Effects of species partition on explanatory variables in direct gradient analysis - a case study from Senegal

Abstract. Species-environment data from Senegal, West Africa, are used to study the effects of partition of a large species data set into subsets corresponding to rare and common species respectively. The original data set contains 129 woody plant species from 909 plots and 60 explanatory variables. By applying Canonical Correspondence Analysis to data subsets, marked differences in the forward-selected variables were detected. The highest resemblance was found between the complete species set and the common species subset. Only one of eight selected variables was common to all species and the rare species groups. These findings were tested with partial ordination, applying the selected variables from the original species group (Vb), as variables and covariables to the analyses of common and rare species. For the common species this application resulted in a constrained ordination with higher eigenvalues as compared to the set of variables selected with reference to the common species group. Using the rare species group, the application of Vb gave a much lower sum of eigenvalues than did the ordination with selected variables based on the rare species group only. Evidently, the set of variables selected on the basis of the rare species data were more significant. Hence, the resulting gradients depend on the frequency of the species. Gradient analysis is apparently only valid for groups of species with closely resembling characteristics. This implies that different functional types of species, with different distributions and abundances, respond individually to environmental variation. Extrapolating deduced gradients from one species group to another maybe risky, particularly when used in vegetation modelling.     

Effects of Forest Use on Aphyllophoraceous Fungal Community Structure in Sarawak, Malaysia

Aphyllophoraceous fungi are expected to reflect changes in the environmental conditions caused by forest use. To reveal the effects of forest uses on the fungal community structure, we performed a 3‐month survey of aphyllophoraceous species in five forest types (undisturbed primary forest, isolated patches of primary forest, old and young fallow forest, and rubber plantations) in Sarawak, Malaysia in 2005. We used a canonical correspondence analysis (CCA) to reveal the relationships between fungal community composition and the environmental variables (canopy openness, soil water potential, amount and composition of coarse woody debris, litter mass, basal area, plant species composition). A total of 155 samples from 67 species were collected during the study period. The fungal species density represented by the number of species in a transect differed significantly among forest types. The fungal species density increased significantly with increasing number of pieces of coarse woody debris (CWD), but decreased significantly with increasing the scores of second axis of principal component analysis (PCA) for plant species composition. In the CCA ordination, automatic forward selection revealed that only the number of pieces of CWD significantly affected the fungal species composition. The occurrences of Flabellophora licmophora, Coriolopsis retropicta, Microporus vernicipes, and Amauroderma subrugosum were positively correlated with the number of pieces of CWD. Our study clearly demonstrated that forest use negatively affected aphyllophoraceous fungal diversity and suggest that the quantity of CWD would be an important determinant of fungal diversity and composition.     

Habitat structure is more important than vegetation composition for local‐level management of native terrestrial reptile and small mammal species living in urban remnants: A case study from Brisbane,Australia

Abstract As urban areas continue to expand and replace natural and agricultural landscapes, the ability to manage and conserve native wildlife within urban environments is becoming increasingly important. To do so we first need to understand species' responses to local‐level habitat attributes in order to inform the decision‐making process and on‐ground conservation actions. Patterns in the occurrence of native terrestrial reptile and small mammal species in 59 sites located in remnant urban habitat fragments of Brisbane City were assessed against local‐level environmental characteristics of each site. Cluster analysis, multidimensional scaling ordination, and principal axis correlation were used to investigate relationships between species' occurrences and environmental characteristics. Native reptiles were most strongly associated with the presence of termite mounds, a high amount of fallen woody material, and a moderate amount of weed cover. Native small mammals were most strongly associated with the presence of grass trees (Xanthorrhoea spp.), and both reptiles and small mammals were negatively influenced by increased soil compaction. Significant floristic characteristics were considered to be important as structural, rather than compositional, habitat elements. Therefore, habitat structure, rather than vegetation composition, appears to be most important for determining native, terrestrial reptile and small mammal species assemblages in urban forest fragments. We discuss the management implications in relation to human disturbances and local‐level management of urban remnants.     

