| Ice storm disaster as an important form of natural disturbances on forest ecosystems could produce a far-reaching impact. A rare great ice-storm occurred at early of 2008 in South China, and it has been becoming important and common-concerned scientific issues that the impacts of the great ice-storm on distribution pattern, biodiversity of seedlings & saplings, and on forest succession. Three different forest communities(DBF, deciduous brodleaves forest; EBF, evergreen broadleaf forest; MF, mixed forest) with different dominant canopy tree species in Nanling National Nature Reserve were selected for studying in this paper. The methods of phytocoenology was used for investigating plant plots in 2012 and 2015, and for analyzing tree spcies composition & structure, biodiversity & distribution patterns of the understory saplings and regerneration & succession of forest ecosystem. By analyzing the differences of the different communities in soil physical and chemical properties and by the soil seed bank germination experiment and observation canopy species composition and structure, the induced causes of the understory saplings quantity, distribution patterns and biodiversity differences were dissected. The reasonable predictions for the regeneration and succession of understory saplings in three different communities were made by observing light environment changes in the forests, the dominant saplings’ photosynthetic property itself and combined with the growth and mortality of understory saplings. The main results are as following:(1) More than 80% of saplings derived from seed germination and a few propotion from spouting regeneration in the different forest communities, the percentage of saplings derived from spouting in the deciduous broad-leaved forest, evergreen broadleaf forest, mixed conifer and broadleaf forest occupied for 8.7%, 12.3% and 5.2% respectively. There were obvious differences in the understory saplings number for different communities, 2.44 individuals/m2 of sapling density was found in the deciduous broad-leaved forest, 1.95 and 1.50 individuals/m2 in evergreen broadleaf forest and mixed forest respectively. For single sapling species, the density of Neolitsea chui in deciduous broad-leaved forest was the largest, reaching 0.72 / m2.(2) The understory saplings biodiversity of different communities showed differences, all biodiversity indexes showed: deciduous forest <evergreen broadleaf forest <mixed forest. Shannon-Wiener index(H’) of understory seedlings and saplings increased with increasing species richness S, showing a similar significant differential changes. Simpson index(D) changes significantly had close positive relation with Pielou index(J) changes.(3) The distribution pattern analysis of dominant sapling species in different communities showed that all of the advantageous sapling species appear aggregated distribution. Gather strength of Neolitsea chui which distributed in all communities was the minimum in the deciduous broadleaf forests, close to the Poisson distribution. Understory saplings distributed across two communities had relatively small gather strength. And the sapling species distributed only within a single community popularly had larger gather strength.(4) There were no significant differences in soil physical and chemical properties at the sam depth among different communities. Soil pH value is about 5.0, soil bulk density is greater, available potassium and effective nitrogen are rich, low content of available phosphorus, N: P ratio is larger. With soil depth increasing, soil bulk density and pH value increased slightly, but organic matter, effective N, available P, available K were decreased.(5) The number of viable seeds of woody tree species in soil seed bank were 25 to 27 seeds/m2, the rank of vigorous seeds in the different communities was deciduous broad-leaved forest > evergreen broadleaf forest > coniferous forest, but there were no significant differences. Seed germination seedlings were mainly belong to deciduous arbor trees or small trees, such as Choerospondias axillaris, Albizia kalkora, Sapium discolor, Mallotus japonicus, Litsea cubeba, Rhus chinensis, Elaeocarpus japonicus, etc., and they were distributed in all experiment communities. There were obvious relationship between soil seed quantitative distribution and tree species composition in community, for example, viable Choerospondias axillaris seeds reached 7.0 / m2 but almost no Neolitsea chui tree seeds in deciduous broad-leaved forest.(6) The quantum conversion efficiency of understory dominant saplings species was relatively high than non-dominant species, the maximum net photosynthetic rate of different saplings existed significant differences. These signs indicated that functional group and life forms of sapling species occurred differentiation, Ligustrum lianum, Fraxinus chinensis, Castanopsis carlesii were higher light saturation point. Water utilization efficency of Daphniphyllum oldhami was low, but that of Machilus kwangtungensis, Daphniphyllum calycinum, Schima superba and Neolitsea chui were higher, their light saturation point were between 600 to 800μmol·m-2s-1.(7) From the point of view canopy openness, there existed obvious seasonal variation in deciduoud broadleaf forest. The canopy openness in mixed forest was larger than that in evergreen broadleaf forest. Comparative observation in 2012 and 2015 indicated that the canopy openness in all communities deceased following forest restoration, a reduction in the performance of evergreen broadleaf forest > mixed forest > deciduous broad-leaved forest, this implied crown restoration rate of evergreen broadleaf fores was fast than that of mixed forest and deciduous broadleaf forest. Change trends of openness in understory saplings layer were not coincided with that in canopy layer.(8) The differen saplings growth and motality in each communities reflects the saplings’ adaptive strategies in response to changing light conditions of the understory. Obvious diameter increment occurred mainly in deciduous broadleaf forest, and tree height increment in mixed forest. No significant increment of diameter and tree height in evergreen broadleaf forest due to small canopy openness. For death amount and mortality rates of understory saplings, it was the largest in the evergreen broadleaf forest, sapling species with the highest mortality rate included Ligustrum lianum, Elaeocarpus japonicus, Daphniphyllum Oldham and Machilus kwangtungensis, Daphniphyllum calycinum, Neolitsea chui had lower mortality rate. |
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