Monday, 20 January 2020

Trees – to plant or not to plant, that is the question.

In my last two blogs I pointed out the dangers of tree planting.  The twentieth century saw massive damage done by reforestation – one of our greatest causes of habitat loss – we should be careful not to repeat the mistakes of the past.  We all want to do the best thing when it comes to addressing the twin problems of climate and ecological emergency.  All habitats contribute to combating climate change - we do not need to think “trees” all the time.  Legitimate questions now are:  when is it right to plant trees?  And how do we do it right?

In my mind you can probably break this down into a 10-stage process:

1.      Survey.  Find out what is present on the land where you are considering tree planting - with a new survey and by collating existing information.  Organisations like the Wildlife Trust will have some information to alert you to special places that would be damaged by planting.  But much is not known.  You don’t need a full species list, but you do need to have enough information to get to the next stage.

2.      Map and understand.  Map your plot, indicating the different habitats present and showing any special interest.  Then interpret what is there.  For instance, is the land degraded and species poor, so would be enhanced by planting or is it rich in species (such as grassland, heathland or wetland) that require open conditions so would be damaged by planting.  Also identify problems such as invasive species, overgrazing from deer or domestic stock etc?

3.      Make a plan.  What is the site like now and what would you like it to be in the future?  Then prescribe what management might be appropriate in different compartments in order to deliver your plan.  This should include planning to look after existing, sensitive, maybe unwooded habitats as well as plans for changing things perhaps with planting.  Get this wrong and you could cause more damage than leaving a site as it was!  So, it will be worth getting good advice.

4.      The role of trees.  You will then have a plan that includes places where more trees will be beneficial and places where they would be damaging. So, what tree species should you chose?  Look at other wooded sites in the area to see what mixtures work for the area.  Native tree habitats have been classified so, knowing the conditions on your site, it should be possible to copy a native wooded habitat.  Again, it may be worth seeking advice.

5.      Tree regeneration.  Natural regeneration is generally preferable to planting, giving a more diverse, locally appropriate mix.  So, will natural regeneration happen on a scale or of a type that fits your plan?  If not, then you have a rationale for planting.

6.      Tree planting.  Some trees are less good at being planted than others!  (eg oak is difficult, willow is usually easy).  Get good advice and ensure it is done well.  Where will stock come from?  Use reputable (eg WoodlandTrust) sources, preferably locally sourced, or even from seeds collected and grown on by local people.

7.      It’s not just trees. There may be value in adding other species, particularly shrubs and smaller sub-canopy trees.  The aim should be to create “vertical structure” – multiple layers of vegetation in clumps across a site rather than one even layer.

8.      Tree aftercare.  Planted trees will need more care than naturally regenerated ones.  They will need watering and removal of weeds in the first year or so.  They may need protecting with tree guards – more single-use plastic in the countryside, not really something we should be encouraging.  Or you could plant far more than you need and just allow for large losses – an approach that could deliver more diversity.

9.      Management.  How will the site be managed in the long term?  Non-intervention is only one option.  Maintaining diversity, especially in small woods, will require management.  This should also include management of open habitat.  However, try to avoid preconceptions about how a site may end up.  Nature may take a site in a different direction to your plan.  You’ll need to work out whether to fight it (eg more planting and more cutting) or adapt your plan.

10.   Long term plan.  For centuries of human history, woods only survived when they had a purpose, traditionally by providing products for people.  So how will you give the site a long-term purpose?  Will it provide products, timber, be a leisure facility, a community asset or what?  Planting and hoping is not good enough.  A future unvalued wood will just be swept away, and any temporary gains will be lost.

Replanting is not the same as rewilding.  Replanting is reforestation.   It may be true that replanting can help with rewilding, but the attitude is one of kick-starting nature, rather than designing and building a forest.

And bear in mind that the best ecological option in an area might be to cut trees down – not to plant them!  All habitats contribute to combating climate change, and healthy ecosystems deliver far more than just climate change mitigation (important though that is).  Nutrient cycling, flood prevention, erosion prevention, pollution amelioration, pollination and so on and so on.  We need to go into ecological restoration with an open mind rather than immediately reaching for the packet of tree seeds.  In nature, succession (tree growth) is in balance with natural disturbance.  Too much of the first and you get a dense, artificially dark forest of very low ecological value, which may also not reach an area’s best potential in terms of climate and the other benefits of nature.  Clearings and open habitats are just as much a part of the forest as the trees.

It would be perfectly legitimate to go through the 10 stages above and then come to a very different conclusion than tree planting.

Friday, 10 January 2020

Trees and the climate emergency

In my last blog I raised the huge potential damage that could be caused to the environment if forest creation was done poorly.  This generated some excellent discussion and I am glad that it stimulated interest. 

I do not plan to respond to all points raised but there was one set of comments where some expansion is worthwhile.  This is the point that we are in a climate emergency, the priority must be to get the trees in the ground as an emergency action.

This is very reasonable.  In nature conservation we often must press forward with the best approximation of the truth so, if the overriding need is carbon sequestration then we better get on with it.  It might be said that the problems are small in comparison to the needs of the emergency.  However, the follow points should nuance this:

First, the UK is only 13% wooded.  It should be possible to double this without causing any ecological problems.  To stress this further, concern about ecological damage should not be an excuse for reducing forest creation – we must just get it right.  For example, high nature value chalk grassland occupies only 4% of the South Downs here in Sussex.  If a tree planting plan can’t restrict itself to the other 96% then it is not trying very hard!

The second point is that, done badly, tree planting can cause a net release of carbon.  Soil disturbance in ground preparation, particularly on peaty soils will release more carbon from soil than the trees will make up, at least in the short term.  This should be avoided by good planting design and good attention to local conditions.  But an attitude that any habitat without a tree on it is a wasted habitat, will be very damaging.

