Fragmented forests may differ in their resilience to stressors such as climate change and disturbances, and how they are managed will impact their future. Credit: Caitlin Littlefield
When we think of enhancing landscape connectivity, it’s easy to picture protected corridors or wildlife crossings. But these physical attributes that contribute to landscape permeability— structural connectivity—represent only one side of the connectivity coin. Functional connectivity describes how organisms respond to the structural elements in the landscape. Functional connectivity is what determines the ecological effects of, for example, land-use change or natural resource management.
When thinking about connectivity, it’s also easy to call critters to mind—those with paws, hooves, wings, or fins. But what about organisms rooted to the ground? What does functionality connectivity look like for tree species and forest communities, particularly under changing climatic conditions?
A recent study sought to explore that question, in southern Quebec, where forests grade from northern hardwoods to mixed woods with southern boreal conifers. The researchers used a forest landscape simulation model to examine how either no management, business-as-usual (BAU) management, or BAU management plus natural disturbances may affect forests under climate change.
They then used those model outputs to examine how three metrics of forest network resilience were affected: 1) functional response diversity, or the suites of traits associated with resistance to stressors and regeneration, like seed dispersal; 2) functional redundancy, or if there’s a “back-up” of functional traits in a community; and 3) functional connectivity, or the degree to which species’ seeds could disperse between forest patches.
Natural disturbances, such as disease, help maintain functional connectivity, allowing forests to adapt to changing conditions. Credit: Halvard
The results confirmed anticipated trends: boreal species will retreat while northern hardwood species expand farther northward. The findings also underscored that climate change, as anticipated, is likely to decrease forest landscape resilience. Functional connectivity declined under nearly all scenarios, with an important exception: when natural disturbances unfolded, functional connectivity fared better than when natural disturbances were excluded. In fact, functional connectivity increased under current climate conditions, it mostly recovered under moderate climate change, and its loss was somewhat ameliorated under severe climate change.
The same pattern held for functional diversity across the network. The authors attribute these positive impacts to the establishment of shade intolerant species in disturbance-created gaps, which in turn fosters functional diversity, including seed dispersal traits.
The findings suggest the importance of natural disturbance dynamics in maintaining functional connectivity, and therefore in supporting the capacity for forests to recolonize and reorganize under changing conditions. It’s echoed in other research that suggests moderate disturbance may accelerate forests’ adaptive response to climate change.
Even so, climate change renders this forest network less resilient by the end of the 2100. This means BAU management alone is insufficient. If we carry on as usual, these forests—and many others—are likely to become more homogeneous, less functionally diverse, and less functionally connected. Instead, we must be more pro-active in pursuing strategic climate adaptive management.
Resources
Mina, M., Messier, C., Duveneck, M., Fortin, M.J. and Aquilué, N. 2020. Network analysis can guide resilience-based management in forest landscapes under global change. Ecological Applications. DOI: 10.1002/eap.2221.
Auffret, A.G., Plue, J. and Cousins, S.A. 2015. The spatial and temporal components of functional connectivity in fragmented landscapes. Ambio 44(1): 51-59.
Brice, M.H., Vissault, S., Vieira, W., Gravel, D., Legendre, P. and Fortin, M.J. 2020. Moderate disturbances accelerate forest transition dynamics under climate change in the temperate‐boreal ecotone of eastern North America. Global Change Biology 26(8): 4418-4435.
D’Amato, A.W., Bradford, J.B., Fraver, S. and Palik, B.J. 2011. Forest management for mitigation and adaptation to climate change: Insights from long-term silviculture experiments. Forest Ecology and Management 262(5): 803-816.
