Understory Herbaceous Species Research Articles

Evaluating the definition and distribution of spring ephemeral wildflowers in eastern North America.

The herbaceous layer accounts for the majority of plant biodiversity in eastern North American forests, encompassing substantial variation in life history strategy and function. One group of early-season herbaceous understory species, colloquially referred to as spring ephemeral wildflowers, are ecologically and culturally important, but little is known about the prevalence and biogeographic patterns of the spring ephemeral strategy. We used observations collected by the Global Biodiversity Information Facility (GBIF) to quantify the ephemerality of 559 understory forb species across eastern North America and classify them according to a continuous ephemerality index (ranging from 0 = never ephemeral to 1 = always ephemeral). We then used this information to model where ephemeral forbs were most common across the landscape with the goal of identifying geographic and environmental drivers important to their distributions and ranges. Only 3.4% of all understory wildflower species were spring ephemerals in all parts of their range, and 18.4% (103 species) were ephemeral in at least part of their range. Spring ephemerals peaked in absolute species richness and relative proportion at mid latitudes. Spring ephemeral phenology is an important shade-avoidance strategy for a large segment of the total understory species in temperate deciduous forests. In North America, the strategy is relatively most important for forest understories at mid latitudes. The definitions of spring ephemerality we provide here serve as an important ecological context for conservation priorities and to evaluate responses of this biodiverse group to future environmental change.

Herbicides Have Variable Effects on Understory Plant and Insect Communities in Southern United States Working Forests

Abstract Working pine (Pinus spp.) forests in the southern United States rely on herbicides to remove competing vegetation and improve productivity. We conducted a review of the effects of herbicides on understory plants in southern working forests. We also discuss the impacts of herbicides on insect taxa associated with understory vegetation and its litter layer, including Coleoptera (carabid beetles), Hemiptera (true bugs), Hymenoptera (bees/ants), Lepidoptera (moths/butterflies), and Orthoptera (grasshoppers). Herbicides have few reported long-term impacts on understory herbaceous cover and species richness/diversity when applied according to labeled uses and application rates. However, the method of chemical treatment (e.g., broadcast spray or banded application) may influence understory plant structure and composition. Responses of insects to herbicides were species- and taxa-specific and highly variable given their forage/habitat requirements and life histories. Long-term research is needed to evaluate the effects of herbicides on vegetation-associated insects to provide a comprehensive profile of herbicide nontarget impacts. Study Implications: Land managers rely on herbicides to remove competing vegetation and increase working forest productivity. Given the objective of sustainable forest management to conserve biodiversity, it is important to understand how biological communities respond to chemical applications in intensively managed forest ecosystems. Our review indicated that herbicides have few reported long-term impacts on understory plant communities when applied appropriately. Despite their taxonomic diversity, invertebrates were rarely included in assessments of forest herbicides. Further research is needed to assess the potential nontarget impacts of herbicide applications on forest insect communities.

Stability in the leaf functional traits of understory herbaceous species after 12-yr of nitrogen addition in temperate larch plantations.

Leaf functional traits play critical roles in plant functioning. Although the functional traits of overstory trees have been extensively studied, minimal research has been conducted regarding understory species, despite the understory layer is an important component of temperate forests. Such insufficiency limit the broader understanding of processes and functions in forest ecosystems, particularly when under the increasing atmospheric nitrogen (N) deposition. Here, we investigated the responses of 18 leaf functional traits in six understory herbaceous species within young and mature stands (three species per stand) in larch (Larix principis-rupprechtii) plantations that subjected to 12 years of anthropogenic N addition. We found that N addition did not significantly impact the photosynthetic traits of understory herbaceous species in either stand; it only led to increased chlorophyll content in Geum aleppicum Jacq. Similarly, with the exception of decreases in the predawn leaf water potential of Sanguisorba officinalis L., N addition did not significantly affect leaf hydraulic traits. With the exception of changes to adaxial epidermis thickness in Potentilla chinensis Ser. (decreased) and G. aleppicum (increased), N addition had negligible effects on leaf anatomical traits and specific leaf area, however, interspecific variations in the plasticity of leaf anatomical traits were observed. Stable responses to N addition were also observed for nonstructural carbohydrates (NSC) and their components (soluble sugars and starch), with the exception of Polygonum divaricatum L., which exhibited increases in NSC. Overall, our results suggest that the functional traits of understory herbaceous species exhibit stability under conditions of long-term N enrichment in temperate plantations.

