Patterns Of Plant Species Richness Research Articles

Functional group dominance and not productivity drives species richness

Background: There is a lack of consensus about the productivity–richness relationship, with several recent studies suggesting that it is not productivity but other factors that are the important drivers that determine species richness.Aims: Here, we examine the relationship between productivity, functional group dominance and plant species richness at the plot scale in Tibetan Plateau meadows. These alpine meadows are ideal to examine the species productivity-richness relationship because they have a very high species richness, a large gradient in productivity, and can be dominated by either graminoids (grasses and sedges) or forbs.Methods: We measured plant species richness and above-ground biomass along a natural gradient of functional group abundance in 44 plots distributed across five natural, winter-grazed but otherwise undisturbed sites in the eastern part of the Qing-Hai Tibetan Plateau, in Gansu province, China in 2008.Results: Graminoid abundance (i.e. graminoid biomass as percent of the total above-ground biomass) explained 39% of plot differences in species richness while neither productivity nor the biomass of the three most abundant plant species, either individually or combined, were a significant predictor of species richness.Conclusions: Our results show that within these alpine meadows, a shift from graminoid to forb dominance, rather than the individual dominant species or productivity itself, is strongly correlated with species richness. Thus, differences in functional group abundance can be a strong driver of observed plant species richness patterns.

Old nurses always die: impacts of nurse age on local plant richness

Palatable exotic shrubs plantation in heavily degraded rangeland has been massively managed in arid and semi-arid Algeria. An associated effect observed to these managements is an increase of plant richness in these plantations due to positive interactions involving nurse species that ameliorate stressful environmental conditions. Our objective was to assess the importance and impact of nurse age on the recovery of herbaceous plant species richness. The impact of the shrub presence on the spatial repartition of herbaceous plant richness was quantified, and we tested whether it remains constant with nurse growth and ageing. Using cumulative species richness on radial transects from the nurse centre to nurse external canopy we described the spatial patterns of plant species richness around different Atriplex canescens from saplings to senescent individuals. Resulting cumulative radial species curves were modelled using linear and non-linear models and tested against null models. Nurse volumes and overall plot species richness exhibited a sigmoid shape from 2 to 15 years. The best-fitted models of the radial cumulative species richness changed with the nurse age. In young life stages, a strong positive effect under the shrub was detected. At intermediate life stages, the richness in the subcanopy was significantly impoverished whereas cumulative richness sharply grew under the shrub external canopy. At senescent life stage, cumulative species richness did not indicate a remaining effect of the shrub. An improved description of planted shrubs nurse effect consequences on plot richness is provided and suggests that late plantation opening to stock can concur to the maximization of species richness in afforested plots.

Influence of socioeconomic status on design of Batswana home gardens and associated plant diversity patterns in northern South Africa

Over the last two decades, home garden studies have markedly increased in both developed and developing countries. However, garden design and its influence on the overall biodiversity of the urban green infrastructure remains a neglected aspect of home garden research. Home garden surveys were conducted in the North West and Gauteng Provinces of South Africa to contribute to this research focus. The two questions asked in this paper were: (1) Are Batswana garden designs associated with socioeconomic status (SES)? (2) Are the different garden designs characterized by specific plant species richness patterns? We hypothesized that SES influences garden design and that, as the SES of Batswana residents increases, the garden design changes from tshimo to colonial. Our results indicated that garden design reflected less cultural influences and took on a more Westernized colonial design appearance with improvement of SES of Batswana inhabitants. Tshimo gardens tended to have more native and utilitarian species. In contrast, colonial gardens have more alien ornamental species. In affluent areas, sampled Batswana gardens completely changed from a tshimo to colonial garden design. This change indicates that improved socioeconomic status overrides traditional cultural practices.

