Community-weighted Mean Of Specific Leaf Area Research Articles

Functional diversity along disturbance and environmental gradients in Ethiopian moist Afromontane forest

Considering multiple measures to fully capture functional diversity is important. However, the effects of disturbance gradients on diversity have been controversial, as species diversity alone may not fully capture these effects. This study aimed to evaluate trait-based diversity across disturbance gradients in the moist Afromontane forest of Ethiopia, Yayu Coffee Forest Biosphere Reserve (YCFBR). Vegetation data and relevant traits related to plant-life strategies, competition, and responses to disturbances were collected. A multiple regression model was used to test the response of functional diversity to disturbances and environmental gradients. The results revealed functional diversity in plant communities, including dendrogram-based functional diversity for plot-based (FDp), functional richness (FRic), functional evenness (FEve), functional divergence (FDiv), functional dispersions (FDis), and community-weighted mean of maximum tree height (CWM.Hmax), showed decreasing patterns with increasing disturbance intensity in the YCFBR. Additionally, the findings highlighted that FDis and Hmax are the most vulnerable functional traits to anthropogenic factors and are less tolerant in disturbed ecosystem environments. Therefore, reducing disturbances is crucial to maintaining higher levels of these functional diversities. For example, the results showed that the CWM.Hmax declined from 27.25 m to 15 m, indicating a shift towards shorter plant species. In contrast, the community-weighted mean of woody density (CWM.WD), the community-weighted mean of specific leaf area (CWM.SLA), and the community-weighted mean of seed mass (CWM.SM) increased significantly with an increase in disturbance intensity. For instance, CWM.SM and CWM.SLA changed from 5 to 14.25 (g) and 90 to 130 (cm2/g), respectively. These indices may serve as indicators of ecosystem resilience at disturbed forest ecosystem sites. Furthermore, the regression results indicated that FDp, FRic, FEve, FDiv, FDis, CWM.WD, and CWM.Hmax showed increasing patterns with increasing species richness, which suggests that protecting and promoting species diversity can contribute to maintaining high levels of functional diversity. The mixed effects model revealed that anthropogenic disturbance and elevational gradients had significant effects on functional diversity in the YCFBR. Therefore, when managing and conserving biodiversity in heterogeneous environments, both anthropogenic factors and environmental variables need to be considered. Species with low SLA and SM are recommended for the restoration of disturbed ecosystems. Overall, this study demonstrates that trait-based functional diversity is useful for predicting the adaptation potentials of species in heterogeneous environments and disturbance gradients.

More effect of ephemeral plant species diversity on aboveground biomass than functional diversity and functional composition

AbstractThe quantification of plant diversity–productivity relationships is essential for accurate productivity assessments. Global change drivers are altering resource availability and biodiversity. However, the extent to which multiple attributes of diversity (species, functions) buffer community productivity in response to the resource availability changes and the potential driver mechanisms of the diversity‐productivity relationship still needs to be the consensus. We investigated the ephemeral plant diversity–productivity relationships of different attributes along a precipitation gradient in the Gurbantunggut Desert, China. To evaluate the potential mechanisms by which diversity and functional composition affect aboveground productivity (niche complementarity and selection effect). Our results showed that (1) the variance of species richness (SR), Rao's quadratic entropy (RaoQ), community‐weighted mean of height (CWMH), and community‐weighted mean of leaf phosphorus concentration (CWMP) was larger among sites (variation between different sites) than subplots (variation between different subplots). Among subplots, the variance of community‐weighted mean of specific leaf area (CWMSLA), community‐weighted mean of leaf carbon concentration (CWMC), and community‐weighted mean of leaf nitrogen concentration (CWMN) was larger than the sites. (2) SR, RaoQ, CWMC, CWMN, CWMH, pH, and mean annual precipitation (MAP) collectively influenced the accumulation of aboveground biomass (AGB). (3) Species diversity and MAP have strongly affected AGB and accounted for 50% and 42%. The study confirms that SR is the optimal predictor of biomass in ephemeral plants. Complementation effects may be the primary mechanism explaining the relationship between biodiversity and productivity in the Gurbantunggut Desert, and thus the effect of plant diversity cannot be downplayed.

