Resistance, Resilience or Change: Post-disturbance Dynamics of Boreal Forests After Insect Outbreaks

Abstract

Understanding and measuring forest resistance and resilience have emerged as key priorities in ecology and management, particularly to maintain forest functioning. The analysis of the factors involved in a forest's ability to cope with disturbances is key in identifying forest vulnerability to environmental change. In this study, we apply a procedure based on combining pathway analyses of forest composition and structure with quantitative indices of resistance and resilience to disturbances. We applied our approach to boreal forests affected by a major spruce budworm outbreak in the province of Quebec (Canada). We aimed to identify the main patterns of forest dynamics and the environmental factors affecting these responses. To achieve this goal, we developed quantitative metrics of resistance and resilience. We then compared forests with different pre-disturbance conditions and explored the factors influencing their recovery following disturbance. We found that post-outbreak forest dynamics are determined by distinct resistance and resilience patterns according to dominant species and stand composition and structure. Black spruce forests are highly resistant to spruce budworm outbreaks, but this resistance is conditioned by the length of the defoliation period, with long outbreaks having the potential to lead the system to collapse. In contrast, balsam fir forests easily change to a different composition after outbreaks but are highly resilient when mixed with hardwood species. Overall, the severity of the disturbance and the tree species affected are the main drivers contributing to boreal forest resistance and resilience. Our procedure is valuable to understand post-disturbance dynamics of a broad range of communities and to guide management strategies focused on enhancing the resistance and resilience of the system.

Advancing and reversing succession as a function of time since fire and insect outbreaks: An 18 year in situ remeasurement of changes in forest composition

“…The 2009 measurements are more than two decades after the documented end of the spruce budworm outbreak in 1987 (Morin et al, 1993) in our study area and yet total BA is still 5 to 10 m 2 /ha lower than before SBW caused mortality. This recovery is slower than that reported for fir-dominated and fir/hardwood forests in other regions (Sánchez-Pinillos et al, 2019).…”

“…When these more vulnerable conifers are killed by the SBW large openings are created, which permit the recruitment of shade-intolerant hardwoods (Kneeshaw and Bergeron, 1998;Vepakomma et al, 2010). In other words, our results demonstrate that SBW outbreaks are a mechanism for forest diversification by interrupting successional processes based strictly on ageing and replacement of shade-intolerant species by more shade-tolerant species (Sánchez-Pinillos et al, 2019;Maleki et al, 2020). Accordingly, gaps created by the SBW lead to three different compositional pathways: they continue to advance succession, they maintain current composition (30%-36% of quadrats) or succession returns to earlier phases (34%45% of quadrats).…”

Demographic traits improve predictions of spatiotemporal changes in community resilience to drought

“…Weighting this resilience by the damage occurred during the drought, High values of relative resilience indicate a high capacity to recover from or compensate for the particular effects of the drought event (Sánchez-Pinillos et al, 2019).…”

Forest multifunctionality is not resilient to intensive forestry

“…The resilience of production ecosystems is often thought of in terms of resilience to damage caused by natural disturbances such as pest outbreaks or extreme weather (e.g., Seidl et al 2016;Sánchez-Pinillos et al 2019). However, in production ecosystems a major source of disturbance is the management itself: resource extraction and activities to increase the efficiency of production can change the structure and functioning of the ecosystem fundamentally (Bennet and Balvanera 2007;Edwards et al 2014).…”