Effects of Stand Structure of Artificial Shelter Forest on Understory Herb Diversity in Desert-Oasis Ecotone

The relationship between the spatial structure of shelter forests and the diversity of understory herbaceous plants in desert–oasis ecotones is important for maintaining biodiversity indices and protecting the oasis ecosystem. In this paper, we explore the coupling relationship between tree layer structure (competition index, angle scale, neighborhood comparison, DBH, etc.) and understory herb diversity in the transition zone of shelter forest plots near oases and near deserts; in addition, we also aim to elucidate the dominant stand structure factors affecting herb biodiversity. The results indicated the following: A total of 13 herbaceous plant species were discovered in the transitional zone, with 11 species found near the oasis area and 4 species near the desert region. The Shannon, Simpson, and Pielou indices of understory herbaceous plants were significantly higher near the oasis area compared to the desert region. The Margalef index mean was higher in the oasis area compared to the desert region. Pearson and canonical correlation analyses revealed significant associations between specific stand structure indicators and diversity in the herbaceous layer. The results of the multiple linear regression analysis revealed that the competition index had a significant impact on the Shannon, Simpson, and Pielou diversity indices of the herbaceous layer in the understory of the shelterbelt forest near the oasis, with corresponding impact coefficients of 0.911, 0.936, and 0.831, respectively. The mingling degree was found to be the primary influencing factor for the Margalef index, with an impact coefficient of 0.825. However, in the understory of the shelterbelt forest near the desert, the neighborhood comparison ratio negatively affected the Shannon and Margalef indices, with impact coefficients of −0.634 and −0.736, respectively. Additionally, tree height negatively impacted the Simpson and Pielou indices, with impact coefficients of −0.645 and −0.677, respectively. In order to enhance the diversity of understory herbaceous species in the transitional zone and preserve the ecological system of the oasis, specific modifications to the forest structure and arrangement are essential. Pruning and thinning are necessary for shelterbelt forests located near desert regions, while shelterbelt forests near oases should use a suitable mix of tree species. These measures can help preserve or enhance the diversity of understory herbaceous plants.

The Influence of Stand Structure on Understory Herbaceous Plants Species Diversity of Platycladus orientalis Plantations in Beijing, China

Species diversity is a crucial index used to evaluate the stability and complexity of forest ecosystems. Studying the relationship between stand structure and understory herbaceous plants species diversity is useful for managers to formulate the best forest structure optimization method with the goal of improving herbaceous species diversity. In this research, Platycladus orientalis plantations in Beijing were taken as the research object. Pearson’s correlation analysis was used to explore the single-factor correlation between stand structure and understory herbaceous plants species diversity; furthermore, a typical correlation analysis and multiple linear regression were used to explore the multi-factor correlation and analyze the dominant stand structure parameters affecting understory herbaceous plants species diversity. In the range of stand structures studied, the results showed that canopy density was negatively correlated with the Shannon–Wiener index and Simpson index (p < 0.01), and tree density was negatively correlated with the Shannon–Wiener index (p < 0.05). In terms of stand spatial structure, the mingling degree was positively correlated with the Shannon–Wiener index, Simpson index, Margalef richness index and Pielou evenness index (p < 0.05), while the uniform angle was negatively correlated with the Pielou evenness index (p < 0.05). The correlation coefficient of the first group of typical variables in the typical correlation analysis was 0.90 (p < 0.05); from this group of typical variables, it can be concluded that canopy density is the most influential indicator affecting the comprehensive index of understory herbaceous plants species diversity, with a load of −0.690, and the Shannon–Wiener index and Simpson index are the most responsive indicators of changes in the comprehensive index of stand structure, with loads of 0.871 and 0.801, respectively. In the process of the management of Platycladus orientalis plantations under a low altitude, south slope, thin soil layer and hard soil parent material, in order to improve the herbaceous species diversity, the canopy density of the overstory and tree density should be appropriately reduced. Additionally, it is necessary to regulate the horizontal spatial structure of stands. When the trees are randomly distributed and the mingling degree is high, the species diversity of herbs can be increased.

Tracing plant source water dynamics during drought by continuous transpiration measurements: An in-situ stable isotope approach.

