Sustainable provision of critical ecosystem services in drylands is reliant on their stability under anthropogenic disturbances. Livestock grazing and shrub encroachment are the primary drivers of ...disturbance that impact their biodiversity and production dynamics. However, the effects of grazing on the stability at multiple scales, particularly following the transition from grass‐dominated to shrub‐encroached drylands, is still largely unexplored.
Here, we conducted comparable sheep‐grazing experiments in two types of drylands (grass‐dominated vs. shrub‐encroached grasslands) on the Mongolia Plateau to explore the effects of grazing and shrub encroachment on biodiversity and stability at multiple scales. We examined how grazing affected the temporal stability of aboveground biomass in herbaceous communities in both grass‐dominated and shrub‐encroached grasslands, through two potential mechanisms: insurance effects and changes in the population‐level stability of individual species.
We found that an increase in sheep grazing intensity had significant and negative effects on insurance effects by decreasing both species asynchrony and spatial asynchrony but it had no effects on population stability, consequently leading to reductions in herbaceous community stability of the grasslands. However, grazing‐increased insurance effects cancelled out grazing‐decreased population stability, contributing to no changes in the community stability of shrub‐encroached grasslands. Likely, because grazing‐induced reductions in the relative abundance of the dominant species were more noticeable in shrub‐encroached grasslands than that of in grasslands. Moreover, the grazing‐decreased abundance of dominant species was directly correlated to increases in insurance effects in shrub‐encroached grasslands but not in grasslands, despite the positive relationships between population stability and the relative abundance of the dominant species in both grass‐dominated and shrub‐encroached drylands.
Synthesis and applications. Our results indicate that grazing can decrease the stability of herbaceous production in drylands but this negative effect is attenuated with the transition from grasslands to shrub‐encroached grasslands, suggesting that grazing effects on herbaceous community stability can be altered by shrub encroachment in drylands. Furthermore, the stability of dominant grasses plays a crucial role in stabilizing herbaceous communities and should be considered in promoting sustainable ecosystem functioning and services in drylands.
Our results indicate that grazing can decrease the stability of herbaceous production in drylands but this negative effect is attenuated with the transition from grasslands to shrub‐encroached grasslands, suggesting that grazing effects on herbaceous community stability can be altered by shrub encroachment in drylands. Furthermore, the stability of dominant grasses plays a crucial role in stabilizing herbaceous communities and should be considered in promoting sustainable ecosystem functioning and services in drylands.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
The widespread extirpation of megafauna may have destabilized ecosystems and altered biodiversity globally. Most megafauna extinctions occurred before the modern record, leaving it unclear how their ...loss impacts current biodiversity. We report the long-term effects of reintroducing plains bison (
) in a tallgrass prairie versus two land uses that commonly occur in many North American grasslands: 1) no grazing and 2) intensive growing-season grazing by domesticated cattle (
). Compared to ungrazed areas, reintroducing bison increased native plant species richness by 103% at local scales (10 m
) and 86% at the catchment scale. Gains in richness continued for 29 y and were resilient to the most extreme drought in four decades. These gains are now among the largest recorded increases in species richness due to grazing in grasslands globally. Grazing by domestic cattle also increased native plant species richness, but by less than half as much as bison. This study indicates that some ecosystems maintain a latent potential for increased native plant species richness following the reintroduction of native herbivores, which was unmatched by domesticated grazers. Native-grazer gains in richness were resilient to an extreme drought, a pressure likely to become more common under future global environmental change.
Climatic extremes, such as severe drought, are expected to increase in frequency and magnitude with climate change. Thus, identifying mechanisms of resilience is critical to predicting the ...vulnerability of ecosystems. An exceptional drought (<first percentile) impacted much of southern Africa during the 2015 and 2016 growing seasons, including the site of a long-term fire experiment in Kruger National Park, South Africa. Prior to the drought, experimental fire frequencies (annual, triennial, and unburned) created savanna grassland plant communities that differed in composition and function, providing a unique opportunity to assess ecosystem resilience mechanisms under different fire regimes. Surprisingly, aboveground net primary productivity (ANPP) recovered fully in all fire frequencies the year after this exceptional drought. In burned sites, resilience was due mostly to annual forb ANPP compensating for reduced grass ANPP. In unburned sites, resilience of total and grass ANPP was due to subdominant annual and perennial grass species facilitating recovery in ANPP after mortality of other common grasses. This was possible because of high evenness among grass species in unburned sites predrought. These findings highlight the importance of both functional diversity and within-functional group evenness as mechanisms of ecosystem resilience to extreme drought.
