Determinants Of Plant Species Richness Research Articles

The Effects of Expansive Shrubs on Plant Species Richness and Soils in Semi‐arid Communal Lands, South Africa

AbstractExpansion by expansive species can have severe ecological, social and economic impacts through the reduction of ecosystem goods and services and species richness. However, expansion by expansive species may also offer benefits to ecosystems and humans, through the supply of ecosystem goods and services (such as firewood, fodder and fruits), as well as potentially offering refugia in heavily used landscapes. Here, we examine the effects of four expansive dwarf shrub species (Aspalathus subtingens, Dicerothamnus rhinocerotis, Pteronia incana and Oedera genistifolia) on plant species richness (at the point scale), vegetation cover, soil properties and whether the expansive species offer refugia to other species. Plant species richness, cover and soil properties were recorded in 1‐m2 quadrats located within a mosaic of expanded and non‐expanded patches for the four expansive shrub species. Plant species richness was significantly higher in the non‐expanded areas compared to the expanded ones for all four expansive species. Some of the expansive shrubs provided refugia to certain plant species and limited the frequency of other species. With regard to species composition, there was little separation of expanded and non‐expanded samples within sites, indicating that the site factors were stronger determinants of plant species richness and composition than expansion. Therefore, it is more likely that the reduction in species richness in expanded sites is caused by multiple drivers, including vegetation attributes cover, litter cover and soil nutrients (organic C, Zn and P) and soil compaction. Copyright © 2017 John Wiley & Sons, Ltd.

Altitudinal patterns and determinants of plant species richness on the Baekdudaegan Mountains, South Korea: common versus rare species

Altitudinal patterns of plant species richness and the effects of area, the mid-domain effect, climatic variables, net primary productivity and latitude on observed richness patterns along the ridge of the Baekdudaegan Mountains, South Korea were studied. Data were collected from 1,100 plots along a 200 to 1,900 m altitudinal gradient on the ridge. A total of 802 plant species from 97 families and 342 genera were recorded. Common and rare species accounted for 91% and 9%, respectively, of the total plant species. The altitudinal patterns of species richness for total, common and rare plants showed distinctly hump-shaped patterns, although the absolute altitudes of the richness peaks varied somewhat among plant groups. The mid-domain effect was the most powerful explanatory variable for total and common species richness, whereas climatic variables were better predictors for rare plant richness. No effect of latitude on species richness was observed. Our study suggests that the mid-domain effect is a better predictor for wide-ranging species such as common species, whereas climatic variables are more important factors for range-restricted species such as rare species. The mechanisms underlying these richness patterns may reflect fundamental differences in the biology and ecology of different plant groups.

Determinants of plant species richness and patterns of nestedness in fragmented landscapes: evidence from land-bridge islands

Land-bridge islands formed by dam construction are considered to be “experimental” systems for studying the effects of habitat loss and fragmentation, offering many distinct advantages over terrestrial fragments. The Thousand Island Lake in Southeast China is one such land-bridge system with more than 1000 islands. Based on a field survey of vascular plant richness on 154 land-bridge islands during 2007–2008, we examined the effects of island and landscape attributes on plant species richness and patterns of species nestedness. We also examined the different responses of plant functional groups (classified according to growth form and shade tolerance) to fragmentation. We found that island area explained the greatest amount of variation in plant species richness. Island area and shape index positively affected species diversity and the degree of nestedness exhibited by plant communities while the perimeter to area ratio of the islands had a negative effect. Shade-tolerant plants were the most sensitive species group to habitat fragmentation. Isolation negatively affected the degree of nestedness in herb and shade-intolerant plants including species with various dispersal abilities in the fragmented landscape. Based on these results, we concluded that the effects of habitat loss and fragmentation on overall species richness depended mostly on the degree of habitat loss, but patterns of nestedness were generated from different ecological mechanisms due to species-specific responses to different characteristics of habitat patches.

Scale-dependent determinants of plant species richness in a semi-arid fragmented agro-ecosystem

