Effects of management on coarse woody debris volume and composition in boreal forests in northern Sweden

Forest management practices have led to a reduction in the volume and a change in the composition of coarse woody debris (CWD) in many forest types. This study compared CWD volume and composition in reserves and two types of managed forest in the central boreal zone of Sweden. Ten areas were surveyed, each containing clear-cut, mature managed and old-growth stands, to determine the volume of standing and lying CWD in terms of species composition, decay class and size class. Volumes of CWD on clear-cuts and in mature managed forests were high compared with previous studies. Old-growth forests (72.6 m³ ha^?1) contained a greater volume of CWD than mature managed forests (23.3 m³ ha^?1) and clear-cuts (13.6 m³ ha^?1). Differences were greatest for the larger size classes and intermediate decay stages. Despite stand ages being up to 144 years, CWD volume and composition in managed forests was more similar to clear-cuts than to old-growth forests.     

Carbon stocks and soil respiration rates during deforestation, grassland use and subsequent Norway spruce afforestation in the Southern Alps, Italy

Changes in carbon stocks during deforestation, reforestation and afforestation play an important role in the global carbon cycle. Cultivation of forest lands leads to substantial losses in both biomass and soil carbon, whereas forest regrowth is considered to be a significant carbon sink. We examined below- and aboveground carbon stocks along a chronosequence of Norway spruce (Picea abies (L.) Karst.) stands (0-62 years old) regenerating on abandoned meadows in the Southern Alps. A 130-year-old mixed coniferous Norway spruce-white fir (Abies alba Mill.) forest, managed by selection cutting, was used as an undisturbed control. Deforestation about 260 years ago led to carbon losses of 53 Mg C ha(-1) from the organic layer and 12 Mg C ha(-1) from the upper mineral horizons (Ah, E). During the next 200 years of grassland use, the new Ah horizon sequestered 29 Mg C ha(-1). After the abandonment of these meadows, carbon stocks in tree stems increased exponentially during natural forest succession, levelling off at about 190 Mg C ha(-1) in the 62-year-old Norway spruce and the 130-year-old Norway spruce-white fir stands. In contrast, carbon stocks in the organic soil layer increased linearly with stand age. During the first 62 years, carbon accumulated at a rate of 0.36 Mg C ha(-1) year(-1) in the organic soil layer. No clear trend with stand age was observed for the carbon stocks in the Ah horizon. Soil respiration rates were similar for all forest stands independently of organic layer thickness or carbon stocks, but the highest rates were observed in the cultivated meadow. Thus, increasing litter inputs by forest vegetation compared with the meadow, and constantly low decomposition rates of coniferous litter were probably responsible for continuous soil carbon sequestration during forest succession. Carbon accumulation in woody biomass seemed to slow down after 60 to 80 years, but continued in the organic soil layer. We conclude that, under present climatic conditions, forest soils act as more persistent carbon sinks than vegetation that will be harvested, releasing the carbon sequestered during tree growth.     

Differences in bird species diversities between a natural mixed forest and a coniferous plantation

Bird species diversity and bird species richness were surveyed in a natural mixed forest (mature forest) and in a coniferous plantation (30–40 years old) monthly from 1990 to 1994. These forests were 20 km apart and had similar weather conditions and soil types. There were larch and cedar plantations, and hardwoods along streams in the coniferous plantation. In the natural mixed forest, 55 bird species were found, whereas 40 species were recorded in the coniferous plantation. The species diversity of bird communities was significantly higher in the natural mixed forest than in the coniferous plantation mixed with hardwood trees. This result indicates that the coniferous plantation mixed with hardwood trees, presumed to be a more simplified environment, is likely to be less inhabitable for many bird species than the natural mixed forest, suggesting a relationship between the diversity of the forest environment and the diversity of the bird community. A higher number of bird species was recorded in the small coniferous forest mixed with hardwood trees compared with those in the coniferous plantation. The mixing of broad-leaved trees in a coniferous plantation was suggested to be effective in increasing number of bird species. These tendencies were recorded all through the year during our study. In snow-covering periods, both the diversity and the bird species richness fell in all study sites every year. Snow cover would have greater effect on bird species diversity in the coniferous plantation than in other forest types probably due to diet shortages caused by the snow cover over the forest floor.     