The isotopic composition of xylem water (δX ) is of considerable interest for plant source water studies. In-situ monitored isotopic composition of transpired water (δT ) could provide a nondestructive proxy for δX -values. Using flow-through leaf chambers, we monitored 2-hourly δT -dynamics in two tropical plant species, one canopy-forming tree and one understory herbaceous species. In an enclosed rainforest (Biosphere 2), we observed δT -dynamics in response to an experimental severe drought, followed by a 2 H deep-water pulse applied belowground before starting regular rain. We also sampled branches to obtain δX -values from cryogenic vacuum extraction (CVE). Daily flux-weighted δ18 OT -values were a good proxy for δ18 OX -values under well-watered and drought conditions that matched the rainforest's water source. Transpiration-derived δ18 OX -values were mostly lower than CVE-derived values. Transpiration-derived δ2 HX -values were relatively high compared to source water and consistently higher than CVE-derived values during drought. Tracing the 2 H deep-water pulse in real-time showed distinct water uptake and transport responses: a fast and strong contribution of deep water to canopy tree transpiration contrasting with a slow and limited contribution to understory species transpiration. Thus, the in-situ transpiration method is a promising tool to capture rapid dynamics in plant water uptake and use by both woody and nonwoody species.

Clonality drives structural patterns and shapes the community assemblage of the Mediterranean Fagus sylvatica subalpine belt.

Past anthropogenic disturbances lowered the altitudinal distribution of the Mediterranean Fagus sylvatica forests below 2,000 m a.s.l. Accordingly, our current understanding of the southern distribution range of F. sylvatica forests is restricted to managed stands below this elevation, neglecting relic forests growing above. This study has shed light on the structure and species assemblage of an unmanaged relict subalpine F. sylvatica stand growing within the core of its southernmost glacial refugia and at its highest species range elevation limit (2,140 m a.s.l.) in southern Apennines (Italy). Here, tree biometric attributes and understory species abundances were assessed in eight permanent plots systematically positioned from 1,650 to 2,130 m a.s.l. In the subalpine belt, F. sylvatica had formed a dense clonal stem population that was layered downward on the steepest slopes. The density and spatial aggregation of the stems were increased, while their stature and crown size were decreased. Above 2,000 m, changes in tree growth patterns, from upright single-stemmed to procumbent multi-stemmed, and canopy layer architecture, with crowns packed and closer to the floor, were allowed for the persistence of understory herbaceous species of biogeographic interest. Clonal layering represents an adaptive regeneration strategy for the subalpine belt environmental constraints not previously recognized in managed Mediterranean F. sylvatica forests. The clonal structure and unique species assemblage of this relic forest highlight the value of its inclusion in the priority areas networks, representing a long-term management strategy of emblematic glacial and microclimatic refugia.

Variations and Factors Characterizing Ecological Niches of Understory Herbaceous Species in Plantation Forests

Plant ecological niche characteristics are powerful representations of plant survival status. Understory herbaceous species in plantation forests are sensitive to local ecological environment changes; patterns of ecological niche changes of herbaceous plants under plantation forests are of great significance for maintaining the stability and sustainable development of plantation forest ecosystems. This study aims to explore the ecological niche characteristics of understory herbaceous species in plantation forests and their influencing factors. Six different site types of Pinus tabulaeformis plantations were selected from a stable plantation community in the feldspathic sandstone area of the Loess Plateau (China). The relative importance value and niche breadth were used as comprehensive quantitative indices to characterize the status, role, and degree of dominance of understory herbaceous species in plantation forests. We found few dominant species of understory herbaceous species in plantation forests, mostly companion species. The niche characteristics of understory herbaceous species in plantation forests varied significantly. For understory herbaceous species, the niche width was positively correlated with slopes and the niche overlap of the sunny slopes was positively relevant with slopes, while that of the shady slopes was negatively correlated. A canonical correspondence analysis indicated that several major factors influencing the niche breadth and niche overlap of understory herbaceous species in plantation forests were different. The canopy density and slope of plantation played a major role in the niche breadth and niche overlap of understory herbaceous species in plantation forests. In summary, the species distribution of understory herbaceous species in plantation forests was determined by site type. The canopy density and geographical slope were the dominant environmental factors for different ecological niche characteristics of understory herbaceous species. The ecological niche variation of different herbaceous species was the consequence of the integrated effects of the plantation and geographical environment.

