Goats at high densities are known to degrade vegetation in arid environments around the world. Their role as potential dispersers of seeds of native and exotic plant species, however, still remains uncertain. This study assesses whether goats, through endozoochorous seed dispersal, may potentially change the plant assemblage of seasonally dry tropical forests. We used seedling emergence as a method to analyze which plant species germinated from goat feces and thus may be dispersed by goats after passing through their intestinal tract. Seedling emergence data were analyzed with respect to the plot vegetation, water availability (permanent, temporary and no water courses), and altitude (as an indicator of anthropogenic pressure). We identified 18 species belonging to 14 families. Feces from the plots near permanent water with the largest anthropogenic pressure were characterized by the highest number of germinated plants. The most common plant species by far found in the experiment was the exotic Prosopis juliflora. This high abundance of P. juliflora seedlings shows that non-native grazers facilitate the spread of exotic plant species in threatened dry forest habitats. We therefore conclude that free-roaming goats may play an important ecological role in changing plant species assemblages of even remote areas.

Aim Exploring the biotic homogenization and diversity resistance hypotheses by assessing the effect of non-native black locust canopy on understorey species turnover. Location Berlin, the Venetian metropolitan area, and Rome. Methods We modelled the zeta (zeta) expression of diversity to compare the understorey species turnover between the non-native black locust and native woodland canopies across multiple sites and through predictors of anthropogenic pressure (road and built-up density) and interior conditions (tree basal area and mean height). Results In Rome, black locust showed the lowest survivability and cover and did not produce any homogenization of the understorey. In Berlin and in the Venetian metropolitan area, black locust caused understorey homogenization, although with a lower intensity in Berlin. Under black locust canopies, distance between sites and road density was more consistently associated with species turnover, across urban areas and multiple sites. Under native canopies in Berlin, factors prominently associated with species turnover were road and built-up density and mean tree height, while in the Venetian metropolitan area it was road density. Main conclusions Evidence in support of the biotic homogenization in contrast to the diversity resistance hypothesis varied across urban areas. Species turnover was influenced by land use patterns more evidently under native tree canopies and where the non-native tree had higher survivability. Similar analyses in other urban areas may confirm these relationships with other types of landscapes.

Crops are the main source of toxic cadmium for humans due to uptake from naturally or anthropogenically polluted soils. Chronic Cd ingestion causes kidney, liver, and skeletal damage along with an increased risk of cancer. Cacao is known to accumulate Cd and may therefore be potentially harmful to human health. Consequently, cocoa production on intensely polluted soils should be avoided. Cocoa products from South America in particular often exceed the limits for Cd, but the factors that drive Cd uptake are as yet poorly studied. In this study, we measured Cd concentrations in defatted cocoa powder from unfermented seeds of 40 different trees on 20 farms in the Huánuco Region, Peru, and associated the Cd levels with the farms’ soil, field management, and nearby vegetation diversity. The mean Cd concentration found in cocoa of the study region was 2.46 mg kg −1 with a range of 0.2–12.56 mg kg −1 . The maximum content measured was an order of magnitude higher than the allowed limit of 1.5 mg kg −1 and was the highest reported so far in the literature. Soil Cd content was the most relevant driver of Cd concentration in cacao. In addition, fertilizer use caused significantly higher Cd concentration in cocoa. Higher biodiversity of herbs was positively correlated with Cd contents in cocoa. The study shows that, apart from the known correlation of soil conditions with Cd accumulation in cacao seeds, changes in fertilization and plant composition may be promising measures to counteract Cd contamination in regions with high soil Cd content.