Ant abundance increases with clearing size

Ants are an important part of biodiversity and are useful bioindicators. Our aim was to determine whether ant species richness and composition differ among large clear-cuts (ca. 3000 m²), small forest gaps (ca. 400 m²), and areas of mature forest. The research was conducted in a large plantation of Picea abies in the Jizerske Mountains in the Czech Republic at an elevation of ca. 900 m a.s.l. Ants were sampled using pitfall traps in three areas, each of which had a large clear-cut, mature forest, and gaps; a randomized complete block design was used. Species richness and composition of ant assemblages differed significantly among plots in the three treatments. The results showed that ant abundance and diversity were similarly low in small gaps and in closed-canopy mature stands; in comparison, large clear-cuts supported significantly higher species richness, more complex species composition, and a higher abundance of ants. Six species were found in large clear-cuts, but only one and two species were collected in small gaps and mature forests, respectively. Our findings suggest that small-scale forest management is not suitable for maintaining ant diversity.     

Epiphytic lichen diversity in old-growth and managed Picea abies stands in Alpine spruce forests

In the last decades, a large body of literature has grown to evaluate the impact of forest management on epiphytic lichens in boreal coniferous forests. However, information is still lacking on coniferous forests of the Alps. This study compares lichen diversity between spruce forest stands of four successional stages: (1) young, (2) intermediate, (3) mature forests managed for timber production with a rotation cycle of 120–180 years, and (4) old-growth protected forests. The emphasis was placed on the occurrence of nationally rare and calicioid species (lichens and fungi traditionally referred to as Caliciales, known to be indicative of forest age and continuity). For each forest successional stage, four plots were selected. In each plot, 7 spruce individuals were surveyed for epiphytic lichens according to a standardised sampling method. Species richness increased from young to mature stands, while no difference was detected between mature and old-growth stands. This pattern was also confirmed for rare and calicioid species which are, however, more frequent in old-growth stands. Differences in species composition were also found between the different forest successional stages. Mature and old-growth plots slightly overlap, indicating that to some extent comparable lichen assemblages could be found in these stands. A nested pattern of species assemblages was found, old-growth stands hosting most of the species which were also found in stands belonging to the previous forest successional stages. Our results support the hypothesis that the management regime applied to spruce forests of the Italian Alps renders mature stands managed for timber production somewhat similar to old-growth stands as lichen habitat. However, we found a higher complexity in old-growth forests, and many species of conservation concern clearly preferred old-growth stands. In this perspective, a further prolongation of the normal cycle it is likely to be a most favourable conservation-oriented management to be recommended at least within protected areas and Natura 2000 sites, where conservation purposes should receive a high priority.     

塞罕坝机械林场地表可燃物类型划分与载量研究

对塞罕坝机械林场8个林分类型108个林班的地表森林可燃物组成、载量、含水率等进行了调查。结果表明落叶松成林和幼林、樟子松成林和幼林、针叶混交林、桦次生林等林分地表可燃物以枯落物为主,栎次生林和灌木林地表可燃物由枯落物与灌木组成,未成林地与草地可燃物以草本植物为主;地表可燃物载量依次为落叶松成林〉落叶松幼林〉针叶混交林〉樟子松成林〉樟子松未成林〉针阔混交林〉桦次生林〉樟子松幼林〉落叶松未成林〉灌木林〉栎次生林〉草地;草地与栎次生林的含水率最低,着火点也最低,火险危险程度最高;将现有林分按燃烧类型划分为5个类型20个亚类,全场地表可燃物总载量约为2．5×10^6t。     

Influence of variable retention harvests on forest ecosystems: Plant and mammal responses up to 8 years post-harvest

Green-tree retention systems are an important management component of variable retention harvests in temperate zone coniferous forests. Residual live trees (“legacy trees”) provide mature forest habitat, increase structural diversity, and provide continuity in the regenerating stand. This study was designed to test the hypotheses that, at up to 8 years after harvest, abundance and species diversity of communities of (i) understory plants and (ii) forest-floor small mammals, and (iii) relative habitat use by mule deer (Odocoileus hemionus), will decline with decreasing levels of tree retention. Communities of plants and forest floor small mammals were sampled in replicated clearcut, single seed-tree, group seed-tree, patch cut, and uncut forest sites in mixed Douglas-fir (Pseudotsuga menziesii)—lodgepole pine (Pinus contorta) forest in southern British Columbia, Canada from 2000 to 2003 (5–8 years post-harvest). Habitat use by mule deer was measured during summer and winter periods each year from 1999 to 2003 in these same sites.     

