| Forest gap is composed of GBTs and influence their growth, the size and height of GBTs also affects the gap dynamics and microhabitat change. Pattern analysis is an important method of researching the relation of populations, community and environment, for the recognition population biology, intraspecific and interspecific relationship and the relationship between population and environment is of great significance. This paper dealt with the characteristic of DBH classes and tree height classes of 358 gap border trees (GBTs) selected from 32 gaps, and analyzed their relationship among DBH classes, tree height classes, the distribution of ratios of crown inclination (RCI) with forest gap area size, respectively, and simulated their distributions with Weibull and Normal distribution models, then checked their fitness by Kolmogorov and Chi-square tests. Species composition and diameter class structure was investigated in 1.5 hm2 (100 m×150 m) permanent plot in Picea koraiensis and Abies nephrolepis forest of Xiaoxing’an Mountains. The spatial distribution pattern and spatial association of main populations and gap makers was analyzed by using point pattern analysis. The results are as follows:(1) The largest proportion of DBH was between 10-20 cm in the survey of 358 GBTs, large DBH classes were less. The largest number and proportion of GBTs was between 15-20 m, few trees were more than 30 m. That the distribution of DBH classes of GBTs followed Weibull distribution, but didn’t follow Normal distribution, the distribution of tree height classes followed both Weibull and Normal distribution.(2) The RCI of 65.36%of GBTs ranged from 0.5 to 0.7 while 15.08%of GBTs had regular crowns. The difference in RCIs between different tree species reached highly significant level. The crown inclination phenomenon of Pinus koraiensis and Picea koraiensis was the most obvious, the former RCI was greater than 0.5.Half of Acer ukurunduense had regular crowns. The relationship between mean RCI in a single gap and its area size was not linearly significantly correlated. The gap proportion with 10 GBTs was the highest, reached 21.88%, each gap had averagely 11.19 GBTs.(3) There were a total of 13 species with diameter at breast height greater than 2 cm in tree layer, and great differences were observed in the densities of main populations. Tree species that their important value was ranking in the first 4 were Abies nephrolepis, Picea koraiensis, Betula platyphylla and Acer ukurunduense in the plot. The diameter class structure of their populations presented an inverse "J" curve. Spatial distribution pattern for Abies nephrolepis and Picea koraiensis was similar, their variation tendency ranged from aggregated and random to uniform distribution with the spatial size. For Betula platyphylla, the distribution was aggregated distribution pattern at≤40 m scale, was random distribution at>40 m scale, whereas for Acer ukurunduense, was aggregated distribution pattern at the whole research scale. Except that negative correlation between Betula platyphylla and Acer ukurunduense existed at the whole research scale, positive correlation between other populations did at small scale and negative correlation did at large scale. Only Abies nephrolepis and Betula platyphylla had significant positive correlation, generally non-significant positive correlation was observed between other populations.(4) Spatial pattern of Abies nephrolepis different age had obvious differences; spatial pattern of Picea koraiensis mainly present random distribution, especially the DBH class II was a little change random distribution all of the scale; aggregated and random distribution were primary for different age of Betula platyphylla, only DBH class II had uniform distribution after 49m scale; different age of Acer ukurunduense had significant aggregated distribution at the whole scale. Spatial correlation for DBH class Ⅱand class Ⅰ、Ⅲ of Abies nephrolepis was non-significant, DBH class I andⅢ had significant positive correlation at small scale, significant negative correlation at big scale. Spatial correlation for DBH class I and class Ⅱ、Ⅲ of Picea koraiensis was similar, their variation tendency ranged from positive correlation to negative correlation with the spatial size, DBH class II and III fluctuated between positive and negative correlation. Different age of Betula platyphylla had the same correlation trend of predominantly positive correlation. Acer ukurunduense were showed significant positive correlation among different age.(5) Spatial distribution patter of gap makers characterized aggregated distribution at in small and middle scale, and random distribution with increasing scale. Spatial point pattern of gap makers formed by uprooting exhibited unimodal type distribution, random, aggregated, and uniform distribution also occurred. Spatial point pattern of gap makers formed by breaking overall presented a little fluctuation, random and aggregated distributions alternatively appeared at small scale, random distribution happened at large scale. Their spatial correlation analysis indicated that significant positive correlation existed at<32 m scale, non-significant negative correlation did at>32 m scale. |
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