Individual Tree Species Research Articles

Inferring changes in foliar mass and area from foliage cover: A mechanistic model

AbstractMeasuring foliar area or mass directly is destructive, and precludes long‐term, repeated observations of individual trees as they suffer or recover from foliar damage. Instead, foliage cover indices are often used as a proxy for foliar mass. Patterns of fluctuations in foliage cover indices can be used to infer qualitative changes in canopy health. However, foliage cover is not necessarily linearly related to foliar area or mass, and this may confound the detection of significant foliar damage, and comparisons of herbivore browse impacts between individual trees, tree species or sites. I derived a mechanistic model to quantify the relationship between foliar area or mass and foliage cover measured as the proportion of sky occluded by leaves. This one parameter model is close to linear for single‐tiered trees, but increasingly non‐linear for multi‐tiered trees. I compared the non‐linear model to a linear model using foliage cover data from an artificial defoliation experiment on two single‐tiered, sub‐canopy species and from simulated photographic images of single‐ and multi‐tiered canopies. The non‐linear model had lower errors than the linear model, and errors did not increase with foliage density (leaf area per unit area), variation (of leaf sizes within and between canopies) or leaf geometry. The non‐linear model can be easily parameterized from relatively low‐cost observations of foliage cover, independently of empirical measurements of foliar area or mass, and is applicable to a wide range of tree species. It should therefore help managers quantify how changes in foliage cover due to natural fluctuations or foliar damage affect foliar area and mass, and can be used to quantify parameters for models of browse impacts in mixed forest.

A nearest-neighbor imputation approach to mapping tree species over large areas using forest inventory plots and moderate resolution raster data

The paper describes an efficient approach for mapping multiple individual tree species over large spatial domains. The method integrates vegetation phenology derived from MODIS imagery and raster data describing relevant environmental parameters with extensive field plot data of tree species basal area to create maps of tree species abundance and distribution at a 250-m pixel size for the entire eastern contiguous United States. The approach uses the modeling techniques of k-nearest neighbors and canonical correspondence analysis, where model predictions are calculated using a weighting of nearest neighbors based on proximity in a feature space derived from the model. The approach also utilizes a stratification derived from the 2001 National Land-Cover Database tree canopy cover layer. Data pre-processing is also described, which includes the use of Fourier series transformation for data reduction and characterizing seasonal vegetation phenology patterns that are apparent in the MODIS imagery.A suite of assessment procedures is applied to each of the modeled dataset presented. These indicate high accuracies, at the scales of assessments used, for total live-tree basal area per hectare and for many of the most common tree species found in the study area. The end result is an approach that enables the mapping of individual tree species distributions, while retaining much of the species covariance found on the forest inventory plots, at a level of spatial detail approaching that required for many regional management and planning applications. The proposed approach has the potential for operational application for simultaneously mapping the distribution and abundance of numerous common tree species across large spatial domains.

The impact of the invasive shrubLonicera maackiion the decomposition dynamics of a native plant community

Invasive plants may have variable effects within a given environment depending on their interactions with the dominant native species, yet little research has examined such species-species interactions within a site. Savanna trees with nonoverlapping canopies offer an ideal opportunity to assess associated changes in the ecosystem processes that result from interactions between an invasive species and different native tree species. We examined the influence of the exotic invasive shrub Lonicera maackii on decomposition dynamics under three native tree species: Fraxinus quadrangulata, Quercus muehlenbergii, and Carya ovata. Litter decomposition rates and litter C and N were evaluated over two years using single- and mixed-species litterbags (L. maackii and individual tree species litter); microarthropod abundance was measured at 6 weeks using Tulgren funnels. Litter from the invasive L. maackii decomposed and lost N more rapidly than the litter of the three native tree species. The rate at which L. maackii decomposed depended on its location, with L. maackii litter decomposing and losing N more rapidly under C. ovata than under the other two native tree species. Mixing L. maackii with the native species' litter did not accelerate litter mass loss overall but did result in synergistic N losses at variable times throughout the experiment, further highlighting the variable interaction between native species and L. maackii. Nitrogen loss was significantly higher than expected in mixtures of C. ovata + L. maackii litter at 6 weeks, in F. quadrangulata + L. maackii litter at 12 weeks, and in Q. muehlenbergii + L. maackii litter at 24 weeks. If the effects of invasive species on certain ecosystem processes, such as litter decomposition, are strongly influenced by their association with native species, this could suggest the need for a more nuanced understanding of the vulnerability of ecosystem processes to invasions of L. maackii and potentially other invasive species.

