Big Tree Big Problem

The debate around tree planting and biodiversity is heating up as the world wakes up to the threat of climate change and the recognition that we need to do more to combat it.

As the founder of a tree planting project focused on species protection and land efficient carbon capture, seeking to provide a viable and scalable part-solution to our warming planet predicament, I’ve encountered a not inconsiderable resistance on the subject of planting non-native trees in the UK.

Absolute credit is due to those championing the cause of native woodlands, natural habitats, and promoting reforestation of the UK as it was before the industrial revolution.  Native woodland biodiversity is key to the survival of our threatened UK species from the smallest of insects up to our larger forest dwelling animals. The protection of our sacred ancient woodlands must be a priority, together with replanting significant areas of the UK with new native woodlands to bring back natural ecology and give animal and insect dwellers space to thrive once again.

This is however a very separate issue to that of climate change brought about by the effects of global warming, caused by decades of mass scale industrial burning of fossil fuels for everything from power grid supply to building heating and mass transport, the consequences of which are visible from the utterly devastating recent wildfires of Australia and California (to name a few) and the swift decline of the polar ice sheets (see Guardian articles in January 2021 titled ‘Climate crisis: world is at its hottest for at least 12,000 years’ and ‘Global ice loss accelerating at record rate’).

Whilst tree planting addresses both biodiversity and carbon capture as a global warming preventative, you cannot with any logical thinking believe you can address both problems with the same tree planting strategy.

Not all trees are created equal

What are the commodities we need to achieve mass tree planting action? Land (suitable for tree growth), and trees.  But not all trees are created equal.

Native tree planting, particularly the likes of oak, rowan, birch, are all wonderful contributors to biodiversity (particularly oak that sustains by far the most invertebrates and fungi of all UK trees), but they are woefully inadequate for any meaningful carbon capture.  To put this in context I quote the England Forestry Commission:

‘A new native woodland can capture 300-400 tonnes of CO2 equivalent per hectare by year 50. By year 100, it can capture 400-600 CO2 equivalent per hectare.’

The average carbon footprint of a UK citizen according to the World Bank is 6.5 tonnes per annum, and the average life expectancy is 80 years, totalling 520 tonnes of CO2 emissions in a lifetime per person. 

So rounded for simplicity that means using native trees 1 hectare of land (1.3 football pitches) can over 100 years recover the lifetime carbon footprint of one UK citizen. With a population size of 60 million that would require a land mass twice that of the UK’s 25 million hectares, and that is just for those alive today.

A big tree for a big problem

Studying Giant Sequoias (aka Redwoods) brought to the UK by the Victorians and planted in the late 1850’s you can use their growth rates to arrive at a 50 year carbon capture estimate of 500 tonnes per hectare, and within 100 years over 4000 tonnes – an astounding 10x that of a new native woodland over the same period.

The equivalent amount of space required for Sequoias to match a UK native woodland over 100 years is 7.5 million hectares, and over 250 years a much smaller area of just over 0.6 million hectares, roughly the size of Norfolk.

With this understanding planting native trees to combat climate change is a little like bringing a water pistol to a gun fight.  Its not just that Sequoias are the world’s fastest growing coniferous species, or that they are the largest trees on the planet, but they also are extremely resilient and can live for more than 3000 years, locking up carbon for millennia or more offering one of nature’s most durable carbon capture means. The largest and oldest ones today were just starting out at the time the pyramids were being built, and already centuries old by the time of the rise of the Roman Empire.  They are extraordinary to behold both in the bark and truly ancient.

A new mindset

The main hurdle to mass tree planting is that land is the commodity in shortest supply, or more accurately land owners willing to part with their asset for no real commercial gain (for what use is it to cut them down if the objective is durable carbon lock up). Tree planting with the intention of timber production, even when sold for carbon credits, after felling results at best in a 50% loss of carbon lock up once it has been through the saw mill. At worst the wood is used for firewood and nearly all the carbon stored is lost back into the atmosphere.

So if we want to get serious about carbon neutrality and climate change then we need to be realistic about which tree to use for which job, and accept there needs to be a different approach for carbon capture.  First an agenda for planting swathes of new native woodlands for the natural regeneration and recovery of biodiversity, and a separate agenda for carbon capture and the UK target of net zero.  There is absolutely no reason why both strategies cannot co-exist. 

The ‘native trees only’ advocates struggle to see that Sequoia planting is one of our most effective actions in protecting native woodlands.  If the climate change scientists are right and we are in for unabated temperature rises of 2-6 degrees over the coming decades, our existing woodlands are going to suffer as they not going to be capable of surviving under that kind of heat and drought stress, not to mention the very real danger of wildfires that may well come to our shores with hotter, dryer conditions.

Where can the Sequoias go?

Felled coniferous timber plantations that were previously monocultures holding very little biodiversity are perfect grounds for planting Sequoias as there is no loss of habitat for in situ species, and due to the generous 100m2 spacing of Sequoias a diversity of natives can be planted to improve biodiversity and create a far more mixed species environment than previously.  This fits well with the UK government agenda for conifer planting (Sequoias are conifers) on exiting plantations as part of their carbon capture modelling, however given they were thinking of the likes of Spruce and Douglas Fir (also a North American species) the Sequoias will far outperform their expectations.

There is no quick fix, there is no silver bullet that covers off both biodiversity and global warming – we need to do all and everything for both natural regeneration and carbon capture.  A separate strategy to address each independently promises a far more effective outcome to protect both the UK’s natural habitat and help combat climate change.

Henry Emson

Founder