High canopy cover of invasive Acer negundo L. affects ground vegetation taxonomic richness

We assessed the link between canopy cover degree and ground vegetation taxonomic richness under alien ash-leaved maple (Acer negundo) and other (native or alien) tree species. We investigated urban and suburban forests in the large city of Yekaterinburg, Russia. Forests were evaluated on two spatial scales. Through an inter-habitat comparison we recorded canopy cover and plant taxonomic richness among 13 sample plots of 20 × 20 m where A. negundo dominated and 13 plots where other tree species dominated. In an intra-habitat comparison, we recorded canopy cover and ground vegetation taxonomic richness among 800 sample plots measuring 1 m2 in the extended urbanised forest, which featured abundant alien (308 plots) and native trees (492 plots). We observed decreased taxonomic richness among vascular ground plant species by 40% (inter-habitat) and 20% (intra-habitat) in areas dominated by A. negundo compared to areas dominated by native tree and shrub species. An abundance of A. negundo was accompanied by increased canopy cover. We found a negative relationship between canopy cover and the number of understory herbaceous species. Thus, the interception of light and the restriction of its amount for other species is a main factor supporting the negative influence of A. negundo on native plant communities.

Fuel load, stand structure, and understory species composition following prescribed fire in an old-growth coast redwood (Sequoia sempervirens) forest

BackgroundWith the prevalence of catastrophic wildfire increasing in response to widespread fire suppression and climate change, land managers have sought methods to increase the resiliency of landscapes to fire. The application of prescribed burning in ecosystems adapted to fire can reduce fuel load and fire potential while minimizing impacts to the ecosystem as a whole. Coast redwood forests have historically experienced fire from both natural and anthropogenic sources, and are likely to respond favorably to its reintroduction.ResultsRandom sampling was conducted in three burned sites and in three unburned sites, in an old-growth coast redwood (Sequoia sempervirens [D. Don] Endl.) forest. Data were collected on fuel, forest structure, and understory species composition and compared between treatments. Downed woody fuel, duff depth, litter depth, and density of live woody fuels were found to be significantly lower on sites treated with fire compared to unburned sites. Density of the dominant overstory canopy species, coast redwood and Douglas-fir (Pseudotsuga menziesii var. menziesii [Mirb.] Franco), remained consistent between treatments, and the abundance of herbaceous understory plant species was not significantly altered by burning. In addition, both downed woody fuel and live fuel measures were positively correlated with time since last burn, with the lowest measures on the most recently burned sites.ConclusionsOur results indicated that the use of prescribed burning in old-growth redwood forests can provide beneficial reductions in live and dead surface fuels with minimal impacts to overstory trees and understory herbaceous species.

Impact of climate change on alpine plant community in Qilian Mountains of China.

There is growing evidence that mountains are experiencing some of the highest rates of climate warming, but assessment of the ecological impacts of climate change is often limited due to a lack of long-term monitoring data for comparative study in many ecosystems. In this study, we present an empirical work for assessing ecological responses with botanical legacy data in the Qilian Mountains of China. Plot-scale and transect-wide survey was conducted for alpine shrub communities along an elevational gradient 20 years ago. Recently, we resampled the permanent plots to investigate how the community changes may be linked to climatic variability. We found no significant temporal shifts in species richness; but the community structure underwent substantial changes, as indicated by visible shifts in the relative density of dominant shrub species and the frequency of occurrence of understory herbaceous species. This reshuffling of plant community composition reflected a series of complex responses to climate change. Specifically, wet-demanding species have become more frequent due to the recently enhanced precipitation, while the replacement of some low-statured plants with different requirements for light was indirectly regulated by climate warming via reshaping the altitudinal patterns of dominant shrubs. Climate-mediated shifts in shrub species distribution altered the expected evolutional trajectory of alpine community, which increased the complexity and nonlinearity of the responses of the communities at different altitudes to climatic variability. Our results suggested that in-depth knowledge of indirect effects can facilitate to lessen the uncertainty in predicting future community dynamics in a changing climate.

