Effects Of Species Diversity Research Articles

Species but not genotype diversity strongly impacts the establishment of rare colonisers

Summary Understanding species coexistence and regulation of biodiversity are major research challenges, yet there is no consensus on the effects of diversity on diversity, including their mediation through plant–plant interactions. We examined how the diversity of recipient communities impacted on the establishment of colonising species. We ran a greenhouse‐based community experiment, creating artificial arable crop communities with varying levels of barley genotype and weed species diversity, analysed with structural equation modelling of responses across trophic levels. Colonising arable weed species establishment was significantly reduced when the recipient communities’ weed species richness, but not barley genotype richness, increased. Recipient plant communities with higher species richness occupied more total niche space and showed stronger competition with colonising species. In contrast, recipient plant communities with higher genotype richness, even though they had slightly greater niche space occupancy, had no significant effects on the colonisation of additional species. Responses were species specific: colonising common weed species establishment was less affected by the recipient plant communities than that of colonising rare weed species. Strong responses of colonising rare species were related to the abiotic rather than the biotic environment created by the recipient communities. The stronger response of colonising rare species suggests greater niche overlap with and competitive inferiority to the recipient plant community, whereas the relative independence of colonising common species indicates less niche overlap and/or competitive equality or superiority. We observed a negative species diversity effect on colonising species, with the effect size increasing with increasing rarity of the colonising species. This differential responsiveness of colonising rare and common arable weed species to the presence of and diversity in the recipient arable plant communities may be crucial in understanding rarity and may result from differential evolutionary pathways in response to interactions.

Biodiversity effects on resource use efficiency and community turnover of plankton in Lake Nansihu, China

The relationship between biodiversity and ecosystem functioning is a central issue in ecology, especially in aquatic ecosystems due to the ecophysiological characteristics of plankton. Recently, ecologists have obtained conflicting conclusions while analyzing the influence of species diversity on plankton resource use efficiency (RUE) and community turnover. In this study, both phytoplankton and zooplankton communities were investigated seasonally from 2011 to 2013 in Lake Nansihu, a meso-eutrophic and recovering lake in China. The effects of phytoplankton diversity on RUE of phytoplankton (RUEPP), zooplankton (RUEZP), and community turnover were analyzed. Results showed that both phytoplankton species richness and evenness were positively correlated with RUEPP. RUEZP had a negative relationship with phytoplankton species richness, but a weak unimodal relationship with phytoplankton evenness. Cyanobacteria community had the opposite influence on RUEPP and RUEZP. Thus, cyanobacteria dominance will benefit RUEPP in eutrophic lakes, but the growth and reproduction of zooplankton are greatly limited. The strong negative relationship between total phosphorus and RUEZP confirmed these results. Phytoplankton community turnover tended to decrease with increasing phytoplankton evenness, which was consistent with most previous studies. The correlation coefficient between phytoplankton species richness and community turnover was negative, but not significant (p>0.05). Therefore, phytoplankton community turnover was more sensitive to the variation of evenness than species richness. These results will be helpful in understanding the effects of species diversity on ecosystem functioning in aquatic ecosystems.

On the structural and species diversity effects of bark beetle disturbance in forests during initial and advanced early-seral stages at different scales

Following disturbances, early-seral stages of forests provide a variety of structures. Whether this variety is a short-term phenomenon or influences forest succession for several decades or even longer is not known. We tested the hypotheses that after spruce dieback caused by bark beetles, a high spatial heterogeneity of stand structures will persist within stands and among stands even in advanced early-seral stages and that species taxonomical and functional diversity measures will reflect this heterogeneity. We used a chronosequence of unmanaged forests in the Berchtesgaden National Park (Germany) consisting of mature undisturbed spruce stands (control), stands belonging to an initial early-seral stage (~3 years after disturbance) and stands in an advanced early-seral stage (~20 years after disturbance). We analysed diversity and heterogeneity of these forest stands including stand structure, species density, species composition and functional–phylogenetic diversity of vascular plants, wood-inhabiting fungi and saproxylic beetles within plots, among plots of the same successional stage and among stages. Stands of the advanced early-seral stage were characterized by a high spatial heterogeneity of structural attributes, such as crown cover, regeneration density and spatial distribution of trees. Among-plot taxonomic beta diversity was highest in the advanced early-seral stage for beetles, but lowest for fungi, while beta diversity of plants among plots remained unchanged during succession. The mosaic of successional stages initiated by bark beetles increased the gamma diversity of the study area, especially for fungi and beetles. Our findings support the hypothesis that structural heterogeneity continues for at least two decades at stand and landscape scales and that species turnover among successional stages is a major mechanism for gamma diversity in forests after bark beetle disturbance.

