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.     

大岗山针叶与阔叶林林分结构比较分析

为研究不同林分径级、树高结构差异,在江西大岗山地区设置样地,选取杉木纯林、马褂木纯林各4块,对样地进行每木检尺,运用SPSS对胸径和树高数据进行处理,对胸径、树高的相关关系进行线性拟合,结果表明:大岗山地区杉木纯林与马褂木纯林胸径、树高分布整体上符合正态分布,假设检验的P值均大于0.05,但曲线陡峭程度杉木纯林(-1.487)大于马褂木纯林(-1.670),曲线偏移程度杉木纯林(0.191)大于马褂木纯林(0.010),树高分布曲线陡峭程度马褂木纯林(2.407)大于杉木纯林(-1.706),曲线偏移程度马褂木纯林(1.134)大于杉木纯林(0.459)。     

Length and classification of natural and created forest edges in boreal landscapes throughout northern Sweden

Forest edges have numerous implications for structure and function of forest ecosystems. Previous studies on edge quantity have used broad classifications. However, edge influence is driven by the contrast in vegetation structure between adjoining ecosystems, and thus we need detailed site-specific data to assess the role of edges in forests. We studied the variability of sharp edges in 28 boreal landscapes (4 km × 4 km) across an 830 km gradient throughout northern Sweden. Our objectives were: (1) to compare the length of natural and created edges, (2) to classify edges in detail by edge origin, maintenance and forest attributes, and (3) to examine relationships between length of edge and landscape variables. Data were collected using stereo-interpretation of high spatial resolution colour infrared aerial photographs, in combination with line intersect sampling and plots. The length of edge varied from 12 to 102 m ha⁻¹ among landscapes, with an overall mean of 54 m ha⁻¹. Created edges dominated most landscapes (mean 33 m ha⁻¹) and had greater variability than natural edges (mean 21 m ha⁻¹). Maintained edges (e.g. roads, agricultural land) were more abundant than regenerating edges caused by logging. Thirty percent of total edges adjoined narrow linear features. Seventy percent adjoined wider patches and showed high variability (35 classes). Overall, high-contrast edges towards mature forest dominated, i.e. ones that may experience strong edge influence. The amount of edge increased with percent of landscape affected by disturbance, and decreased with latitude and elevation. This study shows that edges are both abundant and highly variable in boreal forests and that forestry is the main driver behind edge creation. Detailed classification of edges based on site-specific forest and patch attributes may help to estimate edge influence at landscape level, and can guide experimental design for examining the impact of edges on structure and function of forest ecosystems.     

Weak response of bryophyte assemblages to second commercial thinning in boreal spruce forest of south-central Sweden

Forest management regimes dictate the composition and structure of large parts of the Fennoscandian boreal forest region. The understanding of thinning impacts on understorey plant communities is considerably lower compared to the effects of final felling. We studied the response of bryophyte assemblages to second commercial thinning in spruce-dominated stands sampled to be representative of the dominant forest type of south-central Sweden. Eighteen stands were analysed 6–12 years after second commercial thinning, and were compared with six stands commercially thinned only once, at two spatial scales (0.1 and 0.01?ha), with stand ages varying between 52 and 66 years. We found few strong differences in bryophyte species richness and no differences in bryophyte species composition between stands thinned once or twice. More pioneer species were found in stands thinned only once, a result that needs further study. Species richness declined significantly with time since thinning on both investigated spatial scales. Canopy cover significantly affected the composition of forest floor species. Thinning effects over longer time periods need further study, and also effects in different forest types along productivity gradients. For nature conservation, studies targeted towards thinning response of uncommon species connected to specific habitats and substrates will be essential.     

