How climate change affected Abies - Tsuga forests in high elevation mountain in Taiwan?

Background/Question/Methods

Abies kawakamii and Tsuga chinensis var. formosana are the major species of high mountain forests in Central Taiwan. These forests are likely to be most affected by climate change because of their unique bio-climatic and topographical requirements. In central Taiwan, we conducted tree-by-tree censuses at the 6-ha Hehuan-Mountain forest dynamic plot which is located at the upper part of Tsuga forest zone and lower part of Abies zone. All free-standing trees ≥ 1 cm diameter at breast height (DBH) were identified, measured, and mapped for the plot in 2008 and 2022.

Results/Conclusions

In this two survey, there were 13 species been recorded in the plot. The most abundance species was A. kawakamii, accounting for about 66.28 - 67.53% of the total number of individuals and T. chinensis var. formosana is the second most abundance species (12.43-12.03%) of total stem density. Both A. kawakamii and T. chinensis var. formosana are decreased in stem density in the 14-yrs interval. In spite of the drastic decrease in stem density, the basal area of A. kawakamii increased from 30.32 to 34.78 m2 ha-1, but the basal area of T. chinensis var. formosana dropped from 11.10 to 9.02 m2 ha-1 due to many large trees (DBH ≥ 150 cm) fallen down and only one individuals recruitment. Our 14-yrs field investigation revealed a different result with the upward migration that SDM predicted. It demonstrated that Abies kawakamii, the tree species of the forest line above 3000m in Taiwan, exhibited a stable population and biomass increment; whereas Tsuga chinensis var. formosana, the species that occurred 2800-3000m next to A. kawakamii, displayed a negative population growth without upward range shift.