Relative Abundance Of Plant Species Research Articles

Fine-resolution global maps of root biomass carbon colonized by arbuscular and ectomycorrhizal fungi

Despite the recognized importance of mycorrhizal associations in ecosystem functioning, the actual abundance patterns of mycorrhizal fungi belowground are still unknown. This information is key for better quantification of mycorrhizal impacts on ecosystem processes and for incorporating mycorrhizal pathways into global biogeochemical models. Here we present the first high-resolution maps of fine root stocks colonized by arbuscular mycorrhizal (AM) and ectomycorrhizal (EcM) fungi (MgC ha−1). The maps were assembled by combining multiple open-source databases holding information on root biomass carbon, the proportion of AM and EcM tree biomass, plot-level relative abundance of plant species and intensity of AM and EcM root colonization. We calculated root-associated AM and EcM abundance in 881 spatial units, defined as the combination of ecoregions and land cover types across six continents. The highest AM abundances are observed in the (sub-)tropics, while the highest EcM abundances occur in the taiga regions. These maps serve as a basis for future research where continuous spatial estimates of root mycorrhizal stocks are needed.

Species-Level Versus Community-Level Responses to Microhabitat Type and Diversity in an Experimental Plant Community

Soil heterogeneity has been theoretically predicted to promote plant performance, but empirical evidence is often mixed. By focusing on a gradient of microhabitats (single, three and six types of microhabitats), we tested the hypothesis that increasing the number of microhabitats promotes the diversity and productivity of plant communities. We created different types of microhabitats by adding different forms of nitrogen (NH4+, NO3− and glycine) or combinations of these nitrogen in an even or patchy way. Community biomass, but not evenness, differed in different types of single-microhabitat. Increasing the number of microhabitat types did not alter community growth or evenness, but it increased the difference in the relative abundance of plant species within the community. These results suggest that microhabitat diversity can influence plant competitive hierarchies, and that this effect can lead to changed community growth, but may not be decisive for plant evenness.

PSXII-12 Heritage Raramuri Criollo Cattle Production as a Potential Strategy for Conservation of Black Grama in the Chihuahuan Desert

Abstract The Chihuahuan desert ecosystem has experienced a decrease in black grama (Bouteloua eriopoda), a perennial grass species with high ecological value, alongside a subsequent increase in mesquite (Prosopis glandulosa). This trend is thought to be due to several management- and environment-related factors. We compared diet selection of a heritage Raramuri Criollo (RC) vs. Angus-X-Hereford (AH) cattle, typical of the region, using fecal DNA metabarcoding conducted by a commercial laboratory to determine the proportion of black grama and mesquite in samples. RC and AH cows grazed two adjacent pastures (~1,100 ha) separately, switched at the mid-point of each period. Rectal fecal samples were collected from 10 cows/ breed/ pasture/ period. The study was replicated across seasons (growing and dormant) for three consecutive years (240 total fecal samples) in a completely randomized design. Relative abundance of plant species was ranked over the entire study and by season. The MIXED procedure of SAS 9.4 was used to analyze the proportions of black grama and mesquite in fecal samples by breed, season, year, and all interactions. Black grama was a more important forage resource than mesquite (ranked 8 vs. 11), particularly during dormancy (ranked 3 vs. 7). When examined by breed, AH fecal samples had twice the percentage of black grama vs. RC (P< 0.05) and even more so during the dormant season (P< 0.05). In contrast, RC fecal samples tended to contain a greater percentage of mesquite (P=0.05). Adjustments for BW differences between breeds (545 vs. 350 kg mean BW for AH vs. RC respectively) suggest that AH consumed 3.09-fold more black grama while RC consumed 1.59 times more mesquite. Differences in diet composition appear to support the hypothesis that RC cattle could impose a lighter grazing pressure on black grama populations, potentially serving as a conservation management tool on Chihuahuan Desert rangelands.

