Guest Post by Willis Eschenbach
Anthony recently pointed out a new paper called “Dramatic Response of Montane Plants to Climate Change in the Southwest” by Brusca et al., available here. In that paper, the authors have done an interesting repeat of an earlier study.
In the Brusca2013 study the authors report having done a new plant count following the uphill route along the same road used in a study done by Whittaker and Neiring in 1963 (W&N63). The road runs from Tucson to the top of Mt. Lemmon. They claim that their results show that warmer, drier weather is forcing Arizona plants uphill.
Could this be happening? Sure, it’s possible. Have the authors of Brusca2013 shown it to be a) actually happening and b) the result of climate change? Good questions. Here’s their summary of the results:
ORIGINAL CAPTION, BRUSCA2013 STUDY: Figure 1. Summary of elevation range of the 27 most common upland montane plants along the Catalina Highway. White bars are 1963 elevational range data from Whittaker and Niering (1964), the two terminal (stippled) 1000-ft bands denoting Whittaker’s upper- and lowermost 1000-ft vegetation bands. Black bars represent 2011 elevation data from this study. To be as conservative as possible, a change in a species elevation limit (high or low) was noted only if that species was found outside (above or below) the upper- or lowermost 1000-ft band. Thus, if anything, we underestimate the elevational change in the species since 1963 (see Materials and Methods). Following this protocol, 15 species show an unambiguous increase in lower elevation, four show an increase in upper elevation, and eight show a decrease in upper elevation.
Note that in the original W&N63 study, they only recorded the elevational band (e.g 3,000-4,000 feet) of the lowest and highest specimens. They did not record the actual elevation (e.g 3,232 ft) of the specimens at the extremes. This has created some difficulties in the Brusca2013 authors’ interpretation of their results. For example, look at the grass “Muhlenbergia porteri” (second line from the bottom). It is counted as one of the fifteen species whose lower elevation has been raised. The problem is, the lowest elevation looked at in the new study is 3,500 feet, viz:
Thus, our plant quadrat sampling began at 3500 ft/1067 m and ended at 9111 ft/ 2777 m, excluding desertscrub at the base of the mountains.
Since the new study only began at 3,500 feet, we cannot say that the lower range of this species is increased. They have incorrectly counted it as having an “unambiguous increase in lower elevation”. Does this one error invalidate the study? No. But this kind of error, in favor of their conclusion, does make a person wonder if the authors might have a solution (climate change) and be looking to fit evidence to that solution.
And what makes me wonder even more is that there are three other records with the same problem …
The difficulty is in their analysis of their own data. They want to compare their results to W&N63, which is a good thing, they should do so. But we need to have an apples to apples comparison. To do that, the very first thing you have to do is to convert their data to the “elevational bands” intervals used by W&N63. Yes, you need to throw away information to do it, but if you want to compare the two studies, you have to do it. For an example of what this does, look at Agave schottii, the first succulent in the purple band. It looks like the elevational range has shrunk considerably. But if the proper method were used, counting only by elevational bands as in W&N63, we’d see that there is absolutely no difference between the two records. W&N found it in three bands, and so did the latest study. Now, to their credit, they count it as unchanged. But it is incorrect to present their data for comparison with W&N63 in absolute elevations, rather than elevational bands as in the original study. To compare apples to apples, they have to first convert their data to elevational bands. Their failure to do so has lead them to false conclusions.
With that in mind, look at the bottom row, the grass “Urochloa arizonica”. When we convert their data to the W&N63 elevational bands, we see that there is no evidence of an upward trend at the bottom end, because the new survey only started at 3,500 feet. In terms of elevational bands, all we know from the new data is that that grass is still found between 3,000 and 4,000 feet, just as in the original W&N63 survey. For all we know, the current authors may have found the exact same patch that W&N found in 1963. As a result, we have no new information establishing the bottom end of its range.
The same is true for the woody shrub Mimosa aculeaticarpa, and the grass Aristida ternipes. Once we are comparing apples to apples by converting the data to elevational bands, it’s obvious we know nothing new about the lowest elevations at which they can be found. In all cases, they used to be found between three and four thousand feet, they still are, and we have no new information below 3,500 feet. From that we cannot conclude anything at all about changes in their lower boundaries.
This means that the authors have improperly identified no less than four of the records as showing an increase in lower elevations when the data does not support that claim.
