A meta-analysis of the effects of wildfire,clearcutting, and partial harvest on the abundance of North American small mammals

Wildfires and timber harvest are two of the most prevalent disturbances in North American forests. To evaluate and compare their impact on small mammals, I conducted meta-analyses on (1) the effect of stand-replacement wildfires and several types of forest harvest (clearcutting followed by burning, clearcutting, and uniform partial harvest) on the abundance of deer mice (Peromyscus maniculatus) and red-backed voles (Myodes gapperi), (2) the impact of clearcutting and partial harvest on a broader array of small mammal species, and (3) the responses of small mammals to recent and older clearcuts (i.e. less than 10 years vs. 10–20 years after harvest). In coniferous and mixed forest, all disturbances except for partial harvest triggered significant increases in the abundance of deer mice and declines in red-backed voles. The increase in deer mice after wildfire was stronger than after clearcutting and marginally stronger than after clearcutting and burning. The abundance of red-backed voles was greatest in undisturbed or partially harvested stands, intermediate after clearcutting, and lowest after wildfire or clearcutting and burning. While the positive effect of clearcutting on deer mice did not persist beyond 10 years after disturbance, the negative effect on red-backed voles was similar between recent and older clearcuts. In deciduous forest, clearcutting did not result in a consistent change in abundance of deer mice and red-backed voles. For other small mammals, recent clearcutting tended to increase the abundance of yellow-pine chipmunks (Tamias amoenus), and meadow and long-tailed voles (Microtus pennsylvanicus and Microtus longicaudus). Woodland jumping mouse (Neozapus insignis), masked shrew (Sorex cinereus), and short-tailed shrew (Blarina brevicauda) did not show consistent response to timber harvest. Overall, the impact of different disturbances on the abundance of small mammals (i.e. positive or negative) appears to be species-specific, but disturbance type may influence the magnitude of this effect. Disturbance types can be ranked from severe to mild in terms of small mammal responses. The effects of forest harvest on small mammals are not equivalent to those of wildfire.     

Emulating natural disturbances: the role of silviculture in creating even-aged and complex structures in the black spruce boreal forest of eastern North America

Ecosystem-based forest management is based on the principle of emulating regional natural disturbance regimes with forest management. An interesting area for a case study of the potential of ecosystem-based forest management is the boreal forest of north-western Québec and north-eastern Ontario, where the disturbance regime creates a mosaic of stands with both complex and simple structures. Old-growth stands of this region have multi-storied, open structures, thick soil organic layers, and are unproductive, while young post-fire stands established following severe fires that consumed most of the organic soil show dense and even-sized/aged structures and are more productive. Current forest management emulates the effects of low severity fires, which only partially consume the organic layers, and could lead to unproductive even-aged stands. The natural disturbance and forest management regimes differ in such a way that both young productive and old-growth forests could ultimately be under-represented on the landscape under a fully regulated forest management regime. Two major challenges for ecosystem-based forest management of this region are thus to: (1) maintain complex structures associated with old-growth forests, and (2) promote the establishment of productive post-harvest stands, while at the same time maintaining harvested volume. We discuss different silvicultural approaches that offer solutions to these challenges, namely the use of (1) partial harvesting to create or maintain complex structures typical of old-growth stands, and (2) site preparation techniques to emulate severe soil burns and create productive post-harvest stands. A similar approach could be applied to any region where the natural disturbance regime creates a landscape where both even-aged stands established after stand-replacing disturbances and irregular old-growth stands created by smaller scale disturbances are significant.     