Early primary succession on Mount St. Helens,Washington, USA

Abstract. The north slope of Mount St. Helens was sampled with 141 circular 100-m² plots to describe vegetation and environmental patterns 13 yr after the 1980 eruption. At least 114 vascular plant taxa were encountered. We recognized four habitat types: Refugia, Pumice barrens, Pyroclastic surfaces and Drainages. A fifth category, Lupine patches, includes samples on primary surfaces that were rapidly colonized. Refugia provided small enclaves where underground portions of several species survived the eruption. They retained an inconsistent array of forest understory species and contained 86 species (mean = 20.8 per plot). Refugia are dominated by woody species such as Penstemon cardwellii, Rubus spp., Ribes spp. and Alnus sinuata, with herbs such as Agrostis diegoensis, Luzula parviflora and Anaphalis margaritacea. Anaphalis represents a suite of species that invaded Refugia after the eruption. Diversity (N₂ and H′) is significantly greater in Refugia than in any other habitat. No plants survived on primary sites, which remain sparsely vegetated and dominated by readily dispersed taxa. Total richness ranges from 36 species (9.9 per plot) on pyroclastic surfaces, through 42 species (11.2 per plot) in drainages, to 66 (11.7 per plot) on Pumice barrens. H′ and N₂ of the three habitats do not differ significantly. Lupine-dominated vegetation occurs sporadically in Pyroclastic and drainage habitats. Lupine patches are characterized by high Lupinus cover and a suite of invaders. These sites have high cover and 52 species (12.6 per plot). H′ and N₂ scores were significantly lower than any other habitat due to strong lupine dominance. Canonical Correspondence Analysis showed that site history and slope contributed most to species composition. Geographic effects accounted for 10 25 % of the explained species-environment relationship. Forest understory species have migrated only short distances and have made negligible contributions to vegetation development. A few species common in Refugia, including Agrostis diegoensis and Carex mertensii, have invaded barren surfaces, but most have not. Refugia also have been invaded by open site species abundant on the Pumice Plain. The heterogeneity of plots within habitat types and small statistical linkage of vegetation to environmental and spatial factors suggests that stochastic events have played a leading role in early primary succession.     

Ecological association of birds and vegetation structure in wet tropical forests of Australia

Birds and environments of tropical rainforests were studied in 18 selected areas from sea level to 1520 m within the humid tropical region of northeastern Australia. A total of 122 sites (20 m × 20 m each) were established within the 18 areas, and bird data (observation and mist-netting) and environmental data (pro forma survey and foliage measurements) were collected at each site. The bird data were analysed numerically in two ways: abundance of 146 species in 18 areas and presence and absence of 108 species at 122 sites. Both classification and ordination analyses produced a major discontinuity between the tableland sites and the lowland sites, each divisible further into various types of vine forest and non-vine forest vegetation. The few rare species did not contribute to the general pattern. The environmental data were reduced to a set of those attributes that showed variation among the sites. They included topographic and edaphic features, physiognomic and structural features of vegetation, fruiting and defoliating habits of plants, foliage height diversity and evenness, and canopy cover. The primary pattern in the data set of 135 attributes by 122 sites was vine forest versus nonvine forest, and altitudinal divisions appeared as a secondary pattern, in both classification and ordination. Canonical correlation coefficients between bird vectors and environmental vectors were reasonably high for the first four canonical vectors, which correlated well with major Gower vectors of birds and environments. The back-correlation to the raw data produced bird species and matching environmental attributes with sites sharing them for both positive and negative ends of each canonical vector. In general, the analysis extracted elements of both fauna and environment that characterized the vine forest as opposed to the non-vine forest and the tableland sites as opposed to the lowland sites. Canonical correlation analysis is limited by the unverifiable nature of derived correlations. Such correlations may suggest certain associations to be tested by independent means (hypothesis-generating function), but may also formalize self-evident or fortuitous associations.     

秦岭山地天然次生林群落MRT数量分类、CCA排序及多样性垂直格局

采用多元回归树(MRT)对秦岭山地天然次生林群落进行数量分类,采用典范对应分析(CCA)进行排序,分析了秦岭山地天然次生林群落物种多样性沿海拔梯度的变化规律。结果表明:(1) 275个样方共有种子植物195种,隶属61科128属。乔、灌、草3个层次物种多样性变化沿海拔梯度的变化趋势基本一致,呈单峰模型;(2)经交叉验证认为秦岭山地天然次生林群落可分为2类,Ⅰ冬瓜杨(Populus purdomii)+陇东海棠(Malus kansuensis)+蛇莓(Duchesnea indica)群落,Ⅱ锐齿槲栎(Quercus aliena var. acuteserrata)+黄栌(Cotinus coggygria)+茜草(Rubia cordifolia)群落;(3) CCA排序结果揭示了群落生境的分布范围,反映出生态轴的排序意义,较好地反映秦岭山地天然次生林群落与环境因子的关系,其结果表明,海拔、坡向、凋落层厚度和干扰情况4个变量对该地区次生林群落的分布有较大的影响。     