A forest of grazing and logging: Deforestation and reforestation history of a boreal landscape in central Sweden

Detailed spatial changes in foreststructure in a central Swedish landscape were examinedusing geographic information system techniques. First,the influence of grazing and burning on forest densityand structure in the 19th century landscape wereanalyzed. Then, the development of the landscapeduring the 20th century, together with the impactof modern forest management methods on foreststructure, were analyzed using historical sources. In1907, over 20% of the 2200 hectare study site wassparsely-wooded (12 m³ ha^–1) with old trees.These areas have been reforested with single-storiedmiddle-aged and old pine stands (66 m³ ha^–1in 1989) during the 20th century. Firesuppression and changes in land use from subsistence-to-industrialforestry, facilitated Norway spruceregeneration as undergrowth in open Scots pine standsafter logging. This natural regeneration has, to alarge extent, been cut down and replaced by pineafforestation. During the second half of the 20thcentury, the standing timber volume has steadilyincreased, while the mean age of the forest hasdecreased. Today's young dense forests will result inhigher timber values in the coming decades, but theforest has lost a range of ecological niches.     

Long-term influence of fire and harvesting on boreal forest age structure and forest composition in eastern Québec

In boreal forests, historical variations in the area disturbed by natural disturbances or harvesting have rarely been compared. We measured temporal and spatial variations in areas affected by severe fires and clearcutting throughout the 20th century in a 57, 332 km² section of the eastern Canadian boreal forest. We examined the effects of these disturbances on spatio-temporal variations in the abundance of forests >60 years. Natural variability for the abundance of forests >60 years was estimated from simulations of natural disturbance regimes. We also measured compositional and structural differences between three categories of stands originating from relatively recent disturbances (∼50 years; clearcutting, fires, and clearcutting followed by fires), and one category of stands that were undisturbed for at least 200 years. At the regional level, we observed that forests >60 years gradually became scarcer throughout the 20th century due to a gradual expansion of harvested areas, an effect most pronounced in the southern part of the region, where mature and old forest abundance was clearly outside the range of natural variability at the end of the studied period. At the stand level, forest composition and structure differed between stand-origin categories: clearcutting-origin stands contained more balsam fir (Abies balsamea), fire-origin stands more black spruce (Picea mariana), and fire/clearcutting-origin stands more hardwoods (Betula papyrifera and Populus tremuloides). Overall, we estimate that strict forest management targets based on natural disturbance regimes will be difficult to achieve in eastern North-American boreal forests, most notably because contemporary disturbance rates, including both clearcutting and fire, have gradually become higher than the fire rates observed during the preindustrial period.     

From logging frontier towards sustainable forest management: experiences from boreal regions of North-West Russia and North Sweden

This article describes the transformation of old-growth forest to managed forests, in North (N) Sweden and boreal regions of North-West (BNW) Russia, from economic, social and ecological perspectives. Whereas in BNW Russia, the logging frontier could be kept moving into unharvested regions, N Sweden earlier had to develop solutions where large-scale logging had already taken place. In 1950–1990, Swedish strategies included rationing of old forest, effective regeneration and also precommercial and commercial thinning. Supporting means were legislation, government-funded subsidies and collaboration among enterprises, researchers and political leaders. BNW Russia is currently facing similar challenges and N Swedish experiences should be analysed and used where applicable. In N Sweden, a too low proportion of representative productive old forests remains, but in the last decades, N Swedish forests exempted from economic use have been significantly increased. Ongoing discussions of also defining areas with more intensive forest management would lead to a zoning, bearing some resemblance to the Russian system, in use since 1943. Russian experience should, therefore, be of interest to Swedish forest policy-makers. Both countries have problems with rural social issues. Both can benefit from collaboration on these aspects of sustainable forest management.     

Composition,structure and diversity of phyllostomid bat assemblages in different successional stages of a tropical dry forest