Plant biodiversity of mountain grasslands as influenced by dairy farm management in the Eastern Alps

It has been widely demonstrated that farm management affects the plant species composition of grassland. The present study aimed to investigate the effect of farm management on plant species richness and composition in forty-nine small-scale farms breeding dairy cattle, located in the Eastern Italian Alps at two levels of precision: plot and farm levels. Data on housing system, quality scheme, farm productivity, income from milk yield and livestock density were collected through interviews with farmers. In each farm, botanical surveys were carried out in different plots representing the botanical composition of the farmland vegetation. Elevation, slope, type of use, number of hay cuts and type of fertilisation were also recorded. The botanical surveys of the plots on each farm were analysed to describe plant composition at the plot level, then merged to describe plant composition at the farm level. At both levels, grassland botanical composition was found to be affected by farm management. At the plot level, meadows cut 2 and 3 times per year did not exhibit any differences in plant richness, but they differed in plant species, botanical family and phytosociological class composition, with a general simplification of botanical composition. We found fewer phytosociological classes but not fewer plant species or botanical families in plots fertilised with slurry than in plots fertilised with manure or not fertilised, and a change in the botanical composition due to changes in the relative abundance of plant species. At the farm level, we observed a decrease in the number of plant species and phytosociological classes, and changes in plant composition, with increasing milk yield and livestock density. Changes in botanical composition were less evident at the farm level than at the plot level. However, protecting farms and their economic viability is a means of maintaining biodiversity at the plot level.

Rhizospheric soil fungal community patterns of Duchesnea indica in response to altitude gradient in Yunnan, southwest China.

The magnitude of the impact of altitude gradient on microbial community and diversity has been studied in recent decades. Whereas bacteria have been the focus of most studies, fungi have been given relatively less attention. As a vital part of the macro- and microscopic ecosystem, rhizosphere fungi play a key role in organic matter decomposition and relative abundance of plant species and have an impact on plant growth and development. Using Duchesnea indica as the host plant, we examined the rhizosphere soil fungal community patterns across the altitude gradient in 15 sites of Yunnan province by sequencing the fungal ITS2 region with the Illumina MiSeq platform. We determined the fungal community composition and structure. We found that, surprisingly, rhizosphere soil fungal diversity of D. indica increased with altitudinal gradient. There was a slight difference in diversity between samples from high- and medium-altitude sites, with medium-altitude sites having the greater diversity. Furthermore, the rhizosphere soil fungal community composition and structure kept changing along the altitudinal gradient. Taxonomic results showed that the extent of phylum diversity was greatest at high-altitude sites, with Ascomycota, Basidiomycota, Zygomycota, and Glomeromycota as the most dominant fungal phyla.

Spectral Heterogeneity Predicts Local-Scale Gamma and Beta Diversity of Mesic Grasslands

Plant species diversity is an important metric of ecosystem functioning, but field assessments of diversity are constrained in number and spatial extent by labor and other expenses. We tested the utility of using spatial heterogeneity in the remotely-sensed reflectance spectrum of grassland canopies to model both spatial turnover in species composition and abundances (β diversity) and species diversity at aggregate spatial scales (γ diversity). Shannon indices of γ and β diversity were calculated from field measurements of the number and relative abundances of plant species at each of two spatial grains (0.45 m2 and 35.2 m2) in mesic grasslands in central Texas, USA. Spectral signatures of reflected radiation at each grain were measured from ground-level or an unmanned aerial vehicle (UAV). Partial least squares regression (PLSR) models explained 59–85% of variance in γ diversity and 68–79% of variance in β diversity using spatial heterogeneity in canopy optical properties. Variation in both γ and β diversity were associated most strongly with heterogeneity in reflectance in blue (350–370 nm), red (660–770 nm), and near infrared (810–1050 nm) wavebands. Modeled diversity was more sensitive by a factor of three to a given level of spectral heterogeneity when derived from data collected at the small than larger spatial grain. As estimated from calibrated PLSR models, β diversity was greater, but γ diversity was smaller for restored grassland on a lowland clay than upland silty clay soil. Both γ and β diversity of grassland can be modeled by using spatial heterogeneity in vegetation optical properties provided that the grain of reflectance measurements is conserved.

