Planning woodland and tree management on an arable farm

By Kathryn Smith | 3rd March 2023 |

RSPB Hope Farm, Cambridgeshire; 181 ha arable farm

Aims

RSPB Hope Farm seeks to restore biodiversity, whilst maintaining productivity and profitability. As part of this, the RSPB is seeking nature-positive ways of minimising greenhouse gas emissions, adapting to and mitigating climate change. Trees and shrubs can lock up carbon and the aim here is to plan creation and management to have the highest net value for biodiversity, improve resilience, carbon sequestration and storage whilst maintaining or increasing agricultural productivity and profitability. It is important to note that many semi-natural open habitats, such as species-rich grassland, are also important for carbon sequestration and storage, and so it is essential to protect and restore these alongside any woodland creation.

Key benefits for biodiversity arise from making wooded habitats “bigger, better, more, connected” (Lawton Report), or to list these in priority order for net biodiversity gain: better, bigger, connected, more. Hence the initial focus at Hope Farm is on increasing the wildlife value of existing woodland. Woodland expansion should not be a priority where this would compromise the condition of open habitats or the status of species which thrive in open landscapes, such as Skylarks, Lapwings and Corn Buntings. However, at Hope Farm there is clearly scope to have both more trees and more Skylarks through strategic design of woodland creation. A specific species priority is management to support the Turtle Dove, which is an increasingly rare farmland bird that nests in tall, dense scrub over 4m in height.

Management

Woodland quality and enhancing the wildlife value of the trees is the approach at Hope Farm, using the Lawson principles set out above.

Better

The Woodland Wildlife Toolkit highlighted the likely presence of the following species of conservation concern in this area (species in bold have been recorded on the farm):

Bats: Barbastelle, Noctule, Soprano Pipistrelle, Brown long-eared
Birds: Garden Warbler, Spotted Flycatcher, Willow Warbler, Marsh Tit, wintering Woodcock
Butterflies: White-letter hairstreak
Lichen-rich deadwood
Hazel dormouse

There are no known Invasive Non-native Species of plants in the small existing area of woodland on Hope Farm, but the woods are prone to damage from non-native Grey Squirrel and deer, and rabbits can also prevent natural regeneration in some areas, which may compromise how we manage our woodlands for wildlife.

Audit

We undertook an audit of hedgerow trees on the farm to develop a protection and recruitment plan for mature and over-mature trees. There are no ancient trees (over-mature, age depend upon the species) on the farm currently. There are a few veteran trees (shows signs of over-maturity, but not necessarily old enough to be ancient) including one used for nesting by Barn Owls and a hollowed-out, pollarded Ash.

Veteranisation

There are a number of mature trees present, some of which could be used for veteranisation. This is the act of deliberately causing damage to a tree to mimic natural processes that leads to the creation of tree holes and decaying wood and is done to create the habitat for deadwood invertebrates and ensure the survival of species reliant on this habitat to bridge the gap between the loss of standing deadwood in the landscape and the recruitment of a new generation of ancient trees. Bats would also benefit from increasing the number of veteran trees on the farm. Some trees at the southern area of the farm could be veteranised to provide nesting opportunities for Spotted Flycatchers. Pollarding is another form of tree management than can extend the life and create veteran features in mature trees. Where they are not flower-rich, the wide field margins on Hope Farm can accommodate any fallen deadwood to provide this resource for invertebrates, fungi and lichens.

Hollow pollarded Ash in an open area of the farm. Pollarding it could ensure that it does not become a nesting site for nest predators and may protect it from Ash dieback.

Plantations

There are a few small areas of native woodland and relatively new broad-leaved plantations around the farm. Through opening up the dense plantations by thinning and selective felling of non-native species, we may be able to benefit Spotted Flycatchers, Marsh Tits and wintering Woodcocks. Management could also diversify the canopy height and create a shrub layer, which could be designed for nesting Turtle Doves. Scrub around the edge and within the woodland could be managed on a 20-year coppice cycle to maintain this feature in the habitat in the longer term.

Some of the trees could be veteranised, rather than felled to create the deadwood component for bats and lichen. We will aim to maintain the older native trees as standards and give them space to have full canopies as they mature. Two small plantations within the core area for ground-nesting birds could be converted to tall scrub as potential Turtle Dove nesting habitat, as there is no scope to connect them to other woodland areas without compromising the landscape for species like Lapwing and Skylark.

Two small, dense plantations including a pond in the middle of the core area for ground-nesting birds would be ideal for converting to open tall scrub for Turtle Doves through gradual thinning and establishment of shrub species. Rabbit protection will be needed for the shrubs to establish.