Exploratory analysis for complex-life-cycle amphibians: Revealing complex forest-reproductive effort relationships using redundancy analysis

The relationships among complex life-cycle (CLC) amphibians and their habitats involve interaction of biotic and abiotic variables across multiple spatial and temporal scales. Most studies of species–environment relationships utilize classic distributions and regression methods which may oversimplify results, as they often involve initial reduction of data, a priori model specification, and parsimonious model selection. We re-analyzed a dataset collected in a study of environment-reproductive effort relationships for two amphibian species. This data was originally analyzed using negative binomial regression and AIC model selection; we applied a multivariate analysis, a variant of Redundancy Analysis (RDA), to the same dataset to examine if additional information was revealed. The multivariate analysis identified the same primary drivers as did model selection: in the context of relatively intact forests, hydroperiod was the most important factor contributing to reproductive effort. However, the RDA elucidated what may be new primary and secondary drivers related to forest structure and composition. Reproductive effort was strongly associated with tree species richness, canopy cover, and presence of individual tree species; the strength of these relationships varied between amphibian species and across spatial scales. Spotted salamanders (Ambystoma maculatum) were strongly influenced by microclimate conditions and wood frogs (Lithobates sylvaticus) by pool canopy cover and presence of wetland tree species. A priori, parsimonious model selection assists managers by delivering biologically defensible, simple explanations. However the process reduces hypothesis-generating potential and omits variables that may become important as environments change.

Tree Species Detection Accuracies Using Discrete Point Lidar and Airborne Waveform Lidar

Species information is a key component of any forest inventory. However, when performing forest inventory from aerial scanning Lidar data, species classification can be very difficult. We investigated changes in classification accuracy while identifying five individual tree species (Douglas-fir, western redcedar, bigleaf maple, red alder, and black cottonwood) in the Pacific Northwest United States using two data sets: discrete point Lidar data alone and discrete point data in combination with waveform Lidar data. Waveform information included variables which summarize the frequency domain representation of all waveforms crossing individual trees. Discrete point data alone provided 79.2 percent overall accuracy (kappa = 0.74) for all 5 species and up to 97.8 percent (kappa = 0.96) when comparing individual pairs of these 5 species. Incorporating waveform information improved the overall accuracy to 85.4 percent (kappa = 0.817) for five species, and in several two-species comparisons. Improvements were most notable in comparing the two conifer species and in comparing two of the three hardwood species.

Determination of foliar Ca/Sr discrimination factors for six tree species and implications for Ca sources in northern hardwood forests

Discrimination during foliar uptake between the alkaline earth elements Ca and Sr must be understood to fully utilize Ca/Sr and 87Sr/86Sr ratios as a monitor of Ca sources to trees. The aim of this study was to determine Ca/Sr discrimination factors [DF = (Ca/Srplant tissue)/ (Ca/Srnutrient source)] for six tree species in a northern hardwood forest and use foliar chemistry to consider whether species access measurably different soil reservoirs of Ca and Sr. This was accomplished by measuring the Ca/Sr and 87Sr/86Sr ratios of foliage from individual tree species in mixed stands and comparing these ratios to those of soil extracts from soil pits co-located at six sites in the White Mountains, New Hampshire (USA). For three species for which DFs have been previously determined, the source of Ca and Sr in foliage can be traced predominantly to recycling of material from organic horizons. Foliar and soil chemistry is consistent with each of the tree species in these six sites deriving Ca and Sr predominantly from the Oie horizon. Thus we can estimate DFs (±1sd) for sugar maple (Acer saccharum Marsh.; 1.16 ± 0.13), yellow birch (Betula alleghaniensis Britt.; 1.31 ± 0.10), white birch (Betula papyrifera Marsh.; 1.30 ± 0.14), pin cherry (Prunus pensylvanica L.f.; 1.24 ± 0.09), American beech (Fagus grandifolia Ehrh.; 1.78 ± 0.17) and red maple (Acer rubrum L.; 1.90 ± 0.15). These estimates of discrimination factors allow refinement in the use of Ca/Sr and 87Sr/86Sr ratios of foliage to trace Ca sources to plants.