Defining phytoclimatic units in Galicia,Spain, by means of multivariate methods

Abstract. Floristic and climate data from 150 plots in 25 sites in Galicia, Spain, were analysed to test the hypothesis that climate is the major factor governing the distribution of woody plant species. TWINSPAN classification, Detrended Correspondence Analysis and Canonical Correspondence Analysis were applied in successive stages of the data analysis to describe vegetational variation in relation to climatic gradients. Six groups of species were defined, two clearly oceanic (Maritime and Cool Maritime), one mediterranean maritime, and three mediterranean (Cold Mediterranean, Cool Mediterranean and Temperate Mediterranean). An aridity gradient was revealed as the primary factor regulating the distribution of the species considered. This main gradient reflects the transition between the Eurosiberian and Mediterranean bio-geographic regions. The gradient can be characterized by means of the Vernet bioclimatic index. A value ≥ 4 for this index can be taken to define the mediterranean zone in our study area. The mean minimum temperature in the coldest month was the second most influential climatic variable. Partial ordination analysis revealed that the residual variation was insignificant and that the observed variation in vegetation can be fully accounted for by climatic variables.     

Implications of floristic and environmental variation for carbon cycle dynamics in boreal forest ecosystems of central Canada

Abstract. Species composition, detritus, and soil data from 97 boreal forest stands along a transect in central Canada were analysed using Correspondence Analysis to determine the dominant environmental/site variables that differentiate these forest stands. Picea mariana stands were densely clustered together on the understorey DCA plot, suggesting a consistent understorey species composition (feather mosses and Ericaceae), whereas Populus tremuloides stands had the most diverse understorey species composition (ca. 30 species, mostly shrubs and herbs). Pinus banksiana stands had several characteristic species of reindeer lichens (Cladina spp.), but saplings and Pinus seedlings were rare. Although climatic variables showed large variation along the transect, the CCA results indicated that site conditions are more important in determining species composition and differentiating the stand types. Forest floor characteristics (litter and humus layer, woody debris, and drainage) appear to be among the most important site variables. Stands of Picea had significantly higher average carbon (C) densities in the combined litter and humus layer (43530 kg‐C.ha^‐1) than either Populus (25 500 kg‐C.ha^‐1) or Pinus (19 400 kg‐C.ha^‐1). The thick surface organic layer in lowland Picea stands plays an important role in regulating soil temperature and moisture, and organic‐matter decomposition, which in turn affect the ecosystem C‐dynamics. During forest succession after a stand‐replacing disturbance (e.g. fires), tree biomass and surface organic layer thickness increase in all stand types as forests recover; however, woody biomass detritus first decreases and then increases after ca. 80 yr. Soil C densities show slight decrease with ages in Populus stands, but increase in other stand types. These results indicate the complex C‐transfer processes among different components (tree biomass, detritus, forest floor, and soil) of boreal ecosystems at various stages of succession.     

Riparian Butterfly (Papilionoidea and Hesperioidea) Assemblages Associated with Tamarix-Dominated, Native Vegetation–Dominated, and Tamarix Removal Sites along the Arkansas River, Colorado, U.S.A.

We studied butterfly assemblages at eight riparian sites over five years. Sites included Tamarix spp.–dominated riparian areas; sites where mechanical means or biological control agents (Diorhabda elongata deserticola) were used to limit Tamarix; sites that were mixtures of native woody vegetation (e.g., Populus and Salix) and Tamarix; and native vegetation sites. We identified a gradient in butterfly community composition that changed from treated Tamarix sites, through mixed vegetation, to native vegetation sites. Tamarix sites had lower butterfly metric (riparian butterfly index [RBI]) values than did native vegetation sites. The RBI is based on a combination of richness measures and the presence of specific species and groups of butterflies. There was no significant change in the RBI over sampling periods at any sites, including both Tamarix eradication sites. The RBI at sites where Tamarix control took place did not approach restoration goals based on values at unimpacted sites. Positive effects on riparian butterfly assemblages were not linked to any Tamarix control efforts, nor did we detect a decline from initial butterfly metrics at Tamarix sites. Direct ordination provided information on environmental variables, such as amount of nectar and herbaceous plant richness, which may be important in riparian restoration efforts.     

