Phenology And Seasonal Variability Of Understory Herbs In Broad-leaved Korean Pine Forest In Changbai Mountain

Despite a growing awareness that the herbaceous layer serves a special role in maintaining the structure and function of forests, this stratum remains an underappreciated aspect of forest ecosystems. Species diversity of forest herbs is one of the most striking features of deciduous forests in the temperate zone, and this layer always has wide array of phenology patterns along the growing season. In this study, we compared understory herb diversity in primary Korean pine (Pinus koraiensis) old-growth and secondary aspen-birch (Populus davidiana and Betula platyphylla) forests to understand its seasonal variability and relation to environmental factors in Changbai mountain, North-East China. On two one hectare plots(100 m×100m) a total of 100 1-m2 sub-plots (each 20 m×20 m has 4 1-m2 sub-plots) were monitored monthly from May to September in 2009. Soil properties (soil organic matter, available nitrogen, available phosphorus, available potassium, soil water, pH and litter depth) and light regime (LAI, PPFD and canopy presence) were recorded for each four sub-plots. Flowering phenology of herbaceous were classified into three types:spring bloomers whose flowering usually started at least before the 50% canopy closure from early April to mid-May, early-summer bloomers whose flowering occurred during the progress of canopy closure (mid-May to early June), and late-summer bloomers whose flowering occurred after canopy closure (after late June). In the three sample plot(secondary aspen-birch forest, secondary mixed forest, and primary broad-leaved Korean pine forest),114 species were found, belong to 41 families and 92 genus, including 12 spring bloomers,38 early-summer bloomers,52 late-summer bloomers and 12 ferns. Herbaceous composition varied over the growing season. Herbaceous layer dominated by Anemone amurensis and Corydalis ambigua in early spring, whereas Brachybotrys paridiformis and Cardamine leucantha prevailed in the second part of the growing season. Species number in the old-growth forest was higher than that in the secondary forest in early spring, but the pattern reversed during summer and autumn. The continues low temperature in winter and spring in 2010 result in leaf phenology of 18 understory herbs in broad-leaved Korean pine forest delayed 12.9 days,flowering phenology delayed 10.8 days, and the flowering peried shortened 1.7 days. Phenology is a key temporal element in regulating the herb diversity, while the environmental factors were the key spatial elements. Environmental factors were closely related with trees, shrubs, seedlings and herbaceous, which indicated that trees, shrubs, herbs and seedlings directly, or indirectly interacted by influence their environmental factors. The spatiotemporal interaction created complicated forest ecosystem, the herbaceous layer serves a special role in maintaining the structure and function of the ecosystem.