Influence of snag characteristics on saproxylic beetle assemblages in a south Swedish beech forest

Effects of snag characteristics on saproxylic beetles were studied in an area of managed beech forest in southern Sweden. A snag survey was combined with a beetle survey using 30 small window traps directly attached to beech snags. The total number of species was lower in the snags which were most decayed than in the three younger decay classes, while the number of red-listed species remained the same regardless of the stage of decay. The number of fresh wood species declined and the number of rot hole species increased with increasing snag decay. The diversity of fungicolous and decayed wood species peaked at the intermediate stage of decay in the snags. CCA ordination confirmed that the stage of decay in the snags was most important for species composition, followed by sun exposure. There were no general differences in species density and composition between managed and unmanaged stands. Our study suggests that most species are able to find suitable habitat within a radius of a few kilometres and that the total amount of habitat in an unfragmented forest area is more important for species diversity than the spatial distribution of this habitat. Our data also shows that species diversity increases with habitat diversity. Snags formed from giant beech trees seem to be particularly important for rare species living in rot holes. We conclude that for a high species diversity there is a requirement for snags in different stages of decay, size and degree of sun exposure.     

Snag Benchmarks and Treatment Options for Mixed‐Pine Forest Restoration in Eastern Upper Michigan

Snags (dead‐standing trees) are biological legacies that remain after disturbances in forests. We enhanced the ecological underpinnings of snag management within the context of mixed‐pine forest restoration in the northern Lake States by quantifying characteristics of live trees and snags within eighty-five 500‐m² plots at Seney National Wildlife Refuge (NWR) in eastern Upper Michigan. Study plots represented reference conditions (i.e. no past harvesting, relatively unaltered fire regime) and altered (i.e. harvested, altered fire regime) conditions. We also compared three treatments for creating snags from live trees. Snags were found in 87% of the reference plots and 85% of the altered plots. The only snag variables that differed between plot types were mean snag basal area, which was greater in altered plots (Student's t‐test, p = 0.04), and mean percent total basal area of snags (greater in reference plots, p = 0.06). The composition of snags differed only in the 10‐ and 25‐cm diameter classes (Multi‐Response Permutation Procedure, p < 0.10). The percentage of snags that developed into the most advanced decay class (DC) differed among treatments after 4 years (χ² = 16.49, p < 0.01), with 26% of girdled trees, 3% of prescribed fire trees, and zero topped trees reaching DC5. Logistic regression illustrated that the influence of predictor variables on DC development varied by species and treatment. The findings from this study, past studies, and ongoing projects at Seney NWR are directly applicable to innovative management of snags in mixed‐pine forests.     

Vertical distribution of saproxylic beetles within snag trunks retained in plantation forests

Retention of snags (standing dead trees) is considered to have important effects on saproxylic species conservation in plantation forests because snags would provide vertically stratified deadwood habitats. However, the vertical distribution of saproxylic insects within snag trunks is still unclear. We felled 33 naturally occurring snags of Todo fir Abies sachalinensis in plantation forests and extracted insects from 99 logs sampled from three vertical positions of the snag trunks (basal stem: <2.5 m, lower trunk: 2.5–5 m and upper trunk: >5 m). The mean number of species that emerged from a single log was only 2.69, but we identified 51 morphospecies of saproxylic beetles in total. The total number of species that emerged from the basal stem (34 spp.) was greater than those that emerged from the lower trunk (25 spp.) or the upper trunk (30 spp.). However, rarefaction-extrapolation analysis did not demonstrate a significant difference in species richness among the log positions. Beetle assemblages were separated into two groups by constrained correspondence analysis; one group emerged only from lower and upper trunk logs, while another emerged mainly from basal stem logs. Additionally, vertical position had a significant effect on the distribution of the five main species. Our results show that beetle assemblages within snags in the plantation forests were highly variable, and retaining a sufficient number of high stumps may be important for saproxylic beetle conservation in plantation forests. We propose ‘retention thinning’ as an appropriate method to combine efficient timber production with biodiversity conservation in plantation forests.     

