P. nigra, P. deltoides, P. maximowiczii and P. trichocarpa, P. tremula
Poplar (Populus spp.) belong to the family Salicaeae and are native to the Northern hemisphere. They are fast-growing deciduous flowering dioecious trees with around 30 species present in the genus with many able to naturally hybridise. The species most under investigation for breeding of commercial varieties include P. nigra, P. deltoides, P. maximowiczii and P. trichocarpa.
Poplar is among the fastest growing of temperate trees and is therefore of considerable interest as a bioenergy crop. The plant grows to a height of 15–50m with a trunk diameter of 2.5m. Once established, poplar can be harvested every 2-5 years over a life span of over 20 years. Poplar is a multipurpose crop with several environmental benefits such as reducing erosion, phytoremediation of contaminated soils, windbreaks, and biodiversity.
Work with commercial varieties in Europe is looking to improve species resistance to common pests (including poplar mosaic virus), improve the growth rate further and improve climate/soil condition adaptations of these species.
Cultivation and agronomy
Poplar is suited to most soil types including clay, sand, loam, and humus soils. It grows particularly well on well-drained and fertile loam with a wide range pH of 5-8. Poplar can be grown as a Short Rotation Forestry (SRF) or Short Rotation Coppice (SRC). The plant can grow up to about 1.5m in height during the first year and from 3-5m for each of the following years depending on the cultivar, site conditions, spacing and management practices.
For large scale plantations, it is recommended to plant mixtures of poplar varieties with about 100 trees of a single cultivar in each block, and different cultivars in neighbouring blocks. If considering mechanised harvesting, plant at a spacing of 0.6m apart in twin rows with 0.75m between rows and a 1.5m alley between each twin-row. Poplar can be planted in densities of 1,500 up to 1,800 trees per hectare for bioenergy purposes.
Yields of 20-25m3 of wood/ha/yr is achievable in the UK.
Young growth is attractive to deer, hare, and rabbits. Appropriate fencing may be required in areas where these animals are prevalent. Common pests include the small poplar leaf beetle (Phratora vitellinae), and the large leaf beetle (Chrysomela populi).
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Clifton‐Brown, J., Harfouche, A., Casler, M. D., Dylan Jones, H., Macalpine, W. J., Murphy‐Bokern, D., … & Lewandowski, I. (2019). Breeding progress and preparedness for mass‐scale deployment of perennial lignocellulosic biomass crops switchgrass, miscanthus, willow and poplar. Gcb Bioenergy, 11(1), 118-151.