Having successfully helped my mum pack her house into an articulated lorry, and bring her down here to Dorset yesterday, I have to admit to being a bit knackered.
However I’m looking forward to buying a copy of George Monbiot’s new book “Feral”, and he has been having a fine time this week publicising it, including a piece on Newsnight which I am looking forward to watching on iplayer later.
I commented on a draft of the book for George last year, after we had a lively twitter conversation (or spat as it was also described) on the pros and cons of re-wilding vs conserving semi-natural habitats. Reading the draft certainly gave me a lot of food for thought and challenged my own preconceptions and accreted dogma around conservation.
Without going into the argument of conserving open habitats vs closed forest cover (for the moment), there is one particular aspect of re-wilding, in the sense of restoring natural woodland to the uplands, which I cannot get past – hopefully you dear reader will be able to help me. Bear in mind my knowledge of soil development is a bit thin.
After the end of the last ice age around 10,000 years ago, there was tundra and soils, such as they were, were not able to support forest cover. Soils then developed very slowly over a period of hundreds, perhaps thousands of years, thanks to plants like Mountain avens and its amazing fungal assemblage.
Mountain Avens growing like a bonsai tree over a boulder in the Burren, Republic of Ireland (copyright Miles King)
Eventually soils developed to the point where forest trees could establish, and the holocene forest was born. This was then slowly removed a few thousand years later through first mesolithic, then neolithic clearance for hunting, grazing, timber/wood exploitation; and crops. Those original soils were lost as a result of this land-use. The consequences were that peat soils started to form in the wet north and west of the British Isles, while elsewhere, different soils developed in response to grazing, cultivation and woodland management. We still have tiny remnants of ancient forest soils in ancient woodlands of varying ages (but I don’t think any have continuous woodland cover back to the original holocene forest)
So we now have in the wet north and west 6000 years of peat growth on top of whatever soil was around at the time that people started to alter the land-use beyond hunter-gathering. There’s a fantastic example of this at Ceide Fields north of Connemara in County Mayo, where the oldest known field system in the world was discovered under thousands of years of blanket bog peat growth.
I was struck by the lack of soil in the Burren last week. Tiny stunted trees peeked out from between the limestone pavements, where it is grazed. Hazel scrub is developing rapidly as grazing pressure decreases, but in the absence of much soil it is a very different beast from the original forest cover – oak and wych elm are almost entirely missing for example.
When the Forestry Commission tried to reforest the uplands in the 1970s and 80s they had to use deep ploughs to break through the peat and then drainage channels to keep it dry enough for trees to grow.
So that is my question – how do we recreate the post-glacial holocene soils that would support something like the pre-neolithic holocene woodland again, regardless of where we find the elephants.
I didn’t think George was suggesting total forest cover; just greater variation? Remove sheep – see where it goes without expensive controls.
Thanks Mike. I’m just about to pop down to our local bookshop and hopefully buy a copy of Feral and will get stuck into it later.
However, in the mean time the law of unintended consequences needs considering. There are some invasive non-natives like himalayan balsam (along damp valleys) and rhododendron, ready to take full advantage of a relaxation in grazing or other management: these will need to be tackled/managed. Also, unlike the holocene, between 10 and 20 units of active nitrogen fall on every hectare of land in the UK every year, thanks to emissions from agriculture and transport. This extra nitrogen alters competition within ecosystems and again will affect the way that ecosystems respond to a decline in grazing. And as I say in the blog, the soils are very different now from their previous state before farming – this affects what can grow there. You can’t get an oakwood to grow on blanket peat – in fact few trees grow on blanket peat. What do you do – bulldoze away millions of hectares of peat?
I would like to see some robust modelling showing what sort of forest/scrub communities develop in both upland and lowland situations given a range of reductions in grazing and other land management activities. Perhaps this has already been done?
Attention needs to focus on the ability of Atlantic peatlands to support trees. I suspect the ability of peatland to hold tree cover is underestimated. I think where surface water drops in summer you could have ample scot pine, birch, rowan, willow and some aspen, holly, juniper, yew and oak. In parts there would be a shrubbery low canopy or no trees at all.
There are large scale reconstructions of what vegetation would develop if human intervention ceased. There is a complete reconstruction then for Ireland but it again seems to assume blanket peats would support very little trees.
There is some interesting examples of forested peats in Scotland. Another example is former Bord na Mona raised bogs which are developing birch cover. In these cases the peat hydrology has been greatly altered by past drainage but it is worth comparing. What do people think about this?
There is certainly considerable scope for trees on peat, its just a question of accepting that the dynamics of peat accumulation will differ. Provided that the hydrology is intact or restorable, as long as there is a net gain of carbon accumulation over time, it is still fair to consider it an active peat. It may not reach the accumulation rate of pure sphagnum, but not every system needs to be this focussed. Areas with sub-optimal hydrology would be expected to shift to other vegetation types during dry periods, so there should be a variety of boundary communities including woodland. If you are putting peat formation above everything else, then trees and shrubs would need to be eliminated. If trees and shrubs are considered natural, a new equilibrium for carbon accumulation would evolve, thus limiting peat accumulation to the optimal hydrological locations.
I think human activity fed into the rapid expansion of peatlands as climate tilted towards their favour, so our perception that peatlands are always treeless and should extend to their current bounds is only due to the fact that they evolved in the absence of trees and shrubs (due to grazing, burning, etc.). The appearance of trees and shrubs may set some areas into decline with regards to peat accumulation, or we could simply call it a return to carbon cycling. I’m not a real sphgnum fundamentalist.
thanks very much for your comment and welcome Paul.