Moving riparian management guidelines towards a natural disturbance model: An example using boreal riparian and shoreline forest bird communities

Forest harvesting strategies that approximate natural disturbances have been proposed as a means of maintaining natural species’ diversity and richness in the boreal forests of North America. Natural disturbances impact shoreline forests and upland areas at similar rates. However, shoreline forests are generally protected from harvest through the retention of treed buffer strips. We examined bird community responses to forest management guidelines intended to approximate shoreline forest fires by comparing bird community structure in early (1–4 years) post-burned and harvested boreal riparian habitats and the adjacent shoreline forest. We sampled riparian areas with adjacent: (1) burned merchantable shoreline forest (n = 21), (2) burned non-merchantable shoreline forest (n = 29), (3) 10 m treed buffer with 25% retention in the next 30 m (n = 18), and (4) 30 m treed buffer (n = 21). Only minor differences were detected in riparian species’ abundance and bird community composition between treatments with greater differences in these parameters occurring between post-fire and post-harvest upland bird communities. Indicators of all merchantable treatments were dominated by upland species with open-habitat species and habitat generalists being typical upland indicator species of burned merchantable habitats and forest specialists typical upland indicators of harvested treatments. Riparian species indicative of burned riparian habitats were Common Yellowthroat (Geothlypis trichas), Le Conte’s Sparrow (Ammodramus leconteii) and Eastern Kingbird (Tyrannus tyrannus) and indicators of 30 m buffers were Alder Flycatcher (Empidonax alnorum) and Wilson’s Warbler (Wilsonia pusilla). Multivariate Redundancy Analysis (RDA) of the overall (riparian and upland birds) community showed greater divergence than RDA with only riparian species suggesting less effect of fire and forestry on riparian birds than on upland birds. Higher natural range of variability (NRV) of overall post-fire bird communities compared to post-harvest communities emphasizes that harvesting guidelines currently do not achieve this level of variability. However, lack of a large negative effect on common riparian species in the first 4 years post-disturbance allows for the exploration of alternative shoreline forest management that better incorporates bird community composition of post-fire riparian areas and shoreline forests.     

Natural stand structures, disturbance regimes and successional dynamics in the Eurasian boreal forests: a review with special reference to Russian studies

? This review summarizes early stand-scale studies of pristine forest structures, disturbance regimes and successional patterns carried out in boreal Eurasia. We attempt to reveal, characterize and classify stand dynamic types that can be used as templates for nature-based forest management.

? The studies reviewed demonstrate multiple successional pathways in stand development in all types of pristine forests. All-aged stands driven by small-scale disturbances are formed over successional development of several hundreds of years. This endogenous development can be interrupted by stand-replacing or partial disturbances leading to successions with even-aged or cohort-structured stands, respectively. In Western Europe, the most common disturbances are windthrows, surface fires and fluctuations in moisture regime; in Eastern Europe and Siberia, the most common disturbances are crown and surface fires and insect outbreaks. Type, return interval and severity of disturbances are strongly influenced by the site conditions and successional stage of a stand.

? Based on characteristics of forest stands and disturbance regime, four main types of pristine boreal forest stand dynamics can be distinguished: (1) even-aged, compositional change dynamics, (2) even-aged, mono-dominant dynamics, (3) cohort dynamics and (4) fine-scale gap dynamics. These types can be mimicked in developing scenarios of ecological sustainable forest management in Eurasian boreal forests.

     

Age and growth of a fire prone Tasmanian temperate old-growth forest stand dominated by Eucalyptus regnans, the world's tallest angiosperm

Forests are key components of the global carbon cycle, with deforestation being an important driver of increased atmospheric carbon dioxide. Temperate old-growth forests have some of the highest above ground stores of carbon of any forest types on Earth. Unlike tropical forests, the ecology of many temperate forests is dominated by episodic disturbance, such as high intensity fire. An exemplar of a particularly carbon dense temperate forest system adapted to infrequent catastrophic fires is the Eucalyptus regnans forests of south eastern Australia. Knowledge of the growth and longevity of old-growth trees is crucial to understanding the carbon balance and fire regimes of these forest systems. In an old-growth E. regnans stand in the Styx Valley in southern Tasmania we used dendrochronological techniques and radiocarbon dating to determine the age and stem growth of E. regnans and Phyllocladus aspleniifolius, an understorey rainforest conifer. Our analysis revealed that an even-aged cohort of E. regnans and P. aspleniifolius established in 1490–1510AD, apparently after a stand-replacing fire. The stem growth rates of E. regnans in the first 100 years were very rapid compared to the co-occurring P. aspleniifolius. That the longevity of E. regnans is >500 years challenges the suggested 350–450 year timeframe proposed for the widely held model of succession from eucalypt to rainforest. These forests not only have the potential to store vast amounts of carbon, but can also maintain these high carbon densities for a long period of time. Estimates of the capacity of these forests to sequester and store carbon should explicitly consider past harvesting and fire regimes and the potential increases in the risk of fire associated with climate change.     

