Dynamics of coarse woody debris and decomposition rates in an old-growth forest in lower tropical China

The biomass and decomposition of coarse woody debris (CWD, ≥10 cm in diameter) were studied in a monsoon evergreen broad-leaved old-growth forest in Dinghushan Nature Reserve, Southern China. The study examined the biomass of CWD from 1992 to 2008 and decomposition of three dominant tree species CWD (Castanopsis chinensis, Cryptocarya concinna, Schima superba) from 1999 to 2008. Changes in the wood density of three tree species’ CWD were used to estimate the decay rates with a single exponential model. The results showed that the biomass of CWD in the old-growth forest was increasing from 17.41 tonnes ha⁻¹ (t ha⁻¹) in 1992 to 38.54 t ha⁻¹ in 2008, and a higher decay constant was observed for C. concinna (0.1570 – 19 years for 95% mass loss); the decay rates of S. superba and C. chinensis were 0.1486 (20 years for 95% mass loss) and 0.1095 (27 years for 95% mass loss), respectively. The difference in decay constant rates may be due to their substrate quality and decomposers. The content of carbon (C) in three species declined after 9 years of decay. Nitrogen (N) content increased in all species with decay. The C/N ratio in the three species declined during the decay process.     

A lack of large-diameter logs and snags characterises dead wood patterns in Irish forests

Dead wood is an important component of forest ecosystems and volumes vary depending on forest age, management intensity and productivity. This is the first large-scale study to quantify dead wood in Irish forests and to compare them to forests in other locations. We measured the volume and size distribution of logs, the density and size distribution of snags and the volume of dead wood contained in stumps in Oak (Quercus spp.) and Ash (Fraxinus excelsior) forests and in Sitka spruce (Picea sitchensis) plantations throughout Ireland. We also assigned each log, snag and stump to one of three decay classes (intact, part-rotted and well-rotted). We found no significant difference in log volume between any of the forest types. The majority (>90%) of logs were less than 20 cm in diameter, and large logs (>40 cm diameter) were scarce. We found a relatively high density of snags in all forest types but, as in the case of logs, over 90% of snags were <20 cm DBH and large snags (>40 cm DBH) were rare. The volume of dead wood contained in stumps was significantly higher in plantations than in Oak or Ash forests as a result of thinning and harvesting. Most logs and snags were moderately decayed but, in plantations, most stumps were intact. Log volume and the size of logs and snags were considerably lower than in old-growth forests in other regions. These patterns may reflect historical use of Irish forests for coppice and timber production. Management for biodiversity should aim to accelerate dead wood accumulation to increase the frequency of large-diameter logs and snags. Although management seeking to replicate the dead wood volumes of old-growth forests is ideal, it may be unrealistic in the short term.     

Bryophytes and decaying wood in Hepatica site-type boreo-nemoral Pinus sylvestris forests in Southern Estonia

The aim of the study was to establish the amount of decaying wood (logs and stumps) in various groups of Hepatica site-type pine forests of different age and management intensity and to analyse the composition of bryophytes in dependence of these factors. The average volume of CWD in old unmanaged forests was 47.5 m³/ha, which is rather well comparable with respective estimations from Fennoscandia. Reduced human impact contributes positively to the amount of CWD. Diversity of log diameter classes and decay stages is larger in old forests. Altogether 73 bryophyte species were recorded, 65 species on logs and 55 on stumps. Species richness on stumps was higher in managed forests than in unmanaged ones. At the same time, the species having high indicator value for man-cut stumps are very common species in boreal forests and grow on other substrata as well. Species composition and ecological conditions differed between stumps and logs. Logs are more humid microhabitats than stumps, therefore the occurrence of hepatics is more frequent on them. According to species composition on decaying wood the old unmanaged forests distinguished from others. As the differences of substratum characteristics were notable between old and young forests, the stand age described a considerable part of species variance on logs.     