Studies on successional dynamics in tropical systems have mostly focused on plant communities and mainly have been conducted in tropical humid areas. Here, we document changes in the structure of bat assemblages among secondary successional stages of a neotropical dry forest. We specifically focused on the speciose phyllostomid bat family, comprising most of the foraging guilds found among neotropical bats, including nectarivores and frugivores that play important roles in processes of plant reproduction and forest regeneration. To investigate bat species richness, diversity and abundance during successionnal processes, we mist-netted bat assemblages in 12 sites belonging to 4 different successional stages, namely pastures (0 yrs), early (3–5 yrs), intermediate (8–12 yrs) and late successional stage (>50 yrs). A capture effort of 142 nights using five mist-nets per night yielded 606 phyllostomid bats belonging to 16 species. Late stage was the most speciose sustaining all species found in the study (16 species against 9 for early and intermediate stages and 4 in pastures), and was the only environment where rare species occurred. Species found within any one successional stage were a combination of species found at the previous stage plus additional ones. This additive pattern appeared to be driven by the natural abundance of species, as the abundant species were found across more succesisonal stages than rarer species. Bats were significantly less speciose and less abundant in pastures, regardless of the foraging guild. Bat diversity and abundance did not differ significantly among early, intermediate and late stages. However, nectarivores were more abundant in early compared to late stage, probably as a consequence of differences in patterns of food availability. We conclude that areas of forest, recognized as late stage in our study, are the most important reservoirs of species richness. Secondary vegetation also contains diverse bat assemblages, while pastures only harbour a few abundant and vagile species occasionally crossing this habitat. We suggest that land-use regulations in this region focus on maintaining connectivity of a mosaic of areas of secondary and mature vegetation to insure the conservation of bat diversity as well as their important ecological interactions.     

Wildfire promotes broadleaves and species mixture in boreal forest

Postfire tree species compositions are predicted to be the same prior to fire according to the direct regeneration hypothesis (DRH). We studied 94 upland boreal forest stands between 5 and 18 years after fire in Ontario, Canada. Postfire species-specific regeneration density was positively related to prefire stand basal area for Pinus banksiana, Populus spp., Betula papyrifera and Picea mariana, but not for Picea glauca and Abies balsamea. In addition, seedling density of Populus spp., B. papyrifera, P. mariana, P. glauca and A. balsamea were positively affected by build up index and, except Populus spp., their density increased with age of burn. To facilitate testing the DRH, we introduced a term called compositional difference (CD) that is the difference in a species relative percentage between the postfire and prefire stand. The testable null hypothesis is CD = 0 for a given species. CD was not different from 0 for P. banksiana, was 19.8% for Populus spp., 10.4% for B. papyrifera, −17.9% for P. mariana, −14.6% for P. glauca, and −14.9% for A. balsamea, indicating fire increases broadleaves at the expenses of mid- and late-successional coniferous species. Compositional increases of Populus spp. and B. papyrifera in postfire stands occurred mostly where these species were a minor component prior to fire. In conclusion, the DRH was supported by the specific positive relationships between postfire regeneration densities and prefire basal area for P. banksiana, Populus spp., B. papyrifera and P. mariana. However, if the DRH is used for predicting postfire composition, P. banksiana is the only species that had the same composition between postfire and prefire stands. Nevertheless, CD for P. banksiana was negatively related to its prefire composition. Similarly, CD for other species was negatively related to their prefire compositions with varying effects of build up index and age of burn. Our results suggest, if fire occurrences increase with global change, the boreal landscape will be more dominated by hardwoods and mixtures of conifers and hardwoods.     

Wintertime photosynthesis and water uptake in a boreal forest

Warm air in combination with frozen soil is a major cause of wintertime drought damage in evergreen plants in subalpine and boreal environments. We analyzed diurnal tree stem diameter variation (SDV), which reflects soil water uptake, canopy-level water vapor flux (Fw), stand photosynthesis (Ps), photosynthetically active radiation (PAR), soil and air temperatures (Ts and T air, respectively) and soil liquid water content (theta) to determine under what conditions photosynthesis is possible in wintertime and how crucial water uptake from soil is for photosynthesis. Measurements were made under field conditions in a Scots pine forest in southern Finland during winter 2002-2003. We found four wintertime periods when there was measurable Ps and SDV, the latter always starting 2-7 days after photosynthesis and both usually ending on the same day. Stand photosynthesis began when T air reached 3-4 degrees C and ended when T air dropped below -7 degrees C. The trees appeared to rely on stored stem water first and started taking up water from the soil a few days later, when the transpirational demand became strong enough. The more difficult it was to access soil water because of low Ts or low theta, the longer the trees used water stored in their stems. Even partial stem freezing did not prevent photosynthesis or soil water uptake.     

