How well does Kirtland's warbler management emulate the effects of natural disturbance on stand structure in Michigan jack pine forests?

Jack pine (Pinus banksiana) forests in parts of northern Lower Michigan have been managed with 30 years of extensive clearcut harvesting followed by planted stand establishment in order to maintain habitat for the endangered Kirtland's warbler (Dendroica kirtlandii). We used two, parallel chronosequences to study how this management has affected the structural development of jack pine stands relative to the historically dominant disturbance regime of stand-replacing wildfire. Each chronosequence consisted of three young stands (age range 3–6 years), three intermediate-aged stands (age range of 12–17 years) and three mature stands (age range of 39–69 years). Average stem density in young plantations (2300 stems/ha) was lower than the average for young, fire-origin stands (11,000) and varied over a much narrower range among stands (1403–2667 for plantations and 1552–24,192 in fire stands). In addition, within-stand patchiness of stem density was also much higher in the wildfire sites for young and intermediate ages. Plantation sites possessed very little dead wood at young ages (averaging 3 snags/ha and 12 m³/ha CWD) compared to young fire-origin stands (averaging 252 snags/ha and 49 m³/ha CWD). In contrast, mature plantations had similar levels of dead wood (averaging 269 snags/ha and 22 m³/ha CWD) as mature fire-origin stands (averaging 557 snags/ha and 12 m³/ha CWD). Differences between the plantation and fire-origin chronosequences were driven mainly by young- and intermediate-aged stands, whereas mature stands were typically quite similar in all structural features. Our results show clearly that forest management aimed at preserving and enhancing the population of a single endangered species results in greatly simplified habitat structure at the stand level, and suggest that this simplification is perpetuated across the landscape as well. Of particular concern are the effects of extensive harvesting and planting on the availability of snags and CWD.     

Structure of a Central-European mountain spruce old-growth forest with respect to historical development

This study examines the structural characteristics of the tree layer, dead wood, canopy openings, and regeneration patterns of a spruce old-growth forest in the Bohemian Forest, Czech Republic. An old-growth stand with minor human influence and a stand that was presumably logged about 200 years ago were analyzed and compared, as some forest managers considered the presumable human impact as a reason for salvage logging. Even though the stands differed in tree density, height and DBH structure, it was not possible to conclude whether it was due to management history or the environmental differences. The volume of dead wood also differed between the stands. There was about 142 and 83 m³ ha⁻¹ of dead wood in the old-growth stand and presumably logged stand, respectively. The amount of dead wood found in the old-growth stand was comparable with values reported from spruce old-growth stands across Central Europe. In both stands, many canopy trees were arranged in linear patterns, which was a result of spruce regeneration on nurse logs. This suggests that the origin and development of the stands were characterized by natural processes and during the past 200 years typical old-growth structural characteristics have already evolved.     

Tree mortality after low-intensity prescribed fires in managed Pinus sylvestris stands in southern Finland

Abstract

Tree mortality, its causes, and the input of dead charred wood were studied in 11 managed 30–45-year-old Scots pine (Pinus sylvestris L.) stands 1 year after experimental low-intensity prescribed burnings in southern Finland. First, the relationship between fire-induced tree damage and several external variables, e.g. stand density, within-stand wind speed, open-air wind speed, the Finnish Forest Fire Index (FFI) and flame height, was studied. Secondly, the study examined which damage and morphological characteristics best predicted tree mortality. Tree mortality was very variable in the experimental plots, ranging from 0% to 48% on the basis of stem number and from 0% to 41% in terms of wood volume. The input of dead and charred wood decreased with stand age, being 19.4 m³ ha^?1 in 30–35-year-old stands, but only 1.7 m³ ha^?1 in 45-year-old stands. The input of dead wood was on average 10 m³ ha^?1, representing less than 5% of the mean volume before the prescribed fire. The external variables that best explained fire-induced damage were within-stand wind speed, flame height and FFI. Tree mortality was best predicted by charred stem ratio with bark thickness, and by charred stem ratio with tree diameter. The results indicate that prescribed burning that is conducted downwind increases tree mortality and changes subsequent stand structure with increasing within-stand wind speed.     