山西五鹿山白皮松群落乔灌层的种间分离

The Wulu Mountains,a part of the Luliang Mountain Range,are situated at 36°23′45″—36°38′20″N,111°08′—111°18′E in western Shanxi Province,China.This area has a warm-temperate continental monsoon climate with abundant plant resources and high biodiversity.Appropriate conditions for the growth of Pinus bungeana Zucc.ex Endl.are limited within the Wulu Mountains which include only a part of the overall range of P.bungeana.Therefore,building nature reserves in which P.bungeana can be studied systematically is important both ecologically and academically,with the goal of studying this species in its warm temperate north China climate so it can be preserved in natural forests indefinitely. Interspecific relationships are an important factor affecting community composition,structure,function and dynamics.Interspecific segregation refers to the relative distributions of two or more related species.It reflects the degree of mixing of two species based on their interrelationships.For example,the less two species mix,the higher the degree of interspecific segregation exists. The segregation relationship between different species pairs can be helpful in revealing the phenomena of species interactions,community structure and dynamics.This relationship can be used to explore the impacts of environmental differences on species distribution.Practically,such study is the scientific foundation of species conservation,restoration and the reconstruction of degraded ecosystems. We established 55 quadrats within natural P.bungeana communities to study the intraspecific and interspecific competition relationships of nine tree species and patterns of interspecific segregation of all species in the tree and shrub layers of P.bungeana communities.Using ArcView GIS software and the nearest neighbor method,interspecific segregation was studied with an N × N nearest-neighbor contingency table,a 2 × 2 nearest-neighbor contingency sub-table,and Hegyi′s competition index model for the individual tree species. The results indicate:(1) most of the species pairs are randomly segregated(80%),some species pairs are positively segregated(16.19%),and only a few species pairs are negatively segregated(3.81%).(2) There are some differences among different species in the interspecific segregation of all species.The larger individuals representing dominant species in the communities tended to be positively segregated with the other large trees and shrubs,probably because of their stronger competitive vigor.For example,P.bungeana,which is the most common and dominant species of this community,was positively segregated from Platycladus orientalis,Quercus wutaishanica,Ulmus pumila,Syringa pubescens,Cotoneaster multiflorus,Sophora davidii,Viburnum mongolicum,the dominant species of this community.Negative segregation appeared between dominant species and companion species in the communities,such as P.bungeana and Populus davidiana,P.orientalis and F.vulgaris,S.microphylla and Salix wallichiana.This appeared to be caused by the fact the companion species had fewer individuals,lower coverage and similar habitat requirements to the dominant species.Intensive interspecific competition resulted in a mosaic distribution and full competitive exploitation of resources among species,apparently causing them to be more likely to become negatively segregated. The 15 species from the forest plots were divided into three ecological species groups(ESG),based on their niches and relationships between the species,other plants and the environment.(3) The status of interspecific segregation of species has a close relationship to their intraspecific and interspecific competitive relationships and spatial distribution patterns.The larger individuals representing dominant species with more severe intraspecific competition than interspecific competition and appearing to have an aggregating distribution in the communities tended to be positively aggregated with the other large trees and shrubs.Negative aggregation(segregation) appeared between dominant species and companion species which have more severe interspecific competition than intraspecific competition in the communities.The interspecific competition of species within the same ESGs was more intense than in species in different ESGs.(4) The interspecific segregation is related to the heterogeneity in the communities,in that aggregation often occurs between two species which have different habitat requirements;while the segregation often appears between two species which have same or similar environmentally requirements.(5) The results show the 15 species we studied overlapped in distribution and were characterized by overall non-segregation.(6) The intraspecific and interspecific relationships were caused by ecological niches to which the different species are adapted and their biological requirements,and these differences may be the mechanisms which allow these species to stably coexist in the P.bungeana community of the Wulu Mountain Nature Reserve.

