Priority conifer seed collecting from the Pacific Slope

The Pacific Slope spanning Washington, Oregon and California is one of the best locations in the world to explore conifers, from the majestic coastal redwoods to the ancient and stunted bristlecone pines.

Our Global Tree Seed Bank Project, supported by the Garfield Weston Foundation, is targeting useful and threatened trees around the world; we identified some shared priorities with the US Forest Service and cooperating arboreta in the UK. From the 65 conifers recognised as native to this region, three groups stood out as priority for a joint US-UK seed collecting expedition in 2016: Abies (firs), Picea (spruces) and Cupressus (cypresses). 

The extensive federal and state landholdings in the western US protect tree populations from most changes of land use, and provide opportunities for species to adapt and migrate.

But increasing threats from wildfire, tree pests and climate change have demonstrated that in situ conservation is not sufficient on its own to safeguard key populations of plant species.

Storing large collections of high quality seed at the National Centre for Genetic Resources Preservation in the US, with duplicates at Kew’s Millennium Seed Bank will provide multiple options for research, horticulture and translocation for many decades ahead.

One target of the expedition was the graceful Brewer spruce (Picea breweriana) which survives in six places within the relictual Arcto-Tertiary forests of the Pacific Slope.

It has already been eliminated from several areas prone to fire, and the observed decline in this species has contributed to a conservation assessment by IUCN as ‘Vulnerable’.

Ledig et al. (2012) predicted that current habitats will become significantly warmer and drier in the coming decades, envisaging a managed translocation of this species to suitable future habitat in British Columbia, Canada.

Putting together the expedition team

Clearly we would need skilled arborists able to climb our varied trees, secure themselves in the crown, and to pick an agreed number (typically 50) of mature cones into sacks.

Andrew was able to secure skilled climbers from several FS units, including three of the renowned parachuting firefighters known as ‘smoke jumpers’ who bring impressive field skills.

From the UK, support was offered from the Forestry Commission’s Bedgebury Pinetum, University of Oxford Harcourt Arboretum and Kew’s Wakehurst site, home to the Millennium Seed Bank. Andrew and I coordinated the collecting and acted as ground support for the climbers, keeping an eye out for hazards and assisting in an emergency situation. 

The target cypress trees are unusual in that seeds accumulate in the canopy as cones are produced each year, and are only dispersed when conditions are right.

This is known as serotiny: an ecological adaptation where seeds are only released in response to an environmental trigger, such as after a forest fire. 

Serotiny presents a challenge to obtain seed which is fully mature, ready for dispersal, and yet has not experienced significant ageing.