| AGRICULTURAL RESEARCH - A growing concern
Could the European countryside be about to undergo radical change? The promising results of the SAFE (Silvoarable Agroforestry For Europe) project, on which 70 researchers from eight countries worked for four years, suggest that this could well be the case. Their work calls into question a growing trend in recent decades associated with the drive to boost agricultural productivity: the disappearance of trees. The findings could well influence the future direction of the common agricultural policy.
Scarcely more than 50 years ago, trees were a constant feature of rural landscapes. Standing on the edges or even in the middle of fields and pastures, they provided wood, fruit, shade and protection. They had their rightful place. But the intensification and mechanisation of farming since the Second World War has proved fatal to this tradition. Trees have been felled and pulled up all over the countryside, to the point where it is not unusual to witness kilometre after kilometre of agricultural land without a tree in sight. For forestry and for the dominant agriculture, trees belong in the forest and the crops belong in the fields.
|Traditional agroforestry landscape in the Dauphiné, France. The trees are widely spaced and are isolated or planted in rows or clumps, but always in close vicinity to arable crops.|
© Fabien Liagre – Agroof
Overturning accepted ideas
The results of the SAFE project suggest that this trend, defended on the grounds of productivity, is an aberration. Contrary to accepted ideas, the researchers established that by alternating the planting of rows of trees and crops, carefully selecting the species and varieties, and adopting specific management methods, it was possible to achieve dramatic increases in yields – up to 30% – for both farming and forestry. It is this mix of trees and crops that is the fundamental principle of agroforestry.
Let us take just one example to illustrate the point. The SAFE researchers showed that the production from one hectare of a poplar/wheat mix is the same as for 1.3 hectares separated into two plots, one for wheat covering 0.9 hectares and another for poplars covering 0.4 hectares. This is on the basis, of course, of a complete cycle for the trees (in this case, 20 years for the poplars) and a tree density in agroforestry that is lower than for traditional poplar plantations and makes it possible to maintain satisfactory yields for the wheat until the trees are felled.
What can be the reason for such a result, when our very rational agriculture considers that an improvement of just a few percent, when it is produced by a new variety, is a genuine breakthrough? The answer is simply that given the right association and appropriate management, trees and annuals establish a synergy in the sharing of the vital resources of light, water and soil nutrients.
|A lone oak standing in the middle of a vast agricultural plain in Greece. Reparcelling has often destroyed traditional agroforestry landscapes.|
© Christian Dupraz – INRA
"By having to compete with the crop, the tree naturally lays down deeper roots,” explains Christian Dupraz, a researcher at the INRA (Institut National de la Recherche Agronomique) in Montpellier (FR) and SAFE coordinator. “The trees ultimately develop a network of roots that extends beneath the upper layers of the soil from which the crops draw their nutrients. This enables the trees to draw on water and nutrients that escape the roots of the crops – the main reason for the increased productivity, from a forestry point of view. Each tree also grows more quickly than it would in an exclusively forestry plot as the trees are no longer competing with an immediate neighbour. Finally, the trees actively help the crops by sheltering them from wind, violent rain or scorching sun.”
The benefits for farmers
Such a mix of trees and crops could be considered incompatible with the use of increasingly large and rapid agricultural machinery, but this is not so. Demonstrations carried out by the project have shown that this mix is compatible with the mechanical means currently used, provided the rows of trees stand between 15 and 40 metres apart, depending on the crops, and that the trees are pruned properly and rationally.
An essential argument in convincing farmers to opt for this kind of intercropping is, of course, the question of revenue. Economic analyses carried out by the SAFE project have established that for a constant surface area, and by adopting a progressive rhythm of agroforestry plantations, a farmer can limit the immediate fall in revenue to under 5%. This is a sacrifice that will be more than compensated for over time as he builds up a considerable timber capital, diversifying his activities in the process. The price is just modest maintenance, concentrated above all in the first ten years in the life of a tree – during which time it must be given a good shape. Afterwards, it can simply be left to grow. The recommendation is to plant species with a high added value (service, pear, cherry, maple, walnut, etc.) which yield wood that is in great demand on the market and which, one day, may even be able to replace the tropical woods that Europe continues to import in large quantities.
|Experimental plot at Leeds University (United Kingdom) where poplars and wheat grow in close proximity.|
© Christian Dupraz – INRA
In European terms – as regards the common agricultural policy (CAP) – one of the main strengths of agroforestry is that it lends itself to an almost infinite number of local combinations by varying the species, varieties and growing methods. The SAFE project is therefore also interesting in the way it has brought together countries as different as the Netherlands, Greece, the United Kingdom and Spain so as to confront very diverse situations, in terms of natural conditions (soil, climate, etc.) and the cultural and legislative environment.
Back to nature
In addition to the agricultural benefits of agroforestry demonstrated by the project, the researchers also stress the environmental benefits of this tree and crop combination. In strictly landscaping terms, the introduction of trees, and possibly of a variety of species, is an aesthetic improvement that can only benefit tourism, especially in areas dominated by cereal farming. Also, by encouraging the penetration of water into the soil, trees and their roots combat erosion. They help prevent floods by limiting the run-off that causes rivers to burst their banks and to reduce water table pollution caused by agricultural fertilisers. Agroforestry trees also fix significant carbon quantities, both in their wood and deep in the soil that is enriched in organic matter due to the decomposition of their fine roots, year after year.
Finally, there is a fundamental impact on biodiversity. Trees very quickly attract all kinds of animals, insects and plants back to farm land. Some researchers believe that this too can have a favourable agronomic impact. They have already identified various auxiliary species (those that prey on pests) that have returned to these plots, including insect-eating birds, bats, and insects such as syrphus flies whose larvae have a big appetite for aphids. “However, one must not rule out the possibility that this increased biodiversity could also have negative effects, such as encouraging the return of rodents, slugs and other harmful species. Although, so far there is no significant indication of this effect,” stresses Christian Dupraz. “But the effects of biodiversity, whether positive or negative, are difficult to demonstrate as you need protocols that permit rigorous comparisons.”
Agroforestry is rooted in the general desire for a less one-dimensional and productivist agriculture, one that is less dependent on fertilisers, weed killers, insecticides and other chemical products. “What I like about this line of research,” concludes Christian Dupraz, “is that it leads us to analyse the quality of the models invented by nature itself. When you look at dozens (or even hundreds) of hectares given over to a single crop, with the same genomes infinitely repeated, you are contemplating the exact opposite of what nature produces. What we are trying to do is to reintroduce the logic of the naturally diversified ecosystem into the cultivated agrosystem. It is a way of making it more stable and autonomous, less aggressive for the environment and – paradoxically – more productive.”