Reconstructing 100-150 years of logging history in coastal spruce forest (Picea abies) with special conservation values in central Norway

Coastal spruce forests of central Norway harbour a unique assemblage of epiphytic lichens and are given high priority with respect to conservation of biodiversity. To assess the historical impact of logging during the last 100-150 yrs, 31 remnant stands were studied by means of tree-ring analysis of 2199 trees and the decay stage of 1605 stumps. No stands had been clear-cut, but all had been selectively logged at least twice during the last 150 yrs. Total harvested timber volume ranged from 65 to 409 m³ha-¹ (31-124% of present-day standing volume) and the selective logging kept standing volume low (40-200 m³ha-¹) during 1890-1930. Present-day stand characteristics were strongly correlated with site productivity and topographic position within the ravine valleys. Low amounts of dead wood at sites with high historical logging activity was the only consistent relationship found after covariance of site productivity, topographic position and deciduous trees were taken into account. The results indicate that old-growth stand characteristics, such as reversed J-shaped age distributions and dead wood in advanced decay classes, can be obtained 100-150 yrs after intensive selective logging.     

Stand characteristics of mixed oriental beech (<Emphasis Type="Italic">Fagus orientalis</Emphasis> Lipsky) stands in the stem exclusion phase,northern Iran

The structure of forest stands changes through developmental phases. This study is carried out in the unmanaged, oriental beech (Fagus orientalis Lipsky) stands in the north of Iran. The aim of this research was to quantify structural characteristics of stands in the stem exclusion phase using common structural indices, which include mingling, tree–tree distance, stem diameter, and tree height differentiation. According to our measurements from three stands, naturally regenerated stands tend to be mixed in species composition have slightly heterogeneous diameter distributions and uniform tree height. The average distance between trees was 3.3 m. Stocking volume of the stands had an average of 540 m³ ha^?1 and 412 stem ha^?1. Dead wood volume was 24 m³ ha^?1, and as a standing volume, the most frequent species in dead wood pool was oriental beech (F. orientalis) (48 %). The common form of dead trees was snag (41 %). The mean value of mingling and tree-to-tree interval indices revealed that beech was mixed intensively with hornbeam and appears to be a more successful competitor for space and light compared with hornbeam; moreover, we found relatively high evidence of inter-species competition in this phase. A better understanding of stand characteristics in the stem exclusion phase as a critical part of the natural dynamics of forest ecosystems could facilitate predictions about the future changes within the stand.     

Assemblages of wood-inhabiting fungi related to silvicultural management intensity in beech forests in southern Germany

Current silvicultural treatments in beech forests are aimed at achieving thick logs without discoloured hardwood. Therefore intensive thinning is applied already in younger stands with the objective of large-sized trunks at an age of 100 years. However, this approach bears the risk that dead wood structures and broken trees are completely removed from the forest. The impact of three different silvicultural management intensity levels on wood-inhabiting fungi over decades was investigated in a large beech forest (>10,000 ha) in southern Germany in 69 sampling plots: A Intensive Thinning and Logging with high-value trees, B Conservation-Oriented Logging with integration of special structures such as dead wood and broken trees and C Strict Forest Reserves with no logging for 30 years. The analysis of community showed marked differences in the fungus species composition of the three treatments, independent of stand age. The relative frequencies of species between treatments were statistically different. Indicator species for naturalness were more abundant at sites with low silvicultural management intensity. Fomes fomentarius, the most common fungus in virgin forests and strict forest reserves, is almost missing in forests with high-management intensity. The species richness seemed to be lower where intensive thinning was applied (P = 0.051). Species characteristic for coarse woody debris were associated to low management intensity, whereas species with a significant preference for stumps became more frequent with increasing management intensity. A total amount of dead wood higher than 60 m³/ha was found to enable significantly higher numbers of species indicators of naturalness (P = 0.013). In conclusion, when applying intensive silvicultural treatment, the role of dead wood needs to be actively considered in order to maintain the natural biocoenosis of beech forests.     

