Plant biodiversity

Background

Plants define the habitat of a site, providing structure, shelter and food as well as contributing to the overall biodiversity. They include flowering plants (trees, shrubs, grasses and herbaceous plants), as well as the gymnosperms (which include conifers), ferns and related species, and also the bryophytes (mosses and liverworts). While plant diversity is well represented in rural areas, development pressures have reduced the amount of greenspace in urban and peri-urban areas, resulting in a poorer diversity of plant communities. However, there are still many small pockets of greenspace within the built environment with a rich diversity of plant species, and other areas where improvements to greenspace could encourage the establishment of plants.

Management of urban greenspace directly influences the micro-environment and can create conditions favourable to a range of plants, which in turn can increase habitats for, and therefore the diversity of, other species groups.

Local authorities in the UK are committed to the Local Biodiversity Action Plan process and to promoting species biodiversity within rural, peri-urban and urban habitats. Planning within urban environments can be particularly complicated, as there is a need to balance the requirements of an expanding human population with the conservation of a range of species.

Practical considerations

The UK Biodiversity Action Plan sets out the UK Government’s broad strategy for conserving biodiversity. It includes measures to promote biodiversity conservation in woodlands. Within the plan, 391 species have been identified as being either in rapid decline or globally threatened, and Species Action Plans have produced for these priority species. Species Action Plans detail the status, threats, and targets for conservation and recovery for each species, and identify organisations tasked with carrying out the actions.

Areas of habitat for plant species within the urban and peri-urban environment have become fragmented and isolated through land-use change, particularly with the spread of settlements and transport infrastructure in recent years. As a result, there has been a general decline in biodiversity over the wider countryside.

Plant diversity can often be increased at the local scale by changing or diversifying the management of a site, for example by using less-intensive mowing regimes to encourage butterflies. To encourage particular habitats to develop, the environmental conditions of the site must first be identified as suitable: soil conditions (nutrients, moisture, pH) and factors such as drainage.

Many species have seed-dispersal mechanisms and will, in time, reach a site. New sites will be rapidly colonised by species with wind-dispersed seeds – these are often a good nectar source and will attract insects. But some species, particularly woodland herbs, may not be able to reach a site, especially if it is a long way from other sites. In this case, or if habitat is not developing as quick as hoped, seeding or planting may help.

Long-term strategies to improve plant biodiversity can be considered over a larger geographical area by examining the spatial distribution of plant biodiversity. Areas with a rich plant composition can act as sources for dispersal to other areas. Successful colonisation of new sites can be encouraged by ensuring that greenspace creation and appropriate management are undertaken in areas identified within the dispersal range. This approach has been examined for ancient woodland indicator species within urban, peri-urban, and rural areas (see Case studies). Ancient woodland indicator species include:

  • Barren strawberry
  • Pignut
  • Sweet woodruff
  • Bluebell
  • Primrose
  • Wood-sorrel
  • Common cow-wheat
  • Ramsons (wild garlic)
  • Wood speedwell
  • Dog’s mercury
  • Sanicle
  • Wood spurge
  • Early dog-violet
  • Tutsan
  • Yellow pimpernel,
  • Herb Paris
  • Wood anemone.

Case studies

Ancient woodland species within Edinburgh and the Lothians

An assessment of ancient woodland plant species, and their contribution to biodiversity, was undertaken within urban, peri-urban and rural woodlands in Edinburgh and the Lothians. The outputs were used to evaluate where effort should be targeted to consolidate high-quality habitats.

The quality of woodland biodiversity was assessed using expert knowledge and coincidence mapping of ancient woodland indicator vascular plant species.

The approach recognised that while one ancient woodland indicator species might occur by chance, or may have been introduced, and would therefore not necessarily reflect biodiversity quality, the presence of additional species strengthens the quality argument (Peterken, 2000).

The number of ancient woodland indicator plants used to provide a guide to biodiversity quality was defined as:

  • Fewer than four = low-quality woods
  • Four to seven = good-quality less-fertile woods and moderate-quality fertile woods
  • Eight or more = high-quality fertile woods.

Forest Research’s Biological and Environmental Evaluation Tools for Landscape Ecology (BEETLE) was used to assess the functional connectivity within habitat networks, selecting woodlands of high biodiversity value to form core woodland areas, indicating opportunities for consolidating, expanding and linking forest habitat networks in relation to Local Plans.

Services

Forest Research can provide advice and consultancy on developing the plant diversity of urban greenspace, and has particular skills related to trees and woodland. We have developed an Ecological Site Classification Decision Support System, which advises on which trees are suitable for a particular site.

Rare or protected plants may be listed on the Forest Research HaRPPS website, where information about their seed dispersal characteristics may be found. Our protected species specialists can help with site management for a range of protected plants. We have a wide range of expertise in establishing trees and shrubs from seed or nursery trees.

In addition, the Forestry Commission has a Plant and Seed Supply Branch as well as nurseries throughout the UK, and can advise on seed provenance.

Forest Research is the leading research institute on habitat networks, having undertaken analyses of urban greenspace and ancient woodland indicator plants within urban, peri-urban and rural environments.

Further information

Forest Research

Other resources

UK Biodiversity Research Advisory Group

Peterken, G.F. (2000). Identifying ancient woodland using vascular plant indicators. British Wildlife 11: 153-158