Search

Questions: What will happen to species diversity in a forest when exploitation of the canopy foliage terminates? The foliage of the main canopy tree of a mountain evergreen oak forest was harvested at different intensities prior to a forest survey in 1993 and resampled in 2013 after the harvest of canopy foliage ceased (1995). We predict a decrease in herbaceous species richness with increasing canopy cover, and an opposite trend for vines and woody species. We hypothesise that plant species' alpha and beta diversity will change most in the plots where foliage was most intensively harvested while showing less change in the plots that underwent almost no harvesting. Location: Temperate evergreen laurel–oak forest in the Himalaya, Nepal. Methods: We resampled all non‐epiphytic vascular plants in 64 plots of 10 m × 10 m in 2013, following the same protocol used in 1993. Plant species were categorised into three life forms; woody (except woody vines), herbaceous, and vines. Uni‐ and multivariate numerical methods were used to assess the significance of the changes in species diversity for different life forms. Results: Vines and woody species increased, whereas herbaceous species decreased, but overall gamma diversity remained unchanged. The overall alpha richness for herbaceous species decreased, while the opposite is true for woody and vine richness. Herbaceous richness decreased and woody richness increased in the areas with low and intermediate disturbance (in 1993), whereas vines remained unchanged. Only vine richness increased in the area that was very disturbed in 1993. Total species richness as well as herbaceous and vine richness decreased with increasing tree canopy cover. Conclusions: Plots that were intensively harvested in 1993 did not recover their richness because vines dominated the forest floor. Management should prevent overexploitation, and only allow low‐intensity canopy disturbance, which may facilitate habitat diversity and thereby enhance species richness. [ABSTRACT FROM AUTHOR]

Aim: Existing phytogeographical frameworks for tropical Africa lack either spatial completeness, unit definitions smaller than the regional scale or a quantitative approach. We investigate whether physical environmental variables can be used to interpolate floristically defined vegetation units, presenting an interpolated, hierarchical, quantitative phytogeographical framework for tropical Africa, which is compared to previously defined regions. Location: Tropical mainland Africa 24°N to 24°S. Taxon: 31,046 vascular plant species and infraspecific taxa. Methods: We calculate a betasim dissimilarity matrix from a comprehensive whole‐flora database of plant species distributions. We investigate environmental correlates of floristic turnover with local non‐metric multidimensional scaling. We derive a hierarchical biogeographical framework by clustering the dissimilarity matrix. The framework is modelled using a classification decision tree method and 12 physical environmental variables to interpolate and increase the resolution of the framework across the study region. Results: Floristic turnover is related strongly to water availability and temperature, with smaller contributions from land cover, topographic ruggedness and lithology. Region can be predicted with 90% accuracy by the model. We define 19 regions and 99 districts. We find a novel arrangement of the arid regions. Regional subdivision within the savanna biome is supported with minor variation to borders. Within the forests of west and central Africa, our whole‐flora gridded regionalization supports the divisions identified by a previous analysis of trees only. Main conclusions: Physical environmental variables can be used to predict floristically defined vegetation units with very high accuracy, and the approach could be pursued for other incompletely sampled taxa and areas outside of tropical Africa. Geographical coherence is higher than in previous quantitative phytoregional definitions. For most tropical African vascular plant species, we provide predictions of which species will occur within each mapped district and region of tropical Africa. The framework should be useful for future studies in ecology, evolution and conservation. [ABSTRACT FROM AUTHOR]

Wild reindeer have a range that extends across the circumpolar region. In the last few decades, however, populations of wild reindeer have been on the decline. The reasons for these declines are poorly understood, but are suggested to be linked to both local and global climatic factors, disease, and human interference. Hardangervidda plateau in Norway is home to the largest wild reindeer population in Europe, and is at the southern end of its European range. This population is therefore of particular importance, particularly in the light of climate change. We investigated how weather and hunting have affected the wild reindeer population in Hardangervidda over the last two decades. Our findings suggest that the wild reindeer population in Hardangervidda is most affected by winter temperature and hunting, where colder temperatures and lower harvest rates typically result in higher growth rates. We did not find significant evidence for linear density dependence. Our results show trends across Hardangervidda, and give an indication of how region‐wide weather and hunting pressure can affect the wild reindeer population. As new data emerge, future investigations should look into the existence and nature of density dependence and the influence of other weather and human disturbance related factors. [ABSTRACT FROM AUTHOR]