Variation in the composition and structure of tropical savannas as a function of rainfall and soil texture along a large-scale climatic gradient in the Northern Territory, Australia

Abstract. Variation in structural and compositional attributes of tropical savannas are described in relation to variation in annual rainfall and soil texture along a subcontinental-scale gradient of rainfall in the wet-dry tropics of the Northern Territory, Australia. Rainfall varies along the gradient from over 1500 mm p.a. in the Darwin region ( c . 12° S) to less than 500 mm in the Tennant Creek region ( c . 18° S). Soils are patchy, and sands, loams and clays may occur in all major districts within the region. We utilized a large data set (1657 quadrats ° 291 woody species; with numerous measured and derived sample variables) covering an area of 0.5 million km². Correlations between floristic composition of woody species and environmental variables were assessed using DCA ordination and vector fitting of environmental variables. Vectors of annual rainfall and soil texture were highly correlated with variation in species composition. Multiple regression analyses incorporating linear and quadratic components of mean annual rainfall and topsoil clay content were performed on three structural attributes (tree height, tree cover, tree basal area) and two compositional attributes (woody species richness, deciduous tree species richness). Tree height declined with decreasing rainfall; cover, basal area, woody species richness and deciduous species richness all declined with decreasing rainfall and increasing soil clay content. Regression models accounted for between 17% and 45% of the variation in the data sets. Variation in other factors such as soil depth, landscape position and recent land-use practices (for which there were no data on an individual quadrat basis) are likely to have contributed to the large residual variation in the data set.     

祁连山东段高寒植被群落特征及其与地形气候因子关系研究

地形气候因子与物种分布的关系影响着高寒植被群落的演替,同时对山地水源涵养林功能和结构的维持具有重要的意义。以祁连山东段水源涵养林为研究对象,基于野外植物群落物种组成及地形气候因子调查数据,运用数量分类与排序等方法,探究了高寒植物群落特征及其与地形气候因子的关系。结果表明:65个调查样方中出现181个植物种,隶属40科,124属。科的物种组成及占总物种数比例分别为菊科30个种,占16.57%;蔷薇科17个,占9.44%;禾本科13个种,占7.22%;豆科11个种,占6.11%。毛茛科10个种,占5.56%。单属种82个,占总属数的66.13%。群落层片由乔木层、灌木层和草本层组成,乔木8种,灌木25种,草本148种。乔木层优势种有青海云杉、祁连圆柏、红桦。灌木层优势种有金露梅、山生柳、匙叶小檗、高山绣线菊。草本层优势种有甘肃薹草、珠芽蓼、早熟禾、唐松草、甘青蒿。TWINSPAN将高寒植被群落划分为7个群丛类型:群丛I红桦-红花蔷薇-甘肃薹草B.albosinensis-Rosa moyesii-C.kansuensis,群丛II青海云杉-匙叶小檗-甘肃薹草P.crassifolia-B.vernae-C.kansuensis,群丛III祁连圆柏-高山绣线菊-珠芽蓼Sabina chinensis-Spiraea alpine-P.viviparum,群丛IV高山绣线菊+鬼箭锦鸡儿-珠芽蓼S.alpine+Caragana jubata-P.viviparum,群丛V沙棘+甘青蒿+鼠掌老鹳草Hippophae rhamnoides+A.tangutica+Geranium sibiricum,群丛VI沙棘+苦荬菜+苦荞麦H.rhamnoides+Ixeris polycephala+Fagopyrum tataricum,群丛VII沙棘-冰草+西北沼委陵菜H.rhamnoides-Agropyron cristatum+Comarum salesovianum。7个群丛在DCA排序图上聚集分布,反映了较好的环境梯度。CCA排序结果表明,海拔是祁连山高寒植被群落植物种分布的最重要环境因子,其次是降水、温度、坡向、坡度。     