No Fertile Island Effects or Salt Island Effects of Tamarix chinensis on Understory Herbaceous Communities Were Found in the Coastal Area of Laizhou Bay, China

Tamarix chinensis is a dominant species in both the Yellow River Delta Natural Reserve and Changyi National Marine Specific Protection Area, Laizhou Bay, China, and plays an important role in wetland ecosystems. We investigated the relationship between T. chinensis and environmental factors, and the influences of T. chinensis on understory plants. We selected four T. chinensis communities with different hydrologic conditions and salinities in the Yellow River Delta Natural Reserve and the Changyi National Marine Specific Protection Area. The results showed that the growth of T. chinensis was negatively correlated with soil salinity. Generally no fertile island effects or salt island effects of T. chinensis on herbaceous plant communities were found in the coastal area of Laizhou Bay, China. In areas with high salinity, T. chinensis provided nursery effects for understory herbaceous species, increasing species diversity and enhancing plant growth. In low-salinity environments, T. chinensis appeared to restrain the growth of understory plants. This study observed different influences of T. chinensis on herbaceous species between the Yellow River Delta Natural Reserve and Changyi National Marine Specific Protection Area, providing scientific basis and theoretical foundation for investigating plant distribution and ecological community succession in Laizhou Bay, China.

Incorporating differences between genetic diversity of trees and herbaceous plants in conservation strategies.

Reviews that summarize the genetic diversity of plant species in relation to their life history and ecological traits show that forest trees have more genetic diversity at population and species levels than annuals or herbaceous perennials. In addition, among-population genetic differentiation is significantly lower in trees than in most herbaceous perennials and annuals. Possible reasons for these differences between trees and herbaceous perennials and annuals have not been discussed critically. Several traits, such as high rates of outcrossing, long-distance pollen and seed dispersal, large effective population sizes (Ne ), arborescent stature, low population density, longevity, overlapping generations, and occurrence in late successional communities, may make trees less sensitive to genetic bottlenecks and more resistant to habitat fragmentation or climate change. We recommend that guidelines for genetic conservation strategies be designed differently for tree species versus other types of plant species. Because most tree species fit an LH scenario (low [L] genetic differentiation and high [H] genetic diversity), tree seeds could be sourced from a few populations distributed across the species' range. For the in situ conservation of trees, translocation is a viable option to increase Ne . In contrast, rare herbaceous understory species are frequently HL (high differentiation and low diversity) species. Under the HL scenario, seeds should be taken from many populations with high genetic diversity. In situ conservation efforts for herbaceous plants should focus on protecting habitats because the typically small populations of these species are vulnerable to the loss of genetic diversity. The robust allozyme genetic diversity databases could be used to develop conservation strategies for species lacking genetic information. As acase study of reforestation with several tree species in denuded areas on the Korean Peninsula, we recommend the selection of local genotypes as suitable sources to prevent adverse effects and to insure the successful restoration in the long term.

Analysis of mesophyll conductance in five understory herbaceous species.

Mesophyll conductance (g m) has received over time much less attention than stomatal conductance (g s), although it affects leaf photosynthesis to about the same extent as stomatal conductance does. The objective of this study was to analyze the g m trend in five understory herbaceous species growing in a close-canopy forest in the north-west of Italy. In particular, three of analyzed species were monocots: Carex brizoides Lam., Carex pilosa Scop., and Oplismenus undulatifolius P. Beauv and the others dicots species: Circaea lutetiana L., and Pulmonaria officinalis Ced. The results showed, on one hand, the absence of correlation between g m and the considered environmental variables in the forest understory (i.e. air temperature, photosynthetic photon flux density and carbon dioxide concentration). Moreover, we carried out a principal component analysis considering all the analyzed morphological and physiological variables for the five species. The following correlation between the first component, related to the leaf mass per unit of leaf area and the leaf tissue density, and g m seem to suggest a key role of the leaf structural features in determining g m variations across the five species.