Aims Studies of the climatic responses of plant assemblages via vegetation-based environmental reconstructions by weighted averaging (WA) regression and calibration are a recent development in modern vegetation ecology. However, the performance of this technique for plot-based vegetation datasets has not been rigorously tested. We assess the estimation accuracy of the WA approach by comparing results, mainly the root mean square error of prediction (RMSEP) of WA regressions for six different vegetation datasets (total species, high-frequency species and low-frequency species as both abundance and incidence) each from two sites. Methods Vegetation-inferred environment (plot elevation) calibrated over time is used to quantify the elevational shift in species assemblages. Accuracy of the calibrations is assessed by comparing the linear regression models developed for estimating elevational shifts. The datasets were also used for the backward predictions to check the robustness of the forward predictions. Important Findings WA regression has a fairly high estimation accuracy, especially with species incidence datasets. However, estimation bias at the extremes of the environmental gradient is evident with all datasets. Out of eight sets (each set with a model for total species, low-frequency species and high-frequency species) of WA regression models, the lowest RMSEPs are produced in the four models based on the total species datasets and in three models based on the high-frequency species only. The inferred environment mirrored the estimation precision of the WA regressions, i.e. precise WA regression models produced more accurate calibrated environmental estimates, which, in turn, resulted in regression models with a higher adjusted r 2 for estimating the elevational shift in the species assemblages. Reliable environmental estimates for plot-based datasets can be achieved by WA regression and calibration, although the edge effect may be evident if species turnover is high along an extensive environmental gradient. Species incidence (0/1) data may improve the estimation accuracy by minimizing any potential census and field estimation errors that are more likely to occur in species abundance datasets. Species data processing cannot guarantee the most reliable WA regression models. Instead, generally optimal estimations can be achieved by using all the species with a consistent taxonomy in the training and reconstruction datasets. [ABSTRACT FROM AUTHOR]

Question: Do remote sensing signals represent β‐diversity? Does β‐diversity agree with community types? Location: UNESCO Man and the Biosphere Reserve, La Palma, Canary Islands. Methods: We recorded perennial, vascular plant species abundances in 69 plots (10 m × 10 m) in three pre‐defined community types along an elevational gradient of 2,400 m: succulent scrubland, Pinus canariensis forest and subalpine scrubland. The remote sensing data consists of structural variables from airborne Light Detection and Ranging (LiDAR) and multispectral variables from a time series of Sentinel‐2 (S2) images. Non‐metric Multidimensional Scaling was used to assess β‐diversity between plots. K‐means unsupervised clustering was applied to remote sensing variables to distinguish three community types. We subsequently quantified the explanatory power of S2 and LiDAR variables representing β‐diversity via the Mantel test, variation partitioning and multivariate analysis of variance. We also investigated the sensitivity of results to grain size of remote sensing data (20, 40, 60 m). Results: The β‐diversity between the succulent and pine community is high, whereas the β‐diversity between the pine and subalpine community is low. In the wet season, up to 85% of β‐diversity is reflected by remote sensing variables. The S2 variables account for more explanatory power than the LiDAR variables. The explanatory power of LiDAR variables increases with grain size, whereas the explanatory power of S2 variables decreases. Conclusion: At the lower ecotone, β‐diversity agrees with the pre‐defined community distinction, while at the upper ecotone the community types cannot be clearly separated by compositional dissimilarity alone. The high β‐diversity between the succulent scrub and pine forest results from positive feedback switches of P. canariensis, being a fire‐adapted, key tree species. In accordance with the spectral variation hypothesis, remote sensing signals can adequately represent β‐diversity for a large extent, in a short time and at low cost. However, in‐situ sampling is necessary to fully understand community composition. Nature conservation requires such interdisciplinary approaches. We assessed beta diversity between assemblages of perennial and vascular plant species along an elevational gradient of 2,400 m, crossing three community types on La Palma, Canary Islands. Remote sensing variables were derived from LiDAR and a time series of Sentinel‐2 imagery. In the wet season, up to 85% of beta diversity is represented by RS signals. [ABSTRACT FROM AUTHOR]

