Abstract:
The Iberian dehesa, a grazed Mediterranean
open woodland, is an outstanding example of a
silvopastoral system. Shrub encroachment has been
proposed as an effective method to facilitate natural
tree regeneration and ensure the sustainability of
silvopastoral systems. At the same time, shrubs can
affect both pasture understory and tree overstory
production. The effects of varying intensities of shrub
encroachment on the productivity of four forage
components of this system—pasture, acorns, shrub
browse and tree browse—were tested and the overall
metabolisable energy (ME) under different scenarios
of vegetation structure was calculated. Two common
shrub species with contrasting plant architectures and
ecological functions were studied as models: Cistus
ladanifer and Retama sphaerocarpa. Cistus negatively
affected acorn, tree browse and pasture production,
whereas Retama positively affected pasture and
browse production and was neutral for acorn production. The highest ME values were found when
tree cover was ca. 70 % and C. ladanifer cover was
low or R. sphaerocarpa cover was medium. The
authors recommend conserving and promoting
patched three-layered plots in Iberian dehesas and
similar extensive silvopastoral systems where certain
shrub species could simultaneously encourage the
sustainability of these systems and reinforce (with R.
sphaerocarpa) or maintain (with C. ladanifer) their
productivity.