Simultaneously acquired airborne laser scanning and multispectral imagery for individual tree species identification

The objective of this study was to investigate the use of multispectral imagery in addition to measurements from airborne laser scanning (ALS) for tree species identification. Multispectral imagery from a medium-format digital frame camera acquired simultaneously with ALS data were utilized and compared with imagery from a large-format digital frame camera acquired on a separate flight mission from a higher altitude. The two acquisitions represent cost efficient methods for data collection of both three-dimensional and spectral information. The classification accuracy was assessed using 1520 segmented spruce, pine, and deciduous trees. Furthermore, ALS intensity was normalized using the range from sensor to the target (range normalization). In addition, a source of variation in intensity known as banding, is described together with a normalization procedure for diminishing this effect. The normalized intensity was better than using the raw intensity, but it did not improve the classification compared with using only ALS structural information, which provided overall classification accuracies of 74%–77%. The combined use of ALS and multispectral imagery from the medium-format imagery acquired simultaneously and the separate acquisition of large-format imagery provided overall accuracies of 87%–89% and 83%–85%, respectively. Simultaneous acquisition of ALS and medium-format digital imagery provides an efficient data acquisition strategy for tree species identification in forest inventory and will likely reduce data acquisition costs by 10%–20%.

Response of advance reproduction of oaks and associated species to repeated prescribed fires in upland oak-hickory forests, Missouri

The Chilton Creek prescribed burn project was initiated in 1996 by The Nature Conservancy (TNC) to restore native oak woodlands and test the effect of frequent, low intensity surface fires conducted in the dormant season (March–April) on upland oak-hickory forests in the Ozarks of Missouri. Burning treatments on five sites totaling 1000 ha were initiated in 1998. The prescribed burn treatments included: annual burns (one site was burned annually) and periodic burns (four sites were burned with a mean fire return interval of approximately 4 years). Approximately 3000 stems of advance reproduction with basal diameters ⩽15.0 cm were measured in 1997 (pre-burn), and remeasured in 1998, 2001 and 2007 as the prescribed burn treatments proceeded. Mortality and changes in average and aggregate total height between 1997 and 2007 were analyzed for fourteen selected tree species. Over a ten-year period prescribed burning reduced stem density, mean height and aggregate height by 57%, 36% and 67%, respectively. However, individual tree species responded differently to the repeated burns. Oaks exhibited moderate mortality (36–54%) compared to hickories, sassafras and winged elm, all of which experienced relatively low mortality (18–35%). Flowering dogwood, shortleaf pine, blackgum and other minor species incurred higher mortality (60–76%). Oaks generally had slightly lower reductions in mean height and aggregate height than associated species with the exception of shortleaf pine, but the differences were mostly non-significant. Repeated burning tended to favor the white oak species (white oak, post oak, chinkapin oak) more than the red oak species (black oak, scarlet oak), although the differences were minor. Shortleaf pine was the only species to show increases in mean height following the ten-year period of prescribed burning. Effects of repeated burns on mortality of advance reproduction changed with stem size (e.g., basal diameter, total height). A logistic model quantified mortality changes as a function of the ratio between total stem height and the square of stem basal diameter. Based on this model, fourteen species were classified into four groups characterized by model intercept and slope: group 1: high intercept and high slope (shortleaf pine, flowering dogwood); group 2: high intercept and low slope (blackgum, other minor species); group 3: low intercept and low slope (sassafras, winged elm, black and pignut hickories); and group 4: low intercept and high slope (oaks, mockernut hickory). Species in groups 3 and 4 are more resistant to repeated fires than those in groups 1 and 2 as indicated by their lower mortality, particularly for stems with larger basal diameters. Among species in groups 3 and 4, oaks will likely be favored over the long term because of their conservative reproduction strategies as suggested by the significance of the regression coefficients for slope. If large advance reproduction is present, shortleaf pine will likely survive repeated low intensity fires and maintain its height and competitive position due to its ability to avoid shoot dieback.

