by Shane Coffield (ComSciCon-LA 2020)

From what I’ve seen of The Lord of the Rings trilogy, there’s one scene that stands out to me as a scientist. In The Two Towers, there’s a tree that comes to life and begins walking. These “Ents” are some of the oldest and largest living things in the fantasy world of Middle-earth.

 

The Ents remind me of our coastal redwoods and giant sequoia trees here in California–the oldest and largest trees in the world. Historically they’ve thrived in California because they are well-adapted to mild climates and occasional fires.  

 

I also think about the Ents because our giant trees would really benefit from the ability to walk. In climate science there’s a concept called “climate velocity”, which refers to the rate of climate change not in terms of degrees per year, but in terms of distance per year. The climate velocity describes how fast you would have to move either northward or uphill to maintain a constant climate over time and “keep up” with climate change. For example, I really like summer temperatures around 75°F. Southern California is great for me now. However, in 50 years, it’s going to be a few degrees warmer here. If I wanted to stay living in 75-degree summers on average, I’d have to slowly move north (where it’s cooler) about a mile every year to balance out the climate warming.

 

Sadly, our beloved redwood trees don’t have feet, so as the climate gets warmer, they’re going to be stuck in the same place. Scientists aren’t exactly sure how much temperature increase different tree species can tolerate, but past years in California have clearly shown that climate-driven droughts and wildfires kill massive numbers of trees.

 

 

In my most recent research with some colleagues (see publication and press release), we explored how warming temperatures and changing rain patterns will affect where different types of vegetation, including tree species like redwood, will be able to live at the end of this century. Here are a few key findings and why they matter:

 

1. Climate change will drastically shift the range of coastal redwoods northward, restricting them to the northwestern corner of the state. Currently they grow as far south as central California, like in the Big Basin State Park south of San Francisco (which notably burned in 2020). Redwoods take hundreds of years to grow to maturity, while climate change is happening much faster. Loss of redwoods in the southern part of their range will not be balanced by growth in the north for a long time. This means that the best way to protect this unique species may be to start planting and promoting their growth up north now.

2. In general, climate change will favor oak trees over pine trees. Pine trees often dominate in colder environments, which will be restricted to smaller and smaller parts of the mountains and far north as the state warms. Oaks could slowly expand to take the place of pines throughout much of the state’s mountain regions.

3. In total, warming temperatures will cause California to lose about 16% of its carbon that’s stored in vegetation (especially tree trunks, which are about 50% carbon by mass). This is counter to the state’s goal of increasing the total carbon stored in the land by a few percent to combat climate change. Our findings suggest that the land may not be a reliable place to store carbon. Other places, like deep in the Earth (or better yet, not emitting carbon in the first place!) are probably more effective.

4. Forest carbon offset projects are located in places that are disproportionately vulnerable to climate change. These offset projects are where landowners are being paid to maintain healthy, carbon-storing forests to counterbalance the emissions from big polluters and other entities. If the carbon being stored in offset projects is not actually permanent, then we are dangerously miscalculating our current net emissions. It’s critical that offset programs account for vulnerabilities related to climate change so we can be more confident that these climate solutions are legitimate.

 

The main conclusion of all of this research is that while our natural lands may offer ways for us to mitigate climate change (for example, by planting trees), they are also being impacted by climate change. In other words, the problem of climate change is even more challenging because it’s likely to interfere with our efforts to mitigate it too. By identifying the most vulnerable regions and species in California, we can help land managers plan for the future. We can protect our ecosystems while designing better solutions to climate change in the first place. Perhaps part of those solutions will be to help our most critical tree species migrate to where they have the best chance of surviving this century, especially if they aren’t going to start walking there on their own.

----------------------------------------------

 

Shane Coffield is a postdoctoral researcher at the University of Maryland and the NASA Goddard Space Flight Center, where he uses satellite data to monitor forest ecosystems and track wildfires. His research on climate change and California ecosystems was part of his recently completed PhD in Earth System Science at UC Irvine. Alongside his research, Shane is also an active advocate for science-based policymaking and strives to make his findings accessible to broad audiences.