Demographic vulnerability of the clonal and endangered meadow thistle
Jongejans, E. ; Vere, N. de; Kroon, H. de - \ 2008
Plant Ecology 198 (2008)2. - ISSN 1385-0237 - p. 225 - 240.
population viability analysis - extinction risk - sexual reproduction - biological flora - perennial herb - british-isles - plants - dynamics - grassland - fragmentation
For effective management of endangered species it is pivotal to understand why a species is endangered and which key life cycle components are involved in its response to environmental changes. Our objective was to investigate the response of rosettes of the redlisted clonal herb Cirsium dissectum to anthropogenic nutrient enrichment, which threatens its populations, and the consequences of these responses for its population dynamics. We constructed matrix population models with demographic data from three populations and four annual transitions and we decomposed the spatiotemporal variation in projected population growth rates into contributions from life cycle components. These patterns were compared with below-ground rosette dynamics in different fields, and with the below- and above-ground rosette dynamics in a garden experiment with nutrient enrichment and competing grasses. The decomposition analysis revealed that increased clonal rosette formation and decreased rosette survival were driving the spatial variation in the population growth rate. Excavating the below-ground rhizome network revealed a higher rosette turn-over in experimentally fertilized garden plots, which not only resulted in increased plot-level extinction, but also in increased spread of the clonal offspring. This supported the observed trend among field populations: rosette formation trades off with rosette survival. Surviving seedlings were only found in areas where the topsoil had been removed. The endangered C. dissectum is vulnerable when its habitat becomes more productive, because this species does not have the necessary capability to build up biomass. Small-scale disturbances such as created by sod-cutting or trampling cattle are essential for seedling establishment and necessary to render the explorative strategy of rhizomatous clonal spread successful.
Long-term effects of climate change on vegetation and carbon dynamics in peat bogs
Heijmans, M.M.P.D. ; Mauquoy, D. ; Geel, B. van; Berendse, F. - \ 2008
Journal of Vegetation Science 19 (2008)3. - ISSN 1100-9233 - p. 307 - 320.
increased nitrogen deposition - increased n deposition - vulgaris l hull - vascular plants - sphagnum bogs - british-isles - northern peatlands - biological flora - boreal peatlands - solar-activity
Questions: What are the long-term effects of climate change on the plant species composition and carbon sequestration in peat bogs?Methods: We developed a bog ecosystem model that includes vegetation, carbon, nitrogen and water dynamics. Two groups of vascular plant species and three groups of Sphagnum species compete with each other for light and nitrogen. The model was tested by comparing the outcome with long-term historic vegetation changes in peat cores from Denmark and England. A climate scenario was used to analyse the future effects of atmospheric CO2, temperature and precipitation.Results: The main changes in the species composition since 1766 were simulated by the model. Simulations for a future warmer, and slightly wetter, climate with doubling CO2 concentration suggest that little will change in species composition, due to the contrasting effects of increasing temperatures (favouring vascular plants) and CO2 (favouring Sphagnum). Further analysis of the effects of temperature showed that simulated carbon sequestration is negatively related to vascular plant expansion. Model results show that increasing temperatures may still increase carbon accumulation at cool, low N deposition sites, but decrease carbon accumulation at high N deposition sites.Conclusions: Our results show that the effects of temperature, precipitation, N-deposition and atmospheric CO2 are not straightforward, but interactions between these components of global change exist. These interactions are the result of changes in vegetation composition. When analysing long-term effects of global change, vegetation changes should be taken into account and predictions should not be based on temperature increase alone.