Fire season modifies the perennial plant community composition through a differential effect on obligate seeders in eastern Mediterranean woodlands

AbstractAimPlant species regenerate after fire either through vegetative growth (i.e., obligate resprouters) or seed germination (i.e., obligate seeders), with some species adopting both strategies (i.e., facultative seeders). Fire season can have important consequences for the relative abundance of plant species adopting these regeneration strategies. The present study aimed to test for differential effects of fire season on perennial plant community composition.LocationEastern Mediterranean woodland in the Judea Mountains, Israel.MethodsWe conducted, for the first time, a large‐scale field experiment, involving prescribed spring and autumn burns in a typical eastern Mediterranean woodland. We sampled the perennial plant community before and after the burns, quantifying temporal changes in community composition caused by seasonal fires.ResultsAlthough fire intensity and severity were consistent between the two seasonal fires, plant community composition differed between areas subjected to spring or autumn burns. The abundances of all common species, Pistacia lenticus (obligate resprouter), Cistus spp. (obligate seeders) and Teucrium divaricatum (facultative seeder), were all reduced by both fires. Yet, their dominance in the post‐fire perennial plant community was retained. Differential fire season effects were detected only among obligate seeders, which experienced a stronger reduction in abundance after spring than after autumn burns.ConclusionsDifferential fire season effects on the perennial plant community resulted from phenological rather than fire intensity/severity effects. Such changes in community composition may have important implications for plant community dynamics, because they affect the circle of “fire event–plant regeneration–fire reoccurrence”, determining the probability and intensity of future fires. Furthermore, even though the eastern mediterranean ecosystem is considered highly resilient to disturbances, increased spatio‐temporal variation in fire season, may result in a new vegetation mosaic, differing from the contemporary one, i.e., an alternative stable state.

Plant dominance in a subalpine montane meadow: biotic vs. abiotic controls of subordinate diversity within and across sites.

BackgroundUnderstanding the underlying factors that determine the relative abundance of plant species is critical to predict both biodiversity and ecosystem function. Biotic and abiotic factors can shape the distribution and the relative abundance of species across natural communities, greatly influencing local biodiversity.MethodsUsing a combination of an observational study and a five-year plant removal experiment we: (1) documented how plant diversity and composition of montane meadow assemblages vary along a plant dominance gradient using an observational study; (2) tracked above- and belowground functional traits of co-dominant plant species Potentilla and Festuca along a plant dominance gradient in an observational study; (3) determined whether plant species diversity and composition was directly influenced by commonly occurring species Potentilla and Festuca with the use of a randomized plot design, 5-year plant removal experiment (no removal control, Potentilla removed, Festuca removed, n = 10).ResultsWe found that subordinate species diversity and compositional dissimilarity were greatest in Potentilla and Festuca co-dominated sites, where neither Potentilla nor Festuca dominated, rather than at sites where either species became dominant. Further, while above- and belowground plant functional traits varied along a dominance gradient, they did so in a way that inconsistently predicted plant species relative abundance. Also, neither variation in plant functional traits of Festuca and Potentilla nor variation in resources and conditions (such as soil nitrogen and temperature) explained our subordinate diversity patterns. Finally, neither Potentilla nor Festuca influenced subordinate diversity or composition when we directly tested for their impacts in a plant removal experiment.DiscussionTaken together, patterns of subordinate diversity and composition were likely driven by abiotic factors rather than biotic interactions. As a result, the role of abiotic factors influencing local-level species interactions can be just as important as biotic interactions themselves in structuring plant communities.

Negative plant-soil feedbacks increase with plant abundance, and are unchanged by competition.

Plant-soil feedbacks and interspecific competition are ubiquitous interactions that strongly influence the performance of plants. Yet few studies have examined whether the strength of these interactions corresponds with the abundance of plant species in the field, or whether feedbacks and competition interact in ways that either ameliorate or exacerbate their effects in isolation. We sampled soil from two intermountain grassland communities where we also measured the relative abundance of plant species. In greenhouse experiments, we quantified the direction and magnitude of plant-soil feedbacks for 10 target species that spanned a range of abundances in the field. In soil from both sites, plant-soil feedbacks were mostly negative, with more abundant species suffering greater negative feedbacks than rare species. In contrast, the average response to competition for each species was unrelated with its abundance in the field. We also determined how competitive response varied among our target species when plants competed in live vs. sterile soil. Interspecific competition reduced plant size, but the strength of this negative effect was unchanged by plant-soil feedbacks. Finally, when plants competed interspecifically, we asked how conspecific-trained, heterospecific-trained, and sterile soil influenced the competitive responses of our target species and how this varied depending on whether target species were abundant or rare in the field. Here, we found that both abundant and rare species were not as harmed by competition when they grew in heterospecific-trained soil compared to when they grew in conspecific-cultured soil. Abundant species were also not as harmed by competition when growing in sterile vs. conspecific-trained soil, but this was not the case for rare species. Our results suggest that abundant plants accrue species-specific soil pathogens to a greater extent than rare species. Thus, negative feedbacks may be critical for preventing abundant species from becoming even more abundant than rare species.

