Why we cut down trees

© Paul Gonella

It’s the end of winter for us. 28th of Feb officially means we down tools and stop cutting as the birds are busy setting up territories to breed and nest.

I feel its very important to stick to this, many people do not and fell into March but working for the Wildlife Trust, one must set an example of good practice.

It has come to the end of the season for me to think that I should explain why we do an activity that looks so destructive. I’ve touched on it in other blogs but a number of comments from members of the public across our reserves has made me address the issue in a bit more detail. (I probably should have written this at the start of winter!).

It is all a matter of structure. This is the key work for the day, both in terms of time and space. Structure in the age of the trees within a woodland, as well as structure within the physical state of that woodland. Structure breeds a robust and diverse woodland that can cope with disturbance and provide more niches for specific species to occupy.

Secondary woodland diagram

© Chris Lycett

Diagram A

How do we achieve structure? Well, strangely I know, it involves cutting a lot of that wood down. It is however important to put this into context.

Take Swanwick Lakes nature reserve for instance. Once a clay pit, before that a mixture of woodland and farmland, it has gone through many transformations over the years. When abandoned in the 70’s, the trees grew in place of heavy machinery and industry.

This woodland developing on a site, where woodland has not been constantly is called secondary woodland. The problem with this if left untended is that it all grows up evenly at the same time, developing a uniform structure. Diagram A shows a simplified example of this. We call them lollipop trees as they grow tall and straight, battling for light, and form a little cluster of branches near the top and create a dense canopy with its neighbouring trees.

Little light therefore penetrates to the understory so no plants develop here unless they are very shade tolerant, ferns or ivy generally.

This isn’t to say that there is no value in this woodland, it is however more or less all in the canopy. It lacks structure. It would also mean that all the trees will reach maturity at the same time and all die, more or less at the same time.

So the solution is to cut some trees down. This is a process that we call thinning. How heavy you thin will depend on personal taste and what woodland you are dealing with but normally it is between a 1/3 and 2/3 trees removed. A forester would walk the woods and remove trees around the good looking, straight hardwoods that will grow on and produce a crop.

We however aren’t interested in timber production. we want the trees that remain to grow on and become old and gnarly and rot in places. This adds more value to the tree in terms of biodiversity. In fact we regularly thin and leave the not so nice trees in tact so they grow in weird directions and produce biologically interesting trees.

Thinned woodland diagram

© Chris Lycett

Diagram B 

Diagram B shows a woodland after thinning. There are now gaps in the canopy that allow in light. A flush of ground flora will develop – bluebells or ramsons, lesser celandine or violets. In areas thinned more intensely, grasses and more light specific plants develop and create glades.

Crucially whoever, a middle storey develops. Perhaps shrub species grow on such as nectar rich bramble or trees that have been cut back. Hazel, willow, blackthorn, species that live in the lower section of a wood will create a thick layer from the middle of the wood to the floor. This is vital for many bird species such as the dramatically declining nightingale and many mammals such as hazel dormice.

The trees that are left  grow on and expand, branching out and becoming rounder and more stable.The canopy is still there but is more fragmented so the canopy species persist. It has gone from a 2D landscape of canopy life to a 3D landscape where birds, mammals, invertebrates persist at all levels throughout the woodland.

Go on 50, 100, 200 years and the woodland will have grown and be in the latter stages that the woodland reaches where biodiversity is at its highest. (diagram C) Some trees have grown old and died and but remain standing, producing wonderful habitat for inverts and woodpeckers, holes for tree nesting species.

Given a management regime such as coppicing the woodland will have different generations of trees, giving robustness for the future as well a diversity. The coppicing will have produced a continuous thick middle storey in ever changing parts of the woodland, creating open spaces for wildflowers and nectar producing plants .

Old woodland diagram

© Chris Lycett

Diagram C

Often people tell me that I should be leaving the woodland just to do it’s thing. It’s complicated as other organisations tell people to do this, that trees shouldn’t be cut down as we lack trees within our landscape. And quite rightly too! We do lack significant woodland in the UK.

However, this needs to be taken in context. We lack high biodiversity woodland as well as the physical quantity within our landscape. You could argue that less, well managed woodland would be better than lots of woodland left to its own devices as biodiversity per square metre should be higher. You can imagine that eventually woodland left to its own devices may become dominated by species such as rhododendron or sycamore, significantly reducing its value to our wildlife.

Management (crucially not over-management) is only replicating natural processes from species of large herbivores that no longer live in our country. Therefore it is important that we sympathetically cut down trees in some of our woodland.