Dynamics of dominant tree seedlings in montane evergreen broadleaved forest following a snow disaster in North Guangdong

Effects of a snowstorm on forest disturbance and the canopy changes caused by forest rehabilitation resulted in changes in tree seedling composition.The species and number of tree seedlings vary with the canopy-density dynamics and are embodied in the future species composition and structure of tree layer.With the aim of revealing the seedling regeneration pattern and its response to canopy changes(as indicated by changes in leaf area index \),a 3-year investigation from 2008 to 2010 was undertaken in Chebaling montane evergreen broadleaved forest.The dominant tree seedling dynamics under the recovering canopy was studied by establishing a 2 hm2 sampling area(comprised of fifty 20 m×20 m plots) following the snow storm in 2008.Data from sampling in 2008 identified the top 12 species ranked by their importance as the dominant tree seedling as follows: Castanopsis carlesii,Schima superba,Castanopsis fargesii,Neolitsea chuii,Styrax suberifolia,Alniphyllum fortunei,Cinnamomum porrectum,Randia canthioides,Machilus chinensis,Rhododendron moulmainense,Cinnamomum austrosinensis and Lithocarpus glaber.Dynamic analysis of these 12 species over the 3 years showed that fluctuation was detected in the ranking of the species' importance values,among which 2009 and 2010 shared similar trends while 2008 showed a different trend.Castanopsis carlesii,Schima superba,Randia canthioides and Rhododendron moulmainense showed an increase in their ranking by importance value,whereas Neolitsea chuii,Lithocarpus glaber,Cinnamomum porrectum and Alniphyllum fortunei showed a decrease in their ranking.Styrax suberifolia,Cinnamomum austrosinensis and M.chinensis showed a decreased and then increased ranking while Castanopsis fargesii showed the opposite trend.The 12 dominant tree seedling species showed notable responses to canopy recovery.Permutation-based MANOVA(PerMANOVA) indicated that a highly significant difference was found in composition and distribution of dominant tree seedlings among the 3 years(P0.001),which mainly existed between 2008 and 2009(P0.001),and 2008 and 2010(P0.001),with no significant difference occurring between 2009 and 2010.Variation in LAI showed a corresponding trend,with the lowest LAI obtained in 2008 and a great increase in LAI occurred in 2009,with a lower increment and tendency for a stable LAI observed in 2010 compared with LAI in 2009.The responses to LAI changes varied according to the seedling species.Heliophilous tree seedlings showed a sharp reduction in number with canopy recovery and shade increase,while shade and shade-tolerant tree seedlings increased in number with canopy recovery.Indicator species analysis(ISA) yielded distinct results.Eight species of heliophilous tree seedlings,namely Alniphyllum fortunei,Styrax suberifolia,Cinnamomum porrectum,Lithocarpus glaber,Schima superba,Neolitsea chuii,Machilus chinensis and Cinnamomum austro-sinensis were identified as indicator species in 2008,but only Randia canthioides,a shade-tolerant species,was determined as such in 2010,which further demonstrated the response of tree seedlings to canopy recovery from another aspect.Differences between tree seedling species in the 2 years after the snowstorm diminished gradually in the early stage of forest succession.Fluctuation in the importance-value ranking of the dominant tree seedling species inferred that understory acclimatization was still in equilibrium,and the canopy of the undamaged and less-damaged trees would continue to grow and expand to take advantage of the unused canopy space.