Tree species diversity and identity effects on soil properties in the Huoditang area of the Qinling Mountains, China

AbstractSoil properties, such as carbon stock, nitrogen stock, cation exchange capacity (CEC), bulk density (BD), and pH, may have a different status when the forest type changes. We were interested in how tree species identity and diversity affect soil properties. Forest soil profiles were sampled at a fixed depth (0–10, 10–20, 20–40, and 40–60 cm). The abovementioned soil properties were compared by species to demonstrate the influence of tree species identity. We calculated the true Shannon diversity index and evaluated tree species diversity effects on soil properties. We found that the soil BD, CEC, and pH were all influenced by tree species identity. Tree species diversity only showed a negative effect on soil carbon stock; in contrast, a positive effect on soil nitrogen stock in the 0‐ to 10‐cm soil layer was found. High diversity could lead to a change in the soil nutrient conditions in the form of C/N ratio decreases. In contrast, tree species diversity had a marginal effect on the soil BD, pH, and CEC. We concluded that tree species identity was a strong driver of soil properties in the study area, especially in the 0‐ to 10‐cm layer, and that tree species diversity only altered the soil nutrient condition to some extent.

Investigation of plant growth and flower performance on a semi-extensive green roof

Understanding of plant growth and flower performance is crucial for appropriate planting design. This study was aimed to understand characteristics of growth pattern and flower performance in green roof plants and how plant species diversity effect these characteristics. A semi-extensive green roof was installed in 2005 and 54 species plant species were planted in 10cm and 20cm of the substrate in Rotherham, UK. Thirty-two quadrats (50cm×50cm) were set up through the combinations of plant species diversity (high and low), planting density (high and low). Percentage of coverage and height of each species were recorded at every month from February to November 2006 in these 32 quadrates. Flowering time of each species was studied every two weeks from February to November 2006. Flowering time was various from plants; some showed a very long flowering time, over five months whereas some finished flowering within two weeks. The growth characteristics of individual plant species over time were categorized into six patterns of coverage and vertical growth pattern. Spread of individual plants was larger in high diversity of plants than those in low diversity of plants. Number of flowering was higher and overall flowering term was longer in the quadrats of higher plant species diversity than those of lower plant diversity. However, these tendencies were affected strongly by the combination of species used. Therefore, it is important to be aware of individual plant growth characteristics such as plant size, growth pattern and flower performance for planting design.

The importance of trees for woody pasture bird diversity and effects of the European Union's tree density policy

Summary Recent reforms in the Common Agricultural Policy aim for a greening of the subsidy system with potential improvements for biodiversity conservation. As part of that process, the tree density limit for pastures to qualify for European Union subsidies has been increased from 50 to 100 trees per hectare. However, recent studies show that the high biodiversity values of these habitats may be threatened by these limits, highlighting the need for policy improvements. Still, little is known about the direct effects of tree density limitations on bird communities in woody pastures. We investigated how bird diversity and species composition are affected by tree density in 49 Swedish woody pastures along a gradient of 4–214 trees per hectare. We recorded bird communities, tree density and stand structure estimates in the field and estimated forest cover in the surrounding landscape from aerial photos. Using generalised additive models and redundancy analysis, we analysed how bird territorial species richness, bird abundance and species composition are affected by tree density, taking into account other local and landscape scale explanatory variables. Tree density had a significant positive effect on bird species richness at low tree densities and species richness saturated at approximately 50 trees per hectare. Shrub density had a significant positive linear effect on both bird species richness and abundance. Tree and shrub density were also the major drivers of bird community composition, with secondary effects of tree species diversity and landscape forest cover. Policy implications. Our results show that tree density is not the limiting factor, but rather a driver of bird diversity and species composition in woody pastures and that tree density limits may fail to capture the whole range of biological values. To improve policy recommendations, we therefore stress the importance of considering additional social–ecological drivers associated to management quality, e.g. taking into account moral and cultural motivations among farmers, to preserve biodiversity in woody pastures.