Patterns and determinants of plant richness by elevation in a mountain ecosystem in South Korea: area, mid-domain effect, climate and productivity

We examined patterns of plant species richness on an elevation gradient and evaluated the effects of climatic variables including mean annual temperature and precipitation, area, the mid-domain effect and productivity on species richness along two transects on Mt. Seorak, South Korea. A total of 235 plant species of 72 families and 161 genera were recorded from 130 plots along the two transects. Two different patterns, monotonic decline and a unimodal shape, were observed for woody plants with the change in elevation along the two transects, whereas multimodal patterns were observed for all plant species considered together and for herbaceous plants. Area and productivity showed significant relationships with total plant richness. Climatic variables were better predictors than other variables for variation by elevation in woody plant richness, whereas productivity was a more important variable for herbaceous plant richness. Although area was an important variable for predicting species richness patterns, the effects differed by transect and plant group. No empirical evidence was linked to the mid-domain effect. Different elevational patterns may characterize different groups in the same taxon and there might be fundamental differences in the mechanisms underlying these richness patterns.

Plant species richness patterns along a gradient of landscape modification intensity in Lower Saxony, Germany

Several concepts of landscape modification, landscape naturalness and hemeroby have been put forward to quantify the extent of human activities and impact on landscapes. However, despite numerous studies on the human influence on landscapes, the relationship between these concepts and biodiversity has rarely been tested. On a grid of 1386 lat/long cells (landscape units, c. 30km2) we used simple information on land cover and easily measurable landscape metrics to identify a gradient of landscape modification for the model region of Lower Saxony, Germany. We linked the gradient of landscape modification intensity to richness patterns of eight groups of vascular plants that were aggregated using residence and threat status and habitat preferences of the species. Using k-means cluster analysis a gradient of six landscape modification levels ranging from highly-fragmented urban landscapes to little-fragmented landscapes with large proportions of forest was followed. Richness of the eight species groups considered in the analysis differed significantly along the gradient. For the total and native species pools, for forest, low-nutrient indicating and threatened plants richness peaked at both ends of the modification intensity gradient. For neophytes, urban plants and high-nutrient indicators, richness decreased along the gradient from urbanised to less modified landscapes. Due to its simplicity and coarse scale, our approach may easily be applied to other study areas without comprehensive data on land cover. Furthermore, following proper interpretation by experts, it can be used to identify and preselect priority landscapes for nature conservation planning.

Multi-scale comparison of topographic complexity indices in relation to plant species richness

Topographic complexity is a key component of habitat, which has been linked to increased species richness in many ecological communities. It can be measured in various ways and it is unclear whether these different measurements are mutually comparable when they relate to plant species richness at different spatial scales. Using a densely sampled set of observations for Rhododendrons (406 species and 13,126 georeferenced records) as a test case, we calculated eight topographic complexity indices from a 250-m resolution digital elevation model and examined their correlations with Rhododendron species richness in China at seven spatial scales: grain sizes 0.05°, 0.1°, 0.25°, 0.5°, 1.0°, 1.5°, and 2.0°. Our results showed that the eight topographic complexity indices were moderately to highly correlated with each other, and the relations between each pair of indices decreased with increasing grain size. However, with an increase in grain size, there was a higher correlation between topographic complexity indices and Rhododendron species richness. At finer scales (i.e. grain size≤1°), the standard deviation of elevation and range of elevation had significantly stronger correlations with Rhododendron species richness than other topographic complexity indices. Our findings indicate that different topographic complexity indices may have positive correlations with plant species richness. Moreover, the topographic complexity–species richness associations could be scale-dependent. In our case, the correlations between topographic complexity and Rhododendron species richness tended to be stronger at coarse-grained macro-habitat scales. We therefore suggest that topographic complexity index may serve as good proxy for studying the pattern of plant species richness at continental to global levels. However, choosing among topographic complexity indices must be undertaken with caution because these indices respond differently to grain sizes.

Patterns of fine-scale plant species richness in dry grasslands across the eastern Balkan Peninsula

