Monitoring the Responses of Freshwater Ecosystems to Climate Change - Climate Change Impacts on Freshwater Ecosystems - page 112

native species, an influx of invasives, and a community change towards
dicotyledonous species in northern wetlands (Hogenbirk & Wein 1991). In
bogs, increased temperature, together with an experimentally lowered water
table, caused a 50% increase in the cover of shrubs, and a 50% decrease in the
cover of graminoids (Weltzin et al . 2003). More frequent droughts cause
wetland vegetation to become both woodier and drier. Pond-meadow wetlands
may acquire more species, particularly nonwetland species (Hudon 2004;
Mulhouse et al . 2005).
Soil temperature rise causes shifts in the productivity of plant communities,
e.g. an increase in shrub productivity and decreased forb (herbaceous flowering
plant) productivity. A higher water table caused bryophyte productivity to
increase in bog samples, while shrub productivity was lower (Weltzin et al . 2000).
Altered riparian vegetation (herb vegetation and trees), and an altered biomass
and productivity, affects detritivores and results in lower decomposition rates
(Carpenter et al . 1992). Decomposition in river marginal wetlands is highly
dependent on precipitation, whereas climate change or river flow management
could disrupt floodplain nutrient dynamics, i.e. the periodic processes of organic
matter retention, breakdown, mineralization and release (Andersen & Nelson
2006). Species' sensitivity to climate change is dependent on plant traits and
niche properties (Thuiller et al . 2005). Besides water table height, which reflects
many of these changes to some degree, the occurrences of certain species and
vegetation assemblages may be used as indicators for climate change in plant
communities (Table 5.3).
Secondary production
Lower water tables, increased temperatures and more frequent droughts lead to
a loss of habitat for obligate wetland species. Invertebrates are affected directly
by changing water table or temperature, but also indirectly by shifts in nutrient
availability. Invasive, exotic plant species and changed nutritional quality of
litter affect detritivores (Carpenter et al . 1992; Andersen & Nelson 2006).
Other taxa affected by increased drought, weaker spring flows and reduced
inundation are fish, amphibians, waterfowl and muskrat (Schindler 2001;
Diamond et al . 2002).
Climate change advances the spring arrival of migrating birds, in both short-
and long-distance migrants (Zalakevicius & Zalakeviciute 2001). It also changes
the winter distribution of shorebirds (Gillings et al . 2006). Furthermore, global
climate change alters the ranges and population state of different breeding bird
species and populations. The impact of global warming on terrestrial and
wetland birds is more evident than upon waterfowl (Zalakevicius & Zalakeviciute
2001). Variability of precipitation in wetlands affects population and community
dynamics of wetland birds owing to egg and nestling predation, which was
negatively correlated with water levels in wetlands (Fletcher & Koford 2004).
Suitable indicators might include the beginning of the bird's spring migration
period and metrics related to taxonomic composition of indicator taxa groups
(Table. 5.3).