The effects of forest structure on the risk of wind damage at a landscape level in a boreal forest ecosystem

? The aim of this work was to analyze how the forest structure affects the risk of wind damage at the landscape level in a boreal forest.

? This was done by employing: (i) Monte Carlo simulation technique for generating landscapes with different age class distributions, proportions of open areas (gaps), and tree species composition; and (ii) a mechanistic wind damage model, HWIND, for predicting the critical wind speeds at downwind stand edges of open areas (gaps) for risk consideration. The level of risk of wind damage observed at the landscape level was significantly affected by the presence of gaps and old stands. Even a slight increase in the proportion of gap areas or older stands had a significant impact on the total length of edges at risk. As a comparison, variation in species composition (Scots pine and/or Norway spruce) had much smaller impact on the risk of damage.

? In conclusion, the effects of forest structure on the risk of wind damage should especially be considered by forest managers in day-to-day forest planning in order to reduce the risk of wind damage both at the stand and landscape level.

     

Change in forest structure in the boreal montane ecosystem of Mount Mitchell,North Carolina1

Surveys were undertaken on Mt. Mitchell, N. C. (USA) from Spring 1984 through 1987 to determine the extent and rate of decline and mortality of red spruce and Fraser fir ecosystems. Data indicate that regardless of cause and effect mechanisms the physical structure and integrity of the boreal montane forest has greatly deteriorated over the past 4 years. Along ridges, and particularly on west facing aspects greater than 80% of all mature stands are dead. No definitive conclusions can be made concerning etiological agents; however, current hypotheses include biotic factors, climatic abberations, and/or the acute or chronic stress from anthropogenic pollutants.     

Comparisons of spatial pattern,structure, and tree composition between virgin and cut-over jarrah forest in Western Australia

Several old growth (unlogged) and regrowth (logged) stands in the northern jarrah forest of Western Australia were studied in respect of spatial pattern of tree species, segregation between tree species, distribution of trees of each species by diameter class, and tree species composition. The species are Eucalyptus marginata and Eucalyptus calophylla (overstorey) and Banksia grandis, Allocasuarina fraseriana, Persoonia longifolia and Persoonia elliptica (understorey).Most populations of the species are aggregated at small but random at large scale. This pattern probably originates from non-random seed fall. Eucalyptus marginata and B. grandis are segregated, probably for the same reason. Manipulative experiments showed that interspecific competition does not prevent establishment of B. grandis seedlings. On a local scale, heterogeneity in several surface soil properties does not help explain spatial patterns.The diameter-class distributions indicate that regeneration of all species occurs irregularly. This probably results directly from the release of dormant advance growth following temporary reduction in overwood competition induced by disturbance such as wildfire or logging. Banksia grandis is not a rare or scattered component of old growth jarrah forest. A single logging of jarrah trees does not necessarily alter the density or diameter class distribution of B. grandis.     

Spatial structure and dynamics of predominant populations in a virgin old-growth oak forest in the Qinling Mountains,China

This paper attempts to explore the characteristics of the spatial structure and development dynamics of three predominant tree populations, Quercus aliena var. acutiserrata Maxim.(QA), Acer caesium subsp. giraldii (Pax) E. Murr.(AC), and Ulmus propinqua Koidz (U. japonica) Sag (UG), in a virgin old-growth oak broad-leaved mixed forest in the Qinling Mountains, China. We employed a bivariate distribution of the structural parameters (mingling, dominance, and uniform angle index) based on the relationship between nearest neighbor tree groups and found that all predominant populations with a high species mixture and random distribution pattern. However, QA and UG are recessional populations, and AC is a progressive population. Predominant populations showed a consistent tendency during stand development that the spatial structures became increasingly mixed; the distribution pattern gradually transformed from clumped to random, and the segregation among the tree species increased. This finding demonstrates that the populations are forming a steady-state forest structure. The QA population will continue to maintain its predominance in the forest in the future, and AC will survive and grow as an associated species over the long term. However, UG will decline, and the forest will ultimately become an oak-dominated climax forest community if there are no large-scale disturbances.     

