Prediction of potential suitable areas of Keteleeria calcarea and Keteleeria cyclolepis under climate change

Objective The plants of Keteleeria genus are excellent timber and ornamental tree species, possessing significant ecological and economic values. However, the entire genus is currently under threat, with Keteleeria davidiana var. calcarea (endangered) and Keteleeria fortunei var. cyclolepis (vulnerable) facing severe challenges. This study focused on simulating and predicting the changes in potential suitable habitats of these two species under different climate change scenarios, in order to reveal their response patterns and provide a theoretical basis for the development of comprehensive conservation strategies for Keteleeria genus.

Method Based on the optimized MaxEnt model, the data of existing distribution sites of K. calcarea and K. cyclolepis and 19 environmental variables downloaded by Worldclim were collected to simulate their suitable areas during the present, last interglacial (LIG), last glacial maximum (LGM), mid-holocene (MH), and two future climate scenarios (RCP4.5 and RCP8.5), which covered the periods of 2050s and 2070s. At the same time, key environmental factors affecting their distribution were analyzed and their distribution patterns under future climate change were predicted.

Result (1) The model predictions for K. calcarea and K. cyclolepis showed that the AUC values of both training and test sets exceeded 0.97, indicating high predictive accuracy of the models. (2) The prediction results of modern suitable distribution of K. calcarea and K. cyclolepis were consistent with their actual distributions. In modern times, the total suitable area for K. calcarea was 112.15×10⁴ km² and for K. cyclolepis was 159.35×10⁴ km². In the past three historical periods, the potential suitable areas for both species gradually expanded, with maximum values reached during the mid-holocene: 76.17×10⁴ km² for K. calcarea and 128.88×10⁴ km² for K. cyclolepis. Under future climate change scenarios, the total suitable areas for both K. calcarea and K. cyclolepis were projected to show slight expansion northward and northwestward (toward higher latitudes), but the highly suitable areas were expected to dramatically decrease. Particularly under the RCP8.5 scenario in the 2070s, the highly suitable area for K. calcarea shrank to only 5.88% of the modern suitable area, and the highly suitable area of K. cyclolepis was reduced to 4.25% of modern suitable area. (3) The key environmental variables affecting potential distribution of both Keteleeria species were identified as mean diurnal range and minimum temperature of the coldest month.

Conclusion This study demonstrates that temperature factors play a decisive role in the distribution of K. calcarea and K. cyclolepis, exhibiting significantly stronger influence than precipitation variables. Historical distribution dynamics reveal continuous expansion of suitable habitats for both species since the Last Interglacial period, a trend projected to persist under future climate scenarios. Although the total suitable area shows expansion, the substantial reduction in high-quality habitats may pose critical challenges to population viability. Both species are predicted to respond to climate change through poleward range shifts, a finding that provides essential insights for conservation planning.