High Density of Tree-Cavities and Snags in Tropical Dry Forest of Western Mexico Raises Questions for a Latitudinal Gradient

It has been suggested that a latitudinal gradient exists of a low density of snags and high density of naturally-formed tree-cavities in tropical vs. temperate forests, though few cavities may have characteristics suitable for nesting by birds. We determined snag and cavity density, characteristics, and suitability for birds in a tropical dry forest biome of western Mexico, and evaluated whether our data fits the trend of snag and cavity density typically found in tropical moist and wet forests. We established five 0.25-ha transects to survey and measure tree-cavities and snags in each of three vegetation types of deciduous, semi-deciduous, and mono-dominant Piranhea mexicana forest, comprising a total of 3.75 ha. We found a high density of 77 cavities/ha, with 37 cavities suitable for birds/ha, where density, and characteristics of cavities varied significantly among vegetation types. Lowest abundance of cavities occurred in deciduous forest, and these were in smaller trees, at a lower height, and with a narrower entrance diameter. Only 8.6% of cavities were excavated by woodpeckers, and only 11% of cavities were occupied, mainly by arthropods, though 52% of all cavities were unsuitable for birds. We also found a high density of 56 snags/ha, with greatest density in deciduous forest (70 snags/ha), though these were of significantly smaller diameter, and snags of larger diameter were more likely to contain cavities. The Chamela-Cuixmala tropical dry forest had the highest density of snags recorded for any tropical or temperate forest, and while snag density was significantly correlated with mean snag dbh, neither latitude nor mean dbh predicted snag density in ten forest sites. The high spatial aggregation of snag and cavity resources in tropical dry forest may limit their availability, particularly for large-bodied cavity adopters, and highlights the importance of habitat heterogeneity in providing resources for primary and secondary cavity-nesters.     

Tree selection by the endangered beetle <Emphasis Type="Italic">Rosalia alpina</Emphasis> in a lapsed pollard beech forest

Abandoned pollard beech forests are particular habitats that may require special conservation efforts to preserve the endangered beetle Rosalia alpina, a model species whose protection may perpetuate the habitat of many other saproxylic species. Forest use can determine the tree selection and population size of R. alpina, variables previously not researched in pollard forests. Selected tree traits and population size, indicated by presence of adult specimens and recent exit holes, were determined in a pollard beech forest before the implementation of habitat manipulations targeted to preserve the species. Multivariate analysis showed tree condition (living, snag, fallen) and clearing size and aspect as influential variables, with the former explaining more variance than the latter. R. alpina positively selected pollard snags and trees located in big and dry clearings, avoiding those in small clearings or shaded areas. Snags showed most adults (90 %) and recent emergence holes (84 %). Distance to the nearest occupied tree, trunk diameter, bark thickness and presence of sap leaks had no effect on the occurrence of R. alpina. Population size was estimated in 0.1 individuals day^?1 ha^?1, and 38 % of available habitat trees showed exit holes, values lower than those observed in other European countries. These results show the need to start re-pollardings in the forest to extend pollard standing life and enhance exposure to sunlight. Pinpointing pollard snags and clearing the surrounding vegetation are recommended as the first measures to be taken in order to favor R. alpina populations on pollard stands with closed canopies.     

Characteristics of snags and forest structure in southern mistbelt forests of the Amatole region,South Africa

Standing dead trees (or snags) are an important component of forest ecosystems, especially for tree cavity‐nesting vertebrate species, but their prevalence in South African forests remains under studied. Consequently, we investigated forest structure, and the presence and abundance of snags in six southern mistbelt forests in the Eastern Cape, South Africa. These forests have had varying levels of timber extraction over the past 150 years or more. We found snags were relatively rare in all six forests (<4.3% of trees sampled). Mean diameter at breast height (dbh) of snags ranged from 52 to 82 cm across the forests, with smaller snags in Kologha Forest and larger snags in Tyume Forest. A bimodal distribution of snag successional stages was found, with frequencies peaking at early and late stages, and few in the intermediate stages. Tree species diversity in the forests was relatively low (twelve–nineteen species across forests; only 28 species in total). There was no significant difference in dbh of trees between forests, with most occurring in the 20–29‐cm dbh size class. Future studies are required to identify trees that most likely support suitable cavities for tree cavity‐nesting bird species, and to determine cavity‐nester assemblage requirements in southern African forests.     

