Plant Diversity In Agricultural Landscapes Research Articles

Enhancing plant diversity in agricultural landscapes promotes both rare bees and dominant crop‐pollinating bees through complementary increase in key floral resources

Summary Enhancing key floral resources is essential to effectively mitigate the loss of pollinator diversity and associated provisioning of pollination functions in agro‐ecosystems. However, effective floral provisioning measures may diverge among different pollinator conservation targets, such as the conservation of rare species or the promotion of economically important crop pollinators. We examined to what extent such diverging conservation goals could be reconciled. We analysed plant–bee visitation networks of 64 herbaceous semi‐natural habitats representing a gradient of plant species richness to identify key resource plants of the three distinct conservation target groups: rare bees (of conservation concern), dominant wild crop‐pollinating bees and managed crop‐pollinating bees (i.e. honeybees). Considering overall flower visitation, rare bees tended to visit nested subsets of plant species that were also visited by crop pollinators (46% and 77% nestedness in the dissimilarity between rare bees and wild crop pollinators or managed honeybees respectively). However, the set of preferred plant species, henceforth ‘key plant species’ (i.e. those species disproportionately more visited than expected according to their floral abundance) was considerably more distinct and less nested among bee target groups. Flower visits of all bee target groups increased with plant species richness at a similar rate. Importantly, our analyses revealed that an exponential increase in the flower abundance of the identified key plant species and complementarity in the bee visitation pattern across plant species ─ rather than total flower abundance ─ were the major drivers of these relationships. Synthesis and applications. We conclude that the multiple goals of preserving high bee diversity, conserving rare species and sustaining crop pollinators can be reconciled if key plant species of different target groups are simultaneously available. This availability is facilitated by a high floral resource complementarity in the plant community. The list of identified key resource plant species we provide here can help practitioners such as land managers and conservationists to better design and evaluate pollinator conservation and restoration measures according to their goals. Our findings highlight the importance of identifying and promoting such plant species for pollinator conservation in agricultural landscapes.

Plant diversity and determinant factors across smallholder agricultural management units in Central Ethiopia

Forests in the highlands of Ethiopia have declined considerably, and the supply of forest-based ecosystem services is eroding. Managing agricultural landscapes as well as enhancing plant biodiversity in agro-ecosystems is and will continue to be one possible strategy to preserve biodiversity, ensure an ecosystem service supply and sustain agricultural productivity. This study investigated the current status and prospects of plant diversity and its determinants in an agricultural landscape dominated by smallholder farmers in Southern Ethiopia. Specifically, the study investigated effects of land use, altitudinal gradient, wealth status and household attributes on plant diversity in agricultural landscapes. A complete count, Y-frame transect sampling method and household interviews were used for the study involving 39 households and 115 sample plots. A total of 166 plant species belonging to 134 genera and 56 families were recorded in all land use types. Of these, 101 were woody plant species (51 trees and 50 shrubs), while 65 were cultivated herbs and grasses. Land use, altitude and household wealth status significantly influenced tree and shrub species richness. Among land uses, home gardens hosted the highest number of tree and shrub species. Upper altitudes and rich households also had the highest tree and shrub species richness compared to others. Plant diversity indices (Shannon, Simpson and Margalef) were affected by altitude, wealth status and land use types. Household location, wealth status, the household attributes of landholding and family size had strong and positive influences on the tree species diversity and woody stem density of households, while educational background and off-farm income were negatively related with household-owned tree stem density. Species preference ranking, seedling demand and importance value index computations indicated the dominance of exotic tree species, which may suggest their economic importance over indigenous tree species. In the long term, this might lead to dominance of exotic tree species in the landscapes, which could cause a potential future threat to the remnant indigenous plant diversity that is currently finding refuge in the agricultural landscapes.

River Dikes in Agricultural Landscapes: The Importance of Secondary Habitats in Maintaining Landscape-Scale Diversity

Lowland rivers and their floodplains have changed markedly over the last centuries. River dikes have become among the most extensive secondary habitats of former floodplains. Our main question was, what role do secondary habitats on river dikes play in harbouring plant species and maintaining plant diversity of lowland landscapes dominated by agricultural areas? We compared historical maps and current habitat maps to understand the effects of landscape changes on the vegetation pattern of the study region, in southern Hungary. Dikes and primary vegetation of the landscape were selected for intensive vegetation sampling. We compared the floristic similarity and the Shannon diversity of the vegetation types. We used ordinations to visualize relationships among the vegetation types and among dike vegetation and environmental variables. Our results indicated that profound changes have been brought about in the vegetation during the last 150 years, resulting in a transition from marshland to agricultural land. The species composition and pattern of dike vegetation strongly depended on their relative position to the river and their aspect. We conclude that dikes can harbour many vascular plants that are absent or rare in the surrounding habitats and therefore play a decisive role in maintaining plant diversity in agricultural landscapes.

