Consequences of forest fragmentation in an understory plant community: extensive range expansion of native dwarf bamboo

Understory bamboo species are important and influential components of temperate forests in at least several parts of the world. Here we report a study testing the effect of forest fragmentation on the dynamics of the dwarf bamboo Sasa chartacea and on forest herb communities in the Tokachi plain of Hokkaido, Japan. We studied 16 forest fragments of different sizes and small plots established in these fragments to examine the relationship between the abundance of S. chartacea, landscape and environmental conditions, and forest herb communities. Sasa chartacea was more abundant near forest edges and in smaller fragments, suggesting that the species has expanded its local range and increased its abundance in response to forest fragmentation. Edge‐related changes in light and soil moisture might have facilitated this range expansion. The species richness of forest herbs was strongly negatively related to the density of S. chartacea. Because much larger variation in species richness was explained by S. chartacea density than distance to the nearest forest edge, the expansion of S. chartacea has likely excluded other understory species by competition. In addition, the density of S. chartacea significantly explained variation in the species composition of forest herbs across plots. Taken together, our results emphasize the key roles of dwarf bamboos in changing plant communities following forest fragmentation.     

Environmental correlates of plant diversity in Korean temperate forests

Mountainous areas of the Korean Peninsula are among the biodiversity hotspots of the world's temperate forests. Understanding patterns in spatial distribution of their species richness requires explicit consideration of different environmental drivers and their effects on functionally differing components. In this study, we assess the impact of both geographical and soil variables on the fine-scale (400 m²) pattern of plant diversity using field data from six national parks, spanning a 1300 m altitudinal gradient. Species richness and the slopes of species–area curves were calculated separately for the tree, shrub and herb layer and used as response variables in regression tree analyses. A cluster analysis distinguished three dominant forest communities with specific patterns in the diversity–environment relationship. The most widespread middle-altitude oak forests had the highest tree richness but the lowest richness of herbaceous plants due to a dense bamboo understory. Total richness was positively associated with soil reaction and negatively associated with soluble phosphorus and solar radiation (site dryness). Tree richness was associated mainly with soil factors, although trees are frequently assumed to be controlled mainly by factors with large-scale impact. A U-shaped relationship was found between herbaceous plant richness and altitude, caused by a distribution pattern of dwarf bamboo in understory. No correlation between the degree of canopy openness and herb layer richness was detected. Slopes of the species–area curves indicated the various origins of forest communities. Variable diversity–environment responses in different layers and communities reinforce the necessity of context-dependent differentiation for the assessment of impacts of climate and land-use changes in these diverse but intensively exploited regions.     

Effects of dwarf bamboo, Fargesia nitida (Mitford) Keng f. ex Yi, on bark stripping by ungulates in a subalpine Abies faxoniana Rehder & E. H. Wilson forest, southwest China

Incidence and intensity of bark stripping of trees by ungulates was investigated at no bamboo (Fargesia nitida (Mitford) Keng f. ex Yi) (B-) site and understory bamboo dominant (B+) site of a subalpine Abies faxoniana Rehder & E. H. Wilson forest, southwest China. The percentage of damaged trees in B-site was higher than in B+ site. Bark stripping obviously occurred more frequently on Abies faxoniana compared to other tree species. Appearance of stripped bark and dead stems of the trees in different size-classes of A. faxoniana strongly depended on the density of dwarf bamboo at the site, and also on the size and bark structure of the trees, with highest damage rates occurring on the smaller DBH classes (10–40 cm) in B-site. The bark stripping intensity of A. faxoniana decreased significantly with higher density and coverage of F. nitida around damaged trees. Therefore, there is an indirect negative effect of the distribution of dwarf bamboo, F. nitida, on bark stripping of tree species. We suggest the indirect effects of dwarf bamboo species should be taken into account while considering the succession and regeneration of natural forests.     