Shifts in symbiotic associations in plants capable of forming multiple root symbioses across a long-term soil chronosequence.

Changes in soil nutrient availability during long‐term ecosystem development influence the relative abundances of plant species with different nutrient‐acquisition strategies. These changes in strategies are observed at the community level, but whether they also occur within individual species remains unknown. Plant species forming multiple root symbioses with arbuscular mycorrhizal (AM) fungi, ectomycorrhizal (ECM) fungi, and nitrogen‐(N) fixing microorganisms provide valuable model systems to examine edaphic controls on symbioses related to nutrient acquisition, while simultaneously controlling for plant host identity. We grew two co‐occurring species, Acacia rostellifera (N2‐fixing and dual AM and ECM symbioses) and Melaleuca systena (AM and ECM dual symbioses), in three soils of contrasting ages (c. 0.1, 1, and 120 ka) collected along a long‐term dune chronosequence in southwestern Australia. The soils differ in the type and strength of nutrient limitation, with primary productivity being limited by N (0.1 ka), co‐limited by N and phosphorus (P) (1 ka), and by P (120 ka). We hypothesized that (i) within‐species root colonization shifts from AM to ECM with increasing soil age, and that (ii) nodulation declines with increasing soil age, reflecting the shift from N to P limitation along the chronosequence. In both species, we observed a shift from AM to ECM root colonization with increasing soil age. In addition, nodulation in A. rostellifera declined with increasing soil age, consistent with a shift from N to P limitation. Shifts from AM to ECM root colonization reflect strengthening P limitation and an increasing proportion of total soil P in organic forms in older soils. This might occur because ECM fungi can access organic P via extracellular phosphatases, while AM fungi do not use organic P. Our results show that plants can shift their resource allocation to different root symbionts depending on nutrient availability during ecosystem development.

Temporal partial unmixing of exotic salt cedar using Landsat time series

ABSTRACTIn the south-western United States, the rapid colonization of exotic salt cedar (Tamarix spp.) along the riparian corridors poses a serious threat to the native plant diversity. Monitoring the salt cedar abundance in diversified riparian ecosystems is critically essential for evaluating the biodiversity loss and developing corresponding restoration strategies. To date, it still remains a significant challenge to estimate the abundance of plant species within a pixel, as many plants share similar spectral signatures. This challenge is even more daunting in species diverse ecosystems due to the difficulty of securing all the endmembers (e.g. plant species) in unmixing procedures. The objective of this study is to introduce a new concept, temporal partial unmixing, to estimate the relative abundance of plant species using Landsat time series. Temporal partial unmixing only requires the signature of the target endmember, but it emphasizes the importance of the temporal dimension of the target signature in estimating the corresponding abundance. Two types of temporal signatures that capture the phenological trajectory of the salt cedar growth were devised in this study. Compared to the traditional partial unmixing method (R2 = 0.35), temporal partial unmixing that exploited the temporal signatures greatly improved the relative abundance estimation accuracy (R2 = 0.56 or 0.49). It is concluded that the proposed temporal partial unmixing, along with the readily available Landsat imagery, offers unprecedented opportunities to monitor the abundance dynamics of plant species, especially in spatially heterogeneous landscapes.