Native plant community characteristics explain alien species success in post-industrial vegetation

Biological invasions are one of the major challenges to the restoration of post-mining sites. Most post-mining sites are under technical reclamation with only a few left to spontaneous vegetation processes. Therefore, we know little about alien plant species on spontaneously-vegetated post-coal mine heaps and how native community characteristics predict their establishment. To fill the knowledge gap, we aimed to determine the drivers of alien species colonisation on post-coal mine heaps. Specifically, we asked: (i) Which alien species are the most successful on post-coal mine heaps and why? (ii) What are the drivers of alien species richness and cover, and how are they affected by the native community? (iii) What does it mean for predicting threats from alien species and management? We recorded vascular plant species and their abundance across 400 plots on post-coal mine heaps in Upper Silesia, Poland. We calculated plant community taxonomic and functional characteristics and, using mixed-effects models, we estimated predictors of alien species richness and cover. We found 65 alien species on post-coal mine heaps, comprising 20.4% of all recorded species, including 36 neophytes and 29 archaeophytes. Amongst them – Erigeron canadensis, Solidago gigantea, Solidago canadensis, Erigeron annuus and Impatiens parviflora – were the most frequent on the studied heaps. We showed that native functional richness significantly predicts alien species richness and cover. Similarly, native community-weighted mean (CWM) seed mass and plant height predict alien species cover. However, CWM of specific leaf area for native species marginally predicts alien species richness. We showed that alien species cover decreases with native species cover. Our findings revealed the ecological significance of niche-filling and the biotic acceptance hypotheses on post-coal mine heaps. We demonstrated how exploring native community characteristics can help in understanding the invasibility and management of post-industrial vegetation.

Functionally diverse tree stands reduce herbaceous diversity and productivity via canopy packing

Abstract There is extensive experimental evidence for the importance of biodiversity in sustaining ecosystem functioning. However, such experiments typically prevent immigration by continuously removing non‐target species, thereby questioning the generality of these findings to real‐world ecosystems. This is particularly true in forest ecosystems where understorey herbaceous species are key biodiversity components but are usually weeded in tree diversity experiments. Consequently, little is known about how tree diversity influences the natural dynamics of understorey herbaceous layers. We conducted a 3‐year non‐weeded tree diversity experiment composed of eight woody species differing widely in plant economic strategies. We examined how the functional diversity and identity of tree species mixtures drive the temporal dynamics of understorey productivity, functional diversity and composition through canopy packing (CP). Tree mixtures with high functional diversity experienced increased CP over time, thereby decreasing understorey productivity and diversity. Furthermore, herbaceous communities were dominated by species with functional traits typical of low‐light conditions [lower community‐weighted mean (CWM) of maximum plant height, but larger CWM of specific leaf area] in response to increased CP. Our results provide mechanistic insights into the role of tree functional diversity in shaping the dynamics of biomass, functional diversity and composition of the understorey herbaceous layer during the early successional period. It is expected that the effects of tree functional diversity would also be relevant over time due to the increasing usage of canopy space. This study highlights the significance of natural community processes in determining the effects of tree diversity on the temporal dynamics of previously neglected ecosystem structures and functioning. Read the free Plain Language Summary for this article on the Journal blog.

Plant Functional and Phylogenetic Diversity Regulate Ecosystem Multifunctionality in Semi-Arid Grassland During Succession

