Altered ignition catchments threaten a hyperdiverse fire‐dependent ecosystem

Human activities affect fire in many ways, often unintentionally or with considerable time‐lags before they manifest themselves. Anticipating these changes is critical, so that insidious impacts on ecosystems, their biodiversity and associated goods and services can be avoided, mitigated or managed. Here we explore the impact of anthropogenic land cover change on fire and biodiversity in adjacent ecosystems on the hyperdiverse Cape Peninsula, South Africa. We develop a conceptual framework based on the notion of an ignition catchment, or the spatial extent and temporal range where an ignition is likely to result in a site burning. We apply this concept using fire models to estimate spatial changes in burn probability between historical and current land cover. This change layer was used to predict the observed record of fires and forest encroachment into fire‐dependent Fynbos ecosystems in Table Mountain National Park. Urban expansion has created anthropogenic fire shadows that are modifying fire return intervals, facilitating a state shift to low‐diversity, non‐flammable forest at the expense of hyperdiverse, flammable Fynbos ecosystems. Despite occurring in a conservation area, these ecosystems are undergoing a hidden collapse and desperately require management intervention. Anthropogenic fire shadows can be caused by many human activities and are likely to be a universal phenomenon, not only contributing to the observed global decline in fire activity but also causing extreme fires in ecosystems where there is no shift to a less flammable state and flammable fuels accumulate. The ignition catchment framework is highly flexible and allows detection or prediction of changes in the fire regime, the threat this poses for ecosystems or fire risk and areas where management interventions and/or monitoring are required. Identifying anthropogenic impacts on ignition catchments is key for both understanding global impacts of humans on fire and guiding management of human‐altered landscapes for desirable outcomes.     

Fire history of Pinus nigra in Western Anatolia: A first dendrochronological study

Forests in the Mediterranean basin frequently experience fires due to both anthropogenic and natural causes. There are concerns that the fire season will prolong in the Mediterranean basin, the fire frequency will increase with ongoing climate change, moreover, the fire regimes will shift from surface fires to local crown fires. Here, we aim to improve our understanding of the fire regime components of black pine forests in Turkey by 1) reconstructing a high-resolution fire chronology based on tree rings, 2) revealing the seasonality of fires, 3) investigating the relationship between fire and climate, and 4) comparing our reconstruction results with documentary data from forest management units. We collected 62 fire-scarred trees from three sites in Kütahya and developed a 368 year-long (1652–2019) composite fire chronology using dendrochronological methods. We found that at two sites major fire years coincided with dry years. Two major fire years (1853 and 1879) were common to all sites and two additional fire years (1822 and 1894) were found at two sites. Our results show a sharp decline in fire frequency after the beginning of the 20th century at all sites that can be attributed to increased fire suppression efforts and forest management activities in the 20th century. Our results suggest that the spread of fires has been actively suppressed since the first forest protection law in Turkey. Yet, tree-ring based and documentary data corroboration shows that seasonality did not change over the past +350 years.     

Selective burning of forest vegetation in Canton Ticino (southern Switzerland)

Abstract

Detailed knowledge of factors controlling fire regime is a prerequisite for efficient fire management. We analyzed the fire selectivity of given forest vegetation classes both in terms of fire frequency and fire size for the present fire regime (1982–2005) in Canton Ticino (southern Switzerland). To this end, we investigated the dataset in four categories (all fires, anthropogenic winter fires, anthropogenic summer fires, and natural summer fires) and performed 1000 random Monte Carlo simulations on frequency and size. Anthropogenic winter and summer fires have a similar selectivity, occurring mostly at low elevations in chestnut stands, broadleaved forests, and in the first 50 m from the forest edge. In winter half of the fires in chestnut stands are significantly larger than 1.0 ha and the average burnt area in some coniferous forests tends to be high. Lightning fires seem to occur more frequently in spruce stands and less often in the summer‐humid chestnut and beech stands and the 50–100 m buffer area. In beech forests, in mixed forests, and in the spruce stands affected by natural fire in summer, the fires tend to be small in size. The selectivity observed, especially the selectivity of anthropogenic fires in terms of fire frequency, seems to be also related to geographical parameters such as altitude and aspect, and to anthropogenic characteristics such as closeness to roads or buildings.     

