The Effect of Fire Reintroduction on Endemic and Rare Plants of a Southeastern Glade Ecosystem

Open habitats dominated by herbaceous plants on thin, rocky soils occur within the forests of eastern North America. Although these habitats vary in origin, structure, geology, and species composition, all contribute greatly to regional biodiversity by harboring endemic and/or rare plants. Little is known about how disturbances affect plant populations in these ecosystems. Fire once was a frequent natural disturbance in the Ketona dolomite glades of Alabama, an ecosystem harboring eight endemic taxa and numerous other species of conservation concern. We designed an experiment to determine how the reintroduction of fire into the glades and surrounding longleaf pine forests affects populations of rare glade plant species. Experimental and control plots were established within the glades. Experimental plots were burned in April 2004, and all plots were surveyed during two subsequent growing seasons (2004 and 2005). Populations of three of 14 species of conservation concern declined significantly after the initial fire but recovered the next year. Among other herbaceous species, only five and two differed in population size in 2004 and 2005, respectively. In 2004, more species were more abundant in control than burned plots, but this difference was not detected in 2005. Multivariate community‐level analyses of species presence–absence suggested that the effects of fire were negligible by the 2005 survey. Populations of young trees that had invaded the glades declined dramatically as a result of treatment fires. These results suggest that the reintroduction of fire will not harm glade species and may help prevent encroachment of the surrounding forest.     

Implications of Food Web Interactions for Restoration of Missouri Ozark Glade Habitats

Ozark glades are gaps in forested areas that are dominated by grasses and forbs growing in rocky, nutrient‐poor soil. Historically, these open, patchy habitats were maintained by natural and anthropogenic fire cycles that prohibited tree encroachment. However, because of decades of fire suppression, glades have become overgrown by fire‐intolerant species such as Eastern red cedar (Juniperus virginiana). Current restoration practices include cutting down invasive cedars and burning brush piles, which represent habitat for Northern fence lizards (Sceloporus undulatus). Because Sceloporus actively consumes herbivores, we hypothesized that the presence of these lizards in and around brush piles might result in a trophic cascade, whereby damage on native plants is reduced. Field surveys across six Missouri glades indicated that lizard activity was minimal beyond 1 m from habitat structures. This activity pattern reduced grasshopper abundance by 75% and plant damage by over 66% on Echinacea paradoxa and Rudbeckia missouriensis near structures with lizards. A field transplant experiment demonstrated similar reductions in grasshopper abundance and damage on two other glade endemic species, Aster oblongifolius and Schizachyrium scoparium. These results demonstrate that future glade restoration efforts might benefit from considering top‐down effects of predators in facilitating native plant establishment.     

采伐和火烧对森林氮动态的影响

森林是重要的陆地生态系统类型,它通过特有的养分循环机制维持其结构和功能.其中氮素对林木生长和发育十分重要,而且常是森林生产力的限制因素.另一方面,森林氮动态又常受到人类活动干扰的影响.根据国内外研究结果综述了采伐和火烧对森林氮动态的影响.结果表明采伐后环境因素的变化将影响森林N动态,其中最为关注的是采伐后一系列因素引起的N损失,如:N淋溶增加、伴随生物量的N迁移以及因径流或侵蚀增加造成的枯枝落叶层和土壤层N流失.这些N损失又将影响更新林分的生长和生产力.此外,采伐后N吸收速率一般下降,但随着植被快速生长N吸收速率将不断增加.采伐后氨化和硝化过程增强,但因短期内同化作用较弱,生态系统中大部分N将发生损失.火烧对森林N动态的短期影响主要包括:第一,火烧时N直接挥发损失;第二,火烧后N有效性增加,这主要由灰分沉积、根和微生物死亡及有机质N矿化增强等综合造成.随着时间延长,N有效性逐渐降低,这可能与火烧引起的有机质损失、植物N吸收增加、淋溶或侵蚀损失有关.然而,目前关于火烧造成的长期生态影响,如火烧后地上植被恢复与地下生物地球化学过程变化有何联系仍不太清楚.未来研究应着重于探讨氮素对森林采伐和火烧作出的短期响应将如何长期影响森林的结构和功能.此外,建议在实施营林方案时需考虑采伐和火烧对生态系统氮的影响.     

