The Coarse Woody Debris Effect To Regeneration Of Seedling In A Typical Mixed Broadleaved-Korean Pine Forest In Xiaoxing’an Mountains, China

This study was conducted in a dynamic monitoring plot (9 hm2) of a mixed broadleaved-Korean pine forest in Xiaoxing’an Mountains. All coarse woody debris (CWD) with length (L) ≥2 m and the max. diameter (D1)≥10 cm were measured for length, existing form, decay classes and its regeneration seedlings. All regeneration seedlings (seedling:height< 15 cm; sapling:height≥15 cm, diameter at breast height (DBH)< 5 cm) on the CWD were tagged, measured and identified according to species. The objectives of this research is to explore the response of regeneration seedlings to decay classes and existing types of CWD and the forest floor, according to censuses in 2013,2014 and 2015. Important findings:1) A total of 820 CWD individuals with L≥2 m and D1≥10 cm were recorded in the 9 hm2 plot, and the most of CWD distribution was found in the plot of the northeast and northwest. The surface area of total CWD was 1991.85 m2(2.21% of the total area of the sample area).2) Based on censuses in 2013 and 2014, we found that a total of 32 species and a total of 12784 regeneration seedling individuals with height≥1 cm be recorded on the CWD, including regeneration seedlings and saplings individuals were 11062 and 1722, respectively. The major number of regeneration species were Betula costata and Acer ukurunduense, their numbers were 4281 and 2041 respectively. The highest number mortality of regeneration species were Betula costata,meanwhile the highest number recruitment of regeneration species were Fraxinus mandshurica.3) The regeneration seedlings and saplings on the different decay classes of CWD showed nearly normal distribution curve, peaked at the class Ⅲ and Ⅳ. As the increasing of height, the number of regeneration seedlings on the different decay classes of CWD decreased, and showed typical reverse J-shaped curve. The decay classes of CWD significantly affected the regeneration seedling distribution of 15 major tree species, they were Abies nephrolepis, Pinus koraiensis, Picea spp., Betula costata, Acer ukurunduense, Fraxinus mandshurica, Ulmus japonica, Acer tegmentosum, Ulmus laciniata, Deutzia gladata, Euonymus pauciflorus, Lonicera spp., Corylus mandshurica, Ribes mandschuricum, Actinidia kolomikta. The mortality and recruitment of regeneration seedling on decay class Ⅰ significantly correlated with regeneration seedling on decay class Ⅱ, Ⅲ, Ⅳ and Ⅴ(P< 0.05).4) The regeneration seedlings and saplings on the different existing types of CWD were mainly recruited on the breakage at rootstock, trunk segment and uprooted blow-down. Regeneration seedlings with 0-10 cm height class were most occurred on the different existing types of CWD, and as the increasing of height, the number of regeneration seedlings decreased. The existing types of CWD significantly affected the regeneration seedling distribution of 16 major tree species, they were Abies nephrolepis, Pinus koraiensis, Picea spp., Betula costata, Acer ukurunduense, Fraxinus mandshurica, Ulmus japonica, Acer tegmentosum, Acer mono, Deutzia gladata, Euonymus pauciflorus, Lonicera spp., Philadelphus schrenkii, Corylus mandshurica, Acanthopanax senticosus, Actinidia kolomikta. The different existing types of CWD were not significantly affected the mortality and recruitment of regeneration seedling.5) The regeneration seedling of Betula costata and Spiraea salicifolia only recruited on the CWD, however, Rhamnus davarica, Rosa acicularis, Vitis amurensis, and Populus koreana only recruited on the forest floor. The density of regeneration seedlings and saplings of Pinus koraiensis, Fraxinus mandshurica, Acer tegmentosum, Deutzia gladata, Lonicera spp., Euonymus pauciflorus, Philadelphus schrenkii, Acanthopanax senticosus and Ribes mandschuricum recruited on CWD significantly correlated with the density of regeneration seedlings and saplings on forest floor (P< 0.01). As the increasing of height, the number of regeneration seedling recruited on the CWD decreased, meanwhile the number of regeneration seedling recruited on the forest floor peaked at the classes of 5-10 cm and>50 cm, showed double-hump shaped curve.