Retention of aspen (Populus tremulae) at final cuttings - The effect of dead wood characteristics on saproxylic beetles

To preserve biodiversity in managed forest landscapes dead and living trees are retained at final cuttings. In the present study we evaluated the effect of these practices for saproxylic (wood-dependent) beetles inhabiting dead aspen trees (Populus tremulae). For saproxylic beetles, tree retention at final cuttings can be expected to be especially valuable for species adapted to sun-exposed dead wood, a substrate that only rarely occurs in well managed forest stands. Therefore, the current evaluation was conducted as a comparison of species richness, species density (number of species per sample), assemblage composition and occurrence of individual species between clear-cuts, where aspen trees were retained, and closed forest stands with aspen trees. The study was conducted in central Sweden and the beetles were sampled by sieving of bark from CWD (coarse woody debris) of aspen. There was no significant difference in rarefied species richness between forest and clear-cut sites. Species composition differed significantly between the two stand types. Generalized linear mixed-effects models predicted the species density to be 34% lower in CWD objects in forest sites than on clear-cuts. This pattern could partly be explained by differences in CWD diameter, decay class and bark types between the two stand types (clear-cut/forest). Stand type was a significant predictor of occurrence in individual CWD objects for 30% of analysed individual beetle species. For all species except one, the variable stand type predicted higher occurrence on clear-cuts than in forest stands. To conclude, our results demonstrate that retention of aspen on clear-cuts contributes to population recruitment of a different assemblage of species than CWD within stands.     

Relative importance of thinned and clear-cut stands for bryophyte diversity on stumps

The interest in harvesting logging residues in the form of stumps has recently increased markedly in the Nordic countries of Europe due to the steadily growing market for bio-fuel from forestry. Yet, stumps are currently harvested without a solid knowledge of their importance for forest organisms. To assess the relative importance of thinned, clear-cut, and burned clear-cut stands for the diversity of bryophytes on stumps we investigated bryophyte species composition and richness on 755 spruce stumps in 27 forest stands in southern-boreal Finland. Stumps were sampled within both wet and dry sites. For comparison we also surveyed bryophytes on 669 ground plots in the same stands to assess if patterns were consistent regardless of substrate type.Stand type (i.e. thinned, clear-cut, or burned clear-cut) was the main predictor of both species richness and composition on stumps. Stumps in thinned stands were more species rich than in clear-cuts, and the lowest richness was found on stumps in burned clear-cuts. Differences in species composition were explained by higher frequency of occurrence of species in thinned than in clear-cut stands. Thus, stumps in clear-cut stands tended to host a subset of species from the thinned stands, but there was also a pattern of turnover where different species were present in thinned and clear-cut stands, respectively. The results were similar for bryophytes on ground indicating that canopy cover strongly affected the diversity of bryophytes regardless of substrate.We conclude that stump harvest in open, clear-cut stands will probably have minor effects on bryophyte diversity on dead wood in the managed forest landscape. Conservation efforts in thinned stands (e.g. retention and creation of dead wood) may be important for promoting the diversity of bryophytes in managed forests.     

Effects of stand density on ecosystem properties of subalpine forests in the southern Rocky Mountains, USA

? Mixed coniferous, subalpine forest communities in the Rocky Mountains are historically dense and have experienced infrequent, high-severity fire. However, many of these high-elevation stands are thinned for a number of perceived benefits.

? We explored the effects of forest stand density on ecosystem properties in subalpine forests in Colorado, USA, 17–18 y after forests were managed for timber.