Effects of fire recurrence in Quercus coccifera L. shrublands of the Valencia Region (Spain): II. plant and soil nutrients

The consequences of fire recurrence (1, 2 and 3 fires in 16 years) on plant and soil C, N, P and K from Quercus coccifera garrigues were analysed in the Valencia Region (E Spain). Plant and forest floor (L horizon) nutrient concentrations either changed weakly or showed no change with fire recurrence. At the soil surface (0-2.5 cm), soil potential mineralisable nitrogen increased and available P decreased after an initial increase, whereas exchangeable K was not affected by successive fires. However, the significance of those observed trends for N and P was site-dependent. Despite the rapid formation of the L soil horizon, fire recurrence did not permit the development of the whole forest floor profile observed in the unburned garrigues. These organic layers contained a great proportion of the total nutrient pool, especially for N. Forest-floor and aboveground plant combustion by fire may produce significant losses of N and P compared with those available in mineral soil, whereas soil exchangeable K is large enough to replace these losses. Belowground nutrient reserves may account for the quick recovery of the Quercus coccifera aboveground biomass although successive fires could deplete these reserves and produce a loss of biomass and productivity in this species.     

Glade use by Olive baboons and Blue monkeys in Mount Meru Game Reserve,Tanzania

Forest glades have conservation value for primates, with interspecies differences reported. Blue monkeys (Cercopithecus mitis) are forest‐glade edge species, whereas Olive baboons (Papio anubis) prefer the open grassland of the glade interior. In this study, scan sampling was used to record the presence and absence of each species, group sizes and individual behaviours in three glade types in Mount Meru Game Reserve, Tanzania. Glade characteristics and primate usage for the three glade types were studied: five man‐made, fifteen lower natural and five upper natural glades. During 200 (3‐h morning and afternoon) observation periods, Blue monkeys and Olive baboons were observed during 43% (86/200) and 31% (62/200) of the observation periods, respectively. Blue monkeys used upper natural glades more than man‐made and lower natural; Olive baboons used man‐made glades more than lower and upper natural. Differences in glade type, in regard to vegetation, altitude and disturbance due to trail routes, influenced gladetype use and species behaviours. In conclusion, although the management practice of clearing in and around man‐made glades provides no direct conservation value for Blue monkeys, it likely reduces overuse of natural glades and human–wildlife conflict by enhancing plant species richness and diversity important to Olive baboons.     

Wildfire effects on carbon and nitrogen in inland coniferous forests

A ponderosa pine/Douglas-fir forest (Pinus ponderosa Dougl., Pseudotsuga menziesii (Mirb.) Franco; PP/DF) and a lodgepole pine/Engelmann spruce forest (Pinus contorta Loud., Picea engelmannii Parry ex Engelm.; LP/ES) located on the eastern slopes of the Cascade Mountains in Washington state, USA, were examined following severe wildfire to compare total soil carbon and nitrogen capitals with unburned (control) forests. One year after fire, the average C content (60 cm depth) of PP/DF and LP/ES soil was 30% (25 Mg ha^-1) and 10% (7 Mg ha^-1) lower than control soil. Average N content on the burned PP/DF and LP/ES plots was 46% (3.0 Mg ha^-1) and 13% (0.4 Mg ha^-1) lower than control soil. The reduction in C and N in the PP/DF soil was largely the result of lower nutrient capitals in the burned Bw horizons (12–60 cm depth) relative to control plots. It is unlikely that the 1994 fire substantially affected nutrient capitals in the Bw horizons; however, natural variability or past fire history could be responsible for the varied nutrient capitals observed in the subsurface soils. Surface erosion (sheet plus rill) removed between 15 and 18 Mg ha^-1 of soil from the burned plots. Nutrient losses through surface erosion were 280 kg C ha^-1 and 14 kg N ha^-1 in the PP/DF, whereas LP/ES losses were 640 and 22 kg ha^-1 for C and N, respectively. In both forests, surface erosion of C and N was _∼1% to 2% of the A-horizon capital of these elements in unburned soil. A bioassay (with lettuce as an indicator plant) was used to compare soils from low-, moderate- and high-severity burn areas relative to control soil. In both forests, low-severity fire increased lettuce yield by 70–100% of controls. With more severe fire, yield decreased in the LP/ES relative to the low-intensity burn soil; however, only in the high-severity treatment was yield reduced (14%) from the control. Moderate- and high-severity burn areas in the PP/DF were fertilized with _∼56 kg ha^-1 of N four months prior to soil sampling. In these soils, yield was 70–80% greater than the control. These results suggest that short-term site productivity can be stimulated by low-severity fire, but unaffected or reduced by more severe fire in the types of forests studied. Post-fire fertilization with N could increase soil productivity where other environmental factors do not limit growth. This revised version was published online in June 2006 with corrections to the Cover Date.     

