CR What’s the difference between biodiversity in an intact forest and in one that’s been fragmented?
TL It’s dramatic. A hundred-hectare fragment—about 250 acres—loses half of the bird species of the forest interior in less than 15 years. It’s sort of like a mineral shedding radioactivity and becoming simpler. In this case, the ecosystem is shedding species and becoming simpler.
CR And in this case simplicity is not a good thing. One of the questions people often ponder is why a tropical forest is so much richer than the forests in North America. Can you talk about that?
TL Well, we still don’t know for sure. But basically you don’t have anything that approaches winter, when most of the productivity pauses and most species cease to actually do things. Everything is essentially active all the time in a tropical forest. Evolution is going on all the time. And the Amazon is big—the size of the lower 48 states.
CR People classically underestimate how much of the Amazon forest we still have left despite the bad news about wildfires and deforestation. How much of the Amazon has forest cover?
TL If you look at the entire Amazon, it’s around 84%. But of course in many specific areas in the Amazon, it’s much lower. And the minimum coverage we need is 80%, especially in the Brazilian part. And it’s basically no longer there. You can actually see some species changing. So we think it’s very close to the tipping point. The good news is, something like the Amazon doesn’t just topple over like the Washington Monument might, right? It’s a long, slow process. There is time to aggressively get into reforestation, build back that transpiration capacity, and maintain the hydrological cycle.
CR You’ve published and edited several editions of a book about biodiversity and climate change. Could you talk about where we are right now on climate change, the challenge that we face, and where you see the biggest openings for making a difference?
TL Climate change is driven by two things: the destruction of modern-day ecosystems and the burning of ancient ones, which is what fossil fuels are. We know that keeping global warming to 1.5 degrees Celsius is critical. Ecosystems tend to come apart when you get beyond that. In fact, we’re already seeing it in the response of coral reefs and the coniferous forests of northwestern North America. So the real challenge is, how can we get back to a level of CO2 in the atmosphere that will allow for a relatively smooth landing?
CR What are the most promising approaches to addressing climate change in the context of natural systems?
TL It’s reforestation, it’s restoring degraded grasslands, it’s restoring degraded agricultural systems, designing agricultural systems that actually accumulate carbon in the soil and become more fertile, and preserving coastal wetlands and mangroves. I mean, it’s just about everything, which has this wonderful element to it that anybody can contribute. To so many people, climate change is this big, overwhelming problem. But everybody can help plant a tree or shovel some mud for a coastal wetland. Kids can do it.
