Grasslands of the World.pdf - Disasters and Conflicts - UNEP

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Grasslands of the world
scarcity of manipulation experiments; most results are derived primarily from
observation-type studies. The most frequent issue is the influence of grazing
by domestic herbivores on a number of vegetation and soil variables (over
30 percent of studies reviewed). Next come studies on the influence of water
or nitrogen on ecosystems (13 and 10 percent of reviewed studies, respectively)
and, thirdly, research on the impact of fire on ecosystems (10 percent of
current studies). Research and surveys on wildlife account for 9 percent of
abstracts, and studies of ecosystem processes such as primary productivity and
decomposition are 9 and 5 percent of all studies, respectively. Satellite image
analysis or simulation modelling are only used in about 4 percent of ongoing
research activities.
Grazing (mostly by sheep ) is currently being studied in relation to its effect
on: vegetation structure in the shrub-dominated ecosystems of Patagonia at
either patch or landscape scale (Ares, Bertiller and Bisigato, 2001b; Cecchi,
Distel and Kröpfl, 2001; Ciccorossi and Sala, 2001; Ghersa et al., 2001;
Ripol et al., 2001); overall community plant diversity or population genetic
diversity of endangered plant species at local spatial scales (Aguiar, Premoli
and Cipriotti, 2001; Cesa and Paruelo, 2001; Cibils et al., 2000); riparian
meadow productivity (Collantes, Stoffella and Pomar, 2001; Golluscio et al.,
2000; Utrilla et al., 2000); the demography of native dominant tussock grasses
(Weber et al., 2000; Oliva, Collantes and Humano, 2001); interspecific relations
between shrubs (Cipriotti and Aguiar, 2001); shrub crown shapes (Siffredi
and Bustos, 2001); soil nitrogen mineralization rates in relation to changes
in vegetation composition (Anchorena et al., 2001); shrub recruitment in
relation to soil compaction (Stofella and Anchorena, 2001); and microphytic
crusts in the Monte shrub steppes (Silva et al., 2001). Finally, grazing is also
currently being researched in relation to herbivore diets and lambing rates at
regional scales (Hall and Paruelo, 2001; Pelliza et al., 2001). Water is the single
most important factor regulating processes such as primary and secondary
productivity in Patagonian ecosystems. Nitrogen dynamics is closely tied
to moisture availability. Although there has been much research in the past
decades addressing the use of water by different life forms (Sala, Lauenroth and
Golluscio, 1997, and references therein), only recently have studies begun to
address issues related to the joint effects of water and nitrogen. One of the few
ongoing manipulative field experiments is being conducted in this area, studying
the effects of drought on productivity and N mineralization, using rain shelters
in the shrub steppe ecosystem (Sala, Yahdjian and Flombaum, 2001). Current
studies on the influence of water (alone) include: effects of water deficit on the
germination of an endangered grass species (Flombaum et al., 2001); simulation
of competition for water and light in Festuca tussocks growing in a grass-forest
ecotone (Fernández, Gyengue and Schlichter, 2001); effects of stem flow on soil
water content beneath shrubs (Kröpfl et al., 2001); and Poa ligularis response to
defoliation and water stress in a greenhouse experiment (Sáenz and Deregibus,