Restoration of beech forest for saproxylic beetles—effects of habitat fragmentation and substrate density on species diversity and distribution

The influence of spatial location and density of beech snags on species diversity and distribution patterns of saproxylic beetles was studied in a 2,400 ha forest landscape in southern Sweden. Complete snag surveys were combined with a beetle survey using small window traps directly attached to the beech snags. The density of beech snags ≥30 cm dbh varied between one and seven snags per ha within the study area, corresponding to 1.1–5.1 m³/ha. A total of 2,610 specimens of 180 saproxylic beetles species were trapped, of which 19 species were red-listed. Within the study area, the number of red-listed and formerly red-listed species was highest around traps in old-growth stands, intermediate in managed stands contiguous with old-growth and lowest in managed stands isolated from old-growth by a two km-wide zone without beech forest. Logistic regressions revealed negative relationships between distance to old-growth forest and occurrence of eleven species, among them six red-listed or formerly red-listed species. The number of non red-listed species was not correlated with isolation from old-growth forest. The number of red-listed species also increased with snag density within 200–300 m around the traps. Our results suggest that red-listed species generally have a lower dispersal capacity than other saproxylic beetles. We conclude that retention of dead wood close to existing populations is more beneficial for red-listed species than an even distribution of snags across the forest landscape.     

Temporal dynamics of roost snags of long-legged myotis in the Pacific Northwest,USA

Snags are used as roosting sites by many bats living in coniferous forests of western North America. Thus, providing sufficient numbers of snags both spatially and temporally in forested landscapes is critical to sustaining populations of these species. One aspect that remains poorly understood is length of time that roost snags persist on the landscape in a form suitable for use by bats. This information is critical for forest-planning efforts in ensuring long-term availability of snag resources on forested landscapes. We monitored condition of 339 snags used as roosting sites by long-legged myotis (Myotis volans) 1–5 years post-discovery from 2001 to 2006 across 6 watersheds in Washington, Oregon, and Idaho, USA. Persistence rates (i.e., probability a snag remains standing from year x to x + 1) of roost snags declined with year post-discovery in all study areas. Fir snags (Abies spp.) exhibited lower persistence rates than other conifer species. Data for the Washington area indicated only 4.3% of roost snags likely remain standing 10 years post-discovery, with half-lives of all snag species <3 roost-years. Model ranking of habitat models predicting fall year of roost snags revealed that snag condition models were the most parsimonious in all geographic locations. Roost snags larger in diameter, shorter in height, and with fewer branches on the bole were likely to persist for more years. These data indicate that snags used as roosts by long-legged myotis are suitable as roosting sites for only a few years before falling. We recommend management policies for coniferous forests in the Pacific Northwest, USA, that promote sufficient leave-trees in set-aside areas to provide for future suitable, large-diameter snags for bats in managed, forested landscapes. © 2012 The Wildlife Society.     

浙江天目山种植林管理历史及粗死木残体特征影响柳杉腐木甲虫多样性（英文）

不合理的森林管理是导致腐木甲虫多样性丧失的重要原因。在中国亚热带地区, 多样性较高的天然林已被大面积的人工种植林取代, 然而, 这些人工林对腐木甲虫多样性的影响还研究甚少。本研究对浙江天目山自然保护区人工幼龄林（30~40年）、 人工老熟林（80~100年）和半天然混合林（>200年）中柳杉枯立木上的腐木甲虫群落及多样性进行比较。结果表明： 半天然混合林腐木甲虫个体数量（97.4±66.7）显著高于幼龄林（39.9±16.3）和老熟林（21.9±5.9）, 但半天然林混合林(27.9±11.2)与幼龄林(24.1±3.7)腐木甲虫物种数差异并不显著(P>0.05), 而幼龄林的腐木甲虫物种数和个体数量则显著高于老熟林(P<0.05)。腐木甲虫物种数和个体数量与样地粗死木残体体积相关性显著(P<0.05)。典范对应分析和多响应置换过程分析表明腐木甲虫群落特征在不同林型间差异显著(P<0.001)。柳杉枯立木直径、 粗死木残体的直径和数量以及林冠盖度均对腐木甲虫物种组成具有显著影响(P<0.05)。腐木甲虫营养级组成分析也表明, 半天然混合林菌食性甲虫数量显著高于种植林(P<0.001)。结果提示, 提高种植林粗死木残体的数量和质量可以增加腐木甲虫的物种丰富度, 但种植林腐木甲虫多样性可能在随后的演替阶段有所下降, 而且种植林与天然林在腐木甲虫群落组成上差异十分明显。     

