In addition to playing a vital role supporting productive agriculture, trees can help farms adapt to climate change whilst improving environmental performance, wildlife conservation, and generating income
The importance of shelter
Introducing trees in to the crop environment can help modify soil structure and impact crop water regimes.
Trees reduce the ambient temperature beneath the canopy as a result of the evaporation through leaf surfaces. They also provide shelter that can help reduce the impact of cold weather.
Crop yields can improve with shelterbelts as a result of improving the microclimate and plant growth.
Using native deciduous trees provides the greatest shading during the summer months and the best available solar gain to benefit buildings and livestock during the winter.
What can shelterbelts do?
- Reduce heat costs and carbon emissions;
- increase daytime temperatures;
- alter the speed and direction of wind;
- reduce physical damage to crops and reduce the incidence and variety of plant diseases;
- have a positive impact on pasture growth (by increasing water infiltration);
- encourage pollinating insects, provide food and act as ‘highways’, guiding the movement of bees, hoverflies and other pollinators;
- improve food efficiency, weight gain and animal health of outdoor livestock through reduction in the wind-chill factor (especially with young livestock where it has been shown to improve the survival of lambs);
- help improve animal welfare and productivity;
- help stabilise river banks and prevent further erosion;
- reduce heat loss from buildings in the winter and provide shade in the summer (shelter can reduce heating costs by 5%)
- help reduce soil erosion and siltation of watercourses.
Benefits derived from shelterbelts can be maximised if a detailed farm audit is carried out to find the areas of most need on the farm.
Effects of shelter can vary with shelterbelt design, soil type, crop, stage of crop development and geography. The porosity (how easily wind can flow through the shelterbelt) and height largely determine the level of protection given by a shelterbelt.
- A shelterbelt of less than 40% porosity will reduce wind speeds by as much as 90% and protect an area up to 10 times the height of the shelter.
- Tall shelterbelts with an optimum porosity of between 40-60% protect an area of up to 30 times the height of the shelterbelt creating shelter suitable for crops.
- Those composed of native deciduous trees are well adapted to local conditions and have a leafless period which allows pasture to recover in winter from the adverse effects of shading.
- A well-watered crop protected by shelter may use the same amount of water as a non-sheltered crop but would have increased photosynthesis rates and therefore increased water use efficiency. This is due to lower wind speeds increasing the level of humidity around the plant surface, slowing evapotranspiration water loss.
Potential effects of shelterbelts
- Trees can shade crops and compete for water and nutrients, reducing crop yields adjacent to shelter. Reductions typically occur up to a distance of 1-2H from the shelterbelt (H representing the shelterbelt height). However increases in yield gained throughout the rest of the crop achieved through more efficient water use can counterbalance this.
- Careful selection of trees (choosing deciduous rather than conifers) can reduce the negative effects of shelter.
- In the right conditions, native tree shelterbelts can enable crops to use water more efficiently.
- Shelterbelts can be viewed as an insurance policy by their capacity to buffer crop production when extreme weather events strike; shelter from trees can be beneficial for reduced water use.
To read more about the potential beneficial effects of shelterbelts on the water regime of pasture and arable crops, and specific shelterbelt recommendations, please click here.
Reduction of air born pollutants and emissions
- If located around farm buildings, trees can act as buffers and contribute towards mitigation of air born pollutants including ammonia emitted from livestock units. Studies have shown that shelterbelts next to livestock units can reduce ammonia emissions by up to 10%. The high ratio of leaf surface to ground area of native trees makes them ideally suited for this.
- Native trees can be planted in the path of emissions from livestock units to help buffer important habitats.
- Trees removed as thinnings from plantations or as coppice can be chipped and used to provide bedding for housed livestock. This can have cost advantages over straw and make excellent soil improver, reducing the release of volatile nitrogen compounds in to the air.
Benefits of game cover
- Development of the woodland edge is particularly important and can be achieved by expanding existing woodland.
- Well sited woodland can increase the potential of game shooting on farms through increasing the area for feeding and shelter. The Game and Wildlife Conservation Trust offer advice on sporting woods.
How can trees benefit farm income?
Establishment and management of native woodland to produce timber can help diversify farm income in various ways:
- Large timber can be sold off the farm or converted for use on site;
- smaller diameter timber of species such as oak and sweet chestnut and branch wood can be used for fencing, as firewood, be chipped for livestock bedding or sold to bulk markets;
- specialist uses (with local demand) such as thatching spars, birch for horse jumps and willow for basket making can generate income;
- woodfuel biomass energy generation can help secure part of the farm’s energy needs and lead to reduced on-farm energy costs;
- potential future income from ‘carbon finance’.
