For many centuries, particularly before Common Land was Enclosed, much of the country was farmed as ‘wood-pasture’. The New Forest is an example but Mottistone Common would have been much the same albeit on a smaller scale. It was true then and remains so today that it is perfectly possible for land to provide both grazing for livestock and the products and benefits of tree/woodland cover. Typically, trees were cut at a height beyond the reach of cattle enabling the regrowth of shoots which could then be harvested as poles or firewood etc. Trees managed as pollards have their lifespan much extended with oaks living for many hundreds of years. Windsor Forest is a good example. Our thinking today is such that we mentally separate these land uses. (Have we forgotten that putting sheep into orchards was routine?) Government incentives for tree planting and woodland management have largely required the exclusion of livestock reinforcing the unacceptability of wood-pasture as a method of farming. But now there is a more open-minded attitude towards agroforestry which can operate in several forms (to be discussed below). Perhaps we should take a leaf from our European friends such as the Dehesa system in Portugal and Spain where pigs graze under cork oaks or in Crete and other parts of southern Europe where barley is grown under olive trees. Nearer home The Pig Restaurant in Brockenhurst serves up ‘Pannage Pork’ from New Forest pigs that have feasted on the acorn crop. The product is Britain’s answer to Spain’s world famous Iberico ham.
However, a note of caution. There are many Ancient Woodlands where grazing was not a traditional practice. Introducing livestock to such sites can be damaging to the wildlife interest. Grazing at a high enough density and frequency can kill trees and prevent natural regeneration. Ultimately a woodland can be reduced to pasture only and those trees large enough to resist the grazing pressure. Many upland woodlands have suffered in this way where dilapidated fences permitted excessive grazing particularly when Headage Payments encouraged overstocking.
It is always difficult to pin down exactly where the modern-day term of agroforestry originated. It’s perhaps fair to identify the Wakelyns Farm in Suffolk as the leading light with Professor Martin Wolfe’s pioneering work in 1992. Martin was following ‘the abundant evidence that simple mixtures of crop varieties can provide a way forward from monoculture to more natural control of plant disease without external inputs…’ with ‘…agroforestry being the deliberate integration of trees with other crops on the same land area to gain benefit from the natural interaction within the whole growing system.’
Martin’s approach was to plant rows of trees to form corridors between 12m, 15m or 18m apart termed ‘alley cropping’. The trees could be willow managed on a short, 3-year coppice cycle for use in hedging, weaving or chipped for supplying a biomass boiler. There were also fruit trees: apple, pear, plum, quince, peaches, apricot, medlar etc in different combinations. Further biomass material was based upon longer (7-year) coppicing of hazel. Within the alleys the land was farmed on rotation with the growing of grass and cereal crops. In more recent times the alleys are also being used for vegetable production.
This experiment, which was never intended to be scientifically robust, helped stimulate how the concept of agroforestry could be developed. Some of the, not unexpected, findings were:
- The edge effect of trees reduced crop yields – the middle of the alley less affected than the shaded edges although the yield of some crops such as oats were perhaps less affected
- Grass leys and cereals suffered from the edge effect from the adjacent willow crop but recovered after harvesting the coppice material.
Do these findings negate any benefits agroforestry can provide? Overall no, because whilst cereal or grass production my be reduced the gain in harvested biomass and other food products more than compensates. In other words, more is obtained per hectare of land than would be obtained from growing the crops in separate plots. Yes, the trees create shade, but their roots are extending more deeply than and not necessarily competing for water and nutrients from the alley crop. The annual leaf drop can add fertility to the soil making previously unobtainable nutrients available for the grass/cereal crop.
With hindsight it might be argued that the alley widths were too narrow so some of the results were not to be unexpected. Those practising alley cropping now seem to use much wider distances between tree rows so the balance switches in favour of the cereal/grass crop whilst still gaining much from the tree products.
If the starting point today is that tree planting is needed to capture carbon, ignoring all the other benefits, what are the agroforestry options and how can they be applied in a practical manner?
Agroforestry Options
In its simplest form hedgerows are a very conventional form of agroforestry. They provide, at the very least shelter, but food and fuel can also be harvested. So, should farms be looking to see if new hedge planting could provide a benefit? Few would argue that the 1960’s incentives to grub hedges went too far. It’s not unusual to see where the location of former field boundaries often marked a change of soil type. This usefully meant that the treatment of two fields according to their soil type was more efficient than one large field where cultivation may have suited one part but not all and crops would ripen unevenly. The value of hedgerows for wildlife and the farm’s landscape should of course not be overlooked.
For the keepers of livestock hedgerows are essential to provide protection against the extremes of weather. Heat stress is a very real problem with today’s climate change but exposure to relentless wet winter weather also needs stock protection behind robust hedgerows. Cold wind and rain can so chill an animal it must maintain body heat by increasing its energy requirement. (Mid December this year is recording nights with sub-zero temperatures) Lambs can lose 10C of body heat in their first half hour of life without sufficient shelter. At the extremes of heat (as this year’s summer), the animal will direct blood to the skin to aid cooling leaving the digestive tract permeable to toxins and potentially rumen acidosis. As a guide, cattle may start to suffer heat stress at 18C, moderate heat stress at 20C and severe stress at 25C. A temperature of 31C can be dangerous for the animal. We can all appreciate how the shade of a mature open grown oak tree can bring relief on the hottest of summer days.
