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Highlights: [•] Wetland plants were exposed to flooding treatments in experimental ponds. [•] Growth and expansion were measured in relation to Stratiotes aloides and nutrients. [•] Flooding negatively affected creeping plant species that happen to be rare. [•] Flooding had no negative impact on tall and common reedy species. [•] No short-term effect of S. aloides and variable effects of nutrient availability. [ABSTRACT FROM AUTHOR]

Abstract: Tree species composition in forests can be strongly modulated by high densities of cervid herbivores ultimately leading to local extirpation of species. To establish which cervid densities are compatible with the recruitment of a browse sensitive tree species, seedlings and saplings should be surveyed under variable cervid densities rather than in their presence or absence alone. We studied the growth and survival of different demographic stages of balsam fir (Abies balsamea) on Anticosti island (Québec, Canada) under controlled densities of white-tailed deer (Odocoileus virginianus). In a seven-year experiment using deer enclosures, we followed the life stage and fate of individually tagged balsam fir seedlings/saplings under forest cover and forest logged at the start of the experiment. Almost no regeneration into the sapling stage (>30cm) was observed under ambient deer densities after 7years and decreased survival and growth were observed under an experimental deer density of 15km−2. However, mortality at ⩽15deerkm−2 decreased over time and with age and stem height, converging towards mortality observed at 0deerkm−2. Given the relatively high stem density of saplings at 15deerkm−2 7years after the start of the treatment, our data indicate that at this density considerable balsam fir regeneration may occur, although the ultimate contribution of balsam fir to the canopy remains uncertain. The notion that small seedlings are most vulnerable to deer browsing and that balsam fir recruitment rapidly decreases after logging suggests that maintaining low deer densities is most crucial immediately after a stand-initiating disturbance (e.g. logging). [Copyright &y& Elsevier]

1. Bottom-dwelling charophytes have been observed to replace canopy-forming pondweeds within a few years in de-eutrophied shallow lakes. Competition for bicarbonate (HCO3−) may explain this shift in vegetation dominance but inhibition of pondweeds by Chara spp. through direct competition has not been shown experimentally. 2. We tested whether charophytes inhibited growth of fennel pondweed ( Potamogeton pectinatus) in the absence of belowground competition by growing plants in pots in mesocosms following a replacement series experimental design. To further understand the role of bicarbonate, we studied main and interactive effects of Chara, light and bicarbonate on P. pectinatus growth in a laboratory study. 3. Early in the mesocosm experiment, high charophyte densities had a negative effect on P. pectinatus cover at a time when bicarbonate levels were low. However, bicarbonate levels eventually converged to low levels in all treatments. At final harvest, both species exhibited lower biomasses at higher densities of conspecific pots, indicating that ultimately intraspecific competition was limiting. In a laboratory study, Chara inhibited P. pectinatus the most under a combination of high light and high bicarbonate concentrations, suggesting that Chara may negatively affect P. pectinatus by acting as a general nutrient sink. 4. Our results suggest that Chara growth can reduce bicarbonate levels, delaying but not preventing a P. pectinatus growth pulse. Given the recorded inhibition under ample bicarbonate supply, Chara’s ability to act as nutrient sink may contribute to the decline of P. pectinatus under Chara recovery in shallow lakes. [ABSTRACT FROM AUTHOR]

The degree to which vertebrate herbivores exploitatively compete for the same food plant may depend on the level of compensatory plant growth. Such compensation is higher when there is reduced density-dependent competition in plants after herbivore damage. Whether there is relief from competition may largely be determined by the life-history stage of plants under herbivory. Such stage-specific compensation may apply to seasonal herbivory on the clonal aquatic plant sago pondweed (Potainogetonpectinatus L.). It winters in sediments of shallow lakes as tubers that are foraged upon by Bewick's Swans (cygnus columbianus bewickii Yarrell), whereas aboveground biomass in summer is mostly consumed by ducks, coots, and Mute Swans. Here, tuber predation may be compensated due to diminished negative density dependence in the next growth season. However, we expected lower compensation to summer herbivory by waterfowl and fish as density of aboveground biomass in summer is closely related to photosynthetic carbon fixation. In a factorial exclosure study we simultaneously investigated (1) the effect of summer herbivory on aboveground biomass and autumn tuber biomass and (2) the effect of tuber predation in autumn on aboveground biomass and tuber biomass a year later. Summer herbivory strongly influenced belowground tuber biomass in autumn, limiting food availability to Bewick's Swans. In contrast, tuber predation in autumn by Bewick's Swans had a limited and variable effect on P. pectinatus biomass in the following growth season. Whereas relief from negative density dependence largely eliminates effects of belowground herbivory by swans, aboveground herbivory in summer limits both above- and belowground plant biomass. Hence, there was an asymmetry in exploitative competition, with herbivores in summer reducing food availability for belowground herbivores in autumn, but not the other way around. [ABSTRACT FROM AUTHOR]