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Nutrient additions typically increase terrestrial ecosystem productivity, reduce plant diversity and alter plant community composition; however, the effects of P additions and interactions between N ...and P are understudied. We added both N (10 g m⁻²) and three levels of P (2.5, 5 and 10 g m⁻²) to a native, ungrazed tallgrass prairie burned biennially in northeastern Kansas, USA, to determine the independent and interactive effects of N and P on plant community composition and above‐ground net primary productivity (ANPP). After a decade of nutrient additions, we found few effects of P alone on plant community composition, N alone had stronger effects, and N and P additions combined resulted in much larger effects than either alone. The changes in the plant community were driven by decreased abundance of C₄ grasses, perhaps in response to altered interactions with mycorrhizal fungi, concurrent with increased abundance of non‐N‐fixing perennial and annual forbs. Surprisingly, this large shift in plant community composition had little effect on plant community richness, evenness and diversity. The shift in plant composition with N and P combined had large but variable effects on ANPP over time. Initially, N and N and P combined increased above‐ground productivity of C₄ grasses, but after 4 years, productivity returned to ambient levels as grasses declined in abundance and the community shifted to dominance by non‐N‐fixing and annual forbs. Once these forbs increased in abundance and became dominant, ANPP was more variable, with pulses in forb production only in years when the site was burned. Synthesis. We found that a decade of N and P additions interacted to drive changes in plant community composition, which had large effects on ecosystem productivity but minimal effects on plant community diversity. The large shift in species composition increased variability in ANPP over time as a consequence of the effects of burning. Thus, increased inputs of N and P to terrestrial ecosystems have the potential to alter stability of ecosystem function over time, particularly within the context of natural disturbance regimes.
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Elephant populations are in peril everywhere, but forest elephants in Central Africa have sustained alarming losses in the last decade 1. Large, remote protected areas are thought to best safeguard ...forest elephants by supporting large populations buffered from habitat fragmentation, edge effects and human pressures. One such area, the Minkébé National Park (MNP), Gabon, was created chiefly for its reputation of harboring a large elephant population. MNP held the highest densities of elephants in Central Africa at the turn of the century, and was considered a critical sanctuary for forest elephants because of its relatively large size and isolation. We assessed population change in the park and its surroundings between 2004 and 2014. Using two independent modeling approaches, we estimated a 78–81% decline in elephant numbers over ten years — a loss of more than 25,000 elephants. While poaching occurs from within Gabon, cross-border poaching largely drove the precipitous drop in elephant numbers. With nearly 50% of forest elephants in Central Africa thought to reside in Gabon 1, their loss from the park is a considerable setback for the preservation of the species.
Poulsen et al. estimate the loss of elephants from poaching in an African national park to represent over 70% of the population, more than 25’000 individuals, in one decade.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Poaching is rapidly extirpating African forest elephants (Loxodonta cyclotis) from most of their historical range, leaving vast areas of elephant-free tropical forest Elephants are ecological ...engineers that create and maintain forest habitat; thus, their loss will have large consequences for the composition and structure of Afrotropical forests. Through a comprehensive literature review, we evaluated the roles of forest elephants in seed dispersal, nutrient recycling, and herbivory and physical damage to predict the cascading ecological effects of theirpopulation declines. Loss of seed dispersal by elephants will favor tree species disperse abiotically and by smaller dispersal agents, and tree species composition will depend on the downstream effects of changes in elephant nutrient cycling and browsing. Loss of trampling and herbivory of seedlings and saplings will result in high tree density with release from browsing pressures. Diminished seed dispersal by elephants and high stem density are likely to reduce the recruitment of large trees and thus increase homogeneity of forest structure and decrease carbon stocks. The loss of ecological services by forest elephants likely means Central African forests will be more like Neotropical