Underplanting extends the range of coniferous tree species that could potentially be used to diversify future commercial timber production in the United Kingdom

In the United Kingdom (UK) commercial timber production is dominated by conifer forests consisting primarily of just nine introduced species, which poses serious risks to the UK forest industry due to the likelihood of future climate change and the increasing incidence of damaging pests and diseases. Two experiments were therefore established to test the suitability of 17 alternative species in a relatively warm, dry, location where opportunities for diversification are currently thought to be limited. As expected, five years after planting on a conventional clearfell (clear-cut) site, apart from Scots pine ( Pinus sylvestris L.), few other species had established, However, Maritime pine ( Pinus pinaster Ait.) grew well and would seem to have potential in our future climate on similar sheltered, freely draining clearfelled areas. When planted underneath an existing canopy of trees a much wider range of species thrived, with Douglas fir ( Pseudotsuga menziesii (Mirb.) Franco), grand fir ( Abies grandis Lindl.), European silver fir ( Abies alba Mill.), western red cedar ( Thuja plicata D. Don), coast redwood ( Sequoia sempervirens (D. Don) End.) and Leyland cypress ( Cupressus x leylandii A.B. Jacks. and Dallim.) all growing strongly. During periods of very warm and very cold weather, the temperatures under the canopy were less extreme than on the open site. Underplanting therefore appears to be a potentially useful technique, worthy of further study, for establishing shade tolerant, emerging species, which might otherwise prove to be unsuitable for deployment on clearfell sites, as long as the locations chosen are sufficiently windfirm for an overstorey crop to be retained. • Overreliance on just nine tree species poses serious risks to the UK timber industry. • We tested the suitability of 17 alternatives where only Scots pine is normally grown. • On a clearfell site, apart from Scots pine, only Maritime pine did well. • When underplanted, a much wider range of species thrived e.g. Douglas fir, grand fir. • Underplanted European silver fir, western red cedar, coast redwood, Leyland cypress also thrived.