The legacy of forest logging on organic matter inputs and storage in tropical streams

Riparian forests play an important role in stream ecosystems, as they support biodiversity, reduce water erosion, and provide litter that fuels aquatic biota. However, they are affected by great array of anthropogenic threats (e.g., fire, logging, and organic pollution), which alter species composition and their physical structure. Although forest recovery after disturbance such as logging can take decades, the legacy of forest clear-cut logging on key processes in tropical riparian ecosystems is mostly unknown. Here, we investigated how litter inputs (leaves, twigs, and reproductive parts) and storage, key processes for carbon and nutrient recycling and for forest and stream biota, are influenced by riparian vegetation undergoing succession (after 28 years from logging) through the comparison of reference and logged forest sites in the Cerrado biome. Litterfall was overall similar between forest types, but litterfall of twigs was twofold higher at logged than reference sites. Similarly, litter inputs from the bank to the stream (i.e., lateral inputs) and streambed storage were 50–60% higher at logged than reference sites. The higher litterfall observed in logged forests could be related to higher proportion of tree species that are characteristic of primary and secondary successional stages, including fast-growing and liana species, which often are more productive and common in anthropogenic areas. Our results showed that the legacy impact of clear-cut logging, even if residual woody vegetation is maintained in riparian buffers, can shift the type, quantity, and seasonality of litter subsidies to tropical streams. This knowledge should be considered within the context of management and conservation of communities and ecosystem processes in the forest-stream interfaces.     

Maintaining and restoring biodiversity in European boreal forests by developing natural disturbance regimes

Abstract. A conceptual model is presented as a guide to the maintenance and restoration of ecologically sustainable boreal forest. The model is based on the hypothesis that self-sustained forest ecosystems can be (re-)created, and their biodiversity developed, if forest management can simulate the composition and structure of boreal forest landscapes by introducing and maintaining disturbances leading to naturally dynamic spatial and temporal patterns of forest regeneration. The major explanatory variable in the model is the effect of wildfire on sites with different fuel characteristics and climates found in the European boreal forest. Four levels of fire intensity are distinguished, based on mean fire frequencies. These range from extremely low in some wet tall-herb sites or sites at high altitudes or latitudes with a humid climate, where fire is absent or rare, to dry lichen-rich sites where fire occurs often. The model is called ASIO, after the words Absent, Seldom, Infrequent and Often, indicating the four levels. Three main disturbance regimes are distinguished in the European boreal forest, based on the complex interactions between probabilistic (e.g. mean fire intervals at different site types) and random events (e.g. where and when a fire occurs): (1) gap-phase Picea abies dynamics; (2) succession from young to old-growth mixed deciduous/coniferous forest; and (3) multi-cohort Pinus sylvestris dynamics. The model stems mainly from studies in Fennoscandia, but some studies from outside this region are reviewed to provide support for a more general application of the model. The model has been implemented in planning systems on the landscape level of several large Swedish forest enterprises, and is also used as an educational tool to help private land owners with the location and realization of forest management regimes. Finally, the model can be used to develop an administrative system for the monitoring of biodiversity in boreal forest.     