Questions In many arid and semi-arid regions of the world, livestock husbandry is the main land use and grazing is one of the main challenges for biodiversity conservation. This also applies to the Caatinga, a unique seasonally dry tropical forest in northeastern Brazil. It is considered one of the most threatened ecosystems of Brazil. To protect semi-arid regions from biodiversity loss, degradation, and desertification, sustainable management practices are urgently needed. However, the effect of different grazing intensities on plant diversity is not yet fully understood. In this study, we examined the effect of different grazing intensities on plant species composition, alpha and beta diversity. Location Vicinity of the Itaparica Reservoir, northeastern Brazil. Methods We assessed the effects of different grazing intensities (high, intermediate, no/low) on species composition, alpha and beta diversity of the tree and shrub, and the herb layer in a Caatinga area. Plant diversity of the tree and shrub layer was assessed on 45 study plots (each 20 m x 20 m), while the diversity of herbs was studied on a subset of 36 plots (four subplots, each 2 m x 2 m). Results In total, we recorded 140 plant taxa including morphospecies. Grazing at high intensities significantly reduced almost all measures of alpha and beta diversity (tree and shrub layer) compared to areas with no or low grazing. In contrast, species composition was not significantly related to grazing but instead to altitude, which serves as an indicator of reduced anthropogenic impact such as slash-and-burn agriculture or tree harvesting. Conclusion Overall, the study results show that the current livestock management has negative effects on plant diversity in Caatinga ecosystems. These results have been incorporated into guidelines provided to regional stakeholders including recommendations for adapted land-management practices that protect and foster the biodiversity of dry forests while sustaining local livelihoods.

The phosphorus nutrition status of European forests has decreased significantly in recent decades. For a deeper understanding of complementarity and competition in terms of P acquisition in temperate forests, we have analyzed α-diversity, organic layer and mineral soil P, P nutrition status, and different concepts of P use efficiency (PUE) in Fagus sylvatica L. (European beech) and Picea abies (L.) H. Karst. (Norway spruce). Using a subset of the Second National Soil Survey in Germany, we correlated available data on P in the organic layer and soil with α-diversity indices for beech and spruce forests overall and for individual vegetation layers (tree, shrub, herb, and moss layers). Moreover, we investigated α-diversity feedbacks on P nutrition status and PUE of both tree species. The overall diversity of both forest ecosystems was largely positively related to P content in the organic layer and soil, but there were differences among the vegetation layers. Diversity in the tree layer of both forest ecosystems was negatively related to the organic layer and soil P. By contrast, shrub diversity showed no correlation to P, while herb layer diversity was negatively related to P in the organic layer but positively to P in soil. A higher tree layer diversity was slightly related to increased P recycling efficiency (PPlant/Porganic layer) in European beech and P uptake efficiency (PPlant/Psoil) in Norway spruce. The diversity in the herb layer was negatively related to P recycling and uptake efficiency in European beech and slightly related to P uptake efficiency in Norway spruce. In spruce forests, overall and herb species richness led to significantly improved tree nutrition status. Our results confirm significant, non-universal relationships between P and diversity in temperate forests with variations among forest ecosystems, vegetation layers, and P in the organic layer or soil. In particular, tree species diversity may enhance complementarity and hence also P nutrition of dominant forest trees through higher PUE, whereas moss and herb layers seemed to show competitive relationships among each other in nutrient cycling.

The use of biochar as a soil amendment is being widely studied, whereas clay addition to meliorate soils has only been considered in a few studies. However, there is a limited understanding of the impact of biochar and clay on nutrient retention under field conditions, especially in seasonally dry tropical forests in semi-arid regions. In this study, biochar and clay were added to a tropical Arenosol to quantify nutrient leaching as a measure of nutrient retention to test the potential of both amendments for soil amelioration. In a field experiment, planting holes were prepared with 5 vol% medium-temperature biochar made of Prosopis juliflora (SW) DC, produced locally in the traditional manner in a kiln, or 10 vol% clayey sediment from a temporarily dry lake. Both amendments and control were tested as fertilised and unfertilised treatments. Then seedlings of the endemic tree Spondias tuberosa Arr. were planted. Self -integrating accumulators (SIAs) were used to quantify nutrient leaching at a depth of 0.7 m for ammonium -N (NH4+ - N), nitrate -N (NO3- - N), and potassium (K+). Leaching was assessed for two consecutive periods of eight months each. In the fertilised treatments, biochar addition significantly reduced NO3- - N leaching by 46% in the first period; leaching of all other nutrients was reduced but remained non-significant. In contrast, clay addition significantly reduced NH4+ - N leaching by 790/a in the second period, K+ leaching by 51% in the first period, and by 45% in the second period, but significantly increased NO3- - N leaching by 57% in the second period. Both treatments showed pronouncedly different leaching patterns over time. Between the first and second period, the ability of biochar to reduce leaching relative to the control decreased by about half for the nutrients tested, whereas the ability of the clay treatment remained rather stable over 1.5 years for NH4+ - N and K+. The reason for the distinct decrease in nutrient retention of biochar in the second period may be the rapid decomposition of biochar carbon by 51% within 16 months. Under the given conditions, only clay can be recommended as a sustainable land management strategy to enhance NH4+ - N and K+ retention capacity of Arenosols in seasonally dry tropical forests.

