What makes a grassland?


There was an article published in the most recent issue of Science that seemed like a good way to get the ball rolling here at Borrowed Lands.

William J. Bond. 2016. “Ancient grasslands at risk” Science, Vol. 351, No. 6269, pp. 120-122. http://science.sciencemag.org/content/351/6269/120.full

When you look at a grassland, often you’re looking at what used to be a forest. Knowing that deforestation is a massive contributor to biodiversity loss and carbon dioxide emissions, you might be tempted to plant trees on your grassland, restoring the environment to its previous state.

But what if that grassland was never a forest and is, in fact, an ancient grassland? That’s the question Bond asks in this article, and one which I’ve seen pop up a lot over the past year. In that case, you may not want to blindly reforest the grassland.


Depiction of the life cycle of an underground tree in a tropical grassland. From Bond, Science 2016

A similar debate exists in the salt marsh community. Recent results have suggested that North American marshes may owe their origin to changes in sediment supply driven by colonial-era deforestation and that salt marshes may have an inherently short life-cycle. Conserving marshes exactly as they are now or trying to install marshes as part of a revitalized urban landscape doesn’t reflect their natural dynamics.

However, we may not want to simply recreate the natural dynamics of salt marshes. Instead of framing the question in terms of restoring environments to their pristine, unaltered or natural condition — a frame which may lead us to reforest grasslands that don’t look as old as they are — we need to think about what exactly the various ecosystems provide both to humans and to the local and global environments. Unfortunately, as Bond notes, we don’t even have good maps of old-growth grasslands, much less a firm grasp of their carbon and nutrient budgets, biodiversity, social and ecological roles and environmental history. Similar uncertainties exist in salt marshes, for instance in their carbon budgets.

Even if we do get a handle on these uncertainties, we may yet decide that a tropical forest is worth more than an ancient grassland or that some extra marshes on groynes might do wonders for Boston Harbor. Conservation is far from straightforward.

On the Borrowed Lands reading list: Forgotten Grasslands of the South: Natural History and Conservation by R.F. Noss. I saw this book at the Harvard Bookstore the other day, and now Bond cites it, so I think I’ll have a look at it.