Decomposing stumps influence carbon and nitrogen pools and fine-root distribution in soils

Decomposing stumps could significantly increase soil resource heterogeneity in forest ecosystems. However, the impact of these microsites on nutrient retention and cycling is relatively unknown. Stump soil was defined as the soil fraction directly altered by the decomposition of the primary rooting system (e.g. taproots) and aboveground stumps. Study sites were located in mature hardwood stands within the Jefferson National Forest in the Ridge and Valley Physiographic region of southwest Virginia. The objectives of this study were to: (i) determine the total soil volume altered by the decomposition of stumps and underlying root system, (ii) compare and contrast total C and N, extractable ammonium (NH₄⁺) and nitrate (NO₃⁻), potentially mineralizable N, microbial biomass C (MBC), root length and root surface area between the bulk soil (i.e. O, A, B and C horizons) and stump soil and (iii) evaluate how nutrient concentrations and fine-root dynamics change as stumps decompose over time using a categorical decay class system for stumps. Potentially mineralizable N was 2.5 times greater in stump soil than the A horizon (103 mg kg⁻¹ vs. 39 mg kg⁻¹), 2.7 times greater for extractable NH₄⁺ (16 mg kg⁻¹ vs. 6 mg kg⁻¹) and almost 4 times greater for MBC (1528 mg kg⁻¹ vs. 397 mg kg⁻¹). Approximately 19% of the total fine-root length and 14% of fine-root surface area occurred in the stump soil. Significant differences occurred in C and N concentrations between all four decay classes and the mineral soil. This validated the use of this system and the need to calculate weighted averages based on the frequency and soil volume influenced by each decay class. In this forest ecosystem, approximately 1.2% of the total soil volume was classified as stump soil and contained 10% and 4% of soil C and N. This study illustrates that including stump soil in soil nutrient budgets by decay class will increase the accuracy of ecosystem nutrient budgets.     

Modelling coarse woody debris dynamics in even-aged Scots pine forests

Coarse woody debris (CWD) has become an important component in the study of forest ecosystems, being a key factor in the nutrient cycle as well as a habitat for many species. CWD dynamics varies greatly from primeval to managed forests. To assess the CWD dynamics, a chronosequence trial was established in two Scots pine forests in the Central mountain range in Spain. Although, the shelterwood system has been applied in both forests, one has received more intensive silviculture, whereas in the other, regeneration has been much more gradual and the thinning regime has not been so intensive. In order to inventory CWD, five decay classes and four categories according to size and CWD type (stumps and fallen logs or branches) were defined. The volume of branches and logs (estimated from length and mean diameter) and the number of stumps by size class and decay class are used to characterise the CWD. The most notable differences between the two silvicultural systems can be appreciated in the graph as peaks for temporary distribution of larger logs and stumps when intensive silviculture is applied. The CWD observed in the forests studied is mainly produced by logging. The maximum volume of logs and branches above 5 cm in diameter is 43.25 m³/ha after regeneration felling in the first forest, whereas in the other, a maximum of 16.30 m³/ha is reached at 60 years, just after thinning. Large stumps (diameter equal or greater than 30 cm) make up an important part of CWD biomass in these forests just after the regeneration felling. A model was developed to predict the changes in CWD quantity and quality distribution over time as well as predicting the effect of different silviculture options on CWD dynamics. The model integrates two different processes: the CWD inputs (which may be continuous or instant), and the decay process, modelled through a Richards–Chapman function. The average lifetime of CWD obtained ranges from 30 years for stumps over 30 cm in diameter to 8 years for logs with a diameter less than 10 cm.     

The effects of burning and dead-wood creation on the diversity of pioneer wood-inhabiting fungi in managed boreal spruce forests

