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Wetland restoration - the return of wild nature | |
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Restoring wetland is a growth industry in nature conservation. It may start with a new, small reserve, but the realisation soon comes that this reserve is but part of a wider original wetland landscape that cries out for a more expansive vision – thus the major extension of Wicken Fen by the National Trust, and the many other fenland projects in the East of England. Larger still in scope, the Yorkshire and Humber Wetland Feasibility Study builds on the RSPB’s Lower Aire Valley project, systematically identifying the most suitable areas to restore wetlands in the region's many low-lying river valleys (1). Uplands are also part of this trend with the grips that drain many a moorland being blocked up with log-rolls of cut heather, re-wetting blanket bog before it is blown away as dust in the wind. Wetland restoration usually has clear endpoints, more often than not associated with bird species but sometimes as reserves for uncommon flora. The reserves are inevitably managed because conflicts will arise between this new richness of biodiversity and wild nature’s tendency to want to keep on fashioning the landscape without heed to the neatness of purpose that was intended. As has become standard practice, land managers in the shape of cattle or ponies of historic and robust breed will be introduced (but see later for something even more exotic). The dynamic of wetland restoration is profound, both in pace and diversity. It offers an opportunity to think outside of the either/or straightjacket in most landscapes of a closed canopy woodland or a disclimax meadow. It opens up the whole issue of wilding nature reserves wherein many conservation/regeneration projects are still being carried out independently of landscape considerations, such as all trees being removed from heathland with no attempt to create a mosaic of natural vegetation. wetland restoration I had a first hand opportunity to observe wetland restoration in action on the field trips in the Dyfi estuary associated with the recent Wildland Network meeting in Wales. The course of the Dyfi River has obviously been a huge influence in the historical occupation, access and use of this wide washland, created by its journey to the sea, and the sea itself in creating marshland. Our first stop took us to Cors Dyfi, a new reserve of the Montgomeryshire Wildlife Trust (MontWT) someway inland, where the Sitka spruce plantation had been cleared and the water drainage reversed. A mere eight years had seen a spectacular return of wetland species (presumably the abundant gorse in places was the early returnee that will not be sustained for much longer in these wetland conditions). Flag iris, bulrush, purple willow, bog myrtle, reeds, plus royal fern - and potamageton in a few dug-out pans - are testament to moisture being a key selective pressure, and the driving force for habitat regeneration in a local area that had sufficient remnant species for this recolonisation. To be honest, although birdlife was probably the target of the restoration, the return of nightjars is not the panacea for me, as it is for MontWT conservationists. Although we did not see them, the introduction of three water buffalo by MontWT as an agency for herbivore pressure may be a reasonably appropriate measure, but would need to be carefully monitored. It is difficult to know what the steady-state condition of the reserve should be, but it would be wrong to allow that grazing pressure to be a dominant force, and for it to undo all the wonders of the wetland regeneration. I’ve watched St David’s Head in Pembrokeshire see-saw backwards and forwards over the decades between shrub cover and roughed up ground as ponies were put on and taken off. Fortunately, the characteristic wildflower and shrub species seem indifferent to this lurching landscape management although some more open land species would loose out eventually if all herbivore pressure was removed. The Deer Park at Marloes also gets the same treatment, but with less obvious merit in the plantlife as the fading hope is to maintain an artificial heath. We seem to think that we have to make up for a “missing” natural grazing component, but without having a clue as to what the extent of that should be, or what would be the likely animals and their particular feeding patterns. Water buffalo is no dafter a solution than in putting on Highland cattle (or relying on rabbits) but it doesn’t have the authentic feel of unenclosed, free living wild animals passing through a landscape, or voluntarily making it their home. In Scotland, deer numbers are such that regenerating woodland is regarded as difficult without a period of exclosure (exclusion by enclosure) but with the intention of removing the fencing once the woodland reached a stage of maturity that will give it protection from extinction by grazing. The level of renewal there would be then, over the centuries, would be difficult to forecast since for instance sheep grazing in the uplands has resulted in a break in any renewal growth, leading long term to denudation as old trees die off and are not replaced. This is perhaps what would happen also with cattle, horses, and maybe even deer at current population size and distribution? So how could the situation arise where our best estimate is that we had regeneration of woodland to at least 60% coverage after the last ice age, which hung around for at least 1000-2000 years (i.e. spanning a number of generations of trees) before humans became significant landscape managers? Out further towards the coast, we could see we were in a drained peatland landscape, where local archaeologists have uncovered the causeways made from willow bundles that linked across these wetlands between the rocky island outcrops. Mostly in grazing use, Cors Fochno is in the Dyfi National Nature Reserve owned by CCW. Many parts of the peat lens are undergoing rewetting by the blocking of the deep drainage ditches, turning them into peat-brown lakes. We saw an example of an unintentional exclosure as we passed an ungrazed commons at the edge of Cors Fochno. Grazing had ceased in the commons some 30 years ago as it was unclear who could exercise commoners rights (they were assigned to the poor