森林景观的历史变域研究进展

历史变域概念产生于20世纪90年代,是森林生态系统管理的重要概念之一,可以为生态系统管理提供参考和目标。总结了历史变域领域近期的研究热点:火烧的历史变域研究从定量化火烧特征开始,进而探讨火烧特征的影响因素,并且从火烧特征的单一影响因素向多影响因素、从单一尺度向多时空尺度研究发展;森林景观历史变域研究由描述景观的单一结构特征深入到揭示综合结构特征及功能特征。方法的新进展包括:评估历史数据的误差、探索采样和数据分析方法、重视火疤木数据的多时空特征、以及发掘整合多种来源的历史数据。模拟自然干扰的森林管理是历史变域概念的重要应用之一,最近的研究集中在为森林管理提供更加全面的模拟自然干扰的干扰参数,并且强调这些参数的空间异质性;同时,该管理模式也面临挑战和质疑:气候变化条件下历史变域的概念是否仍旧适用?森林管理是否能够真正达到自然干扰的效果?分析了我国的研究现状,提出发展建议。     

中国东部森林样带典型森林水源涵养功能

通过对我国东部森林样带四个森林生态系统定位研究站（长白山站、北京站、会同站和鼎湖山站）的九种森林类型水源涵养监测数据的分析,研究了水热梯度下不同森林生态系统水源涵养功能。结果表明：在生长季的5-10月份,各森林类型的水源涵养特性表现出较大差异。林冠截留率的大小依次为：阔叶红松林＞杉木林＞常绿阔叶林＞针阔混交林＞季风常绿阔叶林＞落叶阔叶混交林＞马尾松林＞落叶松林＞油松林,最高的长白山站阔叶红松林的截留率是最低的北京站油松林的2.2倍。森林降雨截留量与林外降雨量呈显著的正相关,林冠截留率与降雨量呈显著负相关。枯落物最大持水深（5-10月份）以北京站落叶阔叶林最大,为6.0mm;鼎湖山站的季风常绿阔叶林最小,为1.0mm。0-60cm土层蓄水量最大的是会同站的人工杉木林,为247mm;最小的是北京站的落叶松林,仅为45.5mm;林分总持水量依次为：杉木林＞阔叶红松林＞常绿阔叶林＞针阔混交林＞季风常绿阔叶林＞落叶阔叶混交林＞马尾松林＞落叶松林＞油松林。各林分总持水量主要集中在土壤层,占总比例的90%以上。     

Does It Make Sense to Restore Wildland Fire in Changing Climate?

Forest restoration guided by historical reference conditions of fire regime, forest structure, and composition has been increasingly and successfully applied in fire‐adapted forests of western North America. But because climate change is expected to alter vegetation distributions and foster severe disturbances, does it make sense to restore the ecological role of wildland fire through management burning and related activities such as tree thinning? I suggest that some site‐ and date‐specific historical conditions may be less relevant, but reference conditions in the broad sense are still useful. Reference conditions encompass not only the recent past but also evolutionary history, reflecting the role of fire as a selective force over millennia. Taking a long‐term functional view of historical reference conditions as the result of evolutionary processes can provide insights into past forest adaptations and migrations under various climates. As future climates change, historical reference data from lower, southerly, and drier sites may be useful in places that are higher, northerly, and currently wetter. Almost all models suggest that the future will have substantial increases in wildfire occurrence, but prior to recent human‐caused fire exclusion, fire‐adapted pine forests of western North America were among the most frequently burned in the world. Restoration of patterns of burning and fuels/forest structure that reasonably emulate historical conditions prior to fire exclusion is consistent with reducing the susceptibility of these ecosystems to catastrophic loss. Priorities may include fire and thinning treatments of upper elevation ecotones to facilitate forest migration, whereas vulnerable low‐elevation forests may merit less management investment.     

