AOBPreview originally published online on October 20, 2006
Annals of Botany 2006 98(6):1233-1240; doi:10.1093/aob/mcl208
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Short Delay in Timing of Emergence Determines Establishment Success in Pinus sylvestris across Microhabitats
Grupo de Ecología Terrestre. Departamento de Ecología, Facultad de Ciencias Universidad de Granada. E-18071 Granada, Spain
*E-mail: jorge{at}ugr.es
Received: 8 May 2006 Returned for revision: 24 July 2006 Accepted: 30 August 2006 Published electronically: 20 October 2006
• Background and Aims The date of emergence may have far-reaching implications for seedling performance. Seedlings emerging early in the growing season often have a greater rate of survival or grow better if early emergence provides advantages with respect to an environmental cue. As a result, the benefits of early emergence may be lost if the environmental stress creating the differences among cohorts disappears. The experimental manipulation under field conditions of the factors that constitute the main sources of stress for seedling establishment is thus a straightforward method to evaluate the impact of date of emergence on seedling establishment under realistic conditions.
• Methods Two field experiments were performed to analyse the effect of emergence date on survival and first-year growth of Scots pine seedlings in natural mountain forests in south-east Spain. Two main environmental factors that determine seedling success in these mountains were considered: (1) microhabitat type (monitoring the effect of date of emergence in the three most common microhabitats where seedlings recruit); (2) summer drought (monitored by an irrigation treatment with control and watered sampling points).
• Key Results Overall, early emergence resulted in a higher probability of survival and better growth in the two experiments and across microhabitats. However, the reduction in summer drought did not diminish the differences observed among cohorts: all cohorts increased their survival and growth, but early cohorts still had a clear advantage.
• Conclusions Date of emergence determines establishment success of Pinus sylvestris seedlings, even if cohorts are separated by only a few days, irrespective of the intensity of summer drought. The experimental design, covering a gradient of light intensity and soil moisture that simulates conditions of the regeneration niche of Scots pine across its geographical range, allows the results to be extrapolated to other areas of the species. Date of emergence is thus likely to have a large impact on the demography of Scots pine across its geographical range.
Key words: Cohort effects, cohort of emergence, date of emergence, delayed emergence, irrigation experiments, Pinus sylvestris, seedling establishment, Sierra Nevada National Park, summer drought
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