Response Of Natural Recruitment Characteristics To Gap And Clear Cutting Fixed Number Of Year In Pinus Tabulaeformis Plantation

Forest gaps play an important role in promoting the natural recruitment. Research of effects of thinning on gap characteristics and response of natural recruitment to gap characteristics and clear cutting fixed number of year have important practical significance in revealing mechanism of cutting disturbance on forest recruitment so as to optimize the management measures and realize close to nature management of artificial pure forest. Taking40and50years old pinus tabulaeformis plantation and clearing areas of pinus tabulaeformis plantation2,5and8years after clear cutting were taken as research objects in Pingquan County of Hebei province. On the basis of sample plot and line transect investigation in2011to2013, used analysis method of point pattern and geostatistics, the effects of thinning on gap characteristics as well as effect of gap and clear cutting fixed number of year on recruitment quantitative and age characteristics and distribution pattern, the relationship between gaps as well as clear cutting fixed number of year and litter as well as herbaceous biomass were studied. The results are as follows:(1) In40and50years stand, after thinning there were no change on gaps linear density, the distribution range of opening degree of CG (canopy gap) and EG (extended gap) were enlarged, gaps were more close to round and the boundary wood quantity were increased10.0%and3.0%respectively. After thinning in40years stand, CG and EG average area increased by10.19%and19.84%, EG and CG area proportion increased by35.24%and24.29%; In50years stand CG and EG average area increased by85.51%and50.23%; EG and CG area proportion increased by65.59%and22.95%.(2) In40years stand, pinus tabulaeformis was the only recruit tree species, in50years stand and clearing areas quantity proportion of pinus tabulaeformis were all above90%. From40to50years under the canopy density decreased from2.03/m2to4.90/m2; average height and base diameter increased progressively from26.04cm and4.33mm to29.79cm and4.98mm respectively; average age decreased from5.47to4.94. After clear cutting with the extension of time recruit density decreased progressively from2.10/m2down to0.72/m2; average height, base diameter and age increased progressively from82.03cm,21.71mm and5.85to159.23cm,37.52and7.06. In all sample plot distribution type of height and base diameter were unimodal. In40and50years stand, gap increased recruit density, and recruit density positively correlated and negatively correlated with gaps area respectively; the area of gap suitable for growth was gradually amplified with the increase of recruit age. Gaps had limited impact on the height, base diameter and age.(3) In40and50years stand and all clear areas age structures of pinus tabulaeformis populations were all unimodal type. Recruitment populations were mainly composed of3to7year,2to7years and4to8years in40years stand,50years stand and clear areas respectively. Pinus tabulaeformis age structures were imbalance, there was a serious shortage of seedling number below3years, the average life expectancy was short, generally mortality peak appeared in the eighth year, survival curves closed to Deevey type II.(4) In40and50years stand, the distribution of recruitment population presents a spatial aggregation at all scales under canopy. After clear cutting, the recruitment populations were all exhibited clumped distribution at smaller scales and random distribution at larger scales. Pinus tabulaeformis seedlings were always spatially independent of saplings. Canopy woods were always spatially independent of recruitment poulations. In40years stand, with the increase of gaps area the recruitment poulations were changed from random distribution to clumped at smaller scales and randomly distributed at larger scales. Aggregation intensity was decreased by gaps. In50years stand, the scale values corresponding to peak value of aggregation intensity increased with the increase of gap area.(5) In40years stand, litter density in10-15m2gaps was increased by21.28%and litter in the rest gaps was decreased by30.02-35.42%than that under canopy. Litter thickness and the effective rate in15to20m2were decreased by21.12%and16.60%than that under canopy, and there were no significant differences between that in rest gaps and under canopy. In50years stand, litter density in gaps was increased by16.95-65.61%than that under canopy. Gaps had no significant impact on litter thickness. The effective rate in gaps was decreased by15.73-27.91%than that under canopy. Herb biomass were18.1832.36%higher than that under canopy.2years to8years after clear cutting, litter density and thickness was increased by29.57%and51.64%, the effective rate and herb biomass were decreased by34.71%and19.61%, the trend was favour of settlement and growth of seedlings. In40and50years stand litter density, litter thickness and herb biomass had limited impact on recruitment density. Gaps and clear cutting fixed number of year influenced the spatial heterogeneity of litter characteristics and herb biomass density,(6) After final felling the stand would become multi-layer uneven-age Chinese pine stand in future, the heterogeneity of vertical structure and age structure would be enhanced. However, the stand will still have the difficulty of low tree species diversity. Therefore to enhance the tree species diversity and to establish stratified uneven-aged mixed forest should be considered to induce other tree species in the case of lack of other tree provenance. Therefore, it is necessary to create larger gaps and clear tapes in different age stand to to find out the most effective interference measurements.