Aim The Massenerhebung effect (Mass elevation effect) refers to heat‐ or wind‐driven altitudinal distribution patterns of temperature‐dependent parameters among massifs with narrower range and lower elevation around peripheral and isolated mountains compared to core and continuous ones. Although common in ecology, this effect is rarely discussed in population genetics. Here, we use genetic markers to reveal population genetic patterns and also test the mountain‐ and sky‐barrier hypotheses relevant to the Massenerhebung distribution pattern of Acer morrisonense in Taiwan's rugged topography and varied local climates. Location The alpine and cloud forest of Taiwan. Taxon Acer morrisonense Hayata. Methods Two chloroplast DNA (cpDNA) fragments and 17 expressed sequence tag‐simple sequence repeat (EST‐SSR) loci, respectively, from 200 to 286 individuals were used to elucidate the phylogeographic pattern of pollen and seed dispersal of A. morrisonense. These data were combined with ecological niche modeling (ENM) to infer distribution range shifts and refugia. We also correlated the genetic‐divergence indices with spatial factors to clarify latitudinal and altitudinal effects on genetic diversity. Results The incongruent phylogeographic patterns of genetic distributions between nuclear and cpDNA markers indicate unhindered pollen flow but spatially constrained seed dispersal. Taken together with ENM, the genetic pattern further reflects historical colonization from central‐mountain refugia to edges since the Holocene. The Massenerhebung reduces the gene flow by the surrounding mountains and also causes lower genetic diversity compared to central alpine populations. Main conclusions This study is the first to reveal the influence of Massenerhebung effect on cpDNA genetic structure of montane trees and reflect the spatial trends of seed dispersal. This population genetic pattern can also be attributed to the demography‐related range shifts with paleoclimate fluctuations under complex mountain topography, supporting the mountain‐barrier hypothesis. The results have important implications for conserving the genetic diversity of species with a wide altitudinal distribution range.

Spatial climate heterogeneity may not only affect adaptive gene frequencies but could also indirectly shape the genetic structure of neutral loci by impacting demographic dynamics. In this study, the effect of local climate on population genetic variation was tested in two phylogenetically close Scutellaria species in Taiwan. Scutellaria taipeiensis, which was originally assumed to be an endemic species of Taiwan Island, is shown to be part of the widespread species S. barbata based on the overlapping ranges of genetic variation and climatic niches as well as their morphological similarity. Rejection of the scenario of “early divergence with secondary contact” and the support for multiple origins of populations of S. taipeiensis from S. barbata provide strong evolutionary evidence for a taxonomic revision of the species combination. Further tests of a climatic effect on genetic variation were conducted. Regression analyses show nonlinear correlations among any pair of geographic, climatic, and genetic distances. However, significantly, the bioclimatic variables that represent the precipitation from late summer to early autumn explain roughly 13% of the genetic variation of our sampled populations. These results indicate that spatial differences of precipitation in the typhoon season may influence the regeneration rate and colonization rate of local populations. The periodic typhoon episodes explain the significant but nonlinear influence of climatic variables on population genetic differentiation. Although, the climatic difference does not lead to species divergence, the local climate variability indeed impacts the spatial genetic distribution at the population level.

Under climate fluctuation, species dispersal may be disturbed by terrain and local climate, resulting in uneven spatial-genetic structure. In addition, organisms at different latitudes may be differentially susceptible to climate change. Here, we tracked the seed dispersal of Acer caudatifolium using chloroplast DNA to explore the relationships of terrain and local climate heterogeneity with range shifts and demography in Taiwan. Our results showed that the extant populations have shifted upward and northward to the mountains since the Last Glacial Maximum. The distributional upshift of A. caudatifolium is in contrast to the downward expansion of its closest relative in Taiwan, A. morrisonense. The northern populations of A. caudatifolium have acquired multiple-source chlorotypes and harbor high genetic diversity. However, effective gene flow between the north and south is interrupted by topography, geographic distance, north-south differences in October rainfall, and other climate heterogeneities, blocking southward genetic rescue. In addition, winter monsoon-driven rainfall may cause regional differences in the phenological schedule, resulting in adaptive effects on the timing of range shift and the genetic draft of chlorotype distribution. Terrain, distance, and local climate also differentiate the northernmost populations from the others, supporting the previous taxonomic treatment of Acer kawakamii var. taitonmontanum as an independent variety.

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The genus Scutellaria comprises eight species distributed from 50 to 2000 m in Taiwan. Amongst them, S. barbata and S. taipeiensis are very similar on the basis of morphological and plastid DNA sequence information. Therefore, a comprehensive study of the taxonomic status of S. taipeiensis is necessary. We reviewed the herbarium sheets, related literature and protologues and compared morphologies of these two species, as well as their phylogenetic relationships. All evidence, including the diagnostic characters between S. taipeiensis and S. barbata, suggest that they belonged to a single species rather than two. As a result, S. taipeiensis is treated as a synonym of S. barbata.