Threshold response of Madagascar's littoral forest to sea-level rise

Aim Coastal biodiversity hotspots are globally threatened by sea‐level rise. As such it is important to understand how ecosystems resist, respond and adapt to sea‐level rise. Using pollen, geochemistry, charcoal and diatom records in conjunction with previously published palaeoclimatic records, we investigated the mechanism, interactions and ecosystem response and resilience of Madagascar's littoral forest to late Holocene sea‐level rise. Location Sediment sequences were collected along the south‐east coast of Madagascar in two adjacent habitats in Mandena; the highly diverse littoral forest fragment and species‐poor Erica‐matrix. Methods We used a multi‐proxy approach to investigate the relative influence of environmental changes on the littoral ecosystem. We reconstructed past vegetation and fire dynamics over the past 6500 years at two sites in the littoral forest using fossil pollen and macrofossil charcoal contained in sedimentary sequences. Alongside these records we reconstructed past marine transgressions from the same sedimentary sequences using geochemical analyses, and a salinity and drought index through the analysis of fossil diatoms. Results Our findings indicated that it was the synergistic effect of sea‐level rise coupled with rainfall deficits that triggered a threshold event with a switch from two types of littoral forest (an open Uapaca forest and a closed littoral forest fragment) to an Erica–Myrica heath/grassland occurring in approximately less than 100 years. Resilience to sea‐level rise differed in the two adjacent habitats, suggesting that the littoral forest fragment was more resilient to the impacts of sea‐level change and aridity than the open Uapaca woodland. Conclusions We demonstrated that the littoral ecosystem was influenced by late Holocene sea‐level rise and climatic desiccation. While climate change‐integrated conservation strategies address the effects of climate change on species distribution and dispersal, our work suggests that more attention should be paid to the impacts of interactive climatic variables that affect ecosystem thresholds.     

Stream macroinvertebrate response to catchment urbanisation (Georgia, U.S.A.)

SUMMARY 1. The effects of catchment urbanisation on water quality were examined for 30 streams (stratified into 15, 50 and 100 km² ± 25% catchments) in the Etowah River basin, Georgia, U.S.A. We examined relationships between land cover (implying cover and use) in these catchments (e.g. urban, forest and agriculture) and macroinvertebrate assemblage attributes using several previously published indices to summarise macroinvertebrate response. Based on a priori predictions as to mechanisms of biotic impairment under changing land cover, additional measurements were made to assess geomorphology, hydrology and chemistry in each stream. 2. We found strong relationships between catchment land cover and stream biota. Taxon richness and other biotic indices that reflected good water quality were negatively related to urban land cover and positively related to forest land cover. Urban land cover alone explained 29–38% of the variation in some macroinvertebrate indices. Reduced water quality was detectable at c. >15% urban land cover. 3. Urban land cover correlated with a number of geomorphic variables such as stream bed sediment size (–) and total suspended solids (+) as well as a number of water chemistry variables including nitrogen and phosphorus concentrations (+), specific conductance (+) and turbidity (+). Biotic indices were better predicted by these reach scale variables than single, catchment scale land cover variables. Multiple regression models explained 69% of variation in total taxon richness and 78% of the variation in the Invertebrate Community Index (ICI) using phi variability, specific conductance and depth, and riffle phi, specific conductance and phi variability, respectively. 4. Indirect ordination analysis was used to describe assemblage and functional group changes among sites and corroborate which environmental variables were most important in driving differences in macroinvertebrate assemblages. The first axis in a non‐metric multidimensional scaling ordination was highly related to environmental variables (slope, specific conductance, phi variability; adj. R²=0.83) that were also important in our multiple regression models. 5. Catchment urbanisation resulted in less diverse and more tolerant stream macroinvertebrate assemblages via increased sediment transport, reduced stream bed sediment size and increased solutes. The biotic indices that were most sensitive to environmental variation were taxon richness, EPT richness and the ICI. Our results were largely consistent over the range in basin size we tested.     

Vegetation patterns and environmental gradients in tropical dry forests of the northern Yucatan Peninsula

Patterns of plant species composition and their relationships to soil and topographic variables were investigated in tropical dry forests across the north central Yucatan, Mexico. Seven sites were studied in the oldest accessible forests along a 200–km transect oriented northwest to southeast; an eighth site was located in a little‐disturbed area located 75 km northeast of the transect. Two of the sites were on Mayan ruins. All sites were sampled using 9–24, 10m × 20m plots (<n= 132) for woody stems ≥ 3.0 cm diameter breast height. The important natural forest species were Bursera simaruba, Caesalpinia gaumeri, Gymnopodium floribundum, Piscidia piscipula, and Thouinia paucidentata. The two most important woody species in ruin woodlands were Brosimum alicastrum and Croton lundellii. Forest plots (n=108) had 17 species on average, ruin plots (n= 24) nine species. Mean basal area of stems at the forest plots (20.7 m².ha^‐1) was lower than in ruin plots (28.4 m².ha^‐1). Detrended Correspondence Analysis generally placed plots by site along the geographic transect. Natural forest plots and sites were separated from the plots on ruin sites. The five soil and topographic variables (slope, soil depth, percent surface rock, soil pH, total soil organic matter) differed significantly among sites. Plot values were correlated with DCA axe scores. Intersite floristic variation reflects an overall west to east environmental gradient affected by climate.     