Effects of a prescribed fire on water use and photosynthetic capacity of pitch pines

Although wildfires are important in many forested ecosystems, increasing suburbanization necessitates management with prescribed fires. The physiological responses of overstory trees to prescribed fire has received little study and may differ from typical wildfires due to the lower intensity and timing of prescribed fire in the dormant season. Trees may be negatively affected by prescribed fires if injury occurs, or positively affected due to reduced competition from understory vegetation and release of nutrients from partially consumed litter. We estimated sap flow and photosynthetic parameters before a late-March prescribed fire and throughout the growing season in burned and unburned pitch pine (Pinus rigida L.) sites in the New Jersey Pinelands to determine how water use and photosynthetic capacity were affected. Water use was similar between sites before the fire but 27 % lower in burned trees immediately following the fire. After about a month, water use in the burned site was 11–25 % higher than pines from the unburned site and these differences lasted into the summer. Photosynthetic capacity remained similar between sites but instantaneous intrinsic water use efficiency increased by 22 % and maximum Rubisco carboxylation rate (V _cmax) was over three times greater in the summer compared to the pre-fire period in the burned site, whereas the unburned site exhibited similar V _cmax and intrinsic water use efficiencies between pre-fire and summer measurements. These differences in physiology suggest that the prescribed fire altered the amount of water and nutrients that pines had access to and led to increased water use and water use efficiency; both of which are important in this water- and nutrient-limited ecosystem.     

Evaluation of afforestation development and natural colonization on a reclaimed mine site

Post‐mining restoration sites often develop novel ecosystems as soil conditions are completely new and ecosystem assemblage can be spontaneous even on afforested sites. This study presents results from long‐term monitoring and evaluation of an afforested oil‐shale quarry in Estonia. The study is based on chronosequence data of soil and vegetation and comparisons are made to similar forest site‐types used in forest management in Estonia. After site reclamation, soil development lowered pH and increased N, K, and organic C content in soil to levels similar to the common Hepatica forest site‐type but P, total C, and pH were more similar to the Calamagrostis forest site‐type. Vegetation of the restoration area differed from that on common forest sites; forest stand development was similar to the Hepatica forest‐type. A variety of species were present that are representive of dry and wet sites, as well as infertile and fertile sites. It appears that novel ecosystems may be developing on post‐mining reclaimed land in Northeast Estonia and may require adaptations to typical forest management regimes that have been based on site‐types. Monitoring and evaluation gives an opportunity to plan further management activities on these areas.     

Wildfires in the western Canadian boreal forest: Landscape patterns and ecosystem management

Abstract. Mimicking of natural disturbance for ecosystem management requires an understanding of the disturbance processes and the resulting landscape patterns. Since fire is the major disturbance in the boreal forest, three widely held beliefs about fire behavior and resulting landscape patterns are examined in light of the empirical evidence available. These beliefs are: (1) that there is a ‘natural’ fire frequency for boreal ecosystems; (2) that the landscape mosaic created by wildfire is generally one of small, younger patches embedded within a matrix of older forest; and (3) that forest flammability is largely controlled by fuel accumulation. Despite the apparently logical basis for such beliefs, they are not well supported by empirical evidence. This discrepancy is explained by problems such as failure to appreciate the relationship between number of fires and area burned and inappropriate extrapolations or generalizations from other regions and vegetation types. The most important implications for management are that the natural disturbance processes producing landscape patterns in the boreal forest generally operate at much larger scales than management units, and that humans may have more indirect (through landuse change) rather than direct (through fire suppression) effects on the frequency of wildfires.     

Inverted invasions: Native plants can frequently colonise urban and highly disturbed habitats

There is an enormous body of literature on plant invasions, including many investigations of the types of introduced species that are most likely to invade natural ecosystems. In this study we turn invasion biology upside down, and ask what sort of native species colonise novel anthropogenic habitats such as roadside lawns, infrequently tended road shoulders, railway embankments and fire trails. We quantified species richness and cover in roadside lawns and infrequently tended road shoulders in five regions of New South Wales, Australia. The native vegetation in these regions included sclerophyll forest, fertile and infertile Eucalypt‐dominated woodlands, rainforest, and semi‐arid woodland. We performed a complementary survey of sites spanning five disturbance levels within the region containing sclerophyll forest vegetation. Although many non‐native species were present in disturbed, novel habitats, a total of 136 native species were also found. Most of these native species were in sites with low levels of disturbance (fire trails and railway embankments), but 35 native species were found to colonise roadside lawns, our most highly‐disturbed vegetation type. There was a significant negative relationship between the disturbance level in novel habitats and the number and cover of native species. Native species that colonised novel habitats were disproportionately likely be generalist species whose natural habitat includes both high and low light and high and low disturbance conditions. The native species colonising novel habitats also tended to have traits associated with a fast life‐history, including short stature and small seeds. A surprisingly high number of native plant species are colonising novel, anthropogenic habitats. Our findings highlight the potential importance of urban ecosystems for conservation and restoration biology.     

