Stand‐level drivers most important in determining boreal forest response to climate change

BackgroundClimate change is expected to increase fire activity across the circumboreal zone, including central Siberia. However, few studies have quantitatively assessed potential changes in fire regime characteristics, or considered possible spatial variation in the magnitude of change. Moreover, while simulations indicate that changes in climate are likely to drive major shifts in Siberian vegetation, knowledge of future forest dynamics under the joint influence of changes in climate and fire regimes remains largely theoretical. We used the forest landscape model, LANDIS-II, with PnET-Succession and the BFOLDS fire extension to simulate changes in vegetation and fire regime characteristics under four alternative climate scenarios in three 10,000-km2 study landscapes distributed across a large latitudinal gradient in lowland central Siberia. We evaluated vegetation change using the fire life history strategies adopted by forest tree species: fire resisters, fire avoiders, and fire endurers.ResultsAnnual burned area, the number of fires per year, fire size, and fire intensity all increased under climate change. The relative increase in fire activity was greatest in the northernmost study landscape, leading to a reduction in the difference in fire rotation period between study landscapes. Although the number of fires per year increased progressively with the magnitude of climate change, mean fire size peaked under mild or moderate climate warming in each of our study landscapes, suggesting that fuel limitations and past fire perimeters will feed back to reduce individual fire extent under extreme warming, relative to less extreme warming scenarios. In the Southern and Mid-taiga landscapes, we observed a major shift from fire resister-dominated forests to forests dominated by broadleaved deciduous fire endurers (Betula and Populus genera) under moderate and extreme climate warming scenarios, likely associated with the substantial increase in fire activity. These changes were accompanied by a major decrease in average cohort age and total vegetation biomass across the simulation landscapes.ConclusionsOur results imply that climate change will greatly increase fire activity and reduce spatial heterogeneity in fire regime characteristics across central Siberia. Potential ecological consequences include a widespread shift toward forests dominated by broadleaved deciduous species that employ a fire endurer strategy to persist in an increasingly fire-prone environment.

Forest landscapes at the southern boreal forest transition zone are likely to undergo great alterations due to projected changes in regional climate. We projected changes in forest landscapes resulting from four climate scenarios (baseline, RCP 2.6, RCP 4.5 and RCP 8.5), by simulating changes in tree growth and disturbances at the southern edge of Canada’s boreal zone. Projections were performed for four regions located on an east–west gradient using a forest landscape model (LANDIS-II) parameterized using a forest patch model (PICUS). Climate-induced changes in the competitiveness of dominant tree species due to changes in potential growth, and substantial intensification of the fire regime, appear likely to combine in driving major changes in boreal forest landscapes. Resulting cumulative impacts on forest ecosystems would be manifold but key changes would include (i) a strong decrease in the biomass of the dominant boreal species, especially mid- to late-successional conifers; (ii) increases in abundance of some temperate species able to colonize disturbed areas in a warmer climate; (iii) increases in the proportions of pioneer and fire-adapted species in these landscapes and (iv) an overall decrease in productivity and total biomass. The greatest changes would occur under the RCP 8.5 radiative forcing scenario, but some impacts can be expected even with RCP 2.6. Western boreal forests, i.e., those bordering the prairies, are the most vulnerable because of a lack of species adapted to warmer climates and major increases in areas burned. Conservation and forest management planning within the southern boreal transition zone should consider both disturbance- and climate-induced changes in forest communities.

AimClimate change is expected to influence boreal bird communities significantly, notably through changes in forest habitat (composition and age structure), in the coming decades. How these changes will accumulate and interact with anthropogenic disturbances remains an open question for most species.LocationNortheastern Alberta, Canada.MethodsWe used the LANDIS‐II forest landscape model to project changes in forest landscapes, and associated bird populations (72 passerine species), according to three climatic scenarios (baseline, RCP 4.5 and RCP 8.5) and three forest harvesting scenarios of differing intensity.ResultsBoth forest harvesting and climate‐related drivers were projected to have large impacts on bird communities in this region. As a result of climate‐induced increases in fire activity as well as decreased conifer productivity, our simulations projected that an important proportion of Alberta's boreal forests would transition to treeless habitat (i.e. grass‐ or shrub‐dominated vegetation) while many conifer‐dominated stands would likely be replaced by broadleaf tree cover. Consequently, the abundance of bird species associated with open and deciduous habitats were projected to increase. With a strong anthropogenic climate‐forcing scenario (RCP 8.5), sharp declines in abundance of coniferous trees were also projected, particularly in mature and old forest stands, triggering major declines for bird species associated with coniferous and mixedwood forest types.Main conclusionsAs the most comprehensive simulation of climate change and harvesting impacts on avian habitats in the North American boreal region to date, our study stresses the importance of considering key habitat characteristics like forest age structure and composition through forest landscape modelling and identifies 18 bird species particularly sensitive to climate change. Our simulations suggest that a change in forest management practices could play an important role in the conservation of boreal bird species vulnerable to climate change. The intensive forest harvesting simulated accelerated declines in bird abundance compared to a “no harvesting” scenario.