Environmental factors prevail over dispersal constraints in determining the distribution and assembly of Trichoptera species in mountain lakes

Aiming to elucidate whether large‐scale dispersal factors or environmental species sorting prevail in determining patterns of Trichoptera species composition in mountain lakes, we analyzed the distribution and assembly of the most common Trichoptera (Plectrocnemia laetabilis, Polycentropus flavomaculatus, Drusus rectus, Annitella pyrenaea, and Mystacides azurea) in the mountain lakes of the Pyrenees (Spain, France, Andorra) based on a survey of 82 lakes covering the geographical and environmental extremes of the lake district. Spatial autocorrelation in species composition was determined using Moran's eigenvector maps (MEM). Redundancy analysis (RDA) was applied to explore the influence of MEM variables and in‐lake, and catchment environmental variables on Trichoptera assemblages. Variance partitioning analysis (partial RDA) revealed the fraction of species composition variation that could be attributed uniquely to either environmental variability or MEM variables. Finally, the distribution of individual species was analyzed in relation to specific environmental factors using binomial generalized linear models (GLM). Trichoptera assemblages showed spatial structure. However, the most relevant environmental variables in the RDA (i.e., temperature and woody vegetation in‐lake catchments) were also related with spatial variables (i.e., altitude and longitude). Partial RDA revealed that the fraction of variation in species composition that was uniquely explained by environmental variability was larger than that uniquely explained by MEM variables. GLM results showed that the distribution of species with longitudinal bias is related to specific environmental factors with geographical trend. The environmental dependence found agrees with the particular traits of each species. We conclude that Trichoptera species distribution and composition in the lakes of the Pyrenees are governed predominantly by local environmental factors, rather than by dispersal constraints. For boreal lakes, with similar environmental conditions, a strong role of dispersal capacity has been suggested. Further investigation should address the role of spatial scaling, namely absolute geographical distances constraining dispersal and steepness of environmental gradients at short distances.     

The ecology of Araucaria species in New Guinea. I. Ordination studies of forest types and environments

Previous studies of the ecology and regeneration strategies of Araucaria cunninghamii and A. hunsteinii in New Guinea rainforests have treated these species as ecologically identical and disagree concerning their ability to maintain a stable population size in forest communities dominated by angiosperms. Vegetation data from a number of 0.5 ha forest sites in New Guinea are analysed in order to characterize forest types and their environmental regimes in the altitudinal zone from 700 to 1500 m a.s.l. Particular attention is paid to forests containing Araucaria species. Nodal component analysis identifies a number of distinct forest types or ‘series’, each dominated by a different species. Continuity analysis displays the location of sites and species in non-linear ordination space. Subsequent regression of environmental data on the position of sites in ordination space shows that forest types are separated along gradients related to altitude and rainfall on the one hand, and soil nutrient concentrations on the other. A. cunninghamii is generally found in wetter and less nutrient-rich sites than A. hunsteinii. The analysis of species presence data, as opposed to quantitative data, shows that whilst forest types are easily differentiated according to their dominant species, changes in floristic composition are subtle along the altitudinal and other gradients recognized.     

Seedling regeneration,environment and management in a semi‐deciduous African tropical rain forest

