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Exotic plant invasions threaten biodiversity and are costly to farmers. Land use is a major pathway promoting the spread of exotic plant species; however, little is known about the processes underlying the success of exotic plants in tropical agricultural landscapes. Focussing on the heterogeneous smallholder landscapes of north‐eastern Madagascar, we studied exotic plants of understorey communities across a land‐use intensity gradient from unburned lands (old‐growth forests, forest fragments and forest‐derived vanilla agroforests) to burned ones (fallow‐derived vanilla agroforests, woody fallows and herbaceous fallows).We quantified the absolute species richness, abundance and cover of exotic plants across land‐use types and their proportional contribution to community richness, abundance and cover as indicators of exotic plant invasion. We tested for the effects of land‐use parameters, namely land‐use history, canopy closure and landscape‐level forest cover, on exotic plants. Additionally, we tested whether the phylogenetic relatedness between exotic and native species in the same plot affected invasion success, testing Darwin's naturalisation and pre‐adaptation hypotheses.All indicators of exotic plant invasion were lowest in old‐growth forests and forest fragments and highest in fallow‐derived vanilla agroforests, woody fallows and herbaceous fallows. Absolute and proportional exotic richness were negatively affected by canopy closure, and landscapes with high forest cover had lower proportions of exotic plant richness. High phylogenetic relatedness between exotics and natives was associated with lower proportional richness but higher proportions of exotics in abundance and cover. However, individual exotic species showed contrasting responses to land‐use parameters and relatedness to natives.Synthesis and applications: Our results indicate that maintaining unburned lands, land‐use types with dense canopies and landscapes with high forest cover prevents the spread of exotic plants within the agricultural landscapes of north‐eastern Madagascar. Supporting Darwin's pre‐adaptation hypothesis, exotic plants that are phylogenetically closely related to native plants are more likely to become successful invaders in terms of abundance and cover. Nevertheless, individual species show different responses to land‐use changes and phylogenetic relatedness. Therefore, land‐use decisions and management choices can be tailored to limit the spread of exotic species and to preserve native plants in this global biodiversity hotspot. [ABSTRACT FROM AUTHOR]

Tropical agricultural landscapes often consist of a mosaic of different land uses, yet little is known about the spectrum of ecosystem service bundles and materials they provide to rural households. We interviewed 320 households on the different benefits received from prevalent land-use types in north-eastern Madagascar (old-growth forests, forest fragments, vanilla agroforests, woody fallows, herbaceous fallows, and rice paddies) in terms of ecosystem services and plant uses. Old-growth forests and forest fragments were reported as important for regulating services (e.g. water regulation), whilst fallow lands and vanilla agroforests as important for provisioning services (food, medicine, fodder). Households reported the usage of 285 plant species (56% non-endemics) and collected plants from woody fallows for varying purposes, whilst plants from forest fragments, predominantly endemics, were used for construction and weaving. Multiple land-use types are thus complementary for providing ecosystem services, with fallow lands being particularly important. Hence, balancing societal needs and conservation goals should be based on diversified and comprehensive land management. [ABSTRACT FROM AUTHOR]

The conversion of tropical forests into agriculture reduces biodiversity dramatically. However, species might differ in their responses, depending on their habitat specialisation and geographic origin. In this study, we assess how butterfly assemblages differ between old‐growth forests, forest fragments, forest‐derived vanilla agroforests, fallow‐derived vanilla agroforests, woody fallows, herbaceous fallows, and rice paddies in Madagascar.We recorded 88 butterfly species, of which 65 species are endemic to Madagascar. Land‐use types with woody vegetation sustained many endemic (mean: 6.8 species) and forest butterfly species (mean: 4.8 species). Rice paddies and herbaceous fallows were richer in open‐land species (mean: 7.6 species) and poorer in forest species (mean: 1.7 species) compared to other land‐use types. Compared to herbaceous fallows, fallow‐derived vanilla agroforests hosted more endemic (+164%) and forest (+239%) species. Richness of open‐land species in forest‐derived vanilla agroforests was six times higher than in forest fragments.Overall, 27% of species occurred exclusively in one land‐use type and 19% of all species when old‐growth forests were excluded. We found the highest number of exclusive species in forest‐derived vanilla agroforests.We conclude that all studied land‐use types contribute to butterfly conservation in our study region. Especially the woody vegetation in forest fragments, vanilla agroforests, and woody fallows supports a high butterfly diversity and is pivotal for maintaining a broad diversity of forest butterflies in the agricultural matrix. Our study highlights the importance of preserving the diversity of small‐scale land‐use types, including agroforestry, forests and fallow land in this tropical biodiversity hotspot. [ABSTRACT FROM AUTHOR]

Sustainable land-system transformations are necessary to avert biodiversity and climate collapse. However, it remains unclear where entry points for transformations exist in complex land systems. Here, we conceptualize land systems along land-use trajectories, which allows us to identify and evaluate leverage points, i.e., entry points on the trajectory where targeted interventions have particular leverage to influence land-use decisions. We apply this framework in the biodiversity hotspot Madagascar. In the northeast, smallholder agriculture results in a land-use trajectory originating in old-growth forests and spanning from forest fragments to shifting hill rice cultivation and vanilla agroforests. Integrating interdisciplinary empirical data on seven taxa, five ecosystem services, and three measures of agricultural productivity, we assess trade-offs and cobenefits of land-use decisions at three leverage points along the trajectory. These trade-offs and cobenefits differ between leverage points: Two leverage points are situated at the conversion of old-growth forests and forest fragments to shifting cultivation and agroforestry, resulting in considerable trade-offs, especially between endemic biodiversity and agricultural productivity. Here, interventions enabling smallholders to conserve forests are necessary. This is urgent since ongoing forest loss threatens to eliminate these leverage points due to path dependency. The third leverage point allows for the restoration of land under shifting cultivation through vanilla agroforests and offers cobenefits between restoration goals and agricultural productivity. The co-occurring leverage points highlight that conservation and restoration are simultaneously necessary to avert collapse of multifunctional mosaic landscapes. Methodologically, the framework highlights the importance of considering path dependency along trajectories to achieve sustainable land-system transformations. [ABSTRACT FROM AUTHOR]