Grazing is the main land use in semi-arid regions of the world, and sustainable management practices are urgently needed to prevent their degradation. However, how different grazing intensities affect forest density and ecosystem functions is often not sufficiently understood to allow for management adaptations that safeguard the ecosystems and their functions in the long run. We assessed the aboveground carbon stocks and plant densities along a grazing gradient in the semi-arid seasonally dry tropical forest of north-eastern Brazil (Caatinga). On 45 study plots, we analysed the aboveground carbon stocks of the vegetation and determined forest density and recruitment as well as the population structure of the most abundant tree species. Grazing intensity was accounted for based on the weight of livestock droppings and classified as low, intermediate, or high. Mean aboveground carbon stock was 15.74 ± 1.92 Mg ha−1 with trees and shrubs accounting for 89% of the total amount. Grazing at high intensities significantly reduced aboveground carbon stocks of herbs but not of other plant functional types. Instead, aboveground carbon stocks of trees and shrubs were negatively related to altitude above sea level, which is a proxy for reduced water availability along with lower anthropogenic impact. The population structure of the most common tree species was characterised by abundant recruitment, irrespective of grazing, whereas the recruitment of less frequent woody species was negatively affected by grazing. Overall, our data imply that grazing and forage management need to be adapted, including the reduction of free-roaming livestock and storage of fodder, to maintain carbon storage and forest density.

Spondias tuberosa Arr. Cam. is an endemic fruit-bearing tree of the Brazilian semiarid region with great socioeconomic and environmental importance. This species is a source of sustenance for small-plot farmers during the dry season, creating a close relationship between these human and plant populations. Adult individuals of this species are tolerated in heavily altered human landscapes. However, there is a lack of seedling recruitment in their natural environment, which has been attributed to seed predation, low seed germination and establishment, and the irregularity of rainfall in the region. Furthermore, land use change and overexploitation have been hypothesised to cause a risk of extinction in this species. In this study, we aimed to assess the population trends, seed’s production and predation, as well as the germination in greenhouse, of S. tuberosa from agricultural (AGR) and protected (PA) areas in a sazonal tropical dry forest, Northeastern Brazil. We selected 25 adult individuals and from each tree we measured the diameter. Under the canopy, we counted and collected the seeds of the current season. In a greenhouse, these seeds were germinated and had their growth accompanied. Our results showed that in AGR all the diameter size-class were represented while in PA the first two size-class showed a lack of individuals. The production of seeds was not difference between these two areas although the number of seedm−2 was higher in AGR. Trees located in AGR usually occurred isolated, which may explain the fact that the rate of seed’s predation was more intense in these areas. Seed’s size also were bigger in AGR and the seedlings from these seeds were more vigorous than the ones from PA. We found seedlings exclusively in agricultural areas, probably due to abundance of water and soil nutrients and to absence of wild or domesticated animals. Our results clearly show that somehow the species depends on human action to its regeneration. Thus, researchers and stakeholders (local people) should combine efforts to develop strategies for species conservation.