Wind disturbances shape old Norway spruce-dominated forest in Bulgaria

Correct knowledge of disturbance ecology is essential for understanding the characteristic behavior of forest ecosystems and for guiding appropriate management strategies. However, the role of natural disturbances in shaping European mountain forest ecosystems has not been adequately studied, possibly because of the perception that the development of most European forests is primarily shaped by human influences and/or fine-scale gap-phase dynamics.In the present study, we investigate the long-term disturbance history of old protected forest dominated by Norway spruce in the Parangalitsa Reserve, Bulgaria. We used aerial photo interpretation and dendroecological methods to reconstruct the history of wind, insect, and fire disturbances across a topographically complex landscape. Over the past 150 years wind has been the most important disturbance agent in this ecosystem and at least 18% of the forested area shows evidence of high-severity blowdowns. Windthrow patches ranged in size from <1 ha to >10 ha (minimum 0.11 ha, mean 0.16 ha, maximum 10 ha). Although small disturbances were much more frequent, few larger blowdowns accounted for most of the disturbed area. Pure coniferous and single-cohort coniferous forest patches were more affected by blowdowns than mixed coniferous-deciduous and multi-cohort coniferous forest patches. Although bark beetle (Ips typhographus) populations were large enough to cause mortality of some live trees, the populations did not grow to epidemic proportions during recent decades. Fire disturbance was of limited importance in the last 200 years and only two patches (4% of the study area) showed evidence of fire.The present research indicates that wind disturbances have been characteristic of these ecosystems at least over the past decades to centuries. Thus, blowdowns appear integral to the normal function and structure of the Picea-dominated mountain forests in the region and such events, in and of themselves, do not represent unhealthy forest conditions or environmental emergencies. Management strategies that aim to maintain these ecosystems within a natural range of variation should incorporate wind disturbances into the management strategy. The frequency and magnitude of future wind disturbances may be considered within the historical framework described in the current study to assess potential effects of climate change on altered disturbance regimes.     

Disturbance history affects lightning fire initiation in the mixedwood boreal forest: Observations and simulations

The emulation of natural disturbances such as fire is a prominent harvest management strategy for ecosystems in Canada's boreal forest region, but the effect of harvesting on subsequent lightning fire occurrence has not been studied systematically in the mixedwood boreal forest. We quantified the relationship between annual patterns of lightning fire initiation, forest composition, lightning, and fire weather conditions over eight years (1994–2001) in a 60,000 km² region of actively harvested mixedwood boreal forest in western Canada. Our analyses illustrated that forest harvesting and burning had opposite effects on subsequent fire initiation, so harvest was not a surrogate for fire. Fire initiation increased in landscapes with more area harvested and decreased with area recently burned. Our data suggested that increased fire initiation was most pronounced in harvested stands up to a decade old, and there was some evidence that the effect might last as long as 30 years. We then used a dynamic fire-succession simulation model to quantify the long-term effects of these fuel-based relationships using two metrics. As expected, the first metric demonstrated that the number of years between disturbances was significantly less in stands that were harvested and then burned, than those that were burned and then burned again. However, the more revealing component of the simulations was an illustration that despite the strong, positive relationship between harvested areas and fire initiation, the area affected over the long-term by a reduced disturbance interval was relatively small. Accordingly, our study shows that spatiotemporal regulation of lightning fire initiation through harvesting activity results in a systematic accelerated frequency of disturbance that is novel to the mixedwood boreal system, but the area affected by these events amount to local peculiarities rather than broad-scaled regularities.     

