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.     

Density, Distribution, and Attributes of Tree Cavities in an Old-Growth Tropical Rain Forest

Tree cavities are a critical resource for many animals, especially as nesting sites for birds. Patterns of cavity distribution in temperate forests are well studied, yet little is known of cavities in tropical forests, despite a hypothesized decrease in cavity availability with decreasing latitude. We studied cavity density and distribution in a wet lowland tropical forest in Costa Rica and compared our results with estimates from forests around the world. Cavities at our site were common, occurred frequently in living trees, and were often formed by damage or decay rather than by woodpeckers. Most cavities had small openings, and woodpecker-created cavities were nonrandomly oriented. Contrary to prediction, cavity density appears to increase from the poles to the tropics. We suggest potential mechanisms to explain these patterns.     

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.     

Animal biomass in a New Zealand forest compared with other parts of the world

Summary Data on mammalian, avian and invertebrate biomass in mixed broadleaf-podocarp forest of the Orongorongo Valley are summarised and compared with the biomass in other forests. Animal biomass totalled at least 504 kg/ha — more than twice that in several tropical forests but less than that reported from temperate deciduous forests of Europe. Earthworms (333 kg/ha) provided most animal biomass: arthropods at least 145 kg/ha, mammals (all introduced) 25 kg/ha, and birds 0.6 kg/ha. By world standards the biomass of mammals, and litter-dwelling and underground arthropods, is high and that of birds moderate. Introduced mammals have greatly altered the distribution of biomass in this forest, herbivores and predatory mammals gaining biomass at the expense of some native aboveground invertebrates and birds, several of which have been lost to this community.     

Species Composition, Diversity and Local uses of Tropical Dry Deciduous and Gallery Forests in Nicaragua

The floristic composition and diversity of tropical dry deciduous and gallery forests were studied in Chacocente Wildlife Refuge, located on the Pacific coast in Nicaragua during 1994 and 2000. Density, dominance and frequency as well as species and family important values were computed to characterize the floristic composition. A variety of diversity measures were also calculated to examine heterogeneity in each forest community. A total of 29 families, 49 genera and 59 species were represented in 2 ha dry deciduous forest. In the gallery forest, the number of families, genera and species recorded in 2000 inventory was 33, 48 and 58, respectively and slightly higher than the 1994 inventory. The number of stems ⩽ 10 cm dbh varied from 451 to 489 per hectare in the deciduous forest, and from 283 to 298 per hectare in the gallery forest. The basal area was much larger for species in the gallery than dry deciduous forest. Fabaceae, sub family Papilionoideae, was the most specious family in the deciduous forest while Meliaceae was the dominant family in the gallery forest. Similarity in species composition and abundance between deciduous and gallery forests was low. In terms of species diversity, the gallery forest was found more diverse than the deciduous forest using Fisher's diversity index. Both forest communities were characterized by a typical inverse J shape. Therefore, emphasis should be given to the protection of rare species, i.e. as the forests are still under continued human pressure, an immediate action should be taken to conserve the remaining flora.     

Ecological importance of large-diameter trees in a temperate mixed-conifer forest

Large-diameter trees dominate the structure, dynamics and function of many temperate and tropical forests. Although both scaling theory and competition theory make predictions about the relative composition and spatial patterns of large-diameter trees compared to smaller diameter trees, these predictions are rarely tested. We established a 25.6 ha permanent plot within which we tagged and mapped all trees ≥1 cm dbh, all snags ≥10 cm dbh, and all shrub patches ≥2 m(2). We sampled downed woody debris, litter, and duff with line intercept transects. Aboveground live biomass of the 23 woody species was 507.9 Mg/ha, of which 503.8 Mg/ha was trees (SD?=?114.3 Mg/ha) and 4.1 Mg/ha was shrubs. Aboveground live and dead biomass was 652.0 Mg/ha. Large-diameter trees comprised 1.4% of individuals but 49.4% of biomass, with biomass dominated by Abies concolor and Pinus lambertiana (93.0% of tree biomass). The large-diameter component dominated the biomass of snags (59.5%) and contributed significantly to that of woody debris (36.6%). Traditional scaling theory was not a good model for either the relationship between tree radii and tree abundance or tree biomass. Spatial patterning of large-diameter trees of the three most abundant species differed from that of small-diameter conspecifics. For A. concolor and P. lambertiana, as well as all trees pooled, large-diameter and small-diameter trees were spatially segregated through inter-tree distances <10 m. Competition alone was insufficient to explain the spatial patterns of large-diameter trees and spatial relationships between large-diameter and small-diameter trees. Long-term observations may reveal regulation of forest biomass and spatial structure by fire, wind, pathogens, and insects in Sierra Nevada mixed-conifer forests. Sustaining ecosystem functions such as carbon storage or provision of specialist species habitat will likely require different management strategies when the functions are performed primarily by a few large trees as opposed to many smaller trees.     

