Objective This paper aims to clarify the effects of gap size on regeneration of saplings of Picea schrenkiana in Xinjiang of northwestern China, and to explore the spatial distribution of saplings under different gap sizes, so as to provide theoretical basis for regeneration of saplings in gaps of P. schrenkiana.
Method We investigated the density, growth indexes and spatial location of saplings of 49 gaps in three sample plots (1 ha). Kernel density estimation method and spatial point pattern analysis method were used to analyze the influence of different forest gap sizes on sapling regeneration and spatial distribution patterns within gaps.
Result (1) The density and growth indexes (DBH, tree height, crown width) of saplings were significantly affected by different gap area grades (P < 0.05), but the ground diameter was not significantly affected. The density of saplings was the highest in gap class Ⅰ (< 20 m2). The maximum growth indexes of saplings appeared mostly in gap class Ⅱ(2 040 m2). (2) Saplings mainly concentrated under canopy of gap class Ⅰ(< 20 m2), gap class Ⅱ(20−40 m2) and gap class Ⅲ(40−90 m2) in northeast and under canopy in southeast. Saplings gradually moved from gap edge to gap center with the increase of gap class. (3) The distribution of saplings was random at gap scale, and with the increase of gap scale, the distribution changed from random to aggregated, and then tended to random again.
Conclusion Gap size has significant effect on regeneration of Picea schrenkiana, which smaller than 20 m2 is helpful to the survival of saplings, and 20−40 m2 is helpful to the growth of saplings. Saplings are concentrated under canopy of the northeast and under the canopy in the southeast of the gap. The growth index is the best, which indicates that these two directions are helpful to the growth of saplings. Therefore, gap size can be expanded to 20−40 m2 along these directions to promote the regeneration growth of saplings.
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