Described as one of the finest entrances to a botanical garden anywhere in the world, the magnificent Redwood Avenue at Benmore Botanic Garden, on Scotland’s west coast, is in desperate need of innovative actions or risks being lost to the nation through climate change and disease.

Planted in 1863 by the wealthy American James Piers Patrick, it lined the original driveway to Benmore House. These trees (Sequioadendron giganteum), native to California, were among the earliest to reach British shores when the species had only just been introduced to the outside world, making Benmore’s redwoods some of Europe’s oldest and tallest, reaching up more than 50m high.

Today, the spectre of climate change hangs over the trees and its effects are already marked. Benmore Curator Peter Baxter, said: “The trees are now existing, rather than growing. Their crowns are thinning and many lower branches are completely defoliated. The reasons for the decline, which has accelerated worryingly in recent years, are complex and multifaceted. Soil compaction may be central to the issue, with the Avenue having for many years provided the main vehicle access to the house. Only a very thin layer of topsoil supports the turf that now tops the original hard-core road. This, combined with a typically wet west coast climate, and limited drainage, causes serious waterlogging and puddling around the roots.” 

      

RBGE mycologist and plant health expert Dr Katherine Hayden explained: “The waterlogging can have dangerous consequences, both through creating a favourable habitat for pathogens, and by increasing trees’ disease-susceptibility through stress. The condition of the Benmore redwoods clearly suggests root problems.”

The situation is expected to worsen. Using models developed by the UK Met Office, Benmore is anticipated to experience both increased rainfall, especially during winter, and more intense storms resulting in more rapid ground saturation.

A scientific approach is being taken to resolve the plight of the redwoods. With initial remedial action now in place, more drastic change is required to step up conservation efforts. The hope is that the answer lies in improving and accelerating soil drainage, preventing puddling and waterlogging around these delicate giants’ roots. This, in turn, should significantly reduce the “pathogen pressure” the trees currently face.

But these remedies come at a price, particularly over such a large area (over 1.5 acres require decompaction). The cost of the work is estimated at over £80,000, for the initial phase, and RBGE has mounted a fundraising campaign.

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