Questions: How is seedling regeneration of woody species of semi‐deciduous rain forests affected by (a) historical management for combinations of logging, arboricide treatment or no treatment, (b) forest community type and (c) environmental gradients of topography, light and soil nutrients? Location: Budongo Forest Reserve, Uganda. Methods: Seedling regeneration patterns of trees and shrubs in relation to environmental factors and historical management types were studied using 32 0.5‐ha plots laid out in transects along a topographic gradient. We compared seedling species diversity, composition and distribution patterns along topographic gradients and within types of historical management regimes and forest communities to test whether environmental factors contributed to differences in species composition of seedlings. Results: A total of 85 624 woody seedlings representing 237 species and 46 families were recorded in this rain forest. Cynometra alexandri C.H. Wright and Lasiodiscus mildbraedii Engl. had high seedling densities and were widely distributed throughout the plots. The most species‐rich families were Euphorbiaceae, Fabaceae, Rubiaceae, Meliaceae, Moraceae and Rutaceae. Only total seedling density was significantly different between sites with different historical management, with densities highest in logged, intermediate in logged/arboricided and lowest in the nature reserve. Forest communities differed significantly in terms of seedling diversity and density. Seedling composition differed significantly between transects and forest communities, but not between topographic positions or historical management types. Both Chao‐Jaccard and Chao‐Sørensen abundance‐based similarity estimators were relatively high in the plot, forest community and in terms of historical management levels, corroborating the lack of significant differences in species richness within these groups. The measured environmental variables explained 59.4% of variance in seedling species distributions, with the three most important being soil organic matter, total soil titanium and leaf area index (LAI). Total seedling density was positively correlated with LAI. Differences in diversity of >2.0 cm dbh plants (juveniles and adults) also explained variations in seedling species diversity. Conclusions: The seedling bank is the major route for regeneration in this semi‐deciduous tropical rain forest, with the wide distribution of many species suggesting that these species regenerate continuously. Seedling diversity, density and distribution are largely a function of adult diversity, historical management type and environmental gradients in factors such as soil nutrient content and LAI. The species richness of seedlings was higher in soils both rich in titanium and with low exchangeable cations, as well as in logged areas that were more open and had a low LAI.     

Vertebrate dispersal syndromes along the Atlantic forest: broad-scale patterns and macroecological correlates

Aim To assess the geographical variation in the relative importance of vertebrates, and more specifically of birds and mammals, as seed dispersal agents in forest communities, and to evaluate the influence of geographical and climatic factors on the observed trends. Location One hundred and thirty‐five forest communities in the Brazilian Atlantic forest. Methods We collected data on dispersal modes for 2292 woody species. By combining species × site with species × trait matrices, we obtained the percentages of endozoochory, ornithochory, mastozoochory and the mean fruit diameter for the local forest communities. We used Spearman's correlation to assess bivariate relationships between variables. Subsequently, we performed paired t‐tests to verify if variations in frequency of dispersal modes and mean fruit diameter were influenced by altitude or temperature. Then, we applied multiple linear regressions to evaluate the effect of geographical and climatic variables on variation in the relative frequency of dispersal modes and mean fruit diameter across communities. Results We found no consistent latitudinal or longitudinal trend in the percentage of vertebrate‐dispersed species, neither bird‐ nor mammal‐dispersed species along the Atlantic forest. Endozoochory was affected chiefly by annual mean rainfall, increasing towards moister sites. Forest communities located at higher altitudes had a higher percentage of bird‐dispersed species. Even when sites with identical values of annual mean temperature were compared, altitude had a positive effect on ornithochory. Conversely, we found a higher percentage of mammal‐dispersed species in warmer forests, even when locations at the same altitudinal belts were contrasted. Fruit diameter was clearly related to altitude, decreasing towards higher elevations. Main conclusions This is the first analysis of a large data set on dispersal syndromes in tropical forest communities. Our findings support the hypotheses that: (1) geographical variation in the relative number of fleshy fruit species is mainly driven by moisture conditions and is relatively independent of geographical location, and (2) broad‐scale trends in fruit size correspond to geographical variation in the relative importance of mammals and birds as seed dispersal agents at the community level.     

The identification of the seeds and fruits of common Scottish aquatic herbs

Background: There have been few quantitative observations of the attributes of native animal paths and no studies of their variation between vegetation types. These paths may be important in extending the local ranges of plant species.

Aims: To determine the incidence, cover and characteristics of native animal paths in different vegetation types, their relationships with other variables and the influence of paths on plant species distributions.

Methods: Randomly located line transects, and paired quadrats on and adjacent to paths, were used to record path and environmental attributes at 10 sites in each of 10 vegetation types. The relationships between path cover, number, width and depth and potential predictor variables were determined by using Pearsons product moment correlation.

Results: The mean cover of paths in plant communities varied between 6.5% and 12.6%. Path cover, number, width and depth varied between vegetation types. Penetration resistance, bare ground, scat density and plant species richness had higher values in path quadrats than in controls. Within particular vegetation types, several plant species were restricted to paths.

Conclusions: Animal trampling is an important influence on vegetation structure and the distribution of plant species in the study area.