Effect of landscape structure on agrobiodiversity in western Iran (Gilan-E Gharb)

The widespread transition into intensive agroecosystems has led to a considerable decline in plant biodiversity especially for organisms in the field boundaries. The aim of this study was to survey the vegetation of fields and field boundary types located in an agricultural landscape. We provided the structural map of the landscape and classified it into field boundary types nested in three main groups of natural and seminatural elements. Species recorded in all habitat types were categorized into two emergent groups based on their response to land use intensification: 1) agrotolerant species (AT) and 2) high nature-value species (NV). We analyzed the effect of landscape structure and soil physicochemical properties on species richness of these groups. We found both landscape structure and soil properties significant in explaining variation among AT and NV species richness both at 2-m-×-2-m and landscape scales. The most overall species richness was recorded for agricultural fields (43 species) followed by non-crop field edges (37). Woody green veins and permanent ditches were the elements providing high NV species richness clearly, while fields and other field boundary types were mostly supporters of AT species richness. Diversity of AT species increased along nitrogen and clay content gradients of the soil, while NV species benefited where phosphorus and soil moisture content were high. We recommend agricultural landscapes to be more specified with (semi-)natural habitats which embed high a proportion of rare weeds as nature-value plant species.

当前向集约化农业生态系统的大规模转型，已导致植物生物多样性大幅下降，农田边界中的生物类群受影响尤为显著。本研究旨在对某农业景观中的农田及各类农田边界生境的植被开展调查。我们构建了该农业景观的结构图谱，并将其中的农田边界类型划分为归属于三大自然与半自然要素组的嵌套子类。所有生境类型中记录到的植物物种，依据其对土地利用集约化的响应特征被划分为两类响应类群：1）耐耕作物种（agrotolerant species, AT）；2）高自然价值物种（high nature-value species, NV）。我们分析了景观结构与土壤理化性质对这两类物种的丰富度的影响。研究发现，无论是在2米×2米样方尺度还是景观尺度下，景观结构与土壤性质均能显著解释耐耕作物种与高自然价值物种的丰富度变异。整体物种丰富度最高的生境为农田（共记录43种），其次为非作物田缘（37种）。木本绿廊与永久性沟渠是显著支撑高自然价值物种丰富度的生境要素，而农田及其他农田边界类型则主要助力耐耕作物种的丰富度提升。耐耕作物种的多样性随土壤氮与黏粒含量的升高而增加，而高自然价值物种则在土壤磷含量与含水率较高的生境中更具优势。我们建议农业景观应进一步强化（半）自然生境的配置，这类生境可容纳较高比例的稀有杂草，将其作为高自然价值植物物种。