Livestock with access to hedgerows and other trees or shrubs can also be provided with a valuable natural food source. Aspen and willow are particularly palatable and can withstand grazing, closely followed by ash rowan, hazel, and oak. Holly, birch, and hawthorn can all be grazed with beech and alder being least palatable. Some of these plants also have the additional benefit of having an anthelmintic effect. Trees such as small-leaved lime can be pollarded to provide an endless supply of forage.
If the tree planting goes beyond the hedgerow and into the pasture (Silvopasture) the value of the shelter provided can reduce perinatal hypothermia in lambs but also provide earlier grass growth and a reduction in the time cows, calves and ewes need to be housed. Where trees cover is high enough the effect can be to elevate the ground temperature by up to 6C.
Many famers practising agroforestry have established trees in set plots or as a scatter of trees across pasture to help dry wet ground, improve soil quality and reduce run-off on steep ground with vulnerable soils. Willows can be used to stabilise soils on fields subject to flooding to form a ‘green, leaky dam’. Harvesting the willow for chip is possible and bees make used of early pollen production. Water that would otherwise carry diffuse pollution is filtered out and the drier ground less vulnerable to poaching.
There are no rules as to how trees may be planted, their density or choice of species. Some examples:
George Young, Fobbing Farm, Essex – Woodland belts 40m apart with trials of different crops in between. The inclusion of heritage fruit tree and native shrubs were in one area. Fencing the plots will enable the option to graze the woodland although biodiversity is a key objective with habitat provided for beneficial insects.
Henry Andrews, Leworthy Manor, Devon – Prompted by the observation that cattle, given new access to a 200 x 15m wooded margin of oak, alder, willow and silver birch, appeared more content and grass growth between the trees was better than the open field. Extending this woodland cover with 10 alleys of trees/shrubs 20m apart was established and protected with electric fencing. Livestock graze the alleys which are reduced to 18m in width by the fence. In time, removing the fence on one side will enable livestock to fully benefit from the browse, shelter, shade, nutrition and worming properties.
Simon Peet, Langwathby Hall Farm, Cumbria – 16 ha of willow of different varieties were planted near the River Eden which floods every year. The wood chip has a potential annual return of £618/ha. Trials on a similar plantation have been grazed with ewes prior to harvest gaining protection from the cold and wind. No damage to the crop was identified.
John Pawsey, Shimpling Park Farm, Suffolk – Planting of 4.5m wide trees strips (oak, cherry, hornbeam, aspen, goat willow) separated by 36m wide alleys for two-year grass followed in the third year by spelt . The planting has provided a wildlife corridor and the expected benefits include water efficiency, soil health, carbon sequestration and shelter. Material will be harvested by coppicing the trees/shrubs with goat willow providing browse for the sheep flock.
Bob Waller, L J Fairburn & Son, Lincolnshire – To improve the health and animal welfare of ranging hens, shelterbelts were planted in blocks each containing 30-50 trees within areas of 30-40sqm. The tree mix was silver birch, elder, oak and beech. The woodland environment is reported to have improved bird welfare allowing them to behave more naturally with a reduction in stress. The birds feel safer, scratching is more diverse, heat stress is reduced as is aggression.
Hen Curtis, West Emlett Farm, Devon – A 4ha field was divided into four areas with fenced 12m wide tree belts occupying 20% of the field. The planting set larger trees (oak, scots pine and aspen) centrally which are protected with hawthorn. Alder and birch are planted either side along with additional shrubs. Another area was planted with open grazed tree clumps protected with thorns and shrubs. The project was to create a ‘living barn’ to enhance the production and welfare of their suckler beef herd with the browse providing additional minerals in the sheltered and shaded tree cover.
Agroforestry can also be applicable to land under cultivation. As with silvopasture, S silvoarable can be applied in many ways. One well known example, apart from Wakelyns, is that of Stephen Brigg’s Whitehall Farm in Cambridgeshire. On 50ha of his 100-ha farm he has planted apple trees on semi-dwarf rootstock with 23m wide alleys. This very commercially viable planting also prevents soil erosion, provides resilience to climate change and a significant boost to the farm’s biodiversity.
Another very different approach is being applied at Broadlears Field on the Dartington Estate in Devon. Within a 19 ha fields there are rows of elder and apple trees planted in north/south rows. The elder is in double rows 4m wide with 3m spacings leaving a 15m alley for a range of cropping. The apples are in single lines in strips 3m wide. The choice of species was carefully thought through with the elder being planted for flowers and harvested to produce cordial. The strips are effectively sublet so the farm tenant focuses entirely on the alleys.
At Julian Gold’s, Hendred Farm Partnership in Oxfordshire 100m of a diverse native hedgerow was planted on a Countryside Stewardship flower strip with a double line of hazel with plants at 2m spacing in two staggered rows. This will enable one side to be coppiced on rotation for sticks or biomass chips.
In summary, agroforestry can be applied in all types of farming/food production:
- Silvopasture – trees with animals such as sheep, cattle and poultry etc.
- Silvoarable – trees with field scale crops, typically grain.
- Silvohorticulture – trees with market gardens and fruit and vegetable crops on a smaller sale
The application of agroforestry within a livestock system is an obvious choice but there are opportunities within an arable cropping in which trees can provide an additional product. For those who wish to try agroforestry only tentatively, planting some new hedgerows is a good place to start. Of course, there is almost always scope to establish some extra tree cover on most farms. This may be simply to enhance the farm landscape or provide an extra area of wildlife habitat so why not put tree planting on your ‘things to do’ list but get the planning underway now for next winter’s planting.