Abstract:

Aims Our objectives were to determine the seasonal aspect stages of plant communities at seven sites in the temperate area of eastern China and analyze spatial-temporal variation of the onset dates of seasonal aspect stages and its relation to climatic factors.
Methods We developed a simulating method of phenological cumulative frequency to determine the seasonal aspect stages of plant communities. Basic ideas of the method were to establish a mixed data set composed of the occurrence dates of all phenophases of observed deciduous trees and shrubs for each site and each year, and then calculate the frequency and cumulative frequency of the occurrence dates of phenophases in every five-day period throughout each year and for each site. We used a logistic curve to simulate the phenological cumulative frequency and computed the corresponding dates of maximum changing rate of the curvature as the onset dates of seasonal aspect stages.
Important findings The annual mean dates of greenup and active photosynthesis onsets were delayed with increased latitude, whereas the annual mean dates of senescence and dormancy onsets advanced with increased latitude. Other than the onset dates, the annual mean lengths of greenup, active photosynthesis and senescence periods did not change obviously with latitude but the annual mean length of dormancy period was apparently prolonged with increased latitude. From 1982 to 1996, the regional mean onset date and duration of greenup period significantly advanced at a rate of 0.6 d·a^-1 and lengthened at a rate of 0.7 d·a^-1; the mean onset date and duration of active photosunthesis period were insignificantly delayed and shortened; the mean onset date and duration of senescence period slightly advanced and lengthened; and the mean onset date and duration of dormancy period slightly advanced but significantly shortened at a rate of 0.9 d·a^-1. The onset date of seasonal aspect stages generally correlates better with temperature than with precipitation. The regional mean greenup onset date shows a significantly negative correlation with mean temperature in the current month in a changing rate of 4.3 d·℃^-1, whereas the regional mean active photosynthesis onset date presents a significantly negative correlation with mean temperature during the former second month to the current month in a changing rate of 4.4 d·℃^-1. However, the regional mean senescence and dormancy onset dates do not correlate significantly with mean temperatures.

Key words: simulating method of phenological cumulative frequency, seasonal aspect stages of plant communities, spatial-temporal variation, climatic factors, temperate eastern China