The absence of scrub, a lack of young trees and continuous grazing without adequate rest periods can turn a dehesa into a uniform, ageing landscape with little capacity for renewal.
At first glance, a dehesa with scattered trees and uniform grassland may appear orderly and well maintained. However, this apparent tidiness can conceal a significant problem: the loss of the elements that allow the ecosystem to regenerate and remain viable over the long term.
In this second article devoted to the document “Livestock and scrub management for dehesa regeneration”, the LIFE ScrubsNet project focuses on the concept of a simplified dehesa and the signs by which it can be identified.
According to the protocol, a dehesa can be considered simplified when it displays at least two of the following three characteristics: no shrub layer, no diverse age structure among its trees, and unmanaged continuous grazing, with no summer rest period and an excessive stocking rate.
A uniform landscape that is losing its capacity for renewal
Simplification reduces the variety of habitats found within the dehesa. Patches of scrub disappear, young trees become scarce or entirely absent, and most of the tree population belongs to the same ageing generation.
This uniformity is not merely a landscape issue. When mature trees die and there are no younger specimens to replace them, tree density gradually declines. The result is a dehesa that may continue to appear functional for years, even though its long-term future is at risk.
The document describes as fossilised dehesas those that retain mature trees but show insufficient natural renewal to ensure their continuity. The problem is not only the current loss of individual trees, but also the absence of a new generation able to replace them.
First warning sign: the absence of scrub
For many years, scrub vegetation was regarded as an unproductive feature that should be removed to increase the area available for grazing. However, eliminating it completely disrupts part of the dehesa’s ecological balance.
Shrubs help protect the soil from erosion, improve water infiltration, provide shelter and food for a range of species, and create small microhabitats that are more favourable to the growth of other plants.
Some shrubs also act as nurse plants. Their structure can protect acorns, seedlings and young trees from intense sunlight and browsing, helping them through the most vulnerable stages of their development.
The aim is therefore not to allow scrub to spread across the farm without control, but to retain and manage patches, clusters, hedges and strategically located areas where it can perform valuable ecological and productive functions.
Second warning sign: a lack of young trees
A balanced dehesa should contain trees of different ages. The exclusive presence of mature or ageing specimens indicates that regeneration has been interrupted.
Holm oaks, cork oaks and other species of the genus Quercus grow slowly during their early years. Without protection, they may remain very small for a long time and are particularly vulnerable to browsing and trampling by livestock.
A lack of young trees can have several causes, but the document emphasises the importance of protecting particular plots, boundaries or small areas and adapting grazing practices during the first few years.
Sowing acorns or planting saplings can complement these measures. Nevertheless, the protocol identifies natural regeneration as a particularly effective and viable long-term option when the right conditions are created.
Third warning sign: continuous grazing without rest periods
Livestock are an essential part of the dehesa, and their activity helps shape the landscape. Problems arise when animals remain in the same areas throughout the year and the vegetation is not given enough time to recover.
Continuous grazing may cause new shoots to be eaten repeatedly, preventing young trees and shrubs from growing beyond the height at which they are vulnerable to browsing.
The protocol recommends organising grazing according to the sensitivity of each area and temporarily excluding livestock from zones intended for regeneration. Rest periods, grazing rotations, targeted grazing and the protection of selected patches can make livestock farming compatible with the renewal of the tree population.
Simplification does not always mean better management
Removing all scrub vegetation and maintaining uniform grassland may make certain tasks easier in the short term. However, this model reduces habitat diversity and weakens the relationships between the different components of the system.
A well-conserved dehesa is not simply a combination of trees and grass. It is a mosaic in which grassland, scrub, trees of different ages, field boundaries, hedges and temporarily protected areas coexist.
When this mixture disappears, the system loses stability and resilience. Without changes in management, the gradual loss of the tree layer can become extremely difficult to reverse and may lead to increasingly open and impoverished landscapes.
Restoring diversity to safeguard the future
In response to simplification, LIFE ScrubsNet proposes restoring management based on balance. This means retaining a controlled presence of scrub, encouraging the establishment of new trees and adapting grazing to the needs of each area and season.
The key is not to choose between livestock, grassland, trees or shrubs, but to manage the relationships between all these elements properly.
A dehesa with a future needs regeneration, a diverse age structure and areas where vegetation can complete its life cycle. Only then will it be possible to maintain its productivity, biodiversity and ability to adapt to the effects of climate change.
The LIFE ScrubsNet project is co-funded by the European Union through the LIFE programme, LIFE20 NAT/ES/000978.