Understanding how land-use change affects biodiversity is a fundamental step to develop effective conservation strategies in human-modified tropical landscapes. Here, we analyzed how land-use change through tropical small-scale agriculture affects endemic, exotic, and non-endemic native ant communities, focusing on vanilla landscapes in north-eastern Madagascar, a global biodiversity hotspot. First, we compared ant species richness and species composition across seven land-use types: old-growth forest, forest fragment, forest-derived vanilla agroforest, fallow-derived vanilla agroforest, woody fallow, herbaceous fallow, and rice paddy. Second, we assessed how environmental factors drive ant species richness in the agricultural matrix to identify management options that promote endemic and non-endemic native while controlling exotic ant species. We found that old-growth forest, forest fragment, and forest-derived vanilla agroforest supported the highest endemic ant species richness. Exotic ant species richness, by contrast, was lowest in old-growth forest but highest in herbaceous fallows, woody fallows, and rice paddy. Rice paddy had the lowest non-endemic native ant species richness. Ant species composition differed among land-use types, highlighting the uniqueness of old-growth forest in harboring endemic ant species which are more sensitive to disturbance. In the agricultural matrix, higher canopy closure and landscape forest cover were associated with an increase of endemic ant species richness but a decrease of exotic ant species richness. We conclude that preserving remnant forest fragments and promoting vanilla agroforests with a greater canopy closure in the agricultural matrix are important management strategies to complement the role of old-growth forests for endemic ant conservation in north-eastern Madagascar. [ABSTRACT FROM AUTHOR]

Agroforestry can contribute to an increase in tree cover in historically forested tropical landscapes with associated gains in biodiversity and ecosystem functioning, but only if established on open land instead of underneath a forest canopy. However, declines in yields with increasing shade are common across agroforestry crops, driving shade-tree removal in forest-derived agroforests and hindering tree regrowth in open-land-derived agroforests. To understand trajectories of change in tree cover in forest- and open-land-derived agroforests, and the impacts of tree cover on vanilla yields, we studied 209 vanilla agroforests along an 88-year chronosequence in Madagascar. Additionally, we used remotely sensed canopy cover data to investigate tree cover change in the agricultural landscape. We found yields to vary widely but independently of canopy cover and land-use history (forest- vs. open-land-derived), averaging at 154.6 kg ha−1 year−1 (SD = 186.9). Furthermore, we found that forest- and open-land-derived vanilla agroforests gained canopy cover over time, but that only open-land-derived agroforests gained canopy height. Canopy cover increased also at the landscape scale: areas in the agricultural landscape with medium initial canopy cover gained 6.4% canopy cover over 10 years, but canopy cover decreased in areas with high initial canopy cover. These opposing trends suggest tree cover rehabilitation across areas covered by vanilla agroforests, whereas remnant forest fragments in the agricultural landscape were transformed or degraded. Our results indicate that yield-neutral tree rehabilitation through open-land-derived agroforestry could, if coupled with effective forest protection, provide benefits for both ecosystem functions and agricultural production in a smallholder-dominated agricultural landscape. [ABSTRACT FROM AUTHOR]

Aim: North‐eastern Madagascar is a hotspot of plant diversity, but vanilla and rice farming are driving land‐use change, including slash‐and‐burn management. It still remains unknown how land‐use change and land‐use history affect richness and composition of endemic, native and exotic herbaceous plant species. Location: North‐eastern Madagascar. Methods: We assessed herbaceous plants along a land‐use intensification gradient ranging from unburned land‐use types (i.e. old‐growth forest, forest fragment and forest‐derived vanilla agroforest) to burned land‐use types (i.e. fallow‐derived vanilla agroforest, woody fallow and herbaceous fallow) and rice paddy. We compared land‐use types and analysed the effects of land‐use history, canopy closure and landscape forest cover on species richness. Additionally, we analysed species compositional changes across land‐use types. Results: Across 80 plots, we found 355 plant species (180 native non‐endemics, 57 exotics, 60 endemics and 58 species of unknown origin). Native and exotic species richness increased with increasing land‐use intensity, whereas endemics decreased. Unburned land‐use types had higher endemic species richness (4.28 ± 0.37 [mean ± SE]) than burned ones (2.4 ± 0.21). Exotic and native species richness, but not endemics, decreased with increasing canopy closure. Increasing landscape forest cover reduced exotic, but not native or endemic richness. Species composition of old‐growth forests was unique compared to all other land uses and forest‐derived, not fallow‐derived vanilla agroforests, had a similar endemic species composition to forest fragments. Main conclusions: Our results indicate that old‐growth forests and forest fragments are indispensable for maintaining endemic herbaceous plants. We further show that the land‐use history of agroforests should be considered in conservation policy. In forest‐derived vanilla agroforests, management incentives are needed to halt loss of canopy closure, thereby maintaining or even enhancing endemics. In conclusion, considering species origin (endemic, native and exotic) and composition is essential for the identification of suitable management practices to avoid irreversible species loss. [ABSTRACT FROM AUTHOR]

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