Early Dynamics of Plant Communities on Revegetated Motorway Slopes from Southern Spain: Is Hydroseeding Always Needed?

The increasing global rate of road construction is leading to a parallel increase of areas of degraded soil conditions and steep slopes that need revegetation. Hydroseeding with commercial seeds of fast‐growing grasses and legumes is a common practice in revegetation of motorway slopes. We carried out 3 years of monitoring of vegetation dynamics on hydroseeded and nonhydroseeded motorway slopes (48 slopes) in a maritime Mediterranean zone in Málaga (southern Spain). Our main objectives were to test whether hydroseeding significantly increases species richness and plant cover and whether hydroseeded species act as starters, facilitating the establishment of the vegetation and quickly disappearing once the communities are established. A hydroseeding success index (HSI, ranging from 0 to 1) was used to assess the relative abundance over time of the 14 species from the hydroseeding mixture. Species richness and cover was significantly higher on embankments (50–70 species per embankment, 80–90% cover) than on roadcuts (6–10 species per roadcut, 18–30% cover). Performance of hydroseeded species was poor from the very beginning (HSI, 0.2–0.3). On embankments, either presence or abundance of hydroseeded species did not significantly vary throughout the study. Both hydroseeded and nonhydroseeded communities exhibited a significant decrease in species richness, a significant increase in plant cover, and a highly dynamic species composition over time, with Sorensen index of 0.3–0.5 between years. There were no significant differences in plant cover, species richness, and aboveground biomass between hydroseeded and nonhydroseeded plots on embankments throughout the study. Our results demonstrate that there are situations in which the use of hydroseeding for revegetation is not needed. Further research should focus on understanding the establishment of autochthonous species and identifying environmental conditions under which the addition of commercial seeds may not be needed, or indeed situations where it may be harmful in suppressing autochthonous species.     

茂县土地岭植被恢复过程中物种多样性动态特征

植被恢复是退化生态系统重建的重要途径,植被恢复过程物种多样性的变化反映了植被的恢复程度.通过群落调查和多样性分析,研究了岷江上游土地岭植被恢复过程中群落物种多样性特征.结果表明： 恢复过程中6类不同类型群落分别表现其对于不同环境特征、干扰及更新方式等的响应;森林是较灌丛更适合当地环境状况的植被类型;人工恢复无干扰和轻度干扰群落的多样性相对较高,是较好的恢复模式.重度干扰使得1年生植物与地下芽植物比例增加,其它口食性较好的多年生草本减少.较强的干扰是群落无法更新、长期处于灌丛阶段且多样性较低的重要原因.本地区人工恢复群落在更新进程和多样性维持上优于自然更新群落,种植华山松加速了本地区植被演替进程.建议以适合恢复区域的多种恢复配置方式进行造林,并避免较强干扰,可以加速群落演替进程并保持恢复群落较高的物种丰富度与多样性.     

The influence of aspect on the early growth dynamics of hydroseeded species in coal reclamation areas

Question: Does aspect affect hydroseeding success and the development of vegetation during early vegetation establishment on the steep slopes of coal wastes during the reclamation process? Location: Open‐pit coal mine near Villanueva de la Peña, northern Spain. Methods: In the first year after hydroseeding, we monitored the dynamics of hydroseeded species in three permanent plots of 20 m² on north‐ and south‐facing slopes every two months. Soil properties and weather conditions were also monitored. Results: Aspect was related to total plant cover during early revegetation, and south‐facing slopes had the lowest cover. Aspect also influenced the early dynamics of hydroseeded grasses and legumes establishing on these slopes. Grass cover was greater on the north slope throughout the study, but differences in plant cover between north and south slopes appeared later for the legumes. Aspect also affected the relative contribution of both of grasses and legumes to the total plant cover, with grasses dominant on both northern and southern slopes, except during the summer on the southern slope. The species with the greatest difference in cover between the north‐ and south‐facing slopes were Festuca spp., Lolium perenne and Trifolium repens. Conclusion: In coal mine reclamation areas of Mediterranean climates, differences in the development of hydroseeded species depended on the slope of the coal mine reclamation areas, and this information is of importance to managers in selecting species for use in reclamation.     

