Prescribed burning and browsing to control tree encroachment in southern European heathlands

Land abandonment and the cessation of traditional management practices is favouring scrubland and forest expansion throughout Europe, reducing the extent of many semi-natural open habitats of a high ecological or biodiversity value. Tree encroachment is threatening several Calluna vulgaris (L.) Hull heathlands, particularly in Southern Europe. This paper describes vegetation dynamics resulting from an experiment designed to test management options aiming at controlling the encroachment of Populus tremula (aspen) and favouring heathland recovery. The research was conducted at Vauda Heath, North-western Italy, from 2005 till 2009. We studied prescribed burning and goat browsing, both alone or in combination, assessing their effects on structure and density of encroaching trees, as well as on heathland main species. Treatments were applied to 42 experimental units (300 to 650 m2 each), with each treatment combination replicated from six to twelve times (including untreated controls). Prescribed burning and browsing showed complementary effects. Prescribed burning followed by yearly goat browsing effectively contained tree encroachment while maximising post-fire heathland regeneration. Both back and head fire behaviours were effective in inducing stem mortality of aspen and rejuvenating the heathland, but in the absence of measures to control post-fire suckering, aspen tended to recover the pre-treatment stand structure. A higher fire frequency (annual winter fire) controlled tree encroachment, but hindered Calluna recovery, whilst favouring competing grass species. Goat browsing alone was initially able to reduce tree growth and slow down woodland expansion, until aspen individuals reached an escape size of 1.5 m in height. Our results demonstrated the efficacy of integrating prescribed fire and repeated browsing to control tree encroachment without affecting heathland regeneration, also at the southern limits of Calluna distributional area.