Poplar

Populus spp
P. nigra, P. deltoides, P. maximowiczii and P. trichocarpa, P. tremula

General info

Poplar is a fast-growing deciduous flowering dioecious tree from the northern hemisphere 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.

Whilst poplar species are of interest as bioenergy crops due to their fast-growing status, 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 tends to yield 4–14 m3 ha-1 y-1 and grows on a wide range of soils but some species are best avoided on peaty soils whilst others benefit from ex-agricultural fields for best growth rates. It can be harvested via modified forage harvesters and harvesting via traditional timber methods can be performed on 6–10-year cycles in an SRF system. They can be harvested on 3-year coppice rotation for use as a SRC methodology but is noted as performing better on a slightly longer 4–5-year rotation.

Outside SRF situations, these species have a normal rotation length of 40-55 years and as such can be considered as having a relatively short lifespan. They can grow around 1.5 to 3m a year depending on variety and locations. Many species can reproduce from dormant hardwood stem cuttings like willow, which can act as a beneficial propagation methodology. They can be planted at around 1,500 up to 12,000 trees per hectare for bioenergy purposes, with higher and lower density plantings having different considerations with regards to biomass produced vs costs and time before ROI is observed for example.

During the first few years, they need considerate weed control to avoid competition as well as pest control to avoid the impact of diseases such as leaf rusts and stem cankers including Septoria musiva and plant damage from cottonwood leaf beetles.