Habitat indicators for cavity-nesters: The polypore Phellinus pini in pine forests

Foresters and arborists have long used fruit-bodies of heart-rot fungi as signs of advanced live-tree decay, but such usage has not been elaborated for forest conservation. I analysed relationships between a heart-rot fungus, tree-cavity supply, and cavity-nesting bird assemblage in wet hemiboreal Scots pine (Pinus sylvestris) forests in Estonia. The focal species, Phellinus pini, is the main heartwood decayer of live pines; it typically forms fruit-bodies at the stage of advanced decay on old trees. I found that the pine wetlands had few tree-cavities (mostly in snags) and cavity-nesting birds (woodpeckers being almost absent) despite abundant snag supply. Only one fruit-body of P. pini was found on cavity-tree but stand-scale abundance of the fruit-bodies correlated well with cavity-nester densities. Multifactor models indicated that cavity formation, not tree death, was the limiting process for secondary cavity-nesters, and P. pini could indeed be used (in combination with old-pine abundance) for assessing their habitat quality. This fungus could also serve as an educational flagship species to bridge conservation biology and forest pathology, and its fruit-bodies can signal trees to be retained at harvesting in pine forests. The conclusion is that there is hope for developing practical indicators to manage for the hidden decay processes that govern tree-cavity development.     

Contribution of Dead Wood to Biomass and Carbon Stocks in the Caribbean: St. John, U.S. Virgin Islands

Dead wood is a substantial carbon stock in terrestrial forest ecosystems and hence a critical component of global carbon cycles. Given the limited amounts of dead wood biomass and carbon stock information for Caribbean forests, our objectives were to: (1) describe the relative contribution of down woody materials (DWM) to carbon stocks on the island of St. John; (2) compare these contributions among differing stand characteristics in subtropical moist and dry forests; and (3) compare down woody material carbon stocks on St. John to those observed in other tropical and temperate forests. Our results indicate that dead wood and litter comprise an average of 20 percent of total carbon stocks on St. John in both moist and dry forest life zones. Island-wide, dead wood biomass on the ground ranged from 4.55 to 28.11 Mg/ha. Coarse woody material biomass and carbon content were higher in moist forests than in dry forests. No other down woody material components differed between life zones or among vegetation categories ( P > 0.05). Live tree density was positively correlated with fine woody material and litter in the moist forest life zone ( R = 0.57 and 0.84, respectively) and snag basal area was positively correlated with total down woody material amounts ( R = 0.50) in dry forest. Our study indicates that DWM are important contributors to the total biomass and, therefore, carbon budgets in subtropical systems, and that contributions of DWM on St. John appear to be comparable to values given for similar dry forest systems.     

西双版纳不同森林类型的树洞密度及其特征

树洞是森林生态系统的重要组成部分,它能为许多动物提供栖息、筑巢、繁殖和躲避天敌的场所。因而,树洞的密度和特征通常被认为是限制树洞巢居动物多样性和丰富度的主要因子,然而目前国内外对热带森林的树洞密度和洞口特征研究较少。选取西双版纳20 hm~2热带森林动态监测样地(包括热带季节雨林和热带山地常绿阔叶林)为研究对象,采用地面观测法调查了所有胸径≥5 cm的活体乔木上的树洞,分析其树洞密度和特征(高度、洞口大小、类型和洞口方位,并探讨树洞在不同森林类型间的差异)。结果表明:(1)热带季节雨林和热带山地常绿阔叶林的树洞密度不存在显著差异;(2)两种森林类型的树洞均以高度较低、洞口较小、干中部洞口为主,受盛行风的影响洞口朝向主要集中在东北方向;(3)树洞高度、类型和洞口方位在两种森林间的分布差异显著(P0.01),而洞口大小不存在明显差异。结果表明森林类型会影响树洞的特征,因而加强森林生境异质性的保护对维持树洞巢居动物的需要具有重要意义。     

