Description
In France, the traditional agroforestry often consists in orchards in which fruit trees are mixed within grassland. In general, trees have a negligible negative impact (losses up to 10%) and sometimes they are even beneficial to grassland productivity. Nevertheless, the tree density seems important, as above 60 trees/ha forage yield strongly decreases, whilst an optimum around 30 trees/ha seems to be a good compromise when timber is sought after. But overall the main limiting factor is the amount of light reaching grass. Therefore trees management is important to favour grass yield regardless of their plantation density. Trees create a beneficial microclimate for animals during periods of extreme weather (cold or hot). They also have an impact on the physiological development of plants. By creating a delay at the start of growing season, grass keeps a high protein content for longer time, in comparison to grasslands without trees. This could be used for extending the grazing season, though slightly reducing the forage yield of grass.
Promising results of tree leaf quality analyses have highlighted the suitability of Morus alba and Fraxinus ornus for their digestibility and protein content. Other species seem interesting especially for their crude protein content. Trees have also the advantage of producing biomass at a time when grassland growth is slowing down. The obvious obstacle is forage harvest and the maintenance of the trees. Positive examples where trees are kept at a height accessible to grazing animals have been identified. Some farmers try to cultivate the trees in tight rows and harvest them as silage, others keep the hedgerows and cut branches in years of great forage stock deficit.
