MICROENVIRONMENT OF FOREST GAPS AND ITS EFFECTS ON THE GROWTH OF NATURALLY REGENERATED SEEDLINGS OF DIFFERENT AGES IN SUBALPINE ABIES FAXONIANA FOREST

Background and Aims Canopy gap disturbance drives successional dynamics of forest communities and shapes forest structure, dynamics and biodiversity in the western subalpine region of Sichuan. Gap microenvironment and responses of Abies faxoniana seedlings of different ages have not been investigated. Methods During the growing seasons of 2002 and 2003, we continuously observed microenvironment (solar radiation and soil temperature at 5 and 15 cm depth) in canopy gaps in Abies faxoniana forest in Wanglang National Nature Reserve, Sichuan Province. We studied the growth of 3-20 year seedlings (basal diameter, height growth and biomass) in gaps and under canopy to determine responses to gaps. Key Results Total daily solar radiation was slightly higher in gaps than under canopy in June, but was significantly higher than under canopy in July and August. From June to August, total solar radiation was 8.10× MJ· m~ -2 and 5.02×MJ·m~ -2 in gaps and under canopy, respectively, and average soil temperatures at 5 and 15 cm deep were significantly higher in gaps than under canopy. The basal diameter of 3-8 year Abies faxoniana seedlings in forest gaps was a little smaller than under canopy, but the basal diameter of seedlings 9-20 years was larger in gaps than under canopy. Height growth rate of 3-8 year seedlings was 1.2±0.3 cm· a~ -1 and 1.1±0.3 cm·a~ -1 in gaps and under canopy, respectively, and for 9-20 years old was 6.2±2.4 cm·a~ -1 and 3.0±0.9 cm·a~ -1 , respectively. The average total biomass of seedlings was a little higher in gaps than under canopy. Conclusions Tree seedlings need more illumination with increasing age. Therefore, canopy gaps are an important impetus for growth, forest dynamics and regeneration in subalpine coniferous forest.