Philip J. Burton

Wildfires are increasing in size and severity due to climate change, and pose a serious threat to humans, infrastructure, and industry. In western North America, wildfires often leave unburned blocks of forest known as fire skips, fire islands, or fire refugia. Research elsewhere has suggested that young forests burn more severely, while mature forest is often found unburned as wildfire refugia. However, preliminary observations in central British Columbia suggest that some planted juvenile stands burn less severely than the surrounding mature forests. The existence of these fire skips could be due to differences in fuel moisture content (FMC), stand structure characteristics that influence fire spread, or both. To identify the role of FMC in fire skips, this study develops relationships between 6116 individual ground‐based FMC measurements and remote sensing data collected in 2021 and 2022. Remotely sensed estimates of pre‐fire FMC were then used to analyse burn severities in different stand types encountered in three major wildfires in central British Columbia in 2017 and 2018. Juvenile plantations, mostly dominated by lodgepole pine ( Pinus contorta var. latifolia ), had lower burn severity than mature and recent cutblocks (open sites) in three case study areas. No significant relationships were found between pre‐fire satellite‐estimated FMC and burn severity in mature forest and juvenile plantations. However, at open stands, moderate correlations between estimated duff FMC and difference normalized burn ratio (dNBR) were found in two case study areas. This work provides tools for assessing pre‐fire FMC at large spatial scales and suggests that the limited fire severity in juvenile stands may be a function of stand characteristics other than pre‐fire FMC.

Invertebrates and microorganisms are important but climate‐dependent agents of wood decomposition globally. In this meta‐analysis, we investigated what drives the invertebrate effect on wood decomposition worldwide. Globally, we found wood decomposition rates were on average approximately 40% higher when invertebrates were present compared to when they were excluded. This effect was most pronounced in the tropics, owing mainly to the activities of termites. The invertebrate effect was stronger for woody debris without bark as well as for that of larger diameter, possibly reflecting bark‐ and diameter‐mediated differences in fungal colonisation or activity rates relative to those of invertebrates. Our meta‐analysis shows similar overall invertebrate effect sizes on decomposition of woody debris derived from angiosperms and gymnosperms globally. Our results suggest the existence of critical interactions between microorganism colonisation and the invertebrate contribution to wood decomposition. To improve biogeochemical models, a better quantification of invertebrate contributions to wood decomposition is needed.

The window between snow melt and leaf flush in broadleaf trees defines a critical period of wildfire susceptibility, especially in western boreal forests. Questions remain about how a warming climate might affect those two processes that bookend the spring fire season.

An individual-based, multiple-growthform gap model of forest stand development and succession (ZELIG.MGF) of the JABOWA and FORET lineage was modified to simulate long-term changes in ‘ōhi'a-hāpu'u montane rain forests on the island of Hawai‘i. Based on the autecology, architecture, and life history of the two dominant species, we were able to re-create some of the stand dynamics and population structures observed in these forests. The phenomenon of displacement dieback, which occurs only on rich sites with persistent cloud cover, is portrayed as a natural successional consequence of ‘ōhi’a lehua (Metrosideros polymorpha Gaud.) senescence and shade intolerance, which contrasts with the shorter stature, clonal reproduction, and shade tolerance of hāpu'u pulu tree fern (Cibotium glaucum (Sm.) Hook. & Arn.). ZELIG.MGF predicts that ‘ōhi’a will achieve a maximum basal area of 27 m2/ha in stands 80–90 years old, after which basal area is projected to decline to levels of 8–11 m2/ha that persist after 220 years. Alternating phases of ‘ōhi'a and hāpu'u may dominate individual gaps, but overall old-growth ‘ōhi’a populations do not recover to earlier levels. ‘Ōhi’a overstory mortality is consistent with senescence or a growing imbalance of respiratory to photosynthetic tissue in large trees. Understory mortality as modeled is largely due to shading by adults and by hāpu’u tree ferns, although mechanical damage from dead hāpu’u fronds, which was not modeled, may also be important. ‘Ōhi’a stand rejuvenation can occur when the density of hāpu’u is reduced by harvesting or wind storms.