Transition

The edge of the plantations can be managed to provide a transitional zone from the open grassland of the field margin, through scrub to canopy woodland to provide the widest range of habitats for the greatest range of species. In some cases, the plantation is bordered by a hedge around all sides, and this could be laid to create a barrier to prevent heavy deer browsing. Where dense plantations were created on former farmland, the ground flora is impoverished. This could be enhanced through plug planting native woodland flora of local provenance to take advantage of the more open nature of the habitat letting more light through to the ground layer. Two of the small woodland areas have ponds within them, and the southern border could be opened up more to provide more light to the water surface to enhance the aquatic life of the ponds.

Bigger

At Hope Farm, we have mapped out the areas that are important for ground-nesting birds which avoid tall field boundaries and woodland [insert map of priority ground-nesting bird areas]. These tend to be the larger and open areas of the farm (fields or field combinations with open field boundaries greater than 20ha). Habitats vulnerable to the shading effects of dense tree and woodland cover include open, flower-rich habitats and farm ponds. It is important to prevent shading of the southern border of these habitats. It is also important to avoid planting on existing wetland habitats, but this is not relevant to Hope Farm. . However, any existing mature trees in these locations will be retained. Those with Ivy or old growth features may provide nesting habitat for Spotted Flycatchers.

Some new hedgerow tree recruitment has taken place within the priority area for ground-nesting birds. These could be managed by pollarding to prevent them becoming nest sites for nest predators.

Woodland expansion

Target areas for woodland expansion were determined in reference to areas of existing woodland, areas of habitats and species vulnerable to shading or presence of woodland features and yield maps of crops. In general, areas around existing woodlands were neither good for ground-nesting birds nor highly productive crops, and therefore presented opportunities to make these habitats bigger. These are also likely to be the most effective areas to enhance woodland biodiversity (by buffering existing woodland), allowing natural colonisation and enabling woodland species to move into the developing woodland. This was checked against the woodland creation tool in the e-planner developed by the Centre for Ecology and Hydrology, and this confirmed that woodland creation would be best targeted at expanding Overhall Grove, and along the stream running through the southern area of the farm.

Natural regeneration

Overhall Grove is an ancient Elm woodland SSSI and nature reserve on the eastern boundary of the farm. Where possible, we will use natural regeneration for woodland expansion into field margins and corners abutting existing woodland to ensure local provenance. Overhall Grove also has disease resistant suckers of English Elm, which should ensure their long-term survival. Otherwise, disease-resistant local stock should be sourced.

A couple of mature Elm trees on the farm which could be connected with the Ancient Elm woodland through a taller hedgerow corridor through the farm

Optimum value

For optimum biodiversity value, it is recommended to leave a quarter of the area of new and expanded woodlands as open glade habitat.

Where natural regeneration is not an option, native species found in the landscape from local provenance will be planted to avoid the risk of importing diseases and pests and to ensure that the stock are well acclimatised to the local conditions. Trees will be only sourced from peat-free nurseries. (specific) Elm is an important species of the area, but disease-resistant trees will be required.

The long-term management of new woodland areas will be planned into work programmes, as it is important to set aside sufficient management time to successfully establish and maintain these developing habitats over 20 years or more, rather than seeing woodland creation as a few days of planting. Long-term management will need to consider the trajectory of climate change and whether any additional adaptation and mitigation is required.

Connected

A network of hedgerows currently covers about 80% of the field boundaries around the farm and hedgerow trees are relatively scarce in this open arable landscape.

This exercise started with an audit of woodland and tree cover and record of hedgerow types around the farm. Within the boundaries of the key fields for ground-nesting birds, the aim is to prevent an increase in the height of field boundary hedges or an increase in hedgerow trees. Hedgerow expansion (height and width) and new hedgerow tree recruitment is planned for field boundaries away from these fields and ensuring that such hedgerows form a connected network between woodland areas.

Corridors

In terms of opportunities for woodland connectivity, there is Overhall Grove and several small blocks of broad-leaved woodland within and adjacent to the farm, where we can increase connectivity through the management of the field boundaries. Key connectivity corridors can be targeted along the eastern boundary of the arable land and along the stream entering the southern end of the farm.

These corridors can be enhanced through allowing the hedge to expand in width and height, and allowing more hedgerow trees to grow up through the hedge. These provide better commuting and foraging habitats for bats and less mobile species reliant upon the woodland habitats on the farm. These corridors will become increasingly important as our climate continues to change, allowing species to track their climatic requirements and move through the landscape.

The area of wooded habitat at Hope Farm can be further expanded through the use of Agroforestry. We are currently trialling the use of agroforestry in one field to explore the impacts on productivity and profitability (including produce from the trees themselves), as well as biodiversity and carbon sequestration. Low density planting in the small paddocks on the farm would be another opportunity, which may offer important shade for grazing stock.

Achievements

The plan for better, bigger, connected and more woodlands at Hope Farm is shown in the map below: