Shoreline Vegetation in Axe Lake, Ontario: Effects of Exposure on Zonation Patterns

Abstract

This ~tudy tests several hypotheses relating community structure to environmental disturbance, by test~ng for changes in the zonation patterns of lakeshore vegetation. Twenty-five transects wer~ e~~mmed at ~ifferent positi~ns along an exposure gradient. The range of water depths tolerated by mdividual spec1es (real1zed mche width) changed with exposure. Some (Lobelia dartmanna, Utricularia cornuta) reached their maximum on exposed shores, others (Drosera intermedia Cladium mariscoides) at i~ter~ediate exposure, and others (Pontederia cordata, Triadenumfraseri) on shelter~d shores. Spec1es nchness peaked significantly at intermediate levels of exposure (P < .0_1). In sp1te of chang~s iJ_J b~th species composition and richness, mean niche width did not change w1th ~xposu:e. The d1stnbutwn of the upper and lower limits of species along the gradient was exam1~ed_ usmg measures of boundary clustering. The lower and upper boundaries of species were b?th s1gmficantly c~ustered (P < .001), suggesting discrete communities exist on the shoreline gradient. As exposure mcreased, upper boundanes became more clustered (P < .002); lower boundaries ~ere u~1affected. The dis~ribut_ion of boundaries shifted landward with increasing exposure. This fact IS possibly related to an identical landward shift in the lower boundaries of shoreline shrubs which appear to have a major influence on the distribution of herbaceous shoreline vegetation. '.

Adaptation of submerged macrophytes to both water depth and flood intensity as revealed by their mechanical resistance

“…Aquatic plants grown in slow flows and/ or shallow water generally possess less flexible, but stronger stems than those inhabiting fast running water or deep waters (Brewer & Parker, 1990;Usherwood et al, 1997;Bociag et al, 2009;Miler et al, 2010Miler et al, , 2012. Additionally, the canopy-forming species generally have much higher growth rate than species with other growth forms in lakes with low-light availability (Keddy, 1983;Chambers & Prepas, 1988;Hudon et al, 2000). Therefore, these results can finally suggest that C. demersum was the most adaptive species to both deep water and rapid floods.…”

“…A rapid water level rise, especially that induced by a summer flood after exceptionally strong rainfall events, generally results in large reductions in biomass and shoot spatial extent, as well as the disappearance of SAV in freshwater lakes (Wallsten & Forsgren, 1989;Gacia & Ballesteros, 1996;Fernández-Aláez et al, 1999;Cui et al, 2000;Havens, 2003;Yang et al, 2004), due to low-light availability (Chambers & Kalff, 1985a;Best et al, 2001) and/or increased shoreline wave energy (Scheffer, 1998;Havens et al, 2001). Light availability significantly affects the maximum biomass and colonization depth of SAV (Keddy, 1983;Chambers & Prepas, 1988), as well as the mechanical resistance of terrestrial plants . Hydraulic forces from waves and winds can significantly affect the mechanical resistance of SAV, resulting in mechanical damages (e.g., stem breakage, uprooting, or other damages) (Koehl, 1984;Schutten et al, 2005), which ultimately have adverse effects on plant growth (Idestam-Almquist & Kautsky, 1995;Hudon et al, 2000).…”

Assembly and response rules: two goals for predictive community ecology

“…To illustrate this, consider the functional group of small evergreen rosette plants in wetlands, termed isoetids (Hutchinson 1975) or stress tolerators (Boston & Adams 1986). These species are characteristic of infertile, wave-washed shorelines, and their presence can be predicted from knowledge of substrate (Pearsall 1920), wave and ice scour (Keddy 1983) or vegetation biomass (Wisheu & Keddy 1989a). However, in some habitats this functional group is represented by the common and widespread species Lobelia dortmanna or Eriocaulon septangulare.…”

Developing water level regulation strategies for macrophytes restoration of a large river-disconnected lake, China

“…WLF not only can affect macrophytes directly, but also indirectly by acting on the substrate, nutrient, light, water and gas. Therefore, the spatial and temporal variations of water level are crucial in structuring macrophyte communities of lakes (Keddy, 1983;Wilcox and Meeker, 1991;Rills and Hawes, 2002;Leyer, 2005;Van Geest et al, 2005).…”