Decaying trees improve nesting opportunities for cavity‐nesting birds in temperate and boreal forests: A meta‐analysis and implications for retention forestry

Many studies have dealt with the habitat requirements of cavity‐nesting birds, but there is no meta‐analysis on the subject and individual study results remain vague or contradictory. We conducted a meta‐analysis to increase the available evidence for nest‐site selection of cavity‐nesting birds. Literature was searched in Web of Science and Google Scholar and included studies that provide data on the habitat requirements of cavity‐nesting birds in temperate and boreal forests of varying naturalness. To compare nest and non‐nest‐tree characteristics, the following data were collected from the literature: diameter at breast height (DBH) and its standard deviation (SD), sample size of trees with and without active nest, amount of nest and available trees described as dead or with a broken crown, and amount of nest and available trees that were lacking these characteristics. Further collected data included bird species nesting in the cavities and nest‐building type (nonexcavator/excavator), forest type (coniferous/deciduous/mixed), biome (temperate/boreal), and naturalness (managed/natural). From these data, three effect sizes were calculated that describe potential nest trees in terms of DBH, vital status (dead/alive), and crown status (broken/intact). These tree characteristics can be easily recognized by foresters. The results show that on average large‐diameter trees, dead trees, and trees with broken crowns were selected for nesting. The magnitude of this effect varied depending primarily on bird species and the explanatory variables forest type and naturalness. Biome had lowest influence (indicated by ΔAIC). We conclude that diameter at breast height, vitality, and crown status can be used as tree characteristics for the selection of trees that should be retained in selectively harvested forests.     

Beyond the tropics: forest structure in a temperate forest mapped plot

Question: How do the diversity, size structure, and spatial pattern of woody species in a temperate (Mediterranean climate) forest compare to temperate and tropical forests? Location: Mixed evergreen coastal forest in the Santa Cruz Mountains, California, USA. Methods: We mapped, tagged, identified, and measured all woody stems (≥1 cm diameter) in a 6‐ha forest plot, following Center for Tropical Forest Science protocols. We compared patterns to those found in 14 tropical and 12 temperate forest plots. Results: The forest is dominated by Douglas‐fir (Pseudotsuga menziesii) and three species of Fagaceae (Quercus agrifolia, Q. parvula var. shrevei, and Lithocarpus densiflorus), and includes 31 woody species and 8180 individuals. Much of the diversity was in small‐diameter shrubs, treelets, and vines that have not been included in most other temperate forest plots because stems <5‐cm diameter had been excluded from study. The density of woody stems (1363 stems ha^?1) was lower than that in all but one tropical plot. The density of large trees (diameter ≥30 cm) and basal area were higher than in any tropical plot. Stem density and basal area were similar to most other temperate plots, but were less than in low‐diversity conifer forests. Rare species were strongly aggregated, with the degree of aggregation decreasing with abundance so that the most common species were significantly more regular than random. Conclusions: The patterns raise questions about differences in structure and dynamics between tropical and temperate forests; these need to be confirmed with additional temperate zone mapped plots that include small‐diameter individuals.     

Pattern of changes in species diversity,structure and dynamics of forest ecosystems along latitudinal gradients in East Asia

We examined effects of seasonality of climate and dominant life form (evergreen/deciduous, broad-leaf/coniferous) together with energy condition on species diversity, forest structure, forest dynamics, and productivity of forest ecosystems by comparing the patterns of changes in these ecosystem attributes along altitudinal gradients in tropical regions without seasonality and along a latitudinal gradient from tropical to temperate regions in humid East Asia. We used warmth index (temperature sum during growing season, WI) as an index of energy condition common to both altitudinal and latitudinal gradients. There were apparent differences in patterns of changes in the ecosystem attributes in relation to WI among four forest formations that were classified according to dominant life form and climatic zone (tropical/temperate). Many of the ecosystem attributes—Fishers alpha of species-diversity indices, maximum tree height and stem density, productivity [increment rate of aboveground biomass (AGB)], and population and biomass turnover rates—changed sharply with WI in tropical and temperate evergreen broad-leaved forests, but did not change linearly or changed only loosely with WI in temperate deciduous broad-leaved and evergreen coniferous forests. Values of these ecosystem attributes in temperate deciduous broad-leaved and evergreen coniferous forests were higher (stem density was lower) than those in tropical and temperate evergreen broad-leaved forests under colder conditions (WI below 100°C). Present results indicate that seasonality of climate and resultant change in dominant life form work to buffer the effects of energy reduction on ecosystem attributes along latitudinal gradients.     