The effects of different types of management,functions, and characteristics of stands in Polish forests on the amount of coarse woody debris

In the modern forestry paradigm, many factors influence the amount of coarse woody debris (CWD). The present paper analyzes the effects of both local (national) programs (special functions of forests) and European programs (Natura 2000 sites), as well as the individual characteristics of forest stands. The study was conducted on 2,752 sampling plots distributed over an area of about 17,500 ha and located in lowland stands having a species composition typical of large areas in central Europe. Natura 2000 areas contained significantly more CWD (8.4 m³/ha) than areas not covered by the program (4.8 m³/ha). However, this is due to the fact that Natura 2000 sites involve well-preserved forest areas, such as nature reserves (26.6 m³/ha). In the managed forests that have been covered by the Natura 2000 program over the past several years, the volume of CWD has not increased. Forests with ecological and social functions differed slightly in the amount of CWD. More CWD occurred in protected animal areas (8.7 m³/ha) than in stands damaged by industry (3.9 m³/ha). Intermediate CWD levels were found in water-protection forests and in forests located around cities and military facilities. In managed forests, the lowest CWD volume was observed in middle-aged stands. The species composition of the stand had little effect on the volume of CWD. Only stands with a predominance of ash and alder had higher CWD levels (13.5 m³/ha). More CWD was found in stands whose species composition did not represent the potential site quality (6.4 m³/ha) than in habitats with the optimum species composition (3.8 m³/ha). CWD volume should be systematically increased taking into consideration local natural conditions. Such efforts should be focused on particularly valuable regions, and especially on Natura 2000 sites, where the threshold values reported from other European forests should be reached. Leaving some trees to die naturally and retaining reasonable amounts of such trees ought to be incorporated into CWD management practice in Poland.     

Dead trees and protected polypores in unmanaged north-temperate forest stands of Lithuania

The availability of coarse woody debris (CWD) and distribution of dead trees into categories of mortality (dead standing, broken and uprooted) were investigated in north-temperate forests of central Europe (Lithuania). The studied area comprised 188.7 ha and included 18 different stands 40–130 years of age with a variety of tree species (spruce (Picea abies (L.) Karst.), pine (Pinus sylvestris L.), alder (Alnus glutinosa (L.) Gaertn.), birch (Betula pendula Roth and B. pubescens Ehrh.), aspen (Populus tremula L.), oak (Quercus robur L.), forest types (caricus-sphagnum, vaccinium-myrtillus, oxalis, myrtillus-oxalis, caricus-calamagrostis) and edaphic conditions (peaty, sandy, loamy soils of different moisture). The stands were excluded from wood harvesting for at least 30 years. A total of 11 365 dead trees (over 10 cm in DBH) or 6160.7 m³ of dead wood was found (60.2 trees/ha and 32.6 m³/ha). The volume of CWD per hectare was larger in older stands (r_S=0.78, P<0.01). Tree mortality during the last 2 years consisted of 482 trees and 381 m³, or 1.28 trees/ha×year and 1.01 m³/ha×year. In 25–33% of cases it was wind-related. Uprooted and broken trees were of larger DBH than dead standing. The distribution into the categories of mortality was strongly dependent on tree species (chi-square test, d.f.=10,P=0). Dead standing dominated in CWD of pine and alder. Broken trees comprised almost a half in CWD of aspen, and about one-third in birch, alder and oak. Uprooting most often occurred in spruce, aspen and birch. Edaphic conditions and stand age had a pronounced impact on distribution into mortality categories for spruce (chi-square test, d.f.=20, P<0.00001) and pine (d.f.=8, P≤0.0003). On peat soil, only a minority of trees of both pine and spruce was uprooted, and standing dead prevailed. In CWD of spruce and pine, the proportions of both dead standing and broken decreased and that of uprooted trees increased on mineral soils of higher moisture and bulk density in older stands. By contrast, uprooting in birch and alder occurred less often on more wet sites, where the proportions of standing snags were higher. A total of 41 species of wood-decomposing polypores were found in the study area. Among those, 10 (24%) were of conservation value.     