Plant functional traits reveal the relative contribution of habitat and food preferences to the diet of grasshoppers

Food preferences and food availability are two major determinants of the diet of generalist herbivores and of their spatial distribution. How do these factors interact and eventually lead to diet differentiation in co-occurring herbivores? We quantified the diet of four grasshopper species co-occurring in subalpine grasslands using DNA barcoding of the plants contained in the faeces of individuals sampled in the field. The food preferences of each grasshopper species were assessed by a choice (cafeteria) experiment from among 24 plant species common in five grassland plots, in which the four grasshoppers were collected, while the habitat was described by the relative abundance of plant species in the grassland plots. Plant species were characterised by their leaf economics spectrum (LES), quantifying their nutrient vs. structural tissue content. The grasshoppers' diet, described by the mean LES of the plants eaten, could be explained by their plant preferences but not by the available plants in their habitat. The diet differed significantly across four grasshopper species pairs out of six, which validates food preferences assessed in standardised conditions as indicators for diet partitioning in nature. In contrast, variation of the functional diversity (FD) for LES in the diet was mostly correlated to the FD of the available plants in the habitat, suggesting that diet mixing depends on the environment and is not an intrinsic property of the grasshopper species. This study sheds light on the mechanisms determining the feeding niche of herbivores, showing that food preferences influence niche position whereas habitat diversity affects niche breadth.

Interactive effects of root endophytes and arbuscular mycorrhizal fungi on an experimental plant community

Plant-soil microbial interactions have moved into focus as an important mechanism for understanding plant coexistence and composition of communities. Both arbuscular mycorrhizal (AM) as well as other root endophytic fungi co-occur in plant roots, and therefore have the potential to influence relative abundances of plant species in local assemblages. However, no study has experimentally examined how these key root endosymbiont groups might interact and affect plant community composition. Here, using an assemblage of five plant species in mesocosms in a fully factorial experiment, we added an assemblage of AM fungi and/or a mixture of root endophytic fungal isolates, all obtained from the same grassland field site. The results demonstrate that the AM fungi and root endophytes interact to affect plant community composition by changing relative species abundance, and consequently aboveground productivity. Our study highlights the need to explicitly consider interactions of root-inhabiting fungal groups in studies of plant assemblages.

Does it matter if herbivory is selective? Responses of an endangered herbaceous legume to experimental grazing

Background: Herbivory and inter-specific competition are major determinants of the relative abundance of plant species in grasslands. Herbivores modify competitive hierarchies among plants through selective foraging and as a result of variation in the relative tolerance of plants to herbivory. Aims: We examined the direct effects of herbivory and the role of herbivore preference on the growth, flowering and abundance of an endangered perennial legume, Cullen parvum (F. Muell.) J.W. Grimes, in a temperate Australian grassland grazed by sheep. Methods: Hand clipping was used to simulate herbivory. In each of two populations, three replicates of the factorial combination of C. parvum defoliation (C. parvum grazed or ungrazed), neighbour defoliation (neighbouring vegetation grazed or ungrazed) and three defoliation frequency treatments were randomly applied to 0.25-m2 quadrats containing C. parvum ramets. Results: The abundance, growth and flowering of C. parvum were similarly reduced by both selective and non-selective herbivory. When neighbouring vegetation but not C. parvum was defoliated, growth and abundance were similar and in some cases less than when both neighbours and C. parvum were ungrazed, suggesting little above-ground competitive effect of the grassland sward. Conclusions: The interactions between herbivory and shoot competition by dominant perennial grassy swards had little influence on the growth and abundance of C. parvum. Rather, direct effects of defoliation dominated and we predict that the species persistence in grazed grasslands will be influenced more by poor tolerance of herbivory than by how herbivores modify the competitive effect of neighbouring vegetation.

Hierarchical plant responses and diversity loss after nitrogen addition: testing three functionally-based hypotheses in the Inner Mongolia grassland.

BackgroundNumerous studies have shown that nitrogen (N) deposition decreases biodiversity in terrestrial ecosystems. To explain the N-induced species loss, three functionally based hypotheses have been proposed: the aboveground competition hypothesis, the belowground competition hypothesis, and the total competition hypothesis. However, none of them is supported sufficiently by field experiments. A main challenge to testing these hypotheses is to ascertain the role of shoot and root competition in controlling plant responses to N enrichment. Simultaneously examining both aboveground and belowground responses in natural ecosystems is logistically complex, and has rarely been done.Methodology/Principal FindingsIn a two-year N addition experiment conducted in a natural grassland ecosystem, we investigated both above- and belowground responses of plants at the individual, species, and community levels. Plants differed significantly in their responses to N addition across the different organizational levels. The community-level species loss was mainly due to the loss of perennial grasses and forbs, while the relative abundance of plant species was dependent mainly on individual-level responses. Plasticity in biomass allocation was much smaller within a species than between species, providing a biological basis for explaining the functionally based species loss. All species increased biomass allocation to aboveground parts, but species with high belowground allocations were replaced by those with high aboveground allocations, indicating that the increased aboveground competition was the key process responsible for the observed diversity loss after N addition in this grassland ecosystem.Conclusions/SignificanceOur findings shed new light on the validity of the three competing hypotheses concerning species loss in response to N enrichment. They also have important implications for predicting the future impacts of N deposition on the structure and functioning of terrestrial ecosystems. In addition, we have developed a new technique for ascertaining the roles of aboveground and belowground competition in determining plant responses to N fertilization.