Multivariate path analysis of the relationships between seedling regeneration and environmental factors beneath a dwarf bamboo understory

Seedling emergence and establishment are fragile processes that determine the direction and structure of forest succession and regeneration. However, seedling emergence and establishment are easily affected by biotic and abiotic (environmental) factors. A dense and expanding understory of dwarf bamboo is one such important factor that can seriously hinder the seedling regeneration. We conducted a field experiment to investigate the emergence and establishment of canopy tree seedlings under artificially controlled densities of dwarf bamboo. We found that understory dwarf bamboo obstructed seedling emergence but reduced the death of seedlings. Although understory dwarf bamboo reduced the median retention time of seedlings, dense bamboo increased the mean survival time of seedlings. Our results suggest that understory dwarf bamboo has multiple selectivities for tree seedling emergence and establishment: high‐density dwarf bamboo was beneficial to evergreen species but lower‐density of bamboo was conducive to the survival of deciduous species, it means the dwarf bamboo potentially alters successional trajectories of forest communities. Path analysis revealed that the most important factors affecting tree seedling emergence and death were the abundance of seeds in the seed bank and the density of emerged seedlings, and that the soil temperature promoted seedling emergence but increased seedling death, the thickness of litter limited seedling emergence, and the leaf area index of the bamboo canopy limited seedling death. The present study suggests that dwarf bamboo can directly alter the microenvironment, significantly reducing light levels and soil temperature but increasing the thickness of litter and soil humus, thereby indirectly impacting the regeneration of tree seedlings. Our results indicate that various factors affected seedling emergence, and there were complex indirect relationships among these factors. In general, biological factors had a stronger influence on tree seedling regeneration than environmental factors.     

Does plant diversity increase top–down control of herbivorous insects in tropical forest?

Higher trophic level interactions are key mediators of ecosystem functioning in tropical forests. A rich body of theory has been developed to predict the effects of plant diversity on communities at higher trophic levels and the mechanisms underlying such effects. The 'enemies hypothesis’ states that predators exert more effective top–down control of herbivorous insects with increasing plant diversity. Support for this hypothesis has been found in temperate forests and agroecosystems, but remains understudied in tropical forests. We compared incidence of attacks of different natural enemies using artificial caterpillars in a tropical forest landscape and investigated the role of plant community structure (i.e. species richness, composition and density), and the role of forest fragmentation (i.e. patch size, edge distance and canopy openness) on predation intensity. Plant community effects were tested with respect to three vegetation strata: trees, saplings and herbs. Observed predation was substantially due to ants. Predation rates increased with plant species richness for trees and herbs. Density of saplings, herb cover and herb species composition were important factors for predation. No significant patterns were found for fragmentation parameters, suggesting that forest fragmentation has not altered predation intensity. We conclude that in tropical forests, top–down control of herbivorous insects in the understory vegetation is affected by a combination of plant diversity, plant species composition and structural features of the plant community.     

不同林分类型毛竹林节肢动物群落的多样性与稳定性

通过2001年9月到2002年7月对毛竹Phyllostachys heterocycla cv. pubescens与杉木Cunninghamia lanceolata、毛竹与马尾松Pinus massoniana、毛竹与阔叶树种混交林和毛竹纯林中节肢动物群落的定位与跟踪调查,分析和比较了上述4种不同类型林分中节肢动物群落的多样性与稳定性。结果表明：竹阔混交林中节肢动物群落的丰富度显著高于其他2种混交林和毛竹纯林,主要体现为林下层中同翅目、半翅目、鞘翅目和双翅目及竹冠层中蜱螨目、同翅目、半翅目和鞘翅目等植食性或捕食性物种明显较多;但各类林分中节肢动物群落之间的物种多样性、均匀度和优势集中性无显著差异。总体上混交林竹冠层和林下层中植食性和捕食性功能群的共有种较多,两个层次间的相似性均高于毛竹纯林。不同林分类型中节肢动物群落的稳定性具有显著差异,竹阔混交林和毛竹纯林竹冠层节肢动物类群的稳定性低,天敌对害虫的控制作用小,毛竹叶部植食性螨类和蠕须盾蚧Kuwanaspis vermiformis危害较重。因此认为在两种（类）害虫常发区,可考虑将林分改造为竹杉混交林或竹松混交林。     