Filling a void: Analysis of early tropical soil and vegetative recovery under leguminous, post‐coal mine reforestation plantations in East Kalimantan, Indonesia

AbstractLand degradation in Borneo, one of the world's richest biodiversity hotspots, is extensive. In East Kalimantan, 5,000,000 ha of land are zoned for surface‐mined coal. Deforestation from this mining threatens biodiversity and results in soil degradation, erosion, and polluted runoff, all directly impacting human populations. Revegetation methods developed for temperate forests are commonly used globally for mine rehabilitation. However, few empirical studies of native forest restoration as part of mine rehabilitation exist from wet tropical regions. Here, a chronosequence was established to observe forest succession under leguminous plantations at the PT Singlurus Pratama coal mine in East Kalimantan, Indonesia. Soil and natural regeneration data were recorded from samples of ten 20 × 60‐m plots randomly located in plantings aged 2, 7, and, 9 years postmining. Linear models (LMEMs) did not reveal greater soil pH, woody plant diversity, or soil phosphorus and nitrogen in older plantings. Rather, they showed higher soil carbon in older plantings, whereas nitrogen and pH were positively correlated with woody species diversity and abundance. Graminoids were less abundant, but ferns were more abundant in older sites in an ordination analysis. The implications are exotic tree plantations shade‐out competitive understory herbaceous species (such as graminoids), opening growing space for other vegetation. However, the establishment of woody species is spatially limited possibly by differences in soil degradation among sites. Our results suggest that planting leguminous trees alone may not be sufficient to restore native forests, and future management should conserve and facilitate the establishment of tropical forest topsoil.

Phenolics of the understory shrub Cotinus coggygria influence Mediterranean oak forests diversity and dynamics

Chemical interactions in forested ecosystems play a role in driving biodiversity and ecosystem dynamics. Plant phenolics released by leaching can influence surrounding plants and soil organisms such as bacteria, fungi or arthropods. However, our knowledge about such chemically-mediated biotic interactions in Mediterranean oak forests is still limited, in particular whether they play a role in the limited forest regeneration. In this study, we analyzed how phenolics of Cotinus coggygria, a dominant shrub of Mediterranean downy oak (Quercus pubescens) forests, influence understory herbaceous plant species, downy oak regeneration and soil organisms in order to obtain a more integrative view of possible direct and indirect interactions triggered by this shrub species. We performed a series of experiments testing the effect of aqueous extracts of C. coggygria, mimicking natural leachates, on these organisms. Cotinus coggygria contained a high quantity of phenolics in green and senescent leaves but much less in leaf litter. Extracts from C. coggygria leaves stimulated bacterial communities, exhibited few effects on both saprophytic and symbiotic fungi, and negatively affected Collembola. Herbaceous species growth was particularly impaired by extracts from green and senescent leaves, although these effects were alleviated in the presence of soil microorganisms. In both greenhouse and field experiments, C. coggygria affected early oak seedling establishment in particular through a reduced root growth, but exhibited no effect on later seedling and sapling growth. We discussed the implication of these results for the balance between competition and facilitation in oak forests and concluded that C. coggygria has the potential to strongly alter biotic interactions, understory plant diversity and oak forest dynamics.

Plant performance was greater in the soils of more distantly related plants for an herbaceous understory species.

Growing evidence suggests that plant-soil interactions have important implications for plant community composition. However, the role of phylogenetic relatedness in governing interactions between plants and soil biota is unclear, and more case studies are needed to help build a general picture of whether and how phylogeny might influence plant-soil interactions. We performed a glasshouse experiment to test whether degree of phylogenetic relatedness between Aquilegia canadensis and six co-occurring heterospecifics affects A. canadensis biomass through soil legacy effects. We also compared performance of A. canadensis in soils conditioned by invasive Alliaria petiolata versus native heterospecifics, hypothesizing that conditioning by A. petiolata would suppress the performance of the focal native plant. A. canadensis performed significantly better in distant relatives' soils than in close relatives' soils, and this effect disappeared with soil sterilization, consistent with close relatives sharing similar pathogens. Contrary to our expectations, soils conditioned by the invasive species A. petiolata versus by native species had similar effects on A. canadensis. The greater performance of A. canadensis in soils of more versus less distant relatives is consistent with a hypothesis of phylogenetically constrained pathogen escape, a phenomenon expected to promote coexistence of phylogenetically distant species. However, pairwise plant-soil feedback experiments are needed to create a stronger coexistence prediction.

