| Forest natural regeneration is an important approach for self-reproduction of forestresources, an important way for ecological restoration and reconstruction, and is thefoundation for sustainable utilization of forest. As a hot spot for ecological research, it is ofgreat significance for the sustainable development of forest health. Larixprincipis-rupprechtii plantation is the main vegetation type in Saihanba forest farm, whichhave the largest area of Larix principis-rupprechtii plantations in china. Based on the18plots with different age classes (A-1:30-40a; A-2:20-30a) of Larix principis-rupprechtiiplantation, the regeneration characteristics, spatial distribution pattern of seedlings andfactors affecting regeneration were analyzed, the difference between the age classes wascompared. This research aims to gain an in-depth understanding of the regenerationmechanisms for Larix principis-rupprechtii plantations.(1) The paper analyzed the regeneration characteristics from four aspects, includingthe density of seedlings, characteristics of growth structure, age structure, and the dynamicchange of height and basal diameter with seedlings growing. The results showed that thedensities of30-40a and20-30a were3304n/hm2and2308n/hm2respectively. The densityof regeneration seedlings had no obvious difference between two age classes using themethod of one-way ANOVA. Besides, they also had similarity characteristics of growthstructure. The number of seedlings decreased as the seedlings height grew. The height of85%of all seedlings for each age class was lower than five cm. The relationship betweenthe basal diameter and height of seedlings was linear positive correlation,but the growth rate of seedlings`height in stands with20-30a was faster than the stands of30-40a.With the growth of seedlings, the variation tendency of the number of seedlingsdecreased fast at first, and then was stable. For30-40a, the density of seedlings varied from1779n/hm2to3-37n/hm2; while the plots with20-30year-old, the density of seedlingsvaried from2824n/hm2to a few plants. The above results illustrated a phenomenon thatthere was a high reproductive rate and low survival rate in the18plots. In conclusion, it isnecessary to make a suitable and scientific management for Larix principis-rupprechtiiplantations.The basal diameter showed a exponential correlation with ages of seedlings. But for 30-40a, the annual average growth of seedlings`height was bigger than that in plots with20-30a, and the value was0.0959cm/a and0.0721cm/a respectively. On the other hand,there was no obvious difference between two age classes in growth tendency of height andbasal diameter. The annual average growth rates of basal diameter of seedlings were0.1579cm/a for30-40a and0.1686cm/a for20-30a.(2) Combining with five ordinary indicators, the spatial distribution patterns ofseedlings were analyzed. The paper found that the spatial distribution patterns of seedlingsin18plots were all aggregated distribution. In addition, combining with the statisticalanalysis, the tendency of the number of seedlings increased at first, and then decreased to acertain value with increasing nearest distance. But for two types of plots, the nearestdistance corresponding to the maximum value of the number was different. For20-30a,71.56%of seedlings occurred in the nearest distance range0.3to1.5m; while for30-40a,54.38%of seedlings occurred in the nearest distance range1.2to2.1m.(3) The factors affecting natural regeneration of Larix principis-rupprechtii weredivided into two types, stand structure factors and micro-environmental factors. With thevalues of stand structure factors including basal area and density of stand increasingrespectively, the number of seedlings showed increasing at first, and then decreasinggradually to a constant. The best basal area for seedlings was20-35m2/hm2, while the beststand density was mid-value. The results using multiple regression analysis illustrated thatthe impact of basal area and stand density was different for two age classes, for30-40year-old stand, stand density had more influence on the number of seedlings, while for20-30a,was the combination of the two factors.Among micro-environmental factors, soil–litter factors played a dominant role inaffecting the natural regeneration of Larix principis-rupprechtii. The variations in relativeimportance of factors between two age class stands was mainly due to high density andlow survival rate of seedlings, for stand with two different age classes, the rate ofseedlings<5cm in height and the rate of seedlings <2year in age are both more than85%.There were varied dominant factors to influence the natural regeneration of Larixprincipis-rupprechtii in stand with two different age classes. For30-40a, the main factorsaffecting the seedling density at different heights level were the thickness of litter, soil totalK content, soil pH, stand density and basal area; the main factors affecting the seedlingdensity at different ages level were the herbage coverage, the stand density, soil rapidlyavailable P, soil total N content and soil total K content. While for20-30a, the stand density,soil organic matter, soil available P, soil alkali-hydrolyzed N, the thickness of litter;However, soil pH, herbage coverage, soil total P content, litter natural water content andcanopy coverage were the main factors to hinder the seedling density at different ages.According to the results of factors decomposition analysis, the pure structural factorsaffecting height structure of seedlings in stands with the two age classes contribute to 35.5%and25.3%for the total explanation variation respectively. For20-30a, the growth ofseedling was mainly affected by soil-litter factors during the earlier growth stage, while thestand structure became the critical impact factor with the age. But this tendency was notobvious in the stands of IV age class, in which the stand structure variables (exceptingbasal area) were positive correlated with the seedlings across five-height levels. However,the pure structural factors have more correlation with big age class seedlings.The analysis of the regeneration characteristic, spatial distribution pattern and impactfactors, is helpful for us to have a deeper understanding of the regeneration mechanism.Moreover, revealing the key factors affecting regeneration may provide a basis for wisemanagement of stand structure and rational restoration of function of Larixprincipis-rupprechtii plantations. |
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