In the Footsteps of Sheep Herds: The Neonative Xeranthemum cylindraceum Has No Impact but Indicates Ruderalisation of Overgrazed Pastures in the New Range

BackgroundIncreasing drought induced by global climate changes is altering the structure and function of grassland ecosystems. However, there is a lack of understanding of how drought affects the trade-off of above- and belowground biomass in desert steppe. We conducted a four-year (2015–2018) drought experiment to examine the responses of community above-and belowground biomass (AGB and BGB) to manipulated drought and natural drought in the early period of growing season (from March to June) in a desert steppe. We compared the associations of drought with species diversity (species richness and density), community-weighted means (CWM) of five traits, and soil factors (soil Water, soil carbon content, and soil nitrogen content) for grass communities. Meanwhile, we used the structural equation modeling (SEM) to elucidate whether drought affects AGB and BGB by altering species diversity, functional traits, or soil factors.ResultsWe found that manipulated drought affected soil water content, but not on soil carbon and nitrogen content. Experimental drought reduced the species richness, and species modified the CWM of traits to cope with a natural drought of an early time in the growing season. We also found that the experimental and natural drought decreased AGB, while natural drought increased BGB. AGB was positively correlated with species richness, density, CWM of plant height, and soil water. BGB was negatively correlated with CWM of plant height, CWM of leaf dry matter content, and soil nitrogen content, while was positively correlated with CWM of specific leaf area, CWM of leaf nitrogen content, soil water, and soil carbon content. The SEM results indicated that the experimental and natural drought indirectly decreased AGB by reducing species richness and plant height, while natural drought and soil nitrogen content directly affected BGB.ConclusionsThese results suggest that species richness and functional traits can modulate the effects of drought on AGB, however natural drought and soil nitrogen determine BGB. Our findings demonstrate that the long-term observation and experiment are necessary to understand the underlying mechanism of the allocation and trade-off of community above-and belowground biomass.

The boreal biome is one of the largest in the world and its forests have been widely exploited for centuries. Consequently, large areas have suffered ecological simplification and loss of biodiversity. Under the current circumstances passive conservation measures are no longer enough and active restoration techniques need to be developed and assessed to preserve and recover the loss of biodiversity. We evaluated short- and long-term effects of two restoration methods aimed at mimicking natural disturbances on species richness, Shannon Diversity and community composition of vascular plants in the field layer and bryophytes in the ground layer. The experiment consisted of 18 forest stands in northern Sweden; each assigned to a different treatment: prescribed burning, gap cutting and untreated stands left as controls. A before-after control-impact (BACI) study design was applied and data was collected on three occasions: once prior to restoration (2010) and twice post restoration; one year (2012) and eight years after (2019). We analysed the differences in species richness and Shannon Diversity with linear mixed effect models and community composition changes with multivariate methods. Fire treatment caused an initial decline in diversity for both field and ground layer, but in the long-term, field layer surpassed the species richness and Shannon Diversity values found prior to restoration. Ground layer bryophytes species richness and Shannon Diversity remained lower than pre-treatment. Prescribed burning should, therefore, be used with caution in core areas for bryophyte diversity. Community composition in burned stands differed significantly between each time point as well as when compared to other treatments, for both layers. By contrast, we found no significant differences in diversity measures or community composition after gap cutting. The absence of effects from gap cutting suggests that minor changes in canopy cover does not affect the vegetation structure of forest stands. The organism group-specific responses, and temporal variability to restoration, highlight the importance of including more than one organism group, different restoration methodologies, and long-term studies in order to properly assess restoration outcomes at landscape level.

Predicting diversity versus community composition of aquatic plants at the river scale

This paper reports a study on species richness and composition of Tumbesian dry forest communities. We tested two alternative hypotheses about species assemblage processes in tropical dry forests: (1) species assemblage is determined by the filtering effect of environmental conditions and (2) species assemblage is determined by facilitative processes along the gradient of water availability, and thus, species richness and evenness increase as water becomes limited. In addition, we also explored the effect of climate and soil conditions on species composition in tropical dry forests. Species composition was sampled in 109 plots in terms of cover and tree diameter at breast height. Climatic, edaphic, topographic and anthropogenic degradation variables were obtained for each plot. We used generalized linear models and canonical correspondence analyses to evaluate the effect of environmental variables on species composition, richness and evenness. Water availability negatively affected richness and significantly determined the species assemblage. Species richness increased from ridges to valleys and evenness increased at higher altitudes. Soil characteristics showed no effect on richness and evenness but soil moisture, nitrogen concentration and soil temperature explained significant fractions of species composition. Although timber extraction and livestock in our study area were of low intensity, it negatively affected richness but had only a minor effect on species composition. Our results suggest that species composition in these endangered tropical dry forests may be at least partially explained by the stress-gradient hypothesis, with higher species richness at drier conditions probably induced by facilitation processes.