Effects of trees on soil and watercourses
Trees can help limit effects of waterlogging and drought on soils through:
- Diffusing pollution, by capturing ammonia emissions;
- reducing water run-off and the risk of flooding through targeted tree planting on arable or pasture. Flood alleviation is a cheaper and more sustainable option than hard-engineered flood defences. Strategically sited woodland can delay flood flows, increase flood storage (through the sponge effect), and reduce rapid surface water flooding and peak river flows;
- improving soil infiltration rates; they can be up to 60 times higher under young plantations than heavily grazed pasture, with infiltration rates improving by 90% within two years of tree planting;
- reducing soil sedimentation and runoff; when used as buffer strips alongside watercourses, planted on steep slopes or along contours, trees and hedges can reduce sedimentation and runoff from manure and fertiliser following heavy rainfall by as much as 90%;
- reducing soil erosion – erosion caused by heavy rainfall can be minimised by planting trees across contours or in areas known to be vulnerable, preventing soils being washed away;
- reducing water pollution acting as nutrient sinks by trapping pollutants bound to soil particles. Tree/grass buffers can be effective in removing phosphates and lowering nitrate levels in run-off;
- and by providing dappled shade to watercourses and lowering water temperatures, helping to improve oxygen levels and benefitting fish and other wildlife.
Trees can also:
- Reduce the risk of run-off and leaching of fertilisers and manures into streams and rivers;
- slow the speed at which water reaches rivers and drains and help delay flood peaks by spreading the time over which water runs into streams and rivers;
- act as a buffer around yards and buildings, capturing airborne pollutants and accidental spillages.
Trees as fodder
Species of deciduous trees have historically been used for fodder and research is showing growing interest in exploiting browse as an extra resource from trees planted for other purposes. Research shows that:
- Trees can provide alternative feed resources during periods of low forage availability.
- The nutritional and mineral composition of tree fodder varies depending on the species and cultivars, season, age of growth, climate and plant parts utilised (leaf versus stem)
- Nutritive value and digestibility will peak in spring and decrease through to autumn. Willow for example would be of highest nutritional value in the spring and decline in the summer as plants mature and fibre and lignin content and structural carbohydrates increase while protein content decreases.
- Tree management influences the chemical composition of fodder; management by short rotation coppicing produces fresh growth with a high leaf-to-stem ratio, low in lignin and high potential feeding value compared to mature trees.
- A major consideration with using tree fodder is the method of harvesting and feeding; manual cutting and transporting is laborious and time consuming, direct browsing requires careful management that balances keeping the tree height accessible to livestock with minimising damage to the tree.
- The greatest opportunity for tree fodder may be as a buffer feed during seasonal shortages of forage, reducing the need for purchasing feed imports.
- Fast growing trees can provide a large quantity of material whilst delivering a range of other benefits to animal welfare and the environment as well as providing a local renewable resource energy and helping to diversify a farm economy.
Sources: Integrating willow-based bioenergy and organic dairy production – the role of tree fodder for feed supplementation and The Use of Novel and Under-Utilised Feed Resources in Organic and Low-input Dairy Production
Woodlands and forests provide resilient habitats for wildlife.
- Trees can contribute towards capturing atmospheric carbon.
- Wood fuel as a renewable energy source can also reduce carbon emissions by displacing fossil fuels. This can reduce energy costs associated with the rising price of fossil fuels.
Renewable energy; some wood fuel facts
Wood fuel is a renewable low carbon fuel that can be specifically grown for this purpose or as a co-product of timber production. It can be grown in areas that are difficult to farm.
It can be harvested from existing woodland, from trees planted for other purposes i.e. providing shelter, or by creating new woodland.
Use of native trees species brings a double benefit of producing good quality firewood and supporting biodiversity which helps create a diverse and resilient farming system.
The first harvest of timber from new woodland is likely to be at around 15-20 years.
Three to five hectares of woodland is needed to heat the average three bedroomed house. Larger areas of woodland could feed a boiler to heat other farm buidlings.
Wood fuel can be sold off the farm to create an additional source of income.
The UK Government’s Renewable Energy Strategy highlights the importance of wood fuel as a way of producing heat and reducing emissions. Demand and price of wood fuel has increased since the introduction of the Renewable Heat Incentive.
Looking for information specific to the South West?
The Silvanus Trust can provide advice and signposting on forestry related matters to farmers, and organise forestry related courses through the Skills scheme. This could be useful if you are wanting to diversify into the forestry sector or are interested in managing farm woodlands.
It hosts the SW Woodland Directory, an online searchable database of woodland related businesses, designed so that you can find the right person for the job based the most local to you. Listed businesses include arboriculturalists, timber buyers/suppliers, coppice workers and craftspeople and training providers. So if you are looking for someone to provide agricultural fencing, thin your farm woodland or provide you with woodfuel to heat your premises, then this is the place to look.
Farming and Forestry Improvement Scheme – The Silvanus Trust is able to offer advice and assistance for forestry businesses (which can include farming businesses that have diversified into woodland work e.g. firewood processing) wishing to apply for funding through the FFIS. The service is offered to the whole of the South West but is free of charge for Cornwall based businesses.
Natural England – Farming and Climate Change
Farming Futures magazine – Green Futures March 2011
The Woodland Trust & Harper Adams – Managing the Drought
Farming Futures – Factsheet 15, Focus on forestry and woodland
To read about the challenges for forestry and woodlands in the face of climate change, and actions that can be taken by farmers and foresters to help mitigate the effects please click here.
The Woodland Trust has published a series of reports demonstrating how trees can help support productive agriculture providing multiple benefits such as increasing water infiltration rates, protecting watercourses from pollutants and increasing crop yields. To download the reports and access information on how the Woodland Trust can work with farmers click here.