Benefits of Silvopasture to Farms

Silvopasture is a form of agroforestry - a collective name for land use practices where trees are combined with crops and/or animals in a wide range of scenarios and configurations on the same unit of land, and where there are significant ecological or economic interactions between the tree and the agricultural components.

In Scotland, as the main agricultural land uses are livestock grazing or arable cropping, silvopasture (where trees are grown in grazed or mown pasture in a regular or varied pattern) and silvoarable (where trees are grown in rows between an arable crop) systems are, respectively, the most widespread systems applicable. I like to think of it in the broadest way - i.e. how can we introduce trees into a productive farm platform in as many ways as possible with the least compromise to farm production. For example, integrating trees with a pre-existing or new hedgerow network can bring great benefits to farms.

In Northern Ireland we have had a long-term silvopastoral trial running for over 30 years now (at Loughgall in Co Armagh). In this trial we have compared three land use types:

1. A silvopastoral system with ash trees planted at 400 stems/ha and grazed by sheep.
2. Permanent grassland also grazed by sheep.
3. Planted woodland with ash trees (2,500/ha).

The trial was initially part of a multi-site network - the Scottish site was on the James Hutton research farm at Glensaugh, Aberdeenshire. The Loughgall trial, which is fully replicated internally (3 randomly allocated reps per treatment) has been maintained and consistently managed since establishment in 1989 and is a unique resource to assess the long term impact of silvopastoral systems on a range of outputs, performance, and ecosystem services delivered.

What have we learnt from this trial?

• Firstly, and very importantly, our farm manager was able to carry out normal grassland - based operations within the silvopasture - topping, fertiliser and slurry application etc.
• Sheep production was not reduced in the silvopasture until the trees were about 12 years old (c. 8m ht & 15cm diam) and subsequently recovered after thinning a quarter of the trees.
• Sheep performance was unaffected by the tree presence. From the evidence of animals seeking shade and shelter, individual animal performance benefits and resilience to climate extremes can be inferred.
• Silvopasture is more welfare-friendly than open pasture as sheep have a more varied diet with access to tree fodder, and are healthier – with extension of the grazing season animals have reduced incidence of respiratory diseases. Less tangible benefits but relevant, are the variation in habitat structure which may reduce “boredom”. It is proposed that these benefits represent a significant marketing opportunity for sheep meat.
• Soil zonal exploitation by roots led to greater water infiltration and reduced run-off for flood mitigation, earlier turn-out and later housing of livestock led to an extended grazing season and inferred reduced ammonia emissions.
• A range of biodiversity benefits were measured – more beetles, spiders, pollinators and, very importantly, earthworms.
• We harvested completely (roots and all) some 21 year old trees and found they were storing about 70tC/ha. AFBI scientists have estimated carbon sequestration from the silvopasture at 2.4 tC/ha/yr.

What would we do differently in hindsight?

• Most of the tree damage we encountered occurred later in the season and was probably because the plots were set-stocked throughout the year (to get meaningful animal performance data). In later stages of the trial we moved to rotational grazing, where sheep on the silvopasture were integrated with grassland-only fields and this greatly reduced their interaction with the trees. I would envisage that if farmers were able to plant even a small portion of their farm in silvopasture, then that could be held over in the rotation to be grazed as late in the season as possible - or as early in the season. In that way the benefits of extension to the grazing season – improved animal health and grassland utilisation can be realised.
• This was a research trial so we had to use a square (5m x 5m) spacing to get the 400 trees/ha. In reality there is no need to stick rigidly to this configuration. Certainly if you wanted to cut silage or mow between the rows of trees, why not plant in wider rows with trees a bit closer in the rows? For example 8m x 3m spacing will give you roughly the same density and although the root network will be a bit slower to knit below the trees, you will still be getting most of the value to soil health and structure. And instead of having a post and wire fence to subdivide paddocks in a rotational grazing system why not plant even single rows of trees? These can be protected using offset electric wires splayed out from the ground.
• I would try and match the tree species to the site (soil, drainage, exposure etc.) and use a mixture of species if possible. This will reduce the vulnerability to disease spread - we could never had anticipated what was going to happen to ash but at least we had the trees long enough to learn the lessons and they are proving to be fairly slow at showing symptoms of dieback. Tree species have different rooting structure and patterns as well as different canopy structure and this helps enhance the ecological stability and resilience of the whole system.
• We based the trial on a sheep system as at that time (33yrs ago) there had been little development put into protecting trees in cattle systems. We need to make silvopasture viable on both sheep and cattle farms from establishment and there has been a lot of innovation in re-usable spike-repellent metal guards or electric fencing for tree rows.
• A big benefit of the system, which farmers particularly liked, was the flexibility in decisions on land use that it offers. For example, when the canopy starts to impinge on livestock productivity, the opportunity to either thin trees and allow a sward to recover or to leave them to develop more as a timber resource is attractive. They contrasted this with tying up land in a woodland or forestry system.
• Silvopasture lends itself very well to an organic system and to pig and poultry farming.
• Silvopasture is an ideal environment to establish Multi-Species Swards in – the emphasis could be on mixtures which show good shade tolerance properties.
• I would never envisage a silvopasture as having a clear-fell scenario. New, protected, trees can be introduced into the system at any stage creating a multi-structural canopy with the potential for huge diversity in delivering the multiple ecosystem benefits mentioned above.

How can I find out more about silvopasture?

Among others, there are 3 active organisations providing good advice and support for silvopasture in the British Isles - the Irish Agroforestry Forum and the UK Farm Woodland Forum. At a European level, EURAF, (The European Agroforestry Federation) is an invaluable source of expertise and experience with the wide range and diversity of forms in which agroforestry is practiced across Europe.

Jim McAdam, Irish Agroforestry Forum and Farm Woodland Forum