Plant diversity,species turnover and shifts in functional traits in coastal dune vegetation: Results from permanent plots over a 52‐year period

Question: What is the relationship between plant diversity and species turnover in coastal dune vegetation plots? How is the long‐term change in species composition of vegetation plots related to shifts in functional traits, and what does it tell us about the dominant processes? Location: Coastal dunes, the Netherlands. Methods: Our data set comprised 52 years of vegetation data from 35 permanent plots in grassland/scrub/woodland vegetation. Vegetation dynamics were described in terms of changes in species composition and abundance, and shifts in 13 functional traits related to resources capture and forage quality, regeneration and dispersal. Results: Species turnover in the plots was high, because of local extinction and colonization. Species‐rich plots were more stable in terms of species abundance and composition compared with species‐poor plots. Over time, the plots converged with respect to their abiotic conditions, as reflected by Ellenberg indicator values – indicating that the prevailing process was succession. The high species turnover reflected high invasibility: accordingly, the relative importance of annuals increased. Most newcomer annuals, however, were competitive generalists of little conservation value. The functional trait analysis allowed us to unravel the complexity of effects of disturbances and succession, and yielded information on the processes driving the observed vegetation dynamics. Conclusions: In this study, small‐scale species turnover was negatively related to species diversity, indicating more stability in species‐rich communities. Regarding shifts in trait diversity, unifying filters appeared to be more dominant than diversifying filters. Counteracting this homogenization process poses a challenge for nature management.     

Disentangling the role of management,vegetation structure,and plant quality for Orthoptera in lowland meadows

Seminatural grasslands provide habitats for various species and are important for biodiversity conservation. The understanding of the diverse responses of species and traits to different grassland managenient methods is therefore urgently needed. We disentangled the role of grassland management (fertilization and irrigation), vegetation structure (biomass, sward height) and plant quality (protein and fiber content) for Orthoptera communities in lowland hay meadows in Germany. We found vegetation structure to be the most important environmental category in explaining community structure of Orthoptera (species richness, total individuals, fiinctional diversity and species composition). Intensively used meadows (fertilized, irrigated, high plant biomass) were characterized by assemblages with few species, low functional diversity, and low conservation value. Thereby, the relatively moderate fertilizer inputs in our study system of up to -75 kg N/ha/year reduced functional diversity of Orthoptera, while this negative effect of fertilization was not detectable when solely considering taxonomic aspects. We found strong support for a prominent role of plant quality in shaping Orthoptera communities and especially the trait composition. Our findings demonstrate the usefulness of considering both taxonomic and functional comp on ents (functio nal diversity) in biodiversity research and we suggest a stronger involvement of plant quality measures in Orthoptera studies.     

Dominant plant species modulate responses to hydroseeding,irrigation and fertilization during the restoration of semiarid motorway slopes

Restoring roadside slopes in semiarid regions of the Mediterranean Basin is often constrained by the difficulties arising when developing restoration projects (absence of nearby natural ecosystems serving as reference sites and slow natural colonization) and by the contradictions found between short-term (reduce soil erosion) and long-term (increase plant diversity) restoration goals. Restoration techniques developed in temperate climates are commonly applied in these regions without taking into account their specific characteristics; as a consequence, they often fail. We evaluated the effectiveness of three treatments widely used by practitioners (hydroseeding, fertilization and irrigation) to foster community composition changes that control soil erosion and increase species diversity (restoration goals) during the restoration of motorway embankments. The study was carried out during an 18-month period in five embankments from semiarid central Spain. The most outstanding result was that responses of the plant community to the treatments evaluated were site-specific. Several fast-growing dominant species, some hydroseeded and some already present in the study sites, were responsible for this idiosyncratic variation between sites. On embankments, where plant cover can easily reach values high enough to prevent erosion, the use of non-native herbs that can potentially dominate the community should be avoided. These fast-growing species, although effective as starters the first years following motorway building, can constrain vegetation dynamics in the long term. Our results indicate that these species should be controlled in the field, and their presence avoided in the commercial seed mixtures when the target is to enhance biodiversity and ecosystem stability and resilience.     