The loss of natural forest habitats due to forestry is the main reason for the decline in boreal forest biodiversity of the Nordic countries of Europe. Ecological rehabilitation may provide means to recover and sustain biodiversity. We analyzed the effects of controlled burning and dead-wood creation (DWC) on the diversity of pioneer wood-inhabiting fungi in managed Norway spruce (Picea abies) forests in southern Finland. Altogether 18 stands were first subjected to a partial cutting with ordinary logging residues in form of cut stumps and treetops left on site. The subsequent rehabilitation treatments consisted of a controlled burning applied in half of the stands and three levels of dead-wood creation (5, 30 and 60 m³ ha⁻¹). The DWC involved creation of logs; felling of whole trees to mimic downed logs formed by natural disturbance processes. Each treatment was replicated three times. Inside each stand, substrates were sampled in two different biotopes; one on mineral soil and one on mineral soil with a thin peat layer. We surveyed the fungal flora on the logs (n = 364) and the ordinary residue stumps (n = 1767) and tops (n = 845) five years after the treatments.When comparing different stands, controlled burning had a significant effect on species composition; certain species were significantly more frequent on substrates in burned stands than in unburned stands, indicating that these species were favored by controlled burning. By contrast, we found no significant effects of DWC levels or biotope on species composition or richness. When comparing different substrates, 99% of the logs hosted at least one species and the occurrence probability of certain species was significantly higher on logs than on ordinary residue stumps and tops. Yet, volume-based rarefaction analyses showed that residues were more species dense than the logs, indicating that ordinary logging residues constitute important resources for many pioneer species.We conclude that controlled burning combined with DWC have strong effects on biodiversity; it modifies the composition of the pioneer wood-inhabiting fungal species found in managed forests and may thereby also influence the further succession and diversity of the secondary fungal flora.     

Modeling production and decay of coarse woody debris in loblolly pine plantations

Forest management can have large impacts on the production and yield of coarse woody debris (CWD) in terrestrial ecosystems, yet few modeling tools exist to inform such efforts. The goal here was to develop a set of prediction equations for use in conjunction with loblolly pine (Pinus taeda L.) modeling and inventory systems to estimate CWD yields at scales ranging from individual trees to whole plantations. Permanent field plots from a 21-year study of thinning effects on plantation growth and yield across the commercial range of the species in the southern United States were surveyed to obtain sample data on CWD volume, density, and mass. Measured CWD properties were combined with inventory records of tree mortality over the study duration to characterize CWD production, decay and yield in a series of prediction equations. The resulting equations predict CWD attributes of dead trees including dry weight (kg) and fraction of standing versus downed woody material based on the time since death (years), tree diameter at breast height (cm) and height (m) at time of death and geographic coordinates of latitude and longitude. A stand-level equation predicts total CWD yield (Mg ha⁻¹) for thinned or unthinned stands based on plantation age, stem density (trees ha⁻¹), and the average height of dominant and codominant trees (m). Piece-level equations predict dry density (kg m⁻³) or nitrogen concentration (%) of CWD pieces based on their position (standing or down), ordinal decay classes, and latitude. The tree and stand-level prediction equations are designed for use in GIS or growth and yield modeling systems. The piece-level equations are designed to be used in inventory applications that survey CWD. The equations should facilitate the accurate and facile determination of mass, carbon, and nitrogen contents of CWD in planted loblolly pine forests of the southern United States.     

Spatial variation in respiration from coarse woody debris in a temperate secondary broad-leaved forest in Japan

We measured the rates of respiration from snags and logs (“coarse woody debris”, CWD) of Japanese red pine (Pinus densiflora Sieb. et Zucc.) to examine the rate of decomposition and CO₂ efflux from these materials in a temperate secondary broad-leaved forest in Japan. At this site, a high quantity of CWD of P. densiflora had accumulated as a result of pine wilt disease during the 1970s. Respiration rates were measured using a dynamic closed chamber method combined with an infrared gas analyzer. We measured the respiration rate of 7 samples of snags and 10 samples of logs from August 2003 to January 2004. The responses of the respiration rates of snags (R_snag) and logs (R_log) to changing temperature were both exponential and the responses to water content were quadratic, and the same function could be used to estimate annual values of both R_snag and R_log. Intensive measurements of water contents of snags and logs showed a marked difference in water content. The mean water content of snags was 20% of log water content. This difference was likely responsible for the observed difference in annual R_snag and R_log. The decay rate constants estimated from the respiration rates measurement of snags and logs were 0.019 and 0.081 year⁻¹, respectively. Despite being lower than R_log, R_snag was a significant compartment of the CWD carbon budget at this site.     

