Forests undergoing novel disturbances: understanding and managing the complex new reality of forests

Considering the vast impacts disturbances such as fire and insect outbreaks are having on forests worldwide, Alexandro B. Leverkus and Simon Thorn bring together a selection of work showcasing quality research into these disturbances and strategies being taken to manage them.

This Virtual Issue features articles from across the British Ecological Society journals that are free-to-read for a limited time.

Novel Disturbances ight rail 300x250In recent years, forest disturbances have been making increasing global headlines. Record-breaking wildfires in the Amazon, Australia, Siberia, Mediterranean Europe, Canada, Scandinavia  and California, as well as large-scale beetle outbreaks in Europe  and North America, have sparked global concern about the loss of species and habitats in the world’s forests. During the last century, we have learnt that natural disturbances play fundamental ecological and evolutionary roles. However, the natural regime of disturbances – their ‘normal’ incidence in a region, including their frequency, severity and seasonality – is changing as a result of climate change, alterations in land use, fire suppression, and other human-related factors. Natural disturbances are also affecting larger forest expanses, producing higher impacts, and occurring at unprecedented times and places. Novel disturbance conditions, coupled with increasing human pressure on ecosystems, can produce unexpected outcomes, trigger ecological regime shifts, and put human livelihoods and economies at risk.

To maintain the biodiversity and functions of the world’s forests in the Anthropocene, we require new understanding of the complex novel dynamics surrounding shifting disturbance regimes through conceptual, methodological, modelling, remote sensing, and field-based studies. There is a wealth of recent scientific publications addressing novel forest disturbances, focusing on aspects such as their drivers, their capacity to produce unexpected effects, feedback mechanisms between multiple stressors, solutions for management, and calls for action. In this Virtual Issue, we collate recent papers published since 2018 across the British Ecological Society journals that may help investigate, understand, and manage the increasing amount of forest facing novel disturbance regimes.

Fig 2. European spruce bark beetle outbreak
European spruce bark beetle outbreak

Investigating novel disturbances

A key challenge to learn from natural disturbances is that they usually occur fortuitously and researchers lack the capacity to randomise or replicate them. A recent Review highlights how to overcome statistical challenges in non-experimental control-impact studies such as those on natural disturbances. Drawing from experience in long-term disturbance studies, authors in Australia propose several types of study designs to learn from natural disturbances. To predict the effects of disturbances on biotic communities, we need mechanistic understanding of species responses to disturbance, such as a recent study on how plant species respond to different levels of soil heating during an experimental fire. Also mathematical models can help forecast complex feedbacks between disturbance, post-disturbance regeneration, and subsequent disturbances.

Understanding novel disturbances: fire

Fire is a key evolutionary force and an essential driver of biodiversity and ecosystem functions in many ecosystems worldwide. But changes in the fire regime are also working as an important global-change agent, as highlighted by a recent Review. For instance, in western North American forests, climate change impacts on vegetation extend beyond the effects of climate alone if we consider the climatically-induced increases in wildfire activity. Also Mediterranean ecosystems may be at stake through coupled changes in fire regime and climate, as found in a modelling study in Spain. In Indonesia, tropical forests are threatened by combinations of fire, tree harvesting, conversion to agriculture, and peatland drainage, with feedbacks to more fire. Furthermore, in the Amazon Basin, forests can suffer from combinations of fire, fragmentation, and windstorms.

Understanding novel disturbances: insect outbreaks

Beetle outbreaks are increasing in extent and affecting increasing proportions of forests, with possible impacts on regeneration and huge impacts on the timber industry. Beetle outbreaks are also occurring beyond their native ranges. Novel pest outbreaks can produce ecosystem tipping points, as shown in a study in Scandinavia. A key issue to understand infestations is assessing the spatial distribution of outbreak spots, as done for the mountain pine beetle. We also need to understand the causes underlying novel outbreaks. For instance, the weakening of trees during drought periods can reduce tree defences and increase susceptibility to attack, as found in boreal Canada. In contrast,, there may be negative disturbance feedbacks too, as defoliation by insects may reduce affection by drought by reducing transpiration.

Fig 3. Erosion mitigation management efforts_Donana Natural Park_Spain
Management to mitigate erosion after a 10,000 ha wildfire in the Doñana Natural Park, Spain

Managing novel disturbances

How should novel forest disturbances and their impacts be mitigated ? A Practitioner’s Perspective proposes solutions to reduce fire incidence in Amazonian forests. Contrarily, maintaining the fire regime may involve reintroducing fire in other places, as highlighted in a Policy Direction. A spatially-explicit modelling study analysed the effectiveness of a common management strategy, salvage logging, on the capacity to mitigate insect outbreaks after disturbances. However, while salvage logging  sometimes aims to mitigate future disturbances, it constitutes a second disturbance itself. A recent study demonstrated that salvage logging after fire alters soil fungal communities, with negative consequences on the growth of native tree seedlings. A global study further assessed the impacts of salvage logging after natural disturbances on bird communities.

Ways forward

Based on long-term monitoring of how multiple disturbance combinations affect forest biodiversity in Australia, management schemes have been proposed to limit the possibility of catastrophic ecosystem shifts and associated losses of biodiversity. When designing disturbance management scenarios, the consideration of multiple stakeholders can produce different outcomes related to shifts in climate and the fire regime. Finally, novel disturbances also allow ecosystems as well as human societies to develop adaptational responses to changing climate change and disturbance conditions.

Read the full Virtual Issue, Forests undergoing novel disturbances. The articles featured are free to read for a limited time.

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