Symbiotic soil fungi enhance ecosystem resilience to climate change

Substantial amounts of nutrients are lost from soils through leaching. These losses can be environmentally damaging, causing groundwater eutrophication and also comprise an economic burden in terms of lost agricultural production. More intense precipitation events caused by climate change will likely aggravate this problem. So far it is unresolved to which extent soil biota can make ecosystems more resilient to climate change and reduce nutrient leaching losses when rainfall intensity increases. In this study, we focused on arbuscular mycorrhizal (AM) fungi, common soil fungi that form symbiotic associations with most land plants and which increase plant nutrient uptake. We hypothesized that AM fungi mitigate nutrient losses following intensive precipitation events (higher amount of precipitation and rain events frequency). To test this, we manipulated the presence of AM fungi in model grassland communities subjected to two rainfall scenarios: moderate and high rainfall intensity. The total amount of nutrients lost through leaching increased substantially with higher rainfall intensity. The presence of AM fungi reduced phosphorus losses by 50% under both rainfall scenarios and nitrogen losses by 40% under high rainfall intensity. Thus, the presence of AM fungi enhanced the nutrient interception ability of soils, and AM fungi reduced the nutrient leaching risk when rainfall intensity increases. These findings are especially relevant in areas with high rainfall intensity (e.g., such as the tropics) and for ecosystems that will experience increased rainfall due to climate change. Overall, this work demonstrates that soil biota such as AM fungi can enhance ecosystem resilience and reduce the negative impact of increased precipitation on nutrient losses.     

Postfire nitrogen balance of Mediterranean shrublands: Direct combustion losses versus gaseous and leaching losses from the postfire soil mineral nitrogen flush

Fire is a major factor controlling global carbon (C) and nitrogen (N) cycling. While direct C and N losses caused by combustion have been comparably well established, important knowledge gaps remain on postfire N losses. Here, we quantified both direct C and N combustion losses as well as postfire gaseous losses (N₂O, NO and N₂) and N leaching after a high‐intensity experimental fire in an old shrubland in central Spain. Combustion losses of C and N were 9.4 Mg C/ha and 129 kg N/ha, respectively, representing 66% and 58% of initial aboveground vegetation and litter stocks. Moreover, fire strongly increased soil mineral N concentrations by several magnitudes to a maximum of 44 kg N/ha 2 months after the fire, with N largely originating from dead soil microbes. Postfire soil emissions increased from 5.4 to 10.1 kg N ha^?1 year^?1 for N₂, from 1.1 to 1.9 kg N ha^?1 year^?1 for NO and from 0.05 to 0.2 kg N ha^?1 year^?1 for N₂O. Maximal leaching losses occurred 2 months after peak soil mineral N concentrations, but remained with 0.1 kg N ha^?1 year^?1 of minor importance for the postfire N mass balance. ¹⁵N stable isotope labelling revealed that 33% of the mineral N produced by fire was incorporated in stable soil N pools, while the remainder was lost. Overall, our work reveals significant postfire N losses dominated by emissions of N₂ that need to be considered when assessing fire effects on ecosystem N cycling and mass balance. We propose indirect N gas emissions factors for the first postfire year, equalling to 7.7% (N₂‐N), 2.7% (NO‐N) and 5.0% (N₂O‐N) of the direct fire combustion losses of the respective N gas species.     

