In the run-up to an election, political parties like to talk about planting trees. There is a pleasing simplicity to such promises — everyone understands what planting a tree means — and the numbers are pleasingly big (30 million trees, 60 million trees, etc). What’s not to like? It’s a reasonable place to start a conversation, but a properly climate- and environmentally-savvy political debate needs to move beyond prospective candidates’ love of large numbers and simple metrics. We need political debate that recognises the value of whole landscapes containing trees — ‘treescapes’, if you will. We need to hear arguments especially for old trees, and for new forest types, each suited to their planned location. We need to let people know what changes are ahead in the face of climate change.
Promising to plant trees is not like promising a tax cut (or hike). Every tree planted is an investment, the return on which will not amount to much unless it is properly managed for a specific set of economic, social, or environmental goods and services. Promising to plant trees without promising to look after them is like buying a sausage machine without the wherewithal to make sausages.
The private goods from trees are commercial products like timber and fuelwood; the public goods are much broader and potentially much larger: provision of biodiversity habitat; mediation of water flows; carbon storage (at least temporarily); and improvements in human well-being for those encountering nature. It takes care, and so costs money, to turn planted trees into the diverse treescapes capable of delivering these goods. Such care will protect our investment by seeking to avoid past disasters and build-in resilience to future threats. It is worthwhile to debate how such care is delivered — how much by private enterprise, how much community forest, and so on — but the fact that care is needed is inescapable. Even letting ‘self-willed’ landscapes return to something approaching wildness requires a watchful eye and attention to their edges, if nothing else.
Nurturing trees takes space as well as careful stewardship. Planting 30 million trees at the usual spacing for traditional silviculture will require giving over at least a further 1/16th of the land area of the UK. New treescapes will be more varied and will require more space: diverse planting for fast-growth; short rotation coppice; interleaved grassy crops with trees; or forest stands with hens or pigs beneath. Not everyone will welcome these landscape changes that remain largely hidden when talk is of millions of trees planted.
A social care plan for trees
The oldest trees are exceptionally valuable for biodiversity, while younger trees are usually those which provide economic returns. Some trees can be cut and re-sprout; some trees need to be replanted after harvest. Modern approaches to harvesting can preserve a forest canopy and encourage a healthy age-profile of trees across a landscape. Centuries of ‘wood wisdom’ have furnished us with an abundance of techniques to enact a social care plan for trees. Such a plan would aspire to a diverse and sustainable demography of trees, rather than relying on a boom-and-bust of baby trees determined by election timetables.
So much is understood, but open questions remain and we should all recognise the need for ongoing research. Research is required to inform the location, extent, and uses of treescapes, and to maximize the ecological resilience of both mature forests and new planting in the face of a never-before-seen environmental context. What species are best suited for a climate-changed UK? What genetic resource is available in our existing trees to resist globalised pests and pathogens? Which communities of organisms, from microbe to vertebrate, from grass to pine, form stable and productive woodlands now and in a century from now?
By 2050, UK population may be 77 million,, atmospheric CO2 will likely exceed 550 parts per million (ppm), average UK climate will be ~2oC warmer with stronger NW-SE summer temperature gradients and large seasonal swings in rainfall, and the internal-combustion-driven vehicle may have disappeared from theUK traffic fleet, taking with it a large, inadvertent, and untargeted nutrient addition to forests in the form of deposition of nitrogen oxides. ‘Space for Nature’ will be at a premium, while demand for biomass energy and plastics-replacing fibre will be much increased. Long-lived trees will have experienced a doubling in the abundance of CO2, their primary material substrate, but water availability will be radically altered and important additional sources of nitrogen for growth will have been removed. We are only at the very start of understanding the implications of these changes for real trees in real treescapes.
Hooray for the politicians advocating nature’s very own carbon dioxide removal technology but let’s see the wood for the trees. We need to talk about diversity and resilience if our treescapes are to serve us well. 21st century UK forests will radically alter the UK landscapes but will also themselves be altered by national and global drivers of change, particularly atmospheric composition, climate, and UK population. These challenges are what a climate-savvy political debate should address.