Enhancing bark- and wood-boring beetle colonization and survival in vertical deadwood during thinning entries

Snags are used as habitat by several organisms, including bark- and wood-boring beetles, which contribute to snag decomposition and facilitate subsequent snag colonization by other organisms. However, snags seldom occur in young managed forests. This study examines how snag characteristics and spatial arrangement affect bark- and wood-boring beetle colonization and survival in spruce plantations subjected to commercial thinning, thinning with biomass removal and thinning with snag creation where a few clumps of trees were girdled. To this end, we documented the volume of snags, their characteristics and the number of beetle emergence holes in their basal section. Beetle colonization and survival to adulthood in snags was ~33 times greater when expressed per unit area in plantations supplemented with clumps of girdled trees than in other thinning regimes where low densities of beetle emergence holes per hectare were documented. Snag diameter at breast height, snag species and thinning treatments influenced the number of emergence holes per snag. Positive spatial autocorrelation between the abundance of emergence holes per snag was detected but no other spatial effect was noticeable. This work suggests that vertical deadwood is a limiting factor for bark- and wood-boring beetle colonization within plantations and challenges current thinking about the effect of thinning on beetle communities that was developed from window trap studies. These results underline the importance of large diameter snags for beetle conservation within managed forests and demonstrate that tree girdling during thinning entries is a viable method for creating snags to enhance beetle colonization and survival.     

Diversity and community composition of ectomycorrhizal fungi in a dry deciduous dipterocarp forest in Thailand

Large forest areas of South-East Asia, are dominated by the Dipterocarpaceae tree family, which contains many important timber species. Unlike many other tropical trees, Dipterocarpaceae rely on ectomycorrhizal (ECM) root symbiosis for their mineral nutrition. This study aims to document the richness and community composition of ECM fungi in a dry deciduous forest in Thailand. Combining morphological and molecular identification methods revealed 69 species of ECM fungi that belong to 17 phylogenetic lineages. The /russula-lactarius, /tomentella-thelephora, /sordariales, /sebacina and /cantharellus lineages were the most species-rich. The fungal richness is comparable to other tropical rain forest sites, but the phylogenetic community structure has elements of both tropical and temperate ecosystems. Unlike tropical rain forests, the Cenococcum geophilum complex was one of the most frequent fungal taxa that had a relatively high ITS genetic diversity over the small sampling area. This study provides the first snapshot insight into the fungal community of dry dipterocarp forests. However, it is necessary to broaden the spatial and temporal scales of sampling to improve our understanding of the below-ground relations of dry and humid tropical forests.     

滇南勐宋热带山地雨林木质藤本多样性研究

调查滇南勐宋山地雨林沟谷与坡地两种生境中木质藤本种的丰富度、径级分布、攀缘方式以及样地中被藤本缠绕的树木(dbh≥5cm)的数量和比率。结果表明:沟谷与坡地胸径≥1cm的木质藤本平均密度分别为95.7株/0.1hm2、57株/0.1hm2。调查样地内木质藤本共64种,隶属30个科。茎缠绕是最主要的攀缘方式,占总个体数的57%,卷须缠绕种所占比重最小,仅占3%;沟谷与坡地所调查树木被木质藤本缠绕的比例分别为43.7%和28.6%。与亚洲其它热带地区森林相比,勐宋地区藤本的多样性低,但是木质藤本的密度相当高,并且在一些样地中出现了大型木质藤本,这些可能与该地区森林的演替状态有关。     

Odocoileus virginianus diet (Artiodactyla: Cervidae) in a temperate forest of Northern Oaxaca, Mexico