四川茂县土地岭大熊猫走廊带植被恢复格局及其与干扰的关系

通过样带调查和TWINSPAN、DCCA分析,从植物种、植物群落及其多样性与环境关系方面,研究了岷江上游土地岭大熊猫走廊带恢复植被的干扰状况。结果表明：应用TWINSPAN分类,并结合优势种组成、干扰状况分析及DCCA排序,可将植被划分为6个群落类型,同时划分出响应型、迟钝型、中度干扰忍耐型和重度干扰忍耐型4类干扰响应的植物类型。以样方物种和以样方多样性指数的DCCA分析结果基本一致,物种及群落的空间分布呈明显的聚集格局,反映其与环境因子间的密切关系。DCCA排序图上,海拔差、坡形、与公路距离、坡度及道路条数对群落和物种分布有明显的影响,与干扰相关性最大的坡度、样地道路数目、与公路间的距离3个因子反映了植被的干扰梯度。干扰对土地岭恢复植被影响显著,干扰降低了群落的物种多样性,同时阻碍了演替进程。     

Recovery of mammal diversity in tropical forests: a functional approach to measuring restoration

Ecological restoration is increasingly applied in tropical forests to mitigate biodiversity loss and recover ecosystem functions. In restoration ecology, functional richness, rather than species richness, often determines community assembly, and measures of functional diversity provide a mechanistic link between diversity and ecological functioning of restored habitat. Vertebrate animals are important for ecosystem functioning. Here, we examine the functional diversity of small‐to‐medium sized mammals to evaluate the diversity and functional recovery of tropical rainforest. We assess how mammal species diversity and composition and functional diversity and composition, vary along a restoration chronosequence from degraded pasture to “old‐growth” tropical rainforest in the Wet Tropics of Australia. Species richness, diversity, evenness, and abundance did not vary, but total mammal biomass and mean species body mass increased with restoration age. Species composition in restoration forests converged on the composition of old‐growth rainforest and diverged from pasture with increasing restoration age. Functional metrics provided a clearer pattern of recovery than traditional species metrics, with most functional metrics significantly increasing with restoration age when taxonomic‐based metrics did not. Functional evenness and dispersion increased significantly with restoration age, suggesting that niche complementarity enhances species' abundances in restored sites. The change in community composition represented a functional shift from invasive, herbivorous, terrestrial habitat generalists and open environment specialists in pasture and young restoration sites, to predominantly endemic, folivorous, arboreal, and fossorial forest species in older restoration sites. This shift has positive implications for conservation and demonstrates the potential of tropical forest restoration to recover rainforest‐like, diverse faunal communities.     

Vegetation succession in basalt quarries: Pattern on a landscape scale

Abstract. A spatio‐temporal variation of vegetation during spontaneous succession was studied in 56 basalt quarries spread over 1800 km² in the ?eské st?edoho?í Hills (NW Czech Republic, Central Europe). Differences in the particular habitats inside a quarry, i.e. steep rocky slopes, bottoms and levels; dumps; and screes were considered. The habitats ranged in age from 1 to 78 yr since abandonment. Macroclimate (mean annual temperature and precipitation) significantly influenced the course of succession, which led to a formation of shrubby grassland, shrubby woodland or tall woodland. Participation of target species typical of steppe‐like communities significantly depended on the occurrence of the communities in the vicinity, up to a distance of 30 m from a quarry. Disused quarries may become refugia for rare plant species. Spontaneous successional processes led in the reasonable time of ca. 20 yr to semi‐natural vegetation. Thus, they can be successfully exploited in restoration programs scheduled for the disused quarries.     

Evidence of neotropical anuran community disruption on rice crops: a multidimensional evaluation

Agricultural expansion is a major driver of biodiversity loss, especially in the megadiverse tropics. Rice is among the world’s most important food crops, invariably affecting biodiversity worldwide. Although the effects of habitat conversion to rice crops on biodiversity are not completely understood, landscape modification often creates conditions that benefit some species and excludes others. We conducted an integrative evaluation of the effects that habitat conversion to irrigated rice crops has on anuran communities from a Cerrado-Amazon ecotone. We adopted a multidimensional approach to compare anuran communities from agricultural and pristine environments considering (i) taxonomic metrics; (ii) functional and phylogenetic diversity; (iii) selected and excluded traits and (iv) body condition indices. When compared to their pristine counterparts, agricultural waterbodies showed increased functional divergence and decreased species diversity and functional richness. Furthermore, agricultural anuran communities exhibited lower phylogenetic diversity. Nonetheless, taxonomic diversity did not vary significantly, suggesting that it should not be used without complementary metrics. Species with small range, habitat specialization, small clutches and large body size were excluded from rice crops. Furthermore, frogs showed lower body condition in crops than in pristine areas. Understanding how species traits correlate with specific responses to agriculture will allow better predictions of the functional effects of anthropogenic land-use. Maintaining high diversity in anthropogenic environments is important for ecosystem resilience because diverse communities are more likely to hold multiple species capable of contributing to ecological functions. Our results show that converting natural vegetation to irrigated rice crops drives many species to local extinction, and resilient species to exhibit lower body condition.     