Once that error is corrected, this leaves us with a curious result:
• 11 species have increases in lower elevation. Their range has shrunk from the bottom.
• 8 species have decreases in upper elevation. Their range has shrunk from the top.
• 4 species have increases in upper elevation. Their range has increased at the top.
I would hardly call that a convincing case for much of anything … however, they say it is a consequence of “climate change”, which they are defining as follows
Since the previous survey in 1963, the rainfall has gone up and then back down, not much change there. Arizona is always dry. However, as they point out, the temperature definitely has gone up … in Tucson, down on the valley floor far below the mile-high plants being studied. Measured at an airport which, unlike in 1963, is now half-surrounded by the city. So that might reflect changes up in the mountains … or not, we don’t know.
In addition, with changes in eleven lower and eight upper altitudinal limits in opposite directions, we can’t say the plants are moving up the mountain as they claim. Statistically, those two are no different.
And how is that collection of contradictory results supposed to happen from climate? Are we really to believe that the climate has driven the grass “Muhlenbergia porteri” (second line from the bottom) from 6,000 down to 3,000 feet, and if so, how does that work?
Finally, we have to consider confounding factors, which unfortunately they have ignored. The biggest one of these is the huge interaction between the plants and the animals in any ecosystem. For example, for the first time in decades the bears in Yellowstone Park are feasting on berries as they store fat for the winter. Is the increase in the number of berries a result of climate change modifying the berries’ elevational limits?
In a word … no. Curiously, it’s because of the return of the wolves to Yellowstone Park. The berries have been getting grazed to the bone by the elk for decades, but now that the wolves are keeping the elk in check, the berries are coming back, and the bear are getting their chance.
And although there are no elk in the area of this study, this is Arizona Game Management Unit 33, and the list says “Species within this unit: Javelina, Mule Deer, White-tailed Deer, Cottontail Rabbit, Dove, Tree Squirrel, Quail”. Pigs, rabbits, mule and white-tail deer … how have their numbers changed over time, and what effect has this had on the local plant species? Where I live, the deer exert a huge control over the shape and nature of the biome. And pigs are noted for their effect on the local plant ecology. What’s happening with the pig population?
SUMMARY
• The study has significantly over-counted the number of species whose lower limits have increased. The number of species whose lower limits increased drops from their claim of over half (56%) of the species studied, down to 41% of the species.
• Over a quarter of the species studied had upper limits that moved down the mountains, not up as might be predicted.
• The study used temperature data which is from the valley floor, which has a good chance of being contaminated to an unknown degree by urban heating effects.
• The study failed to consider changes in local animal populations as an alternate explanation for at least some of the plant changes.
• Some species showed huge changes in their range, beyond what a few degrees in average temperature might reasonably explain. This indicates that other factors are likely at play.
• There was no discussion of natural fluctuations in the ranges of the plants. Plants are subject to a host of ever-changing forces. Is the current variation in range outside their normal variation, whatever that may be?
Overall, while it is an interesting study and I commend them on repeating the earlier transect, I’d say they have totally failed to demonstrate that the plants are responding in any meaningful or predictable way to the vagaries of the local climate …
w.
Good work Willis. Keep your eyes open. Sooner or later the madness will subside and more thought will be put into these types of papers. If not, you will continue to have easy targets. 😉
Rud, a close look at satellite images and Google Earth images of the fire shows that nowhere is did the fire come near the 5,000 foot level along the transect. So the photo you reference, their PR photo, is either on the other side of the hill where the fire was, or just a stock photo. It’s not a photo of a juniper at 5,000 feet along the transect.
w.
Willis, it’s been a long day, so maybe I’m just misunderstanding due to being frazzled, but
is this a typo? Either the 11 species decreased in lower elevation or the range increased, I’da thunk.
Nice article regardless, thanks.
[REPLY] By saying “lower elevation” I was referring to the lowest elevation at which they are found. If that increases, their range shrinks. -w.
Mark B says:
August 15, 2013 at 2:55 pm
Well caught, Mark. However, I don’t see how that’s possible. The 2003 Aspen Fire burned all the way to the ridgeline (where it met exposed rock on the other side) between Summerhaven and the summit, and part of Summerhaven as well. Here’s an image from September 2003, after the fire.
http://i863.photobucket.com/albums/ab195/weschenbach/burnextent2003aspenfire_zps16528499.jpg
The summit is at the upper left, above the “S” in “Summerhaven”. The entire road from Summerhaven to the summit, which you can see on the far side of the ridgeline, is burned on both sides. Summerhaven is at about 7800 feet. The summit is at about 9100 feet.