Modern analogues from the Southern Urals provide insights into biodiversity change in the early Holocene forests of Central Europe

Aim The diversity changes that occurred in Central European forests during the early Holocene can be better understood using ecological knowledge of modern analogues of these forests, which occur in far Eastern Europe. Here we compare the diversity of vascular plants, bryophytes and snails among different forest types of the Southern Urals to provide insights into the palaeoecology of the vanished Central European forests. Location Southern Ural Mountains, Bashkortostan, Russia. Methods We recorded all species of vascular plants, ground-dwelling bryophytes and land snails, and measured biotic and abiotic variables, in 100-m² plots located in four forest types dominated by different trees: Pinus sylvestris–Larix sibirica, Betula pendula–Populus tremula, Quercus robur and Acer platanoides–Tilia cordata–Ulmus glabra. These types correspond to the chronosequence of forest communities that occurred in Central Europe in the early Holocene. Results The species richness of herb-layer plants was most affected by the canopy-transmitted light. The former three forest types had open canopy and were rich in species, whereas the Acer–Tilia–Ulmus forests were darker and poor in species. The species richness of ground-dwelling bryophytes decreased from coniferous to broad-leaved deciduous forests. In contrast, the highest species richness of snails was in the Acer–Tilia–Ulmus forests owing to the higher calcium content in the litter of these trees. Main conclusions Based on the modern analogue of the Southern Ural forests, we propose the hypothesis that the late-glacial open-canopy pine and larch forests of Central European lowlands were rich in light-demanding species of vascular plants, many of which were also typical of tall-grass steppes or mesic grasslands. They also contained several species of ground-dwelling bryophytes. The spread of birch, aspen and oak in the early Holocene reduced the local species richness of ground-dwelling bryophytes but not of vascular plants. The subsequent spread of elm, lime, maple and ash caused canopy closure, a retreat of the light-demanding herbs and a decline in the local species richness of vascular plants. Besides the increased shading by these tree species, their litter enriched soils in calcium, and enhanced decomposition and nutrient cycling. This supported an increase in the species richness of land snails.     

Factors influencing the distribution and growth of dwarf bamboo, <Emphasis Type="Italic">Fargesia nitida</Emphasis>, in a subalpine forest in Wolong Nature Reserve,southwest China

Dwarf bamboos impose intense resource competition in subalpine coniferous forests, and their exclusive densities have crucial impacts on tree regeneration and understory species diversity. We studied the factors influencing the distribution and growth of dwarf bamboo, Fargesia nitida, in a subalpine forest in southwest China. TWINSPAN, based on an attribute matrix, could divide the subalpine forest into 11 sub-associations, and more clearly reflected ecological functional features of the subalpine forest than analysis based on a species matrix. TWINSPAN was also generally consistent with DCA ordination based on the attribute matrix. DCA and DCCA ordination showed relationships between the distribution of F. nitida population and environment factor. The first DCCA axis showed topography and disturbance gradients (except fallen trees and broken branches); the second DCCA axis showed canopy density and composition gradients. Stepwise multiple regression analyses showed that distribution (culm density and coverage) of F. nitida decreased significantly with landslide and slope aspect, and increased significantly with soil status. The light condition had positive effects on growth and size of bamboo. A stable environment in the northern slope and more broadleaved species dominating in canopy would increase the dwarf bamboo biomass. Thus, the disturbance regimes, the slope aspect and the BA of evergreen conifer trees can provide useful guidelines for the control and management of F. nitida populations, and in helping to understand the succession and regeneration of subalpine forest in this region.     