Bird communities following high-severity fire: Response to single and repeat fires in a mixed-evergreen forest,Oregon, USA

Fire is a widespread natural disturbance agent in most conifer-dominated forests. In light of climate change and the effects of fire exclusion, single and repeated high-severity (stand-replacement) fires have become prominent land management issues. We studied bird communities using point counting in the Klamath-Siskiyou ecoregion of Oregon, USA at various points in time after one or two high-severity fires. Time points included 2 and 3 years after a single fire, 17 and 18 years after a single fire, 2 and 3 years after a repeat fire (15 year interval between fires), and >100 years since stand-replacement fire (mature/old-growth forest). Avian species richness did not differ significantly among habitats. Bird density was highest 17 and 18 years after fire, lowest 2 years after fire, and intermediate in repeat burns and unburned forest. Bird community composition varied significantly with habitat type (A = 0.24, P < 0.0001) with two distinct gradients in species composition relating to tree structure (live to dead) and shrub stature. Using indicator species analysis, repeat burns were characterized by shrub-nesting and ground-foraging bird species while unburned mature forests were characterized by conifer-nesting and foliage-gleaning species. Bird density was not related to snag basal area but was positively related to shrub height. Contrary to expectations, repeated high-severity fire did not reduce species richness, and bird densities were greater in repeat burns than in once-burned habitats. Broad-leaved hardwoods and shrubs appear to play a major role in structuring avian communities in the Klamath-Siskiyou region. In light of these results, extended periods of early seral broadleaf dominance and short-interval high-severity fires may be important to the conservation of avian biodiversity.     

Influence of post-harvest silviculture on understory vegetation: Implications for forage in a multi-ungulate system

Natural disturbance emulation has emerged as a key management approach to maintaining biodiversity in logged boreal forests. Forest managers’ success in emulating understory forest ecosystem functions, e.g., for the provision of habitat even for large mammals, has not been tested due, in many cases, to incomplete records of silviculture. We examined regenerating areas of previously conifer-dominated forests in northwestern Ontario, Canada, 10 and 30 years after logging and 10 and 30 years after fire to test if understory development and moose (Alces alces) forage abundance differed between the two disturbance types and artificial or natural regeneration approaches. In addition, we counted moose pellet groups as a measure of moose use of the region. Specific treatments included: (1) naturally regenerating, fire-origin forests, (2) post-harvest, regenerating forests with natural establishment of trees, and (3) post-harvest, regenerating forests with mechanical or chemical site preparation and planting and/or herbicide spraying. We hypothesized that the understory in post-harvest stands would support higher forage availability for moose compared to similarly-aged, fire-origin stands. Abundance of hardwoods, shrubs, and herbaceous plants was greater in naturally-regenerated post-harvest stands than in fire-origin and artificially regenerated post-harvest stands at both 10 and 30 years post-disturbance. However, post-harvest, naturally regenerating stands were not significantly associated with higher moose use, rather evidence of moose use increased as a function of the amount of naturally regenerating logged forest in the surrounding landscape. This study suggests that, relative to fire, the intensity of post-harvest silviculture influences habitat suitability for moose. The effect likely cascades to other ungulates, such as woodland caribou (Rangifer tarandus caribou), and vegetation management needs to be considered at scales greater than the stand level in order to achieve habitat management for large mammals.     