Species-specific effects of genetic diversity and species diversity of experimental communities on early tree performance

Aims Changing biodiversity can affect ecosystem functioning. However, the role of genetic diversity within species, relative to the one of species diversity, has hardly been addressed. Methods To address the effects of both genetic diversity and species diversity during the important stage of early tree life, we used eight seed families (SF) taken from each of 12 evergreen and deciduous tree species of subtropical forest to perform a factorial experiment. We established 264 communities of 16 trees each. Each community had a species diversity of either one or four species and a genetic diversity of either one, two or four SF per species. We measured plant survival, growth rate, final biomass and herbivory 20 months after sowing. Important Findings Species differed from each other in biomass, growth rate, herbivory and survival (P < 0.001). Deciduous species tended to have much higher biomass (P < 0.1) and experienced higher herbivory (P < 0.05) than evergreen species. Species diversity affected the performance of different species differently (species diversity by species interaction, P <0.001 for all variables but survival). Biomass differed between SF and increasing genetic diversity from one to two, and from two to four, SF per species increased biomass for some species and decreased it for others (P < 0.001). Our study showed pronounced species–specific responses of early tree performance to species diversity and less pronounced responses to genetic diversity. These species–specific responses suggest feedbacks of species diversity and genetic diversity on future species composition.

Positive effects of tree species diversity on litterfall quantity and quality along a secondary successional chronosequence in a subtropical forest

Litterfall, as an important link between aboveground and belowground processes, plays a key role in forest ecosystems. Here, we test for effects of tree species richness on litter production and litter quality in subtropical forest. The study further encompasses a factorial gradient of secondary succession that resulted from human exploitation. Given that a large percentage of subtropical forests are in secondary successional stages, understanding the role of biodiversity on forest re-growth after disturbance appears critical. From January 2009 to December 2014, we monitored forest litterfall in 27 Comparative Study Plots that spanned a gradient of tree species richness (3–20 species) and secondary successional ages (~20 to 120 years) in Gutianshan Natural Nature Reserve, Zhejiang Province, China. The experiment is part of the biodiversity–ecosystem functioning research platform ‘BEF-China’. Tree litterfall was collected in monthly intervals using litter traps. Samples were separated into leaf and non-leaf components. Leaf litter was further sorted into dominant and other species. Community level monthly leaf litter C and N contents were analysed through a full year. General linear mixed-effects models were applied to test for effects of tree species richness and successional age on litter quantity and leaf litter C/N. Litterfall increased with species richness among and within successional age and this effect was consistent across years. Successionally older stands had higher litterfall and this effect was related to increased tree species richness. However, species richness did not change the intra- and inter-annual temporal stability of litterfall. Increasing tree species richness increased leaf litter quality (decreased C/N), while successional age had no effect. Our study indicates that more diverse forest stands produce more leaf litter and that this litter has higher N concentrations, which could promote forest growth through accelerated nutrient re-cycling.

Intraspecific variability in growth response to environmental fluctuations modulates the stabilizing effect of species diversity on forest growth

SummaryDifferences between species in their response to environmental fluctuations cause asynchronized growth series, suggesting that species diversity may help communities buffer the effects of environmental fluctuations. However, within‐species variability of responses may impact the stabilizing effect of growth asynchrony.We used tree ring data to investigate the diversity–stability relationship and its underlying mechanisms within the temperate and boreal mixed woods of Eastern Canada. We worked at the individual tree level to take into account the intraspecific variability of responses to environmental fluctuations.We found that species diversity stabilized growth in forest ecosystems. The asynchrony of species’ response to climatic fluctuations and to insect outbreaks explained this effect. We also found that the intraspecific variability of responses to environmental fluctuations was high, making the stabilizing effect of diversity highly variable.Synthesis. Our results are consistent with previous studies suggesting that the asynchrony of species’ response to environmental fluctuations drives the stabilizing effect of diversity. The intraspecific variability of these responses modulates the stabilizing effect of species diversity. Interactions between individuals, variation in tree size and spatial heterogeneity of environmental conditions could play a critical role in the stabilizing effect of diversity.