The relationship between biodiversity and ecosystem multifunctionality (EMF) is crucial for understanding the processes of ecological restoration in semi-arid regions. However, partitioning the relative influence of various biodiversity attributes, namely taxonomic, functional, and phylogenetic diversity, on EMF during secondary succession is still unclear. This study aimed to bridge the gap by employing field measurements and the chronosequence approach at 21 plots with different stand ages and precipitation conditions on the Loess Plateau of China. For diversity indices, we calculated the Shannon–Wiener diversity index, Simpson’s dominance index, Pielou evenness index, community weighted mean (CWM), functional variance (FDvar), and Faith’s phylogenetic diversity (PD) based on the empirically measured composition and traits of plant species. The EMF was expressed as the averaged value of eight function variables (including aboveground biomass, root biomass, soil total carbon, total nitrogen, and total phosphorus content, soil organic carbon, available nitrogen and available phosphorus content). The results showed that species evenness and CWM of leaf dry matter content (LDMC) significantly increased yet the CWM of specific leaf area (SLA) decreased with stand age, indicating the resource-use strategy of the plants became more conservative through succession into its later stages. The EMF increased with both stand age and mean annual precipitation. The structural equation model revealed that stand age, soil water content (SWC), and the multiple diversity indices altogether accounted for 56.0% of the variation in the EMF. PD and the CWMs of plant height and LDMC had positive effects on the EMF, and the FDvar of leaf nitrogen had negative effects on EMF. However, the Shannon Wiener diversity had no significant effect on the EMF. Our results suggest that functional and phylogenetic diversity are more important than taxonomic diversity in predicting EMF, and that multidimensional biodiversity indices should be jointly considered to better predict EMF during the succession of semiarid grasslands.

Plant Functional Diversity Is Linked to Carbon Storage in Deciduous Dipterocarp Forest Edges in Northern Thailand

Studies of carbon storage using functional traits have shown that it is strongly affected by functional diversity. We explored the effects of functional diversity on carbon storage at the edge of a deciduous dipterocarp forest (DDF) ecosystem in Thailand. Aboveground biomass carbon (AGBC), soil organic carbon (SOC), and total ecosystem carbon (TEC) were used as indicators of carbon storage. Five functional traits were measured in 49 plant species to calculate the community-weighted mean (CWM) and Rao’s quadratic diversity (FQ). We assessed which functional diversity metrics best-explained carbon storage. The results indicated that AGBC had a significant, positive relationship with the FQ of wood density, and a negative relationship with the CWM of leaf thickness. SOC had a significant, negative association with the FQ of leaf thickness and a positive relationship with the CWM of specific leaf area (SLA). TEC was best predicted by increases in the FQ of wood density and the CWM of SLA. These findings indicate that CWM and FQ are important for understanding how plant traits influence carbon storage in DDF edge ecosystems and suggest that promoting a high diversity of species with dissimilar wood density and high SLA may increase carbon storage in chronically disturbed DDF ecosystems.

Effects of thinning on the demography and functional community structure of a secondary tropical lowland rain forest

Tropical secondary forests play a prominent role in conserving biodiversity and providing ecosystem services, but their recovery can be slow and their succession trajectory is distinct from old-growth forests. Thinning is an essential silvicultural approach to enhance the recovery rate and timber production of forests. However, the selection of trees to thin has been mainly based on size class rather than on species identity. There is little empirical or experimental evidence of species-focused thinning with the goal of altering species composition. We examined the effects of thinning on community structure, demographic rates, species richness and functional diversity of woody plants in a detailed investigation of 60-year-old secondary tropical lowland rain forest on Hainan Island, South China. The density and basal area of trees ≥5 cm DBH (diameter at breast height) increased significantly after five years' recovery with no significant change for saplings (DBH < 5 cm). Species composition after thinning changed significantly and mid-to late-successional species of both saplings and trees were more abundant after five years’ recovery. The relative growth rates (RGR) and recruitment rates were significantly higher in thinning plots for both saplings and trees, and RGRs increased by 127% and 48%, respectively. The mortality rate decreased by 13% for trees and increased by 47% for saplings in thinning plots compared to the control. The community weighted mean (CWM) of the specific leaf area (SLA) of saplings showed a significantly decreasing trend while CWMs of wood density (WD) and mean maximum height (Hmax) of saplings increased after thinning. By contrast, CWMs of SLA and Hmax of trees were significantly higher, but WD was significantly lower- in thinning plots than the control. RGR and recruitment rate of saplings and trees increased significantly as thinning intensity increased. However, the thinning intensity had a weak or nil effect on the mortality rate. Our results support the selective removal and girdling of pioneer and mid-successional species in a way that could accelerate recovery and improve the growth and recruitment of late-successional species in tropical secondary forests. Thinning at a relatively low intensity can maintain species diversity and alter species functional composition. This outcome shows promise for improved future management of tropical forests in human-modified tropical forest landscapes.