? Forest structure significantly altered the composition and chemical signature of plant communities. Previously managed stands contained lower density of overstory trees and higher ground cover compared to paired reference stands. Foliar phenolic concentration of several species was negatively related to basal area of overstory trees. Furthermore, reductions in stand density increased total foliar phenolic:nitrogen ratios in some species, suggesting that gap formation may drive long-term changes in litter quality. Despite significant changes in forest structure, reductions in stand density did not leave a strong legacy in surface soil properties, likely due to the integrity of soil organic matter reserves.

? Changes in forest structure associated with past management has left a long-term impact on plant communities but has only subtly altered soil nutrient cycling, possibly due to trade offs between litter decomposability and microclimate associated with reductions in canopy cover.

     

Saproxylic beetles in high stumps and residual downed wood on clear-cuts and in forest edges

Abstract

This study evaluates how the placement and the different possible outcomes of a spruce retention tree affected species richness and assemblages of spruce-associated saproxylic beetles. In a field experiment in the boreal zone of central Norway, high stumps were created and compared with residual wood pieces (i.e. top boles with branches), in clear-cuts versus in forest edges. Flight interception traps were mounted close to the substrate. The results were analysed using rarefaction techniques, ordination (DCA) and anova. It was found that the placement of retention trees of spruce does matter: beetle assemblages were significantly different in stumps in the four treatments. For all species pooled, the species richness was higher in stumps in clear-cuts than in stumps or boles in the forest edge. Four red-listed species were more abundant near stumps than boles, and two red-listed species were more abundant in clear-cuts than forest edge. To cater for the variety of habitat preferences among forest beetles in managed forest, managers should leave both standing spruce trees (many of which will end up as windthrown, downed boles) and some high stumps (to secure some upright dead wood), in both exposed clear-cut and semi-shaded forest edge.     

Deciduous trees affect small-scale floristic diversity and tree regeneration in conifer forests

Abstract

There is a growing interest in the effects of deciduous trees on biodiversity, soil processes and long-term productivity in boreal, conifer-dominated forests. This study investigated whether individual birch trees allowed to grow to maturity in the coniferous forest can have a local effect on floristic richness and regeneration of tree saplings. The ground vegetation was compared in 2?m radius plots around the stem under the canopies of matched conifer–deciduous trees in a mature, conifer-dominated forest, and included in the analysis variables that could potentially mediate the tree effect (soil pH, cover of lichens, bryophytes, leaf and needle litter). The field layer vegetation was more species rich under birch (Betula pendula and B. pubescens) than under conifers (Picea abies and Pinus sylvestris), and several vascular plant species (including saplings of tree species) occurred more often under birch than under conifers. However, when the effect of the number of subordinate trees was taken into account the difference between birch and pine was not significant. The number of tree regenerations (saplings) was lowest under pines, but did not differ between spruce and birch. There were no effects of the canopy species on soil pH or on cover of lichens and bryophytes. The difference in diversity may be caused by the different effects of leaf and needle litter, and it is also likely that canopy structure has an influence via interception and throughfall and by affecting the light and microclimate.     

Fire cycle and fire adaptation of main tree species in Daxing’anling forest region,China

Based on the fire statistics, the Daxing’anling forest area were classified into three fire cycle regions: northern coniferous virgin forest region with a fire cycle ofl 10–120 years, middle conifer-broad-leaved mixed forest region with a fire cycle of 30–40 years, and southern broad-leaved secondary forest region with a fire cycle of 15–20. The percentage of conifers and broad-leaved trees, forest age and natural mature period of main tree species in different fire cycle regions were discussed in concern with fire occurrence. The characteristics of fire adaptation and fire resistance of main tree species, such as sexual and asexual reproduction, were discussed and evaluation of the synthetical fire adaptation was made.     

FIRE CYCLE AND FIRE ADAPTATION OF MAIN TREE SPECIES IN DAXING''''ANLING FOREST REGION, CHINA

FIREENVIRONMENT,FUELSANDFlRECAUSESFireEnvir0nmcntDaxing'anlingf0restareabelongstothefrigid-temPeratemonsoonclimate.Ithasalongwinterandashortsununer.Thereare9monthsofdailytemPeratUreunderlOCandlessthan3OdaysofdailytemPerabeabove22C.ThemeantemperatUreinthecoldestmonth(January)is-25V~-30C,withtheextrCmeof-52.3C,andinthewarmestmonth(July)isl5~2OC,withtheextremeof39C.Thegrowingsea-soninthisareaisonly9O~ll0days.Theaverageannualprecipitationisabout35O~500nun,and80Percentofwhich…     

