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.....
