Charity websites proudly display counters with the number of trees planted. They number in the millions. Photos of singing and dancing villagers are shown with their hundred thousandth or their millionth tree. "Deforestation" proclaim the sites "ruins livelihoods and contributes to global warming. We can fix it".
Schoolchildren celebrate arbour day by planting trees in their schoolyard. They are taught from an early age how important trees are to the environment, and how, if we are to save the biosphere, we must plant trees, more trees, millions of trees. These kids are the next generation; when they grow up, they will understand the importance of forests and trees and they will make a difference. They will influence policymakers and set up charities of their own.
All this has some ecologists very, very worried.
Forests around the world are threatened with habitat destruction, and reforestation efforts are a major tool in conservationists' toolbox to restore degraded forest ecosystems. Reforestation efforts are generally intended to provide employment and business opportunities for local communities, restore forest ecosystems, and sequester carbon for carbon credits.
All laudable goals. But what about when forest restoration efforts harm other ecosystems?
That's the question posed by Professor William Bond in a paper in the journal Science. Bond, an ecologist at the University of Cape Town, has studied grasslands, savannas, fire, grazing and biodiversity for decades. And he was deeply concerned by the implications of a new global reforestation initiative.
Bond looked at the recently-announced Atlas of Forest and Landscape Restoration Opportunities, an ambitious and much-needed effort by the World Resources Institute to map degraded forests globally. They have identified 1.5 million square kilometres of land for restoration by 2020, much of which, Bond argued, may, in fact, be natural grassland.
To the frustration of grassland ecologists, grasslands have frequently been overlooked in the international consciousness as places worthy of, well, anything. But grasslands store more than a third of the world's terrestrial carbon stocks (almost all of it underground), and hold a huge proportion of global terrestrial biodiversity, second only to tropical forests. Yet to many people, and particularly policymakers and the public, they are simply tidy places to plant crops or build suburbs. Many natural grasslands are viewed by influential thinkers as "degraded forest", partly because it can often be difficult to tell the difference between ancient grassland and grassland that was once forest.
The question that Prof. Bond asks in his paper is: how much of that 1.5 million square kilometres is, in fact, degraded forest, and how much is ancient natural grasslands?
So Bond's concerns are real. If the Atlas project identifies areas of natural grassland as "degraded forest", huge amounts of resources could be misdirected towards transforming an intact and healthy grassland ecosystem into an artificial forest ecosystem.
Encouragingly, the authors of the Atlas project, in their response to Bond's concerns, invited grassland ecologists to collaborate with them to refine the model. But at some point, models reach their limits and knowledge and experience take over. Once projects get to the point of actually preparing to plant trees, they will need experienced local biologists to guide project managers in making the final assessments about a particular patch of land.
How can we tell if a grassland is "natural"?
Certainly, grasses and trees have engaged in a millennia-long tug-of-war, with trees alternately advancing into and retreating from grasslands as environmental conditions shifted and changed. Indeed, in the modern era, encroachment of woody plants into grasslands is a subject of major concern to conservationists, and a major subject of research for ecologists the world over (and the subject of a future blog).
Despite all the uncertainties, we have enough knowledge now to be able, with a reasonable degree of certainty, to determine whether a particular area of grassland has a long evolutionary history as a grassland, or whether it is a degraded ex-forest that should be rehabilitated by planting trees. We can survey the vegetation and determine whether there is a high proportion of grassland endemics; we can examine historical records and aerial photos; we can compare the physical environment to well-studied ecosystems with similar rainfall, soils and topography. And ultimately, we can make a judgment based on evidence and experience about what our vision for the ecosystem should be.
Intact, natural grasslands play a vital role in our biosphere, far more so than most people realise. Forest rehabilitation programs are hugely important for restoring degraded forest ecosystems, but a lot more consideration needs to be given by activists, policymakers and funders to the role of grasslands and to ensuring that forest rehabilitation efforts are focused where they are needed - in forests - and do not encroach into grasslands.