Relative influence of environmental, stand factors and functional traits on allocation of forest productivity during the restoration of subtropical forests in central China

Many studies have examined plant biomass allocation among leaf, stem and root organs in relation to environmental and ontogenetic factors. But the drivers for allocation of stand-level productivity across restoration stages, and the potential role of functional traits, are still poorly understood. Here we investigated 24 plots across four restoration stages in subtropical forests on Mt. Shennongjia, central China. We examined the relative effects of environment (slope, aspect and canopy openness), stand factors (forest height, total basal area, stand density and age), and community-weighted mean (CWM) of key functional traits (wood density and specific leaf area), on the allocation of forest productivity to stems, leaves and roots. The results showed that forest productivity, and the stem fraction of stand productivity, both increased during forest restoration; while leaf and root productivity fractions showed an overall decrease. A higher fraction of productivity was allocated to leaves and roots while lower fraction was allocated to stems towards harsher site condition. Stem fraction was positively related to stand age and forest height, whereas root fraction showed a converse pattern. None of the stem, leaf or root fraction was significantly correlated with the proxies of competition (stand density and total basal area). As for the effect of functional traits, stem productivity fraction was negatively related to the CWM of wood density, while leaf fraction was positively related, which can be explained by the optimal theory and growth strategy together. However, CWM of specific leaf area has no significant effect on productivity allocation. Multivariate analyses showed that topography (slope) and stand age were main drivers for the productivity allocation to woody organs (stem and root), and wood density was also important for stem productivity fraction. Meanwhile, leaf fraction is mainly affected by wood density and aspect. Our results suggest that, in addition to environmental and stand factors, functional traits (e.g. wood density) are also important in affecting the allocation of stand productivity. However, there are still many equivocal results about the influence of functional traits. Allocation of productivity among organs, and key functional traits (e.g. wood density and specific leaf area), are both indispensable parameters in ecosystem processes models. Further studies are needed to explore the mechanisms how functional traits and stand factors affect productivity allocation, to better predict forest carbon balance under future global change, and to better guide forest management to increase ecosystem services and carbon sink.

Intraspecific trait variability shapes leaf trait response to altered fire regimes.

Understanding impacts of altered disturbance regimes on community structure and function is a key goal for community ecology. Functional traits link species composition to ecosystem functioning. Changes in the distribution of functional traits at community scales in response to disturbance can be driven not only by shifts in species composition, but also by shifts in intraspecific trait values. Understanding the relative importance of these two processes has important implications for predicting community responses to altered disturbance regimes. We experimentally manipulated fire return intervals in replicated blocks of a fire-adapted, longleaf pine (Pinus palustris) ecosystem in North Carolina, USA and measured specific leaf area (SLA), leaf dry matter content (LDMC) and compositional responses along a lowland to upland gradient over a 4 year period. Plots were burned between zero and four times. Using a trait-based approach, we simulate hypothetical scenarios which allow species presence, abundance or trait values to vary over time and compare these with observed traits to understand the relative contributions of each of these three processes to observed trait patterns at the study site. We addressed the following questions. (1) How do changes in the fire regime affect community composition, structure and community-level trait responses? (2) Are these effects consistent across a gradient of fire intensity? (3) What are the relative contributions of species turnover, changes in abundance and changes in intraspecific trait values to observed changes in community-weighted mean (CWM) traits in response to altered fire regime? We found strong evidence that altered fire return interval impacted understorey plant communities. The number of fires a plot experienced significantly affected the magnitude of its compositional change and shifted the ecotone boundary separating shrub-dominated lowland areas from grass-dominated upland areas, with suppression sites (0 burns) experiencing an upland shift and annual burn sites a lowland shift. We found significant effects of burn regimes on the CWM of SLA, and that observed shifts in both SLA and LDMC were driven primarily by intraspecific changes in trait values. In a fire-adapted ecosystem, increased fire frequency altered community composition and structure of the ecosystem through changes in the position of the shrub line. We also found that plant traits responded directionally to increased fire frequency, with SLA decreasing in response to fire frequency across the environmental gradient. For both SLA and LDMC, nearly all of the observed changes in CWM traits were driven by intraspecific variation.