Leaf phenology in relation to canopy closure in southern Appalachian trees

Leaf phenology varies markedly across tree species of temperate deciduous forests. Early leafing in spring may increase light capture and carbon gain prior to canopy closure, allowing saplings to survive in understory sites deeply shaded in midsummer. We quantified sapling leaf phenology for 18 tree species and seasonal variation in understory light availability at three sites along a ridge-slope-cove landform gradient in the Great Smoky Mountains National Park. Early leafing species (e.g., Aesculus flava, Carpinus caroliniana) broke bud an average of 24 d before late leafers (e.g., Magnolia fraseri, Nyssa sylvatica). Canopy closure occurred 14-18 d earlier and summer understory light was on average 63-74% lower on intermediate and mesic sites than on the xeric site. Early leafing species intercepted 45-80% of their growing season photon flux before canopy closure vs. 8-15% for late leafers. However, earlier leafing increased exposure to freezing temperatures by 5.5% per week near the mean time of bud break. Early leafing is strongly correlated with midsummer shade, risk of freezing temperatures, and distribution on mesic sites across a "main spectrum" of 15 deciduous species. Differences in leaf phenology and resultant impacts on spring carbon gain may help determine tree shade tolerance and distribution in southern Appalachian forests.     

Structural diversity and representativeness of forest vegetation in a protected area of Kumaun Himalaya, India: implications for conservation

Forest vegetation of a Protected Area (Askot Wildlife Sanctuary) in Kumaun (west Himalaya) was analysed for structure, composition and representativeness. A high percentage of non-natives was noticed in herbaceous flora of all representative forest types. Floristic representativeness in all growth forms (tree, shrub and herbs) increased significantly (tree, p<0.05; shrub and herbs, p<0.01) with altitude. The population structures of trees suggest, (i) expansion of riverine and Pinus roxburghii forests; (ii) compositional changes in Quercus leucotrichophora and Quercus lanuginosa forests, largely owing to preferred extraction demand of inhabitants; and (iii) infrequent regeneration and declining population of Quercus semecarpifolia and Abies pindrow forests. The possible pathways of non-native introduction in the study area were examined. Considering the existing status of forest vegetation and future trends, proliferation of non-native species in most forest types was discussed. It is suggested that the compositional changes vis-a`-vis proliferation of non-native species need priority attention while initiating conservation activities in the reserve.     

Rainforest expansion reduces understorey plant diversity and density in open forest of eastern Australia

The expansion of rainforest pioneer trees into long‐unburnt open forests has become increasingly widespread across high rainfall regions of Australia. Increasing tree cover can limit resource availability for understorey plant communities and reduce understorey diversity. However, it remains unclear if sclerophyll and rainforest trees differ in their competitive exclusion of understory plant communities, which contain most of the floristic diversity of open forests. Here, we examine dry open forest across contrasting fire histories (burnt and unburnt) and levels of rainforest invasion (sclerophyll or rainforest midstorey) to hindcast changes in understorey plant density, richness and composition. The influence of these treatments and other site variables (midstorey structure, midstorey composition and soil parameters) on understorey plant communities were all examined. This study is the first to demonstrate significantly greater losses of understorey species richness, particularly of dry open‐forest specialists, under an invading rainforest midstorey compared to a typical sclerophyll midstorey. Rainforest pioneers displaced over half of the understorey plant species, and reduced ground cover and density of dry forest specialists by ~90%. Significant understorey declines also occurred with increased sclerophyll midstorey cover following fire exclusion, although losses were typically less than half that of rainforest‐invaded sites over the same period. Understorey declines were closely related to leaf area index and basal area of rainforest and wattle trees, suggesting competitive exclusion through shading and potentially belowground competition for water. Around 20% of displaced species lacked any capacity for population recovery, while transient seed banks or distance‐limited dispersal may hinder recovery for a further 68%. We conclude that rainforest invasion leads to significant declines in understorey plant diversity and cover in open forests. To avoid elimination of local native plant populations in open forests, fires should occur with sufficient frequency to prevent overstorey cover from reaching a level where shade‐intolerant species fail to thrive.     