兴安落叶松老龄林落叶松林木死亡格局以及倒木对更新的影响

对兴安落叶松老龄林落叶松林木死亡格局和死亡木对更新的影响进行了研究 .结果表明 ,丛桦落叶松林和杜香落叶松林的枯立木以中径木占多数 ,赤杨落叶松林主要为中、大径木 ,草类落叶松林主要是中、小径木 .落叶松枯立木主要因火烧、受压和老死而形成 .丛桦落叶松林和赤杨落叶松林掘根倒木较多 .杜香落叶松林和草类落叶松林的倒木以风折为主 .地形、山体走向和盛行风向对树倒方向影响很大 .丛桦落叶松林倒木方向杂乱 ,赤杨落叶松林林木均向东倒下 ,杜香落叶松林和草类落叶松林的掘根木分别向南、东北方倒下 ,两者的风折木倒向随机性较大 .草类落叶松和赤杨落叶松老龄林内 ,倒木更新为 1 8和 40株·m- 2 ,远远高于矿物土基质上 2株·m- 2 的水平 .丛桦落叶松林内倒木和林地上更新均相当好 ,约为 2 8株·m- 2 .杜香落叶松林倒木更新效果不突出 .     

Changes in spatial pattern of trees and snags during structural development in Picea mariana boreal forests

Questions : How do gap abundance and the spatial pattern of trees and snags change throughout stand development in Picea mariana forests? Does spatial pattern differ among site types and structural components of a forest? Location : Boreal forests dominated by Picea mariana, northern Quebec and Ontario, Canada. Methods : Data on the abundance, characteristics and spatial location of trees, snags and gaps were collected along 200 m transects at 91 sites along a chronosequence. Spatial analyses included 3TLQV, NLV and autocorrelation analysis. Non‐parametric analyses were used to analyse trends with time and differences among structural components and site types. Results : Gaps became more abundant, numerous and more evenly distributed with time. At distances of 1–4 m, tree cover, sapling density and snag density became more heterogeneous with time. Tree cover appeared to be more uniform for the 10–33 m interval, although this was not significant. Patch size and variance at 1 m were greater for overstorey than for understorey tree cover. Snags were less spatially variable than trees at 1 m, but more so at intermediate distances (4–8 m). Few significant differences were found among site types. Conclusions : During stand development in P. mariana forest, gaps formed by tree mortality are filled in slowly due to poor regeneration and growth, leading to greater gap abundance and clumping of trees and snags at fine scales. At broader scales, patchy regeneration is followed by homogenization of forest stands as trees become smaller with low productivity due to paludification.     

Coarse woody debris in Australian forest ecosystems: A review

Abstract Coarse woody debris (CWD) is the standing and fallen dead wood in a forest and serves an important role in ecosystem functioning. There have been several studies that include estimates of CWD in Australian forests but little synthesis of these results. This paper presents findings from a literature review of CWD and fine litter quantities. Estimates of forest‐floor CWD, snags and litter from the literature are presented for woodland, rainforest, open forest and tall open forest, pine plantation and native hardwood plantation. Mean mass of forest floor CWD in Australian native forests ranged from 19 t ha^?1 in woodland to 134 t ha^?1 in tall open forest. These values were generally within the range of those observed for similar ecosystems in other parts of the world. Quantities in tall open forests were found to be considerably higher than those observed for hardwood forests in North America, and more similar to the amounts reported for coniferous forests with large sized trees on the west coast of the USA and Canada. Mean proportion of total above‐ground biomass as forest floor CWD was approximately 18% in open forests, 16% in tall open forests, 13% in rainforests, and 4% in eucalypt plantations. CWD can be high in exotic pine plantations when there are considerable quantities of residue from previous native forest stands. Mean snag biomass in Australian forests was generally lower than the US mean for snags in conifer forests and higher than hardwood forest. These results are of value for studies of carbon and nutrient stocks and dynamics, habitat values and fire hazards.     