Recovery of carbon and nutrient pools in a northern forested wetland 11 years after harvesting and site preparation

We measured the change in above- and below-ground carbon and nutrient pools 11 years after the harvesting and site preparation of a histic-mineral soil wetland forest in the Upper Peninsula of Michigan. The original stand of black spruce (Picea mariana), jack pine (Pinus banksiana) and tamarack (Larix laricina) was whole-tree harvested, and three post-harvest treatments (disk trenching, bedding, and none) were randomly assigned to three Latin square blocks (n = 9). Nine control plots were also established in an adjoining uncut stand. Carbon and nutrients were measured in three strata of above-ground vegetation, woody debris, roots, forest floor, and mineral soil to a depth of 1.5 m. Eleven years following harvesting, soil C, N, Ca, Mg, and K pools were similar among the three site preparation treatments and the uncut stand. However, there were differences in ecosystem-level nutrient pools because of differences in live biomass. Coarse roots comprised approximately 30% of the tree biomass C in the regenerated stands and 18% in the uncut stand. Nutrient sequestration, in the vegetation since harvesting yielded an average net ecosystem gain of 332 kg N ha⁻¹, 110 kg Ca ha⁻¹, 18 kg Mg ha⁻¹, and 65 kg K ha⁻¹. The likely source for the cations and N is uptake from shallow groundwater, but N additions could also come from non-symbiotic N-fixation and N deposition. These are the only reported findings on long-term effects of harvesting and site preparation on a histic-mineral soil wetland and the results illustrate the importance of understanding the ecohydrology and nutrient dynamics of the wetland forest. This wetland type appears less sensitive to disturbance than upland sites, and is capable of sustained productivity under these silvicultural treatments.     

Decomposition of Pinus radiata coarse woody debris in New Zealand

The decomposition of Pinus radiata (D. Don) stems, coarse woody roots and stumps was studied in Tarawera forest, Bay of Plenty region, North Island, New Zealand. The study examined the residues from two thinning events with 6 and 11 years of decay. Changes in the mass of stems, and density of roots and stumps were used to estimate the decay rate constants using a single exponential model. The decay rate of stems was not significantly related to DBH and averaged 0.1374 year⁻¹ (22 years for 95% mass loss). The decay rate of coarse woody roots was not significantly different to stem decay and averaged 0.1571 year⁻¹ (19 years for 95% mass loss). A large range in stump decay rates was measured and a significantly lower decay constant was observed for stumps (0.1101 year⁻¹, 27 years for 95% mass loss), possibly due to the stumps being kept alive after felling through root grafting and a resistance to decay due to the presence of resin. The concentration of C remaining in stems and stumps increased with mass loss from 52% to 55% C after 11 years of decay. The C concentration in coarse woody roots initially increased but then declined near to the original level of 50% after 11 years of decay. Nitrogen concentrations increased substantially in all components with decay.     

Spatial patterns of litter-dwelling taxa in relation to the amounts of coarse woody debris in European temperate deciduous forests

We studied the leaf litter-dwelling fauna of managed deciduous forests and primeval reference sites in Western and Central Europe and addressed the questions if the higher overall species richness close to downed coarse woody debris (CWD) is related to intra-specific or inter-specific aggregation, if the aggregation pattern changes with the amount of CWD on the forest floor, and how much CWD is needed for different taxa. The analysis is based on shelled Gastropoda, Diplopoda/Isopoda, Chilopoda and Coleoptera. Among-sample heterogeneity was lower close to CWD than distant from CWD. This was most pronounced in Diplopoda/Isopoda and Gastropoda. Diplopoda/Isopoda are comparatively mobile and assemblages were already quite homogenous close to CWD at levels above 5 m³ downed deadwood ha⁻¹. Gastropoda have a low mobility, and more than 20 m³ downed deadwood ha⁻¹ is needed for assemblage homogeneity. We further focused on the Gastropoda as sensitive indicators. Enhanced densities and species richness close to CWD were not a simple function of leaf litter weight, thus effects of densities on heterogeneity are not solely driven by leaf litter accumulation close to CWD. In contrast to euryecious litter-dwellers such as the Punctidae, stenecious slow active dispersers such as the Clausiliidae clearly require more than 20 m³ CWD ha⁻¹ for an even distribution. Specialists depending on CWD even seem to have gone extinct in some managed forests. For conserving the litter-dwelling fauna, we propose a target of at least 20 m³ downed CWD ha⁻¹ in already managed forests and rigorous restrictions for deadwood removal from still (almost) pristine systems.     