Aims: (1) Understanding how the relationship between species richness and its determinants depends on the interaction between scales at which the response and explanatory variables are measured. (2) Quantifying the relative contributions of local, intermediate and large-scale determinants of species richness in a fragmented agro-ecosystem. (3) Testing the hypothesis that the relative contribution of these determinants varies with the grain size at which species richness is measured. Location: A fragmented agro-ecosystem in the Southern Judea Lowland, Israel, within a desert–Mediterranean transition zone. Methods: Plant species richness was estimated using hierarchical nested sampling in 81 plots, positioned in 38 natural vegetation patches within an agricultural matrix (mainly wheat fields) among three land units along a sharp precipitation gradient. Explanatory variables included position along that gradient, patch area, patch isolation, habitat heterogeneity and overall plant density. We used general linear models and hierarchical partitioning of variance to test and quantify the effect of each explanatory variable on species richness at four grain sizes (0.0625, 1, 25 and 225 m2). Results: Species richness was mainly affected by position along a precipitation gradient and overall plant density, and to a lesser extent by habitat heterogeneity. It was also significantly affected by patch area and patch isolation, but only for small grain sizes. The contribution of each explanatory variable to explained variance in species richness varied with grain size, i.e. scale-dependent. The influence of geographic position and habitat heterogeneity on species richness increased with grain size, while the influence of plant density decreased with grain size. Main conclusions: Species richness is determined by the combined effect of several scale-dependent determinants. Ability to detect an effect and effect size of each determinant varies with the scale (grain size) at which it is measured. The combination of a multi-factorial approach and multi-scale sampling reveals that conclusions drawn from studies that ignore these dimensions are restricted and potentially misleading.

Patterns of plant species richness in Alpine hay meadows: Local vs. landscape controls

Habitat type and quality are recognised as important local determinants of species richness, but other processes operating at the landscape scale can also affect diversity patterns. The evidence regarding the relative importance of landscape context on vascular plants is diverse, and little is known about the effects of this complex factor in Alpine environments. Hence, the primary purpose of the study was to elucidate the relative effects of the determinants of plant species richness by decomposing the variation into local and landscape components. We sampled 99 hay meadows in the Italian Alps, and recorded 14 explanatory variables ascribed to three sets: two sets of local variables, meadow management and abiotic environment, and a set of landscape variables. Plant diversity was affected primarily by local determinants. Species richness tended to increase in less fertilised meadows, confirming the detrimental effect of intensive meadow management on plant diversity. Site conditions such as steep slopes also enhanced plant species richness, showing a most pronounced positive effect in meadows that were cut less frequently. As to the landscape determinants, a high proportion of urban elements affected species richness negatively probably due to further eutrophication. In contrast, an increased length of meadow edges had a positive effect, particularly in meadows located on shallow soils. Partitioning analyses revealed that the three sets of variables showed relatively large shared effects with each other (over half of the total variation explained). In conclusion, the composition of the surrounding landscape had a lower impact on vascular plant species richness than did meadow management and local abiotic environment. Habitattyp und -qualität werden für wichtige lokale Determinanten des Artenreichtums gehalten, aber auch andere Prozesse, die auf der Landschaftsskala wirken, können Diversitätsmuster beeinflussen. Die Hinweise auf die relative Wichtigkeit dieses Landschaftszusammenhangs sind divers, und bisher ist wenig über die Effekte dieses komplexen Faktors in alpinen Umwelten bekannt. Daher war der primäre Grund dieser Untersuchung, die relativen Effekte der Determinanten des Pflanzenartenreichtums zu untersuchen, indem die Variation in lokale und Landschaftselemente zerlegt wurde. Wir beprobten neunundneunzig Heuwiesen in den italienischen Alpen und erfassten vierzehn erklärende Variablen, die drei Gruppen zugeordnet wurden: zwei Gruppen lokaler Variablen und einer Gruppe von Landschaftsvariablen. Die Pflanzendiversität wurde vor allem durch die lokalen Determinanten beeinflusst. Der Artenreichtum tendierte zu einer Zunahme in weniger gedüngten Wiesen und bestätigte den negativen Effekt einer intensiven Bewirtschaftung auf die Pflanzendiversität. Flächenbedingungen, wie steile Steigungen, verbesserten den Pflanzenreichtum, und zeigten einen besonders großen positiven Effekt in Wiesen, die weniger häufig gemäht wurden. In Bezug auf die Landschaftsdeterminanten beeinflusste ein hoher Anteil urbaner Elemente den Artenreichtum vermutlich aufgrund der zusätzlichen Eutrophierung negativ. Im Gegensatz dazu hatte eine zunehmende Länge der Wiesenränder einen positiven Effekt, besonders bei Wiesen auf flachgründigem Boden. Die „Partitioning"-Analyse ließ erkennen, dass die drei Gruppen von Variablen relativ große gemeinsame Effekte miteinander zeigten (mehr als die Hälfte der erklärten Variation). Es ließ sich schlussfolgern, dass die Zusammensetzung der umgebenden Landschaft einen geringeren Einfluss auf den Artenreichtum von Gefäßpflanzen hat als die Wiesenbewirtschaftung und die lokale abiotische Umwelt.

Determinants of plant species richness in an alpine meadow

1.Nutrient availability, defoliation and soil disturbance are important factors that influence the richness of plant communities. However, few studies have examined the interactions between these f ...