Retention patches maintain diversity of epiphytic and epixylic indicator lichens more effectively than solitary trees

The effectiveness of retention trees and patches in preserving diversity of nine epiphytic and epixylic old-growth forest lichens was studied in north boreal spruce forests in Finland. We compared (1) 7–8-year-old retention cuts, with at least 5–10 living or dead retention trees per hectare, (2) 10–12-year-old clear-cuts, with some scattered living and dead retention trees on the sites, (3) old-growth spruce forests, and (4) 7-8-year-old retention patches (0.06–0.45?ha) representing the original tree species composition of old-growth forests. The occurrence of indicator lichens was studied on 150 deciduous trees and snags in each forest category. The species richness was significantly higher in old-growth forests than in the clear-cuts and retention cuts, but did not differ between old-growth forests and retention patches. Only three species were found in clear-cuts and two in retention cuts. Foliose cyanolichens Leptogium saturninum and Nephroma bellum thrived on solitary retention trees, whereas humidity-requiring pin lichens from the genus Chaenotheca were found only in old-growth forests and retention patches. Our results suggest that the ability of epiphytic and epixylic species to survive on retained trees depends on several factors: (1) substrate quality (tree species, tree type and diameter of a tree), (2) environmental factors (e.g. humidity, slope exposition), and (3) morphological and physiological characteristics of species. Besides of substrate trees, the retained conifers (esp. spruce) seem to be important in retention patches to provide the shading necessary to maintain humidity.     

半干旱黄土丘陵沟壑区人工林土壤水分与其群落特征研究

2009年,对定西巉口林场人工针叶林、阔叶林及针阔混交林23个植被类型土壤水分和林下物种多样性特征进行了连续观测和调查.结果显示:山杏林地土壤水分最低,青杨林和青杨+油松混交林地最高,均与其他林地存在显著性差异,荒草地土壤水分高于其他林地介于中间;土壤水分亏缺量最大的为阔叶乔木或灌木林,其次为针叶林或针阔混交林,衰退的人工林地土壤水分亏缺量最小;浅层土壤水分(0～80 mm)与Margalef丰富度指数、Shannon-wiener多样性指数和均匀度指数相关性极显著,存在线性关系.而深层土壤水分与上面3个植物多样性指数无相关性.该研究对阐明人工林地土壤水分环境以及其与群落发育阶段和植物多样的相应关系,指导科学培育人工林提供理论基础.     

Changes in soil acidity and organic matter following the establishment of conifers on former grassland in New Zealand

Effects of a land use change from grassland to coniferous plantation forestry (Pseudotsuga menzieii [Douglas fir]; Pinus radiata [radiata pine]) on soil acidity and organic matter were assessed at two sites in New Zealand. The sites differed with respect to soils, climate, vegetation cover and type, relative maturity and management of the forest stands. Results obtained at the different sites were, therefore, not directly comparable, although they represented a comparison of a similar change in land use and some overall trends were evident. The change from grassland to conifers decreased levels of organic carbon, total nitrogen and exchangeable cations and increased exchangeable acidity in the upper 20–30 cm of soil. Exchangeable aluminium and exchangeable acidity were more sensitive measures of the effects of afforestation on soil acidity than pH.     

Individual legacy trees influence vertebrate wildlife diversity in commercial forests