Effect of host diversity and species assemblage composition on bovine tuberculosis (bTB) risk in Ethiopian cattle.

Current theories on diversity-disease relationships describe host species diversity and species identity as important factors influencing disease risk, either diluting or amplifying disease prevalence in a community. Whereas the simple term 'diversity' embodies a set of animal community characteristics, it is not clear how different measures of species diversity are correlated with disease risk. We therefore tested the effects of species richness, Pielou's evenness and Shannon's diversity on bovine tuberculosis (bTB) risk in cattle in the Afar Region and Awash National Park between November 2013 and April 2015. We also analysed the identity effect of a particular species and the effect of host habitat use overlap on bTB risk. We used the comparative intradermal tuberculin test to assess the number of bTB-infected cattle. Our results suggested a dilution effect through species evenness. We found that the identity effect of greater kudu - a maintenance host - confounded the dilution effect of species diversity on bTB risk. bTB infection was positively correlated with habitat use overlap between greater kudu and cattle. Different diversity indices have to be considered together for assessing diversity-disease relationships, for understanding the underlying causal mechanisms. We posit that unpacking diversity metrics is also relevant for formulating disease control strategies to manage cattle in ecosystems characterized by seasonally limited resources and intense wildlife-livestock interactions.

Plant species diversity reduces N2O but not CH4 emissions from constructed wetlands under high nitrogen levels.

Constructed wetlands (CWs) have been widely used for treating wastewater. CWs also are the sources of greenhouse gas (GHG) due to high pollutant load. It has been reported that plant species diversity can enhance nitrogen (N) removal efficiency in CWs for treating wastewater. However, the influence of plant species diversity on GHG emissions from CWs in habitats with high N levels still lack research. This study established four species richness levels (1, 2, 3, 4) and 15 species compositions by using 75 simulated vertical flow CWs microcosms to investigate the effects of plant species diversity on the GHG emissions and N removal efficiency of CWs with a high N level. Results showed plant species richness reduced nitrous oxide (N2O) emission and N (NO3--N, NH4+-N, and TIN) concentrations in wastewater, but had no effect on methane (CH4) emission. Especially, among the 15 compositions of plant species, the four-species mixture emitted the lowest N2O and had under-depletion of N (DminTIN<0). The presence of Oenanthe javanica had a significantly negative effect on the N2O emission but had no effect on N removal efficiency. The presence of Rumex japonicus significantly reduced the N (NO3--N and TIN) concentrations in wastewater but had no effect on the N2O and CH4 emissions. The N concentrations and GHG emissions in the community of R. japonicus × Phalaris arundinacea were as low as those in the four-species mixture. Assembling plant communities with relatively high species richness (four-species mixture) or particular composition (R. japonicus × P. arundinacea) could enhance the N removal efficiency and reduce the GHG emissions from CWs for treating wastewater with a high N level.

Species Diversity Effects on Productivity, Persistence and Quality of Multispecies Swards in a Four-Year Experiment.

