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Global Climate Change Digest
A Guide to Information on Greenhouse Gases and Ozone Depletion
Published July 1988 through June 1999

FROM VOLUME 12, NUMBER 5, MAY 1999

BIOTIC RESPONSE TO CLIMATE CHANGE

Item #d99may9

“Population Dynamics of Fraxinus Nigra in Response to Flood-Level Variations, in Northwestern Quebec,” J. Tardif and Y. Bergeron, Ecological Monographs, 69 (1), 107-125 (1999).

A study of black ash around a lake in Quebec that is subject to gradual fluctuations in spring flood levels shows that they adapt to their changing environment by strategically different reproduction methods. Trees in the floodplain relied mainly on vegetative sprouting; less-exposed trees relied on seed dispersion. These strategies make black ash resilient to flooding disturbance and may be their natural defense against climate change and its associated environmental changes.

Item #d99may10

“Why Do Fast- and Slow-Growing Grass Species Differ So Little in Their Rate of Root Respiration, Considering the Large Differences in Rate of Growth and Ion Uptake?” I. Scheurwater et al., Plant, Cell and Environment, 21 (10), 995-1005 (1998).

Uptake of O2 by roots is very similar in fast- and slow-growing grasses, even though fast-growing grasses have a higher specific respiratory cost for biomass maintenance. After inhibition by CO₂ buildup, diurnal variation in respiration rates, increased respiratory release of CO₂, and alternative-pathway activities were ruled out, a one-third-less respiratory cost for ion uptake on the part of fast-growing grasses was found to account for their relatively lower O2 root respiration.

Item #d99may11

“Biological Response to Climate Change on a Tropical Mountain,” J. A. Pounds, M. P. L. Fogden, and J. H. Campbell, Nature 398, 611-615 (1999).

Twenty species of frogs and toads in a 30-km2 study area in the highland forests at Monteverde, Costa Rica, have disappeared since 1987. Demographic studies indicated that these population crashes are probably part of a widespread alteration of the distribution and abundance of bird, reptile, and amphibian communities in the area. The crashes are linked to environmental warming, which has altered patterns of dry-season mist frequency. Dry-season mist is inversely correlated with equatorial-Pacific sea-surface temperatures. As the ocean has warmed since the mid-1970s, dry-season mist has declined, and the base of the orographic cloud bank has risen in altitude. Birds and some other animals have migrated up the mountainsides with the cloud banks; but some species, such as the golden toad, have not been able to adapt and have become extinct.

Item #d99may12

“Simulating the Effects of Climate Change on Tropical Montane Cloud Forests,” C. J. Still, P. N. Foster, and S. H. Schneider, Nature, 398, 608-610 (1999).

An exploration of the effects of changing the values of atmospheric parameters in a global climate model, including (1) the vertical profiles of the relative and absolute humidity surfaces and (2) the warmth index, indicated that, during glacial periods, cloud forests would shift downward (which agrees with available paleodata) and that, during CO₂- induced global warming, they would be shifted upwards hundreds of meters. In the latter case, temperature-induced evapotranspiration would also increase, which could have serious implications for the already stressed forests.