Use of topographic variability for assessing plant diversity in agricultural landscapes

The relationship between plant diversity and topographic variability in agricultural landscapes was investigated, with the aim of determining whether sampling landscape units of 1 km 2 (LUs) across a gradient of topographic variability is more efficient than a random design for assessing the range of biodiversity in climatically and biogeographically homogenous areas called sub-regions. Representative plant species data from the Swiss biodiversity monitoring programme were analyzed covering a broad environmental gradient of four altitudinal belts and seven biogeographic regions. The focus of the study laid on agricultural areas but the whole dataset was as well analyzed to put the agricultural LUs in a general context. Plant species lists of LUs were used to calculate two diversity components: ECOrichness, the number of ecological plant types per LU (as a measure of beta diversity) and AGROrichness, the number of species of conservation importance for agriculture. Mixed regression models were used to analyse the effects of topographic variability on the two plant diversity components, including sub-regions (areas with the same combination of altitudinal belt and biogeographic region) as random factor. These analyses were performed for the whole dataset (419 LUs within 22 sub-regions) and for the focal subset of 187 agricultural LUs within 13 sub-regions. ECOrichness increased significantly with topographic variability for both the general and the agricultural dataset. The partial correlations within the sub-regions revealed consistent trends for the agricultural LUs but some inconsistencies for the whole dataset. For the monitoring of agricultural LUs the sampling along a gradient of topographic variability is therefore suggested as an efficient means for assessing the range of plant species diversity within sub-regions. Compared to other measures of landscape heterogeneity like habitat heterogeneity, sampling LUs along topographic variability is cheap and easily applied and it was demonstrated to work over large environmental gradients.

Species richness of hedgerow habitats in changing agricultural landscapes: are α and γ diversity shaped by the same factors?

Understanding the determinants of hedgerow plant diversity in agricultural landscapes remains a difficult task, because the potential drivers affect the complete range of biodiversity components (alpha to gamma diversity). We surveyed herbaceous plant communities (of a height <1.5 m) in 84 hedgerows in the Seine river floodplain of France. Two types of potential drivers for species richness, accounting for landscape mosaic and hedgerow network, were recorded at both hedgerow and site scale. The distribution of species richness through the components of alpha hedgerow diversity (i.e. the average diversity within a habitat) and gamma hedgerow diversity (i.e. the total diversity across habitats) were assessed using additive partitioning methods, while the relationship between species diversity and its potential landscape drivers at both scales was modeled using Generalized Additive Models. Our results indicated that gamma hedgerow diversity is explained by the heterogeneity of the landscape structure, which is correlated with the mosaic of agricultural land use. At this scale, intrinsic properties of the configuration of the hedgerow networks have a weak influence on species richness. Alpha hedgerow diversity is also explained by landscape variables, accounting for both the configuration of agricultural mosaics and hedgerow networks, but to a lesser extent. Time lags for species responses are shown at both scales, and for the two types of drivers. Extinction or colonization debt may be indicated at both scales, while the remnant effects of former practices may also be responsible for such patterns at a local scale. We suggest that hedgerow management should take the specific parameters of both scales into account. At a local scale, management actions should aim to decrease the influence of adjacent land use when the impact is negative, through the implementation of extended buffer zones, while at the landscape and farm scales, agri-environmental schemes should be dedicated to the conservation of specific agricultural land uses.

Traditional farming and plant species diversity in agricultural landscapes of south-western Uganda

An effort was undertaken in Bushwere Parish (Mbarara district, south-western Uganda) between 1999 and 2000 to develop sustainable and participatory approaches to plant biodiversity conservation at the farm level. One hundred farmers were interviewed on their socio-economic profiles and plant use strategies. Plant diversity was assessed in 400 plots of 5 m×5 m established in 53 field types of seven land-use categories. The most species-rich land-use category was under annual crops (149 plant species) while the most species-rich field type was planted with bananas (118 species). Shannon diversity and Sørensen’s similarity indices were used to compute species diversity and similarity, respectively, between field types and land-uses. The most plant diverse land-use was natural woodland, the least fallow. Canonical correspondence analysis (CCA) showed that occurrence of species, field type or land-use depended upon environmental factors such as elevation, position on the slope and soil type. Redundancy analysis (RDA) showed that species utility and occurrence were related to the socio-economic status of farmers. Plant species were most diverse in land-uses located on hill tops and steep slopes. Farmers should therefore be advised on how to maintain plant diversity in agricultural landscapes.