Restoration fire and wood-inhabiting fungi in a Swedish Pinus sylvestris forest

A growing awareness of the negative consequences of efficient fire prevention in boreal Fennoscandia has resulted in an increasing use of fire as a restoration method. The primary purpose of restoration fire is to recreate features of natural forests that have been lost during long periods of fire suppression. We used the occurrence of fruiting bodies from wood-inhabiting fungi to assess the conservation value of and gain ecological information about restoration fire in a Pinus sylvestris dominated forest. The general pattern for the majority of the species was a drastic decline the first two years after the restoration fire. However, our results clearly demonstrate that most of the species that declined the first years after the fire rebounded after four years and were frequently found on charred wood. Species that increased after the fire and often occurred on charred logs were: Antrodia sinuosa, Botryobasidium obtusisporum, Galzinia incrustans, Phlebia subserialis and Tomentella spp. In addition, three threatened, red-listed and fire-favored species were also found on heavily charred logs: Antrodia primaeva, Dichomitus squalens and Gloeophyllum carbonarium. Our results indicate that fire disturbance creates a unique type of dead wood important for fungal species richness. The results also support the use of restoration fires in maintaining forest biodiversity.     

Toward reference conditions: wildfire effects on flora in an old-growth ponderosa pine forest

Remote ponderosa pine (Pinus ponderosa) forests on the North Rim of Grand Canyon National Park, Arizona, USA provide valuable examples of reference conditions due to their relatively uninterrupted fire regimes, limited grazing history, and protection from logging. Wildfire is an important disturbance agent in upland forests of the Interior West, yet repeated measurements taken before and after lightning-ignited fires are rare. In 1999, a low-severity Wildland Fire Use fire burned 156 ha on Fire Point, a peninsula dominated by old-growth ponderosa pines, which had not burned for at least 76 years. We measured understory plant community and forest floor characteristics in 1998 (1 year before the fire) and 2001 (2 years after the fire) at this site and at nearby reference sites that did not burn in 1999 but have had continuing fire regimes throughout the past century. After the wildfire, the plant community at Fire Point shifted toward higher compositional similarity with the reference sites. Analysis of functional group composition indicated that this change was due primarily to an increase in annual and biennial forbs. Gayophytum diffusum, Polygonum douglasii, Chenopodium spp., Solidago spp., Elymus elymoides, Calochortus nuttallii, Hesperostipa comata, and Lotus spp. were indicative of forests influenced by recent fires. Species richness, plant cover, plant layer density and plant diversity were significantly lower at Fire Point than at the reference sites, possibly due to long-term fire exclusion, but the fire did not increase the rate of change in these variables after 2 years. Few exotic species were present at any site. Forest floor depths at Fire Point were reduced to depths similar to the reference sites, primarily due to consumption of the duff layer. There was a significant inverse relationship between the ratio of duff:litter and species richness. Compared to fire-excluded forests, old-growth ponderosa pine forests influenced by low-intensity surface fires generally have greater plant species richness (especially annual forbs) and lighter fuel loads. This study supports the continued application of the Wildland Fire Use strategy in old-growth montane forests to maintain and improve forest health by altering understory species composition and reducing fuel loads.     

Spatial variability in stand structure and density-dependent mortality in newly established post-fire stands of a California closed-cone pine forest

Fire is an important process in California closed-cone pine forests; however spatial variability in post-fire stand dynamics of these forests is poorly understood. The 1995 Vision Fire in Point Reyes National Seashore burned over 5000 ha, initiating vigorous Pinus muricata (bishop pine) regeneration in areas that were forested prior to the fire but also serving as a catalyst for forest expansion into other locales. We examined the post-fire stand structure of P. muricata forest 14 years after fire in newly established stands where the forest has expanded across the burn landscape to determine the important factors driving variability in density, basal area, tree size, and mortality. Additionally, we estimated the self-thinning line at this point in stand development and compared the size-density relationship in this forest to the theorized (−1.605) log-log slope of Reineke’s Rule, which relates maximum stand density to average tree size. Following the fire, post-fire P. muricata density in the expanded forest ranged from 500 to 8900 live stems ha⁻¹ (median density = 1800 ha⁻¹). Post-fire tree density and basal area declined with increasing distance to individual pre-fire trees, but showed little variation with other environmental covariates. Self-thinning (density-dependent mortality) was observed in nearly all stands with post-fire density >1800 stems ha⁻¹, and post-fire P. muricata stands conformed to the size-density relationship predicted by Reineke’s Rule. This study demonstrates broad spatial variability in forest development following stand-replacing fires in California closed-cone pine forests, and highlights the importance of isolated pre-fire trees as drivers of stand establishment and development in serotinous conifers.     

