By Chelsea Harvey August 29 - washingtonpost.com
The Amazon is famous for being one of the most diverse places on Earth — its forests are home to tens of thousands of plant species alone. And now, scientists are claiming that all of these different plants may be key to the Amazon’s survival during future climate change.  
A new study, published Monday in the journal Nature Climate Change, suggests more diverse forests are better at adapting to the changing climate. Using a model that simulates tree growth in the Amazon, the researchers found that as climate change causes some trees to die off, other plants in the forest — more suited to the new conditions — can grow in to take their place. In these cases, the composition of the forest does change, but it’s able to at least partially recover the amount of vegetation it had before.  
“I think this is a nice and elegant study illustrating the practical stakes of a classical debate in ecology…about whether diversity begets stability,” said Scott Saleska, a professor of ecology and evolutionary biology at the University of Arizona, who was not involved with the new research, in an emailed comment to The Washington Post.  
In the past, models have often been used to demonstrate how the Amazon might react to future climate change, which is expected to bring not only higher temperatures, but also increased drought in some regions, increased flooding in others and a general uptick in extreme weather events. But these models have not always included the most detailed information on the Amazon’s vegetation.
According to Boris Sakschewski, lead author of the new study and a researcher at the Potsdam Institute for Climate Impact Research, the models have often lumped collections of similar plants together into just a few large groups, failing to adequately represent the unique traits that may affect the way individual plant species respond to climatic changes. These can include traits like the size or thickness of a plant’s leaves, which help influence how that plant might react to water or heat stress.
For the new study, Sakschewski and a group of colleagues expanded on one such vegetation model, creating an updated version that can simulate the growth of individual trees and their diverse characteristics. The researchers then ran a series of simulations with both the new model and several older versions to see whether the added diversity would make a difference in forest responses under various future climate scenarios.
Specifically, the researchers tested out two different scenarios. One was a “business-as-usual” trajectory, in which greenhouse gas emissions are assumed to continue on unabated, resulting in high temperature increases and severe climate effects. The other was a more moderate scenario, in which mitigation efforts are able to cut down on global carbon output and reduce the severity of future climate change.
Sure enough, the more diverse forests in the new model were better able to recover under future climate change scenarios. However, that doesn’t mean that they escaped totally unscathed. None of the simulations suggested that Amazon forests would be able to grow back 100 percent of the trees they lost to the changing climate — and, in fact, the business-as-usual climate scenarios resulted in low amounts of recovery in all the models, even though the more diverse model produced slightly better results.
“You definitely see a higher positive contribution of biodiversity under a moderate climate change scenario,” Sakschewski said.  
It’s also important to note that even the areas that showed recovery were still changed afterward, with different types of plants growing in and becoming dominant under the evolving climate. This could mean that the animals and other organisms that rely on plants for food and habitat might still be affected, Sakschewski said.
The idea that high diversity can improve the resilience of an ecosystem is not a new concept — it’s been touted by ecologists for decades. Rather, the new study helps to support previous research by showing it “on a big scale in a sub-continental simulation,” Sakschewski noted in a follow-up email to The Post.  
And the study also helps to emphasize the importance of accurately reflecting biodiversity in the models we use to make predictions for the future. It’s an issue that other research groups have recently begun to explore as well. Saleska, the University of Arizona scientist, pointed to a December study led by Harvard researchers, suggesting that better reflecting diversity in Amazon models gives us a more accurate look at how these forests will respond to future climate change.  
Each of these studies suggests that protecting the biodiversity present in the Amazon — trying to preserve as many different types of species as possible — is one key tool that conservationists can use to help the ecosystem survive in a changing world. It’s not an end-all solution, Sakschewski was careful to note, but it’s one important step.  
Because the projections were still grim under the business-as-usual climate scenario, even for the more diverse simulations, Saleska pointed out that the Amazon’s resilience does have clear limits. But he added that the researchers “are absolutely right when they emphasize the critical importance for conservation of the connection between preserving biodiversity and mitigating climate change.”