In addition, there is a stretch of road on the lower right which is burned on both sides.
So … I’m not clear how they got any samples above 7,800 feet, that was all burnt. I’ve confirmed that with the satellite photos of the period, it was quite photogenic.
And lower down, it sounds like they just skipped over the areas that show evidence of burning. It seems to me, however, that such an occurrence in the last decade, and its overall effects even if not all of the transect was burned, merit more discussion than that.
w.
Yeah, all sorts of complications with this analysis. To start with:
“…we did not sample in any areas of significant forest fire history since 1963, including the 2002 Bullock Fire or 2003 Aspen Fire”
As observed earlier, the aforementioned dead junipers were likely killed by the lower elevation fire, so my approach would be to sample within the burned area and look for evidence of regeneration. If they are re-occupying the site (which is a slow process), then no low-elevation contraction is indicated.
I have data from live alligator juniper extending down to about 4300ft between latitudes 31.4N and 33.8N (the part of the highway where they would be found is around 32.4N), so they definitely persist in some areas well below the lower limit found by this study. In addition, the average elevation for alligator juniper at this latitude is about 6500ft, and the vast majority of occurrences are found between 5000 and 8000. Anything below 5000 would be the fringe of its elevational range, no matter where you’re looking. If Whittaker did find juniper in the 3000-4000 band, then it’s highly likely that he found it in a moist microsite that wasn’t sampled in the recent study (if they don’t know the ’63 locations, there’s a lot of sampling noise involved with establishing a whole new set of quadrats).
One of the big questions in the West is whether junipers as a group are creeping down into former grassland, or whether they are just re-occupying former woodlands that were cut or burned during white settlement. Judging from the young-ish look of the dead tree in the PR photo, it would suggest a relatively recent downhill expansion, perhaps “undone” by fire.
I’d scratch alligator juniper off the list as an example of “unambiguous increase” in lower elevation, at least due to climatic influence.
Willis, you obviously have more time for this stuff than I do. Ask Anthony for the photos I resurrected. You are probably right about the burn details, since I have no time to check. But last time this farmer plus looked, any such catastrophic event changes the biome for a very long time.
We may disagree on fossil fuels, but we sure agree on palpably bad science like this.
How about possible effects of the Aspen Fire on Mt. Lemmon in 2003 that burned almost 86,000 acres? Without reading the original study, it is hard to assess exactly which variables the researchers considered, but I would certainly want to have accounted for them if the study were mine.
Here’s a map of the previous 2002 “Bullock” fire extent:
The transect is along the black line. The fire stopped at the road along much of its length. The lowest elevation of the fire along the transect is just under 6000 feet.
In addition, the road runs at or near the ridge, and the fire burned the east side but not the west side. And typically, those two sides of a ridge have very different biomes and plant types and climate.
So as a result, if they are avoiding taking samples where it was burned, they’re missing out on sampling half the local ecosystem … and it’s known to be different from the half they are sampling. No bueno …
w.
Good point on herbivores modifying the vegetation. A recent study confirms it happens: http://www.ecori.org/natural-resources/2013/6/19/study-finds-abundant-deer-reduce-plant-diversity.html
packera neomexicana? Nice plant, really likes it dry, really realyy dry.
Novermebr 1962 to Dec 1963 look drier than normal.
http://weather-warehouse.com/WeatherHistory/PastWeatherData_Oracle2Se_Oracle_AZ_January.html
If someone knows where the nearest rain gauges are to the site and have a look at the amount of water there was in the three years before 1963 and 2012.
Apply the Starbucks Hypothesis.
Start at 3500 feet and work your way -down- doing sampling.
Hmmm … looks like they reauthorized grazing on six allotments of government land in the Santa Catalina Mountains in 2008 … I hadn’t considered the effect of grazing. Wonder what’s changed in that regard since 1963?
w.
Gary says:
August 15, 2013 at 4:11 pm
True ‘dat … now consider what happens right after a fire. Fires generally run up-slope, often stopping (as in this case) at the ridge. Now consider the deer and rabbits and pigs. They are all driven in front of the fire, up over the top of the ridge and to safety on the other side.
