Effects of climate, disturbance and soil factors on the potential distribution of Liaotung oak (Quercus wutaishanica Mayr) in China

Liaotung oak (strictly named as Quercus wutaishanica Mayr, but usually called Q. liaotungensis Koidz) is the main dominant tree species in deciduous broad-leaved forests and mixed coniferous and broad-leaved forests occupying the warm-temperate zone and temperate zone of China. It plays important roles in soil and water conservation. We collected occurrence data of Liaotung oak together with environmental variables, and used 24 environmental layers as indicators of climate, human disturbance and soil characteristics (at a spatial resolution of 5 arc-min) across China. The genetic algorithm for rule-set prediction (GARP) was used to predict the potential distribution area of Liaotung oak. Forward selection, Monte Carlo permutation tests and variation partitioning methods were used to identify the key environmental factors that determined the distribution pattern of Liaotung oak. The results show that (1) GARP predicts the potential distribution area of Liaotung oak with high accuracy, with areas under the receiver operating characteristic curve (AUC) and Kappa index values being relatively high (0.96 ± 0.01, 0.91 ± 0.01); (2) the highest probability of Liaotung oak occurrence is located mainly in Gansu, Shaanxi, Shanxi, Henan, Shandong, Hebei, Liaoning, Jilin, and Heilongjiang provinces in China; (3) climate and disturbance intensity are predominant in determining the geographical boundary of Liaotung oak, with human footprint and precipitation of the coldest quarter being the most important (both explaining 71% variation) among the factors investigated across continental China. While climate and soil factors play important roles in determining the suitability index of Liaotung oak, soil organic carbon and temperature are the critical factors (both explaining 55% variation) among the factors investigated across the potential distribution area.