Wen-Yun Chen

LEAF MARGIN ANALYSIS: A NEW EQUATION FROM HUMID TO MESIC FORESTS IN CHINA

Abstract Leaf margin analysis (LMA) is a widely used method that applies present-day linear correlation between the proportion of woody dicotyledonous species with untoothed leaves (P) and mean annual temperature (MAT) to estimate paleotemperatures from fossil leaf floras. Previous works demonstrate that LMA shows regional constraints and to date, no equation has been modeled directly from Chinese forests. Fifty humid to mesic Chinese forests were chosen to understand the relationship between percentage of untoothed leaf species and MAT in China. Consistent with previous studies, the Chinese data indicate that P shows a strong linear correlation with MAT, but the actual relationship is a little different from those recognized from other regions. Among the several currently used LMA equations, the one resulting from North and Central American and Japanese data, rather than the widely used East Asian LMA equation, yields the closest values to the actual MATs of the Chinese samples (mean absolute error = 1.9 °C). A new equation derived from the Chinese forests is therefore developed, where MAT = 1.038 + 27.6 × P. This study not only demonstrates the similarity of the relationship between P and MAT in the Northern Hemisphere, but also improves the reliability of LMA for paleoclimate reconstructions of Chinese paleofloras.

Distribution of Cenozoic plant relicts in China explained by drought in dry season

Cenozoic plant relicts are those groups that were once widespread in the Northern Hemisphere but are now restricted to some small isolated areas as a result of drastic climatic changes. They are good proxies to study how plants respond to climatic changes since their modern climatic requirements are known. Herein we look at the modern distribution of 65 palaeoendemic genera in China and compare it with the Chinese climatic pattern, in order to find a link between the plant distribution and climate. Central China and Taiwan Island are shown to be diversity centres of Cenozoic relict genera, consistent with the fact that these two regions have a shorter dry season with comparatively humid autumn and spring in China. Species distribution models indicate that the precipitation parameters are the most important variables to explain the distribution of relict genera. The Cenozoic wide-scale distribution of relict plants in the Northern Hemisphere is therefore considered to be linked to the widespread humid climate at that time, and the subsequent contraction of their distributional ranges was probably caused by the drying trend along with global cooling.

First occurrence of Cedrelospermum (Ulmaceae) in Asia and its biogeographic implications

Cedrelospermum (Ulmaceae) is an extinct genus with extensive fossil records in Europe and North America. However, no fossil of the genus has been reported from Asia. Here we describe Cedrelospermumasiaticum L.B. Jia, Y.J. Huang et Z.K. Zhou sp. nov. based on compressed fruits from the late Miocene of Yunnan, southwestern China. The fossil fruits are characterized by an ovate fruit body adjoined by double wings, with the veins on the primary wing converging toward a stigmatic area. According to the historical geographic distribution of the genus, we hypothesize that Cedrelospermum originated in North America where both single-winged and double-winged fruits were reported. The single-winged form subsequently spread into Europe via the North Atlantic land bridge and the double-winged form dispersed into Asia via the Bering land bridge. From the Eocene to Oligocene, a southward retreat of the genus distribution probably took place, which coincided with the global surface cooling initiated during the Eocene–Oligocene transition. The extinction of Cedrelospermum from Asia may be related to the intensification of the East Asian monsoon.

Climatic envelope of evergreen sclerophyllous oaks and their present distribution in the eastern Himalaya and Hengduan Mountains.

Abstract  Evergreen sclerophyllous oaks (the E.S. oaks, Quercus section Heterobalanus) are the dominant species of the local ecosystem in the eastern Himalaya and the Hengduan Mountains, southwest China. In this study, we document the climatic envelope of the seven E.S. oak species and examine the relationships between climate and their distribution. This was done using a principal components analysis (PCA) and multiple regression analysis (MRA) of nine climatic indices. The main climatic envelope of the E.S. oaks were: mean temperature of the warmest month (MTW)=12.0–19.5 °C, warmth index (WI) = 33.2–88.9 °C month, annual biotemperature (BT)=−6.9–−0.3 °C, coldness index (CI)=−30.4–−10.1 °C month, mean temperature of the coldest month (MTC)=−3.7–3.0 °C and annual precipitation (AP)=701–897 mm at the lower limits; and MTW=8.3–16.1 °C, WI=15.7–59.1 °C month, BT=3.6–8.9 °C, CI=−55.4–−19.3 °C month, MTC=8.3–16.1 °C and AP=610–811 mm at the upper limits. The climatic range of the E.S. oaks is wide and includes two climatic zones, the cool‐temperature zone and the subpolar zone. The PCA and MRA results suggest that the thermal climate plays a major role and precipitation plays a secondary role in controlling the large‐scale distribution of the E.S. oaks, except Quercus monimotricha. In thermal regimes, BT and/or MTW are most important for both lower and upper limits of the E.S. oaks. Furthermore, our results indicate that the upper distribution limits of the E.S. oaks are less determined by low temperatures and their duration (CI) than by other factors.