of the parish rather than named people, and no one put their hand up to qualify!). The commons was exclosed from the grazing land around it and had thus filled with a willow carr woodland. As we saw, by virtue of the fallen relics in other wetland places, any larger tree is not supported in this habitat, falling over when reaching a particular size. Thus the willow is the main climax species in this wetland. On the main area of Cors Fochno, we were told that Welsh ponies and Highland cattle were run during the growing season to control scrub growth, and taken off for the winter as the Molinia grass has no food value then. The restraint of scrubland was explained as a requirement to maintain diversity of the re-wetted peat lens. I just saw quantities of bog asphodel, bog rosemary, cross-leaved heath and lots of stunted bog myrtle in what looked like the usual attenuated vegetation of a non-improved landscape run with livestock/herbivores (the rocky limestone uplands of southern Spain, for example, or the grazed understorey in remnant Caledonian Forest). It always tends to look very sad and degraded. It was also in stark contrast to the rich shrubland vegetation of a small exclosed area within the general grazed peatland of the Cors Fochno SSSI. Here instead were colourful growths of bog myrtle fringing the willow and looking for all the world like an unenclosed wetland scene in Ireland where grazing seems less intensive than in our marginal land. Why did the CCW warden express regret at the small exclosed area? How much bog rosemary do we need to maintain, and in so doing perpetuate a landscape that looks to me to be degraded? (Improved farmland doesn’t look as sad and degraded by livestock because there is only grass there to suffer, and we do think a mown lawn is neat!). Would it not be possible to have a mosaic of vegetation at Cors Fochno whereby a proportion of the peat lens is exclosed – say in a series of drifting islands taking up 60% of the area – and succession allowed until the point where the fences could be taken down? This would be wild nature by human design (gardening) but I suppose we need to experiment like this, learning from our landscapes, instead of assuming we know everything. Would those drifting shrubland islands be resistant to extinction from herbivore pressure? Can they renew when herbivore pressure is restored? Can we ever hope by our own interventions to get the balance right so that we have the dynamic but essentially natural steady state landscapes that seem to appear without human intervention in the wildland of other countries? glacial retreat I can give a near contemporary example of the latter. After a final glacial surge in the Little Ice Age in the mid-18th century, the area now known as Glacier Bay on the SE Alaskan coast was covered in ice 4000 feet thick, forcing the Tlingit people to abandon their villages. For whatever reason, the ice then receded rapidly, withdrawing 60 miles inland in just 120 years. Successional vegetation followed, creating a mosaic landscape, and mammals moved back in. Designated first a National Monument in 1925, the 3.3 million acres of this rewilding landscape (mostly designated wilderness) makes up what became the Glacier Bay National Park and Preserve in 1980 (2). Glacier Bay provides a supreme example of how vegetation returns to a landscape following deglaciation. Land near the mouth of the bay emerged from the ice around 250 years ago and has had the most time to recover from the effects of the glaciers. Traveling north toward the glaciers, the more mature forests of spruce and hemlock give way to fast-growing deciduous forests of cottonwood and alder. Further up, these are replaced by shrub lands and then tundra before reaching the glaciers where nothing grows at all. Emergence from ice releases the land to wild nature, but edaphic factors (soil conditions such as moisture, fertility etc) and climatic factors have also been important selective pressures for re-vegetation. Salt marsh is found near the shore; open beach meadow is at and above extreme high water; lowland forests are dominated by Sitka spruce and western hemlock, with cedar to the south and on the outer coast; upland forest occurs higher up with mountain hemlock replacing western hemlock; then up to sub-alpine meadow where tree growth is reduced and halted by low summer temperatures, wind, and damage from snow creep or avalanche; reaching finally alpine tundra where summers are brief and winter winds blow away protective mantles of snow, revealing tundra mats of prostrate shrubs, tiny herbs, mosses and lichens. Wetland bog communities spring up where, over time, the land has become too wet to sustain good tree growth: such as low-lying land; where there is a hard pan; or where there is acidic spongy peat moss. Mountain goat and brown bear were the first to return after the thaw. Coyote, moose and wolf moved in later, and black bear inhabits the forest of the lower bay. River otters are widespread, as are marten, mink and weasel, but the wolverine is scarce and not often seen. The Alsek River delta in the Preserve to the NE of the National Park is home to lynx, snowshoe hare and beaver - species that have reached the coast from the Canadian interior by traveling along the river corridor to the Bay.
Our contemporary, mostly farmed landscapes
in Britain don’t have the range of edaphic factors that would naturally
produce such a mosaic of rich habitats that can be seen in Glacier Bay. In
producing the highly cultural landscapes we see today, we have smoothed
everything out, draining the land and unusually increasing its fertility,
and banishing native species from which a wild, natural landscape could
regenerate. But I don’t think that means we should give up some of our
greater aspirations for wildland. A few years after the passage of the
Wilderness Act in America, the Forest Service opposed the designation of
new wilderness in West Virginia as they argued that Eastern woodland was
not without a significant history of human disturbance. Senator Frank
Church (3), the floor manager of the Eastern
Wilderness Areas Act, said that the Forest Service: Mark Fisher, 29 April 2006
(1) A wider regional vision for wetlands.
www.rspb.org.uk/england/northwest/conservation/loweraire/vision.asp www.self-willed-land.org.uk mark.fisher@self-willed-land.org.uk -top |