The role of herbivory by wood-boring insects in mangrove ecosystems in Belize

The roles wood-boring insects play in modifying mangrove ecosystems were examined on small, offshore mangrove islands in Belize. Several species of xylem- and phloem-feeding woodborers consume the wood of living mangrove trees. By girdling, pruning, and hollowing, woodborers killed over 50% of the Rhizophora mangle canopy in experimental plots arrayed across a tidal-elevation gradient. In contrast, leaf-feeding herbivores removed less than 6% of the canopy. In the plots, stem girdlers killed over three branches per tree. The patterns of herbivory by three functional feeding groups were heterogeneous and did not vary consistently with tidal elevation. Because R. mangle lacks viable axillary buds or the ability to produce epicormic shoots to replace pruned branches, the canopy architecture was significantly modified by this damage. The branches that were pruned by stem girdlers created numerous small holes or gaps in the mangrove canopy. Shoot growth and flowering increased in R. mangle trees with 50% of their branches experimentally girdled. Because branches and twigs attacked by woodborers lost their leaves prematurely as greenfall, the quantity and quality of leaf litter were altered when a leaf-bearing branch was girdled or hollowed. These changes suggest that wood-boring insects also significantly affect internal and external nutrient cycling processes in mangrove ecosystems.     

Influence of tree hollow characteristics and forest structure on saproxylic beetle diversity in tree hollows in managed forests in a regional comparison

Tree hollows are among the rarest habitats in today''s Central European managed forests but are considered key structures for high biodiversity in forests. To analyze and compare the effects of tree hollow characteristics and forest structure on diversity of saproxylic beetles in tree hollows in differently structured managed forests, we examined between 41 and 50 tree hollows in beech trees in each of three state forest management districts in Germany. During the two‐year study, we collected 283 saproxylic beetle species (5880 individuals; 22% threatened species), using emergence traps. At small spatial scales, the size of hollow entrance and the number of surrounding microhabitat structures positively influenced beetle diversity, while the stage of wood mould decomposition had a negative influence, across all three forest districts. We utilized forest inventory data to analyze the effects of forest structure in radii of 50–500 m around tree hollows on saproxylic beetle diversity in the hollows. At these larger spatial scales, the three forest management districts differed remarkably regarding the parameters that influenced saproxylic beetle diversity in tree hollows. In Ebrach, characterized by mostly deciduous trees, the amount of dead wood positively influenced beetle diversity. In the mostly coniferous Fichtelberg forest district, with highly isolated tree hollows, in contrast, only the proportion of beech trees around the focal tree hollows showed a positive influence on beetle diversity. In Kelheim, characterized by mixed forest stands, there were no significant relationships between forest structure and beetle diversity in tree hollows. In this study, the same local tree hollow parameters influenced saproxylic beetle diversity in all three study regions, while parameters of forest structure at larger spatial scales differed in their importance, depending on tree‐species composition.     

Micro and macro-habitat associations in saproxylic beetles: implications for biodiversity management

Restoration of habitats is critically important in preventing full realization of the extinction debt owed as a result of anthropogenic habitat destruction. Although much emphasis has been placed on macrohabitats, suitable microhabitats are also vital for the survival of most species. The aim of this large-scale field experiment was to evaluate the relative importance of manipulated microhabitats, i.e., dead wood substrates of spruce (snags, and logs that were burned, inoculated with wood fungi or shaded) and macrohabitats, i.e., stand types (clear-cuts, mature managed forests, and forest reserves) for species richness, abundance and assemblage composition of all saproxylic and red-listed saproxylic beetles. Beetles were collected in emergence traps in 30 forest stands in 2001, 2003, 2004 and 2006. More individuals emerged from snags and untreated logs than from burned and shaded logs, but species richness did not differ among substrates. Assemblage composition differed among substrates for both all saproxylics and red-listed saproxylic species, mainly attributed to different assemblage composition on snags. This suggests that the practise of leaving snags for conservation purposes should be complemented with log supplementation. Clear-cuts supported fewer species and different assemblages from mature managed forests and reserves. Neither abundance, nor species richness or assemblage composition differed between reserves and mature managed forests. This suggests that managed stands subjected to selective cutting, not clear-felling, maintain sufficient old growth characteristics and continuity to maintain more or less intact assemblages of saproxylic beetles. Thus, alternative management methods, e.g., continuity forestry should be considered for some of these stands to maintain continuity and conservation values. Furthermore, the significantly higher estimated abundance per ha of red-listed beetles in reserves underlines the importance of reserves for maintaining viable populations of rare red-listed species and as source areas for saproxylic species in boreal forest landscapes.     