Woody and herbaceous competition effects on the growth of naturally regenerated loblolly and shortleaf pines through 11 years

Four levels of vegetative competition were used to quantify the growth of loblolly and shortleaf pines (Pinus taeda L. and P. echinata Mill.) in naturally regenerated, even-aged stands on the Upper Coastal Plain of southeastern Arkansas, USA. Treatments included: (1) no competition control, (2) woody competition control, (3) herbaceous competition control, and (4) total control of nonpine vegetation. After pines became established from natural seeding, herbicides were used to control herbaceous plants for 4 consecutive years and woody plants for 5 consecutive years. Even though 89% of crop pines on untreated check plots were free-to-grow 11 years after establishment, crop pines on vegetation control plots were larger (P<0.001) in mean dbh, total height, and volume per tree. From age 5 through 11 years, crop pine diameter growth increased on woody control plots and decreased on herbaceous control plots because of hardwood competition in the latter treatment. At age 11, crop pine volume production averaged 207 m³/ha on total control plots, 158 m³/ha on herbaceous control plots, 130 m³/ha on woody control plots, and 102 m³/ha on untreated check plots.     

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.     

Development and activity of early saproxylic fungal communities in harvested and unmanaged boreal mixedwood stands

Limited scientific information is currently available regarding saproxylic fungal communities in the boreal forest of North America. We aimed to characterize the community development, richness and activity of saproxylic fungi on fresh wood in harvested and unmanaged boreal mixedwood stands of northwestern Québec (Canada). Fresh wood blocks (n = 480) of balsam fir (Abies balsamea (L.) Mill.) and trembling aspen (Populus tremuloides Michx.) were placed on the forest floor in a range of stand conditions (n = 24). Blocks were harvested every 6 months for up to 30 months and characterized for species composition and richness (PCR–DGGE, DNA sequencing), respiration, wood density and lignin and cellulose content. Colonization by a wide range of functional groups proceeded rapidly under different stand conditions. We detected a total of 35 different fungal operational taxonomic units, with the highest species richness at the wood block level being observed within the first 12 months. No differences in community composition were found between wood host species or among stand conditions. However, the variability in fungal communities among blocks (β diversity) was lower on trembling aspen wood compared with balsam fir and decreased over time on trembling aspen wood. Also, fungal activity (respiration and wood decomposition) increased on trembling aspen wood blocks and species richness decreased on balsam fir wood over time in partial-cut sites. The overlap in tree composition among stands, the high volume of logs and the recent management history of these stands may have contributed to the similarity of the saproxylic fungal community among stand types and disturbances.     

Diversity and spatio-temporal dynamics of dead wood in a temperate near-natural beech forest (<Emphasis Type="Italic">Fagus sylvatica</Emphasis>)

The diversity, spatial patterns and temporal dynamics of dead wood were examined within the near-natural beech forests (Fagus sylvatica) of Serrahn (North-eastern Germany). Data were collected in an 8 ha sample plot and in two permanent plots (0.36 and 0.25 ha) that had been established at the end of the 1960s. The mean volume of dead wood was 94 m³ ha⁻¹, amounting to 14% of the total volume of all trees. The dead wood displayed a large variation in dead wood type, tree size and decay class. Standing dead wood accounted for about one-third of the total dead wood volume. The densities of standing dead trees were about 10% of the densities of the living trees over a wide range of diameters. The overall spatial distribution of dead trees exhibited a random pattern. Among the different dead wood types, standing entire dead trees and uprooted trees deviated from this pattern by displaying a significantly aggregated pattern. In the permanent plots a high mortality of overstorey trees was observed (1.3% year⁻¹) and the average amount of dead wood increased greatly from 2.9 to 111.6 m³ ha⁻¹ over the 35-year observation period. The near-natural beech forests of Serrahn have experienced a long period of low human interference. Nevertheless, our results suggest that the structure and dynamics of dead wood are strongly affected by the last major disturbance events that took place at the end of the Middle Ages. Information about the forest history is therefore a basic requirement when interpreting the results obtained in near-natural forests.     