Water and Nutrient Outflow Following the Ecological Restoration of a Ponderosa Pine-Bunchgrass Ecosystem

In the late 1800s, fire suppression, livestock grazing, and a wet and warm climate led to an irruption of pine regeneration in Pinus ponderosa Laws. (ponderosa pine) forests of the southwestern United States. Pines invaded bunchgrass openings, causing stand structure changes that increased the number of stand-replacing fires. Ecological restoration, via thinning and prescribed burning, is being used to decrease the risk of stand-replacing fires and ameliorate other effects of pine invasion. The effects of aboveground restoration on belowground processes are poorly understood. We used a hydrologic model and soil water nutrient concentrations, measured monthly below the rooting zone, to estimate restoration effects on nutrient losses by leaching from a mature ponderosa pine forest near Flagstaff, Arizona. Replicated restoration treatments included thinning to pre-1880 stand densities (partial restoration), thinning plus forest floor fuel reduction followed by a prescribed burn (complete restoration), and an untreated control. Water outflow occurred only between January and May and was lowest from the control (47 and 28 mm in 1995 and 1996) and highest from the partial restoration treatment (67 and 59 mm in 1995 and 1996). The concentrations (typically <0.10 mg/ L) and estimated annual losses (<0.02 kg/ha) of NH₄⁺-N, PO₄^{3 ?} -P, and organic P were similar among treatments. Nitrate and organic N concentrations were as high as 0.80 mg N/L; however, these concentrations and estimated annual losses (<0.13 kg N/ha) were similar among treatments. Our results suggest that restoration will not enhance nutrient loss by leaching or alter stream chemistry in ponderosa pine forests.     

Fire severity and nutrient availability do not constrain resprouting in forest shrubs

Plants often survive disturbances such as fire by resprouting which involves having both protection traits and carbohydrate storage capacity. Protection traits not only act directly to insulate meristems but also prevent combustion of carbohydrate stores. Rapid stem growth also allows replenishment of carbohydrate stores ensuring persistence through another event. Resource availability may, however, constrain the ability to develop resilience to high-severity fires through either nutrient limitation or light limitation. We tested whether fire severity influenced resprouting ability of woody plants in two contrasting environments, low nutrient dry sclerophyll forest and more fertile wet sclerophyll forest. We tested which fire protection and growth traits were associated with resprouting ability (27 species) and resprouting vigour (16 species). Fire severity did not limit the ability of most species to resprout in either forest type. There was no generalized protection syndrome for surviving top kill, but combinations of bud protection and growth together with storage capacity appear to drive resprouting ability. In nutrient-limited forests, low specific leaf area (SLA) may reduce stem growth in resprouters, causing more reliance on bud protection through bark thickness. Conversely, in the more fertile forests, where light becomes limiting with time-since-fire, high SLA appears to increase the capacity for rapid stem growth with less emphasis on developing thicker bark. These different syndromes appear to be adaptive as fire severity did not influence survival in either forest type.     

Seasonal fire effects on the diversity patterns,spatial distribution and community structure of forbs in the Northern Mixed Prairie,USA

The effects of fire season on forb diversity patterns, density, and composition were determined for a northern Mixed Prairie site, USA. Repeated spring burns (dormant season), summer burns, fall burns (dormant season), and unburned treatments were compared over a 3-yr period characterized by wet and dry moisture conditions. Alpha and beta diversity were highest on unburned and summer burn treatments, while landscape mosaic diversity was highest on fall burns. Forb density was highest on fall and spring burn sites. Nine forb species comprised 82% of total densities and were significantly affected by fire season and year to year variations in moisture. Forb composition for unburned and spring burn treatments was similar, but both treatments were different from the summer burn and fall burn treatments which were similar to each other. Fire alone did not appear to be an intense enough disturbance to initiate drastic changes in the forb component of vegetation patches. Specific fire seasons did appear to either mask or enhance forb structure arising from other disturbance(s). Fire season also affected the scales of forb organization in the landscape. Contrasting spatial characteristics of the forb component of prairie plant communities may provide a diagnostic technique for exposing the interaction of disturbances at different temporal and spatial scales.     