Third, it is not only trees that lock up carbon.  Peatland holds more carbon than all our forests. Kelp forests in the sea lock it up far quicker than trees, and wetlands are particularly good at soaking up carbon on land.  Salt marsh is so good at building up soil on the coast that it is likely to keep pace with sea level rise from climate change – if left to itself.  Even grassland, which do not appear to have the obvious standing crop of carbon that you associate with trees, are very good at pumping carbon into the soil.  As roots in grasslands die off their carbon is left in the soil.  Rewilding is turning out to be one of the best ways of getting carbon into soils.  The mixture of trees, shrubs, ground cover plants, animals, dung and dung fauna working together to build up soils almost twice as quickly as organic farming.  And most of that new soil is carbon.

A fourth point is that planting a tree, or regenerating a forest, is only the start.  This is a long-term investment.  Throughout history, woods only survived because they had a purpose in the local community.  Traditionally, this meant woods being kept and managed to provide products for local use.  Hence, managed woods were more likely to remain than unmanaged ones.  This is still true today.  One of the best ways to create and maintain forests is to demand products made of wood, not just to plant a tree.  However, a purpose for forests might be broader today.  Wild unmanaged forests may be as valuable, but in a different way, to forests providing sustainable products for human use.

Part of the same fourth point is that we should not deify trees so much that management becomes a sin!  Part of appreciating trees is to appreciate the products they provide us and therefore drive their sensitive management.  Cutting trees down as part of sustainable management is not an ecological compromise, it is part of a much-needed woodland culture.  Furthermore, cutting down trees in the right way creates diversity in woods, mimicking the natural disturbance that wild forests might once have had.  One felled tree in a well-managed wood will be replaced by hundreds of saplings – without any planting.  (This is not carte blanche for any old management though!)

As I said before, simple answers to complex problems are always wrong.  I would add now that this is not an excuse for inaction, it is more a drive to understand and celebrate complexity.  Nature is complex – and that’s just great!

Tuesday, 7 January 2020

Trouble with trees

The creation of forests and woods can be a major contribution to restoring nature and can draw carbon out of the atmosphere, so helping fight climate change.  Indeed, with a UK average tree cover of just 13%, it would not be unreasonable to double this. 

Done badly, however, tree planting and tree regeneration can cause major ecological damage.  We must make sure that a frantic rush to plant trees does not repeat the errors of the past.

Enormous ecological damage was done in the mid-20th century through tree planting.  Vast areas of the Flow Country in NE Scotland were drained and planted with non-native conifer trees devastating the local ecology and (by causing the drying of peat) was a major emitter of carbon dioxide.  Many other upland areas saw similar devastation.  In Sussex too some of our most valuable habitats were lost to tree planting.  For example, over a period of about 100 years we lost roughly 80% of our heathland, nearly half of that to tree planting.  In the 1990s it was feared that many of our heathland species would disappear altogether as a result.  Fortunately, however, conservation management projects managed to reverse this trend.  Management – mainly tree removal not planting – averted an ecological disaster.

Similarly, loss of chalk grassland to tree planting and the spread of scrub is second only to loss to arable cultivation.  Chalk grassland can have about 40 species of sensitive plant per sq m; this reduces to a small number of common species if scrub invades or trees are planted.  It is likely that we have also lost hay meadows – one of our most threatened habitats – to tree planting. 

Large areas of the most diverse habitats in England have therefore been lost to trees.  These habitats were often as good as trees in locking up carbon and so fighting climate change.  We now have only small areas of these habitats remaining, tree planting on these would be unforgivable.

The desire for trees can come about from a misunderstanding about the natural ecology of Britain.  There is a presumption that a dense canopy of trees is the natural state for our country.  This is not true.  We’ve known it was nonsense since I was in college in the 1970’s.  And it is nonsense still promulgated by people who should know better.  So, let’s try to put this myth to bed!

If dense tree cover was the natural state for Britain, then most of our native species would logically require dense woodland.  They do not.  More than half of our species require open habitats or forest edges; very few require continuous dense trees.  Even species we associate with dense forest often require open habitats at some stage – oak and hazel for instance regenerate better in the open.  If the natural state of Britain was dense trees then most of our native species would never have colonised Britain, indeed they could never have evolved, in the first place.  The natural state of our landscape is one of great diversity not a continuous monotonous tree cover.  This diversity of original natural habitats is now maintained as “semi-natural” habitats through centuries of management. 

We may think of tree growth as natural, but tree growth is not the only natural process.  Importantly, there are processes of natural disturbance that limit or hold back tree growth (think of beavers!).  It is this balance of tree growth against natural disturbance that creates diversity.  Too much of one or the other and nature suffers.  This is the real value of management – it replaces natural disturbance with disturbance caused by management, putting back the diversity that can be lost through a lack of natural disturbance.

Fortunately, the situation is better today than it was in the mid-20th century.  Organisations involved in tree planting (such as Forestry Commission and Woodland Trust) are very aware of the potential problems.  These will plan planting properly, delivering benefit and avoiding problems.  Anyone wishing to plant trees should show similar care.  There are also better alternatives to planting. Natural regeneration and rewilding are more likely to deliver diversity, are cheaper, fit local ecology better and require less aftercare. 

I do worry, however, that a destructively naive view of nature and a rush to get trees in the ground will sweep all before it.  We risk repeating the errors of the past and once again cause great ecological damage.  Simple solutions to complex problems are always wrong.  We should move the conversation from “tree planting” to “natural regeneration” then to “rewilding” and to “natural climate solutions”.  Tree planting may have a role, but only as part of a diverse nature recovery network, not as an unquestioning paradigm.