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Phenology and Seed Development of the Alpine Sedges Carex curvula and Carex firma in Response to Contrasting Topoclimates

Johanna Wagner and Barbara Reichegger
Arctic and Alpine Research
Vol. 29, No. 3 (Aug., 1997), pp. 291-299
DOI: 10.2307/1552143
Stable URL: http://www.jstor.org/stable/1552143
Page Count: 9
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Phenology and Seed Development of the Alpine Sedges Carex curvula and Carex firma in Response to Contrasting Topoclimates
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Abstract

Flowering phenology and seed development of two alpine sedges were investigated at 2200-2300 m on sunlit sites with little winter snow cover and on northern slopes with deep winter snow accumulation. During the growing season daily mean canopy temperatures between such sites differ by about 2°C. Additionally, tussocks were transplanted to 600 m a.s.l. in order to study the reproductive responses in an environment about 10°C warmer. At high altitudes the timing of reproductive processes in both Carex species strongly depended on the date of snowmelt. Carex curvula flowered as soon as the mean daily temperature exceeded 5 to 6°C. For the later flowering C. firma no specific threshold temperature could be found, indicating that the onset of flowering is regulated by complex environmental triggers. Depending on the site, C. curvula required 7 to 8 wk, and C. firma 8 to 10 wk for seed formation; under lowland conditions seeds matured within 6 wk and 8 wk, respectively. Abnormal changes in temperature may cause phenological anomalies and developmental disturbances, as could be observed after transplantation of Carex plants to the lowland. In both species, about half of the ovules matured into seeds (seed/ovule ratio 0.5-0.6), except for C. firma plants growing on the north-facing slope (S/O ratio 0.3). After transplantation the S/O ratio was 0.5 for C. curvula and 0.4 for C. firma. Seeds from sunlit sites germinated better than those from the north-facing sites. Generally, more warmth and a longer growing season promote seed production and seed size. It can be expected that a moderate climate warming will not only favor upward migration of both Carex species, but also colonization of bare ground by means of seed dispersal.

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