Many studies project future bird ranges by relying on correlative species distribution models. Such models do not usually represent important processes explicitly related to climate change and harvesting, which limits their potential for predicting and understanding the future of boreal bird assemblages at the landscape scale. In this study, we attempted to assess the cumulative and specific impacts of both harvesting and climate-induced changes on wildfires and stand-level processes (e.g., reproduction, growth) in the boreal forest of eastern Canada. The projected changes in these landscape- and stand-scale processes (referred to as “drivers of change”) were then assessed for their impacts on future habitats and potential productivity of black-backed woodpecker (BBWO; Picoides arcticus), a focal species representative of deadwood and old-growth biodiversity in eastern Canada. Forest attributes were simulated using a forest landscape model, LANDIS-II, and were used to infer future landscape suitability to BBWO under three anthropogenic climate forcing scenarios (RCP 2.6, RCP 4.5 and RCP 8.5), compared to the historical baseline. We found climate change is likely to be detrimental for BBWO, with up to 92% decline in potential productivity under the worst-case climate forcing scenario (RCP 8.5). However, large declines were also projected under baseline climate, underlining the importance of harvest in determining future BBWO productivity. Present-day harvesting practices were the single most important cause of declining areas of old-growth coniferous forest, and hence appeared as the single most important driver of future BBWO productivity, regardless of the climate scenario. Climate-induced increases in fire activity would further promote young, deciduous stands at the expense of old-growth coniferous stands. This suggests that the biodiversity associated with deadwood and old-growth boreal forests may be greatly altered by the cumulative impacts of natural and anthropogenic disturbances under a changing climate. Management adaptations, including reduced harvesting levels and strategies to promote coniferous species content, may help mitigate these cumulative impacts.

Diverse aquatic ecosystems in Tanzania provide economically important ecosystem services. The rich supply of these services is under threat. Projections show critical water scarcity in the country by the year 2050. Demography, excessive withdrawals, land use changes, exotic species invasions and climate change that result in loss of perennial flows, eutrophication, sedimentation, and algal blooms are among the major drivers of aquatic ecosystem changes in Tanzania. Water resources uses and their management in Tanzania are mainly determined by the national macroeconomics and policies. In this review, Great Ruaha River (GRR) and Lake Victoria Basin (LVB) are used as case examples for demonstrating status, trends and drivers of ecosystem changes, and their management options in Tanzania through government and donor efforts. As a way forward, in the new Tanzania National Water Policy (NAWAPO) of 2002, Integrated Water Resource Management (IWRM) approaches as tools to ensure ecosystem protection and stakeholder’s participation have been adopted. Water for environment is given a second priority in water allocation after basic human needs. The Integrated Water Resources management and Development (IWRMD) plans currently being developed will form legal basis in management of water in an environmentally and ecosystem responsible manner. Through the IWRMD approved plans, drastic actions can be legally taken to protect and/or restore important ecosystem services in hotspot areas like the GRR.

Abstract. Tropical forests have been a permanent feature of the Amazon basin for at least 55 million years, yet climate change and land use threaten the forest's future over the next century. Understory forest fires, which are common under the current climate in frontier forests, may accelerate Amazon forest losses from climate-driven dieback and deforestation. Far from land use frontiers, scarce fire ignitions and high moisture levels preclude significant burning, yet projected climate and land use changes may increase fire activity in these remote regions. Here, we used a fire model specifically parameterized for Amazon understory fires to examine the interactions between anthropogenic activities and climate under current and projected conditions. In a scenario of low mitigation efforts with substantial land use expansion and climate change – Representative Concentration Pathway (RCP) 8.5 – projected understory fires increase in frequency and duration, burning 4–28 times more forest in 2080–2100 than during 1990–2010. In contrast, active climate mitigation and land use contraction in RCP4.5 constrain the projected increase in fire activity to 0.9–5.4 times contemporary burned area. Importantly, if climate mitigation is not successful, land use contraction alone is very effective under low to moderate climate change, but does little to reduce fire activity under the most severe climate projections. These results underscore the potential for a fire-driven transformation of Amazon forests if recent regional policies for forest conservation are not paired with global efforts to mitigate climate change.