Strong leaf morphological, anatomical, and physiological responses of a subtropical woody bamboo (Sinarundinaria nitida) to contrasting light environments

Dwarf bamboos are an important understory component of the lowland and montane forests in the subtropical regions of Asia and South America, yet little is known about their physiology and phenotypic plasticity in response to changing light environments. To understand how bamboo species adapt to different light intensities, we examined leaf morphological, anatomical, and physiological differentiation of Sinarundinaria nitida (Mitford) Nakai, a subtropical woody dwarf bamboo, growing in open and shaded natural habitats in the Ailao Mountains, SW China. Compared with leaves in open areas, leaves in shaded areas had higher values in leaf size, specific leaf area, leaf nitrogen, and chlorophyll concentrations per unit area but lower values in leaf thickness, vein density, stomatal density, leaf carbon concentration, and total soluble sugar concentration. However, stomatal size and leaf phosphorus concentration per unit mass remained relatively constant regardless of light regime. Leaves in the open habitat exhibited a higher light-saturated net photosynthetic rate, dark respiration rate, non-photochemical quenching, and electron transport rate than those in the shaded habitat. The results of this study revealed that the bamboo species exhibited a high plasticity of its leaf structural and functional traits in response to different irradiances. The combination of high plasticity in leaf morphological, anatomical, and physiological traits allows this bamboo species to grow in heterogeneous habitats.     

Trait variation and functional diversity maintenance of understory herbaceous species coexisting along an elevational gradient in Yulong Mountain,Southwest China

Characterizing trait variation across different ecological scales in plant communities has been viewed as a way to gain insights into the mechanisms driving species coexistence. However, little is known about how changes in intraspecific and interspecific traits across sites influence species richness and community assembly, especially in understory herbaceous communities. Here we partitioned the variance of four functional traits (maximum height, leaf thickness, leaf area and specific leaf area) across four nested biological scales: individual, species, plot, and elevation to quantify the scale-dependent distributions of understory herbaceous trait variance. We also integrated the comparison of the trait variance ratios to null models to investigate the effects of different ecological processes on community assembly and functional diversity along a 1200-m elevational gradient in Yulong Mountain. We found interspecific trait variation was the main trait variation component for leaf traits, although intraspecific trait variation ranged from 10% to 28% of total variation. In particular, maximum height exhibited high plasticity, and intraspecific variation accounted for 44% of the total variation. Despite the fact that species composition varied across elevation and species richness decreased dramatically along the elevational gradient, there was little variance at our largest (elevation) scale in leaf traits and functional diversity remained constant along the elevational gradient, indicating that traits responded to smaller scale influences. External filtering was only observed at high elevations. However, strong internal filtering was detected along the entire elevational gradient in understory herbaceous communities, possibly due to competition. Our results provide evidence that species coexistence in understory herbaceous communities might be structured by differential niche-assembled processes. This approach--integrating different biological scales of trait variation--may provide a better understanding of the mechanisms involved in the structure of communities.     

Forest plant community as a driver of soil biodiversity: experimental evidence from collembolan assemblages through large‐scale and long‐term removal of oak canopy trees Quercus petraea

Plant–soil interactions are increasingly recognized to play a major role in terrestrial ecosystems functioning. However, few studies to date have focused on slow dynamic ecosystems such as forests. As they are vertically stratified by multiple vegetation strata, canopy tree removal by thinning operations could alter forest plant community through tree canopy opening. Very little is known about cascading effects on soil biodiversity. We conducted a large‐scale, multi‐site assessment of collembolan assemblage response to long‐term canopy tree removal in sessile oak Quercus petraea temperate forests. A total of 33 experimental plots were studied covering a large gradient of canopy tree basal area, stand age and local abiotic contexts. Collembolan abundance strongly declined with canopy tree removal in early forest successional stage and this was mediated by negative effect of understory plant community composition changes, i.e. shift from moss and forb to tree seedling, fern, shrub and grass species. Negative effect of this composition shift on collembolan species richness was largely offset by positive effect of the increase in understory plant species richness. This gives support to both the plant mass‐ratio and functional diversity hypotheses. Collembolan functional groups had contrasting response patterns, which were mediated by different ecological factors. Epedaphic (r‐strategist) abundance and species richness increased with canopy tree removal in relation with the increase in understory plant species richness. In contrast, euedaphic (K‐strategist) abundance and species richness declined with canopy tree removal in early forest successional stage in relation with changes in understory plant community composition and species richness, as well as microclimatic conditions. Overall, our study provides experimental evidence that forest plant community can be a strong driver of collembolan assemblages. It also emphasizes the role of trees as foundation species of forest ecosystems that can shape soil biodiversity through their regulation of understory plant community and ecosystem abiotic conditions.     