Mild cycles open closed communities to ecological restoration

Species loss is a global issue. With up to a million species at risk and insufficient protected area to maintain the world's biodiversity, humanity will increasingly need to rely on species re‐introductions to locally restore diversity and function. However, such restoration attempts are bound to fail when ecological communities get locked in a closed state that is resistant to recovery. It is presently unknown how to repair these closed systems. We use mathematical models to identify ways out of this problem. We first show how ecological communities may enter a closed state, to then explain how to open them up again for restoration of their original diversity. We find that restoration is often still possible shortly after initial species loss, as (1) the secondary extinctions that produce closure have not happened yet and (2) mild population fluctuations still allow successful repair during a transient postdisturbance phase. However, after this typically short window of opportunity for restoration, the system enters a new equilibrium, which may be a closed state. Our analysis shows how to take ecological communities out of the closed state: Appropriate management of carrying capacities produces a regime of mild population fluctuations that opens a window for successful species re‐introductions. These windows can be perpetually recurring or permanently open. Such opportunities for repair can be absent under regimes of wild cycles or perfect stability. We conclude that mild cycles may open windows of opportunity for the repair of communities that have become resistant to recovery.     

Fine‐scale habitat heterogeneity influences browsing damage by elephant and giraffe

Effects of large mammalian herbivores on woody vegetation tend to be heterogeneous in space and time, but the factors that drive such heterogeneity are poorly understood. We examined the influence of fine‐scale habitat heterogeneity on the distribution and browsing effects of two of the largest African terrestrial mammals, the elephant and giraffe. We conducted this study within a 120‐ha (500 x 2,400 m) ForestGEO long‐term vegetation monitoring plot located at Mpala Research Center, Kenya. The plot traverses three distinct topographic habitats (“plateau,” “steep slopes,” and “valley”) with contrasting elevation, slope, soil properties, and vegetation composition. To quantify browsing damage, we focused on Acacia mellifera, a palatable tree species that occurs across the three habitat categories. Overall tree density, species richness, and diversity were highest on the steep slopes and lowest on the plateau. Acacia mellifera trees were tallest and had the lowest number of stems per tree on the steep slopes. Both elephant and giraffe avoided the steep slopes, and their activity was higher during the wet season than during the dry season. Browsing damage on Acacia mellifera was lowest on the steep slopes. Elephant browsing damage was highest in the valley, whereas giraffe browsing damage was highest on the plateau. Our findings suggest that fine‐scale habitat heterogeneity is an important factor in predicting the distribution of large herbivores and their effects on vegetation and may interact with other drivers such as edaphic variations to influence local variation in vegetation structure and composition.     

Management and micro-scale landform determine the ground flora of secondary woodlands and their verges in the Tama Hills of Tokyo,Japan

We investigated the influence of management and micro-scale landform on the species composition and richness of ground flora in secondary woodlands and their verges next to paddy fields in the Tama Hills, Tokyo, Japan. Sites representing various micro-scale landforms and different management regimes were sampled. The results of Detrended Correspondence Analysis and Indicator Species Analysis showed that there was no significant difference between management regimes on species composition in head hollow sites. However, species composition was unique in other landform types having the same management regimes. Micro-scale landform units had less effect on species composition than management regime on crest slopes and side slopes of secondary woodlands. A large variation in species composition of verges, all on the lowermost side slopes, was found within sites, but the composition was different when compared with other sites. We recognized five habitat types associated with species composition that resulted from the combined effects of landform and management regimes. Among habitat types, the verges and the well-managed woodlands had high species richness. Management practices within woodlands have enhanced the species richness on crest slopes and side slopes. High beta diversity of ground flora could be due to the variation in micro-scale landform along soil moisture regimes. Intensive management involving clear-cutting on the lower side slopes (an ecotone of mesic and wet environments) accompanied by paddy cultivation on valley bottoms enhanced the diversity of herbaceous vegetation in the verges.     