Small-scale variation of vegetation in a mixed forest understorey is partly controlled by the effect of overstory composition on litter accumulation

We investigated how richness and composition of vascular plant species in the understory of a mixed hardwood forest stand varied with respect to the abundance and composition of the overstory. The stand is in central Spain and represents the southernmost range of distribution of several tree and herbaceous species in Europe. Understory species were identified in 46 quadrats (0.25 m2) where variables litter depth and light availability were measured. In addition, we estimated tree density, basal area, and percent basal area by tree species within 6-m-radius areas around each plot. Species richness and composition were studied using path analysis and scale-dependent geostatistical methods, respectively. We found that the relative abundance of certain trees species in the overstory was more important than total overstory abundance in explaining understory species richness. Richness decreased as soil litter depth increased, and soil litter increased as the relative proportion of Fagus sylvatica in the overstory increased, which accounted for a negative, indirect effect of Fagus sylvatica on richness. Regarding understory species composition, we found that some species distributed preferentially below certain tree species. For example, Melica uniflora was most frequent below Fagus sylvatica and Quercus petraea while the increasing proportion of Q. pyrenaica in the overstory favored the presence of Cruciata glabra, Arenaria montana, Prunus avium, Conopodium bourgaei, Holcus mollis, Stellaria media and Galium aparine in the understory. Overall, these results emphasize the importance of individual tree species in controlling the assemblage and richness of understory species in mixed stands. We conclude that soil litter accumulation is one way through which overstory composition shapes the understory community.

Distinctive Phyllosphere Bacterial Communities in Tropical Trees

Recent work has suggested that in temperate and subtropical trees, leaf surface bacterial communities are distinctive to each individual tree species and dominated by Alpha- and Gammaproteobacteria. In order to understand how general this pattern is, we studied the phyllosphere bacterial community on leaves of six species of tropical trees at a rainforest arboretum in Malaysia. This represents the first detailed study of 'true' tropical lowland tree phyllosphere communities. Leaf surface DNA was extracted and pyrosequenced targeting the V1-V3 region of 16S rRNA gene. As was previously found in temperate and subtropical trees, each tree species had a distinctive bacterial community on its leaves, clustering separately from other tree species in an ordination analysis. Bacterial communities in the phyllosphere were unique to plant leaves in that very few operational taxonomic units (0.5%) co-occurred in the surrounding soil environment. A novel and distinctive aspect of tropical phyllosphere communities is that Acidobacteria were one of the most abundant phyla across all samples (on average, 17%), a pattern not previously recognized. Sequences belonging to Acidobacteria were classified into subgroups 1-6 among known 24 subdivisions, and subgroup 1 (84%) was the most abundant group, followed by subgroup 3 (15%). The high abundance of Acidobacteria on leaves of tropical trees indicates that there is a strong relationship between host plants and Acidobacteria in tropical rain forest, which needs to be investigated further. The similarity of phyllosphere bacterial communities amongst the tree species sampled shows a significant tendency to follow host plant phylogeny, with more similar communities on more closely related hosts.

Exploring adaptation to climate change in the forests of central Nova Scotia, Canada

The threat of climate change is now recognized as an imminent issue at the forefront of the forest sector. Incorporating adaptation to climate change into forest management will be vital in the continual and sustainable provision of forest ecosystem services. The objective of this study is to investigate climate change adaptation in forest management using the landscape disturbance model LANDIS-II. The study area was comprised of 14,000 ha of forested watersheds in central Nova Scotia, Canada, managed by Halifax Water, the municipal water utility. Simulated climate change adaptation was directed towards three components of timber harvesting: the canopy-opening size of harvests, the age of harvested trees within a stand, and the species composition of harvested trees within a stand. These three adaptation treatments were simulated singly and in combination with each other in the modeling experiment. The timber supply was found to benefit from climate change in the absence of any adaptation treatment, though there was a loss of target tree species and old growth forest. In the age treatment, all trees in a harvested stand at or below the age of sexual maturity were exempt from harvesting. This was done to promote more-rapid succession to climax forest communities typical of the study area. It was the most effective in maintaining the timber supply, but least effective in promoting resistance to climate change at the prescribed harvest intensity. In the composition treatment, individual tree species were selected for harvest based on their response to climate change in previous research and on management values at Halifax Water to progressively facilitate forest transition under the altered climate. This proved the most effective treatment for maximizing forest age and old-growth area and for promoting stands composed of climatically suited target species. The size treatment was aimed towards building stand complexity and resilience to climate change, and was the most influential treatment on the response of timber supply, forest age, and forest composition to timber harvest when it was combined with other treatments. The combination of all three adaptation treatments yielded an adequate representation of target species and old forest without overly diminishing the timber supply, and was therefore the most effective in minimizing the trade-offs between management values and objectives. These findings support a diverse and multi-faceted approach to climate change adaptation.