Stand structure and successional trends in virgin boreal forest reserves in Sweden

Fire history and stand structure was examined in twelve virgin forest stands situated within forest reserves in northern Sweden. The selected stands represented fire refuges as well as different successional stages after fire. Six of the stands were dominated by Norway spruce (Picea abies L. Karst.), three were dominated by Scots pine (Pinus sylvestris L.), and three were dominated by hairy birch (Betula pubescens Ehrh.) or aspen (Populus tremula L.). In 3 of the southernmost stands, the average fire interval was 34 to 65 years during the late 1600s to late 1800s, but since 1888 no fires had occurred in any of the stands. The absence of fire disturbance since 1888 is probably caused by the fire suppression in the overall landscape. The standing volume of living trees ranged between 87 and 511 m³ ha⁻¹ while the volume of dead trees, including both snags and logs, ranged between 27 and 201 m³ ha⁻¹. The volume of dead trees constituted ca. 30% of the total stem volume. In the conifer dominated stands, there was a statistically significant relationship between total stem volume, including both living and dead trees, and site productivity. A comparison between the amount of dead and living trees indicated substantial changes in tree species composition in several stands. It is suggested that data on the amount of dead trees, especially logs, and its distribution over decay classes could be used to examine the continuity of certain tree species. All stands had a multi-sized tree diameter distribution, which in most cases was similar to a reversed J-shaped distribution. In general spruce was numerous in the seedling cohort and in small diameter classes, indicating that its proportion in the stands was stable, or was increasing at the expense of pioneer tree species such as pine, aspen and silver birch (Betula pendula Roth.). The most numerous species in the seedling cohort, rowan (Sorbus aucuparia L.), was almost totally missing in the tree layer, indicating a high browsing pressure preventing rowan seedlings from growing into trees. The general increase of spruce and the sparse regeneration of pioneer species, in the stands previously affected by fire, are discussed in relation to natural disturbance regimes, biological diversity and nature conservation policies. It is proposed that reintroduction of fire disturbance is a necessity for future management plans of forest reserves. Other management practices to increase species diversity within forest reserves are also discussed.     

The response of land snail assemblages below aspens to forest fire and clear-cutting in Fennoscandian boreal forests

Species can persist in a landscape with recurrent disturbances either through local survival or by dispersing to sites of a preferred successional stage. This study investigated in what extent forest floor dwelling land snails survived forest fires and clear-cutting. Snail fauna in LFH (litter, fermenting litter and humus) samples below retained aspen trees in disturbed areas were compared with samples under scattered aspens in adjacent forests by extracting snails from LFH samples below five aspens in several stands of each type (five forest fires, six clear-cuts, and seven undisturbed forests). LFH samples from burnt sites had a higher pH than from forests, but on average a lower abundance of individual snails (11 vs. 30 in 0.5 l LFH) and 50% lower species density (3 vs. 6 species). The abundances and species densities in the clear-cuts were less affected. There was generally a positive relationship between pH and both species density and abundance in all the stand types. Burning apparently depleted the snail fauna considerably and some species may be dependent on dispersal if they are to recover within the burnt area, while the snail assemblages at clear-cuts did not differ significantly in species composition from adjacent forests. The positive relationship between pH and snail prevalence on the burnt sites raises questions regarding the pre- and post-fire spatial variation in pH (and available minerals) within and among stands and how it relates to snail survival rates and their capacity to track suitable places after the disturbance. Retained aspens at clear-cuts seem to harbour a forest like land snail fauna.     