Fine-scale plant species richness varies across habitats, climatic and biogeographic regions, but the large-scale context of this variation is insufficiently explored. The patterns at the borders between biomes harbouring rich but different floras are of special interest. Dry grasslands of the eastern Balkan Peninsula, situated in the Eurasian forest-steppe zone and developed under Mediterranean influence, are a specific case of such biome transition. However, there are no studies assessing the patterns of fine-scale species richness and their underlying factors across the eastern Balkans. To explore these patterns, we sampled dry and semi-dry grasslands (phytosociological class Festuco-Brometea) across Bulgaria and SE Romania. In total, 172 vegetation plots of 10 × 10 m2 were sampled, in which all vascular plant species were recorded, soil depth was measured, and soil samples were collected and analysed in a laboratory for pH and plant-available nutrients. Geographic coordinates were used to extract selected climatic variables. Regression trees and linear regressions were used to quantify the relationships between species richness and environmental variables. Climatic factors were identified as the main drivers of species richness: (1) Species richness was strongly positively correlated with the mean temperature of the coldest month: sub-Mediterranean areas of S and E Bulgaria, characterized by warmer winters, were more species-rich. (2) Outside the sub-Mediterranean areas, species richness strongly increased with annual precipitation, which was primarily controlled by altitude. (3) Bedrock type and soil pH also significantly affected dry grassland richness outside the sub-Mediterranean areas. These results suggest that fine-scale species richness of dry grasslands over large areas is driven by processes at the regional level, especially by the difference in the species pools of large regions, in our case the Continental and Mediterranean biogeographic regions. Local environmental factors are of secondary importance over broad extents, but their effect on fine-scale species richness increases within climatically and biogeographically homogeneous regions.

Patterns of species richness and conservation in the Caatinga along elevational gradients in a semiarid ecosystem

Altitudinal gradients provide a useful model for studying plant community composition along environmental gradients. Altitudinal gradients also vary in their degree of human exploitation, as human activity is generally greater at lower elevations than at higher elevations. We examined the effect of altitude on plant community composition along an altitudinal gradient ranging from 400 to 600 m a.s.l. by sampling 75 plots in a Brazilian savanna steppe characterized by a diversity of plant community types. Plant species richness increased with elevation, and the lowest species richness was associated with lower elevation areas dominated by human disturbance. Our results suggest that increased human pressure at lower altitudes, together with enhanced microclimates and reduced access at higher altitudes, determine the plant species richness patterns in dry tropical forests.

Network biogeographical analysis of the central Aegean archipelago

AbstractAimAlthough the factors shaping plant species richness patterns across the islands of the central Aegean are well known, the processes driving the assembly of these island communities remain unclear. To shed light on these processes, we identified biogeographical modules within the phytogeographical area of the Cyclades and tested for nestedness across the islands.LocationThe Cyclades, Greece.MethodsWe used a network approach to detect island biogeographical roles and modules, based on a large and detailed database of the Greek endemic plant taxa of the Cyclades, and we tested for nestedness in the island–species matrices.ResultsThe Cyclades were significantly modular and divided into five biogeographical modules. Three of the modules were significantly nested and two displayed all four possible biogeographical roles (connectors, module hubs, network hubs, peripherals). Most of the network's taxa are classified as peripherals and widespread endemics.Main conclusionsThe borders of the five modules correspond remarkably well to the palaeogeographical and climatic compartmentalization of the Cyclades. The flora of the Cyclades has not yet reached the relaxation phase and the region may act as an ecogeographical filter for the distribution of several plant lineages. Naxos, Milos and Anafi play an important role for the network's connectivity, while at least five adjacent phytogeographical regions affect the distribution patterns of the endemic taxa present in the Cyclades.

Patterns of Plant Species Richness Along Environmental Gradients in German North Sea Salt Marshes

In salt marshes, species richness changes along environmental, disturbance and productivity gradients forming a complex network of abiotic and biotic factors. On 2,691 plots along 121 transects, we sampled vegetation along the German mainland North Sea coast (13 regions) during 1987–1989. Applying regression tree analysis (RTA), we now used this large data set to analyse variance in species richness (SRich) in relation to 13 explanatory variables varying on different scales. SRich (mean, 4.9 per m2) was significantly correlated to most variables. Only six variables were included in our final model, together explaining 68.5 % of variance in SRich, in hierarchical order: moisture, salinity, evenness, nitrogen, region and elevation. Predominantly, SRich was limited by environmental heterogeneity (moisture, salinity and nitrogen, each explained approx. 50 % variance). SRich tended to be high on plots exhibiting a combination of low moisture, salinity and nitrogen values, with high evenness—and especially high in some regions when plots were lying high in relation to mean high tide. Grazing regimes did not affect SRich significantly. In conclusion, our model showed that SRich in the study area was predominantly explained on a small scale and less along large-scale gradients. RTA proved suitable to identify the set of variables that mainly explained variance in SRich. Our tree model improves the understanding of richness patterns in salt marshes and can be used to predict species richness for the study area. Furthermore, our data provide a reference to detect richness changes due to, for example, management changes or sea level rise.