Plant species diversity may benefit natural grassland productivity, but its effect in managed grassland systems is not well understood. A four-year multispecies grassland experiment was conducted to investigate the effect of species diversity–legumes and non-leguminous forbs–on productivity, persistence and sward quality under cutting or grazing regimes and with or without slurry application. Three mixtures were established– 3-mix: grass, red and white clover, 10-mix: 3-mix plus birdsfoot trefoil and six non-leguminous forbs, and 12-mix: 10-mix plus lucerne and festulolium. Species diversity increased sward production and yield persistence under cutting regime. The 12-mix had the highest yield from the second year onwards and no statistically significant yield reduction over four years, while annual yields in the 3-mix and 10-mix decreased significantly with increasing grassland age. The higher yield in the 12-mix was mainly due to the inclusion of high-yielding lucerne. The 10-mix and 12-mix had lower proportions of unsown species than the 3-mix, the difference being dependent on grassland age. Generally, the 3-mix had higher concentrations of in-vitro organic matter digestibility (IVOMD), neutral detergent fiber (NDF) and crude protein (CP), and a lower concentration of ash than the 10-mix and 12-mix. Slurry application increased annual yield production by 10% and changed the botanical composition, increasing the proportion of grass and decreasing the proportion of legumes. Compared to cutting, grazing increased forage production by 9% per cut on average and lowered legume and forb proportions in the mixtures, but yields did not differ among the three mixtures. Overall, our results suggest that species diversity increases sward productivity and persistence only under an ungrazed cutting regime. We conclude that increasing species diversity by selecting appropriate species with compatible management is key to achieving both high yields and high persistence in managed grasslands.

Scale dependent effects of species diversity and structural diversity on aboveground biomass in a tropical forest on Barro Colorado Island, Panama

Scale dependent effects of species diversity and structural diversity on aboveground biomass in a tropical forest on Barro Colorado Island, Panama

A two-species stage-structured model forWest Nile virustransmission

We develop a host–vector model of West Nile virus (WNV) transmission that incorporates multiple avian host species as well as host stage-structure (juvenile and adult stages), allowing for both species-specific and stage-specific biting rates of vectors on hosts. We use this ordinary differential equation model to explore WNV transmission dynamics that occur between vectors and multiple structured host populations as a result of heterogeneous biting rates on species and/or life stages. Our analysis shows that increased exposure of juvenile hosts generally results in larger outbreaks of WNV infectious vectors when compared to differential host species exposure. We also find that increased juvenile exposure is an important mechanism for determining the effect of species diversity on the disease risk of a community.

Diversity and competition influence tree allometric relationships – developing functions for mixed‐species forests

Summary Promoting mixed‐species forests is an important strategy for adaptation and risk reduction in the face of global change. Concurrently, a main challenge in ecology is to quantify the effects of species diversity on ecosystem functioning. In forests, the effects of individual tree species on ecosystem functions depend largely on their dimensions, which are commonly predicted using allometric equations. However, little is known about how diversity influences allometry or how to incorporate this effect into allometric equations. Ignoring the effects of interspecific interactions on allometric relationships may result in severely biased predictions. This study examined the effects of tree‐species diversity, competition and tree social status on crown‐projection area (cpa), height (h) and live‐crown length (lcl) of trees using a European‐wide data set containing 17 target species and 12 939 trees. The cpa, h and lcl were predicted as functions of stem diameter at 1·3 m, tree‐species diversity, tree height relative to the stand mean height (rh) and a competition index (CI) that accounted for stand density and interspecific differences in competitive ability based on species‐specific wood density or shade tolerance. Averaged across species, diameter had the greatest effect on cpa and lcl, followed by the competition index, while rh had the greatest effect on lcl. Tree‐species diversity had the smallest effect on cpa, h and lcl. Interspecific variability in cpa, h or lcl responses to diversity, CI, or rh was sometimes related to wood density or shade tolerance. Synthesis. This study shows the strong influence of stand structure and species composition on allometric relationships. These influences can be quantified using measures of competition, tree‐species diversity and relative tree height so that general equations can be developed for a given species to be applied to a wide range of species compositions and stand structures. This new approach will greatly improve predictions of biomass and carbon stocks in structurally and compositionally diverse forests.

Heterogeneous microcommunities and ecosystem multifunctionality in seminatural grasslands under three management modes.

