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Tree Planting and Flooding

From Philip M

Saturday, 16 January 2016

There is widespread pressure for large scale tree planting in the belief it will help prevent flooding. Not necessarily - it could make the situation worse. If one looks at our existing mature woodlands we have to ask ourselves if they are a good model on which to base future woodlands. With few exceptions (where beneficial management is taking place) many suffer from excessive shade, poor or nil ground flora and lack of natural tree regeneration. This often results in soil erosion, particularly in the steep cloughs, which clogs up our rivers with silt and debris. Managing some clough woodlands may be a better immediate course of action for flood protection.

Tree planting needs to have management options from the outset. Otherwise we may create problem woods of the future which mirror problem woods of the present. The current fashion for closely planted trees will inevitably cast deep shade, potentially killing the ground cover and exposing the soil to erosion. There is also the serious biodiversity loss of existing flora, particularly when planting into species rich areas, as well as the loss of Carbon storage from a decaying sod. Water absorption is an important function of a good deep sod and soil. Trees that have space to grow have more branches and leaf area for absorbing Co2 and for water uptake. They are also more resilient and have stronger roots.

It is worth trying to avoid problems by creating a more natural landscape using much wider spacing for saplings, releasing them from the straightjacket of the numbers game. The space between the trees can then accommodate a diverse flora as well as native shrubs.

Much can be learnt from the numerous woodlands planted in the last 20 years or so. Ask questions. Have they been managed or abandoned? Is the ground flora shaded and dying or is it healthy? Was the species mix appropriate? Have the individual trees a long term future or are they struggling? Is the woodland attractive to look at? Is there enough space for trees to grow or will they become telegraph poles? Has the area become better or worse for wildlife? I can think of some plantations that are a graveyard for trees.

Until we learn and adapt from the best of the past (and there are good examples) what is the point in creating more of the same? It is often the gaps, glades and particularly the varied edge habitat which help define woodland and provide the best opportunities for wildlife and water absorption as well as interest for people.

In suitable places it may be better to plant scrub such as Hawthorn, Blackthorn and Brambles; then trees will naturally follow without the need for expensive and littering plastic tubes. Birds are attracted to scrub and will deposit tree seeds which then grow in the thorny shelter, well protected from the predation of the ever present Roe Deer.