Hydraulic architecture of evergreen broad-leaved woody plants at different successional stages in Tiantong National Forest Park,Zhejiang Province,China

Aims Hydraulic architecture is a morphological strategy in plants to transport water in coping with environmental conditions. Change of hydraulic architecture for plants occupying different canopy layers within community and for the same plant at different successional stages reflect existence and adaptation in plant's water transportation strategies. The objective of this study was to examine how hydraulic architecture varies with canopy layers within a community and with forest succession.Methods The study site is located in Tiantong National Forest Park, Zhejiang Province, China. Hydraulic architectural traits studied include sapwood-specific hydraulic conductivity, leaf-specific hydraulic conductivity, Huber value, sapwood channel area of twigs, total leaf area per terminal twig, and water potential of twigs. We measured those traits for species that occur in multiple successional stages (we called it "overlapping species") and for species that occur only in one successional stage (we called it "turnover species") along a successional series of evergreen broadleaved forests. For a given species, we sampled both overstory and understory trees. Hydraulic architectural traits between overstory and understory trees in the same community and at successional stages were compared. Pearson correlation was used to exam the relationship between hydraulic architectural traits and the twig/leaf traits.Important findings Sapwood-specific hydraulic conductivities and leaf-specific hydraulic conductivities were significantly higher in overstory trees than those in understory trees, but did not significantly differ from successional stages. Huber value decreased significantly for understory trees, but did not change for overstory trees through forest successional stages. For overstory trees, a trend of decreasing sapwood-specific hydraulic conductivity was observed for overlapping species but not for turnover species with successional stages. In contrast, for understory trees, a trend of decreasing Huber values was observed for turner species but not for overlapping species with successional stages. Across tree species, sapwood-specific hydraulic conductivity was positively correlated with sapwood channel area and total leaf area per terminal twig size. Huber value was negatively correlated to water potential of twigs and total leaf area per terminal twig size. These results suggest that water transportation capacity and efficiency are higher in overstory trees than in understory trees across successional stages in evergreen broadleaved forests in Tiantong region. The contrasting trends of sapwood-specific hydraulic conductivity between overlapping species and turnover species indicate that shift of microenvironment conditions might lead to changes of hydraulic architecture in overstory trees, whereas species replacement might result in changes of hydraulic architecture in understory trees.     

浙江天童常绿阔叶林不同演替阶段木本植物的水力结构特征

水力结构是植物应对环境形成的与水分运输相关的形态策略.探索不同演替阶段和群落不同高度层植物的水力结构特征, 有助于理解植物的水分运输和利用策略.该研究以浙江天童常绿阔叶林演替前中后期群落的上层木(占据林冠层的树种)和下层木(灌木层物种)为对象, 测定了演替共有种(至少存在于两个演替阶段的物种)和更替种(仅存在于某一演替阶段的物种)的枝边材比导率,叶比导率和胡伯尔值, 以及边材疏导面积,末端枝总叶面积和枝条水势, 分析植物水力结构在群落上层木和下层木间以及在演替阶段间的差异, 及其与枝叶性状的相关关系.结果显示: (1)上层木植物边材比导率和叶比导率显著高于下层木植物(p < 0.05); (2)上层木和下层木的边材比导率与叶比导率在演替阶段间均无显著差异(p > 0.05); 上层木的胡伯尔值在演替阶段间无显著差异, 下层木的胡伯尔值随演替显著下降(p < 0.05); (3)上层木共有种仅边材比导率随演替进行显著降低(p < 0.05), 更替种的3个水力结构参数在演替阶段间无显著差异; 下层木共有种水力结构参数在演替阶段间无明显差异, 更替种仅胡伯尔值随演替减小(p < 0.05); (4)植物边材比导率与枝疏导面积和末端枝所支撑的总叶面积显著正相关(p < 0.01), 胡伯尔值与枝条水势及末端枝总叶面积显著负相关(p < 0.01).以上结果表明: 天童常绿阔叶林演替各阶段上层木比下层木具有更大的输水能力和效率; 随着演替进行, 上层木与下层木的共有种和更替种边材比导率的相反变化表明上层木水力结构的变化可能由微生境变化引起, 而下层木水力结构特征的变化可能由物种更替造成.     