Spatial distribution of dead wood and the occurrence of five saproxylic fungi in old-growth timberline spruce forests in northern Finland

Abstract

Adequate understanding of the factors that determine the establishment and survival of dead-wood-dependent species in natural forests is a prerequisite to the successful maintenance of these species in managed forests. This study investigated the factors affecting the occurrence of five wood-inhabiting polypores in old-growth timberline spruce forests in northern Finland, including the substrate availability and the spatial arrangement of large-diameter logs. The volume of coarse woody debris (CWD) varied significantly between the sites (range 15–30 m³ ha^?1), large-diameter logs comprising on average 35% of the total CWD volume. However, the within-site variation in CWD volume was 10–15 times larger than the between-site variation. The spatial distribution of large-diameter logs was aggregated or initially aggregated on four sites and random on one site, creating local patches of high CWD volume. An individual target species occurred on average on 8% of all large-diameter logs, and on 11% of optimal logs (as determined by the decay stage). The characteristics of the logs and stand variables explained partly the occurrence of the target species; furthermore, the mortality pattern of trees (stem breakage versus uprooting) and the presence of primary decomposers also significantly affected the occurrence of the target species. The results indicate that besides substrate availability and quality, local habitat factors and species interactions also play a role in the occurrence of wood-inhabiting fungi in boreal timberline forests.     

缙云山常绿阔叶林粗木质残体储量及特征

【目的】实地调查缙云山常绿阔叶林粗木质残体(CWD)的储量和特征,分析其影响因素,为深入认识常绿阔叶林生态系统中与粗木质残体相关的物质循环等关键生态过程提供理论依据,并为全球碳汇及相关学科的研究提供基础数据。【方法】以缙云山常绿阔叶林内已建立的2块0.5 hm^2样地为对象,调查并分析样地CWD的储量、类型组成、分解等级、径级分布格局以及地形对CWD储量的影响。【结果】缙云山常绿阔叶林CWD储量为38.42 t·hm^-2,其中倒木、枯立木、大枯枝和木桩储量分别为27.70,4.91,2.91和2.90 t·hm^-2,倒木是CWD的主要组成部分; CWD的树种组成与群落优势树种的组成相似,栲占CWD总量的88.44%;从径级分布来看,直径>35 cm的倒木和枯立木是CWD的主体; CWD主要处于分解中后期,中级分解和高级分解CWD的比例分别为63.20%和23.01%;地形对CWD的分布具有显著影响,坡面和山脊CWD储量高于沟谷(P<0.01)。【结论】缙云山常绿阔叶林CWD储量较大,处于该类森林系统的前列; CWD主要以处于分解中后期的优势种大径级倒木和枯立木为主,并主要分布在坡面和沟谷。在森林管理中应降低对CWD的人为干扰和去除,维持森林中枯立木、倒木、大枯枝和树桩等组分的自然状态。     

An ecosystem approach to biodiversity effects: Carbon pools in a tropical tree plantation