Alteration and Recovery of Slash Pile Burn Sites in the Restoration of a Fire‐Maintained Ecosystem

Restoration practices incorporating timber harvest (e.g. to remove undesirable species or reduce tree densities) may generate unmerchantable wood debris that is piled and burned for fuel reduction. Slash pile burns are common in longleaf pine ecosystem restoration that involves hardwood removal before reintroduction of frequent prescribed fire. In this context, long‐lasting effects of slash pile burns may complicate restoration outcomes due to unintended alterations to vegetation, soils, and the soil seed bank. In this study, our objectives were to (1) examine alterations to the soil seed bank, soil physical and chemical characteristics, and initial vegetation recolonization following burn and (2) determine the rate of return of soil and vegetation characteristics to pre‐burn conditions. We found that burning of slash piles (composed of scores of whole trees) results in elevated nutrient levels and significant impacts on vegetation and the soil seed bank, which remain evident for at least 6 years following burn. In this ecosystem, formerly weakly acidic soils become neutral to basic and levels of P remain significantly higher. Following an initial decrease after burn, total soil N increases with time since burn. These changes suggest that not only does pile burning create a fire scar initially devoid of biota, but it also produces an altered soil chemical environment, with possible consequences for long‐term ecosystem restoration efforts in landscapes including numerous fire scars. To facilitate restoration trajectories, further adaptive management to incorporate native plant propagules or suppress encroaching hardwoods within fire scars may be warranted in fire‐dependent ecosystems.     

The effects of slash burning on ecosystem nutrients during the land preparation phase of shifting cultivation

The most commonly observed change in soil following slash-and-burn clearing of tropical forest is a short-term increase in nutrient availability. Studies of shifting cultivation commonly cite the incorporation of nutrient-rich ash from consumed aboveground biomass into soil as the reason for this change. The effects of soil heating on nutrient availability have been examined only rarely in field studies of slash-and-burn, and soil heating as a mechanism of nutrient release is most often assumed to be of minor importance in the field. Few budgets for above and belowground nutrient flux have been developed in the tropics, and a survey of results from field and laboratory studies indicates that soils are sufficiently heated during most slash-and-burn events, particularly in dry and monsoonal climates, to cause significant, even substantial release of nutrients from non-plant-available into plant-available forms in soil. Conversely, large aboveground losses of nutrients during and after burning often result in low quantities of nutrients that are released to soil. Assessing the biophysical sustainability of an agricultural practice requires detailed information about nutrient flux and loss incurred during management. To this end, current conceptual models of shifting cultivation should be revised to more accurately describe these fluxes and losses. This revised version was published online in June 2006 with corrections to the Cover Date.     

Genetic restoration in the eastern collared lizard under prescribed woodland burning

Eastern collared lizards of the Ozarks live in glades—open, rocky habitats embedded in a woodland matrix. Past fire suppression had made the woodlands a barrier to dispersal, leading to habitat destruction, fragmentation and local extinction. Reintroduced populations of lizards were subjected to 10 years of habitat fragmentation under continued fire suppression followed by twelve years of landscape restoration with prescribed burns. Prior to prescribed burning, genetic diversity decreased within glades and differentiation increased among glades. With woodland burning, genetic diversity within glades first decreased during an expanding colonization phase, but then increased as a dynamically stable metapopulation was established. Population differentiation among glades also stabilized in the metapopulation under weak isolation‐by‐distance. This study is one of the first to examine the genetic changes in a species of conservation concern throughout all the stages of decline and recovery and shows the importance of landscape‐level restoration for maintaining the genetic integrity of populations. This study also demonstrates how mark–recapture and genetic data together can yield detailed insight into metapopulation dynamics that would be impossible from just one type of data alone.     

