Urban meadows as an alternative to short mown grassland: effects of composition and height on biodiversity

There are increasing calls to provide greenspace in urban areas, yet the ecological quality, as well as quantity, of greenspace is important. Short mown grassland designed for recreational use is the dominant form of urban greenspace in temperate regions but requires considerable maintenance and typically provides limited habitat value for most taxa. Alternatives are increasingly proposed, but the biodiversity potential of these is not well understood. In a replicated experiment across six public urban greenspaces we used nine different perennial meadow plantings to quantify the relative roles of floristic diversity and height of sown meadows on the richness and composition of three taxonomic groups – plants, invertebrates and soil microbes. We found that all meadow treatments were colonised by plant species not sown in the plots, suggesting that establishing sown meadows does not preclude further locally determined grassland development if management is appropriate. Colonising species were rarer in taller and more diverse plots, indicating competition may limit invasion rates. Urban meadow treatments contained invertebrate and microbial communities that differed from mown grassland. Invertebrate taxa responded to changes in both height and richness of meadow vegetation, but most orders were more abundant where vegetation height was longer than mown grassland. Order richness also increased in longer vegetation and Coleoptera family richness increased with plant diversity in summer. Microbial community composition seems sensitive to plant species composition at the soil surface (0–10 cm), but in deeper soils (11–20 cm) community variation was most responsive to plant height, with bacteria and fungi responding differently. In addition to improving local residents’ satisfaction, native perennial meadow plantings can produce biologically diverse grasslands that support richer and more abundant invertebrate communities, and restructured plant, invertebrate and soil microbial communities compared with short mown grassland. Our results suggest that diversification of urban greenspace by planting urban meadows in place of some mown amenity grassland is likely to generate substantial biodiversity benefits, with a mosaic of meadow types likely to maximise such benefits.

当前城市地区对绿地建设的呼声日益高涨，但绿地的生态质量与数量同等重要。温带地区主流的城市绿地形式多为专为休闲设计的短剪草坪，但这类草坪需要大量维护，且对多数生物类群的栖息地价值普遍有限。替代方案的呼声日渐增多，但此类方案的生物多样性潜力尚未得到充分认知。本研究在6处公共城市绿地中开展重复试验，设置9种不同的多年生草甸种植处理，量化分析播种草甸的植物区系多样性与冠层高度，对植物、无脊椎动物与土壤微生物这3类生物类群的丰富度及群落组成的相对影响。研究发现，所有草甸处理组均被试验样地未播种的植物物种定植，这表明若管理得当，播种草甸的建设不会阻碍后续由本地群落主导的草地群落拓展。更高且植物多样性更丰富的样地中，定植物种更为稀少，这提示种间竞争可能会限制外来物种的入侵速率。城市草甸处理组的无脊椎动物与微生物群落组成与修剪草坪存在显著差异。无脊椎动物类群对草甸植被的冠层高度与物种丰富度变化均有响应，但多数目级类群的丰度在植被高度高于修剪草坪的样地中更高。植被更高的样地中，无脊椎动物的目级丰富度也有所提升；夏季时，鞘翅目（Coleoptera）的科级丰富度随植物多样性升高而增加。土壤表层（0~10cm）的微生物群落组成对植物物种组成较为敏感；而在深层土壤（11~20cm）中，群落变异对植物冠层高度的响应最为显著，且细菌与真菌的响应模式存在差异。本地多年生草甸种植方案不仅能提升当地居民的满意度，还可形成具有高生物多样性的草地群落：相较于短剪草坪，此类草甸能够支撑更为丰富多样的无脊椎动物群落，并重塑植物、无脊椎动物与土壤微生物的群落结构。本研究结果表明，通过将部分休闲修剪草坪替换为城市草甸来实现城市绿地的多样化，有望带来可观的生物多样性效益；而采用多种草甸类型镶嵌配置的方式，则可最大化此类效益。