This paper presents a synthesis of experiments conducted in a tropical tree plantation established in 2001 and consisting of 22 plots of 45 m × 45 m with either one, three or six native tree species. We examined the changes in carbon (C) pools (trees, herbaceous vegetation, litter, coarse woody debris (CWD), and mineral topsoil at 0-10 cm depth) and fluxes (decomposition of CWD and litter, as well as soil respiration) both through time and among diversity levels. Between 2001 and 2009 the aboveground C pools increased, driven by trees. Across diversity levels, the mean observed aboveground C pool was 7.9 ± 2.5 Mg ha⁻¹ in 2006 and 20.4 ± 7.4 Mg ha⁻¹ in 2009, a 158% increase. There was no significant diversity effect on the observed aboveground C pool, but we found a significant decrease in the topsoil C pool, with a mean value of 34.5 ± 2.4 Mg ha⁻¹ in 2001 and of 25.7 ± 5.7 Mg ha⁻¹ in 2009 (F_1,36 = 52.12, p < 0.001). Assuming that the biomass C pool in 2001 was negligible (<1 Mg ha⁻¹), then the plantation gained in C, on average, ∼20 and lost ∼9 Mg ha⁻¹ in biomass and soil respectively, for an overall gain of ∼11 Mg ha⁻¹ over 8 years. Across the entire data set, we uncovered significant effects of diversity on CWD decomposition (diversity: F_2,393 = 15.93, p < 0.001) and soil respiration (monocultures vs mixtures: t = 15.35, df = 11, p < 0.05) and a marginally significant time × diversity interaction on the loss of total C from the mineral topsoil pool (see above). Monthly CWD decomposition was significantly faster in monocultures (35.0 ± 24.1%) compared with triplets (31.3 ± 21.0%) and six-species mixtures (31.9 ± 26.8%), while soil respiration was higher in monocultures than in mixtures (t = 15.35, df = 11, p < 0.001). Path analyses showed that, as diversity increases, the links among the C pools and fluxes strengthen significantly. Our results demonstrate that tree diversity influences the processes governing the changes in C pools and fluxes following establishment of a tree plantation on a former pasture. We conclude that the choice of tree mixtures for afforestation in the tropics can have a marked influence on C pools and dynamics.     

Carbon storage in old-growth and second growth fire-dependent western larch (Larix occidentalis Nutt.) forests of the Inland Northwest,USA

There is limited understanding of the carbon (C) storage capacity and overall ecological structure of old-growth forests of western Montana, leaving little ability to evaluate the role of old-growth forests in regional C cycles and ecosystem level C storage capacity. To investigate the difference in C storage between equivalent stands of contrasting age classes and management histories, we surveyed paired old-growth and second growth western larch (Larix occidentalis Nutt)–Douglas-fir (Pseudostuga menziesii var. glauca) stands in northwestern Montana. The specific objectives of this study were to: (1) estimate ecosystem C of old-growth and second growth western larch stands; (2) compare C storage of paired old-growth–second growth stands; and (3) assess differences in ecosystem function and structure between the two age classes, specifically measuring C associated with mineral soil, forest floor, coarse woody debris (CWD), understory, and overstory, as well as overall structure of vegetation. Stands were surveyed using a modified USFS FIA protocol, focusing on ecological components related to soil, forest floor, and overstory C. All downed wood, forest floor, and soil samples were then analyzed for total C and total nitrogen (N). Total ecosystem C in the old-growth forests was significantly greater than that in second growth forests, storing over 3 times the C. Average total mineral soil C was not significantly different in second growth stands compared to old-growth stands; however, total C of the forest floor was significantly greater in old-growth (23.8 Mg ha⁻¹) compared to second growth stands (4.9 Mg ha⁻¹). Overstory and coarse root biomass held the greatest differences in ecosystem C between the two stand types (old-growth, second growth), with nearly 7 times more C in old-growth trees than trees found on second growth stands (144.2 Mg ha⁻¹ vs. 23.8 Mg ha⁻¹). Total CWD on old-growth stands accounted for almost 19 times more C than CWD found in second growth stands. Soil bulk density was also significantly higher on second growth stands some 30+ years after harvest, demonstrating long-term impacts of harvest on soil. Results suggest ecological components specific to old-growth western larch forests, such as coarse root biomass, large amounts of CWD, and a thick forest floor layer are important contributors to long-term C storage within these ecosystems. This, combined with functional implications of contrasts in C distribution and dynamics, suggest that old-growth western larch/Douglas-fir forests are both functionally and structurally distinctive from their second growth counterparts.     

