RESEARCH WORK

Reflections on silvopastoral systems

R. O. Russo¹

¹Estación Experimental Alfredo Volio Mata, Universidad de Costa Rica, Ochomogo, Cartago, Costa Rica.
E-mail: ricardo.russo@ucr.ac.cr

ABSTRACT

The objective of this analysis is to reflect on more sustainable family and extensive integrated livestock production models, in which the woody component is integrated, contributing to the reduction of greenhouse gases and favoring the mitigation of the climate change. For such purpose, a revision was made referring to the integration of the forestry activity in livestock production, as a viable alternative of production system. A start is made from the criterion that silvopastoral systems (SPSs), within the agroforestry ones, are agroecosystems in which a tree component is associated with a herbaceous (natural or improved pastures) and a farming component (livestock) in the same site, where biological interactions exist among them and land use is maximized. This paper also describes how SPSs are grouped; their opportunities from the economic, productive, social and environmental points of view; and the effects of the interaction among its components. This analysis allows to state that SPSs are a product of the relation among biology, society and culture, and in them there is a large diversity; likewise, they allow the reconversion of the very little productive extensive livestock production into more productive and sustainable systems, as well as the rehabilitation of the areas degraded by this type of livestock production, deforestation and soil depletion.

Key words: Climate change, land rehabilitation, livestock production.

When I was invited to give a lecture titled «Agrosilvopastoral systems in the context of sustainable agriculture», on October 18, 1993, at the 9^th National Agronomic and Natural Resources Congress, in San José, Costa Rica (Russo, 1993), I did not imagine that it would be published (Russo, 1994, 1996) or that, twenty years later, I would still be reflecting on silvopastoral systems (SPSs) and their relation to sustainability. In general, it is accepted that SPSs and the livestock production-complementary forestry activities constitute a viable production alternative. The products and services provided by trees and the tree component allow to obtain short-, medium- and long-term benefits. If it is achieved that each production unit works as a true integrated system, with the adequate interrelation of each of its components animals, forestry and pastures , complemented with good management, better yields and the sustainability of production can be reached, which will be shown in an increase of productivity per hectare.

The objective of this analysis was to reflect upon integrated family and extensive livestock production models, more stable and sustainable, in which the woody component is integrated, contributing to the reduction of greenhouse gases and favoring the mitigation of the climate change. For such purpose, a series of concepts and aspects of the integration of the forestry activity in livestock production are reviewed, which can be an aid to implement the alternative that is better adapted to each production system in particular, without intending to make an exhaustive analysis.

How are SPSs defined?

Agroforestry (AF) can be defined as an induced anthropic strategy that turns agroecosystems into more sustainable. SPSs are part of AF, and are agroecosystems in which a tree component is deliberately associated to a herbaceous one (natural or improved pastures) and a livestock production component (livestock) in the same site, so that there are biological interactions between both in order to maximize the land use (fig. 1). In other words, they temporarily and spatially combine the maintenance of pastures (natural or cultivated ones) with livestock production activities, along with tree species. To this the silvopastoral practices can be added, in which it is not necessary that the woody component is in the same site as the animal component, because forage can be transported; such is the case of forage banks or living fences, which are pruned and the forage produced by the pruning is supplied to confined animals.

How can SPSs be grouped?

SPSs can be grouped, depending on the approach or main objective of the systems, into the following sets:

1. SPSs with forestry approach

a) Grazing of plantations

b) Grazing of natural forests

c) Grazing in orchards

2. SPSs with livestock production approach

a) Silvopastures (grasslands with forage trees or shrubs)

b) Isolated trees in paddocks

c) Living fences

d) Integrated mixed systems with forage or multipurpose trees for cutting (forage banks)

e) Agroforestry practices in livestock production

f) Intensive silvopastoral systems SPSi (specialized in animal production)

Opportunities of SPSs

SPSs present opportunities from the economic, productive, social and environmental point of view (Iglesias et al., 2011). In the economic aspect, the diversification of production allows to obtain short-, medium- and long-term incomes; as well as to attenuate the fluctuations of prices and of the product market. In addition, it generates additional incomes for the production of timber and its derivatives.

From the productive point of view, the pastures as well as the animals are benefitted by the effects exerted by the shade and shelter. The decrease of the heat stress in the animals allows a higher daily gain per animal with regards to the ones which do not have shade, and the shelter generates the decrease of their energy requirements for maintenance. Likewise, the evapotranspiration of pastures decreases because of the shade.

In the social aspect, the references found are less. Nevertheless, SPSs are considered important to increase the quality of life of the rural population in the poverty threshold most vulnerable group to climate and market variations and to diseases , because they contribute to risk diversification and to the increase of resilience to the system external disturbances.

