Sustainability Issue #2 July 2009

Traditionally managed meadows and semi-natural pastures are the home for a biodiversity that is of unequalled richness compared with many other habitats. Owing to the large number of species on a small area, the biodiversity of these north European grasslands is sometimes compared to the biodiversity in tropical rain forests. The reason for this high diversity of species is the constant disturbance by grazing  animals or by harvesting, which creates favourable conditions for species which are otherwise weak competitors. It has been known for a long time that some types of disturbance give rise to a great diversity of species, and Darwin already found that grasslands that are regularly cut house more species than grasslands that are not cut.

It has however been found that long continuity of management is also needed in  order that our grasslands may retain this species richness. Many of the lands that have the greatest species richness have also been managed continuously since the early iron age. Grasslands of more recent date, for example previous arable land that is grazed, have only a fraction of the species richness found in the older unfertilised grasslands. Many typical grassland plants are hard to find in other places than in the species rich grasslands. In addition, they are also important for many other organisms such as fungi and insects.

Historic maps

In an international comparison, Sweden has a unique map material. The oldest maps date from the 17th century and provide information on ownership, land use and production at a very detailed level. The purpose of these cadastral maps was to make possible a fair redistribution of land types so that farming may become more effective. Apart from the map itself, there are written documents which describe production and sometimes also physical characteristics such as "stony" or "damp" for each unit. By transferring maps and aerial photographs from different times to a digital environment in a geographic information system GIS, we can analyse how land use has changed because of different natural and social geographic conditions.

Unfertilised grassland has decreased by about 90 per cent over the past 150 years. This drastic reduction is one of the greatest threats to biodiversity today in the agricultural landscape. Our agricultural landscape today has a smaller wealth of variation than the historical landscape, and the remaining grasslands are often in an isolated position in the landscape. This makes it more difficult for many species – both plants and animals – to spread. Despite these great changes, Sweden has a relatively high proportion of old grasslands left compared with many other countries in Western Europe.

By studying the maps, we have found that landscapes with a relatively high proportion of clayey soils were changed earlier than landscapes which have till or a thin soil cover that cannot be used as arable land. The grassland that remains today is most often situated on till or thin soil. Even on the abandoned grasslands we have found that overgrowth can proceed relatively slowly. This is due to the types of soil and the fact that many typical grassland plants may remain despite the cessation of management.

Delayed effects

It takes time for plants to react to changes in the landscape. It is not only land use in a specific grassland but also management of the entire landscape that affects diversity in a single grassland. We have even seen that areas situated in a landscape that had been fragmented for a long time have fewer species than landscapes where fragmentation had been less evident or took place recently. This is true irrespective of how much grassland is left in today's landscape. This delay in the effects may be likened to an "extinction debt" where species are expected to vanish in time because of earlier changes in land use.

Species are however affected to different degrees by fragmentation depending on what properties they have. Short-lived species (annuals) without a seed bank are expected to vanish most rapidly, while long-lived, easily dispersed perennials, with many seeds in the seed bank, may persist for a long time in grassland. This happens even if local conditions are no longer favourable.  In such places, the species may build up remnant populations which can be very important for dispersion and species richness at landscape level.

Remnant habitats and grasslands

In our research, we have studied not only the most species rich semi-natural grasslands but also other types of environments such as small remnant habitats which were formerly grasslands but are today deciduous forest, and also modern grasslands which may be significant for grassland plants and the biodiversity of the entire landscape. We can follow the development of even these biotopes with the help of the historic maps. Formerly, hay was gathered from areas of uncultivable land in arable fields, they were grazed after the harvest had been gathered from the field, and even in years when the fields were left fallow. In landscapes that have not been fragmented for such a long time, roadside verges and areas of uncultivable land may house a species abundance that is almost as rich as that in well managed semi-natural grasslands.

Since many plant species can survive for such a long time, overgrown grasslands are important, for instance when grasslands are to be restored. These remnant habitats are potentially very important since they may act as a source for seed dispersion in the landscape so that biodiversity may increase when arable fields are changed into pastures.

Understanding tomorrow's diversity

In order that more general conclusions may be drawn as to how changes in the agricultural landscape will affect biodiversity, it is essential to compare many different types of farming landscape and not only to focus on "hot spot" landscapes where there is both a lot of traditionally unfertilised grassland and  great species abundance.

In an international comparison, present Swedish reseaerch is well ahead as regards historic landscapes and their coupling to today's biodiversity. Understanding what significance the distribution of grasslands has had historically can help us conserve and improve the conditions for biodiversity in the agricultural landscape in the future also. This provides an excellent platform for the development of interdisciplinary studies for sustainable agricultural development, multifunctional landscapes and the production of ecosystem services in the future.

• Tell a friend
• Like
• Push Delicious Digg

Back issues

Conferences