Patterns of plant species richness on a glacier foreland in the Tropical Andes

Patterns of plant species richness on a glacier foreland in the Tropical Andes

Prioritizing conservation of tropical dry forests in the Pacific

AbstractTo identify forests of high priority for conservation in tropical dry forests of New Caledonia, Fiji, the Marquesas and Hawaii, we examined patterns of woody plant species richness (total, native and endemic) and threatened species (IUCN categorization and density) at the stand level, using Gentry's transect method. There were associations between total, native and endemic plant species richness in all four Pacific dry forest regions but we found no significant association with the presence or density of species listed on the IUCN Red List. Dry forests in New Caledonia and Hawaii merit the highest conservation priority in the Pacific, based on level of endemism and number of threatened species. The study sites that merit high conservation priority are Metzdorf, Nekoro and Pindai, in New Caledonia, Kokee and Kaupulehu, in Hawaii, and Vatia, in Fiji. New Caledonia and Fiji have a small dry forest extent and protected area extent compared with other dry forests in biodiversity hotspots. Although we identified priority areas for dry forest conservation, more comparative plot data, presence/absence data in fragments and regional geographical data are needed to adequately manage and protect dry forests in the Pacific.

Elevational patterns of plant richness in the Taibai Mountain, China.

The elevational distribution of plant diversity is a popular issue in ecology and biogeography, and several studies have examined the determinants behind plant diversity patterns. In this study, using published data of the local flora of Taibai Mountain, we explored the effects of spatial and climatic factors on plant species richness. We also evaluated Rapoport's elevational rule by examining the relationship between elevational range size and midpoint. Species richness patterns were regressed against area, middle domain effect (MDE), mean annual temperature (MAT), and mean annual precipitation (MAP). The results showed that richness of overall plants, seed plants, bryophytes, and ferns all showed hump-shaped patterns along the elevational gradient, although the absolute elevation of richness peaks differed in different plant groups. Species richness of each plant group was all associated strongly with MAT and MAP. In addition to climatic factors, overall plants and seed plants were more related to area in linear regression models, while MDE was a powerful explanatory variable for bryophytes. Rapoport's elevational rule on species richness was not supported. Our study suggests that a combined interaction of spatial and climatic factors influences the elevational patterns of plant species richness on Taibai Mountain, China.

Environment and dispersal paths override life strategies and residence time in determining regional patterns of invasion by alien plants

Abstract We describe a novel dissimilarity framework to analyze spatial patterns of species diversity and illustrate it with alien plant invasions in Northern Portugal. We used this framework to test the hypothesis that patterns of alien invasive plant species richness and composition are differently affected by differences in climate, land use and landscape connectivity ( i.e. Geographic distance as a proxy and vectorial objects that facilitate dispersal such as roads and rivers) between pairs of localities at the regional scale. We further evaluated possible effects of plant life strategies (Grime's C-S-R) and residence time. Each locality consisted of a 1 km 2 landscape mosaic in which all alien invasive species were recorded by visiting all habitat types. Multi-model inference revealed that dissimilarity in species richness is more influenced by environmental distance (particularly climate), whereas geographic distance (proxies for dispersal limitations) is more important to explain dissimilarity in species composition, with a prevailing role for ecotones and roads. However, only minor differences were found in the responses of the three C-S-R strategies. Some effect of residence time was found, but only for dissimilarity in species richness. Our results also indicated that environmental conditions ( e.g. climate conditions) limit the number of alien species invading a given site, but that the presence of dispersal corridors determines the paths of invasion and therefore the pool of species reaching each site. As geographic distances ( e.g. ecotones and roads) tend to explain invasion at our regional scale highlights the need to consider the management of alien invasions in the context of integrated landscape planning. Alien species management should include (but not be limited to) the mitigation of dispersal pathways along linear infrastructures. Our results therefore highlight potentially useful applications of the novel multimodel framework to the anticipation and management of plant invasions.