Deadwood volume in strictly protected,natural, and primeval forests in Poland

Standing and downed deadwood at different stages of decay provides a crucial habitat for a wide range of organisms. It is particularly abundant in unmanaged forests, such as strictly protected areas of national parks and nature reserves. The present work used the available data for such sites in Poland, analyzing a total of 113 studies concerning 79 sites to determine the causes contributing to variation in deadwood volume based on the duration of conservation, changes in deadwood volume over time (for those sites which were examined multiple times), elevation above sea level, forest type, stage of forest development, input of dead trees from the years preceding deadwood measurements, live tree volume, and the proportion of downed to standing deadwood). Depending on species composition and site altitude, most tree stands fell into one of four categories: subalpine spruce forests, montane beech-fir forests, low altitude beech-fir forests, or oak-hornbeam and riparian forests. The mean deadwood volume for all forest types amounted to 172.0 m³/ha. The mean volume of deadwood in montane beech-fir forests (223.9 m³/ha) was statistically significantly greater than in the other three forest types, for which it ranged from 103.5 to 142.5 m³/ha. A direct effect of the duration of conservation on deadwood volume was not identified. Nevertheless, analysis of repeated measurements on the same sample plots at 10-year intervals showed a consistent rise in mean deadwood volume. A linear regression model for all the analyzed factors reported from montane beech-fir forests and subalpine spruce forests showed that in addition to site altitude, another statistically significant variable was the input of dead trees (R²?=?63.54%).     

Targets for maintenance of dead wood for biodiversity conservation based on extinction thresholds

Abstract

Forestry decreases the amount of dead wood, thereby threatening the persistence of many saproxylic (wood-living) organisms. This article discusses how targets for efforts to maintain and restore dead wood in managed forest landscapes should be defined. Several studies suggest extinction thresholds for saproxylic organisms. However, because the thresholds differ among species, the relationship between species richness and habitat amount at the local scale is probably described by a smoothly increasing curve without any distinct threshold. The most demanding species require amounts of dead wood that are virtually impossible to reach in managed forests. This means that unmanaged protected forests are needed. In managed forests, conservation efforts should focus on the landscape scale and on certain types of dead wood, but it is impossible to come up with any particular amount of dead wood that is desirable at the forest stand level.     

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

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

Impact of silviculture on dead wood and on the distribution and frequency of tree microhabitats in montane beech-fir forests of the Pyrenees

In forest ecosystems, the level of biodiversity is strongly linked to dead wood and tree microhabitats. To evaluate the influence of current forest management on the availability of dead wood and on the abundance and distribution of microhabitats, we studied the volume and diversity of dead wood objects and the distribution and frequency of cavities, dendrothelms, cracks, bark losses and sporophores of saproxylic fungi in montane beech-fir stands. We compared stands unmanaged for 50 or 100 years with continuously managed stands. A total of 1,204 live trees and 460 dead wood objects were observed. Total dead wood volume, snag volume and microhabitat diversity were lower in the managed stands, but the total number of microhabitats per ha was not significantly different between managed and unmanaged stands. Cavities were always the most frequent microhabitat and cracks the least frequent. Dendrothelm and bark loss were favored by management. Beech (Fagus sylvatica) carried many more microhabitats than silver fir (Abies alba), especially cavities, dendrothelms and bark losses. Fir very scarcely formed dendrothelms. Secondary tree species played an important role by providing cracks and bark losses. The proportion of microhabitat-bearing trees increased dramatically above circumference thresholds of 225 cm for beech and 215 cm for fir. Firs with a circumference of less than 135 cm did not carry microhabitats. In order to conserve microhabitat-providing trees and to increase the volume of dead wood in managed stands, we recommend conserving trees that finish their natural cycle over 10–20% of the surface area.     

Effects of density and structure on production in the communal forests of the Mexican Sierra Madre Occidental

The Sierra Madre Occidental in the Mexican State of Durango, is home to about 5 million ha of species-rich forest ecosystems. Local communities depend on these forests for their livelihood. The preservation of the species richness and productivity of this unique resource requires improved understanding of the effects of forest structure and density on production. The community structure was analysed for three species groups (all species; 12 species of Pinus; and 16 species of Quercus). Based on data gathered in 580 remeasured observational field plots, the main results of this study were as follows: (1) two distinct clusters were identified in each species group, (a) the dominant species with a smaller range of growth rates, and (b) the remaining species which have a smaller maximum size and a greater variation of growth rates. (2) Density (expressed as basal area per hectare) and the percentage contribution to the total basal area of all pine species have a significant effect on forest production (expressed as volume increment per hectare per year). (3) Potential production is surprisingly high (in excess of 20 m³ ha^?1 y^?1 for some stands) in these forests, but the high potential cannot be realised in many areas because of reduced basal areas caused by overharvesting. (4) The available evidence does not confirm the findings of a recent study that suggests a continuous increase in production with increasing richness. Our observations show that production attains a potential maximum at intermediate levels of richness (between 7 and 9 species per 0.25 ha) and declines with further increases in species richness. This study represents a comprehensive analysis of the effects of density and structure on the community forests of the Sierra Madre Occidental based on a large set of permanent field plots where all trees have been mapped.     

