Regeneration response to canopy gap size in a Chinese pine plantation: Species diversity patterns, size structures and spatial distributions

- The effect of canopy gap size on regeneration was studied in Chinese pine plantation.
- Gaps had limited effects on plant biodiversity on a mid-term basis.
- Gap size had no effect on regeneration density but positively affected their height.
- All gaps showed approximately normal height and ground diameter distributions.
- The random pattern mainly occurred in two height groups of regeneration in all gaps.

Chinese pine (Pinus tabuliformis Carr.) is one of the most commercially important conifers in northern China because of its important economic and ecological value. However, most Chinese pine plantations have suffered degradation following fertility declines, pests and disease outbreaks. In this study, to evaluate whether gap creation can help achieve canopy recruitment for sustainable management, we analyzed the species diversity patterns of woody plant regeneration, growth status and the spatial distribution of Chinese pine regeneration in three control plots (C, 10 × 10 m) and four classes of gaps seven years after gap creation. The diameters of the gap classes were 1.00 (G-I, 10.0 m), 1.25 (G-II, 12.5 m), 1.50 (G-III, 15.0 m), and 1.75 (G-IV, 17.5 m) times the mean canopy height. There were no differences in diversity patterns between the tested gap sizes, between gaps and under the canopy, this finding may be attributed to trees and shrubs require a relatively long time to become established. Although gap size had no influence on the density of Total (all regeneration), it significantly decreased and increased the density of seedlings (height ≤ 100 cm) and saplings (height > 100 cm), respectively, along the gap size gradient, which likely resulted from the differences between these two categories of regeneration in terms of shade tolerance and resource requirements. Similarly, the height, ground diameter and height growth of Total, seedlings and saplings in the current year showed positive responses to gap size. All gap size classes showed approximately normal height and ground diameter distributions, with a longer tail toward larger individuals with greater gap sizes. These results suggested that Chinese pine can be managed by gap creation in plantations, especially when combined with gradual gap expansion. In addition, Total and seedlings showed mostly random patterns across all scales, with aggregation at smaller scales, and the percentage of random patterns of saplings was greater than that of seedlings for all gap sizes. These differences in spatial patterns may have been associated with the survival strategies of tree species and the density-dependent processes. Further monitoring and gap expansion will likely be required to determine the long-term efficacy of gap creation to ensure successful canopy recruitment and to maintain sustainable management.