Plants take a hike as temperatures rise

February 10, 2009 by Megan Levardo
Miniature woolly star, known to scientists as Eriastrum diffusum, is one of the plants that has been blooming at higher elevations in Arizona's Santa Catalina Mountains as the summer temperatures warm. Credit: C. David Bertelsen

Plants are flowering at higher elevations in Arizona's Santa Catalina Mountains as summer temperatures rise, according to new research from The University of Arizona in Tucson.

The flowering ranges of 93 plant species moved uphill during 1994 to 2003, compared to where the same species flowered the previous ten years. During the 20-year study period, summer temperatures in the region increased about 1.8 degree Fahrenheit (1 degree C.).

"For years, probably decades now, scientists have been trying to understand how species are going to respond to the anticipated global changes and global warming," said Theresa Crimmins, research specialist for the UA's Arid Lands Information Center and the network liaison for the National Phenology Network.

To better understand how plants respond to climate change, Crimmins and her husband, UA climatologist Michael Crimmins, teamed up with naturalist Dave Bertelsen. He's been hiking the Finger Rock trail about one to two times a week since 1983 and recording what plants were in flower.

The 5-mile hike starts in desert scrub vegetation and climbs 4158 feet (1200 meters), ending in pine forest. Bertelsen has completed 1,206 round-trip hikes and recorded data along the trail for nearly 600 plant species, he said in an e-mail.

Lead author Theresa Crimmins said Bertelsen's data shows that some species flowered farther upslope than before, others stopped flowering at lower elevations, and some species did both.

Because some plant species are moving and others staying put, she said the changes may divide plant communities, increase the growth of invasive species and even cause local extinctions by affecting the food sources of local insects and animals.

"I think we can be confident that things are going to continue to change and we don't necessarily know the ripple effects of all these changes in flowering ranges," Crimmins said.

Theresa Crimmins, Michael Crimmins, assistant professor and climate science extension specialist for the UA's department of soil, water, and environmental science, and Bertelsen will publish their paper, "Flowering range changes across an elevation gradient in response to warming summer temperatures." The paper is published this week in the online Early View of the journal Global Change Biology.

Many scientists have wanted to study the movement of flowering ranges, but lack the years of detailed data required for this research, Theresa Crimmins said.

At a meeting about monitoring plant species held by the U.S. Bureau of Land Management in 2005, Crimmins discussed his need for data to study the effect of climate change on ecosystems over time.

Bertelsen was at the meeting and told Crimmins about the extensive data he had collected during his many years hiking Finger Rock trail. Bertelsen had the sense some plants were flowering farther uphill and had observed many changes he attributed to drought.

Bertelsen had begun hiking the trail in 1981 and fell in love with the flora and fauna. He had just taken up macrophotography and took close-up pictures of all types of plants and animals while recording his observations in a journal.

"Somebody once said that I have this compulsion. I don't feel driven at all, it's drawn. If I miss a week, I miss it. I just feel that I'm really part of that canyon and it's a part of what I am. It's just good old human curiosity," Bertelsen said. "There's always something different. It's just absolutely amazing."

In 1983 he developed a checklist to document each species in bloom along each of five one-mile long trail segments. Thus, on a single day, if a particular plant was seen in bloom in three segments, there would be three different records. Bertelsen collected flowering data from 1984 to 2003.

To see whether the plants had shifted their flowering, the Crimminses compared Bertelsen's location records from 1984 to 1993 for 363 plant species with his records from 1994 to 2003 for the same species.

The Crimminses used climate data from six National Weather Service Cooperative Observer Network stations surrounding the trail to see how the temperature varied during the 20-year study period.

The Crimminses' collaboration with Bertelsen is a great example of how scientists and amateur naturalists can work together, Theresa Crimmins said. As part of its mission, the National Phenology Network encourages such collaborations to document events in the life cycles of plants and other organisms.

Theresa and Michael Crimmins plan to do additional analyses of the data to determine whether climate change is also causing flowers to bloom earlier in the year.

"The changes are happening fast enough now that more eyes on the ground are going to be much more useful as the human species tries to understand how these other systems, that we rely upon so dearly, are going to change," Theresa Crimmins said.