Local and global pyrogeographic evidence that indigenous fire management creates pyrodiversity

Despite the challenges wildland fire poses to contemporary resource management, many fire‐prone ecosystems have adapted over centuries to millennia to intentional landscape burning by people to maintain resources. We combine fieldwork, modeling, and a literature survey to examine the extent and mechanism by which anthropogenic burning alters the spatial grain of habitat mosaics in fire‐prone ecosystems. We survey the distribution of Callitris intratropica, a conifer requiring long fire‐free intervals for establishment, as an indicator of long‐unburned habitat availability under Aboriginal burning in the savannas of Arnhem Land. We then use cellular automata to simulate the effects of burning identical proportions of the landscape under different fire sizes on the emergent patterns of habitat heterogeneity. Finally, we examine the global extent of intentional burning and diversity of objectives using the scientific literature. The current distribution of Callitris across multiple field sites suggested long‐unburnt patches are common and occur at fine scales (<0.5 ha), while modeling revealed smaller, patchy disturbances maximize patch age diversity, creating a favorable habitat matrix for Callitris. The literature search provided evidence for intentional landscape burning across multiple ecosystems on six continents, with the number of identified objectives ranging from two to thirteen per study. The fieldwork and modeling results imply that the occurrence of long‐unburnt habitat in fire‐prone ecosystems may be an emergent property of patch scaling under fire regimes dominated by smaller fires. These findings provide a model for understanding how anthropogenic burning alters spatial and temporal aspects of habitat heterogeneity, which, as the literature survey strongly suggests, warrant consideration across a diversity of geographies and cultures. Our results clarify how traditional fire management shapes fire‐prone ecosystems, which despite diverse objectives, has allowed human societies to cope with fire as a recurrent disturbance.     

Notes on phenology and abundance of Psocoptera from primary and secondary dryland forest in Central Amazonia,Brazil

Psocoptera were collected from soil (by Kempson extraction) and from tree trunks (by arboreal photoeclectors) at two contrasting sites near Manaus, Brazil, for one year. The predominant soil taxa were Epipsocetae, especially Isthmopsocus, and a number of minor constituents are probably casual litter‐frequenters. Tree trunks yielded several taxa absent from soil. Soil in a secondary forest site yielded about four times as many psocids as a primary forest site and psocids were more abundant in the dry season than in the rainy season. Arboreal photoeclectors collected more psocids in the primary forest, but catches at both sites were larger in the dry season than in the rainy season. About 81 per cent of the psocids were immature stages.     

Climatic change and fire potential in South-Central British Columbia, Canada

The incidence and severity of forest fires are linked to the interaction between climate, fuel and topography. Increased warming and drying in the future is expected to have a significant impact on the risk of forest fire occurrence. An increase in fire risk is linked to the synchronous relationship between climate and fuel moisture conditions. A warmer, drier climate will lead to drier forest fuels that will in turn increase the chance of successful fire ignition and propagation. This interaction will increase the severity of fire weather, which, in turn, will increase the risk of extreme fire behaviour. A warmer climate will also extend fire season length, which will increase the likelihood of fires occurring over a greater proportion of the year. In this study of the North Okanagan area of British Columbia, Canada, the impacts of climate change of fire potential were evaluated using the Canadian Forest Fire Danger Rating System and multiple climate scenario analysis. Utilizing this approach, a 30% increase in fire season length was modelled to occur by 2070. In addition, statistically significant increases in fire severity and fire behaviour were also modelled. Fire weather severity was predicted to increase by 95% during the summer months by 2070 while fire behaviour was predicted to shift from surface fire‐intermittent crown fire regimes to a predominantly intermittent‐full crown fire regime by 2070 onwards. An increase in fire season length, fire weather severity and fire behaviour will increase the costs of fire suppression and the risk of property and resource loss while limiting human‐use within vulnerable forest landscapes. An increase in fire weather severity and fire behaviour over a greater proportion of the season will increase the risks faced by ecosystems and biodiversity to climatic change and increase the costs and difficulty of achieving sustainable forest management.     