Forest and grassland ecosystems are sometimes located adjacently within the same climate. In Interior British Columbia, Canada, there are complex forest–grassland mosaics within the Interior Douglas‐fir biogeoclimatic zone. Historically, both grassland and forest ecosystems experienced high‐frequency, low‐severity fire regimes. Since European settlement and introduction of livestock grazing and fire exclusion, trees have encroached on grasslands, and tree densities in forests have increased. In this study, we characterize plant communities and near‐surface soil moisture in forest and grassland sites, and in historical grassland sites affected by tree encroachment. We hypothesized that spatial and temporal patterns of near‐surface soil moisture are reflected in aboveground plant community composition and structure. After initial sampling of soil moisture and plant communities, the study area was burned in a wildfire. Applying a multifactorial approach to comparing adjacent grassland and forest sites, we treated the wildfire event as a natural experiment, sampling post‐wildfire plant species composition and soil moisture, and measuring the severity and spatial heterogeneity of surface burn conditions. Evidence supports the concept of mutually exclusive fire‐reinforced bistable grassland and forest states, with greater spatial heterogeneity of soil moisture and burn severity in forests, and highly uniform patterns of soil moisture, vegetation, and burn severity in grasslands. Areas of forest encroachment on grasslands had understory plant communities dominated by exotic species, while restored grasslands had native bunchgrass cover like typical grasslands of the region. Additionally, there was post‐wildfire divergence of forest‐ and grassland‐associated plant communities. Viewed through a resilience theory conceptual framework, we suggest that ecosystem legacies are reinforcing post‐wildfire ecosystem identity and associated native plant communities. External factors—particularly past heavy livestock grazing and fire suppression—have caused ecosystem precariousness that can be addressed with management actions.

Understanding natural disturbance regimes and their impacts is crucial in designing ecosystem management strategies. However, disturbances do not always occur in isolation; the occurrence of one disturbance influences the likelihood or the effect of another. In this chapter, we illustrate the importance of disturbance interactions by focusing on a subset of interactions present in different parts of the boreal forest. The selected interactions include insects and wind, insects and fire, and wind and fire. The potential consequences of climate change on these interactions are also discussed.

The amount of carbon stored in deadwood is equivalent to about 8 per cent of the global forest carbon stocks¹. The decomposition of deadwood is largely governed by climate^2,3,4,5 with decomposer groups—such as microorganisms and insects—contributing to variations in the decomposition rates^2,6,7. At the global scale, the contribution of insects to the decomposition of deadwood and carbon release remains poorly understood⁷. Here we present a field experiment of wood decomposition across 55 forest sites and 6 continents. We find that the deadwood decomposition rates increase with temperature, and the strongest temperature effect is found at high precipitation levels. Precipitation affects the decomposition rates negatively at low temperatures and positively at high temperatures. As a net effect—including the direct consumption by insects and indirect effects through interactions with microorganisms—insects accelerate the decomposition in tropical forests (3.9% median mass loss per year). In temperate and boreal forests, we find weak positive and negative effects with a median mass loss of 0.9 per cent and −0.1 per cent per year, respectively. Furthermore, we apply the experimentally derived decomposition function to a global map of deadwood carbon synthesized from empirical and remote-sensing data, obtaining an estimate of 10.9 ± 3.2 petagram of carbon per year released from deadwood globally, with 93 per cent originating from tropical forests. Globally, the net effect of insects may account for 29 per cent of the carbon flux from deadwood, which suggests a functional importance of insects in the decomposition of deadwood and the carbon cycle.

Restoration of degraded drylands is urgently needed to mitigate climate change, reverse desertification and secure livelihoods for the two billion people who live in these areas. Bold global targets have been set for dryland restoration to restore millions of hectares of degraded land. These targets have been questioned as overly ambitious, but without a global evaluation of successes and failures it is impossible to gauge feasibility. Here we examine restoration seeding outcomes across 174 sites on six continents, encompassing 594,065 observations of 671 plant species. Our findings suggest reasons for optimism. Seeding had a positive impact on species presence: in almost a third of all treatments, 100% of species seeded were growing at first monitoring. However, dryland restoration is risky: 17% of projects failed, with no establishment of any seeded species, and consistent declines were found in seeded species as projects matured. Across projects, higher seeding rates and larger seed sizes resulted in a greater probability of recruitment, with further influences on species success including site aridity, taxonomic identity and species life form. Our findings suggest that investigations examining these predictive factors will yield more effective and informed restoration decision-making.

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.