Long-term spruce forest continuity – a challenge for a sustainable Scandinavian forestry

Macroscopic charcoal and pollen analysis were used to study the disturbance history and development of a boreal Norway spruce (Picea abies (L.) Karst.) forest landscape in southeastern Norway. The sites studied were natural forests and the charcoal records showed no evidence of fire disturbance that could have broken the continuity in the spruce forests that were established ca. 1700 years ago. Consequently, true spruce forest ecosystem continuity was documented on a landscape level. However, fire disturbed the mixed pine-deciduous forest ecosystems that preceded the present spruce forests, suggesting a shift from fire-prone, to fire-free forest ecosystems.It is argued that the studied forest landscape has the potential to be an important natural reference for future forestry, that would be required to mimic natural forest dynamics to be biologically sustainable. A stereotypic promiscuous use of fire in the regeneration phase may cause serious damages in forest ecosystems that have developed without the impact of fire disturbance.     

Forest structure and woody plant species composition along a fire chronosequence in mixed pine–oak forest in the Sierra Madre Oriental, Northeast Mexico

Although wildfires are occurring frequently in the pine–oak forests in the Sierra Madre Oriental (northeastern Mexico), data on post-fire succession and forest structure are still rare. Our objectives were to (1) assess the changes in woody plant species composition after fire and to (2) to relate successional patterns to environmental variability. Based on their fire history 23 plots were selected in the Parque Ecológico Chipinque (PECH). Changes in forest structure across the chronosequence of burned stands were deduced from density, height and diameter measurements of trees and shrubs (>5 cm in diameter) in all plots of 1000 m². Differences in woody plant species composition among the plots were evaluated using Shannon evenness measure and the Whittaker's measure and by Hierarchical cluster analysis and Detrended Correspondence Analysis. Hierarchical cluster analysis showed a high similarity among all recently burned plots, independed of the aspect. Multivariate analysis showed that local environmental factors, including time since fire, continue to structure species composition. Oak species (mainly Quercus rysophylla) resprouted successfully after fire and dominated young post-fire stands. Pine species (Pinus pseudotrobus and Pinus teocote) only appeared 18 years after fire and were the dominating species in mature stands (62 years after fire). In contrast, woody plant species composition in older stands tended also to be influenced by factors such as aspect and by the potential solar radiation (PSR) during the growing season. The results demonstrate that in the PECH, natural regeneration is sufficient and woody plant species composition will be similar to pre-fire conditions after 60 years of succession. We conclude that the park managers should consider incorporating natural disturbance regimes into their management practices.     

Emulating natural disturbances as a forest management goal: Lessons from fire regime simulations

Emulating natural forest disturbance is an increasingly popular forest management paradigm that is considered a means of achieving forest sustainability. Adopting this goal requires a sound understanding of natural disturbances at scales that correspond to management policies and strategies. In boreal forest landscapes driven by periodic stand-replacing fires this requires knowledge of fire regime characteristics, especially their spatial and temporal variability as well as stochasticity. The major goal of this study was to demonstrate the utility of fire regime simulation modeling to explore the variability of fire regime characteristics, with respect to formulating and assessing forest management strategies. We conducted a modeling experiment in a boreal forest landscape of northwestern Ontario, Canada, to examine its long-term fire regime in relation to forest policies on harvest size distribution. We used BFOLDS, a spatially explicit fire regime model that simulates individual fire events mechanistically in response to fire weather, fuel patterns, and terrain. The fire regimes in four large eco-regions were modeled for a 200-year period under three fire-weather (cold, normal, and warm) scenarios, with replications. We found that fire size distribution in all eco-regions followed power law under all weather scenarios, but their slopes and intercepts varied among eco-regions and fire weather scenarios. Warming fire weather increased burn rates and fire numbers in all eco-regions, albeit to different degrees. Overall, the variability among eco-regions was higher than the variability among fire weather scenarios, and among replicates. Comparisons of simulated fire size classes with those from an 86-year long fire history showed that empirical data cannot capture the variability that could be revealed by simulation modeling. We also show that fire size distribution is spatially heterogeneous within eco-regions, and provide several suggestions for forest policy directions with respect to forest harvest size distributions and harvest rates, based on the variability of fire regime characteristics. An assessment of present forest policies of emulating natural disturbances that guide forest harvest sizes showed that these are incongruent with simulated fire size distributions under all scenarios with one exception. Overall, this study illustrates the value of scenario simulation modeling to explore and quantify the variability of forest fire regime, for use in forest policies and strategies that attempt to emulate natural disturbance.     