Assessing Ecosystem Restoration Alternatives in Eastern Deciduous Forests: The View from Belowground

Both structural and functional approaches to restoration of eastern deciduous forests are becoming more common as recognition of the altered state of these ecosystems grows. In our study, structural restoration involves mechanically modifying the woody plant assemblage to a species composition, density, and community structure specified by the restoration goals. Functional restoration involves reintroducing dormant‐season, low‐severity fire at intervals consistent with the historical condition. Our approach was to quantify the effects of such restoration treatments on soil organic carbon and soil microbial activity, as these are both conservative ecosystem attributes and not ones explicitly targeted by the restoration treatments, themselves. Fire, mechanical thinning, and their combination all initially resulted in reduced soil organic C content, C:N ratio, and overall microbial activity (measured as acid phosphatase activity) in a study site in the southern Appalachian Mountains of North Carolina, but only the effect on microbial activity persisted into the fourth post‐treatment growing season. In contrast, in a similar forest in the central Appalachian Plateau of Ohio, mechanical thinning resulted in increased soil organic C, decreased C:N ratio, and decreased microbial activity, whereas fire and the combination of fire and thinning did not have such effects. In addition, the effects in Ohio had dissipated prior to the fourth post‐treatment growing season. Mechanical treatments are attractive in that they require only single entries; however, we see no indication that mechanical–structural restoration actually produced desired belowground changes. A single fire‐based/functional treatment also offered little restoration progress, but comparisons with long‐term experimental fire studies suggest that repeated entries with prescribed fire at intervals of 3–8 years offer potential for sustainable restoration.     

Fire-Regime Disruption and Pine-Oak Forest Structure in the Sierra Madre Occidental, Durango, Mexico

Fire is a common but poorly understood disturbance in the forested ecosystems of the Sierra Madre Occidental of Mexico. In this study, fire history, forest structure (density, species composition, regeneration, forest floor fuels, herbaceous cover, and age of pines), and the dendrochronological tree-ring record were measured at two unharvested 70-ha pine-oak sites near Ojito de Camellones, Durango, Mexico. Study sites were matched in slope, aspect, elevation, slope position, and plant composition, but they differed in fire history since 1945 and in forest structure. The long-term mean fire intervals (MFI) for all fires at both sites up to 1945 were similar—4.0 years at Site 1 (1744–1945) and 4.1 years at Site 2 (1815–1945)—but Site 1 burned only three times at the site margins since 1945 while Site 2 had 9 fires that scarred two or more sample trees and 15 total fires since 1945. Density measurements and age and diameter distributions showed that Site 1 was dominated by numerous, younger, smaller trees (mean total basal area of 23.4 m²/ha and 2730 trees/ha), while Site 2 had fewer, older, larger trees (basal area of 37.2 m²/ha, 647 trees/ha). Large, rotten fuel loading and duff depth were also greater at Site 1. Because regeneration averaged 6200 stems/ha at Site 1 and 8730 stems/ha at Site 2 (no significant difference), forest density at Site 2 was not limited by regeneration capability. The distributions of overstory diameter and pine age at both sites indicate that tree establishment occurred in pulses, with the largest cohort of trees establishing at Site 1 following the 1945 fire. The dense regeneration and heavy fuel accumulation at Site 1 are likely to support a switch from the former low-intensity fire regime to a high-intensity, stand-replacing fire across the site when the next suitable combination of ignition and weather occurs. Baseline quantitative information on fire frequency and ecological effects is essential to guide conservation or restoration of Madrean forests and may prove valuable for restoration of related fire-dependent ecosystems that have experienced extended fire exclusion elsewhere in North America.     

