Friday, 15 November 2013

Trees + Cows = Wood Pasture

"Trees seldom grow old in woodland...ancient upstanding trees are an indication that a site is not an ancient wood" (Rackham 2006)

What is Wood Pasture?

Wood pasture is the combination of the right sort of grazing animals and widely scattered ancient trees.

This definition sounds simple but there is more to it than that. By the right sort of grazing animals we mostly mean cows, and accept that some wild deer will pass through. Cows graze by using their long dextrous tongue to wrap around the vegetation and rip out clumps, which sounds less than ideal but this method produces a variety in height of vegetation and the tiny pockets of bare ground created are perfect for tree seeds to fall into and germinate. Deer browse more on young trees than they do on plants but provided their numbers don't get too high then the regeneration of trees should outweigh deer consumption. Cows may also browse on the shoots of young trees but provided the numbers are low, for example 8 spread over 50ha then plenty of young trees will grow.

Wood pasture with its sun-loving ground plants and ancient, open-grown trees.

What isn't Wood Pasture?

Wood pasture is not improved farmland (made so by added fertilisers) on which sheep are grazing with large trees dotted around the fields or their edges. The definition of grazing animals around mature trees fits but this landscape is lacking in native herbs, grasses, sedges, ferns, bracken, heather, mosses, deadwood laying on the floor and wet, boggy or marshy areas, together with all the other wildlife that is associated with them.

Wood Pasture is not the remnant of a woodland, it was not a closed canopy of trees that has been damaged by grazing and slowly the young trees died out leaving just a few to remain. Wood pasture, which 1000 years ago covered one-tenth of the whole of England, will soon in-fill with young trees shading out the veteran trees and forming a woodland if grazing stops. However woodland plants which spread at a glacial pace will take a very long time to colonise any new woodland.

So What is the Difference Really?

Wood pasture has trees from acorn to ancient and plants adapted to open sunny ground, whereas ancient woodland contains shorter lived trees but has ancient shade-adapted plants. Farmland may have veteran trees surrounded by mostly rye-grass and parkland will be similar but hopefully with young trees in guards.

Parkland trees like these oak and beech at the St Catherine's estate near Windermere had the space to become open grown, however parkland trees sometimes lack lower branches which were removed long ago for access. The oak's successor can be seen bottom left of the photo in a wooden guard.

What is the Significance of Wood Pasture?

The misconception that Britain was a long, long time ago covered wall-to-wall in trees is proved wrong by the wood pasture ecosystem. The late Francis Rose thought the same because of the native wildlife, especially lichens that existed in Britain and Europe in this particular habitat.
Many birds that are considered common are most at home in the environment of wood pasture or at least in the sunnier edges of woodlands along with many insects and especially butterflies. If Britain was a vast carpet of trees then why do we have countless thousands of species adapted to, or benefiting most from the open sunny areas that are found between the trees?
Those who are familiar with Franz Vera will know of his (2000) hypothesis that pre-Neolithic 'wildwood' had more in common with landscapes that can be described as savanna - which I'm sure will put a very different image in peoples minds.

So the bombshell is that what we call wood pasture, or what Franz Vera called savanna could possibly be the original, and oldest ecosystem in Britain and possibly Europe since the last ice age. If we want to restore some areas of the country to what we deem 'natural' then is this it?

The Significance of the Trees in Wood Pasture

The trees will naturally regenerate but their numbers are kept in check by the grazing of large animals such as big hairy cows. These native trees have it good; they are not in strong competition with one-another for light or water and can in fact grow to their full potential (climate and altitude depending). These trees will be what's called open grown - their trunk will be short and fat and they will have thick branches that will spread horizontally and wide. The overall shape of the tree will be that of a dome - this is the optimum shape for placing leaves in positions to capture the most sunlight which in turn provides the tree with the materials it needs to grow. The shape is also the best for diffusing the strong winds which will push on the dome shaped crown but the power will be dissipated throughout the tree. Open grown trees develop substantial buttress roots in response to continual exposure to wind. They therefore have a greater number, diversity and mass of micro-organisms associated with the roots (Ted Green, 2010).

An ancient open-grown oak in Gowbarrow Park SSSI.

A tree that has naturally grown in a woodland will be taller with its less spreading branches higher up as it tries to compete with its closely positioned neighbours for light and water. These trees will live shorter lives and provide less opportunities for wildlife to benefit from them.

Woodland or 'forest' trees grow taller, straighter with less branching lower down.

"A single 400-year-oak...can generate a whole ecosystem...for which ten thousand 200-year-old oaks are no use at all" (Rackham 2006)

Open grown trees found in wood pasture therefore have the opportunity to live their full lives and become veterans, so oak could live up to and beyond 900 years and ash can even have their life spans tripled by pollarding giving incredible continuity of an ecosystem. Open grown trees can therefore provide habitats to birds, bats, beetles, spiders, and lichens for several centuries longer than a woodland tree.

Looking to the Future

Tree experts agree that old, open grown trees are one of the most important contributions the UK can make to the biodiversity of Europe. The continuity of biodiversity over many centuries makes this habitat historically and ecologically extremely important. The National Trust in the Lake District is restoring ancient wood pasture in the Windermere and Ullswater valleys in some exciting and large scale projects starting this year.

A few open-grown trees can still be found in Gowbarrow Park SSSI, and dead trees like this alder are just as valuable as living ones. Here sheep will be replaced by cows over 50ha to allow tree regeneration.

The plantation in the background will be felled to create room for 12ha of new wood pasture. The site of the plantation and the foreground will give rise to open-grown trees grazed underneath by cows.

Troutbeck Park, Glenamara Park and Gowbarrow Park SSSI are three locations where, with help from Natural England, Forestry Commission and the Lake District National Park, we are removing sheep in favour of just a small number of hardy cows and extracting nearly 12ha of dense conifer plantations to restore a vast tract of Lake District into the most important ecosystem in Europe. These projects will be the focus of future blogs so please look out for them.

Troutbeck Park is the home of over a hundred veteran and ancient pollarded ash trees and is also the site of a wood pasture restoration project following sheep exclusion from part of this ancient deer park.

Like this Topic?
Visit other exceptional National Trust wood pasture at Calke Abbey in Derbyshire and Hatfield Forest in Essex.

Sources used for this blog:
Woodlands by Oliver Rackham, 2006 HarperCollins
The Importance of Open-grown Trees, Ted Green, British Wildlife Volume 21 number 5

Ben Knipe
Woodland Ranger

1 comment :

  1. ash and hawthorn branches were in the past given to sheep to nibble to stop them scouring and make them thrive