Sunday, 8 October 2017

Building resilience into nature reserve design and management

Too often on visits to nature reserves there is the assumption that the site is performing well, yet there is a nagging concern that somehow it just doesn't look right and perhaps could be delivering more.  There is a feeling of stability: the site looks 'tired'.  Maybe it's just a bad day out for an old and increasingly grumpy ecologist, but is it just plain grumpiness or perhaps something else of deeper concern that is affecting our nature reserves?
Wetland nature reserves that have been restored or created often have this air of stability or ‘tiredness’.  A while ago, I was at a conference where conservation academics were arguing that the attempts of conservation ecologists to recreate wetland habitat were a very poor second to maintaining existing habitat.  There can be little disagreement with this, but their key point was that research showed that even the best attempts to recreate habitat will only manage to recover around 70% of biological reference conditions (of plants and invertebrates) and even then, only after many decades. They argued that most recreated wetlands were far too simple compared with the complexity of natural habitat.  They may well have a point and although this shouldn’t stop us creating new sites, it should certainly make us consider just how effective our habitat designs and management systems are.
If you just flood the corner of a field, you can attract waterbirds. Relatively simple wetland designs, for example recreating wet grasslands from farmland, can have immediate success.  High numbers of target species such as breeding waders can be achieved in the short term. The basic factors are seemingly few: water regime and sward structure and we know that predation has a major influence. Allegedly a reserves manager once stated “even a monkey could manage wet grassland”.  Well it must have been a very clever monkey as this couldn’t be further from the truth. The fact is that experience shows us that many sites peak and then decline over a period of time.  Why does this happen?
There are probably a number of issues at play.  The first is all about natural ecological processes and cycles. We know that wetlands can be highly productive in the early years: large amounts of food can be available and early colonising species can go through a rapid growth phase.   As declines of some key species set in, habitat quality is often looked at first.   The site manager may claim; “but it's just the same as it's always been”.   In fact changes are likely to be occurring every year as the habitat moves from this period of rapid growth to a more stable phase.  In natural wet grasslands and marshes, although the ongoing processes of natural succession may be somewhat balanced by grazing animals, changes are continually happening as the habitat is shaped by the effects of processes such as wetting and drying.   The subtle mosaics of water, mud and vegetation will continue to alter.  In some areas, early successional species decline, grasses thicken, coarser rushes and sedges move in.  In others dynamic processes set the clock back.  These subtle changes go on year after year, shifting the balance of suitability from one species to another. Other changes are also taking place.  Nutrients become locked up in the muds and vegetation.  Successional changes take place in the invertebrate populations, shifting from simple abundance of a few, to a diversity of many.
The conservation management of nature reserves tends to seek to achieve similar ‘ideal’ conditions for target or priority species year after year, often with little or no recognition of these wider processes. Site designations and agri-environment schemes may also promote the stability of these ‘ideal’ conditions.  In wetlands, this often results in a controlled consistency in wetting, drying, grazing regimes and cutting that ignores natural processes and fails to acknowledge how the ecosystem as a whole works.  As these opposing actions clash, the result can be a state of arrested and impoverished habitat development lacking the full diversity created by dynamic processes and ecological cycles.  In addition, the drive to increase management efficiency and reduce costs once sites are ‘favourable’ or ‘steady-state’ fails to acknowledge the secondary effects and feedbacks that can act to change the system, and ultimately lead to declines.
A second issue is the aforementioned point about habitat restoration design. The habitat designs for many wetlands are too simple, for example, wet grassland are often based extensively on networks of flooded ‘foot-drains’ in each field.  These are basically linear, straight, uniform shallow ditch systems within the grassland. These designs seem to get repeated irrespective of soil type or end function (nature reserve or farmland in an agri-environment scheme).  As we re-wet sites, we know the vegetation will change and become more flood tolerant, with rush, sedge or club-rush increasing and thicker grass swards covering previously bare ground.  The lack of complexity, and then increasing stability, in such created wetlands reduces the options for species.  We create simple food chains with our target species in the middle.  The simple foot-drain design and predictably stable management regime lacks any resilience against the range of changing factors that will apply from year to year. The problem may be that the prized Lowland Wet Grasslands that these creations aim to reproduce are themselves just an artifact of a natural wetland for the purpose of agriculture.  Perhaps LWG per se should not be a target habitat on nature reserves but remain a poor, but realistic target for agri-environment schemes in a farmland context.  Our wetland nature reserve management should be much more imaginative.
Flooding an area that has a varied, complex, fine-scale topography and allowing it to dry out slowly should provide more opportunities for wetland species than a simple system comprising dry land interspersed with flooded foot-drains.  The former should deliver wider benefit to nature conservation and probably exhibit increased resilience over the latter.
A related issue is that with the widespread decline in wet grassland waders, much research is undertaken, and often on these restored or recreated wetlands.   The research may make claims about the factors and features that affect our waders.  However, simple science doesn’t always see the wider ecological picture.  The result may have been correct for that moment in time on that site but completely wrong the year after and elsewhere.  The conclusion that waders like foot-drains is a good example. This may merely be a reflection of the conditions the species chose from those available at that time, not the ideal conditions the species would choose.
Predation is another serious issue.  Predators will exist in most circumstances and are known to be beneficial overall to the ecosystem.  However, where large numbers of conservation-priority birds are attracted to breed on small nature reserves set within a degraded wider countryside, they can act as a honey-pot for a range of both mammalian and avian predators.  It is of course possible to continually remove predators such as Foxes but this is arguably unsustainable in the long-term and abhorrent to many conservationists.  A standard policy should be to look for non-lethal methods of managing predation if we can, and this may begin with habitat design.
As a result of these inter-related issues, a predictable pattern of growth and decline is apparent on a number of wetland reserves for breeding waders that are, for example, a mix of restored old grassland and newly created wetland on ex-arable land.  After increasing to a peak some years after creation, wader numbers are frequently seen to drop steadily, losing a significant proportion of the peak population.
Management for Lapwings, frequently a target species on wet grasslands, is a good example of this. As the Lapwing, which favours short swards and bare ground, struggles to cope with successional habitat changes it also faces a revolving door of predator-prey relationships. Most predators will have preferred prey, shifting to alternates when it becomes scarce.  Foxes eat voles but their diet is affected by cycles in the vole population.  When voles are scarce they may seek out more bird food, such as Lapwing eggs. When voles are abundant, Foxes may eat less Lapwing eggs. However, other predators; mustellids or crows or raptors, may be following different cycles and may switch on to wader chicks in those years.  Predators also learn where the food resources are at different times of the year.  A reliable hot-spot of wader eggs will be noted in the predator memory.  In a complex natural system, Lapwings will move around in response to habitat, food and predation.  We don’t give them this option at many of our reserves and they suffer for it.
A more dynamic and resilient management approach typical of a natural wetland and with the understanding of ecological cycles is required.  We need to improve overall ecosystem integrity rather than focusing on the status of a single or a few species.  This should involve measures that allow or simulate natural processes of distructive/creative change such as flood or drought: varying water regimes, varying grazing patterns, turning areas on and off, targeted rejuvenation through various disturbance measures. One study showed that managers can almost double the area of suitable habitat by more dynamically managing water levels and managing invasive vegetation.  We should aim to create and manage habitats that are more resilient and sustainable in the face of climate change than engineered channels and narrow focussed targets.
So how do we improve our wetland creation and management?  More to follow.....

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