Progression of ash canopy thinning and dieback outward from the initial infestation of emerald ash borer (Coleoptera: Buprestidae) in southeastern Michigan

Our objective was to characterize the rate at which ash (Fraxinus spp.) trees decline in areas adjacent to the leading edge of visible ash canopy thinning due to emerald ash borer, Agrilus planipennis Fairmaire (Coleoptera: Buprestidae). Trees in southeastern Michigan were surveyed from 2003 to 2006 for canopy thinning and dieback by comparing survey trees with a set of 11 standard photographs. Freeways stemming from Detroit in all directions were used as survey transects. Between 750 and 1,100 trees were surveyed each year. A rapid method of sampling populations of emerald ash borer was developed by counting emerald ash borer emergence holes with binoculars and then felling trees to validate binocular counts. Approximately 25% of the trees surveyed for canopy thinning in 2005 and 2006 also were sampled for emerald ash borer emergence holes using binoculars. Regression analysis indicates that 41-53% of the variation in ash canopy thinning can be explained by the number of emerald ash borer emergence holes per tree. Emerald ash borer emergence holes were found at every site where ash canopy thinning averaged > 40%. In 2003, ash canopy thinning averaged 40% at a distance of 19.3 km from the epicenter of the emerald ash borer infestation in Canton. By 2006, the point at which ash trees averaged 40% canopy thinning had increased to a distance of 51.2 km away from Canton. Therefore, the point at which ash trees averaged 40% canopy thinning, a state of decline clearly visible to the average person, moved outward at a rate of 10.6 km/yr during this period.     

Poor effectiveness of Natura 2000 beech forests in protecting forest-dwelling bats

With the establishment of the Natura 2000 (N2000) network, the European Union intends to develop strategies to conserve Europe's threatened habitats and species, including bats. Forest-dwelling bats are highly reliant on forest structures, such as snags and hollow trees, which the bats need as roosts. The decrease in such forest microhabitats significantly affects the habitat use and, therefore, the activity in forests. To determine whether N2000 beech forests under active timber production offer better habitats for bats compared to commercially used non-N2000 forests, we measured the bat activity and assessed the potential roosts in trees and snags in eleven pairs of stands. All survey stands represented mesotrophic beech forests (Fagus sylvatica L.) of the N2000 habitat type 9130 (Asperulo-Fagetum) in three European Biogeographic Regions. The activity of all bat species, the activity of priority N2000 species, the species number, the number of trees with roosts and the snag volume did not differ significantly between the N2000 and non-N2000 stands. We conclude that the current management of the N2000 beech forests is almost identical to that of non-N2000 commercial forests, and thus, the N2000 status has not led to an increase of bat-relevant habitat variables yet. Consequently, additional efforts beyond the administrative assignment of N2000 areas are required to build and ensure an ecologically effective and sustainable network of beech forests in Europe, including increasing important forest requirements for bats, such as roosts and snags.     

Biodiversity conservation in old-growth boreal forest: black spruce and balsam fir snags harbour distinct assemblages of saproxylic beetles

Biodiversity conservation of forest ecosystems strongly relies on effective dead wood management. However, the responses of saproxylic communities to variations in dead wood characteristics remains poorly documented, a lack of knowledge that may impede the development of efficient management strategies. We established the relationship between saproxylic beetles—at the species and community levels—and attributes of black spruce and balsam fir in old-growth boreal forests. The relationship was first evaluated for individual snag bole segments, and then for forest stands. A total of 168 bole sections were collected in summer 2006 along a compositional gradient ranging from black spruce-dominated stands to balsam fir-dominated ones, in a boreal forest dominated by >90-year-old stands. A total of 16,804 beetles belonging to 47 species emerged from bole segments, with 21% of the species being found exclusively in black spruce snags and 36% exclusively in balsam fir snags. Black spruce and balsam fir snags thus contributed differently to forest biodiversity by being inhabited by different saproxylic communities. Wood density was an important attribute in the host-use patterns for several species of saproxylic beetles, but no relationship was found between snag availability within stands and abundance of beetles strongly linked to either black spruce or balsam fir. Our study outlines the relative contribution of tree compositional diversity to saproxylic species, while highlighting the contribution of black spruce and balsam fir to animal diversity in old-growth boreal forests.