The regeneration of Eucalyptus regnans F. Muell. under retained overwood: seedling growth and density

The native Eucalyptus regnans forests of South East Australia are managed for multiple use, including wood production. The primary silvicultural system used for wood production is clearfelling. Some criticisms of clearfelling concern differences between the resulting stand structure and that following wildfire, particularly in relation to the frequency and distribution of both living and dead hollow bearing trees. The Victorian Silvicultural Systems Project is evaluating the potential of alternative systems to clearfelling, including the retention of live overwood, either permanently or temporarily. This study examines the establishment and early growth of E. regnans under increasing levels of overwood retention.Retained overwood had a strong negative effect on seedling growth, vigour and density, even at low retention levels. The pattern of height and diameter growth suppression at three years was almost linear, with height and diameter under full overwood retention (40–45 m²/ha) being approximately 57% and 62% respectively of that observed under negligible overwood competition. Stem volume reduction of the order of 50% occurred by a retention level of 12 m²/ha (ca. 20%). Seedling vigour, as indicated by the height to diameter ratio, was also strongly influenced by overwood retention. An increasing height to diameter ratio was observed as the overwood retention increased, with the trend accelerating at levels greater than about 20 m²/ha. The density of seedlings in a dominant or co-dominant competitive position by three years reduced with increasing overwood competition, with the number of dominant and co-dominant seedlings under full overwood retention approximately 17% of that under negligible competition.     

Accumulation of dead wood in abandoned beech (Fagus sylvatica L.) forests in northwestern Germany

Currently, there is much debate about what strategy is most suitable for increasing old-growth attributes in forests that have been managed intensively for wood production in the past. Passive restoration, i.e. cessation of forestry interventions, should be considered when the old-growth attributes desired can be restored within a feasible period of time.Our study focuses on standing and lying coarse dead wood (≥20 cm diameter) in beech-dominated forests in northwestern Germany. We analyzed monitoring data of 545 sample plots (sized 500-1000 m²) from 12 strict forest reserves (SFRs). The SFRs had been without forestry intervention for up to 28 years.Both, number of dead objects and volume of dead wood (m³ ha⁻¹) increased significantly with ongoing time since abandonment from forestry interventions. The mean amount doubled from 9 to 18 m³ ha⁻¹ within 10 years. The proportion of standing dead wood was about 40% of the total dead wood pool ≥20 cm diameter.With mixed linear modeling we showed that dead wood increased by a mean net rate of about 1 m³ ha⁻¹ a⁻¹. Therefore, after three decades critical values for restoring the dead wood pool could be reached. We hypothesized that the rate of dead wood input is mainly determined by disturbance driven tree mortality such as oak decline, bark beetle infestations and storms.A comparison with primeval forests or reserves abandoned more than 100 years ago showed that the SFRs studied are at the beginning of a long process of dead wood accumulation.Based on our results, the abandonment of forest activities in harvestable pure and mixed beech stands is an effective strategy for restoring the dead wood pool.     

Prediction of tree height,basal area and stem volume in forest stands using airborne laser scanning

The aim of this study was to develop prediction models using laser scanning for estimation of forest variables at plot level, validate the estimations at stand level (area 0.64 ha) and test the effect of different laser measurement densities on the estimation errors. The predictions were validated using 29 forest stands (80×80 m²), each containing 16 field plots with a 10 m radius. For the best tested case, mean tree height, basal area and stem volume were predicted with a root mean square error of 0.59 m (3% of average value), 2.7 m² ha^?1 (10% of average value) and 31 m³ ha^?1 (11% of average value), respectively, at stand level. There were small differences in terms of prediction errors for different measuring densities. The results indicate that mean tree height, basal area and stem volume can be estimated in small stands with low laser measurement densities producing accuracies similar to traditional field inventories.