Phylogenetic niche conservatism implies that sister taxa will have similar niches, although the niches of disjunct subspecies may evolve differently. This study uses Macaca assamensis, subspecies assamensis and pelops, to investigate the similarities of realized climatic niches of two disjunct subspecies (separated by the Brahmaputra River) along with a similarity analysis of their respective regions' climate. Modeled distributions were used to quantify their potential distribution under current and future climate scenarios. The climatic similarity between regions of each subspecies was tested with principal component analysis (PCA), and the realized climatic niche overlap between two subspecies was tested with a multivariate analysis of variance (MANOVA) on a subset of the least correlated variables out of 24 publicly available topo‐bioclimatic variables. Tukey's honest significance difference (HSD) was used to test the range differences (on all 24 variables) between subspecies. The potential distribution of both taxa in the current climate and projected future climate was model‐predicted using MaxEnt and Random Forest. We found significantly different climatic ranges for 21 predictors (HSD; p < 0.05) for the two subspecies, significantly different climatic conditions for their regions (using PCA; p < 0.001), and significantly different realized climatic niches for the two subspecies (MANOVA; p < 0.001). The distribution models generated a larger potential area than the currently known distributions. Although literature show that the Brahmaputra River is an effective dispersal barrier, we found some of the neighboring geographic range for both subspecies appears to be potentially suitable for the other taxon. The projected future potential areas indicate that some parts of the currently occupied geography, mostly southern parts, may become climatically unsuitable, whereas other new geographical areas may become suitable. Most of these new potential areas will be toward the north where higher and fragmented mountains, which has conservation implications. This study used Macaca assamensis subspecies assamensis and pelops to investigate the similarities of realized climatic niches of two disjunct subspecies We found significantly different ranges for 21 (of 24) predictors (p < 0.05) and significantly different realized climatic niches (p < 0.001). The distribution models generated a larger potential area than the currently known distribution as some of the neighboring areas of the current geographic range of each sister taxa appear to have climatically suitable geography for both subspecies. [ABSTRACT FROM AUTHOR]

Aim Climate change is expected to modify growth trends of forests around the world. However, this modification may vary in strength and intensity across a species' biogeographical range. Here, we study European populations of silver fir ( Abies alba) across its southern distribution limits in Spain, Italy and Romania. We hypothesized that growth trends of silver fir will differ across its distribution range, with a marked decline in growth in drought-prone regions near the species' southernmost biogeographical limits. Location Europe (Spain, Italy, Romania). Methods We collected tree-ring data from at least 1300 silver fir trees located in 111 sites. The dataset was used to assess and model growth trends, quantified as changes in basal area increment, and to determine how growth responds to climate. Results We found contrasting patterns of basal area increments among countries and sites. Populations of silver fir located outside the Mediterranean area (e.g. northern Italy, Romania) have shown a clear increase in growth over the last two decades, whereas most populations in Spain and southern Italy have displayed a marked decline in growth since the 1980s. The growth of silver fir forests at the south-western distribution limit is severely constrained by low spring-summer water availability, whereas growth of silver fir forests in non-Mediterranean areas is limited by cold conditions in late winter to early spring. Main conclusions Climate warming is distinctly modifying growth patterns and responses to climate in silver fir across most of the species' European distribution area. In south-western Europe the reduction in growth of many populations is related to an observed increase in aridity, whereas in more temperate areas warming is enhancing growth. Our results confirm a decline in the growth of silver fir at its south-western distribution limits as a consequence of climate warming. [ABSTRACT FROM AUTHOR]

Aim Comparisons of how different species respond to changing climatic conditions offer insight into future community composition and the potential formation of novel communities. This study investigated changes at a subarctic forest-tundra ecotone, or 'tree line'. Our objectives were: (1) to explore species-specific growth forms; (2) to identify temporal patterns of establishment and stand density; and (3) to explore relationships between climate and recruitment/survival amongst co-dominant tree species, with the expectation that climate change will affect species differentially. Location The Mealy Mountains in the High Subarctic Tundra ecoregion in central Labrador, Canada. Methods We examined tree line dynamics for four tree species over the past two centuries. Using ecological and age-structure data, we compared diameter/height relationships across the tree line and generated static age structures from which changes in stand density through time were compared. In addition, model residuals were used to quantify relationships between multi-decadal windows of temperature/palaeotemperature/Palmer Drought Severity Index and decadal tree recruitment. Results Trees were more stunted as elevation increased, except for white spruce ( Picea glauca) for which tree islands became the dominant growth form. The only tree seedlings found at the tree line were of larch ( Larix laricina) and to a lesser extent black spruce ( Picea mariana). From the age structure of trees (height > 2.0 m), only black spruce showed evidence of an advancing tree line. Larch and balsam fir ( Abies balsamea) have become established at the tree line most recently and have undergone greater increases in density over the past few decades. Variability in recruitment increased with elevation: larch recruitment was positively correlated with temperature and negatively correlated with drought at low elevations but negatively correlated with temperature and positively correlated with drought at high elevations, whereas black spruce recruitment was consistently positively correlated with temperature and drought. Main conclusions The multispecies approach provides evidence that species are responding differentially to climate. With continued climate change, we expect density increases and advances of larch and black spruce, giving rise to novel tree line communities. [ABSTRACT FROM AUTHOR]