Aboveground carbon (C) sequestration in trees is important in global C dynamics, but reliable techniques for its modeling in highly productive and heterogeneous ecosystems are limited. We applied an extended dendrochronological approach to disentangle the functioning of drivers from the atmosphere (temperature, precipitation), the lithosphere (sedimentation rate), the hydrosphere (groundwater table, river water level fluctuation), the biosphere (tree characteristics), and the anthroposphere (dike construction). Carbon sequestration in aboveground biomass of riparian Quercus robur L. and Fraxinus excelsior L. was modeled (1) over time using boosted regression tree analysis (BRT) on cross-datable trees characterized by equal annual growth ring patterns and (2) across space using a subsequent classification and regression tree analysis (CART) on cross-datable and not cross-datable trees. While C sequestration of cross-datable Q. robur responded to precipitation and temperature, cross-datable F. excelsior also responded to a low Danube river water level. However, CART revealed that C sequestration over time is governed by tree height and parameters that vary over space (magnitude of fluctuation in the groundwater table, vertical distance to mean river water level, and longitudinal distance to upstream end of the study area). Thus, a uniform response to climatic drivers of aboveground C sequestration in Q. robur was only detectable in trees of an intermediate height class and in taller trees (>21.8m) on sites where the groundwater table fluctuated little (≤0.9m). The detection of climatic drivers and the river water level in F. excelsior depended on sites at lower altitudes above the mean river water level (≤2.7m) and along a less dynamic downstream section of the study area. Our approach indicates unexploited opportunities of understanding the interplay of different environmental drivers in aboveground C sequestration. Results may support species-specific and locally adapted forest management plans to increase carbon dioxide sequestration from the atmosphere in trees.

Riparian woodlands consist of different landscape units characterized by different hydroecomorphological site conditions that are reflected in the distribution of soils and tree species. These conditions are determined by flooding frequency and duration, distance to river channels, elevation and water flow velocity. The influence of these environmental drivers on the stabilization of soil organic matter (SOM) has as yet not been investigated. Hence, the aim of our study is to link soil formation and its drivers with stabilizing processes of SOM in riparian floodplain forests. We investigated soils and sediments at two sites in the ash-maple-elm-oak alluvial forest zone (AMEO sites) and two sites in the willow-poplar alluvial forest zone (WiP sites) within the riparian zone of the Danube near Vienna (Austria). Sediments and soils were characterized based on texture, contents of organic carbon (OC), nitrogen, Fe oxides, and soil pH. Density fractionation was used to separate OC fractions in terms of stabilization process and resulting organic matter (OM) turnover time: the free light fraction (fast turnover), the light fraction occluded in aggregates (intermediate turnover) and the heavy fraction of OM associated tightly to mineral surfaces (slow turnover).At both sites, soil and sediment properties reflect the hydroecomorphological site conditions for formation of the landscape units in the riparian zone: Soils at AMEO sites develop during constant deposition of fine-textured sediment while water flow velocity is low. Progressing soil development causes a continuous decrease in OC content with increasing soil depth, mainly from fractions with fast and intermediate turnover. As a consequence the heavy fraction clearly dominates with around 90% of OC. Temporally variable flooding conditions with occurring turbulences found at WiP sites result in a discontinuous change of soil properties with increasing soil depth. Former topsoil horizons buried by huge amounts of sediments seem to keep the OC fractionation typical for topsoil horizons with extraordinarily high amounts of light fraction OM (free and occluded) representing 20-40% of total OC. The presented results confirm that sedimentation and soil formation are simultaneous processes at AMEO sites. At WiP sites both processes seem uncoupled with alternate phases of sedimentation and soil formation. Thus, the frequent burial of topsoil material formed at WiP sites seems to enable the conservation of unstable organic matter fractions at this part of active floodplains. (C) 2015 Elsevier B.V. All rights reserved.

Model documentation of carbon sequestration in litterfall including climate and flooding parameters.

