Knowledge and experiences for the development of sustainable silvopastoral systems in heathlands in Asturias : doctoral thesis

An important proportion of the countryside of the Northern Iberian mainland is covered by shrublands. In particular, 212,147 ha of the surface of Asturias are covered by this type of vegetation, most of them (21% of the total surface area) are heathlands, ericaceous shrubs mainly originated by humanactivity over the centuries such as forest clearances, grazing introduction, burning, turf cutting and firewood gathering. Nowadays, heathlands in Northern Spain are actually widespread as a consequence of the underutilisation of the resources. The abandonment of agricultural and livestock managements since the 1950s has led to this spread of heathlands, particularly where the land is more infertile and erodible and where the succession to forests is restricted by soil thickness and fertility, as well as by frequent fires. Hence, many of these shrublands comprise rural areas in state of abandonment with low productivity, thus marginal or less-favoured areas. The search for sustainilibity of these less-favoured areas requires a multidisciplinary approach with new land use strategies or plans in order to manage these large and underutilised areas. Therefore, a wide knowledge of different topics (soil, pastoral, silvopastoral, forestry, socioeconomic analysis) is required, involving the incorporation of new techniques or components into the planning and management of agrarian systems in order to attain the desired environmental and economic objectives. Bearing this in mind, the general objective of this work is to place a renewed value on these less-favoured and abandoned lands covered by heathlands in the Northwestern Spain, specifically in Asturias. Particularly, four main complementary topics will be focused in this thesis in order to achieve this main target: 1. Review of silvopastoralism in temperate regions: effects of evergreen and deciduous trees on pasture dynamics. Experiences in New Zealand. New Zealand is a pioneer country in the study of silvopastoral systems in temperate regions, with prolific scientific production in relation to the introduction of wide-spaced trees on farms, mainly Pinus radiata and Populus spp. 2. Analysis of the current socio-economic and agrarian scenario. An understanding of the socio-economic scenario in the study area is crucial, especially in the so-called less-favoured areas. We need to know about the financial and human resources as well as the characteristics of the population and the land (structure of farms). 3. Pastoral management in heath and gorse communities. To develop sustainable silvopastoral systems in such less-favoured areas covered by heathlands, it is essential to understand the grazing behaviour of domestic herbivores and their overlap. In this respect, two trials have been carried out in order to better understand: ? The grazing behaviour and performance of cattle and sheep when are managed under single grazing vs. under mixed grazing with goats in partially improved heath and gorse communities. The grazing behaviour of domestic ruminants: cows, ewes and does grazing all together in partially improved heathlands. 4. Tools for land use planning. Another key aspect in the development of silvopastoral systems is the utilisation of tools to assess the productive potential of land as well as for the land use planning. It is evident that the characteristics of sites will differ significantly from one site to another and may limit the vegetal production, including forest productivity. For this reason, the last chapter comprises two studies in which the usefulness of different models and tools for estimating vegetal production in these abandoned and underutilised areas is evaluated: ? Different geostatistical techniques are compared to check their usefulness in modelling ecological variables. In particular, they are tested using a climate variable related to plant productivity: air temperature. These previously tested techniques are used to model the inputs required in order to spatially estimate the (potential) site productivity of forested areas, based on a geocentric index.