Silvopastoral farming in Colombia. Photo: Neil Palmer, CIAT

Trees on farms increase milk yield by a factor of five

‘Silvopastoral’ farming has multiple benefits for farmers, cows and the environment

A new paper published by the Royal Society demonstrates an extraordinarily wide range of co-benefits from a relatively simple technique: silvopastoral farming (farming with trees). Planting trees on grazing land not only cuts greenhouse gas emissions but also improves animal welfare, reduces air and water pollution, avoids soil erosion, protects biodiversity and can increase the milk yield by a factor of five.

The review was produced by Professor Donald Broom at the University of Cambridge, working with co-authors from Mexico and Columbia. It challenges the conventional model of grazing, in which livestock eat only grass, by showing that introducing trees and shrubs to pasture can increase productivity.

“Excessive focus on pasture plants for the feeding of farmed ruminants has been a major mistake in almost all parts of the world,” explain the authors. By growing trees and shrubs with edible shoots and leaves, in combination with pasture plants, farmers can produce more fodder per hectare and provide a richer diet for their animals.

The greatest benefits come from growing leguminous species, which fix nitrogen from the air. This also avoids the need to apply artificial fertilisers, saving money as well as avoiding air and water pollution. Widely used leguminous “fodder trees” include various species of Leucaena – a drought-tolerant shrub that is loved by cattle and grows fast in tropical conditions. One trial showed that growing Leucaena on pasture increased the mass of fodder available to cattle by 27% and the protein content by 64%. A similar trial showed that milk yield per hectare increased by a factor of four to five, mainly because many more cattle could be kept on each hectare.

Trees and shrubs provide valuable habitat for native wildlife. “Conservation need not just involve tiny islands of natural vegetation in a barren world of agriculture, as there can be great increases in biodiversity in farmed areas,” the authors explain. Silvopastoral farms can provide wildlife corridors, connecting the remaining areas of natural habitat. And because milk yield per hectare is higher, there is less need to clear more forests for agriculture, giving further benefits for biodiversity.

Climate benefits are significant – through increasing the amount of carbon stored in the soil and vegetation and avoiding deforestation, but also through cutting emissions associated with manufacturing and applying fertilisers. Fertilisers are energy-intensive to produce, and once applied to the land they emit nitrous oxide, which is a greenhouse gas with a warming effect more than 300 times that of carbon dioxide.

Trees and shrubs also stabilise the soil, reducing soil erosion. The deep network of roots increases the ability of the soil to absorb and retain water, making the farm less vulnerable to droughts and floods. Soil fertility improves, as the tree roots bring up nutrients from deep in the ground, and recycle them to the land when leaves fall. The paper cites “islands of extra soil fertility under the canopy of trees”, and more favourable conditions for earthworms and beneficial insects such as dung beetles. And farmers gain a free source of wood to harvest for fuel or building, or for sale as an alternative source of income.

Perhaps the most surprising benefit is that the cows themselves are happier, exhibiting more settled and less aggressive behaviour. It seems that they like having trees to hide behind – it gives them a sense of security. Trees also provide shade in hot weather and shelter from wind and rain. There is even a reduction in diseases from parasites such as ticks, as the trees attract birds which are natural predators of ticks. These factors make working conditions more pleasant for the farm staff as well, and silvopastoral farms report higher retention of staff and higher job satisfaction.

Silvopastoral farming offers the tantalising prospect of genuinely sustainable high-welfare livestock production, and the authors conclude that it should be further developed.

Sustainable, efficient livestock production with high biodiversity and good welfare for animals

D A Broom, F A Galindo and E Murgueitio (2013). Proceedings of the Royal Society B, 280, 1771, November 2013. doi: 10.1098/rspb.2013.2025