Road Slope Revegetation in Semiarid Mediterranean Environments. Part I: Seed Dispersal and Spontaneous Colonization

The importance of neighboring vegetation as a seed reservoir for spontaneous colonization of adjacent road slopes was analyzed in a semiarid region of east Spain. Two independent methodological approaches were used to examine the relative contribution of seed from neighboring vegetation and the efficiency of different seed dispersal strategies in plant colonization. We first used a randomization test to compare floristic similarity between road slopes, neighboring flora, and local flora (the regional species pool found in the same climate and soil conditions as the road slopes). Second, we compared seed dispersal mechanisms of road slope vegetation with those of the surrounding area using frequency analysis. Species composition of road slopes was more similar to that of the flora of adjacent surrounding areas than expected by chance. Anemochorous (wind‐dispersed) plants were over‐represented in road slopes 8 years after road slopes were built. We concluded that seed dispersal from neighboring vegetation is an important factor in the vegetative colonization of road slopes. However, this initial species pool was also strongly shaped by the harsh environmental conditions of roadcuts and southern aspect. These results have important implications in road slope restoration because they suggest that naturally vegetated areas should be maintained adjacent to road slopes to enhance seed immigration from species adapted to local site conditions, which will accelerate the successional process. The application of this single reclamation strategy and mixed strategies that combine the use of natural colonization and soil amendment for road slope restoration in Mediterranean environmental conditions is discussed.     

Vegetation restoration patterns and their relationships with disturbance on the Giant Panda Corridor of Tudiling, Southwest China

Human activities such as deforestation, cultivation, and overgrazing have contributed to the destruction of forest ecosystems in the upper Minjiang River basin for a long time, which has led to the reduction in forest coverage and biodiversity. On the Giant Panda Corridor of Tudiling in this basin, the effects of the existing disturbance regimes on plant communities after the vegetation restoration in the 1980s were assessed, and the community composition, the species diversity and their relationships with environmental factors significantly associated with the disturbance were analyzed using the transect sampling method, the two-way indicator species analysis (TWINSPAN) and the detrended canonical correspondence analysis (DCCA). The results were as follows: communities could be classified into six types, and species were clustered into four functional groups (responsive to disturbance, retarded disturbance, resistant to intermediate disturbance, and resistant to heavy disturbance) based on both TWINSPAN and DCCA. DCCA with species composition of plots is similar to that with species diversity of plots. The communities were separated into distinct groups along the DCCA axis, and this pattern was significantly correlated with environmental factors. Elevation differences, shape, slope, distance to roads, and the number of paths in the plots had an evident influence on the distribution of the species and communities. Environmental factors including slope, distance to roads, and the number of paths revealed the gradient of disturbance among the communities along the DCCA axis. High disturbance intensity caused significantly lower species diversity and inhibited the regeneration of vegetation compared with the more diverse undisturbed communities. Artificial restoration was more effective than natural restoration in maintaining high species diversity. The process of succession was inhibited in natural restoration because of the failure of tree establishment, growth, and survival during regeneration.     

Vegetation restoration patterns and their relationships with disturbance on the Giant Panda Corridor of Tudiling, Southwest China

Human activities such as deforestation, cultivation, and overgrazing have contributed to the destruction of forest ecosystems in the upper Minjiang River basin for a long time, which has led to the reduction in forest coverage and biodiversity. On the Giant Panda Corridor of Tudiling in this basin, the effects of the existing disturbance regimes on plant communities after the vegetation restoration in the 1980s were assessed, and the community composition, the species diversity and their relationships with environmental factors significantly associated with the disturbance were analyzed using the transect sampling method, the two-way indicator species analysis (TWINSPAN) and the detrended canonical correspondence analysis (DCCA). The results were as follows: communities could be classified into six types, and species were clustered into four functional groups (responsive to disturbance, retarded disturbance, resistant to intermediate disturbance, and resistant to heavy disturbance) based on both TWINSPAN and DCCA. DCCA with species composition of plots is similar to that with species diversity of plots. The communities were separated into distinct groups along the DCCA axis, and this pattern was significantly correlated with environmental factors. Elevation differences, shape, slope, distance to roads, and the number of paths in the plots had an evident influence on the distribution of the species and communities. Environmental factors including slope, distance to roads, and the number of paths revealed the gradient of disturbance among the communities along the DCCA axis. High disturbance intensity caused significantly lower species diversity and inhibited the regeneration of vegetation compared with the more diverse undisturbed communities. Artificial restoration was more effective than natural restoration in maintaining high species diversity. The process of succession was inhibited in natural restoration because of the failure of tree establishment, growth, and survival during regeneration.     

