Abstract
Understanding how past climate changes affected biodiversity is a key issue in contemporary ecology and conservation biology. These diversity changes are, however, difficult to reconstruct from paleoecological sources alone, because macrofossil and pollen records do not provide complete information about species assemblages. Ecologists therefore use information from modern analogues of past communities in order to get a better understanding of past diversity changes. Here we compare plant diversity, species traits and environment between late-glacial Abies, early-Holocene Quercus, and mid-Holocene warm-temperate Carpinus forest refugia on Jeju Island, Korea in order to provide insights into postglacial changes associated with their replacement. Based on detailed study of relict communities, we propose that the late-glacial open-canopy conifer forests in southern part of Korean Peninsula were rich in vascular plants, in particular of heliophilous herbs, whose dramatic decline was caused by the early Holocene invasion of dwarf bamboo into the understory of Quercus forests, followed by mid-Holocene expansion of strongly shading trees such as maple and hornbeam. This diversity loss was partly compensated in the Carpinus forests by an increase in shade-tolerant evergreen trees, shrubs and lianas. However, the pool of these species is much smaller than that of light-demanding herbs, and hence the total species richness is lower, both locally and in the whole area of the Carpinus and Quercus forests. The strongly shading tree species dominating in the hornbeam forests have higher leaf tissue N and P concentrations and smaller leaf dry matter content, which enhances litter decomposition and nutrient cycling and in turn favored the selection of highly competitive species in the shrub layer. This further reduced available light and caused almost complete disappearance of understory herbs, including dwarf bamboo.
Highlights
Understanding how past climate changes affected biodiversity is a key issue in contemporary ecology and conservation biology
The multidimensional fuzzy set ordination (MFSO) ordination revealed strong differences in forest composition between the cool areas at high elevation, where the coniferous Abies koreana and Taxus cuspidata trees dominated, and the warm areas at low elevation, where these cool temperate trees were replaced by warm temperate to subtropical trees of the Carpinus spp., Quercus spp., evergreen shrubs (Ilex crenata) and small trees (Daphniphyllum macropodum) (Figure 2)
Such precondition is hardly met in mainland Korea because the late-Pleistocene coniferous forests along with alpine tundra vegetation largely retreated owing to the early Holocene spread of oak species [21], and because the mid-Holocene oak-hornbeam lowland forests were largely replaced by conurbation and paddy fields
Summary
Understanding how past climate changes affected biodiversity is a key issue in contemporary ecology and conservation biology. These diversity changes are, difficult to reconstruct from paleoecological sources alone, because macrofossil and pollen records do not provide complete information about species assemblages. There are relatively precise fossil data on the diversity of trees, which is linked to the ability of long-distance pollen dispersal in many tree genera [1], a high level of deposition and good preservation of woody macro-remains [2]. Much less information is available for herbaceous species because their pollen identification to species level is usually impossible [3], pollens of insect-pollinated herbs are locally dispersed and underestimated in pollen records, and the limited amount of wellpreserved herb macrofossil deposits. Excluding herbaceous species from paleoenvironmental assessments could lead to misleading conclusions about the vascular plant diversity changes
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