In grasslands, trees and shrubs can act as genuine islands of biodiversity. They provide shade, food and shelter, protect the soil, support pollinators and help young holm oaks and cork oaks become established.
At first glance, a small patch of woody vegetation in the middle of a grassland may appear to be of little importance. Its value, however, extends far beyond the area it occupies.
In a well-managed dehesa, trees, shrubs, hedges and small wooded patches create centres of shelter and biological activity. They increase landscape diversity and strengthen its capacity to cope with drought, erosion and other environmental pressures.
The LIFE ScrubsNet document “Livestock and scrub management for dehesa regeneration” highlights that these features can function as true islands of biodiversity within grasslands.
Shade, shelter and food
Woody species offer shade and protection from heat, wind, rain and cold. This benefits both livestock and the many wild species that use them as resting, sheltering and breeding sites.
Some plants also provide leaves, shoots, browse, flowers and fruit. These resources can supplement livestock diets when herbaceous pasture is scarce, while also providing food for birds, insects and other animals.
Their value should therefore not be measured only in terms of the grazing area they occupy, but also through the range of services they provide to the entire system.
Protecting soil and water
The roots of trees and shrubs help bind the soil and reduce erosion. Vegetation slows surface run-off during heavy rainfall, improves water infiltration and helps retain sediment and nutrients.
Organic matter also accumulates beneath woody plants, creating small areas with greater fertility and better moisture conditions.
These functions are particularly important on slopes, in stony areas, along field boundaries and close to watercourses, where soil loss may be more severe.
Resources for pollinators and beneficial wildlife
The flowers and fruit of many woody species provide food for pollinators, birds and beneficial wildlife. These animals, in turn, contribute to essential ecological processes such as pollination, seed dispersal and the natural control of certain pests.
A completely uniform dehesa provides fewer resources and places of refuge. By contrast, a mosaic landscape, where open grassland is interspersed with trees, shrubs, hedges and small patches of vegetation, creates many more opportunities for wildlife.
A refuge for young trees
Patches of vegetation can also play a decisive role in tree regeneration.
During their early years, holm oak and cork oak seedlings are highly vulnerable to heat, water shortages, trampling and browsing. Some shrubs act as nurse plants, creating a more favourable microclimate and making it harder for livestock to reach the young trees.
A single shrub can therefore become the place where the next generation of dehesa trees begins to grow.
Every patch matters
Protecting these islands of biodiversity does not mean allowing scrub to spread without control. The key is to decide where it should be retained and how it can be integrated into livestock management.
Hedges, field boundaries, riverbanks, sloping areas and patches reserved for regeneration can become strategic spaces for conserving woody vegetation.
The LIFE ScrubsNet message is clear: in a well-managed dehesa, every patch of vegetation matters. Together, they create a more diverse, stable landscape that is better prepared to face the effects of climate change.
The LIFE ScrubsNet project is co-funded by the European Union through the LIFE programme, LIFE20 NAT/ES/000978.