The Vision of Managing for Pest-Resistant Landscapes: Realistic or Utopic?

Abstract

Purpose of Review Forest managers have long suggested that forests can be made more resilient to insect pests by reducing the abundance of hosts, yet this has rarely been done. The goal of our paper is to review whether recent scientific evidence supports forest manipulation to decrease vulnerability. To achieve this goal, we first ask if outbreaks of forest insect pests have been more severe in recent decades. Next, we assess the relative importance of climate change and forest management–induced changes in forest composition/structure in driving these changes in severity. Recent Findings Forest structure and composition continue to be implicated in pest outbreak severity. Mechanisms, however, remain elusive. Recent research elucidates how forest compositional and structural diversity at neighbourhood, stand, and landscape scales can increase forest resistance to outbreaks. Many recent outbreaks of herbivorous forest insects have been unprecedented in terms of duration and spatial extent. Climate change may be a contributing factor, but forest structure and composition have been clearly identified as contributing to these unprecedented outbreaks. Summary Current research supports using silviculture to create pest-resistant forest landscapes. However, the precise mechanisms by which silviculture can increase resistance remains uncertain. Further, humans tend to more often create pest-prone forests due to political, economic, and human resistance to change and a short-sighted risk management perspective that focuses on reactive rather than proactive responses to insect outbreak threats. Future research efforts need to focus on social, political, cultural, and educational mechanisms to motivate implementation of proven ecological solutions if pest-resistant forests are to be favoured by management.

Multi‐model projections of tree species performance in Quebec, Canada under future climate change

“…This projected decline could affect the quantity and types of trees that can be harvested in the future, as well as carbon sequestration abilities of forest ecosystems (Brecka et al, 2020;Dymond et al, 2010). Strategies favouring forest resiliency or ecosystem transition should be implemented to reduce ecological and economical risks associated with cold-tolerant species decline (Duveneck & Scheller, 2015;Kneeshaw et al, 2021), especially if radiative forcing reaches RCP 8.5 levels. It is also important to mention that apparent uncertainty in model outcome is mostly explained by differences in how the different processes are being simulated/predicted, particularly with respect to the explicit inclusion of species migration and natural disturbances, rather than model disagreements in overall response to climate change.…”

Managing for the unexpected: Building resilient forest landscapes to cope with global change

“…Although, in some cases, the promotion of tree species, genera, and traits might result in potentially greater outbreak severity, more diverse communities still have higher chances of containing species that can contribute to recovery processes and increase overall ecological resilience. This is also highlighted in a recent review study by Kneeshaw et al (2021), suggesting that forest resistance to pests can be effectively increased by enhancing tree structural and compositional diversity at stand, neighborhood, and landscape scales.…”

Understanding and Modeling Forest Disturbance Interactions at the Landscape Level

“…Climate-driven synergies underlying explosive outbreaks of this insect have been further exacerbated by a long history of spruce plantation establishment in the region (Jansen et al, 2017), leading to relatively continuous food resources (Seidl et al, 2016b, Figure 6). While this example appears like a "perfect storm" event, it is a pattern replicated across many forest insect systems across the globe, particularly in bark beetle systems subject to similarly strong non-linear feedback processes (Burton et al, 2020;Kneeshaw et al, 2021).…”

“…Nonetheless, model designs are ultimately constrained by supporting knowledge and data. In the insect examples above, there is greater consensus on the landscape factors controlling bark beetle dynamics than there are for defoliator dynamics (Kneeshaw et al, 2021). Indeed, bark beetles were included in all four of the disturbance interaction studies that explicitly addressed cross-scaled interactions (Table 5).…”