Susceptibility of Sitka spruce and grand fir trees to decay by Heterobasidion annosum

The susceptibility of Sitka spruce (Picea sitchensis) and grand fir (Abies grandis) to decay by Heterobasidion annosum was compared on a site with a previous history of serious disease. The incidence of decay 15–16 years after planting was 1.5% in grand fir, compared with 34.8% in Sitka spruce. These results are broadly similar to those reported from other trials. More information is required for older trees in Britain but the evidence so far available suggests that grand fir is more resistant to H. annosum than Sitka spruce. Planting grand fir on severely infested sites may therefore significantly reduce the serious losses that could be expected with Sitka spruce. In 14 out of 271 decayed Sitka spruce H. annosum was absent from the middle or base of the decay column but present at the top. Approximately 3% of infected spruce showed features suggesting some degree of resistance. Resin bleeding was observed at the base of 23.2% of the infected spruce, and the mean height of the decay column in these trees was significantly greater (0.96 m) than in those without this feature (0.66 m). The inoculum for infection was provided by stumps of the previous crop, and the genets of H. annosum that were present in some infected trees were also identified in stumps. The majority of infected trees contained only a single genet but three trees contained two genets. In this young crop individual genets were smaller than those found elsewhere; the largest extended to include six trees.     

Defoliation and growth relationships for mid-rotation Sitka spruce attacked by the green spruce aphid, Elatobium abietinum (Walker) (Homoptera: Aphididae)

Green spruce aphid (Elatobium abietinum) feeds primarily on the 1-year-old and older needle leaves of spruce (Picea spp.) and is a major defoliator of commercial Sitka spruce plantations in the UK and other maritime regions of north-west Europe. The impact of E. abietinum on mid-rotation (23-28-year-old) Sitka spruce in Radnor Forest, in mid-Wales, was determined by comparing aphid population densities, defoliation and growth between plots of trees that were either treated with insecticide or were left untreated. The experimental treatments were maintained for 5 years and over this period (2002-2006) peak E. abietinum densities in the untreated plots varied from 5 to 36 aphids per 100 needles. These densities, which were representative of low to moderate rates of infestation, were associated with low rates of defoliation (0-8%), but they had a significant (P ? 0.01) impact on mean radial increment (RI) and mean volume increment (VI). In 2005, the year with the highest aphid populations, peak densities in the untreated plots averaged 14 aphids per 100 needles and this rate of infestation reduced RI by 17%, VI by 10% and the dry weight of current-year needles by 10%. On average, across all years, infestation by E. abietinum reduced mean annual VI by 6%. Comparisons with previous studies on the impact of the aphid on 4-year-old, 7-year-old and 9-year-old Sitka spruce (Straw et al., 2005) indicate that defoliation by E. abietinum, on a per capita basis, decreases as trees grow older, but that the impact on VI increases. The different growth response of young and mid-rotation Sitka spruce to infestation is related to differences in canopy structure, particularly in the ratio of current-year needles to older needles, and the greater demands on photosynthetic production in older trees that arise from the need to support an increasing quantity of non-photosynthetic structural tissues in branches, stem and roots.     

Abundance and attributes of wildlife trees and coarse woody debris at three silvicultural systems study areas in the Interior Cedar-Hemlock Zone,British Columbia

Unmanaged cedar (Thuja plicata)-hemlock (Tsuga heterophylla) forests of the northern Interior Wetbelt of British Columbia support standing and dead trees with a variety of structural features that provide habitat for wildlife. We describe the pre-harvest abundance and characteristics of wildlife trees (standing trees with special characteristics that provide habitat for wildlife) and coarse woody debris (CWD) at three silvicultural systems trials in cedar-dominated stands, and the short-term effects of forest harvesting on the abundance and attributes of CWD. The treatments were clearcut, group retention (70% volume removal), group selection (30% volume removal), and unlogged control. We measured standing trees in 75 0.125-ha plots and CWD along 225 24-m transects, using a functional classification system to characterize habitat attributes of trees and logs. CWD assessments were repeated on the same transects after the harvest. The relationship between tree size and occurrence of habitat features was strong for both standing trees and logs. Each of the four major tree species in the study area was associated with specific habitat features that occurred more often in that species than in any other. Large concealed spaces at the bases of trees, providing den sites and escape cover, were associated with hybrid white spruce (Picea engelmannii × glauca). We suggest that these trees had originated on nurse logs that subsequently rotted away; if that supposition is correct, there may be shortages of these structures in future stands that originate from plantations. Forest harvesting had little effect on the volume of CWD, but did affect the decay class distribution, reduce the proportion of pieces having structural habitat attributes, and reduce piece lengths; these effects were generally proportional to the level of harvest removal. Partial-cut silvicultural systems have the potential to mitigate anticipated deficits in large wildlife trees and logs in managed stands, if components of the stand are managed on longer rotations than those planned for timber production alone.     