Increasing attention has been paid to the relationship between biodiversity and ecosystem functioning (BEF) because of the rapid increase in species loss. However, over the past 20 years, most BEF studies only focused on the effect of species diversity on one or a few ecosystem functions, and only a few studies focused on ecosystem multifunctionality (i.e., the simultaneous provision of several ecosystem functions). Grassland ecosystems have important economic, environmental, and esthetic value; thus, this study focused on the heterogeneous microcommunities in grasslands under three management modes. The multifunctionality index (M‐index) was assessed at community and microcommunity scales, and the relationship between species diversity and multifunctionality was investigated. The communities were found to be respectively composed of one, three, and six microcommunities in grazing, clipping, and enclosure management, based on a two‐way indicator species analysis (TWINSPAN) and detrended correspondence analysis (DCA) for community structure. Biodiversity and soil indicators showed an apparent degradation of the grazing community, which had the worst M‐index. Clipping and enclosure communities showed no significant difference in biodiversity indices, soil variables, and M‐index; however, these indices were clearly different among microcommunities. Therefore, the microcommunity scale may be suitable to investigate the relationship between vegetation and multifunctionality in seminatural grassland ecosystems. Dominant species richness had more explanatory power for ecosystem multifunctionality than subdominant species richness, rare species richness, and the number of all species. Therefore, it is important to distinguish the role and rank of different species in the species richness–multifunctionality model; otherwise, the model might include redundant and unclear information. Communities with more codominant species whose distribution is also even might have better multifunctionality.

Rehabilitation of Sodic Waste Land through Agro-Forestry System

Sodic soils are widely distributed in arid and semi arid regions of the world and suffer from high values of pH, exchangeable sodium percentage (ESP), sodium absorption ratio (SAR) and low fertility. In north India, Uttar Pradesh, which is a major contributor to the national food grain stock, due to its large arable land, is occupying about 1.6 Mha of this type of sodic waste land. To alleviate the pressure of fulfilling the demand of wood, timber, fodder and food for the enormous population of human and cattle, the vast sodic soil area has to be rehabilitated by planting trees or adopting agro-forestry system. In this context, an attempt has been made to rehabilitate sodic waste land through the establishment of green cover, with diverse plant communities at Distant Research Centre of CSIR-National Botanical Research Institute, Lucknow during last few decades. A rehabilitated forest ecosystem was developed consisting of a number of herbs, shrubs and trees. Derris indica, Dalbergia sisso, Azadirachta indica, Cassia siamea, Terminalia arjuna, Syzigium cumini were the dominant species in this rehabilitated forest, resulting in significant amelioration process, influenced greatly by diversity of species and their productivity. A combined effect of both biomass productivity and species diversity contributed about 92% towards amelioration. There was reduction in soil pH and ESP and an increase in organic C and N contents showing that sodicity has receded in the forest soil. To meet the increasing demand of medicinal, aromatic, dye, gum, fibre, fodder yielding plants in the present scenario, the shade loving plants of these categories can be grown successfully in between the rows of economic trees like teak, poplar, Eucalyptus etc. Such agro-forestry models have been tried with various inter-crops like Curcuma longa, Rauvolfia serpentina, Zingiber officinale, Desmodium gangeticum and Asparagus racemosus etc. The findings of such studies are very useful for fulfilling the demand of economic plants by utilizing the waste land and free spaces of trees cultivated in such lands.

Individual tree size inequality enhances aboveground biomass in homegarden agroforestry systems in the dry zone of Sri Lanka

Individual tree size variation, which is generally quantified by variances in tree diameter at breast height (DBH) and height in isolation or conjunction, plays a central role in ecosystem functioning in both controlled and natural environments, including forests. However, none of the studies have been conducted in homegarden agroforestry systems. In this study, aboveground biomass, stand quality, cation exchange capacity (CEC), DBH variation, and species diversity were determined across 45 homegardens in the dry zone of Sri Lanka. We employed structural equation modeling (SEM) to test for the direct and indirect effects of stand quality and CEC, via tree size inequality and species diversity, on aboveground biomass. The SEM accounted for 26, 8, and 1% of the variation in aboveground biomass, species diversity and DBH variation, respectively. DBH variation had the strongest positive direct effect on aboveground biomass (β=0.49), followed by the non-significant direct effect of species diversity (β=0.17), stand quality (β=0.17) and CEC (β=−0.05). There were non-significant direct effects of CEC and stand quality on DBH variation and species diversity. Stand quality and CEC had also non-significant indirect effects, via DBH variation and species diversity, on aboveground biomass. Our study revealed that aboveground biomass substantially increased with individual tree size variation only, which supports the niche complementarity mechanism. However, aboveground biomass was not considerably increased with species diversity, stand quality and soil fertility, which might be attributable to the adaptation of certain productive species to the local site conditions. Stand structure shaped by few productive species or independent of species diversity is a main determinant for the variation in aboveground biomass in the studied homegardens. Maintaining stand structure through management practices could be an effective approach for enhancing aboveground biomass in these dry zone homegarden agroforestry systems.