"We can really start to think about what the true impacts of those changes are and how can we mitigate these impacts."

National Phenology Network:

Source: University of Arizona

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2.3 / 5 (3) Feb 10, 2009
Plants are flowering at higher altitudes as perceived temperatures increase... Huh?
2.3 / 5 (3) Feb 10, 2009
Somebody once said that I have this compulsion. I don't feel driven at all, it's drawn. If I miss a week, I miss it.

Yep, Scientific data at it's finest....
2.3 / 5 (3) Feb 10, 2009
Yes plants flowering and growing at higher altitudes is pretty basic stuff guys. As altitude increases on a mountain side it gets colder. Thats a major reason different plants and animals live at different altitudes going up a mountain.


Bertelsen has completed 1,206 round-trip hikes and recorded data along the trail for nearly 600 plant species.

over 20 years. Yeah I think that is prety good scientfic data.

You guys are getting pretty desperate lately aren't you. I mean you have keep making more and more uninformed statements so as to find something to criticise in these articles.

I guess your just down to voting down all articles containing evidence of global warming now.
5 / 5 (2) Feb 10, 2009
Actually I'm not voting on the articles and as of recent I've resisted downranking commentors simply because it feels like I'm stifling conversation if I do. If anything that action is completely contrary to the spirit of the site which is to deseminate information from the field.

ryuuguu, My comment is relating directly to his quote, which is why I included it in my commentary.
It's a rather lacadaisical attitude for a nature enthusiast to take especially when the topic involves his written observations on a heavily polarized issue.

Secondly, look at it this way, if I have 20 years of data it is exactly that, raw data. Now when you start sifting through that raw data to get solid information on trending, which is the basis of this study, and you are missing data points the study loses a lot of merit.

Let's say I have a log book of observations made over 20 years on the weathering of a rock (silly hypothetical I know, sorry) and you want to start using that data to show a trend.
You pick a date, April 20th, and you want to chart my observations on that day for each year. You have 20 data points, unless I skipped that day, let's say, half the time, now you have 10. Well 4 of those ten are all over the place, the other 6 are sloppy and inaccurate readings. Now you have jack.

Collected data has to be uniform in the collection process. 20 years of observations made by someone who was not making the observations by a set standard are at best a loose approximation that won't hold up to any real scrutiny, and most likely not as useful as would be necessary to disprove or support a hypothesis.
1 / 5 (1) Feb 10, 2009
No one has said this yet so I will say that this study is alarming!
3 / 5 (2) Feb 13, 2009
I'm the guy who collected all the data, and I find it interesting that a few "geniuses" can critique a study based on a press release. That's really scientific. For the record, we analyzed 111,012 observations recorded along a "transect" of approximately 1.6 million square feet. There was a "set standard" in making observations, but I don't want to confuse you with facts. My "lacadaisical attitude" resulted in 1024 field trips in 20 years, learning to identify and recording flowering of nearly 600 taxa (while collecting dozens of plants and reams of data for the Tucson Mountain flora, co-authoring the Arizona Rare Plant Guide, and a few other projects). You've done better? You missed our first paper, published last year in the International Journal of Biometeorology, in which we looked at the relationship between blooming (which I defined as anthesis, specifically the presence of pollen) and precipitation/temperature. That analysis led us to the current paper. No preconceived notions, it's called "following the data." Some apparently don't understand what it means when we say the range of a species moves or contacts upward. That means, for example, a species which was once found primarily in desert scrub is now found primarily 400 or 1000 feet higher in scrub grassland or oak woodland. The data concerns alpha diversity, presence or absence, not abundance, so our analysis did not pick up a species, say, that may have once been common down to 5200 feet but is now rare below 6400 feet. Nor did it pick up on species that moved up 400 feet or more within a given elevation range. Suffice it to say, there are more species moving upwards, particularly in the last few years, than we reported in the paper. Results similar to ours have been recently reported from California and France. A plant species doesn't bloom only on one day but over a period of several days or even months, and it blooms at different times at different elevations, so a specific date doesn't mean jack. As for climate change being a "heavily polarized issue" all I can say is even George W. finally admitted it was occurring. We didn't address the causes of climate change, and that, if anything, is what is debatable. Personally, I think it's caused by hot air.
5 / 5 (1) Feb 13, 2009
I'm the guy who collected all the data, and I find it interesting that a few "geniuses" can critique a study based on a press release. That's really scientific. For the record, we analyzed 111,012 observations recorded along a "transect" of approximately 1.6 million square feet. There was a "set standard" in making observations, but I don't want to confuse you with facts. My "lacadaisical attitude" resulted in 1024 field trips in 20 years, learning to identify and recording flowering of nearly 600 taxa (while collecting dozens of plants and reams of data for the Tucson Mountain flora, co-authoring the Arizona Rare Plant Guide, and a few other projects).