Tree Classification with Fused Mobile Laser Scanning and Hyperspectral Data

Mobile Laser Scanning data were collected simultaneously with hyperspectral data using the Finnish Geodetic Institute Sensei system. The data were tested for tree species classification. The test area was an urban garden in the City of Espoo, Finland. Point clouds representing 168 individual tree specimens of 23 tree species were determined manually. The classification of the trees was done using first only the spatial data from point clouds, then with only the spectral data obtained with a spectrometer, and finally with the combined spatial and hyperspectral data from both sensors. Two classification tests were performed: the separation of coniferous and deciduous trees, and the identification of individual tree species. All determined tree specimens were used in distinguishing coniferous and deciduous trees. A subset of 133 trees and 10 tree species was used in the tree species classification. The best classification results for the fused data were 95.8% for the separation of the coniferous and deciduous classes. The best overall tree species classification succeeded with 83.5% accuracy for the best tested fused data feature combination. The respective results for paired structural features derived from the laser point cloud were 90.5% for the separation of the coniferous and deciduous classes and 65.4% for the species classification. Classification accuracies with paired hyperspectral reflectance value data were 90.5% for the separation of coniferous and deciduous classes and 62.4% for different species. The results are among the first of their kind and they show that mobile collected fused data outperformed single-sensor data in both classification tests and by a significant margin.

Forest structure and tree species composition of the understory of two central Amazonian várzea forests of contrasting flood heights

We investigated species composition, distribution, and forest structure of understory trees (≥1m height, <10cm diameter at breast height) in two late-successional várzea forests subject to contrasting levels of inundation within the Mamirauá Sustainable Development Reserve, western Brazilian Amazon, and compared it with the overstory flora at the same study sites. In total, 1486 individuals and 116 woody species were recorded on an area totaling 3140m2. Individual densities and tree species richness were considerably higher in the high várzea than in the low várzea, which suggests that the heights and durations of the annual inundations are the main factor limiting species regeneration. In addition, approximately one third of the recorded species with densities ≥8 individuals showed regular or random spatial distribution patterns, which suggests that floodwaters act on dispersal strategies and species establishment.Independent of the forest type, floristic similarity between the understory and the overstory amounted to approximately 35%, and to approximately 10% when compared to other understory inventories in Amazonian várzea. Although the inventoried area of the understory amounted to only 16% of that of the overstory, species richness accounted for approximately 52–56% of that of the overstory. The results indicate that the understory flora of várzea forests is distinct and that it significantly increases local tree species richness. The understory flora of várzea forests therefore should be addressed in floristic inventories that provide the basis for regional and/or basin-wide estimations of tree diversity.

A further test of a palaeoecological thermometer: Tropical rainforests have more herbivore damage diversity than temperate forests