Association of Community-level Traits with Soil Properties in a Tropical Coastal Sand Dune

There is limited information regarding plant functional traits for plant communities in tropical coastal sand dunes. This study investigated differences in species trait compositions and the relationship between community-weighted mean (CWM) traits and soil properties on the windward and leeward sides of the Bang Boet coastal sand dunes in southern Thailand. Ten sampling plots were randomly selected from each side of the dune. All woody plant species were collected and their functional traits were assessed. Soil samples were also collected. A redundancy analysis (RDA) was used to examine the relationship between CWM traits and soil properties. The results showed that species trait compositions and the CWMs of specific leaf area, leaf thickness, and leaf toughness were significantly different between windward and leeward sides. The RDA showed significant correlation between CWM traits and soil properties, particularly for specific leaf area, a functional trait that plays an important role in nutrient turnover on the leeward side. These results indicate that soil properties are predictable based on CWM traits and that leeward sand dune sides can support greater soil formation than windward sides. Hence, functional traits, as well as species, should be considered in coastal sand dune restoration and conservation programs.

Functional diversity enhances, but exploitative traits reduce tree mixture effects on microbial biomass

Abstract Soil micro‐organisms play key roles in terrestrial biodiversity and ecosystem functions. Despite recent progress in elucidating the association between plant diversity and soil micro‐organisms, it remains unclear whether the functional properties of plant mixtures might alter this association. We examined whether the effects of tree species mixtures on soil microbial biomass were impacted by the functional diversity (FD) and community‐weighted mean (CWM) of tree mixtures, by conducting a global meta‐analysis involving 123 paired observations of tree mixtures and the corresponding monocultures from 38 studies in forests. We found that the tree mixture effect on microbial biomass increased with the FD of specific leaf area (SLA) and leaf N and P contents, as well as the FD based on all of these traits plus leaf dry matter content. Meanwhile, the responses of microbial biomass to tree mixtures decreased with the CWM of SLA and leaf N and P contents. The effects of FD and CWM remained consistent, despite variable tree species richness, stand age and climatic factors. Our results provide a new insight that the functional properties of plants may alter the magnitude of the association between plant diversity and soil micro‐organisms. A free Plain Language Summary can be found within the Supporting Information of this article.

The effect of environmental filtering on variation in functional diversity along a tropical elevational gradient

AbstractQuestionsElevational gradients encompass multiple resource or non‐resource stressors, but how these different gradients drive functional structure is not well understood. Abiotic variables and functional traits were sampled along a 1,400 m tropical elevational gradient to answer the following questions: (a) how do the functional diversity and functional structure of tree communities change with environment; (b) how does the different assembly vary along the elevational gradient?LocationTropical forests on Hainan Island, South China.MethodsAlong an elevational gradient from 180 m to 1,521 m, sixty 0.05‐ha transects were established. We recorded all woody stems ≥5 cm dbh (diameter at breast height) and measured functional traits and soil features in each transect. The patterns of abiotic variables, functional diversity and community‐weighted mean (CWM) of functional traits were explored along the elevational gradient by using a regression model. The assembly along the elevational gradient was compared with a null model that shuffled species identities.ResultsThe functional richness (FRic), functional dispersion (FDis) and CWMs of specific leaf area, leaf phosphorus and nitrogen content decreased with increasing elevation, as well as with the first axis of the principal components analysis (PCA1) of abiotic variables. The CWMs of leaf dry matter content and maximum height did not show significant change with elevational change, but the CWM of maximum height increased with PCA1. Both FRic and FDis became less divergent and more convergent with increasing elevation and with PCA1, which differed from the predicted outcome under the null model.ConclusionsAll these observations support that environmental filtering selects species with either acquisitive or conservative strategies at low elevations, but it only selects species with conservative strategies at high elevations. The presence of different stressors, resources (water) and non‐resources (temperature and pH) leads to distinct community assemblages with different functional structures.