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.

Patterns of endemism along an elevation gradient in Sierra Nevada (Spain) and Lefka Ori (Crete, Greece)

Aim: High mountains in the Mediterranean region of Europe are particularly rich in endemic vascular plants. We aimed to compare the altitudinal patterns of vascular plant species richness and the proportion of endemic species in two Mediterranean region: Lefka Ori on the island of Crete (Greece) and Sierra Nevada on the Iberian peninsula. Location: Sierra Nevada, Granada (Spain); Lefka Ori, Crete (Greece). Methods: Data from standardised permanent plots settings on summit sites (comprising eight plot sectors, covering the upeermost 10 altitudinal metres) of different elevations were used (GLORIA Multi-Summit approach; www.gloria.ac.at). Species numbers, rates of endemic species, and soils temperature were compared by means of ANCOVA and linear regression. Results: The two regions, though climatically similar, showed strikingly different patterns: In Sierra Nevada, the proportion of endemic vascular plants (species restricted to Sierra Nevada) showed a stepwise increase from the lowest to the highest summit. In contrast, the proportion of endemic species restricted to Crete was not significantly different between the four summits in Lefka Ori. In both regions the observed trends were largely consistent with the altitudinal distribution of the endemic species obtained from standard floras. Main conclusions: The geographic positions of the two regions, i.e. island versus mainland and the higher elevation of Sierra Nevada are suggested to be the primary causes of the observed differences. The high degree of endemism in the cold environments of Mediterranean mountains’ upper bioclimatic zones indicates a pronounced vulnerability to the impacts of climate change. A continued and intensified species monitoring in the mountains around the Mediterranean basin, therefore, should be considered as a priority research task.

Geographical sampling bias in a large distributional database and its effects on species richness–environment models

AbstractAimRecent advances in the availability of species distributional and high‐resolution environmental data have facilitated the investigation of species richness–environment relationships. However, even exhaustive distributional databases are prone to geographical sampling bias. We aim to quantify the inventory incompleteness of vascular plant data across 2377 Chinese counties and to test whether inventory incompleteness affects the analysis of richness–environment relationships and spatial predictions of species richness.LocationChina.MethodsWe used the most comprehensive database of Chinese vascular plants, which includes county‐level occurrences for 29,012 native species derived from 4,236,768 specimen and literature records. For each county, we computed smoothed species accumulation curves and used the mean slope of the last 10% of the curves as a proxy for inventory incompleteness. We created a series of data subsets with different levels of inventory incompleteness by excluding successively more under‐sampled counties from the full data set. We then applied spatial and non‐spatial regression models to each of these subsets to investigate relationships between the species richness of subsets and environmental factors, and to predict spatial patterns of vascular plant species richness in China.ResultsLog10‐transformed numbers of records and documented species were strongly correlated (r = 0.97). In total, 91% of Chinese counties were identified as under‐sampled. After controlling for inventory incompleteness, the overall explanatory power of environmental factors markedly increased, and the strongest predictor of species richness switched from elevational range to annual wet days. Environmental models calibrated with more complete inventories yielded better spatial predictions of species richness.Main conclusionsOur results indicate that inventory incompleteness strongly affects the explanatory power of environmental factors, the main determinants of species richness obtained from regression analyses, and the reliability of environment‐based spatial predictions of species richness. We conclude that even large distributional databases are prone to geographical sampling bias, with far‐reaching implications for the perception of and inferences about macroecological patterns.

Elevational gradient of vascular plant species richness and endemism in Crete--the effect of post-isolation mountain uplift on a continental island system.

