A summary of their past, present & future
Giant redwoods – the world’s most massive trees measured by volume that can reach heights of up to 95 metres [300ft] and have a lifespan of up to 3,500 years – have been around for over 200 million years. Until about one million years ago they were widespread across the Northern Hemisphere, including Europe & Ireland. Then the the advance of the glaciers in the recent ice age left them with only one limited area of refuge on the western slopes of the Sierra Nevada mountains of California. Elsewhere in the region they died out due to moisture stress. After their discovery in 1852 there was sadly some felling of them over the next 70 years or so. This felling included in 1853 a redwood named ‘The Discovery Tree’ whose stump was used as a dance floor – see drawing below.
Now they are protected thanks to the activities of many conservationists. Seed of the giant redwoods reached Europe in 1853 with first plantings from 1856.
In California there are 68 groves of giant redwoods with the tree known as General Sherman [seen above] being the largest and the General Grant tree [seen on right] being almost as large.
In their home habitat, natural regeneration is assisted by a number of factors including forest fires and the activities of both the Douglas squirrel and a beetle larva which help to scatter the seeds.
Planting in Europe & elsewhere has mostly been of individual specimens or small groups with no large groves. The mild maritime climate in Britain & Ireland has suited the giant redwood. Growth rates of young trees have been higher than in the California. The tallest has reached 54 metres in 150 years in Scotland but its volume is still only 6% of that of the General Sherman tree. The tree in Ireland with the largest girth is on the Charleville Estate. It is shown below, together with a group of three giant redwoods on the neighbouring Powerscourt Estate. They were probably amongst the first to be planted outside California.
Redwoods – the Threat to their Future
As mentioned in the history section, giant redwoods are sensitive to moisture stress. In their present habitat the melting of winter snows has provided the necessary moisture to take them safely through the dry summer period. However, the winter snows in the Sierra Nevada have already decreased by 15% compared to the 1950’s and the latest IPCC forecast is for further decreases, including in the north of California where there are plantations of giant redwoods – see p.1455 of Climate Change 2014, Impacts, Adaptation, and Vulnerability. Part B Regional Aspects.This then is the background to a warning in March 2013 [see link below] from Nate Stephenson, a research ecologist with the U.S. Geological Survey (USGS). He said that if climate warming continues as projected, tens of thousands of these ancient trees will be at risk in the coming century from destruction by either drought or climate-induced pathogens. “In 25 years, we would see trouble for sequoia seedlings, then in 50 years trouble for the whole population and in 100 years time, we could lose most of the big sequoias.”
Although there are many individual giant redwood specimens in Europe, for good seed fertility a grove of redwoods is needed. This may be the reason that so far the giant redwood has never been able to naturally reseed itself outside its native range.
Fortunately climate change predictions for Ireland are that it should continue to have a moist maritime climate. So Giants Grove – the project to create in Ireland the largest grove of redwoods outside of California – could represent an important additional insurance policy for the continued survival of this species.