing season. Plants exposed to elevated C a did not sustain greater damage, nor did they recover faster than plants grown under ambient C a . Thus, our results indicate that hurricanes capable of causing significant defoliation with negligible damage to stems have negligible effects on NEP under current or future CO 2 -enriched environment.

Diel patterns of soil respiration in a tropical forest after Hurricane Wilma

“…Our result of increased soil respiration 1 year after hurricane Wilma contrast with previous studies in which a reduction in soil respiration was observed following hurricane disturbances in tropical and subtropical forests [ Steudler et al , 1991; Li et al , 2007]. However, our study site suffered considerably more damage from a hurricane category IV compared to the hurricanes category I and II in those studies.…”

“…Impacts of large, infrequent disturbances are among the most difficult events to study, as they are unpredictable in space and time, but are critical to understanding the functioning of ecosystems [ Turner and Dale , 1998]. Soils have usually been ignored while studying hurricane disturbances and this study is one of the first attempts to study soil CO 2 dynamics following a hurricane event [ Steudler et al , 1991; Li et al , 2007]. Furthermore this is the first study that report automated measurements and diel patterns of soil respiration in a seasonally dry tropical forest (SDTF).…”

“…We hypothesized that soil respiration rates would increase with the added decomposition of leaves and fine roots after the hurricane, but would return to prehurricane values in the following months. Previous studies have shown that soil respiration rates are lower than prehurricane rates 1 year after the event in tropical [ Steudler et al , 1991] and subtropical [ Li et al , 2007] ecosystems. We further investigate how the recovery of damages in the canopy after the hurricane, may influence the relationship between soil temperature and soil respiration at the diel scale.…”

Risks to forest carbon offset projects in a changing climate

“…McCarthy et al (2006) found that $20-year-old loblolly pine trees growing in elevated (ambient + 200 mmol mol À1 ) CO 2 were slightly more resistant to ice damage and recovered more quickly than trees in ambient CO 2 . In contrast, Li et al (2007) found that wind damage from Hurricane Frances was just as great on 8-year-old oak trees growing in elevated (ambient + 350 mmol mol À1 ) CO 2 as in ambient CO 2 . Uncertainties in how disturbance and physiology interact reduce the confidence investigators might have for predictions of forest productivity based solely on the physiology of trees and other co-occurring species.…”

Nonstructural Carbon in Woody Plants

“…Multiple disturbances can cause a loss of leaves and/or fine roots, which limits the capacity to photosynthesize and take up nutrients and water and which may further reduce ecosystem gross primary production following disturbances (77,138). Defoliation studies have shown that NSC stores often decrease soon after defoliation (78,135).…”