Reindeer husbandry in a mountain Sami village in boreal Sweden: the social and economic effect of introducing GPS collars and adaptive forest management

Reindeer husbandry in northern Sweden, Norway, and Finland is an extensive agroforestry system, and the management of reindeer occurs alongside other land uses such as forestry, hunting, and tourism. The economic, social, and environmental impact of using GPS collars to track the reindeer was evaluated in the Sami village of Njaarke in boreal Sweden. A second objective was to evaluate how adapted forest management influenced reindeer husbandry. The results show that the use of GPS tracking enables the improved monitoring of the reindeer but the financial costs were greater than the financial benefits. The increased income did not cover the costs of depreciation and maintenance. Whilst the labour inputs associated with reindeer husbandry were high, 30–40% of the gross value added by village activities were related to hunting, tourism, and the renting of fishing rights. The use of adaptive forest management was assumed to increase the number of reindeer that could be reared through to slaughter and it was calculated to increase the gross value added by reindeer husbandry by more than 30%.     

Patterns of field layer invertebrates in successional stages of managed boreal forest: Implications for the declining Capercaillie Tetrao urogallus L. population

Capercaillie (Tetrao urogallus L.) populations in Finland have decreased markedly during past decades. One of the assumed reasons is the decreased quality of brood feeding grounds since current forest management transfers mature forests to younger successional stages. We studied how different types of managed Finnish forests offer resources for capercaillie broods by comparing the vegetation and invertebrate fauna of four successional stages in the two most common forest types in Finland, spruce dominated Vaccinium myrtillus (MT) and pine dominated Vaccinium vitis-idaea (VT) type. Forest age class had a significant effect on the cover of bilberry. There was a positive correlation between bilberry cover and the biomass of larvae and of all invertebrates (including all developmental stages) both at the stand and the sample level. Both forest type and age class significantly affected the biomass of larvae. Mature stands and young stands had the highest biomass of larvae in both MT and VT. In both forest site types the sapling stands hosted the smallest biomass of larvae. The results suggest that successional stages that follow clear cutting seriously lowers the food availability for capercaillie chicks and also reduces the shelter that field layer might provide. However, already the young stages that follow sapling phases seem to provide both bilberries and invertebrates so it is quite unlikely that the bilberry abundance alone could explain the dramatic decline of the capercaillie.     

Stand dynamics and the evaluation of forest decline

The importance of understanding effects of stand dynamics on growth as they relate to identifying and evaluating forest declines is discussed. Decline diseases and some of their characteristics are reviewed, as are general patterns of normal growth and development of forest trees and stands. The need to develop an expectation of normal growth is discussed and a minimally sufficient set of growth stratifying factors; namely, site quality, stand density and age, is proposed.     

Early successional sites and the recovery of vegetation structure and tree species of the tropical dry forest in Veracruz,Mexico

Secondary successional vegetation represents one-third of the 7% of the original area covered with tropical dry forest that remains in central Veracruz, Mexico. In this region, fallow periods are short, in general, no longer than 7–10 years, and old secondary successional sites are not available. Therefore we evaluated the potential of very early successional stages of tropical dry forest with different land use histories for recovering the structure and composition of regional forest. We compared five early successional sites (7–72 months) with five nearby forest remnants. Successional sites had reached 38 and 30%, respectively, of the average basal area and density recorded for the forest understories, but only 5 and 10%, respectively, of the basal area and density of forest overstories. A total of 132 tree species were recorded, 45 at successional and 107 at forest sites. Individuals of tree species with animal-dispersed seeds (57%) were significantly better represented than wind-dispersed (22%) and self-dispersing (21%) species in both successional and forest sites. Successional sites had already recruited 10% of the intermediate and shade-tolerant species that grow in forest remnants. However, only 20 species occurred in both early successional and forest sites, several showing resprouting ability. We conclude that the entry of forest species to the successional process at very early stages and the recruitment of individuals from resprouting may facilitate the recovery of the dry forest in Veracruz.