Woodland thinning and tree removal are an essential part of greenkeeping. It’s necessary to ensure optimum turfgrass quality by way of air flow and light penetration. Every site is different, displaying its own unique ecological and environmental characteristics. So greenkeepers must be clued-up or seek professional ecological advice from experts, before they start tree work. Getting guidance from social media or greenkeepers sporting ‘ecologist’ after their name could put you in hot water.
There are many factors that need to be considered, but in this article, I’m going to focus on structural diversity and the need to acknowledge the value of all trees big and small. Removing smaller trees and leaving only larger trees will be negative from a wildlife and longer term landscape perspective.
Tree removal for benefit of the turf should not be undertaken under the guise of ecological improvement. If greenkeepers consider such work, then the advising ecologist should also recognise the need for mitigation and compensation. They must also work with the club to ensure ecological gain elsewhere.
Understanding Structural Diversity
Well managed grassland heath and woodlands all have one thing in common – canopy structure. These habitats are characterised by their own unique vegetative structure consisting of several vertical layers.
Grasslands will support a dense surface mat of more fibrous growth that may give way to a low-level canopy of lower growing species, such as is found with the Agrostis genus.
Fescue will provide a slightly higher canopy level, which in turn will give way to yet taller species such as false oat grass or cocksfoot. This will provide a whole suite of ecological niches for invertebrates from which they can feed.
Heathlands are also built up as a series of canopies from low growing plants, to grasses and heather. Single patches of heather are often discussed in terms of the need to develop structural diversity.
Woodlands are the most obvious and most distinct to view. Woodlands in optimum condition will support a low ground layer supporting the plants of the woodland floor, such as bluebell wood anemone and wood sorrel.
This layer gives way to the taller field layer of species such as bracken bramble or the taller forbs like foxglove. Young seedling trees will occupy both layers.
The next understory layer is also often known as the scrub layer. This is an important layer as it contains the trees that are waiting their turn to move higher, to the low mid and higher canopy layers. Some trees such as rowan or hawthorn will only ever form the scrub to low canopy layers. However, birch and alder will go on to form a mid-canopy. Oak and beech will grow on through to eventually provide the tallest upper levels.
The importance of structural diversity
Why is all this important? The fact is the stronger the structural diversity, the far greater the opportunity for niche occupation.
Different species of birds will feed and sing at alternative levels through the woodland canopy. They will use the margin of the woodland at varying heights for vantage and territorial display. Within heather, different invertebrates will utilise differing sections of the canopy.
Grouse are well known on our moorlands for their need of structural diversity. Therefore we burn the heather on a phased rotation.
Bats are often thought to inhabit the cracks and crevices of taller trees but they are also found in similar places within smaller trees, look at the two pictures. Bats have been found in trees supporting stem diameters less than 9cm.
A major reason why structural diversity is important within woodlands is because it provides woodland continuity; young trees waiting their turn to grow and become mature. Greenkeepers can flippantly view dense woodlands as untidy crowded or scrubby and undertake erroneous management to improve them.
The normal management in improving woodlands tends to concentrate on the removal of the smaller scrub and weak or spindly trees. But this is the understory or low canopy layer. Removing it will take away a fifth of the woodland.
This will have a major impact on the resident wildlife that formerly sought benefit. We often pay homage to the larger trees but the understory, “that scrub layer”, is the future forest. This layer is just as important as the more obvious and more significant trees.
Crucially, you must understand the importance of structural diversity in all habitat types and recognise the key components. It you are struggling, seek professional advice before imparting management that could have a very negative and devastating impact on your course.
For further information on any of the above, please contact our qualified ecology team on 01274 565 131 or email firstname.lastname@example.org