Grazing by domestic ungulates can have substantial impacts on forests in arid and semi-arid regions, possibly including severe loss of carbon from the soil. Predicting net livestock impacts on soil organic carbon stocks remains challenging, however, due to the dependence on animal loads and on soil and environmental parameters. The objective of this study was to better understand grazing effects on soil organic carbon in seasonal tropical dry forests of north-eastern Brazil (Caatinga) by quantifying carbon stocks of the upper soil profile (0-5 cm depth) and greater soil depths (>5 cm depth down to bedrock) along a gradient of grazing intensity while accounting for other influencing factors such as soil texture, vegetation, landscape topography, and water availability. We analysed soil organic carbon, soil clay content, altitude above sea level, soil depth to bedrock, distance to the nearest permanent water body, species diversity of perennial plants and aboveground biomass on 45 study plots located in the vicinity of the Itaparica Reservoir, Pernambuco, Brazil. Livestock (mainly goats and cattle) are unevenly distributed in the studied ecosystem, thus grazing intensity was accounted for based on the weight of livestock droppings per square metre and classified as no or light, intermediate, or heavy grazing. The mean soil organic carbon in the area was 16.86 +/- 1.28 Mg ha(-1) C with approximately one-quarter found in the upper 5 cm of the soil profile (4.14 +/- 0.43 Mg ha(-1) C) and the remainder (12.57 +/- 0.97 Mg ha(-1) C) in greater soil depths (>5 cm). Heavy grazing led to significantly lower soil organic carbon stocks in the upper 5 cm, whereas no effect on soil organic carbon of the soil overall or in greater soil depths was detectable. The soil's clay content and the altitude proved to be the most relevant factors influencing overall soil organic carbon stocks and those in greater soil depths (>5 cm). Our findings suggest that grazing causes substantial release of carbon from Brazilian dry forest soils, which should be addressed through improved grazing management via a legally compulsory rotation system. This would ultimately contribute to the conservation of a unique forest system and associated ecosystem services. (C) 2016 Elsevier B.V. All rights reserved.

Tropical dry forests are increasingly threatened by land degradation. For the Caatinga seasonally dry forests in Northeast Brazil, recent studies revealed both woody vegetation loss and (re-)gain. A conclusive analysis of land cover and landscape diversity changes is still lacking. To fill this gap, we surveyed pattern-process relationships for the Caatinga phytogeographical domain on different spatial levels for the years 2001-2012 from MODIS land cover data. By a landscape pattern analysis, a set of five landscape metrics was calculated using FRAGSTATS. The spatio-temporal results revealed a general decrease of fragmentation and diversity. The savanna class which comprises also Caatinga dry forests covered large parts of the landscape and gained considerably, whereas other vegetation classes decreased. The distribution of the low vegetated shrublands and grasslands implied degradation risks, in particular at the Sao Fransisco River valley. Large-scaled agriculture was found in the proximity to water reservoirs in the lowlands, which led to local increases of the landscape's diversity. We quantified both gains and losses of woody vegetation with a notable net gain of 6.7% of the study area. Main changes may be attributed to socio-economic shifts from local to large-scaled agriculture and water infrastructural activities. Overall, our study shows that a multi-temporal, global dataset along with a landscape pattern analysis provides valuable contributions to landscape research and for detecting land cover and landscape diversity changes. (C) 2016 Elsevier Ltd. All rights reserved.

The ability to accommodate crop production for an ever-growing human population and achieve conservation of rapidly declining biodiversity remains a challenging task worldwide. In agroecosystems, weed diversity and biomass are frequently assumed to be negatively related to crop yield and biomass. However, positive effects of weed species (pollinator and parasitoid attraction) and different resource acquisition strategies may reduce the competitive character of weeds a potential that can be exploited within land-sharing approaches (i.e., biodiversity conservation and agriculture on the same site). This study aimed at analyzing the relationships of weed diversity and biomass to crop yield and biomass in coconut and banana fields within an irrigation farming scheme established in former Caatinga seasonal dry forest ecosystems around the Itaparica Reservoir, Pernambuco, Brazil. Within each of 21 selected crop fields, we collected weed diversity and biomass data in the fields' center and edge along with general information on crop yield and the use of fertilizers and other agrochemical inputs. We found no evidence for a negative relationship of crop yield or biomass and weed diversity. On the contrary, crop yield and weed alpha diversity were significantly positively correlated (Shannon and Simpson indices, evenness). In contrast, weed biomass showed a significant negative correlation to crop yield. The use of organic fertilizer had a significant positive effect on crop yield, whereas no impact of herbicides or insecticides was detected. In addition, the field edge provided habitat for more weed species than the field center. Overall, our data show that in perennial tropical crop fields high yield is not opposed to high weed diversity. Moreover, the data suggest that organic farming in the area will likely not lead to yield losses. Nevertheless, the related weed assemblages inhabited only a few typical species of the native dry forest vegetation which makes their contribution to biodiversity conservation at the landscape scale debatable. (C) 2016 Elsevier B.V. All rights reserved.

Biodiversity may be positively related to crop yield, but the mechanisms by which such effects are realized are as yet poorly understood. Reduced pest incidence may be one cause. To better predict the quality and strength of biodiversity effects in cacao agroforestry systems and to disentangle potential drivers, we analyzed relationships of plant diversity with crop quantity (yield, fruit set, fruit size), pathogen incidence (Moniliophthora perniciosa,Moniliophthora roreri, Phytophthora spp.), and with the profile of selected secondary compounds (methylxanthines and polyphenols) in seeds of 48 cacao trees cultivated on 14 farms in Peruvian Amazonia. Our results revealed no correlation of yield per hectare or total fruit set with plant alpha diversity measures on the studied cacao farms. However, the number and size of ripe fruits without fungal infestation increased at higher diversity of the herb and shrub layer and at lower diversity and smaller basal area of shade trees. Greater diversity in the herb and shrub layer reduced the incidence of the Phytophthora pathogen but increased the incidence of M. roreri. At higher alpha diversity in the understory, contents of caffeine, theobromine, and catechin hydrate in cacao seeds significantly increased. The changes in plant secondary compounds showed inconsistent relations with the infestation rates of fungal pathogens. While trees infested with M. perniciosa showed higher contents of polyphenols and caffeine in seeds, cacao trees with higher caffeine content in seeds were less likely to be affected by Phytophthora. Similarly, a higher epicatechin content in seeds was associated with reduced M. roreri incidence. Our data provide evidence for a tight interplay of biodiversity, pathogen incidence, and the crop's secondary metabolism on cacao farms. Overall, considering biochemical traits in yield diversity relationships allowed for a better understanding of the contribution of biotic interactions to biodiversity effects in tropical agroforestry systems. (C) 2016 Elsevier B.V. All rights reserved.

A floristic survey was conducted in eighteen areas in the municipalities of Itacuruba and Floresta, Pernambuco, northeast Brazil. The objective was to investigate if the species richness of terrestrial plant species of the Caatinga is affected by grazing intensity. Eighteen 20x20 m2 plot were established in areas of low grazing intensity (9), and areas with high grazing intensity (9). We recorded 136 species belonging to 97 genera and 43 families. The most species-rich families were Poaceae (14), Fabaceae (13), and Asteraceae (11). The most species-rich genera were Aristida (Poaceae), Sida (Malvaceae) and Ipomoea (Convolvulaceae). The number of species in each study area (Itacuruba and Floresta) varied according to the distribution of the precipitation, the soil types, the land-use history type, and the actual land-use. Areas with a low grazing pressure show a higher species richness of plant species than areas with higher grazing intensity.

Riparian forests are expected to play a crucial role in the global carbon (C) cycle but the complex mechanisms of C sequestration in forests remain poorly understood. This study used a comprehensive approach to analyze C sequestration that included the main C compartments in forests, i.e., litterfall, fine roots, and aboveground woody biomass. We aimed at modeling each of them in response to an array of environmental drivers to untangle the functioning of C sequestration by compartment. The study was conducted in a Central European riparian forest that is part of the Donau‐Auen National Park in Austria. Carbon sequestration by compartment was correlated with environmental parameters (climate, stream flow, hydrological, spatial, and forest stand parameters) using generalized linear mixed models (GLMM), and the correlations were prioritized by hierarchical partitioning. Our results suggest divergent responses of C sequestration in different ecosystem compartments under dry and wet soil conditions. In particular, dry conditions led to significantly higher C sequestration in aboveground woody biomass (larger distance to the low groundwater table), whereas wetter conditions fostered C sequestration in fine‐root (smaller magnitude of fluctuation in the groundwater table) and leaf biomass (smaller distance to the low groundwater table). Fine roots and litterfall responded to short‐term variations in climate (mean annual temperature) and flooding parameters (duration of the low to mean Danube River water level in the previous dormant season), highlighting the pivotal role of the dynamic fine‐root and leaf biomass compartments for C uptake in forest ecosystems. Consequently, litterfall and fine roots should be considered to improve the sensitivity of C sequestration model responses to climate scenarios.