Being a generalist herbivore in a diverse world: how do diets from different grasslands influence food plant selection and fitness of the grasshopper Chorthippus parallelus?

1. Generalist insect herbivores occupy a variety of habitats that differ in food plant composition. Dietary mixing has been proposed as a possibility for generalists to overcome nutritional deficiencies of single plant species, but only a few studies have investigated herbivore feeding and fitness for diets that resemble natural scenarios. We studied feeding behaviour, survival, and reproduction of the generalist grasshopper Chorthippus parallelus raised on food plants of four typical habitats.2. Grasshopper diet consisted of grasses (92.5%), legumes (6.7%) and, in small quantities, other forbs (0.8%). Diet selection differed between the four food plant mixtures, and depended on grasshopper sex and developmental stage. There was no correlation between the relative abundance of plant species in the field and the fraction of these species in the grasshopper diet.3. Grasshoppers survived on average for 40.4 ± 1.0 days before maturity, grew 106.8 mg until maturity moult, and females laid 4.1 ± 0.4 egg pods, each of which contained 8.5 ± 0.4 eggs. However, despite the differences in feeding behaviour, grasshopper fitness was the same in all of the four food plant mixtures. While the digestibility of ingested food was similar in the four different treatments, indices indicated differences in the conversion efficiency to body mass.4. Our results show that C. parallelus is a plastic feeder with no fixed preferences in diet composition. The results emphasise that generalist herbivores can counteract putative quality deficiencies of single food plants by selective dietary mixing.

Microhabitat preferences for the errant scorpion, Centruroides vittatus (Scorpiones, Buthidae)

Vegetation as a preferred microhabitat for scorpions has rarely been considered despite many Buthidae (the bark scorpions) being non-burrowing errant scorpions that are active on both the ground and vegetation. Microhabitats can serve multiple functions for Centruroides vittatus (Say 1821), but a particular microhabitat can be preferred for a certain function such as a refuge, foraging, or feeding. Observations of microhabitat use by C. vittatus were performed in Laredo, Texas of the Tamaulipan Biotic Province. Comparisons of microhabitat use by C. vittatus at different temperatures or precipitation levels were performed. Foraging and feeding by C. vittatus among microhabitat classes were also compared. The observed use of vegetation by C. vittatus during different seasons was compared to the expected use based on relative abundance of vegetation in the habitat. Air temperature, but not precipitation, had a significant effect on microhabitat use by C. vittatus. Microhabitat had a significant effect on foraging of C. vittatus with caterpillars comprising 34.6% of the prey items and half of the scorpions feeding on caterpillars were in blackbrush (Acacia rigidula). The lowest proportion of scorpions observed feeding was on the ground (3.8%) and the highest in blackbrush (40.4%). The frequency of C. vittatus among vegetation classes was significantly different compared to the relative abundance of plant species in the plot. Scorpions were observed on prickly pear cactus (Opuntia engelmannii) and strawberry cactus (Echinocereus enneacanthus) at a higher frequency than expected, and scorpions were observed on guajillo (Acacia berlandieri) and tasajillo (Opuntia leptocaulis) at a lower frequency than expected. The frequency of scorpions on blackbrush was higher than expected during the spring. Vegetation is an important microhabitat for C. vittatus in south Texas. The results indicate the possibility that C. vittatus in south Texas used various plant species to carry prey captured on the ground into vegetation to feed, used blackbrush to forage for caterpillars, and used strawberry and prickly pear cacti as a possible refuge.