Effects of grazing disturbance on plant diversity, community structure and direction of succession in an alpine meadow on Tibet Plateau, China

Effects of grazing disturbance on plant diversity, community structure and direction of succession in an alpine meadow on Tibet Plateau, China

Species abundance distributions (SADs) have been the focus of many ecological studies. Understanding the causes of SAD patterns is a major stepping stone toward understanding of how ecological communities are organized. While SAD patterns have been well studied in marine environments and forests, knowledge of SADs in response to environmental or human‐induced gradients is limited, especially in desert environments. In this study, we used structural equation modeling to analyze the effects of grazing disturbance and climate on plant SADs in a desert steppe of Inner Mongolia, China, aiming to shed light on the assembly of plant communities in this region. We found both grazing disturbance and climate influenced SADs but through different pathways and with different magnitude. Grazing intensity affected SADs by reducing evenness and richness of common species, while increases in annual mean temperature and annual rainfall affected SADs by increasing richness of rare species. Climate had 30% greater effect on community structure than grazing disturbance, highlighting the role of climate in community assembly in desert environments where biological processes are highly constrained by water. We further found geometric series was associated with low annual rainfall and low richness, and log‐normal with high annual rainfall, high richness and evenness. Geometric best fit for majority of the cases (60%) regardless of grazing intensity suggesting niche differentiation on the local scale is the principal community assembly process operating in the study region. Environmental filtering and niche differentiation may be concurrently operating to structure plant communities in this region.

Influence of tree species and soil properties on ground beetle (Coleoptera: Carabidae) communities

Nitrification is the two-step aerobic oxidation of ammonia to nitrate via nitrite in the nitrogen-cycle on earth. However, very limited information is available on how fertilizer regimes affect the distribution of nitrite oxidizers, which are involved in the second step of nitrification, across aggregate size classes in soil. In this study, the community compositions of nitrite oxidizers (Nitrobacter and Nitrospira) were characterized from a red soil amended with four types of fertilizer regimes over a 26-year fertilization experiment, including control without fertilizer (CK), swine manure (M), chemical fertilization (NPK), and chemical/organic combined fertilization (MNPK). Our results showed that the addition of M and NPK significantly decreased Nitrobacter Shannon and Chao1 index, while M and MNPK remarkably increased Nitrospira Shannon and Chao1 index, and NPK considerably decreased Nitrospira Shannon and Chao1 index, with the greatest diversity achieved in soils amended with MNPK. However, the soil aggregate fractions had no impact on that alpha-diversity of Nitrobacter and Nitrospira under the fertilizer treatment. Soil carbon, nitrogen and phosphorus in the soil had a significant correlation with Nitrospira Shannon and Chao1 diversity index, while total potassium only had a significant correlation with Nitrospira Shannon diversity index. However, all of them had no significant correlation with Nitrobacter Shannon and Chao1 diversity index. The resistance indices for alpha-diversity indexes (Shannon and Chao1) of Nitrobacter were higher than those of Nitrospira in response to the fertilization regimes. Manure fertilizer is important in enhancing the Nitrospira Shannon and Chao1 index resistance. Principal co-ordinate analysis revealed that Nitrobacter- and Nitrospira-like NOB communities under four fertilizer regimes were differentiated from each other, but soil aggregate fractions had less effect on the nitrite oxidizers community. Redundancy analysis and Mantel test indicated that soil nitrogen, carbon, phosphorus, and available potassium content were important environmental attributes that control the Nitrobacter- and Nitrospira-like NOB community structure across different fertilization treatments under aggregate levels in the red soil. In general, nitrite-oxidizing bacteria community composition and alpha-diversity are depending on fertilizer regimes, but independent of the soil aggregate.

Switch of tropical Amazon forest to pasture affects taxonomic composition but not species abundance and diversity of arbuscular mycorrhizal fungal community

<p> </p><p> </p><p>The interplay between topographic complexity (aka. Geomorphology) and ecological communities is of growing interest by ecologists in the rapidly growing field of eco-engineering. This work brings a biogeomorphological lens to these studies, examining the influence of lithology and different types of geomorphic features found on rocky coasts. Geomorphic features such as pools, pits, cracks, crevices and ledges vary spatially and are closely linked to geological contingency and this in turn effects on rocky shore biodiversity (species richness, abundance and community composition). We studied these interactions in four ways: (1) a comparative study of rock mass and rock material properties at four sites in Scotland to establish the role of rock type and geomorphic feature type on ecology, (2) a comparison of two lithologies (limestone and sandstone) at the same site to identify the importance of rock type and geomorphic feature type on ecology (3) a further study integrating Terrestrial Laser Scans of geomorphic complexity overlain with ecological variables (species richness and mobile species abundance) to create a model of rocky shore species density in relation to geomorphic features and (4) a study of species density at the Glamorgan coast, Wales, comparing the effects of one geological factor – low and high density jointing (crevices and cracks) within the same bed layer. Species richness and abundance was found to significantly differ with rock type and the presence of geomorphic features on each shore, with deep pools being the optimal habitat type with regards to these ecological variables. The higher abundance of species in pools and crevices (depending on site) highlights that the presence of larger-scale features such as pools, crevices and ledges are important for the survival of intertidal species as crevices can function as refuge from predators and wave stress and pools can reduce desiccation stress at low tide.  Features that performed well in attracting higher species richness or abundance, which were ledges, deep pools and crevices, were examined in greater depth. Pits were also examined due to their common use as retrofitted ecological enhancement on coastal infrastructure (Firth et al., 2014b; Hall et al., 2018; Loke et al., 2017; Martins et al., 2010), where generalised linear models were used to examine the significance of width, depth and water holding % on species richness and abundance for each feature, allowing us to make quantitatively based assessment of which feature types are most ecologically optimal.  This greater provision of habitat through increased surface area, increased protection and greater variety of surface topography suggest that complex rock types and associated landform features/geomorphic features are more likely to have higher species richness and abundance, particularly when compared to adjacent areas of shore platforms that lack this geomorphic complexity.  These natural rocky shore biogeomorphology findings can be used to optimise future eco-engineering designs, enriching the design process and considerations for improving ecological outcomes on urbanised coasts. It also allows us to bring in geomorphic features, and thus rocky shore geomorphology into urban landscapes, enriching human interactions with geomorphology as well as ecology.</p>