Quantifying determinants contributing to plant species richness in mosaic landscapes: a single- and multi-patch perspective

Despite good theoretical knowledge about determinants of plant species richness in mosaic landscapes, validations based on complete surveys are scarce. We conducted a case study in a highly fragmented, traditional agricultural landscape. In 199 patches of 20 representative multi-patch-plots (MPPs, 1 ha) we recorded a total of 371 plant species. In addition to an additive partitioning of species diversity at the (a) patch- and (b) MPP-scale, we adopted the recently proposed ‘specificity’ measure to quantify the contribution of a spatial subunit to landscape species richness (subunit-to-landscape-contribution, SLC). SLC-values were calculated at both scales with respect to various spatial extents. General regression models were used to quantify the relative importance of hypothesis-driven determinants for species richness and SLC-values.

Multi‐scale analysis of plant species richness in Serengeti grasslands

AbstractAim To assess scale dependence between environmental factors and plant species richness. Additionally, we aimed to identify the scales at which niche relations and habitat heterogeneity, as hypothesized by A. Shmida & M.V. Wilson (1985)Journal of Biogeography, 12, 1–20, operate in the savanna grasslands that were the focus of this study.Location Savanna grassland plant communities of Serengeti National Park, Tanzania.Methods Plant species richness was sampled in 102 modified Whittaker plots and tested for associations with two climate factors, mean annual rainfall (MAP) and potential evapotranspiration (PET), and two landscape variables, plot aspect (ASP) and topographic variation (TOPO), using multiple regressions. Scale dependence was assessed by conducting regressions after altering three aspects of spatial scale: grain, extent and focus. Grain was altered by analysing plant richness at 1, 10, 102 and 103 m2; extent was investigated by restricting the maximum distance between samples to 75, 100, 125 and 150 km; and focus was manipulated by averaging samples spatially according to geographical land regions. Within the context of our data, we assumed that niche relations were represented by climate factors and habitat heterogeneity by landscape factors.Results Across all 102 plots, plant species richness between 1 and 102 m2 had a negative relation to PET and a weak positive relation to MAP. Plant species richness at 103 m2 had a positive association with TOPO and weaker associations with climate factors. ASP stayed in the model between grains of 10 and 103 m2, but had a very weak positive association with richness. When the focus was changed to land regions, associations between plant species richness and explanatory variables strengthened, but were not qualitatively different. At spatial extents of 75 and 100 km, PET was the strongest correlate of plant species richness across all spatial grains. At spatial extents ≥ 125 km, PET explained the majority of the model variance at spatial grains ≤ 102 m2, whereas TOPO explained equal amounts or more of the model variance at spatial grains of 103 m2.Main conclusions Both climate and topographic variation explained plant species richness in Serengeti grasslands, but specific patterns depended on grain, extent and, to a lesser degree, focus. Consistent with the ideas of Shmida & Wilson (1985), determinants of plant species richness shifted from niche relations to habitat heterogeneity between spatial grains of 1 and 103 m2, although this occurred only at relatively large spatial extents (≥ 150 km). Finally, the signs, strength and shape of plant species richness relationships in Serengeti closely match those that describe macro‐scale patterns of woody plant species richness across the entire African continent.

Effects of local factors on plant species richness and composition of Alpine meadows

The determinants of plant species richness and composition of meadows are often mutually related, showing joint effects on plant diversity. Thus, the specific objective of this paper was to evaluate the relative importance of soil, topography, and field management explanatory variables on plant species richness and composition of mown meadows in an area of the Southern Alps. The data consisted of 159 taxa sampled during the summer of 2003 in 56 10 × 10 m2 sampling plots. For each plot, 25 explanatory variables were recorded. The variation in species richness and composition was divided into the three sets of explanatory variables using a variation partitioning method. Species richness was mostly controlled both by the short-term effect of nitrogen fertilisation, and, as stressed by studies in other landscape contexts in Europe, by the long-term effect of soil phosphorus accumulation. The decrease of plant species number on the most fertile meadows was the consequence of the dominance of few competitors or ruderals, which prevented the establishment of small stress-tolerant species. In contrast to species richness, plant species composition presented an important pure effect of topography (altitude and slope). Species composition depended on several topography, soil, and field management factors. Thus, for both conservation and restoration of species-rich hay meadows, it is necessary to maintain a low level of soil P content, and to prevent the abandonment of parcels on steep slopes and in marginal areas, because these hosted the highest level of plant diversity.