forests, from which megafauna were extirpated thousands of years ago. Without intervention, as much as 96% of Central African forests will have modified species composition and structure as elephants are compressed into remaining protected areas. Stopping elephant poaching is an urgent first step to mitigating these effects, but long-term conservation will require land-use planning that incorporates elephant habitat into forested landscapes that are being rapidly transformed by industrial agriculture and logging. La caza furtiva está extirpando rápidamente a los elefantes africanos del bosque (Loxodonta cyclotis) de la mayor parte de su extensión histórica, lo que deja áreas extensas de bosque tropical libres de elefantes. Los elefantes son ingenieros ecológicos que crean y mantienen el habitat del bosque; por esto, su pérdida tendrá consecuencias para la composición y la estructura de los bosques afrotropicales. Por medio de una revisión exhaustiva de la literatura, evaluamos el papel de los elefantes del bosque en la dispersión de semillas, reciclaje de nutrientes, herbivoría, y daño físico para predecir los efectos ecológicos en cascada de la declinación de sus poblaciones. La falta de la dispersión de semillas realizada por elefantes favorecerá a las especies de árboles dispersadas abióticamente y por agentes dispersores más pequeños, y la composición de las especies de árboles dependerá de los efectos derivados de los cambios en el pastoreo y circulación de nutrientes de los elefantes. La ausencia de pisoteo y de la herbivoría de brotes y retoños resultará en una alta densidad de árboles conforme estas especies sean liberadas de la presión del pastoreo. La disminución en la dispersión de semillas por los elefantes y la alta densidad de tallos probablemente reduzcan el reclutamiento de árboles grandes, lo que incrementará la homogeneidad de la estructura del bosque y disminuirá las reservas de carbono. La pérdida de servicios ecológicos generados por elefantes probablemente implique que los bosques del centro de África sean más como los bosques neotropicales, en los que la megafauna fue extirpada hace miles de años. Sin una intervención, hasta el 96% de los bosques del centro de África tendrán una composición y estructura modificadas conforme los elefantes son restringidos dentro de las áreas protegidas. Detener la caza furtiva de elefantes es un primer paso urgente para mitigar estos efectos, pero la conservación a largo plazo requerirá una planeadón de uso de suelo que incorpore al habitat del elefante dentro de los paisajes boscosos que están siendo transformados rápidamente por la industria agrícola y maderera. 偷猎正在导致非洲森林象(Loxodonta cyclotis)从它们大部分的历史分布区消失，留下大片没有大象的热 带森林。大象是创造和维持森林生境的生态工程师，因此它们的消失会对非洲热带界森林的组成和结构产生很 大影响。通过全面的文献综述，我们评估了森林象在种子传播、营养循环、食草作用以及对森林的直接破坏中 的作用，以预测它们种群下降产生的生态级联效应。失去了大象对种子的传播,将有利于树种通过非生物途径和 更小型的传播者来传播种子，而树木种类的组成将取决于大象的营养循环和食草作用变化的下游效应。没有大 象来踩踏、取食幼苗和小树会导致树木密度増大，因为树木不再受到被取食的压力。大象对种子传播作用的下 降和树木密度的增高可能减少森林中大树的补充因此增加了森林结构的均质性，減少了碳储量。森林象带来的 生态服务功能衰退可能意味着中非森林将变得像几千年前巨型动物群灭绝了的新热带界森林。在没有干预的情 况下,随着大象的分布区收缩到剰余的保护区中,高达96%的中非森林的物种组成和结构会发生改变。要减缓 这些影响，刻不容缓的第一步是停止偷猎,但长期的保护还需要土地利用规划将大象的生境纳入到正在因农业产 业化和伐木而快速转化的森林景观中。
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Precipitation is a primary determinant of plant community structure in drylands. However, the empirical evidence and predictions are lacking for how plant functional diversity in desert and steppe ...communities respond to altered precipitation regimes.
We examined how precipitation changes along the natural and experimental gradients affect different components of functional diversity in desert‐shrub and steppe‐grass communities. We compared the associations of precipitation changes with community‐weighted means (CWMs) of six traits, functional divergence (FDvar) of each single‐trait and multi‐trait functional richness (FRic) and dispersion (FDis) for shrub and grass communities along the natural and experimental gradients. We also disentangle the roles of species turnover and intraspecific variations in affecting the responses of different functional diversity to precipitation changes.
We found that in general, the similar responses of functional traits or diversity to both the natural and experimental precipitation gradients were dependent on plant community type. Across both two gradients, precipitation was positively associated with CWM of plant height and negatively associated with the CWM of SLA and leaf thickness in grass community, while positively associated with FDvar of four traits and FDis in shrub communities. Both species turnover and intraspecific variations contributed to the responses of grass community traits to precipitation changes across both two gradients, and to FDvar of traits and FDis in shrub community along the natural gradient. In contrast, species turnover variations contributed to FDvar of traits and FDis in shrub community in experiment.
