Temperate mixed forests of the Amur-Heilong River basin are likely the most biologically diverse temperate forests in Asia. Due to the basin’s peculiar glaciation history, which spared large portions from ice cover, and given the complex of river valleys and mountain ridges that cross the area in latitudinal and longitudinal directions, the basin became a crossroads for migration and dispersal. This resulted in a unique mix of species entering the basin from the north (central Siberia) and south (east China).
Manchurian floral communities harbor the greatest diversity of plant species. This type of vegetation is found mainly in southern Primorsky Province, in the Ussuri watershed, on the coast of the Sea of Japan, along the middle Amur-Heilong River and in northeast China. Manchurian flora consists primarily of forest species from the Tertiary Period that are adapted to warm temperatures. The closest relations of these species are found in the subtropics and, in some cases, in the tropics of East Asia. Forests of Manchurian species are dense, moist, and seemingly tropical with deciduous trees such as Mongolian oak (Quercus mongolica), Manchurian and Japanese elm (Ulmus laciniata, U. propinqua), Manchurian walnut (Uglans mandshurica), and Amur cork tree (Phellodendron amurense). Hanging tangled among the trees are climbing schizandra (Schizandra chinensis), Amur grape (Vitis amurensis), and tara vine (Actinidia arguta). Korean pine is the most prevalent conifer in mixed forests.
The large number of relic species in the temperate zone is due to the unique geological history of the region. For example, sixty species of forest orchids are found only in the Russian Far East. Yet the ranges of many of the relics found here have been steadily shrinking as a result of human pressures. In addition to those species that survived from ancient times, a number of plants originated in the region and are endemic to the southern Russian Far East. Three genera are endemic to Khabarovsky and Primorsky Provinces of Russia: Microbiota, Astrocodon, and Popoviocodonia. Rare species of Manchurian flora include the Japanese yew (Taxus cuspidata), Asian ginseng (Panax ginseng)., sen (Kalopanax septemlobus), and two species of rhododendron (Rhododendron sichotense, R. faurieri). Alpine areas present at higher altitudes in the Badzhal, Bureya, Changbaishan and Sikhote-Alin Mountain Range is particularly rich in endemic species.
The variety of habitats in the basin supports a diverse fauna. One of the unique features is the weaving together of different species far from their geographical centers of origin. The most species-rich areas of the basin are those where ranges of northern taiga species overlap with those of southeastern Asian communities (Changbaishan, small Hinggan Ridge, southern Primorsky Province, forests along the Amur-Heilong River, and along tributaries of the Ussuri-Wusuli River. Along biogeographic boundaries, brown bears coexist with Asiatic black bears, Amur tigers cross paths with lynx (Felix lynx), and both Manchurian and mountain hares (Lepus mandschuricus, L. timidus) scurry from predators.
Different authors assign these temperate forests to various biogeographic zones. This is often based more on convenience, scope, and objectives for specific studies rather than on distinctive natural features of the forests.
From the nature conservation prospective all mixed broadleaf-coniferous temperate forest ecoregions distinguished in the Amur-Heilong River basin share the following important features:
Korean pine (Pinus koraiensis) is typically abundant and is always the dominant coniferous species;
All have been optimal habitat for the northernmost subspecies of tiger (Panthera tigris altaica), with the best habitat in earlier times located in the foothills of the Changbai mountains;
All lie in the historic range of ginseng (Panax ginseng) and
All are the most species-rich temperate mixed broadleaf-coniferous forests in North East Asia.
“Ussuri Broadleaf and Mixed Forests” (also known as “Mixed Broadleaf-Coniferous Forests of the Russian Far East”) “Global 200 Eco-Region” was identified in this area: and that simply reflects the sad fact that only there in Russia some least fragmented habitats and animal populations are still rather abundant. Actual maps of species diversity based on many years of work by WWF and the scientific community of the Russian Far East unanimously agree that the most species-rich terrestrial communities are found in southern Primorsky Province, on the border with China and North Korea (see a map of species diversity from ECAP-RFE). And this suggests that most probable historic center of dissemination for many forest species was somewhere in this transboundary area. Conservation programs should therefore consider "Russia forest ecosystems" and "China forest ecosystems" along with adjacent forests in North Korea as a single ecosystem and must emphasize the importance of transboundary conservation efforts. However, to link biogeography with the history of ecosystem fragmentation caused by human activities, several eco-regions are distinguished presently in this area:
Ussuri broadleaf and mixed forests
Manchurian mixed forests
Changbai Mountains mixed forests
Autumn on Zhanhe River. Small Hinggan Mountains in Heilongjiang. (Photo by E.Simonov)