兴安落叶松林火干扰后土壤有机碳含量变化

在大兴安岭兴安落叶松林区,选择不同恢复年限各种火烧强度(重度、中度、轻度)的火烧迹地进行调查并采集土壤样品,对火后有机层和矿质层有机碳含量变化进行研究,以期为进一步开展森林火灾对区域碳平衡影响的定量评估提供科学依据。研究结果表明:火干扰对土壤有机碳含量变化的影响包括火烧即时影响和火后生境条件变化带来的间接影响。火干扰样地有机层的积累与转化主要是通过火后林冠郁闭度的变化影响的,其有机碳总储量低于对照样地。对于矿质层土壤,重度和中度火干扰后,如果样地发生植被序列演替,即阔叶林植被入侵,样地郁闭度增加迅速,凋落物积累量增大,土壤有机碳含量将随着过火年限的增加而增加;如果样地发生自我更新,样地郁闭度增加缓慢,凋落物分解量大于积累量,土壤有机碳含量将会在一定时间内随着过火年限的增加而减少;但是,无论样地发生植被序列演替还是自我更新,土壤有机碳含量短时间内均无法恢复到火前水平。轻度火干扰后,土壤有机碳含量短期内先增加,随着植被更新情况的发展最终趋于平衡。     

Impacts of fire on sources of soil CO2 efflux in a dry Amazon rain forest

Fire at the dry southern margin of the Amazon rainforest could have major consequences for regional soil carbon (C) storage and ecosystem carbon dioxide (CO₂) emissions, but relatively little information exists about impacts of fire on soil C cycling within this sensitive ecotone. We measured CO₂ effluxes from different soil components (ground surface litter, roots, mycorrhizae, soil organic matter) at a large‐scale burn experiment designed to simulate a severe but realistic potential future scenario for the region (Fire plot) in Mato Grosso, Brazil, over 1 year, and compared these measurements to replicated data from a nearby, unmodified Control plot. After four burns over 5 years, soil CO₂ efflux (R_s) was ~5.5 t C ha^?1 year^?1 lower on the Fire plot compared to the Control. Most of the Fire plot R_s reduction was specifically due to lower ground surface litter and root respiration. Mycorrhizal respiration on both plots was around ~20% of R_s. Soil surface temperature appeared to be more important than moisture as a driver of seasonal patterns in R_s at the site. Regular fire events decreased the seasonality of R_s at the study site, due to apparent differences in environmental sensitivities among biotic and abiotic soil components. These findings may contribute toward improved predictions of the amount and temporal pattern of C emissions across the large areas of tropical forest facing increasing fire disturbances associated with climate change and human activities.     

Soil phosphorus and microbial response to a long-term wildfire chronosequence in northern Sweden

In the prolonged absence of major disturbances, ecosystems may enter a stage of retrogression, which is characterized by decreased ecosystem process rates both above and belowground, and often reduced availability of phosphorus (P). Disturbance through wildfire can increase soil P losses through leaching or erosion, but in the long-term absence of fire, soil P could potentially become increasingly bound in more stable forms that are less available to microbes. We studied forms of P and microbial respiration kinetics in the humus layer of a group of islands that vary considerably in wildfire frequency (40–5,300 years since last fire), and which are known to enter retrogression in the prolonged absence of fire. We found a decrease in labile P with decreasing fire frequency but no change in total P. Soil microorganisms responded more strongly to N than to P addition, and microbial biomass N:P ratios remained unchanged across the gradient. However, the concentration of labile P was the best predictor of microbial respiration responses across the islands, and this provides some evidence that declining access to P could contribute to the decline in soil microbial activity during retrogression. Our results show that even though N is arguably the main limiting nutrient during retrogression in this chronosequence, long term absence of fire also causes a decline in P availability which negatively affects microbial activity. This in turn could potentially impair microbially driven processes such as decomposition and mineralization and further contribute to the reduced availability of soil nutrients during retrogression.     