The Sierra Madre de Oaxaca region, located in the Northern state of Oaxaca, Mexico, is an area of forest ecosystems subject to high exploitation rates, although in some areas its temperate forests are conserved by indigenous community initiatives that live there. We analyzed the diet of white tailed-deer (Odocoileus virginianus) in the localities of Santa Catarina Lachatao and San Miguel Amatlán from June 1998 to August 1999. Sampling was done during both the wet and dry seasons, and included the observation of browsing traces (238 observations), microhistological analysis of deer feces (28 deer pellet-groups), and two stomach content analysis. The annual diet of white-tailed deer was composed of 42 species from 23 botanical families. The most represented families in the diet of this deer were Fagaceae, Asteraceae, Ericaceae and Fabaceae. There were significant differences in the alpha diversity of the diet during the wet and dry seasons (H'=2.957 and H'=1.832, respectively). The similarity percentage between seasons was 56%. Differences in plant species frequency were significantly higher during the wet season. Herbaceous plants made up the greatest percentage of all the species consumed. The preferred species throughout the year were Senecio sp. (shrub), Sedum dendroideum (herbaceous), Arctostaphylos pungens (shrub) and Satureja macrostema (shrub). Diet species richness was found to be lower than that observed in a tropical forest (Venezuela), tropical dry forest (Mexico) and temperate deciduous and mixed forest (Mexico), but similar to the diet species richness observed in a tropical dry forest (Costa Rica) and temperate coniferous and deciduous forests (USA).     

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.     

西双版纳热带森林树洞丰富度及其分配特点

树洞是森林生态系统的重要结构,对动物多样性的维持起着重要作用。为研究热带森林树洞的数量特征及其分配特点,选取西双版纳20hm2热带森林动态监测样地为研究对象,采用地面观测法调查了样地内所有胸径≥5cm活立木上的树洞。结果表明:(1)该样地森林的树洞密度为108.4个·hm-2,具有树洞的树1725株(占树木总数的6.22%),隶属于208个种;(2)树木个体的树洞数量随径级增加而增加,并在种间变化不均匀;(3)树木出现空心的概率随胸径级的增加而显著增加,并且在树种间存在显著差异;(4)与其他纬度地区森林的树洞密度比较,本研究结果支持了Boyle等(2008)提出的低纬度森林具有较高树洞密度的推测。     

The role of body size in nest-site selection by secondary cavity-nesting birds in a subtropical Chaco forest

Most bird species that nest in tree cavities globally occur in diverse assemblages in little-studied tropical and subtropical forests which have high rates of habitat loss. Conservation of these communities will require an understanding of how species traits, such as body size, influence nest-site selection. We examined patterns of nest-site selection of secondary cavity-nesting birds at the nest patch, tree and cavity scale, and investigated how these patterns are influenced by body size. Using conditional logistic regression, we compared characteristics of 155 nest tree cavities paired with 155 unused tree cavities in quebracho Schinopsis balansae forests in Chaco National Park, Argentina (2016–2018). The odds of a cavity being used for nesting increased with its depth and height above ground, decreased with entrance size, and were greater for dead trees than live. Small-bodied (13–90 g) species used floor diameters in proportion to availability, but medium- (150–200 g) and large-bodied (400–700 g) species selected cavities with larger floors. Model selection indicated that characteristics at the nest patch scale (canopy cover, tree density) had little effect on nest-site selection when cavity-scale variables were included. Cavity floor diameter, entrance size, cavity height and tree diameter (but not cavity depth) increased with body mass, and larger bird species more often used live trees. Two tree species proved to be key for the community: large and medium-sized birds used almost exclusively large live Schinopsis balansae, whereas small birds used live and dead Prosopis spp. in a proportion greater than its availability. Small birds could be differentiated according to species-specific cavity characteristics, but medium and large species overlapped considerably with one another. Although body mass explained much of the overall variation in tree and cavity characteristics between small and medium/large species, several small-bodied species consistently used cavities outside of the expected characteristics for their body size, suggesting that other natural history traits may play important roles in nest-site selection by small-bodied birds. To retain the full suite of secondary cavity-nesters in species-rich tropical and subtropical forests, it is necessary to conserve a diversity of trees and cavities that meet the full range of nesting requirements of these trait-diverse communities.