Assessing top- and subsoil organic carbon stocks of Low-Input High-Diversity systems using soil and vegetation characteristics

The soil organic carbon (SOC) stock is an important indicator in ecosystem service assessments. Even though a considerable fraction of the total stock is stored in the subsoil, current assessments often consider the topsoil only. Furthermore, mapping efforts are hampered by the limited spatial density of these topsoil measurements. The aim of this study was to assess the SOC stock in the upper 100cm of soil in 30,556ha of Low-Input High-Diversity systems, such as nature reserves, in Flanders (Belgium) and compare this estimate with the stock found in the topsoil (upper 15cm). To this end, we combined depth extrapolation of 139 measurements limited to the topsoil with four digital soil mapping techniques: multiple linear regression, boosted regression trees, artificial neural networks and least-squares support vector machines. Particular attention was given to vegetation characteristics as predictors. For both the stock in the upper 15cm and 100cm, a boosted regression trees approach was most informative as it resulted in the lowest cross-validation errors and provided insights in the relative importance of predictors. The predictors of the stock in the upper 100cm were soil type, groundwater level, clay fraction and community weighted mean (CWM) and variance (CWV) of plant height. These predictors, together with the CWM of specific leaf area, aboveground biomass production, CWV and CWM of rooting depth, terrain slope, CWM of mycorrhizal associations and species diversity also explained the topsoil stock. Our total stock estimates show that focusing on the topsoil (1.63Tg OC) only considers 36% of the stock in the upper 100cm (4.53Tg OC). Given the magnitude of subsoil OC and its dependency on typical ecosystem characteristics, it should not be neglected in regional ecosystem service assessments.

Intensity of soil disturbance shapes response trait diversity of weed communities: The long-term effects of different tillage systems

Disturbances have a prominent role in structuring plant communities. However, in agroecosystems, the long-term effect of disturbances on determining trait distributions within weed communities remains little studied. We analyzed the effect of three tillage treatments, which differ in the intensity of soil disturbance, on the mean, the range and the distribution of four response traits within weed communities. We aim to test whether tillage acts as a filter restricting the range and the distribution of response traits within weed communities and leads to reduced response trait diversity or whether tilling may have a diversifying effect, creating opportunities for more phenotypes to coexist and increasing response trait diversity. To test this idea, we used data on weed abundance recorded over 24 years from an experiment in which conventional tillage (CT), minimum tillage (MT) and no-tillage (NT) systems were compared. We selected four response traits, maximum height, specific leaf area (SLA), seed weight and seed output, and computed the community weighted mean (CWM) of each trait, as well as four multi-trait metrics related to a different aspect of functional diversity. We found that soil disturbance increases available niche opportunities for weeds especially in terms of regenerative traits. CT, the greater soil disturbance, leads to a greater range and even distribution of the studied traits and that abundant weed species from CT plots hold more divergent trait values than those from MT and NT plots. Our results may be explained by the idiosyncrasy of our disturbance treatments that affect weed seed placement in the soil layers as well as the stratification and availability of soil nutrients. We also found that NT system selected for lower CWM of seed weight (and higher seed output) than MT and CT systems. NT places weed seeds mostly on the soil surface, where having a large seed output may be necessary to avoid the risk of decay or depredation. Conversely, MT and CT systems offer some advantage to other strategies such as larger seed sizes useful to germinate from depth. CWM of SLA was higher in NT and MT than in CT plots and this could be related to greater soil nutrient content in NT systems. In addition our results showed a general trend over experimental time for weed communities to increase in height (and slightly in SLA and seed production) while reducing in seed size. These features are generally associated with intensive farming systems.