Modeling silviculture after natural disturbance to sustain biodiversity in the longleaf pine (Pinus palustris) ecosystem: balancing complexity and implementation

Modeling silviculture after natural disturbance to maintain biodiversity is a popular concept, yet its application remains elusive. We discuss difficulties inherent to this idea, and suggest approaches to facilitate implementation, using longleaf pine (Pinus palustris) as an example. Natural disturbance regimes are spatially and temporally variable. Variability leads to a range of structural outcomes, or results in different pathways leading to similar structures. In longleaf pine, lightning, hurricanes, surface fires, and windthrow all lead to similar structures, but at different rates. Consequently, a manager can select among various natural disturbance patterns when searching for an appropriate silvicultural model. This facilitates management by providing flexibility to meet a range of objectives. The outcomes of natural disturbances are inherently different from those of silviculture, for example, harvesting always removes boles. It is instructive to think of silvicultural disturbances along a gradient in structural outcomes, reflecting degree of disparity with natural disturbance. In longleaf pine this might involve managing for two-cohort structure, instead of multi-cohort structure characteristic of old growth stands. While two-cohort structure is a simplification over the old growth condition, it is an improvement over single-cohort management. Reducing structural disparity between managed and unmanaged forests is key to sustaining biodiversity because of linkages that exist between structural elements, forest biota, and ecosystem processes. Finally, interactions of frequency, severity, intensity, seasonality, and spatial pattern define a disturbance regime. These components may not have equal weight in affecting biodiversity. Some are easier to emulate with silviculture than are others. For instance, ecologists consider growing-season fire more reflective of the natural fire regime in longleaf pine and critical for maintenance of biodiversity. However, dormant season fire is easier to use and recent work with native plants suggests that seasonality of fire may be less critical to maintenance of species richness, as one component of biodiversity, than is generally believed. Science can advance the goal of modeling silviculture after natural disturbances by better illustrating cause and effect relationships among components of disturbance regimes and the structure and function of ecosystems. Wide application requires approaches that are adaptable to different operational situations and landowner objectives. A key point for managers to remember is that strict adherence to a silvicultural regime that closely parallels a natural disturbance regime may not always be necessary to maintain biodiversity. We outline examples of silvicultural systems for longleaf pine that demonstrates these ideas.     

Low- to moderate-severity historical fires promoted high tree growth in a boreal Scots pine forest of Norway

Abstract

Fire is the most important ecological factor governing boreal forest stand dynamics. In low- to moderate-severity fires, the post-fire growth of the surviving trees varies according to fire frequency, intensity and site factors. Little is known about the growth responses of Scots pine (Pinus sylvestris L.) following fires in boreal forests. We quantified changes in tree growth in the years following 61 historical forest fires (between 1210 and 1866) in tree-ring series collected from fire-scarred Scots pine trees, snags and stumps in Trillemarka nature reserve in south-central Norway. Basal area increment 10 years pre-, 5 years post-, and 11–20 years post-fire were calculated for 439 fire scars in 225 wood samples. We found a slight temporary growth reduction 5 years post-fire followed by a marked growth increase 11–20 years post-fire. Beyond 20 years post-fire, the long-term tree growth declined steadily up to approximately 120 years. Our results indicate that recurring fires maintained high tree growth in remnant Scots pines, most probably due to a reduction in tree density and thus decreased competition.