Linking Restoration and Ecological Succession (Springer ... - Inecol

To restore abandoned land there are two potential constraints, high pH and
high nutrient supplies (usually P), both linked to past fertilizer/lime additions.
There are a variety of techniques available for reducing soil pH such as the
addition of elemental or pelleted S or addition of acidic plant materials. The
most effective has been the addition of S, either directly (Owen et al. 1999),
or as pyrite-rich peat (Davy et al. 1998). Experience has shown that application
rates need to be calculated empirically for individual sites (Owen et al.
1999).
When attempting to set back succession on heathlands where succession has
proceeded to woodland stages, it is essential to remove the woodland species
(in Europe these are usually Betula spp., Pinus sylvestris, Pteridium aquilinum,
Rhododendron ponticum) and especially their litter. Control of the colonizing
species is essential (Marrs et al. 1998a). Control of conifers such as P. sylvestris
is done easily by cutting, because it does not regenerate from cut stumps, but for
all other colonizing species, either mechanical treatment needs to be repeated
on a regular basis (e.g., Pteridium aquilinum control; Marrs et al. 1998a),
or a herbicide should be included in the strategy (Marrs 1988). One of the
techniques used in heathlands is “sod cutting and removal,” and subsequent
restoration proceeds in a nutrient-poor, subsurface layer (Werger et al. 1985,
Diemont 1994). This approach has been commonly used in The Netherlands
and Belgium.
Like grasslands, heathlands require manipulation in the Secondary Management
Phase, and usually this will include grazing, cutting, and burning.
However, young heathland plants are very sensitive to grazing, and they need
protection from grazing until they become established (Gimingham 1992).
6.4.2.3 Wetlands
Highly dynamic systems such as river floodplains have high nutrient turnover
rates and are normally very productive. In Europe, such systems were once
dominated by species such as Carex spp., Phragmites australis, and Typha spp.
in the wettest parts and soft- and hardwood forests in less-flooded parts. Because
of their fertility, the majority of such sites are exploited for agriculture and
pristine floodplains are now amongst the most endangered ecosystems worldwide
(Olson and Dinerstein 1998). After abandonment, restoration to sedge
or reed beds and softwood forests (e.g., Salix spp., Populus spp.) can proceed
quickly but a conversion to hardwood forests (e.g., Quercus spp., Ulmus spp.,
Frangula spp.) is less common. Existing evidence of hardwood development
comes mainly from North America and results suggest that unassisted succession
takes at least 50–100 years, depending on site conditions and proximity
to seed sources (Collins and Montgomery 2002). Planting native tree mixtures
can accelerate this process somewhat but even after 50 years there were considerable
differences in the understory composition of planted woodland and
historic bottomland forests (Shear et al. 1996).
Wet systems with less dynamic water regimes (see Chapter 5) usually exhibit
lower site fertility, because organic matter decomposes slowly and is deposited
as peat. The nutrient stocks of such mires are large but nutrient availability is low
(Koerselman and Verhoeven 1995). Human interference almost always involves
drainage, with a consequent initial large release of stored nutrients (Grootjans
et al. 1985). Even after just a short drainage period and soil structural change,
Chapter 6 Manipulation of Succession 135