Fir trees disappeared 500 years ago in the Liupan Mountains on the southwestern Loess Plateau, China

Abstract

The study of macrofossils provides a means of reconstructing the expansion, shrinkage and extinction of the key ecological species within a region. In this study, we have used plant macrofossils to examine the species composition of the predominant vegetation in Liupan Mountains on the southwestern Loess Plateau in central China. A series of plant macrofossils (wood and needles) was recorded in the Tianchi Lake, indicating the distinct range changes of one conifer species in this region over the past 6200 years. Further morphological and anatomic analyses of these plant macrofossils, as well as a comparison with current-day needle samples, suggest that they are undoubtedly historical macrofossils of fir trees (possibly originating from species Abies fargesii). However, no corresponding fir trees are currently found within 100 km of our study area. The deposited fir needles are highly abundant in sediment between 6200 and 2200 cal yr BP. Their amount decreases after 2200 cal yr BP, and they suddenly disappear after 530 cal yr BP. Comparison with several types of records (local population data, historical records, fir pollen and stalagmite isotope data) indicates that the decrease and disappearance of the fir trees after 2200 yr BP in this region is associated with increasing anthropogenic activities. These findings suggest that the distribution of fir trees (i.e. A. fargesii) were more widespread in China in the past, species of A. fargesii extended to the Liupan Mountains. Our results further suggest that anthropogenic activities have destroyed the endemic populations of a few key tree species in China. This highlights the necessity of their conservation in the future.