Determinants of Species Richness in the Park Grass Experiment

The Park Grass Experiment at Rothamsted in southeast England was started in 1856, making it the longest-running experiment in plant ecology anywhere in the world. Experimental inputs include a range of fertilizers (nitrogen, phosphorus, potassium, and organic manures) applied annually, with lime applied occasionally, and these have led to an increase in biomass and, where nitrogen was applied in the form of ammonium sulfate, to substantial decreases in soil pH. The number of species per plot varies from three to 44 per 200 m(2), affording a unique opportunity to study the determinants of plant species richness and to estimate the effect sizes attributable to different factors. The response of species richness to biomass depends on the amount and type of nitrogen applied; richness declined monotonically with increasing biomass on plots receiving no nitrogen or receiving nitrogen in the form of sodium nitrate, but there was no relationship between species richness and biomass on plots acidified by ammonium sulfate application. The response to lime also depended on the type of nitrogen applied; there was no relationship between lime treatment and species richness, except in plots receiving nitrogen in the form of ammonium sulfate, where species richness increased sharply with increasing soil pH. The addition of phosphorus reduced species richness, and application of potassium along with phosphorus reduced species richness further, but the biggest negative effects were when nitrogen and phosphorus were applied together. The analysis demonstrates how multiple factors contribute to the observed diversity patterns and how environmental regulation of species pools can operate at the same spatial and temporal scale as biomass effects.

Determinants of plant species richness on small Bahamian islands

AimI investigated the determinants of plant species richness in two archipelagos, comparing the predictive power of different explanatory variables. I evaluated both conventional variables and alternative variables not commonly used in such analyses. I also investigated the effect of island location in relation to neighbouring landmasses on plant species richness and the predictive ability of regression models.LocationArchipelagos of small islands in the central Exumas and near the north‐east coast of Andros, Bahamas.MethodsI surveyed plant species richness and obtained measures of seven predictor variables: total island area, the ratio of perimeter to total area, vegetated area, the ratio of vegetated area to total area, distance to the nearest large island, elevation and protection from surrounding islands. All seven predictor variables were evaluated as determinants of plant species richness in simple and stepwise multiple linear regressions. Analyses were conducted for each archipelago overall, and then separately for three categories of islands in the Exumas. Total area, elevation, and distance were evaluated as predictors of vegetation incidence in simple and stepwise multiple logistic regressions for both archipelagos.ResultsSome expression of insular area was always the best single predictor of plant species richness in the linear regressions. Total area was a relatively poor predictor compared with other expressions of insular area. Distance, elevation, and protection explained relatively little of the overall variation in plant species number, although all variables were selected as significant in some models. A greater amount of variation in plant species richness was explained by the linear regression models in the Exumas (69.0%) compared with Andros (60.9%). Different variables were entered into the models for the three categories of islands in the Exumas, and adjusted coefficients of multiple determination ranged from 68.9% to 85.7%. In the logistic regressions, the model including total area and distance yielded almost 90% correct classification of vegetation incidence in the Exumas; no significant variables were selected for Andros. A group of exposed, outer islands supported many fewer species than more sheltered islands, on the basis of total island area or elevation.Main conclusionsThe three variables commonly used in studies of determinants of insular species richness – total island area, distance, and elevation – were relatively poor predictors in most analyses. Alternative expressions of insular area – indicative of disturbance or shape in combination with area – were usually better predictors than total area and may more realistically reflect habitable area. Alternative predictors explained similar amounts of variation in plant species richness compared with commonly used predictors, and combinations of all variables into a single stepwise model resulted in increased predictive power. The predictive power of the models tended to be higher for groups of islands that were more sheltered by neighbouring islands. Exposed islands, although separated by relatively small distances from nearby protected islands, may be impacted by storms much more severely and possess many fewer species. The location of small islands relative to large landmasses, as well as their geological histories, should be taken into account in such analyses.

Stand and neighbourhood parameters as determinants of plant species richness in a managed forest

Abstract. Patterns of species richness in a managed forest were related to ecological factors at two spatial scales. Local variables within a plot (5 m × 5 m) included 13 soil classes and nine stand classes. Neighbourhood variables were defined within a 25 m radius from the focal plot and were measured using a Neighbourhood Diversity Index (NDI ‐ total diversity of different stand classes) and nine Neighbourhood Scores (NS ‐ relative dominance of a given stand class).224 species were registered in the survey of which 138 were true forest species. Local parameters (stand and soil class) were weak predictors of total and forest species richness. High total and forest species richness were significantly related to high values of NDI (i.e. heterogeneous neighbourhoods). Regression trees showed that total species richness was best predicted by the amount of roadside habitat in the neighbourhood and NDI. Forest species richness was positively related to NDI and negatively related to the amount of coniferous stands in the neighbourhood.