Understanding diversity patterns along environmental gradients and their underlying mechanisms is a major topic in current biodiversity research. In this study, we investigate for the first time elevational patterns of vascular plant species richness and endemism on a long-isolated continental island (Crete) that has experienced extensive post-isolation mountain uplift. We used all available data on distribution and elevational ranges of the Cretan plants to interpolate their presence between minimum and maximum elevations in 100-m elevational intervals, along the entire elevational gradient of Crete (0–2400 m). We evaluate the influence of elevation, area, mid-domain effect, elevational Rapoport effect and the post-isolation mountain uplift on plant species richness and endemism elevational patterns. Furthermore, we test the influence of the island condition and the post-isolation mountain uplift to the elevational range sizes of the Cretan plants, using the Peloponnese as a continental control area. Total species richness monotonically decreases with increasing elevation, while endemic species richness has a unimodal response to elevation showing a peak at mid-elevation intervals. Area alone explains a significant amount of variation in species richness along the elevational gradient. Mid-domain effect is not the underlying mechanism of the elevational gradient of plant species richness in Crete, and Rapoport's rule only partly explains the observed patterns. Our results are largely congruent with the post-isolation uplift of the Cretan mountains and their colonization mainly by the available lowland vascular plant species, as high-elevation specialists are almost lacking from the Cretan flora. The increase in the proportion of Cretan endemics with increasing elevation can only be regarded as a result of diversification processes towards Cretan mountains (especially mid-elevation areas), supported by elevation-driven ecological isolation. Cretan plants have experienced elevational range expansion compared to the continental control area, as a result of ecological release triggered by increased species impoverishment with increasing elevation.

Effects of altitude and climate in determining elevational plant species richness patterns: A case study from Los Tuxtlas, Mexico

Altitudinal changes of composition and richness of montane plant assemblages are complex, depending on the taxonomic group and gradient conditions, with different factors involved that are directly altitude-dependent (e.g., temperatures, air pressure) and altitude-independent (e.g., precipitation, cloud cover, area). In order to assess the relative impacts of temperature, precipitation, air humidity, and area of altitudinal belts on plant diversity, we analyzed diversity patterns of five species-rich groups, mostly herbaceous plants, in 74 forest plots along three climatically contrasting elevational transects from humid tropical lowland vegetation up to cloud forests at Los Tuxtlas, Mexico. We recorded 278 plant species, with ferns being the most species-rich group followed by orchids, bromeliads, aroids, and piperoids. The most striking results were the contrasting patterns and model results for terrestrial and epiphytic taxa. Whereas the richness of all terrestrial species taken together did not change significantly with elevation, vascular epiphytes showed increasing species numbers with altitude. However, a number of individual terrestrial taxa showed also significant elevation-related changes: aroids showed a marked decline with hight, orchids and piperoids increased, and ferns displayed a hump-shaped pattern with highest richness in mid-altitudes. Among the epiphytes, aroids declined while most other groups increased with altitude. This distinction is relevant for projections of responses of plant communities to climate change, which will lead to increased temperatures and to changing precipitation and cloud condensation regimes and thus will likely affect terrestrial and epiphytic species in different ways.

Wetland plant species richness across estuarine gradients: The role of environmental factors and the mid-domain effect

This article describes an evaluation of the predictive power of the mid-domain effect (MDE) on observed plant species richness patterns along two estuarine gradients possessing strong environmental factors known to affect plant species distributions and abundance. In this study, tidal wetland plant species richness data (the number of species in 1000-m2 plots) were collected along estuarine gradients of two Chesapeake Bay subestuaries (Nanticoke River – 56km and Patuxent River – 46km). The data were input into a one-dimensional MDE model (RangeModel 5.0), and the output was analyzed against collected environmental variables using regression analysis. The MDE was generally a weak predictor of observed plant species richness, describing none of the total variance in observed plant species richness along the Patuxent River and only 2% of the total variance for the selected model of the small-ranged species dataset along the Nanticoke River. Environmental variables consistently explained a greater proportion of the variance observed in the pattern of plant species richness along both rivers, with factors including mean porewater salinity and soil nitrate-nitrogen accounting anywhere from 39 to 71% of the total variance depending on the dataset and selected model for either the Patuxent or Nanticoke Rivers. These results suggest that for estuarine gradients (≈50km long) possessing strong environmental drivers of community structure (i.e., salinity, soil nitrate-nitrogen, and inundation), an MDE signal can be detected (i.e., Nanticoke River), however, the observed pattern of plant species richness is better described by environmental effects.