SPECIES RESPONSES TO NITROGEN FERTILIZATION IN HERBACEOUS PLANT COMMUNITIES, AND ASSOCIATED SPECIES TRAITSEcological ArchivesE089-070

This synthetic data set contains plant species relative abundance measures from 35 nitrogen (N) fertilization experiments conducted at 10 sites across North America. The data set encompasses the fertilization responses of 575 taxa from 1159 experimental plots. The methodology varied among experiments, in particular with regard to the type and amount of N added, plot size, species composition measure (biomass harvest, pin count, or percent cover), additional experimental manipulations, and experimental duration. At each site, each species has been classified according to a number of easily identified categorical functional traits, including life history, life form, the number of cotyledons, height relative to the canopy, potential for clonal growth, and nativity to the United States. Additional data are available for many sites, indicated by references to publications and web sites. Analyses of these data have shown that N enrichment significantly alters community composition in ways that are predictable on the basis of plant functional traits as well as environmental context. This data set could be used to answer a variety of questions about how plant community composition and structure respond to environmental changes.

Plant community response to burning and herbicide site preparation in eastern Louisiana, USA

High yield commercial forests are an important source of fiber for global forest product needs and the southeastern United States is a key region for global wood supply needs with intensively managed pine stands ( Pinus spp.) an important component of forested landscapes in this region. Concern has arisen over possible effects of stand establishment practices on vegetation communities within commercial forests, particularly relative to use of herbicides and burning. Therefore, we examined response of plant communities to site preparation within intensively managed pine stands in eastern Louisiana, USA that were either prescribe burned (PF; n = 5) or treated with a combination of herbicides (imazapyr and triclopyr) and prescribe burned (PFH; n = 5) during 2002. We used 5 m line intercepts ( n = 10 per stand) to quantify species richness, diversity, and relative abundance of plant species for 3 years post-treatment (2003–2005) with a repeated measures analysis of variance. We documented 80 genera or species of plants and neither species richness nor diversity differed between treatments. Site preparation with PFH appeared to promote development of an herbaceous plant community and reduced relative abundance of woody plants, whereas PF-treated sites were dominated by woody vegetation. Our results demonstrate that different plant communities result from PF and PFH site preparation and may place stands on different successional trajectories. We suggest PFH site preparation may increase availability of early successional vegetation associations on managed forest landscapes and may extend the time stands stay in this successional stage. However, increased crop tree growth from site preparation may shorten open canopy conditions.

Does the endangered Knysna seahorse, Hippocampus capensis, have a preference for aquatic vegetation type, cover or height?

The Knysna seahorse, Hippocampus capensis, is an endangered teleost confined to three South African estuaries. Its abundance within these systems is low and distributions are patchy. Consequently, monitoring population sizes is labour-intensive. The aim of this study was to establish if Knynsa seahorses are associated with specific regions within the estuaries, on which conservation efforts could concentrate. The relationship of Knysna seahorses with aquatic vegetation was analysed in the Knysna Estuary (the largest of the three estuarine systems inhabited by H. capensis) to determine whether this species shows a preference for a particular plant species, vegetation density or vegetation height. Seahorses were associated with five dominant aquatic plants: Zostera capensis, Caulerpa filiformis, Codium extricatum, Halophila ovalis and Ruppia cirrhosa. Together, these comprised 96% of the submerged objects with which seahorses were associated. The relative abundance of plant species changed along the estuary, but seahorses were present throughout the system, except at the estuary mouth, which was characterized by low plant densities and strong currents. No significant difference was found between the proportion of plant species present in a particular region of the estuary and the proportion of plants that seahorses used as holdfasts. However, when Z. capensis and C. filiformis were present at the same sites, adult seahorses preferred C. filiformis as holdfast. Adult seahorse density (individuals/m2) was significantly correlated with percentage vegetation cover and with holdfast length, but juvenile seahorse density was not. Nonetheless, significantly more adult and juvenile seahorses were found at sites characterized by high vegetation cover (>75%) than at sites with lower cover. Our results indicate that although there is some evidence that Knynsa seahorses prefer certain plant species over others, they are likely to be encountered anywhere in the estuary where aquatic plants are present. Conservation efforts in the Knysna Estuary should thus concentrate on such vegetated areas, which comprise approximately 11% of the total submerged surface area.