These results suggest that there is better concordance between the effects of naturally and experimentally increased precipitation on functional diversity of plant communities, but different mechanisms behind the relationship of functional diversity–precipitation between shrub and grass communities. Grass communities can adapt to precipitation changes by average trait differences, while shrub communities persist through FDvar of single‐trait and multi‐trait dispersion, thus highlighting the important differences in adaptive strategies between shrub and grass communities. Our findings demonstrate that short‐term responses of plant communities to manipulative precipitation changes can reflect long‐term shifts at spatial scales depending on the specific functional trait and diversity.
A free Plain Language Summary can be found within the Supporting Information of this article.
A free Plain Language Summary can be found within the Supporting Information of this article.
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Temporal stability of ecosystem functioning increases the predictability and reliability of ecosystem services, and understanding the drivers of stability across spatial scales is important for land ...management and policy decisions. We used species‐level abundance data from 62 plant communities across five continents to assess mechanisms of temporal stability across spatial scales. We assessed how asynchrony (i.e. different units responding dissimilarly through time) of species and local communities stabilised metacommunity ecosystem function. Asynchrony of species increased stability of local communities, and asynchrony among local communities enhanced metacommunity stability by a wide range of magnitudes (1–315%); this range was positively correlated with the size of the metacommunity. Additionally, asynchronous responses among local communities were linked with species’ populations fluctuating asynchronously across space, perhaps stemming from physical and/or competitive differences among local communities. Accordingly, we suggest spatial heterogeneity should be a major focus for maintaining the stability of ecosystem services at larger spatial scales.
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Ecosystems are faced with an onslaught of co-occurring global change drivers. While frequently studied independently, the effects of multiple global change drivers have the potential to be additive, ...antagonistic, or synergistic. Global warming, for example, may intensify the effects of more variable precipitation regimes with warmer temperatures increasing evapotranspiration and thereby amplifying the effect of already dry soils. Here, we present the long-term effects (11 years) of altered precipitation patterns (increased intra-annual variability in the growing season) and warming (1 °C year-round) on plant community composition and aboveground net primary productivity (ANPP), a key measure of ecosystem functioning in mesic tallgrass prairie. Based on past results, we expected that increased precipitation variability and warming would have additive effects on both community composition and ANPP. Increased precipitation variability altered plant community composition and increased richness, with no effect on ANPP. In contrast, warming decreased ANPP via reduction in grass stems and biomass but had no effect on the plant community. Contrary to expectations, across all measured variables, precipitation and warming treatments had no interactive effects. While treatment interactions did not occur, each treatment did individually impact a different component of the ecosystem (i.e., community
vs
. function). Thus, different aspects of the ecosystem may be sensitive to different global change drivers in mesic grassland ecosystems.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
1. Nitrogen (N) deposition and phosphorus (P) deposition due to pollution and land-use change are dramatically altering biogeochemical cycles. These altered nutrient inputs affect plant communities ...by generally increasing dominance and reducing diversity, as well as altering community variability (heterogeneity). Less well studied are the effects of changes in community variability on ecosystem functions, such as productivity, or the stability of those functions. 2. Here, we use a twelve-year nutrient addition experiment in tallgrass prairie to determine the variability in community responses to N and P additions and link these responses to ecosystem productivity and stability. We added two levels of N and four levels of P in a fully factorial design to 25-m2 plots in native tallgrass prairie in north-eastern Kansas, USA. Each year percentage cover of each species was measured in June and August in a 1-m2 subplot of each plot, and annual net primary productivity was measured in two 0.1-m2 subplots in each plot at the end of each growing season. 3. The addition of N and P together increased plant community variability across space (i.e. the replicates were significantly more different from each other in the N + P treatments than they were in the control treatment). We also found that the variability of the plant community within a single plot through time increased with the addition of N alone and N and P together. The highest level of both spatial and temporal variability occurred in plots with the highest level of nutrient addition (10 g m−2 of both N and P). 4. While we found no linkage between spatial variability of community composition and the spatial stability of productivity, the temporal stability of productivity decreased with increasing temporal plant community variability. Additionally, the ability to predict the productivity response to growing season precipitation, a key environmental variable, also decreased under higher temporal community variability. 5. Synthesis. Using a 12-year nutrient addition experiment, we found that nutrient addition leads to both spatial and temporal community variability in mesic tallgrass prairie. The changes in community variability through time were directly related to ecosystem stability. While overall shifts in community structure in response to nutrient additions are important, the change in variability of local communities has significant implications for our ability to predict how patterns of biodiversity and ecosystem function will respond to a rapidly changing world.
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