Search

In their 2013 paper, Lenz et al. illustrated how trees growing at the low-temperature limit respond to a chronic in situ warming or cooling by 3 K, by employing Peltier-thermostated branch collars that tracked ambient temperatures. The micro-coring-based analysis of seasonal tree ring formation included double-staining microtome cross sections for lignification, but these data had not been included in the publication. In this short communication, we complement these data, collected in 2009 at the Swiss treeline, and we show that a 3 K cooling that corresponds to a 500–600 m higher elevation, had no influence on lignification. However, when a frost event occurred during the early part of ring formation, the 3 K cooling produced a blue (non-lignified) layer of cells, followed by normally lignified cells for the rest of the season. Hence, the event did not affect the cambium, but interrupted cell wall maturation in cells that were in a critical developmental stage. We conclude, that chronic cooling does not affect lignification at treeline, but it increases the risk of frost damage in premature xylem tissue.

The Sino-Himalaya region is located in the southeast margin of the Qinghai-Tibetan Plateau (QTP) with several Asian rivers in this area, namely the Yarlung Zangbo River (YZR), Salween, Mekong, and Jinshajiang River and their tributaries. All these rivers currently flow independently into the Indian Ocean, the South China Sea (Pacific Ocean) and the East China Sea (Pacific Ocean). In geologic history, however, these rivers flowed southward into the Paleo-Red River (PRR), forming a huge drainage system, which then flowed into the South China Sea. From the end of the Neogene to the beginning of the Quaternary, with further uplift of the QTP, the monsoon climate was formed and strengthened bringing abundant precipitation leading to river erosion, rapid undercutting and a series of river capture events resulting in modern drainage systems and the beheading of the huge PRR. The reorganization of the PRR led to changes in the spatial pattern of river systems, subsequently affecting the geographical distribution of plants in the river valley. This paper reviews the effects of drainage evolution on the genetic structure and geographical pattern of plants in this region, and summarizes the resulting four types of discontinuous distribution patterns observed, namely: (1) the discontinuous distribution pattern between the Three River Valleys (TRV) (Salween, Mekong, Jinshajiang and their tributaries) and the Red River Basin (RRB); (2) the discontinuity between the Yarlung Zangbo River and the TRV–RRB; (3) the discontinuity among the TRV, and (4) the discontinuity between the east and west ends of the QTP. The conclusions from this review, while providing botanical evidence supporting and confirming the drainage evolution in Sino-Himalaya China, are the following: (1) the reorganization of drainage systems made the original continuous distribution pattern discontinuous, forming unique genetic and biogeographical characteristics, promoting the genetic differentiation of species and the formation of new taxa; (2) river capture events link different river systems together, bringing together the genetic diversity of different river valley species, increasing the richness of genetic diversity and the exchange of genes among populations; (3) the reorganization of river systems impacts the evolutionary history of valley plants and shapes their modern distribution patterns.

Mountain ecosystems are becoming increasingly threatened by non-native plant invasions. In this paper, the occurrence of non-native plant species was examined in a protected area (Laojun Mountain Area) in the eastern Himalayas, China. Sampling plots were systematically set up along elevation from 1950 to 3500 m a.s.l. Sixty-one non-natives were recorded that account for 24% of the roadside flora. The number of non-native species decreased continuously with increasing elevation and significant nestedness was found between the low- and high-elevation plots. Moreover, all non-native species distributed at high elevation were also found at low elevation and mountain specialists were not found among non-natives. These results indicate that the eastern Himalayan ecosystem is not immune to invasion and most of the non-natives spread from lowland areas upward to the highlands. Future efforts to manage plant invasions in this region should concentrate on low-elevation areas where agriculture and disturbances by tourism are increasing rapidly.