Dehesa Ecosystem: Trees, Pastures, and Sustainability

Dehesa and Trees

The grove is essential in the pasture. In addition to the so-called "tree effect", which changes the microclimate, the influence on vegetation makes it early and late.

This appears to be due to the possibility of extraction of nutrients from deep horizons, and thermal differences of the crown and roots.

According to Law 7/2010, of July 14, regarding the Dehesa:

a) Formation of open stands:

A forest area occupied by a layer of trees with a canopy cover between 5% and 75%, composed mainly of oaks, cork oaks, and olive trees, and occasionally other trees, allowing the development of an essentially herbaceous layer (grass) to be used for livestock or game species.

b) Pasture: A farm constituted mostly by the formation of open stands, subject to land use and management based primarily on ranching, which builds on the grass, fruits, and ramoneo (browsing), as well as other forest uses, hunting, and agriculture.

Dehesa has approximately 40 trees/ha.

The control of scrub and undergrowth is made primarily for the management of domestic livestock and hunting.

• There are rules agreed upon that, at the very least, are not excessive:
  • Prune upright branches, seeking an open, balanced, and clean crown.
  • Do not cut branches with more than 15 cm in diameter.
  • Cut without tearing the bark.
  • Give bevel cuts.
  • Prune only in the dormant season.
  • Do not cut more than 1/3 of the initial biomass. Once pruned, the volume of the crown should be at least twice that of what was pruned.
  • Repeat the pruning every 6-12 years, depending on the tree's growth rate, without having to cut branches exceeding 15 cm in diameter.

Activities in the Dehesa

Crafts, food production, tourism, and an important cultural heritage are all part of the Dehesa.

Oak Decline

"The Dry" refers to the illness suffered by the oaks, first described in the 1990s. It is manifested by a general decay that can lead to death. It starts with defoliation, chlorosis, dieback of branches, or sudden death.

Direct Factors (Biotic)

• Fungi
• Gypsy moth (Lymantria dispar). Defoliator.
• Green oak moth (Tortrix viridana). Defoliator.

Predisposing Factors

• Weather (heat and drought)
• Silvicultural practices (pruning, treatments)
• Genetic factors (trees formed from volunteers)

Challenges Facing the Dehesa

• Insufficient regeneration of the tree layer.
• Progressive aging of the population and loss of expertise.
• Depopulation.
• General decline of regenerative capacity (Oak Decline).