Soricid response to coarse woody debris manipulations in Coastal Plain loblolly pine forests

We assessed shrew (soricids) response to coarse woody debris (CWD) manipulations in managed upland loblolly pine (Pinus taeda) stands in the upper Coastal Plain of South Carolina over multiple years and seasons. Using a completely randomized block design, we assigned one of the following treatments to 12, 9.3-ha plots: removal (n = 3; all CWD ≥ 10 cm in diameter and ≥60 cm long removed), downed (n = 3; 5-fold increase in volume of down CWD), snag (n = 3; 12-fold increase in standing dead CWD), and control (n = 3; unmanipulated). Therein, we sampled shrews during winter, spring, and summer seasons, 2003–2005, using drift-fence pitfall arrays. During 1680 drift-fence plot nights we captured 253 Blarina carolinensis, 154 Sorex longirostris, and 51 Cryptotis parva. Blarina carolinensis capture rate was greater in control than in snag treatments. Sorex longirostris capture rate was lower in removal than downed and control plots in 2005 whereas C. parva capture rate did not differ among treatments. Overall, the CWD input treatments failed to elicit the positive soricid response we had expected. Lack of a positive response by soricid populations to our downed treatments may be attributable to the early CWD decay stage within these plots or an indication that within fire-adapted pine-dominated systems of the Southeast, reliance on CWD is less than in other forest types.     

Dead wood volume to dead wood carbon: the issue of conversion factors

Requirements for emission reporting under the Kyoto protocol demand an estimate of the dead wood carbon pool in forests. The volume of dead wood consists of coarse woody debris, smaller woody debris and dead roots. The measurement of dead wood volume was included in the most recent National Forest Inventory in Switzerland. To convert dead wood volume into carbon two conversion factors are required: (a) carbon (C) concentration and (b) wood density. So far internationally accepted default values for C concentration (50%) and for wood density (density of alive trees) were used as default values to estimate dead wood carbon, since local measurements were lacking. However, in a field study at 34 sites in Switzerland, the C concentration and density of CWD from Picea abies and Fagus sylvatica of four decay classes were measured recently. The results showed that C concentration in CWD differed significantly between species but did not change due to decay class. The density of CWD decreased significantly with an increase in decay class and it also differed between species. The decrease in CWD density was more pronounced for F. sylvatica than for P. abies. We assessed correlations between climate attributes and CWD density using regression analysis. The modeled densities and measured C concentrations were then expanded with the help of CWD volume data from the NFI3. Spruce CWD and thus spruce CWD carbon is much more abundant in Swiss forests than beech CWD carbon. The majority of spruce CWD is located in the Alps and Pre-Alps. The CWD volume from P. abies was 10 times higher than that from F. sylvatica. Thus, changes in conversion factors for P. abies CWD affected the overall estimate of dead wood carbon in Swiss forests much more than changes in conversion factors for F. sylvatica CWD. Current improvements in CWD conversion factors decreased the estimated amount of spruce CWD carbon by 23.1% and that of beech by 47.6%. The estimated amount of CWD carbon in Swiss forests is decreased by 31%. Since improved estimation methods are currently not applied to smaller woody debris and dead root material, the estimated amount of dead wood carbon is only reduced by 15%. Improving conversion factors for all dead wood fractions would presumably decrease the amount of dead wood carbon by additional 16%.