Environment + Climate

Uphill battle for California’s native plant species

Largest study yet of plant species shifting with climate change finds ecosystems unraveling in California

Sequoia tunnel
Ernie Tyler/Flickr

California’s ecosystems are being pulled apart in an era of climate change, according to the largest-ever empirical study of how different plant species are moving.

For the study, which was led by Jon Christensen of the UCLA Institute of the Environment and Sustainability, researchers analyzed 681,609 historical specimen records of 4,426 plant species. All were collected in California between 1895 and 2009. Everywhere they looked, from valleys to mountaintops, from inland deserts to the coast, life was on the move. Species have been shifting geographic ranges, generally upslope in elevation.

Invasive species have moved faster than native species, colonizing and competing in new territories. But endemic species — those unique to California — have largely stayed put. Endemics currently occupy spaces where they can successfully compete against invasive species and other disturbances – but climate change could prove too challenging.

UCLA Newsroom talked with Christensen and lead author Adam Wolf about their groundbreaking study and what comes next.

How did you discover this amazing dataset and what was the main challenge in using it for the study?
Christensen: We used historical botanical specimen records digitized by the Consortium of California Herbaria, run by the University of California. When we got a full download of all the specimen records, close to a million records had geographic locations. And when we visualized those popping up over time on a map of California, we were blown away. We wondered whether we could see patterns of response to climate change. Many of those patterns revealed biases in the way that people collected specimens — close to roads, in blitzes of collecting in particular places, looking for particular groups of plants, and so on. And that presents a difficult problem for analyzing the data to see changes in where plants actually are over time. It turns out a lot of people have had the same thought we did — to use the data to look for responses to climate change — and they’ve not been able to do it. But Adam led our team in developing a new statistical technique to analyze the data while dealing with the bias.

Adam Wolf
Courtesy of Wolf
Adam Wolf

Wolf: It was obvious at the outset that we were trying to use a dataset that was not collected for our purposes. As a historian, Jon saw the human stories in this data. You can trace the path of an individual, such as the pioneering California botanist Willis Jepson, as he explored a remote valley in northern California. And with that data you can begin to paint a picture of the state in the late 19th century. But in this project we had to strip away the human story to see if there was an ecological signal hidden in the big data of the entire dataset. We did research showing that if we didn’t figure out how to deal with the idiosyncratic behavior of collectors we would almost certainly come to incorrect conclusions. So then we had to develop a new statistical method to test whether the distributions of particular species that we see in the historical record are likely to represent the real distributions of those species given the overall sampling effort in particular areas at different times.

Species have been moving around for millennia. Why should we be concerned about this now?
Wolf: The people who are really worried about this are working at Nestlé and Sainsbury’s, where they are wondering where cacao and strawberries will grow in the future. Here in California, there is considerable worry about the fate of redwoods in a future with less coastal fog, or the giant sequoias in a future with less snowpack and drier summers. These are endemic species that grow nowhere else on Earth and are holdovers from California’s long and complex geological and ecological history. The dinosaurs are extinct but the sequoias are still with us, along with nearly a thousand other endemic species in California’s flora. We found that these species unique to California are essentially stuck in place, with little evidence that they are colonizing new environments to adapt to the warming climate that California has experienced during the past century.

Jon Christensen
Jon Christensen

Christensen: What we’re seeing is a shuffling of some of the most basic relationships in nature, between what plants are found where, what plants are found with other plants, on which kind of soils, and with what kind of climate, temperature and precipitation. We don’t really know how big of a problem this is, yet. But this study raises the basic concern that we could be seeing the unraveling of the fabric of California’s ecosystems. And that could pose enormous challenges for protecting species and ecosystems.

Wolf: And I have to add, this isn’t just speculation based on models and projections of what the future might bring. We went back to empirical data of what has actually happened on the ground. And our study is not just about a small number of species for which there are large amounts of well-structured data, such as timber trees. We’re looking at the whole of California’s flora. It’s no coincidence that our research included more species than any other study of its kind, using data from museum collections largely held by the University of California, which also employed many of the collectors as researchers and professors over the years. This is a testament to California’s rich natural history and to the perspicacity of University of California researchers who first collected, and then later digitized these collections to make studies like ours possible.

What comes next?
Wolf: A lot of studies extrapolate that plants will need to move tens or even hundreds of miles in order to stay in their climate niches with global warming. But anyone who has taken a hike around California knows that you can see manzanita, which is adapted to hot, dry landscapes, just a hundred yards from a redwood grove dripping with fog. It makes you think, “Couldn’t they just move over there to the other side of the hill?” The changes we see underfoot are real, but I have sympathy for the folks who think environmental studies can be alarmist. For me, models without empirical data are science fiction. We are swimming in models, but not enough data. I believe the greatest contribution I can make is to develop tools for us to collect and analyze natural resource data at scale, which is why I’ve left academia to found a startup called Arable, to collect and analyze all kinds of data to better manage natural resources. This is not just about the changing temperature envelope of a certain monkeyflower, but about the climate sensitivity of major crop plants and the changing microclimates of our economically vital agricultural regions, from Oxnard and Salinas, to Napa and Mendocino. We need so much more data and new ways of analyzing and acting on it to adapt to our ever-changing world.

Christensen: I’m involved with the UC-wide Institute for the Study of Ecological and Evolutionary Climate Impacts, which is using the 39 natural reserves in the UC system as a network for studying climate change and ecosystems in California. Researchers have been studying nature and collecting data in these reserves for more than a hundred years. And the historical data and archives are now being organized and sometimes digitized to make them available for studies such as this one, at the same time that we’re using monitoring equipment such as Adam is developing to collect current data. We’re in a very exciting period for using historical data and current monitoring to understand how our ecosystems are changing. The big question is whether we can also change fast enough to stem climate change.

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