Concealed truth: Modeling reveals unique Quaternary distribution dynamics and refugia of four related endemic keystone taxa on the Tibetan Plateau.

Understanding the factors driving the Quaternary distribution of in the Tibetan Plateau (TP) is crucial for biodiversity conservation and for predicting future anthropogenic impacts on ecosystems. Here, we collected Quaternary paleo-, palynological, and phylogeographical records from across the TP and applied ecological niche models (ENMs) to obtain a profound understanding of the different adaptation strategies and distributional changes in trees in this unique area. We identified environmental variables affecting the different historical biogeographies of four related endemic taxa and rebuilt their distribution patterns over different time periods, starting from the late Pleistocene. In addition, modeling and phylogeographic results were used to predict suitable refugia for , var. , var. , and . We supplemented the ENMs by investigating pollen records and diversity patterns of cpDNA for them. The overall reconstructed distributions of these taxa were dramatically different when the late Pleistocene was compared with the present. All taxa gradually receded from the south toward the north in the last glacial maximum (LGM). The outcomes showed two well-differentiated distributions: var. and occurred throughout the Longmen refuge, a temporary refuge for the LGM, while the other two taxa were distributed throughout the Heqing refuge. Both the seasonality of precipitation and the mean temperature of the driest quarter played decisive roles in driving the distribution of var. and , respectively; the annual temperature range was also a key variable that explained the distribution patterns of the other two taxa. Different adaptation strategies of trees may thus explain the differing patterns of distribution over time at the TP revealed here for endemic taxa.