Abstract: To understand the effects of seasonal freeze-thaw on the ecological processes of subalpine forest ecosystem, the enzyme activities in Abies faxoniana and Betula platyphylla litters under freeze-thaw were measured from October 2006 to October 2007 by the method of litter bags. There was an obvious monthly change in the enzyme activities, but the peak time varied with enzymes. Compared to the control, freeze-thaw had significant effects on the activities of invertase, urease, cellulase, and dehydrogenase in the litters (P＜005). Over a growth season, the invertase, cellulase, and urease activities in fir litter increased by 661%, 148%, and 763%, respectively while dehydrogenase activity decreased by 184%, and the invertase activity in birch litter increased by 394% while the urease, cellulase and dehydrogenase activities decreased by 182%, 287% and 156%, respectively. As for the activities of peroxidase and polyphenol oxidase in fir and birch litters, they were less affected by freeze-thaw. All of these revealed that seasonal freez e-thaw had definite effects on the litter decomposition of subalpine forest, which closely related to the kind of litter and its decomposition stage.

Key words: modified Logistic-CA, multi-scenario, ecosystem services, simulation and prediction, coastal area.