Understanding what determines wildlife species richness and community composition in urban green spaces is important for wildlife management and urban planning. Numerous studies have assessed the relationships between attributes of urban green spaces (size, vegetation, isolation, urbanization) and bird species richness, but little is known about how these factors influence community composition. I censused breeding land birds in 93 urban green spaces in Oslo, Norway, and species were grouped according to ecology (habitat preference, nest site, migration, diet, and red-list status). I analysed how species richness and, in particular, how community composition (relative proportion of different ecological groups) was influenced by size of urban green spaces, presence of native forest, isolation (i.e. distance from the periphery of the city) and urban zone (i.e. centre or periphery of city). Species richness increased with size of green spaces and presence of native forest, but did not decrease towards the city centre. Community composition was affected most strongly by presence of native forest, but site size and urbanization affected some ecological groups. Specifically, sensitive ecological groups of birds (in particular forest species, ground-nesters, migratory species, and species with a specialist diet) depended in particular on the presence of native forest in urban green spaces, with additional positive effects of increasing size of urban green spaces and location close to the periphery of the city.

Summary 1. Biotic homogenization (BH), a dominant process shaping the response of natural communities to human disturbance, reflects both the expansion of exotic species at large scales and other mechanisms that often operate at smaller scales. 2. Here, we examined the relationship between BH in plant communities and spatio-temporal landscape disturbance (habitat fragmentation and surrounding habitat conversion) at a local scale (1 km²), using data from a standardized monitoring programme in France. We quantified BH using both a spatial partitioning of taxonomic diversity and the average habitat specialization of communities, which informs on functional BH. 3. We observed a positive relationship between local taxonomic diversity and landscape fragmentation or instability. This increase in local taxonomic diversity was, however, paralleled by a decrease in average community specialization in more fragmented landscapes and in more unstable landscapes around forest sites. The decrease in average community specialization suggests that landscape disturbance causes functional BH, but there was limited evidence for concurrent taxonomic BH. 4. Synthesis. Our results show that landscape disturbance is partly responsible for functional BH at small scales via the extirpation of specialist species, with possible consequences for ecosystem functioning. However, this change in community composition is not systematically associated with taxonomic BH. This has direct relevance in designing biodiversity indicators: metrics incorporating species sensitivity to disturbance (such as species specialization to habitat) appear much more reliable than taxonomic diversity for documenting the response of communities to disturbance.

Impact of Parthenium hysterophorus L. invasion on plant species composition and soil properties of grassland communities in Nepal

Timber tree plantations are considered for rehabilitating forest biodiversity in the tropics, but knowledge on determinants of faunal diversity patterns in such human-modified forest landscapes is scarce. We quantified the composition of beetle assemblages on three native timber species (Anacardium excelsum, Cedrela odorata and Tabebuia rosea) planted on former pasture to assess effects of tree species identity, tree species diversity, and insecticide treatment on a speciose group of animals in tropical plantations. The beetle assemblage parameters ‘abundance’, ‘species richness’, ‘Chao1 estimated species richness’ and ‘Shannon diversity’ were significantly reduced by insecticide treatment for each tree species. Shannon diversity increased with stand diversification for T. rosea but not for A. excelsum and C. odorata. Species similarity was highest (lowest species turnover) between beetle assemblages on T. rosea, and it was lowest (highest species turnover) for assemblages on insecticide-treated trees of all timber species. Considering trophic guilds, herbivorous beetles dominated on all tree species and in all planting schemes. Herbivores were significantly more dominant on T. rosea and C. odorata than on A. excelsum, suggesting that tree species identity affects beetle guild structure on plantation trees. Insecticide-treated stands harbored less herbivores than untreated stands, but exhibited a high abundance of predator beetle species. Our study revealed that even young pasture-afforestations can host diverse beetle assemblages and thus contribute to biodiversity conservation in the tropics. The magnitude of this contribution, however, may strongly depend on management measures and on the selected tree species.