Old-growth forests provide important habitat elements for many species of wildlife. These forests, however, are rare where lands are managed for timber. In commercial forests, large and old trees sometimes exist only as widely-dispersed residual or legacy trees. Legacy trees are old trees that have been spared during harvest or have survived stand-replacing natural disturbances. The value of individual legacy trees to wildlife has received little attention by land managers or researchers within the coast redwood (Sequoia sempervirens) region where 95% of the landscape is intensively managed for timber production. We investigated the use of individual legacy old-growth redwood trees by wildlife and compared this use to randomly selected commercially-mature trees. At each legacy/control tree pair we sampled for bats using electronic bat detectors, for small mammals using live traps, for large mammals using remote sensor cameras, and for birds using time-constrained observation surveys. Legacy old-growth trees containing basal hollows were equipped with ‘guano traps’; monthly guano weight was used as an index of roosting by bats. The diversity and richness of wildlife species recorded at legacy trees was significantly greater than at control trees (Shannon index=2.81 versus 2.32; species=38 versus 24, respectively). The index of bat activity and the number of birds observed was significantly greater at legacy trees compared to control trees. We found no statistical differences between legacy and control trees in the numbers of small mammals captured or in the number of species photographed using remote cameras. Every basal hollow contained bat guano and genetic methods confirmed use by four species of bats. Vaux’s swifts (Chaetura vauxi), pygmy nuthatches (Sitta pygmaea), violet-green swallows (Tachycineta thalassina), and the long-legged myotis (Myotis volans) reproduced in legacy trees. As measured by species richness, species diversity, and use by a number of different taxa, legacy trees appear to add significant habitat value to managed redwood forests. This value probably is related to the structural complexity offered by legacy trees. The presence of a basal hollow, which only occur in legacy trees, was the feature that appeared to add the greatest habitat value to legacy trees and, therefore, to commercial forest stands. The results of our study call for an appreciation for particular individual trees as habitat for wildlife in managed stands. This is a spatial resolution of analysis that, heretofore, has not been expected of managers. The cumulative effects of the retention of legacy trees in commercial forest lands could yield important benefits to vertebrate wildlife that are associated with biological legacies.     

Think globally,manage locally: The importance of steady-state forest features for a declining songbird

Changes in historical forest composition and structure may have cascading effects throughout the forest community. Perhaps nowhere is there a better example of current forests that carry a legacy from their past than in eastern North America. The Cerulean Warbler (Dendroica cerulea), a declining Neotropical migratory bird of high conservation concern, is one excellent example of a species that seems to be sensitive to both landscape configuration and subtle features of eastern forests of North America. We used the Cerulean Warbler as a model species to demonstrate how an appreciation of fine-scale structural attributes of forests may improve our ability to conserve late-successional forest species. To do this we evaluated the extent to which multiscale habitat features were associated with density, spatial distribution, and nesting success of Cerulean Warblers in 12 mature forest sites in southeast Ohio, 2004–2006. Results suggest that adjacency of regenerating clear-cuts did not influence density or nesting success of Cerulean Warblers in adjacent mature forest. Instead, variation in demographic parameters was best explained by local habitat features. Density and nesting success were positively associated with canopy openness, numbers of large-diameter trees, and number of grapevines—all of which are typical of heterogeneous steady-state phase forests. Thus, improved management for Cerulean Warblers may require creating features (e.g., large canopy gaps) that mimic old-growth forests. Although fragmentation and habitat loss remain important contributors to population declines of many mature forest species, our work provides evidence that subtle changes in forest structure, particularly to features associated with old forests, warrant additional attention from the conservation community.     

Stand specific occurrence of coarse woody debris in a managed boreal forest landscape in central Sweden

Forests long subjected to management for timber production contain only a fraction of the volumes of coarse woody debris (CWD) found in pristine forests. This is a threat to many organisms that depend on CWD. Forest management practices have been altered to achieve an increase in the amounts of CWD. Few studies have attempted to analyze the occurrence of CWD at the landscape level. We studied the occurrence of CWD in stands of different ages and management background in a boreal forest landscape in central Sweden. Volume of CWD in unmanaged stands (nature reserves and set-asides) was twice that in managed stands. The composition of CWD was influenced by stand age and management regime. Standing CWD was more common in unmanaged stands than in managed stands. Pine CWD was particularly prevalent in young forest stands (8–59 years of age). Bark-covered CWD was most common on deciduous and spruce wood and uncommon on pine. Bark area in young forest stands was almost 10 times lower than that in other managed stands. Using the age distribution of stands, we estimated the volume and bark area of CWD in the landscape. Recent clear-cuts harvested in accordance with new management guidelines contained more early decay CWD per ha than old managed stands. Young forests covered over half the landscape and had significantly lower volumes of spruce and deciduous CWD compared with other stands. The consequences of these results for biodiversity-oriented forest management are discussed.