Building Tools to Reconstruct Forest Disturbances

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Climate change is the greatest challenge facing forest ecosystems. The frequency and the severity of natural disturbances, such as wildfire, insect outbreaks, and windthrow, will increase with warming. Therefore, it is essential to understand how forests have responded to past disturbances to predict how they will react to future conditions. Paleoecological and dendroecological approaches are the main tools for reconstructing forest dynamics, disturbance regimes, and biotic-abiotic interactions. To date, dendroecological and paleoecological research has focused mainly on wildfires, whereas other disturbances have often been neglected (e.g., insect outbreaks at the millennial scale and historical harvesting) despite being known as major drivers of forest structure and dynamics. This knowledge gap stems from the absence of reliable proxies or methodological approaches for reconstructing their past occurrence and severity. The long-term objective of my research is to improve our understanding of forest disturbance regimes at multiple temporal and spatial scales. This 5-year program aims to reconstruct the natural (insect outbreaks and their interaction with wildfires) and anthropogenic (harvesting) disturbance regimes in the temperate-boreal forest interface using novel dendroecological and paleoecological methods. The specific objectives are to (1) reconstruct insect outbreaks and their interactions with fire regimes over the last 300 to 400 years using recovered log-drive samples; (2) reconstruct, using subfossil samples and historical archives, the harvest criteria (species, age, diameter) applied during historical harvests and determine their impact on the pre-industrial forest; and (3) reconstruct the millennial history of insect outbreaks using lepidopteran scales. Attaining these objectives relies on three approaches. (i) I will recover subfossil trees felled during historical log drives to reconstruct past insect outbreaks, fire regimes, and historical harvests. I will use dendroecology to study subfossil logs preserved in the anoxic zone of selected boreal lakes. (ii) By identifying the logotypes of historical logging companies on the collected log-drive samples combined with the use of historical archives, I will georeference past forest harvesting patterns. (iii) I will apply my novel and recently tested paleoindicator, lepidopteran scales, to produce a millennial-scale reconstruction of the two main lepidopteran defoliator species in eastern Canadian forests (spruce budworm and the forest tent caterpillar). This program will significantly advance the reconstruction of forest disturbances that is essential to provide a more realistic projection of future forest ecosystem response to disturbance under climate change.