Environmental Engineering Reference
In-Depth Information
disturbance on biodiversity (Wilson and Johns, 1982). There is a substan-
tial literature that shows that human-induced disturbance and habitat
degradation can result in a decline in biodiversity and species extinction.
Highly intensive agricultural practices that reduce spatial habitat com-
plexity leading to homogenization of the landscape may lead to biodiver-
sity loss. The decline in most of Europe's SPECS (Species of European
Conservation Concern) has been linked to land use and management
changes with agricultural intensii cation being cited as the most signii cant
threat to bird populations (Tucker and Heath, 1994). Arable farming
systems in parts of Europe are thought to have played a part in the decline
of many species. For example, as a consequence of changing conditions in
agricultural i elds in Britain many bird species have undergone signii cant
population declines. Fuller et al.
(1991) report that many British farmland
birds have declined dramatically over the last three decades as agricultural
land use has altered, hedgerows have declined and farms have developed
to form larger contiguous areas. A reduction in forest area due to agricul-
tural expansion can also reduce species diversity. Studies of the avifauna
of fragmented forests have shown that some species are absent or infre-
quent in very isolated sites and that smaller woodland size gives rise to
less bird species diversity (Lynch and Whigham, 1984; Opdam et al.,
1985;
Ford, 1987; van Dorp and Opdam, 1987).
Data from censuses of domestic animals collected for tax purposes as
well as from hunting statistics have been combined with palynological
reconstructions of vegetation to demonstrate the long-term ecological
ef ects of management practices. For example, hunting statistics for moose
and roe deer in Sweden suggest dramatic recent population increases that
have probably contributed to the decline of deciduous tree species (Ahlén,
1975). Peterken and Tubbs (1965) related l uctuating grazing regimes of
horses, pigs and cattle in the New Forest, England, to waves of regenera-
tion based on the age structure of existing trees. In Poland pollen data has
enabled reconstructions of vegetation successions (Mitchell and Cole,
1998). This has been combined with data on herbivore densities for forests
in eastern Poland over the last 200 years (Faliñski, 1986) and shows that
the proportion of conifers, principally
Picea abies
, increased dramati-
cally at the expense of broadleaved species during the period of intensive
grazing. Tree regeneration in the subsequent low-intensity grazing period
was dominated by broadleaved taxa, initially
Betula, Populus
and
Caprinus
and, subsequently,
Tilia
and
Quercus
.
Jorritsma et al.
(1999) used a dynamic simulation model FORGRA
to evaluate the impact of grazing on Scots pine regeneration in the
Netherlands. They showed that even low densities of ungulates could have
a signii cant impact on forest development. Their model indicates that