Trait variation and functional diversity maintenance of understory herbaceous species coexisting along an elevational gradient in Yulong Mountain, Southwest China

Characterizing trait variation across different ecological scales in plant communities has been viewed as a way to gain insights into the mechanisms driving species coexistence. However, little is known about how changes in intraspecific and interspecific traits across sites influence species richness and community assembly, especially in understory herbaceous communities. Here we partitioned the variance of four functional traits (maximum height, leaf thickness, leaf area and specific leaf area) across four nested biological scales: individual, species, plot, and elevation to quantify the scale-dependent distributions of understory herbaceous trait variance. We also integrated the comparison of the trait variance ratios to null models to investigate the effects of different ecological processes on community assembly and functional diversity along a 1200-m elevational gradient in Yulong Mountain. We found interspecific trait variation was the main trait variation component for leaf traits, although intraspecific trait variation ranged from 10% to 28% of total variation. In particular, maximum height exhibited high plasticity, and intraspecific variation accounted for 44% of the total variation. Despite the fact that species composition varied across elevation and species richness decreased dramatically along the elevational gradient, there was little variance at our largest (elevation) scale in leaf traits and functional diversity remained constant along the elevational gradient, indicating that traits responded to smaller scale influences. External filtering was only observed at high elevations. However, strong internal filtering was detected along the entire elevational gradient in understory herbaceous communities, possibly due to competition. Our results provide evidence that species coexistence in understory herbaceous communities might be structured by differential niche-assembled processes. This approach –– integrating different biological scales of trait variation –– may provide a better understanding of the mechanisms involved in the structure of communities.

Seasonal variability of biomass, total leaf area and specific leaf area of forest understory herbs reflects their life strategies

Seasonal variability of forest understory herbs is not well understood and there are almost no data about seasonal changes of individual plant biomass and specific leaf area (SLA) of this functional group, even though they are a crucial element of forest ecosystem plant biodiversity. The aim of the study was to characterize the seasonal variation of individual aboveground standing biomass, total leaf area and SLA of understory herbaceous species during a growing season. The study was conducted in the Czmoń Forest (W Poland; 52°15′N, 17°05′E) and covered 12 plant species, i.e. Aegopodium podagraria, Alliaria petiolata, Anemone nemorosa, Anemone ranunculoides, Asarum europaeum, Corydalis cava, Ficaria verna, Galium aparine, Galeobdolon luteum, Hepatica nobilis, Maianthemum bifolium and Paris quadrifolia. Plants were harvested 14 dates, between the 109th and 287th day of year. In all species there were statistically significant differences (p<0.05) in SLA and total leaf area among harvest dates and in individual plant biomass for all except two species (A. ranunculoides and G. aparine). Changes in SLA and total leaf area were related to changes in light conditions during the growing season. However, responses of the species studied to seasonal changes of light availability were different: those species which persisted through the whole sampling period differed from spring ephemerals, which resulted in different patterns of biomass production and SLA seasonal variation. In most cases, flowering individuals had lower SLA than vegetative plants, which may indicate that light availability is more important than light use efficiency for their generative propagation.

Long-term Protection from Heavy Livestock Grazing Affects Ponderosa Pine Understory Composition and Functional Traits

Making accurate predictions of plant community responses to grazing management is a major objective of rangeland ecology. Metrics such as species composition are site specific, whereas others such as functional groups and functional traits can be generalized across different rangeland types. We analyzed long-term (1912–1941) shifts in the understory community at five sites in a ponderosa pine (Pinus ponderosa P. & C. Lawson var. scopulorum Engelm.) forest when protected from heavy livestock grazing. We examined differences in total basal cover, species composition, species richness, functional group composition, and community-weighted mean (CWM) functional traits between heavily grazed and ungrazed areas in four time periods (1912, 1920, 1930, 1940). Total understory basal cover was greater in ungrazed than heavily grazed areas in 1920 but not in later time periods. Understory species composition diverged by 1930 and continued to differ in 1940. Functional group composition differed from 1920 onwards. In 1920 and 1930, C3 graminoids declined more in relative abundance in heavily grazed than ungrazed areas. By 1940, forbs accounted for much more of the cover in heavily grazed than ungrazed areas. During the study period, CWM specific leaf area and foliar Nmass declined by 8% and 11%, respectively, in ungrazed quadrats, while CWM leaf dry matter content increased 8%. Leaf traits, but not maximum height or seed mass, demonstrated consistent and predictable responses to protection from heavy grazing. Herbaceous understory species with leaf traits that allow for slower resource acquisition became more abundant in response to protection from heavy grazing. Our results indicate that managers should expect to observe more rapid changes in functional group composition and leaf functional traits than in species composition and species richness following protection from heavy livestock grazing.