Silvopastoral agroforestry pastures can be managed in exactly the same way as conventional pastures. Pastures may be fertilised as for conventional pastures, though the current trend for replacement of nitrogen fertilisers with grass/clover pastures might offer some benefits if it reduces the use of machinery and the potential for compaction of the soil which can slow the growth of young trees.
If pastures are to be renovated or upgraded and soil cultivation is involved, it is better to carry out the work before the trees are planted. Surface seeding may be carried out at a later stage but the trees should be well established. Tree roots occupy the top 10cm or so of the soil for up to five years so the use of machinery should be minimised and any surface cultivation avoided for at least five years.
Experience in a number of trials with sheep across the UK has shown that with sycamore trees planted at 400 per hectare there is no reduction in annual livestock production after 12 years of tree growth.
With very fast growing larch trees on an upland site and ash on a lowland site, both planted at 400 per hectare, reduction of around 10% in annual livestock production due to shading was found after 10 to 11 years of tree growth. Pruning of the larch trees then maintained annual livestock production at around 90% of the original level on the upland site. Despite pruning, the ash trees on the lowland site developed crowns large enough to shade the pasture and reduce annual livestock production further; in this case, if livestock production is to be maintained, the trees will have to be thinned.
There was no evidence of any change in the species composition of the pastures under trees of a number of species up to 14 years old, except in the area immediately around each tree where bare ground had been created through the use of herbicide for the first three years. In these herbicide-treated areas, species which had not been in the original seeds mixture tended to appear; the older the pasture, the greater the variety of new species. However these changes in species composition would have very little impact on potential pasture production.
Pastures under the canopy of 35-year-old poplar trees, thinned to 156 trees per hectare have shown changes in pasture composition. While perennial ryegrass, white clover, rough-stalked meadow grass and creeping thistle were prevalent in nearby conventional pastures, the pastures under the 35-year-old trees had more shade tolerant species such as creeping bent, Yorkshire fog and annual meadow grass. Feeding values to grazing animals may be reduced with these changes and management, including rates of fertiliser application, may have to be adjusted.
Changes in the seasonal pattern of grass production have been found in pastures growing in more mature silvopastoral systems. Increased production, compared with conventional pastures, has been found in early spring, before the trees flush and in autumn after leaf fall. These increases occur when there is adequate light and temperatures at the extremes of the growing season are higher in the silvopastoral system because of the sheltering effect of the trees. In mid-season with mature trees, pasture production may be lower than in a conventional pasture because of shading. Overall, annual production may be little affected in thinned and pruned silvopastoral systems.
In the east of the country where dry summers can reduce pasture production, the presence of trees in silvopastoral agroforestry systems can increase pasture production compared with a conventional pasture, through reducing soil moisture deficits. This happens because, provided the tree canopy is not large enough to cause significant shading of the pasture, the trees reduce incoming sunlight energy, reduce windspeeds and reduce maximum temperatures, the combination of which reduces evaporative loss of water from the surface of the pasture (evapotranspiration).
Sheep are the best livestock species for silvopastoral agroforestry. The trees require less expensive protection with sheep than with cattle, goats are naturally browsers and often prefer trees and shrubs to pasture species.
There is no need to change the management of sheep in a silvopastoral agroforestry system provided that the tree canopy has not reached a size that will reduce pasture growth. If the tree canopy has been allowed to grow large enough to reduce pasture production, stocking rates of sheep will have to be adjusted accordingly.
Livestock welfare benefits
The trees can actually provide some benefits to the livestock. Shade from the sun is available under the trees in hot summers. Shelter from wind is available at other times of the year. A longer growing season for pastures has been shown under silvopastoral agroforestry, the pastures start to grow a couple of weeks earlier in spring and continue to grow for a couple of weeks later in the autumn compared with conventional pastures. The early "bite" from pastures coupled with the direct benefits of shelter from the trees to the lactating ewes and lambs could lead to a greater milk supply and better lamb growth. The late "bite" from pastures and the direct benefits of shelter from the trees in autumn could lead to ewes putting on better condition prior to mating.
A note of caution:
While over-wintering sheep in a silvopastoral system may appear very attractive because of the shelter benefits, care must be taken as with any pasture to avoid excessive winter poaching and loss of pasture production in the following year.