The fossil record suggests greater diversity of insect leaf-feeding during warm climate intervals. Much published work in the palaeobotanical literature has been based on the presumed validity of this pattern. Here we investigated whether, in a tropical rainforest climate, leaves are being eaten in more ways than in a temperate forest climate. We compared forests at five sites in Malaysia (2–3°N, MAT ca. 26.5 °C) with five sites in northern Florida, USA (30°N, MAT ca. 19.5 °C) and in the north-eastern (NE) USA (40–42°N, MAT 7–9 °C). Presence and absence of damage types was determined using a standard leaf damage guide. In bulk floras, there was a consistent difference in damage diversity, per unit number of leaves (as in the fossil studies), between Malaysian and cool temperate NE USA sites. Malaysian tropical forest sites had a significantly greater number of damage types. Florida occupied an intermediate position, too similar to both Malaysia and NE USA to be statistically significant. When damage diversity on leaves of individual tree species was compared, consistently higher damage diversity was found in the five most abundant tropical species sampled, than in the five most abundant temperate species sampled in the NE USA. In Malaysia, the percentage of leaves receiving any damage was statistically significantly greater than in NE USA, a difference of around 10%. The results appear to validate that the trend of damage diversity with temperature seen in the fossil record is not a spurious effect of preservation bias. Tropical forests and tropical tree species do appear to have greater damage diversity than temperate forests and species. This may have broader, as yet unexplored, implications for community ecology.

The ecology of the phyllosphere: geographic and phylogenetic variability in the distribution of bacteria on tree leaves

Large populations of bacteria live on leaf surfaces and these phyllosphere bacteria can have important effects on plant health. However, we currently have a limited understanding of bacterial diversity on tree leaves and the inter- and intra-specific variability in phyllosphere community structure. We used a barcoded pyrosequencing technique to characterize the bacterial communities from leaves of 56 tree species in Boulder, Colorado, USA, quantifying the intra- and inter-individual variability in the bacterial communities from 10 of these species. We also examined the geographic variability in phyllosphere communities on Pinus ponderosa from several locations across the globe. Individual tree species harboured high levels of bacterial diversity and there was considerable variability in community composition between trees. The bacterial communities were organized in patterns predictable from the relatedness of the trees as there was significant correspondence between tree phylogeny and bacterial community phylogeny. Inter-specific variability in bacterial community composition exceeded intra-specific variability, a pattern that held even across continents where we observed minimal geographic differentiation in the bacterial communities on P. ponderosa needles.

Patterns from the past: modeling Public Land Survey witness tree distributions with weights-of-evidence

The Public Land Survey (PLS) witness tree data provide one of the few quantitative data sets of pre-and early-European settlement composition and structure of the forests and woodlands in the western United States. However, quantifying the areal extent of individual woody species from PLS records has proven difficult due to the coarse sampling structure of the data. Several attempts have been made to convert the discrete PLS witness tree data into continuous distributions through the use of various interpolation techniques. While these methods may adequately represent the spatial patterns of individual species over large areas, they fail to consider the numerous environmental covariates that can influence the distribution of individual tree species at finer scales. A more statistically rigorous method calls for combining species–environment relationships to estimate the areal extent of individual species from point data. In this study, we utilize weights-of-evidence (WofE), a discrete multivariate method, to estimate the probable historical distribution of six important woody plant taxa of the cross timbers of south-central Oklahoma. We successfully created posterior probability distribution maps for Quercus stellata, Q. marilandica, Q. velutina, Carya texana, C. illinoinensis, and Juniperus spp. Each posterior probability map was classified into four predictive categories, thereby enabling better estimations of the historical distribution of individual taxon from coarse-resolution PLS data. Model validation indicated that the WofE method effectively estimated the posterior probabilities of all taxa under consideration.

Leaf litter decomposition in temperate deciduous forest stands with a decreasing fraction of beech (Fagus sylvatica)

We hypothesised that the decomposition rates of leaf litter will increase along a gradient of decreasing fraction of the European beech (Fagus sylvatica) and increasing tree species diversity in the generally beech-dominated Central European temperate deciduous forests due to an increase in litter quality. We studied the decomposition of leaf litter including its lignin fraction in monospecific (pure beech) stands and in stands with up to five tree genera (Acer spp., Carpinus betulus, Fagus sylvatica, Fraxinus excelsior, Tilia spp.) using a litterbag approach. Litter and lignin decomposition was more rapid in stand-representative litter from multispecific stands than in litter from pure beech stands. Except for beech litter, the decomposition rates of species-specific tree litter did not differ significantly among the stand types, but were most rapid in Fraxinus excelsior and slowest in beech in an interspecific comparison. Pairwise comparisons of the decomposition of beech litter with litter of the other tree species (except for Acer platanoides) revealed a “home field advantage” of up to 20% (more rapid litter decomposition in stands with a high fraction of its own species than in stands with a different tree species composition). Decomposition of stand-representative litter mixtures displayed additive characteristics, not significantly more rapid than predicted by the decomposition of litter from the individual tree species. Leaf litter decomposition rates were positively correlated with the initial N and Ca concentrations of the litter, and negatively with the initial C:N, C:P and lignin:N ratios. The results support our hypothesis that the overall decomposition rates are mainly influenced by the chemical composition of the individual litter species. Thus, the fraction of individual tree species in the species composition seems to be more important for the litter decomposition rates than tree species diversity itself.

