Diversity and breeding potential of poplar species in China

The genus Populus is composed of many species with an impressive variety of growth characteristics. Nevertheless, this abundant natural offering has been only partially utilized to date with the objective of promoting poplar breeding and cultivation. Following an old tradition, more or less inflexible production systems are mainly keyed to a few high-yielding P. x euramericana and P. x interamericana clones in most countries. Consequently, considerable economic failures have to be accepted repeatedly as a result of serious calamities. China ranks among the countries characterized by an exceptionally multifarious indigenous flora. Based on ample genetic variation, poplar species were able to settle in divergent habitats and to conserve the ability to survive and reproduce over long periods owing to adaptation processes. The diversity is concentrated, above all, in the subtropical mountain regions of southwest China. Comprehensive studies of the genus Populus in the southern and eastern mountain chains of the Qinghai-Tibet Plateau turned out to be particularly impressive; 3 sections, 17 species and 15 varieties have been recorded and taxonomically classified there. They grow at altitudes between 1500 m and 4300 m above sea level. Many of these poplar sources are notable for their remarkable site adaptation even in harsh conditions and also for their fast and vigorous growth. Species expected to be suitable for international breeding and cultivation objectives in the near future are presented in a general way. The necessarily subjective selection is based on the state of available knowledge mainly about site requirements, environmental importance, growth characteristics, regeneration ability, silvicultural behaviour, yield estimation and wood utilization. In particular, the following species are characterized in the paper in an abridged fashion: P. cathayana, P. davidiana, P, euphratica, P. simonii, P. szechuanica, P. ussuriensis and P. yunnanensis. The potential of poplars in China is considered to be instrumental in expanding and stimulating poplar breeding activities worldwide. Measures to be specified in the paper are considered important and could be implemented on the basis of a close and confident co-operation with Chinese colleagues and institutes relevant to the subject and under the umbrella of the International Poplar Commission.