On the significance of belowground overyielding in temperate mixed forests: separating species identity and species diversity effects

Complementary soil exploration by the root systems of coexisting tree species has been hypothesised to result in a higher root biomass of mixed forests than of monocultures but the existing evidence for a belowground diversity effect in forests is scarce and not conclusive. In a species‐rich temperate broad‐leaved forest, we analysed the fine root biomass (roots ≤ 2 mm) and necromass in 100 plots differing in tree species diversity (one to three species) and species composition (all possible combinations of five species of the genera Acer, Carpinus, Fagus, Fraxinus and Tilia) which allowed us to separate possible species diversity and species identity effects on fine root biomass. We found no evidence of a positive diversity effect on standing fine root biomass and thus of overyielding in terms of root biomass. Root necromass decreased with increasing species diversity at marginal significance. Various lines of evidence indicate significant species identity effects on fine root biomass (10–20% higher fine root biomass in plots with presence of maple and beech than in plots with hornbeam; 100% higher fine root biomass in monospecific beech and ash plots than in hornbeam plots; differences significant). Ash fine roots tended to be over‐represented in the 2‐ and 3‐species mixed plots compared to monospecific ash plots pointing at apparent belowground competitive superiority of Fraxinus in this mixed forest. Our results indicate that belowground overyielding and spatial complementarity of root systems may be the exception rather than the rule in temperate mixed forests.     

Danish deciduous forest types

In this study, the first comprehensive multivariate statistical analysis of Danish native forest vegetation, based on 1768 sample plots, is presented. Data were composed of data from literature sources and newly collected data. A series of cluster analyses resulted in 24 forest community types, grouped in beech (Fagus sylvatica), oak (Quercus robur-Q. petraea), hornbeam (Carpinus betulus), alder-ash (Alnus-Fraxinus) and lime (Tilia cordata, T. platyphyllos) types, in addition to mixed forest communities with several co-dominant tree species. The described communities are provisionally arranged syntaxonomically, when possible, according to the international phytosociological system. The distribution of ecological indicator values of pH, soil moisture and nitrogen is gradual in relation to the perceived plant communities. Many forest types, such as beech and oak dominated types, obtain indicated values for pH that span most of the indicated gradient. It is suggested that natural Danish forests probably would be composed of a multitude of canopy forming tree species. The present stands with one or a few tree species forming the canopy is the result of long anthropogenic influence and selective logging.     

Rapid Increases in Forest Understory Diversity and Productivity following a Mountain Pine Beetle (Dendroctonus ponderosae) Outbreak in Pine Forests

The current unprecedented outbreak of mountain pine beetle (Dendroctonus ponderosae) in lodgepole pine (Pinus contorta) forests of western Canada has resulted in a landscape consisting of a mosaic of forest stands at different stages of mortality. Within forest stands, understory communities are the reservoir of the majority of plant species diversity and influence the composition of future forests in response to disturbance. Although changes to stand composition following beetle outbreaks are well documented, information on immediate responses of forest understory plant communities is limited. The objective of this study was to examine the effects of D. ponderosae-induced tree mortality on initial changes in diversity and productivity of understory plant communities. We established a total of 110 1-m² plots across eleven mature lodgepole pine forests to measure changes in understory diversity and productivity as a function of tree mortality and below ground resource availability across multiple years. Overall, understory community diversity and productivity increased across the gradient of increased tree mortality. Richness of herbaceous perennials increased with tree mortality as well as soil moisture and nutrient levels. In contrast, the diversity of woody perennials did not change across the gradient of tree mortality. Understory vegetation, namely herbaceous perennials, showed an immediate response to improved growing conditions caused by increases in tree mortality. How this increased pulse in understory richness and productivity affects future forest trajectories in a novel system is unknown.