Idiosyncratic responses of evergreen broad-leaved forest constituents in China to the late Quaternary climate changes

Abstract

Subtropical evergreen broad-leaved forest (EBLF) is one of the most important vegetation types in China. Inferences from palaeo-biome reconstruction (PBR) and phylogeography regarding range shift history of EBLF during the late Quaternary are controversial and should be reconciled. We compared phylogeographic patterns of three EBLF constituents in China, Castanopsis tibetana, Machilus thunbergii and Schima superba. Contrary to a chorus of previous phylogeographic studies and the results of species distribution modelling (SDM) of this study (in situ survival during the LGM), the three species displayed three different phylogeographic patterns that conform to either an in situ survival model or an expansion-contraction model. These results are partially congruent with the inference of PBR that EBLF was absent to the north of 24° N at the LGM. This study suggests that the constituents of EBLF could have responded idiosyncratically to climate changes during the Late Quaternary. The community assemblages of EBLF could have been changing over time, resulting in no palaeo-analogs to modern-day EBLF, which may be the main reason responsible for the failure of PBR to detect the occurrence of EBLF north of 24° N at the LGM.

Figure 1

(a) Locations of sampled populations of Castanopsis tibetana, Machilus thunbergii, and Schima superba. The circle in the inset illustrates the distribution range of subtropical evergreen broad-leaved forest (EBLF) in China and the dashed line shows the boundary between two subregions of EBLF. (b) Geographic distribution and median-joining network of C. tibetana haplotypes (CH1–19). (c) Geographic distribution and median-joining network of M. thunbergii haplotypes (MH1–13). (d) Geographic distribution and median-joining network of S. superba haplotypes (SH1–9). Brown dashed lines denote lineage divergences identified by network and SAMOVA analysis. For each network in (b–d), the size of circles corresponds to the frequency of each haplotype. Vertical bars indicate unsampled or extinct haplotypes. Each solid line represents one mutational step that interconnects two haplotypes. Each population code in Supplementary Table S2 is preffixed by a letter C in (b), M in (c) and S in (d) that particularly denotes the sampled populations of Castanopsis tibetana, Machilus thunbergii and Schima superba, respectively. One population (M69) remote from others in Machilus thunbergii is not shown in (c). The red dashed lines show the approximate northern borders of EBLF during the LGM based on PBR (modified after Harrison et al., 2001). Maps were generated using ArcGIS version 9.3 (http://www.esri.com/software/arcgis/arcgis-for-desktop) and Adobe Illustrator CS3 13.0 and modified using Adobe Photoshop CS 8.0.

Figure 2. The relationship between haplotype diversity (h) and latitude (°N) in three broad-leaved evergreen tree species in subtropical China.

Figure 3

Distribution of the number of pairwise nucleotide differences for cpDNA sequence data in (a) Castanopsis tibetana as a whole, (b) Machilus thunbergii as a whole, (c) Schima superba as a whole, (d) eastern populations of Schima superba and (e) western populations of Schima superba. The solid line shows observed distributions of differences among haplotypes whereas the dashed line represents simulated distributions under a model of sudden (stepwise) population expansion (Rogers & Harpending, 1992).

Figure 4

(a) Predicted distributions of Castanopsis tibetana, Machilus thunbergii and Schima superba based on species distribution modeling (i) at present (1950–2000), (ii) at the Last Glacial Maximum (LGM; c. 21 kya). Species distribution models were established with bioclimatic variables on the basis of extant occurrence points (black dots) of the three species using maxent version 3.3.3 k (http://www.cs.princeton.edu/~schapire/maxent/). The dashed lines indicate the northern borders of EBLF today and during the LGM inferred from PBR (modified after Harrison et al., 2001). Maps were generated using ArcGIS version 9.3 (http://www.esri.com/software/arcgis/arcgis-for-desktop). (b) The results of identity tests using enmtools version 1.3. The black Bar indicates the null distributions of D, and gray bar indicates the null distributions of I. Both are generated from 100 randomizations. X-axis indicates value of I and D, Y-axis indicates number of randomizations. The arrow indicates the value in actual maxent runs. The Histograms were drawn using SigmaPlot 10.0.