Is tree planting good for biodiversity and does it help reduce the risk of flooding?

By Mr. Phillip Marshall

Planting trees is only the beginning of the process to reduce flood risk, capture carbon and make an area more beautiful.  Phillip Marshall, a local resident in Todmorden has managed woodlands for many years and he has written below about how well managed woodlands can reduce flood risk and provide many other benefits to the communities in which they are created.  

However, clearly, woodlands must be managed, not just planted and Phillip sets out his views about this in the blog below. 

You can read about other woodland schemes on our website like the one at Carr Head in Pecket Well, Hebden Bridge.  Soil health is also hugely important, and you can read more about how healthy soils are just as important as planting trees here

Slow The Flow is delighted to support the work of local people like Phillip who work to ensure woodlands are managed properly.

Phillip’s Blog

Is tree planting good for biodiversity and does it help reduce the risk of flooding?  My answer would be ‘not necessarily’, or even ‘probably not’

Why would I say this? 

Having watched tree planting schemes in various places over the last 40 years, I wonder about their future.

Perhaps this wouldn’t matter so much if the original schemes had taken place over a number of years and reflected the historic disturbance and variation that woodlands have always been subjected to.  But the close spacing of various species, that have different habitat requirements, is also part of the problem. 

It remains a popular notion that planting many trees and creating shade will eventually make a woodland.  Historically, woodlands were never so.  There is much evidence that trees and scrub were interspersed with open glades and extensive grassland.  It is recognised that today’s mature woodlands are the shadiest they have been in all history, yet much of the new planting is well on the way to replicate this if no intervention takes place.

Most biodiversity of insect, plant and birdlife is on woodland edge.  Butterflies need grassland and scrub.  How many butterflies do you see in a woodland?

Over the last 35 years I have been managing woodland and been amazed by the difference it makes.  Where the soil was totally bare due to shade; grasses, flowers and scrub have appeared, leading to a vast increase in birds and butterflies. 

Very few native trees enjoy shade.  Most prefer space and sunlight.  Oaks, for instance, are not a climax tree within a woodland, they are a pioneer; their acorns are always planted by Jays and mice in open ground. 

Oaks are not happy with competition and lose heart.  They become stressed by close neighbours.  Give them room to grow and you get trees with branches, which allow for more growth in the trunk diameter, root strength, and Carbon capture. 

Was bare ground. Now Reeds and flora, all absorbing water in the deep sod

It is essential that management of new woodlands is planned from the start.  It is quite depressing to enter a dark, even-aged 30 year old plantation and find that little representing a tree remains. 

Think trees with branches.  Leave, or promote space.  A sod of grass is full of stored Carbon.  To destroy its function of storing water and Carbon, by killing it with shade, should be seen as failure.

Open glade with ground flora. Water run-off stopped and absorbed by plant roots

Coppicing (promoting new shoots by cutting near ground level) is a traditional way of management but it has become an uncertain task, with Roe Deer browsing the new growth.

An alternative is to cut young trees as Pollards (cutting the stem above browsing height).  It is a very ancient practice.  The advantage of pollarding is no loss of regrowth due to animal browsing; the trunk continues to grow, which creates opportunities for nesting birds, beetles, larvae and fungi.

Oak pollards creating varied woodland structure and open ground flora

I find that maiden mature Oaks require a spacing of at least 30 metres to avoid competition with each other.  It gives space in between where young trees can be pollarded and shrubs, brambles, grasses and flowers have sunlight to grow.

An open woodland, with pollards can mimic the essential disturbance that woodlands have always thrived on. It promotes the extra light which keeps the essential sod intact, which absorbs rainwater and prevents run-off.  Carbon capture is not diminished and biodiversity is increased.

Oak tree given space for branches, allowing other species to flourish

Slow the Flow would be able to incorporate some of these ideas in their stream and wet flush areas, if more light was introduced and good wetland plants and grasses were encouraged. Water diverted sideways can then be absorbed by vegetation and roots.  Of course this will depend on other agencies which are responsible for managing the woodland.

We really do need to rethink what a woodland is; what a tree is; and how to protect the intact soil which contains grasses, flowers, carbon, and excess water. 

Trees matter—soils and flora matter—an essential partnership that succeeds.