Effects of Prescribed Fire on Nutrient Pools and Losses from Glades Occurring Within Oak-Hickory Forests of Central Kentucky

Forest openings, also known as glades, arise through a variety of mechanisms including disturbance (fire and blow downs) and local variation in soil or bedrock geology. They are common in many forest types and are often dominated by locally rare herbaceous species. Prescribed burning is increasingly used as a management approach for maintaining glades although little is known about the effects of fire on these habitats. Of particular concern is the potential for nutrient loss during and after fire because glades are often characterized by nutrient‐poor soils. We quantitated nutrient losses through combustion and leaching for glade and adjacent forest habitats subjected to a prescribed burn. Our findings suggest that spring burns do not result in appreciable loss of nutrient capital from glades in comparison with those observed in the surrounding forest. Fire resulted in a substantial loss of litter mass (37%) in the forest but no measurable loss in the glade. Nitrogen losses through combustion were significant in the forest and were equivalent to 4.5 years of atmospheric inputs. Fire significantly increased soil nitrate pools in forest but not in glade plots. No detectable increases in nitrogen, phosphorus, or base cation leaching were observed in either forest or glade habitats within 4 months after the burn. These findings suggest that plant and microbial nutrient uptake rapidly reestablish control over leaching losses when burns are conducted at the start of the growing season. Biotic retention minimizes fire impacts on nutrient loss from the ecosystem.     

Species richness of soil gamasid mites (Acari: Mesostigmata) in fire-damaged mountain sites

Gamasid mites are important regulators of soil food webs in forest ecosystems. Wildfire is a dominant disturbance factor in forest ecosystems. We assessed the impact of fire on the species composition of soil gamasid mites at mountain sites following fires of four different degrees of severity and at one control site (5 years post-fire). In total, 14 families, 28 genera, and 54 species or species complexes were found. The abundance and richness were poor in severely burned sites compared to the less damaged sites. The different species compositions, especially in the medium-burned site, require further ecological study to improve our understanding. The fire response and recovery processes of selected species are also discussed.     

Influence of cattle grazing practices on forest understorey structure in north‐eastern New South Wales

Abstract In eastern Australia the practice of grazing cattle in eucalypt forests and woodlands, as a supplementary activity to farmland grazing, is widespread. It is typically accompanied by burning at frequent intervals by graziers to promote more nutritious and digestible growth of the ground cover for their livestock. Collectively, these forest grazing practices affect understorey structure, which in turn affects other biotic and abiotic components of these ecosystems. In order to test how significant the effects of forest grazing practices are relative to the effects of other management practices and environmental variables and the degree to which grazing practices determine understorey vegetation structure, we surveyed 58 sites on the northern tablelands of New South Wales, Australia. All sites were located in eucalypt forest and were stratified by grazing status (presence or absence): time since logging, time since wildfire, geology, aspect, slope and topographic position. At each site an index of vegetation complexity and the most abundant plant species were recorded. The data were analysed by a backwards stepwise multiple regression. Grazing practices had the greatest influence on understorey vegetation complexity of any of the measured attributes. The grazed sites were characterized by a significantly lower vegetation complexity score, different dominant understorey species, reduced or absent shrub layers, and an open, simplified and more grassy understorey structure compared with ungrazed sites. Time since logging and time since wildfire also significantly affected understorey structure. Our results indicate that cattle grazing practices (i.e. grazing and the associated frequent fire regimes) can have major effects on forest structure and composition at a regional level.