Rapid assessment of forest canopy structural resistance to disturbance along an increasing gradient of severity
Abstract
Forests in the Great Lakes region have demonstrated resistance to moderate (i.e. non-stand replacing) disturbance. An untested hypothesis is that this functional resistance is supported -- up to some threshold of disturbance severity -- by structural changes to the canopy that lead to greater complexity and, consequently, greater efficiency. The Forest Threshold and Resilience Experiment (FoRTE) explores where this threshold lies via a replicated gradient of disturbance severity (i.e. 0 to 85 % defoliation) across an array of regionally representative forest types that span an existing biological and structural complexity gradient. Within this framework, disturbance is applied by either targeting smaller, subcanopy trees (Bottom-Up) or larger, canopy trees (Top-Down). Following the spring 2019 stem-girdling of ~3600 trees, we examined rapid canopy structural response to disturbance across the disturbance severity gradient using terrestrial NDVI camera imagery as well as 2- and 3-D terrestrial lidar. Our goal in the first season following disturbance was to assess how rapidly canopy structure responded to stem-girdling. We found changes in canopy structure diverged more by species than disturbance severity. Plots with a higher presence of oaks ( Quercus sp .) showed greater changes in leaf area, NDVI, and canopy structural complexity measures over both control plots and pre-disturbance measurements. Oaks had both delayed and diminished leaf-out compared to other species resulting in the counter-intuitive finding that greater variance in canopy structure was explained by differences in species composition than by disturbance severity during the initial growing season following stem-girdling. We hypothesize these species effects are transient and isolated to the initial growing season following disturbance, but have potentially profound implications for understanding how forest resistance is influenced by pre-disturbance species composition and how the timeline of structural response unfolds. The uses of heterogeneous data sources, in this case terrestrial lidar that can quantify structural multidimensionality and hemispherical cameras which can be used quickly and repeatedly, creates a more nuanced and informative understanding of the timeline of disturbance mediated structural response.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.B54B..01A
- Keywords:
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- 0439 Ecosystems;
- structure and dynamics;
- BIOGEOSCIENCES;
- 0480 Remote sensing;
- BIOGEOSCIENCES;
- 1615 Biogeochemical cycles;
- processes;
- and modeling;
- GLOBAL CHANGE;
- 1910 Data assimilation;
- integration and fusion;
- INFORMATICS