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Comparisons of competitor selection approaches for spatially explicit competition indices of natural spruce-fir-broadleaf mixed forests

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Abstract

Determining the competitor selection methods for spatial explicit competition indices is important for individual tree growth modelling and forest management. There is a lack of systematic comparisons on these methods for natural mixed forest, however. In this paper, subplots with the area of 0.0625 ha were randomly sampled from 3 one-hectare remeasured and stem-mapped plots and repeated 200 times for natural spruce-fir-broadleaf mixed forests in northeast China with a bootstrapping method. Totally 600 subplots were used to examined the optimal competitor selection methods. Nine distance-dependent competition indices (CIs) and nine main competitor selection methods were tested by including them in the individual tree basal area growth models. After the analysis of the difference in the performance between partial model (only DBH was included) and full model (both DBH and CIs were included), we found that the difference among the statistically valid methods was weak (the increase in the adjusted coefficient of determination were 0.042 to 2.014%, the mean square errors were 0.060 to 2.851%). According to the magnitude and consistency of the contribution of the selection methods for a CI and the sensitivity to distinguish the competition effects on tree growth among the constituent tree species, we comprehensively concluded that the optimal competitor selection method was dependent on the CI, but the difference among these methods was weak. In addition, the CI from Alemdag (Alemdag IS (1978) Evaluation of some competition indexes for the prediction of diameter increment in planted white spruce. Information Report Forest Management Institute (Canada) No. FMR-X-108.) with the gradually expanding radius of circle method and 8 m radius of influence circle was the best combination which could efficiently detect the difference in competition effects on tree growth among tree species groups.

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Data availability

The processed data required to reproduce these findings cannot be shared at this time as the data also forms part of an ongoing study.

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Acknowledgements

We would like to thank all people contributing to sample plot survey for this study. We wish to express our appreciation to the editor and two anonymous reviewers for your in-depth comments, suggestions, and corrections, which have greatly improved the manuscript.

Funding

This research was funded by National Natural Science Foundation of China (Grant No. 31870623) and National Key R&D Program of China (Grant No. 2017YFC0504101).

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Authors and Affiliations

Authors

Contributions

MZ collected the field data, performed data analysis, and wrote the paper; XL supervised and coordinated the research project, designed and installed the experiment, took some measurements, and revised the paper; JL and WG designed and installed the experiment, and took some measurements and collected the field data; HZ supervised and coordinated the research project. All authors have read and agreed to the published version of the manuscript.

Corresponding author

Correspondence to Xiangdong Lei.

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Conflicts of Interest

The authors declare no conflict of interest.

Code availability

The R code generated or used during the study are available from the corresponding author by request.

Additional information

Communicated by Thomas Seifert.

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Appendices

Appendix 1

See Table 11.

Table 11 The fitting statistics and difference of full and partial models generated by different CIs and competitor selection methods (p values were from partial F tests)

Appendix 2

See Table 12.

Table 12 The \( R_{{{\text{adj}}}}^{2}\) and MSER (values in the bracket) for tree growth models generated by different distance-dependent CIs and competitor selection methods

Appendix 3

See Table 13.

Table 13 The parameter estimates of tree species indicator variables in individual basal area growth models

Appendix 4

See Table 14.

Table 14 The statistics of CI8 with M9-8 and the diameter at breast height (DBH) measured in 2013 and 2018 by tree species

Appendix 5

See Table 15.

Table 15 The statistical difference of competition effects among all tree species groups with CIs

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Zhou, M., Lei, X., Lu, J. et al. Comparisons of competitor selection approaches for spatially explicit competition indices of natural spruce-fir-broadleaf mixed forests. Eur J Forest Res 141, 177–211 (2022). https://doi.org/10.1007/s10342-021-01430-8

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  • DOI: https://doi.org/10.1007/s10342-021-01430-8

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