Some of the interactions among SPS components, which started to be summarized and enriched by many authors since more than three decades ago (De Alba, 1959; Borel, 1981, Bronstein, 1983, Torres 1985; Montagnini, 1992; Pezo, 1998; Hernández et al., 2000; Ibrahim, 2011), are the following:

• Trees contribute organic matter to the soil in the form of dead leaves, flowers, fruits, branches and roots that are periodically detached. In addition, they absorb elements in the deepest horizons and deposit them on the surface, for which they are available for pastures. In the case of nitrogen-fixing trees, it is logical to assume an additional benefit.
• Trees provide a favorable microclimate for the animals (shade and decrease of temperature). The magnitude of shade depends on the quantity of trees per surface unit, the crown diameter and their luxuriance. The shade protects them from the excessive heat by direct sunshine and reduces the ambient temperature, which is related to the thermal balance of the animal; a temperature lower than the body temperature is translated into higher intake, although it is discussed whether productivity is also higher.
• Trees can compete with pastures for water, nutrients, light and space, and the effect will be higher as the requirements are similar. The natural falling of leaves and the branch pruning modify the requirements and availability of water, light and nutrients in the components of the system. The adequate selection of the species, the season and the pruning frequency can help to attenuate competition or conveniently direct it.
• If the stocking rate is high or the trees are in groups under them the animals gather looking for shade , soil compaction can damage their growth; while trampling can affect the herbaceous cover and cause erosion patches.
• The feed preference of the animals can affect the forest composition (with the passing of time, there is predominance of species which are not palatable for livestock).
• The presence of the animal component changes and can accelerate some aspects of nutrient recycling, by returning feces and urine to the soil.
• The animals can disseminate seeds or scarify them, which favors germination.
• The presence of trees produces goods and environmental or ecosystem services.

These interactions can be grouped into four main effects: a) of trees on the soil, b) of the canopy on the pastures and animals, c) of the soil on the pastures and animals, and d) of the management of the SPS (fig. 2). The integration of such effects forms the silvopastoral dynamics. However, to this it should be added that the best integration of the different components should be defined for each particular case, depending on the conditions, the available resources and the short-, medium- and long-term goals.

FINAL CONSIDERATIONS

It could be interpreted that SPSs are a sociocultural and historical construction, because, beyond the biological characteristics of their components, there is a complex of determinations and economic, social, juridical-political and psychological, that is cultural, particularities, which have conferred them traits of their own. SPSs, being products of the relation among biology, society and culture, have historical character; and also show large diversity.

However, the existing ambiguity about some of the central concepts of the silvopastoral issue in its different modalities and its relations to the climate change, mitigation, adaptation, sustainable development and clean development, favors and stimulates the appearance of the so-called «discursive traps». This notion, reported by Rosenfeld (2004), refers to speeches that display complex and dense concepts (such as that of sustainability), with which the treatment of the necessary transformations to make that stated by the speech viable, that is, strategic changes in the political, economic, social and technological scenarios implied in the prevailing development styles, is avoided.

An example of these discursive traps is the use of such terms as: `good silvopastoral practices', `learned silvopastoral lessons', `agroforestry networks', `silvopastoral rotational grazing', `arborization of paddocks', `guides for the silvo-farming integration', `pasture-trees integration', `alternative livestock production systems' or `directed research', which can constitute additional barriers and restrictions that hinder the effective local construction of shared operational capacities, because they hide the systematic treatment of the conditions of viabilization of the transformations intended with the silvopastoral topic.

The consequences of the use of silvopastoral systems and practices on sectoral policies, strategic plans and territorial organization, such as the initiatives of national actions for mitigation and adaptation (NAMA), cannot be analyzed through optimization equations with given restrictions; but they should be explored and critically revised through indicators numerical as well as qualitative such as: kilograms of milk per hectare, kilograms of meat per hectare, tons of sequestered C per hectare, reduction of emissions per hectare, which include the participation of the involved sectors.

The links between the academic interpretation about silvopastoral production and the interest of the population of small livestock producers are multiple and sometimes divergent. Their immediate antecedents turn out to be complex and are rapidly transformed, in the light of the local political and ideological unrest.

SPSs are a production choice in the buffering zones of protected or conservation areas, which also favor the preservation of biodiversity and are adjusted to the strategies of the programs of reduction of emissions by deforestation and degradation of forests (REDD+), because they allow to widen the forest cover, produce timber and contribute to the decrease of emissions.

These systems would allow the reconversion of very little productive extensive livestock production into more productive systems, and also the rehabilitation of the areas degraded by extensive livestock production, deforestation and soil depletion.

Received: June 28, 2014
Accepted: November 4, 2014

Footnotes

¹Dr. Ricardo O. Russo, Agronomic Engineer, is a professor-researcher of the University of Costa Rica and Member of the Managing Board of the National Association of Farming and Forestry Extension Workers (ANEAF, for its initials in Spanish). He has two Master of Sciences degrees: one in Business Administration and the other in Natural Resources, as well as the scientific degree of Doctor in Forestry Sciences.