Abstract:

Objective: The study was intended to evaluate the effect of different diameter-classes of Larix principis-rupprechtii on diversity pattern of neighbor species at different scales for coniferous-broadleaved mixed forest dominated by L. principis-rupprechtii in the National Nature Reserve of Xiaowutai Mountains of Hebei, and clarify the effect of different ecological processes on the formation of diversity pattern of neighbor species of the L. principis-rupprechtii to contribute to a better understanding of the mechanism of maintaining species diversity. Method: In the National Nature Reserve of Xiaowutai Mountains of Hebei, a 2.4 hm² (80 m × 300 m) plot for monitoring forest dynamics was established in a typical coniferous-broadleaved mixed forest, and species composition and community structure were analyzed. Based on the distribution of DBH (Diameter at Breast Height) for all individuals, all individuals of dominant species L. principis-rupprechtii were divided into nine DBH classes with a spacing of 3 cm to explore the effect of L. principis-rupprechtii within different diameter-classes on of neighbor species using the individual species-area relationships (ISARs) combined with the heterogeneous Poisson null model. Result: There were 4 275 independent individuals with DBH ≥ 1 cm, belonging to 35 species 26 genera 17 families. The structure of L. principis-rupprechtii within each diameter-class all showed approximately normal distribution, in which diameter-class V (19-22 cm) had the largest number of individuals (92). Within a scope of 30 m, the ISARs(r) values of L. principis-rupprechtii of the nine diameter-classes all displayed a increasing tendency with increase of the scope. In addition, ISARs(r) curves of IV (16-19 cm) and IX (≥ 31 cm) diameter-classes showed both maximum and minimum values for all the scopes. L. principis-rupprechtii displayed a neutral impact on the diversity pattern of neighbor species for the three diameter-classes III (13-16 cm), VII (25-28 cm) and VIII (28-31 cm) for all the scopes. Promotional or inhibitory impacts on the diversity of neighbor species all occurred in the small scopes and changed to neutral with increase of the scope. Among the small scopes, five diameter-classes I (< 10 cm), II (10-13 cm), IV, V and VI (22-25 cm) of L. principis-rupprechtii showed promotional impact to some extents, and only diameter-class IX showed an inhibitory impact at the scope of 2-4 m. Conclusion: The scope-dependent impact of L. principis rupprechtii significantly affected the diversity pattern of neighbor species. Although the neutral impact of L. principis-rupprechtii on diversity pattern of neighbor species was the dominant process for different diameter-classes at multiple scales, the promotional impact of L. principis-rupprechtii on the diversity pattern of neighbor speceis at smaller scales is not ignoreable. The IV and IX diameter-classes of L. principis-rupprechtii are the two key growth stages for the formation and maintenance of the diversity pattern of neighbor species.

Key words: coniferous-broadleaved mixed forest, Larix principis-rupprechtii, diameter-class, species diversity pattern, individual species-area relationships, neutral process, biotic interactions