Aim The aim of this study was to test, based on biological theory, which facet of temperature is most closely associated with the elevational and latitudinal low-temperature limits of seven European broad-leaved tree species. We compared three temperature-related potential constraints across three study regions: (1) absolute minimum temperature within 100 years; (2) lowest temperatures during the period of bud-break; and (3) length and temperature of the growing season. Location Western and Eastern Swiss Alps (1165-2160 m a.s.l.) and southern Sweden (57° N-59° N). Methods In situ temperature was recorded at the high-elevation and high-latitude limits of seven broad-leaved tree species and correlated with temperatures at the nearest weather stations, in order to reconstruct the temperature regime for the past 50 years. By applying generalized extreme value distribution theory, we estimated the lowest temperatures recurring during the life span of a tree. Results At their high-elevation limits, five out of the seven tree species experienced winter minimum temperatures considerably warmer than their known maximum freezing resistance in winter. For the bud-break period, potentially damaging temperatures occurred at both the elevational and the latitudinal limits and for all four species for which phenological data were available. Three out of five species for which a latitudinal replicate was available showed a similar length of growing season at their respective elevational and latitudinal limits. The mean temperature during the growing season was always warmer at a species' latitudinal limit than at its elevational limit, and hence this variable does not bear general explanatory power for the range limit. Main conclusions Low-temperature extremes during bud-break are the most likely candidates for controlling the elevational and latitudinal limits of broad-leaved tree species. The absolute minimum temperature in winter and the mean temperature during the growing season are unlikely to constrain the cold limits of these species. Thus, the results call for the use of temperature data (extremes) during key stages of spring phenology when attempting to explain the low-temperature range limits and to predict the potential range shifts of deciduous tree species. [ABSTRACT FROM AUTHOR]

Seminatural grasslands have long been shaped and maintained by human-induced fire and grazing regimes in order to utilise extensive land areas, not suitable for intensive cultivation, for the production of protein for human consumption. Changes in either management regimes have great implications for vegetation cover and composition. In this context, we qualitatively examined 18 grasslands used by transhumance agro-pastoralists in western Gorkha, Nepal, to 1) show that the pastoral landscape is undergoing change due to shrub and tree encroachment; 2) understand the role of change in grazing and fire regimes in shrub encroachment dynamics; and 3) discuss management practices and policy implications of shrub control. In this region, grassland abandonment and livestock population decline have been the overriding land-use change trend over the last four decades brought on by out-migration of local people from these marginal areas. Our results revealed thatBerberisshrub encroachment started approximately three decades ago and attained a problematic cover approximately 15 to 20 years ago. The shrub encroachment drivers are discussed in the context of changed fire and grazing practices. We underscore the necessity of management intervention to maintain the services provided by these seminatural systems; and suggest synergistic application of burning, weeding and grazing, rather than sporadic single treatment. [ABSTRACT FROM AUTHOR]

Aim As a consequence of multiple cycles of deforestation and reforestation, most forest landscapes in Europe consist of a complex mosaic of patches of different successional ages. Despite the biogeographical distinctiveness of the Mediterranean region, studies on the effects of forest age on plant species diversity and composition are almost lacking for this area. This paper evaluates the influence of forest successional age on plant species richness and composition in various forest types of Mediterranean Italy. Location The Natura 2000 network of Siena Province, Tuscany, Italy. Methods Occurrence data on vascular plant species in 208 forest plots were obtained from a larger data set sampled with a stratified random design. The forest successional age of each plot was quantified through a series of historical maps. Species richness and composition were related to the age of the forest by means of GIS techniques and univariate and multivariate statistical analyses. Results Total species richness markedly decreased with increasing successional age due to a significant decrease in the richness of open-habitat species which was not matched by increasing richness of mature forest species. Successional age was the key factor in controlling species richness, while local environmental properties emerged as the main factors shaping community composition. The different forest types showed different temporal trends of species richness and composition and different hierarchies of explanatory factors. Main conclusions Forest successional age emerged as an important factor affecting both species richness and composition, even within the same forest type. Thus, the classification and prioritization of Mediterranean forests exclusively based on present physiognomy or environmental variables causes loss of information about species richness and composition; this could be detrimental for biodiversity conservation. [ABSTRACT FROM AUTHOR]