Fire as a Recurrent Event in Tropical Forests of the Eastern Amazon: Effects on Forest Structure,Biomass, and Species Composition1

The effects of fire on forest structure and composition were studied in a severely fire-impacted landscape in the eastern Amazon. Extensive sampling of area forests was used to compare structure and compositional differences between burned and unburned forest stands. Burned forests were extremely heterogeneous, with substantial variation in forest structure and fire damage recorded over distances of <50 m. Unburned forest patches occurred within burned areas, but accounted for only six percent of the sample area. Canopy cover, living biomass, and living adult stem densities decreased with increasing fire inrensiry / frequency, and were as low as 10–30 percent of unburned forest values. Even light burns removed >70 percent of the sapling and vine populations. Pioneer abundance increased dramatically with burn intensity, with pioneers dominating the understory in severely damaged areas. Species richness was inversely related to burn severity, but no clear pattern of species selection was observed. Fire appears to be a cyclical event in the study region: <30 percent of the burned forest sample had been subjected to only one burn. Based on estimated solar radiation intensities, burning substantially increases fire susceptibility of forests. At least 50 percent of the total area of all burned forests is predicted to become flammable within 16 rainless days, as opposed to only 4 percent of the unburned forest. In heavily burned forest subjected to recurrent fires, 95 percent of the area is predicted to become flammable in <9 rain-free days. As a recurrent disturbance phenomenon, fire shows unparalleled potential to impoverish and alter the forests of the eastern Amazon.     

火烧强度对兴安落叶松群落叶片功能性状及功能多样性的影响

林火是北方针叶林的重要生态因子,直接影响火烧迹地物种多样性及功能多样性,进而影响森林群落的演替.以牙克石地区火后自然恢复12年的兴安落叶松群落为研究对象,在群落尺度上分析火烧迹地土壤养分含量、叶片功能性状、物种多样性和功能多样性在不同火烧强度(轻、中和重度火烧)下的变化规律.结果表明: 火烧显著降低了土壤全氮含量,对土壤全磷含量无显著影响.轻、中度火烧有助于维持群落较高的物种多样性和功能多样性;中度火烧显著增加了群落的物种多样性,物种丰富度指数、Shannon指数、Simpson指数和Pielou均匀度指数均在中度火烧时有最大值;火烧降低了群落的功能丰富度和功能离散度指数,二者分别在中、轻度火烧时最大(除未过火外),而群落的功能均匀度和二次熵指数在林火干扰后增加,轻度火烧后最大.随火烧强度增加,叶干物质含量、叶组织密度和叶磷含量总体呈显著增大趋势,而比叶面积、叶含水量、叶氮含量和叶N∶P则表现出未过火>中度火烧>轻度火烧>重度火烧的规律,叶片厚度呈先增大后减小的变化规律.火烧强度对森林群落的叶片功能性状和功能多样性均有显著影响,且适度的火干扰对森林群落的恢复具有促进作用.     

Sustainable forestry: A model of the effects of nitrogen removals in wood harvesting and fire on the nitrogen balance of regrowth eucalypt stands

Abstract Sustainable forest use is an integral part of Australia's recently adopted National Forest Policy; consequently, there is an urgent need for quantitative, ecologically based measures of sustainability. One process that may affect ecosystem sustainability is the removal of nutrients through forest harvesting and fire. This paper presents a model-based analysis of the combined consequences of harvesting and fire management practices for the nitrogen (N) budgets of managed forest ecosystems. The model, called N-BAL, evaluates the balance between N removals due to harvesting and fire (prescribed and regeneration burns), and N inputs (both natural and as added fertilizer), and leads to a criterion for the maintenance of site N reserves. That criterion can be used to estimate the accretion (or depletion) of site N over a single forest rotation, or to predict sustainable stem productivity for given N inputs and management practices. The analysis is applied to managed stands of karri (Eucalyptus diversicolor F. Muell.) in southwestern Australia to investigate whether natural N inputs are sufficient to maintain site N capital under current harvesting and fire practices. Model predictions for stands harvested at age 100 years with slash burns and regular prescribed burns range from a rotation-averaged depletion rate of 22 kg ha^?1 year^?1 to an annual accretion of 14 kg ha^?1 year^?1, depending on assumed N inputs and fire frequency and intensity. The mean annual N balance is highly sensitive to rates of natural N inputs, fire intensity and inter-fire period, and less sensitive to rotation length. These results are tentative and highlight the need for further research to improve estimates of several key model parameters and relationships.