Present-day testing of a paleoecological pattern: Is there really a latitudinal difference in leaf-feeding insect-damage diversity?

The fossil record suggests greater diversity of insect leaf feeding during warm climate intervals. Much published work in the paleobotanical literature has been based on the presumed validity of this pattern. However, the existence of this pattern in nature has never been tested from the present-day world. Here we ask, is it true that on average, in warmer climates, a leaf is being eaten in more ways? We compared forests at seven sites in northern Florida (30° N, MAT ca. 19.5 °C) to seven sites across the north-eastern USA (40–42° N, MAT 7–9 °C). Presence and absence of damage types were determined using a standard leaf damage guide; 93 damage types were found in the Florida samples and 80 in the north-eastern samples. In bulk floras, there was a consistent difference in damage diversity, on a per-leaf basis (as in the fossil studies), between Florida and north-eastern sites. Florida sites had a greater number of damage types. When northern and southern populations of individual tree species were compared, higher southern damage diversity was found in four species ( Acer rubrum, Acer saccharum, Fagus grandifolia, and Quercus coccinea), though with no difference with latitude in a fifth species ( Quercus alba). These results appear to validate that the trend seen in the fossil record is not a spurious effect of site differences. They also extend a pattern seen in deep time into the present day, adding greatly to its generality.

Impacts of individual tree species on carbon dynamics in a moist tropical forest environment

In the moist tropical forest biome, which cycles carbon (C) rapidly and stores huge amounts of C, the impacts of individual species on C balances are not well known. In one of the earliest replicated experimental sites for investigating growth of native tropical trees, we examined traits of tree species in relation to their effects on forest C balances, mechanisms of influence, and consequences for C sequestration. The monodominant stands, established in abandoned pasture in 1988 at La Selva Biological Station, Costa Rica, contained five species in a complete randomized block design. Native species were: Hieronyma alchorneoides, Pentaclethra macroloba, Virola koschnyi, and Vochysia guatemalensis. The exotic species was Pinus patula. By 16 years, the lack of differences among species in some attributes suggested strong abiotic control in this environment, where conditions are very favorable for growth, These attributes included aboveground net primary productivity (ANPP), averaging 11.7 Mg C x ha(-1) x yr(-1) across species, and soil organic C (0-100 cm, 167 Mg C/ha). Other traits differed significantly, however, indicating some degree of biological control. In Vochysia plots, both aboveground biomass of 99 Mg C/ha, and belowground biomass of 20 Mg C/ha were 1.8 times that of Virola (P = 0.02 and 0.03, respectively). Differences among species in overstory biomass were not compensated by understory vegetation. Belowground NPP of 4.6 Mg C x ha(-1) yr(-1) in Hieronyma was 2.4 times that of Pinus (P < 0.01). Partitioning of NPP to belowground components in Hieronyma was more than double that of Pinus (P = 0.03). The canopy turnover rate in Hieronyma was 42% faster than that of Virola (P < 0.01). Carbon sequestration, highest in Vochysia (7.4 Mg C x ha(-1) x yr(-1), P = 0.02), averaged 5.2 Mg C x ha(-1) x yr(-1), close to the annual per capita fossil fuel use in the United States of 5.3 Mg C. Our results indicated that differences in species effects on forest C balances were related primarily to differences in growth rates, partitioning of C among biomass components, tissue turnover rates, and tissue chemistry. Inclusion of those biological attributes may be critical for robust modeling of C cycling across the moist tropical forest biome.