科尔沁沙地植被恢复系列上群落演替与物种多样性的恢复动态

通过对科尔沁沙地植被恢复系列上不同阶段的群落取样,研究了植被恢复过程中群落物种组成、物种多样性的变化过程.在演替时间分别为1年、3年、5年、12年、20年和30年的群落中,物种丰富度分别为7、11、17、14、28和30种,而物种多样性指数分别为1.458 8、2.610 0、3.108 4、1.696 8、3.738 6、3.639 6.在生活型结构上,一年生植物的种类数量占绝对优势,但随着演替进展,多年生植物的种类数量增加且单种植物的优势度超过了一年生植物,表明多年生植物在群落功能维持中占据重要地位.随演替进展,来自不同科属的植物增加.藜科植物在演替过程中种类数量较为稳定,特别是在演替早期藜科植物占有很高的优势度.禾本科种类随演替进展不断增加,且在群落中的优势度逐渐上升.总体上,随演替进展群落种类组成与物种多样性增加,群落生态优势度下降,而均匀度增加,群落趋向稳定.     

种、种的多样性及退化生态系统功能的恢复和维持研究

物种多样性是生态系统的重要特征并维持系统的功能支行,生物种和不同种类构成的群落为人类提供诸如营养物质循环、生物生产力、营养功能等形式的重要生态服务,特种多样性与生态系统抵御逆境和干扰的能力紧密相关,多样性的提高会增加系统的稳定性,与单个种和种类的数量相比,功能群和功能多样性对生态系统功能的影响效应要大得多,且易于被用来测度稳定性和预测群落变化,本文提出并探讨了种对生态系统功能作用的几种形式,理解物种多样性与生态系统的功能关系能指导退化生态系统恢复和维持其功能的实践活动,尤其为恢复的初始阶段进行群落的“种类组装”提供生态理论基础。     

Response of wild bee diversity,abundance, and functional traits to vineyard inter‐row management intensity and landscape diversity across Europe

Agricultural intensification is a major driver of wild bee decline. Vineyards may be inhabited by plant and animal species, especially when the inter‐row space is vegetated with spontaneous vegetation or cover crops. Wild bees depend on floral resources and suitable nesting sites which may be found in vineyard inter‐rows or in viticultural landscapes. Inter‐row vegetation is managed by mulching, tillage, and/or herbicide application and results in habitat degradation when applied intensively. Here, we hypothesize that lower vegetation management intensities, higher floral resources, and landscape diversity affect wild bee diversity and abundance dependent on their functional traits. We sampled wild bees semi‐quantitatively in 63 vineyards representing different vegetation management intensities across Europe in 2016. A proxy for floral resource availability was based on visual flower cover estimations. Management intensity was assessed by vegetation cover (%) twice a year per vineyard. The Shannon Landscape Diversity Index was used as a proxy for landscape diversity within a 750 m radius around each vineyard center point. Wild bee communities were clustered by country. At the country level, between 20 and 64 wild bee species were identified. Increased floral resource availability and extensive vegetation management both affected wild bee diversity and abundance in vineyards strongly positively. Increased landscape diversity had a small positive effect on wild bee diversity but compensated for the negative effect of low floral resource availability by increasing eusocial bee abundance. We conclude that wild bee diversity and abundance in vineyards is efficiently promoted by increasing floral resources and reducing vegetation management frequency. High landscape diversity further compensates for low floral resources in vineyards and increases pollinating insect abundance in viticulture landscapes.     

Invaded grassland communities have altered stability‐maintenance mechanisms but equal stability compared to native communities

Theory predicts that stability should increase with diversity via several mechanisms. We tested predictions in a 5‐year experiment that compared low‐diversity exotic to high‐diversity native plant mixtures under two irrigation treatments. The study included both wet and dry years. Variation in biomass across years (CV) was 50% lower in mixtures than monocultures of both native and exotic species. Growth among species was more asynchronous and overyielding values were greater during and after a drought in native than exotic mixtures. Mean‐variance slopes indicated strong portfolio effects in both community types, but the intercept was higher for exotics than for natives, suggesting that exotics were inherently more variable than native species. However, this failed to result in higher CV's in exotic communities because species that heavily dominated plots tended to have lower than expected variance. Results indicate that diversity‐stability mechanisms are altered in invaded systems compared to native ones they replaced.