I'm glad you were available and took the time to comment as the abstract has certainly done you a disservice as well as failed to properly link the research itself.

Under the stated conditions I would be interested to read the actual research itself. You'll have to forgive my use of the term lacadaisical as you've proven to be anything but.

Now that you're here and you've read the abstract, what do you think of how they've painted your reseach and what are your views on climate change and it's possible relationship to anthropogenic sources of CO2? Do you believe that as humans we are culpable for the current changes in climate to the touted degree of 50% purely through CO2?
not rated yet Feb 13, 2009
I don't think the press release distorted our findings although there are a couple of errors. Temperatures are increasing, the range of 10-15% of reproducing taxa in the flora are moving up-slope. Facts are facts.

As far as the cause of current climate changes, I'm not competent to respond because I haven't studied climate change. It's important to know what you don't know.

I do know that the changes I'm seeing on the ground seem to be accelerating since 2003. This year, for example, a saguaro at 5200 feet was blooming--it's been there since the beginning of my study but never bloomed. In 2006 I found several invasive non-native grasses at record elevations, some 1000 to 2000 feet higher that they had ever been found before. I also saw a tarantula in the open at 5200 feet elevation last month, and that's unheard of, even in the low desert, according to arachnid specialists I know.

I never considered climate change as a driving factor until we looked at some of the results. In the elevation range at the top of my study area, the alpha diversity (number of taxa) in bloom during summer was steadily increasing along with temperature, a high correlation. That's why we took a closer look. We actually expected to see range changes largely at the higher elevations, but found they are occurring across the entire gradient. We also expected annuals to show the most change, but most of the range changes were of perennial species.

I definitely have seen significant effects of drought (which may itself be a result of climate change), but I don't think drought alone can fully explain what we are seeing--especially since temperature is very important at higher elevations. This part of Arizona had a severe drought in the 1950s, but all of the 91 saguaros, 44 ponderosa pines, and 60 white oaks that have died since 2002 survived that drought. The current drought is accompanied by higher temperatures over the entire region, and that may be what the difference is.

As far as a link to the actual article, the best you could get free is the abstract on the Global Change Biology web site. Scientific journals charge for copies, and their subscription rates are really high ($383/yr for an individual, over $4000 for an institution for this one), so the easiest way to read the article is to go to a University that subscribes to the journal.
not rated yet Feb 13, 2009
Thanks, I certainly appreciate the information and thanks for your time.
not rated yet Feb 14, 2009
There are many reasons plants migrate.

From another blog:

"Potential problems with estimating temperature are one reason for looking more to integrators of climate. I study lakes, there we can look at long term trends in temperature and the number of days of ice cover. Botanists in Europe are studying the invasion of plants from the south (e.g. Spain) into northern countries, while ornithologists are studying advances in bird migration timing and egg laying. Glacier melting is another good integrator. Presumably, the kinds of changes that I listed above are not dependent on the placement of weather stations.

The award for the best study by a Ph.D. student at a conference that I recently attended in the Netherlands, went to an excellent study that combined a green house experiment and field data to show that plant species that have recently invaded the Netherlands from the south are more resistant to generalist (insect) herbivores than closely related species (congeners) that are natives. This paper was already published in Nature, which is the most prestigious scientific journal (along with Science). The study included a very elegant experimental design with very convincing results. The importance of generalist predators is that species that are expanding their ranges often leave their specialist predators and pathogens behind."

In the good old USA, it seems that every change automatically means we are doomed.

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