Aim The arctic forest-tundra boundary is expected to advance rapidly northwards in response to climate warming. The purpose of this study was: (1) to analyse region-wide changes in the positions of the latitudinal forest line and tree line since the early 20th century; (2) to calculate rates of northward movement and to estimate uncertainties from different sources of data; (3) to analyse how rates of advance differ between two common tree species, Betula pubescens (downy birch) and Pinus sylvestris (Scots pine); and (4) to place the results in the context of dynamic global vegetation models. Location The study covers Finnmark county in northern Norway, which has warmed by 1-2 °C since the early 20th century. Methods Historical forest maps, topographic maps, aerial photographs and satellite imagery were used to delineate region-wide, species-specific and time-specific subarctic forest lines and tree lines. Rates of advance were calculated using two geometrical methods, placing different emphases on the shape and mean position of the lines, but yielding similar results. Results The analyses revealed an average northward advance of the birch and pine forest lines of 156 and 71 m year−1, respectively. Both showed considerable spatial and temporal variation. The birch tree line showed the most pronounced advance (340 m year−1), whereas the pine tree line showed very limited advance (10 m year−1). Data sources contributed an uncertainty of around 10 m year−1 to these rates. Main conclusions The analysis of historical and recent forest delineation data showed a very restricted advance rate compared to the predictions of dynamic global vegetation models. If these results are representative of the behaviour of the entire circumarctic forest-tundra zone over the present century, they suggest that the modelled prediction of the loss of 40% of the current tundra is a serious overestimate. A stronger focus on factors limiting the response of the forest-tundra ecotone to climate change is needed to refine the output from dynamic global vegetation models. [ABSTRACT FROM AUTHOR]

Aim The aim of this study was to assess the effect of Holocene fire activity and drought on the mesic forests of the Upper Beni and the extent of ecotone migration in south-western Amazonia during the mid-Holocene. An additional goal was to address the hypothesis of Amazonia as a manufactured landscape prior to the arrival of European colonizers in the New World in ad 1492. Location Lakes Chalalán and Santa Rosa, Upper Beni, Bolivian Amazon. Methods Holocene vegetation and fire activity were reconstructed based on pollen and microcharcoal records from sediments of lakes Chalalán and Santa Rosa. Chronologies were based on accelerator mass spectrometry radiocarbon analyses, and vegetation changes were summarized using detrended correspondence analysis. The normalized difference vegetation index was used to classify and determine the extent of the modern savanna-forest ecotone using MODIS satellite image data. Results Mesic evergreen forests persisted in the Upper Beni throughout the Holocene. Fire was frequent during the early and mid-Holocene and temporally consistent in both records. Ordination of pollen data showed an increase in forest change during the late Holocene when fire activity was asynchronous in the two records. Main conclusions The Upper Beni sites were not reached by expanding savannas during periods of major environmental change, suggesting forest resilience and a degree of ecotone stability. We associated the largest observed change in these forests with late Holocene fires that were most probably ignited by humans. We found little evidence supporting widespread pre-1491 cultural landscapes. [ABSTRACT FROM AUTHOR]

Secondary succession is an increasing phenomenon due to global changes in agriculture policies and practices. The empirical findings are biased towards the temperate zone. Abandonment of agriculture fields is less frequent in the subtropical and tropical zones where agriculture areas are, in general, expanding. But there are exceptions; a rapid rate of abandonment of agricultural fields have taken place in the arid trans-Himalayan region, due to today’s globalization of economy. We analysed agriculture fields that were abandoned between 1950 and 2003 in a large u-valley in central Nepal (3400 m a.s.l.). The potential forest vegetation is dominated by Pinus wallichina and shrubs of junipers and cotoneaster species. We tested the intermediate richness hypothesis in relation to vegetation cover, soil development and whether old-field succession is convergent or divergent with species data from 242 1 m2 plots in 5 age-classes. The main species compositional turnover expressed by Detrended Correspondence Analyses (DCA) correlated, as expected, with time after abandonment. Fields that were abandoned a long time ago are closer to forest at the periphery of the agricultural landscape. Moisture of the soil significantly increased with age of abandonment, but total vegetation cover and pH were negatively related to age. Beta diversity expressed in DCA SD-units showed an increasing trend with age of abandonment, supporting the divergence pattern in old-field succession. The reason why the succession is not converging may be due to browsing by domestic animals that prevent a closed canopy of pines and juniper to develop. There was a significant hump-shaped pattern in species richness along the temporal gradient, which agrees with the intermediate species-richness hypothesis. There was a rapid increase in species richness in plots close to the villages that were used for haymaking which increased the seed input significantly. [ABSTRACT FROM AUTHOR]

Copyright of Tropical Ecology is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)