Yearto Year Climate Variability and Plant Flowering

Every summer since 1980, G. Shaver has counted the average number of flowers of the cotton grass (Eriophorum vaginatum) at 38 sites along the highway from Fairbanks to Prudhoe Bay (Shaver 1986b) (figure 5.10). The variability from year to year was amazing; the average ranged from 1% to 46% (figure 5.11). Even more remarkable was the synchrony of flowering along the entire transect that covered ~650 km. This is evident in figure 5.12, where the mean inflorescence for a year is compared, for each site, with the long-term mean. Years of above-average flowering, that is, those above the 0.0 line, have above-average flowering almost everywhere along the transect, whereas years of below-average flowering are below average everywhere.

The environmental cause of the synchronous flowering must be linked to events of the past one or two years, because the flower buds are set at the end of the previous summer. When the detailed climate record at Toolik Lake was examined, there was a good correlation between the number of flowers per plot and the cumulative degree-days above 0°C at a depth of 20 cm in the soil (figure 5.13). The

Figure 5.10 Eriophorum vaginatum (arctic cotton grass) in bloom at Toolik Lake.

best correlation was found when the period for the degree-days was the 12 months beginning in the fall and extending to the end of the summer in the year before the counting. For example, the number of flowers counted in July 2000 correlated well (R2 = 0.69) with the degree-days in the fall of 1998 and the spring and summer of 1999.

One hypothesis that arises from these findings is that the plants flower after c s=

1988 1990

Year

Figure 5.11 The yearly average number of inflorescences for 38 plots along the highway from Fairbanks to Prudhoe Bay from 1980 to 2001.

1980

1982

1984

1986

1992

1994

1996

1998

2000

1980-1985

Mean Inflorescence Count Relative to the Longterm Mean

Figure 5.12 The mean inflorescence counts relative to the long term mean for sites from Fairbanks to Prudhoe Bay. Only 5 years of data are shown.

Figure 5.13 Number of flowers of Eriophorum vaginatum per 2-m by 2-m plot at the Too-lik site plotted against the cumulative degree-days above 0°C at a 20-cm depth in the soil. The degree-days cover one complete year beginning 22 months before the counting time.

20 cm Soil Degree-days above 0

Figure 5.13 Number of flowers of Eriophorum vaginatum per 2-m by 2-m plot at the Too-lik site plotted against the cumulative degree-days above 0°C at a 20-cm depth in the soil. The degree-days cover one complete year beginning 22 months before the counting time.

they have accumulated a threshold quantity of nitrogen from the soil. The nitrogen is made available to the plants through the process of decomposition in the soil. This microbial process will be slightly faster during years when the soils are warmer.

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