Vegetation, climate and fire regime changes in the Andean region of southern Chile (38°S) covaried with centennial-scale climate anomalies in the tropical Pacific over the last 1500 years

AimKnowledge of the drivers of ecosystem changes in the past is key to understanding present ecosystem responses to changes in climate, fire regimes and anthropogenic impacts. Northern Hemisphere‐focussed studies suggest that climate and human activities drove turnover during the Holocene in temperate ecosystems. Various drivers have been invoked to explain changes in Southern Hemisphere temperate vegetation, but the region lacks a quantitative assessment of these drivers. To better understand the regional drivers of past diversity, we present a quantitative meta‐analysis study of turnover and richness during the lateglacial and Holocene in Australian temperate ecosystems.LocationSouth‐east Australia (Tasmania, Bass Strait, SE mainland).MethodsWe conducted a meta‐analysis study of 24 fossil pollen records across south‐east Australian temperate ecosystems, applying an empirical turnover threshold to fossil records to identify periods of major turnover for the first time in Australia. We tested pollen richness as a proxy for vegetation richness to estimate past richness and applied this to fossil pollen data. The resulting reconstructions were compared to independent records of climate, sea‐level change and fire through generalized linear modelling.Results and conclusionOur results show changes in available moisture and sea level drove turnover and richness in most parts of SE Australia in the past, explaining up to c. 97% deviance. However, fire mainly drove turnover in Bass Strait. Our richness reconstructions also support the intermediate disturbance hypothesis, suggesting that high biodiversity was partially maintained by anthropogenic‐managed fire regimes. While temperature change is considered key to Northern Hemisphere palaeodiversity, past turnover and richness in Southern Hemisphere temperate ecosystems responded mainly to moisture availability and sea‐level change (considering its role in modulating regional oceanic climate).

An important aspect of the UN Framework Convention on Climate Change (UNFCCC), which aims to limit the increase in global temperature to 1.5 °C by 2050, has been the development of monitoring and evaluation plans that integrate climate change perspectives into new policies and programs for the protection and functioning of ecological systems. These include measures that enhance adaptive capacity, strengthen resilience and reduce vulnerability to climate change. Ecosystem change and the interaction of the different drivers of change in ecosystems have been studied at different temporal and spatial scales across different disciplines. However, the use of long temporal records documenting environmental and climatic change in understanding the impacts of the interacting drivers of change and planning sustainable use of resources is relatively new. We present examples of the use of palaeoecological data from East Africa in planning for the long-term sustainable use of natural resources by providing long-term historical perspectives on human–environment–societal–wildlife interactions and engagement with the biocultural heritage and societal evaluations of these spaces to achieve an increasingly diverse set of conservation, social and economic objectives. We link the Earth system processes whose associated boundaries can be directly related to sustainable development goals in our attempt to prevent unacceptable environmental change. The realisation that humans are having a significant impact on climate and landscapes means we now need to showcase the societal relevance of palaeoecological research and utilise its output especially in our efforts to remain within a safe operating space for humanity and ecosystems.

Paleoecological records of past fire events and forest composition provide long‐term ecological context for modern changes in fire regimes and forest dynamics. Here, we use pollen and contiguous macroscopic charcoal analyses of lake sediments from Pender Island, British Columbia, Canada to reconstruct changes in fire regimes over the last 10,000 years and investigate how these interact with changes in climate and forest composition with a focus on fire‐related plant functional types. The relatively warm and dry early Holocene was characterized by high charcoal accumulation rates, fire episodes of moderate severity, and a mean fire return interval of 100 ± 27 years. Forests at the time were open‐canopy Pseudotsuga menziesii forests with abundant fire endurer taxa (e.g., Pteridium aquilinum) that have a competitive advantage in regimes of frequent fire. Fire continued to occur every ~100 years, on average, during the establishment of Quercus garryana savanna communities; however, a decrease in charcoal peak magnitudes suggests the fire regime shifted to one characterized by smaller and/or lower intensity surface fires. As temperature and moisture deficits decreased in the mid‐ and late Holocene (i.e., after ~6000 calendar years before present), mean fire return intervals lengthened to 176 ± 54 years and increased variability in charcoal peak magnitudes suggests a mixed fire regime of low‐moderate‐intensity fires combined with infrequent crown or stand‐replacing fires. Relatively stable and moderate climate, longer fire return intervals, and mixed‐severity fires allowed P. menziesii (a fire resister) to dominate closed‐canopy forests and for fire avoiders to gradually become more common forest constituents. Millennial‐scale climate change has acted as the dominant driver of changes in both fire regimes and forest composition over the last 10,000 years; however, changes in fire‐related plant functional types highlight the important role that interactions between vegetation and fire play in long‐term fire regimes and forest dynamics.