Effects of species diversity on fine root productivity increase with stand development and associated mechanisms in a boreal forest

Summary There is a growing interest in understanding the relationship between diversity and below‐ground productivity due to the critical contribution of below‐ground systems to overall terrestrial productivity. Yet, the temporal (seasonal and developmental) changes in diversity effects on below‐ground productivity and their underlying mechanisms remain unclear. We hypothesized that (i) diversity effects on fine root productivity increase with stand development, and (ii) increased diversity effects associated with stand development result from augmented horizontal soil space utilization, increased forest floor depth for rooting, enhanced effects in nutrient‐poor soil layers and/or foraging towards high nutrient availability. We investigated the effects of tree species diversity on fine root productivity by sampling 18 stands dominated by single species and their mixtures in post‐fire boreal forests of two stand ages (8 and 34 years following stand‐replacing fire). Species evenness was significantly higher in species mixtures than in single‐species‐dominated stands at both age classes, while species richness did not differ across stand types and age classes. We found that the annual fine root production was higher in mixtures than the mean of single‐species‐dominated stands in both stand ages, with a significantly higher magnitude of effects in the 34‐year‐old than 8‐year‐old stands. Mixtures had higher horizontal soil volume filling than single‐species‐dominated stands with a more pronounced increase in the 34‐year‐old than 8‐year‐old stands. Compared with the 8‐year‐old stands, the 34‐year‐old stands had increased forest floor depth and greater overyielding with soil depth, and their fine root productivity was more responsive to the vertical variation in soil phosphorus concentrations among soil layers. Synthesis. Our results provide evidence for increasing positive diversity effects on fine root productivity with stand development in heterogeneous natural forests. Moreover, our results indicate that the increased positive diversity effects with stand development was the result of multiple mechanisms, including higher horizontal soil volume filling, a thicker forest floor layer for rooting, a higher magnitude of complementarity in nutrient‐poor deep soil layers and stronger nutrient foraging towards soil layers with high nutrient concentrations in older than younger stands.

Magnitude of Species Diversity Effect on Aboveground Plant Biomass Increases Through Successional Time of Abandoned Farmlands on the Eastern Tibetan Plateau of China

AbstractRecent empirical and theoretical studies have shown that magnitude and direction of biodiversity effects on ecosystem functioning can shifts over time. Here, we used species richness and plant abundance (total individual plant stem density) as proxies for species diversity and aboveground biomass for productivity. We used an analytical approach combining both chronosequence and 6 year of vegetation monitoring in a subalpine ecosystem as a model system to assess temporal species richness–abundance–aboveground biomass relationships at different successional stages and spatial scales. We observed that both species richness and plant aboveground biomass increased rapidly early in succession after land abandonment, then after 10 years of abandonment reached a steady state. We found that the relationship between species richness and plant abundance with aboveground biomass was strengthening over successional time. In all successional stages, species richness had stronger positive effects as compared with plant abundance on plant aboveground biomass. Species richness was linearly correlated with aboveground biomass, whereas plant abundance showed a humped‐back relationship with aboveground biomass across all successional stages. Our results showed an increase in the effect of plant diversity over time, and a combination of both plant species richness and abundance is correlated with plant productivity throughout successional time, knowledge that maybe important to managing ecological restoration and conservation. Copyright © 2016 John Wiley &amp; Sons, Ltd.