ABSTRACTA paucity of empirical non‐marine data means that uncertainty surrounds the impact of climate change on terrestrial ecosystems in tropical regions beyond the last glacial period. The sedimentary fill of the Bosumtwi impact crater (Ghana) provides the longest continuous Quaternary terrestrial archive of environmental change in West Africa, spanning the last ∼1.08 million years. Here we explore the drivers of change in ecosystem and climate in tropical West Africa for the past ∼540 000 years using pollen analysis and the nitrogen isotope composition of bulk organic matter preserved in sediments from Lake Bosumtwi. Variations in grass pollen abundance (0−99%) indicate transitions between grassland and forest. Coeval variations in the nitrogen isotopic composition of organic matter indicate that intervals of grassland expansion coincided with minimum lake levels and low regional moisture availability. The observed changes responded to orbitally paced global climate variations on both glacial–interglacial and shorter timescales. Importantly, the magnitude of ecosystem change revealed by our data exceeds that previously determined from marine records, demonstrating for the first time the high sensitivity of tropical lowland ecosystems to Quaternary climate change.

Anticipating future fire activity at global and regional scales is critical in a changing climate. Indeed, fire seasons are expected to lengthen and fire prone areas are expected to extend, but the magnitude, location and timing of such increases remain uncertain. Moreover, an intensification is expected during the core of the fire season of already fire-prone regions. However, quantifying seasonal and spatial impacts of climate change on fire activity is challenging. Here, we projected future fire activities in Southern France using the Firelihood model. This Bayesian probabilistic model operates on a daily basis in 8-km pixels, allowing to analyze both seasonal and spatial distributions of fire activities in a framework integrating stochasticity. Projections were computed for 13 GCM-RCM couples under two RCP scenarios (4.5 and 8.5), assuming that the only factor of change in future fire activity was the daily fire weather. The fire season was defined as the period with fire-activity level higher than the level of the 15th of July of the present period. The fire prone region corresponded to locations with fire-activity levels higher than the 2nd level of a 5-level fire-activity scale derived from numbers of fires larger than 1ha, 100ha (N1ha and N100ha) and burnt areas (BA). Simulations under RCP8.5 show that large increases in fire activity should be expected from the mid-century and that the rate of increase should then accelerate, leading to up to three-fold increases for number of fires larger than 100ha by the end of the century. In particular, all metrics except N1ha increased faster than the mean FWI and even the mean DSR. Such increases were partly caused by a massive seasonal lengthening from 45-50 days to up to 125 days, equally distributed between spring and autumn. However, the intensification during the present fire season was found to contribute slightly more to the overall increase than the lengthening itself. For example, for N100ha, the intensification would represent a 280 % increase in fire activity with respect to the present seasonal reference, whereas the lengthening outside of the present season would represent +230%. The fire prone area would increase by 168%, shifting from 22 to 56% of region total area. However, the intensification inside the already fire-prone region was found to contribute more to the increase than the spatial extension. For example, for N100ha, the intensification would represent a 190% increase with respect to the present fire-prone regional reference, whereas the extension outside of this area would represent +110%. These drastic increases provide a good indication of the potential lengthening of the fire season, spatial extension and intensification of future fire activities under RCP 8.5, all three being importantly concerned, but dominated by intensification. Extending and lengthening suppression policies may allow to mitigate projected increases, but the intensification of fire activity during the core of the fire season overwhelm current fire suppression capacities.

It is widely accepted, based on data from the last few decades and on model simulations, that anthropogenic climate change will cause increased fire activity. However, less attention has been paid to the relationship between abrupt climate changes and heightened fire activity in the paleorecord. We use 35 charcoal and pollen records to assess how fire regimes in North America changed during the last glacial-interglacial transition (15 to 10 ka), a time of large and rapid climate changes. We also test the hypothesis that a comet impact initiated continental-scale wildfires at 12.9 ka; the data do not support this idea, nor are continent-wide fires indicated at any time during deglaciation. There are, however, clear links between large climate changes and fire activity. Biomass burning gradually increased from the glacial period to the beginning of the Younger Dryas. Although there are changes in biomass burning during the Younger Dryas, there is no systematic trend. There is a further increase in biomass burning after the Younger Dryas. Intervals of rapid climate change at 13.9, 13.2, and 11.7 ka are marked by large increases in fire activity. The timing of changes in fire is not coincident with changes in human population density or the timing of the extinction of the megafauna. Although these factors could have contributed to fire-regime changes at individual sites or at specific times, the charcoal data indicate an important role for climate, and particularly rapid climate change, in determining broad-scale levels of fire activity.

Managing flood risks in a changing climate

Late Holocene vegetation and fire history at the southern boreal forest margin in Alberta, Canada