Now, consider the pressure that would put on the plants, particularly those just on the other side of the ridge top, and everywhere the animals scattered to. Everybody coming through will eat on the existing plant stocks, and the overpressure won’t stop for a while. To be sure, overpopulations will diminish through natural causes, but the effects could last for years.
In addition, “natural causes” sometimes includes deer populations dropping through starvation. This is very bad for the trees, because in that situation they are known to resort to eating tree bark, often severely damaging or destroying the tree in the process.
w.
I don’t think that plants care about changes in the mean annual temperature or the mean annual rainfall. It’s not the mean conditions that will kill them off and change their range. It is the extreme events like getting frozen, fried, flooded or dried. Mean annual conditions are a poor proxy for extremes within the year.
Busca et al claim to have shown that warmer, drier weather has shifted upward the altitude range of Arizona plants.
However, even if there has been a shift why do the authors expect the causal factor to be an uncertain mean temperature increase when there is a far more certain factor in play- namely increased carbon dioxide partial pressure?
The only good quadrat is a dead quadrat!
(Sorry Willis, great post, but baiting rat traps tonight….)
Looks like they missed the forest because the trees were in the way..
Excellent post Willis!
Looks like they were to busy making sure it would meet the desired outcome to notice the cherry trees they were picking from…
So the plants move uphill. Whoop de do ! That would almost make you believe that there was plenty of uninhabited space, up the hill. Could be; I don’t know for sure, but I have been up quite a few hills, and there does seem to be more uninhabited space up there.
So if I was a plant, that wanted space to grow foliage to reach for the sunlight, and it was more crowded down the hill than up the hill, I would prefer to go up the hill, rather than down the hill; I hate crowds.
It is well known that diffusion processes are driven by concentration gradients (and other things).
So a seed that gets blown up the hill is more likely to fall on arable land, than a seed that blows down the hill, and simply lands on top of somebody who is already there.
Ergo, plants tend to diffuse to unoccupied spaces. Sort of like, how mankind diffused out of Africa, without ever being aware they were going to America, via one of the Istans, and Siberia. Why would it have anything to do with Temperature ? Food for the African Bushmen migrants, is the same thing as empty ground for plants
I don’t have the foggiest idea whether plants prefer 59.1 deg F over 58.9 deg F, but I do know for sure they prefer unoccupied spaces over occupied spaces..
And they don’t read the road signs, to see if they’ve been up this hill before, so one hill is as good as another hill.
The range of Javelina has expanded. Here just North of Phoenix I planted a pickly pear cactus in the wash behind my house and, in less than 3 days, it was done it! The narrow jaws of the Javelina let it eat cactus protected by fortress like spines.
Excellent work Willis.
Philip Bradley says:
Alongside a highway?
The highway itself could well be a significant factor, facilitating transport of seeds, diseases, competing plants, affecting browsing animals, insect pests, and creating a micro-climate alongside the road.
Not to mention the effects of all of Obama’s TOXIC CO2 coming out of tail-pipes. That must have a devastating effect on wildlife.
Hey, don’t call those Javelina pigs, they don’t like that.
I dislike studies like this because they use the empirical data that they have gathered to further their own agenda. They believe in AGW and skew legitimate data to that single minded point of view. The data that they have accumulated shows that plants are moving into areas that they were not present in during studies conducted 40-50 years ago. They then apply their own agenda as to why the plants have expanded to these new areas, while ignoring or dismissing all the other factors – to them it is obvious that climate change is responsible.
I counter with known conditions that can cause the same effect:
How do plants spread? Their seeds need to be spread to the areas which are amenable to their survival. Most plants have evolved to have their seeds spread using animal vectors – animals eat the seeds which are indigestible, and excrete them in their feces. Some seeds also stick to animals and are spread when they fall off the animals. Others spread by wind movement or gravity.
Roads – the studies were done along roads in the wilderness. Roads provide easy access to animals for movement from one area to another. Recently, I was watching a documentary on the Sleeping Giant, an island in Lake Superior off of Thunder Bay, Ontario. There is a large Provincial Park there which has several trails cut through the forest for Snowmobiles in the winter. Deer, Moose, Wolves, and many other animals use these trails as transit routes, facilitating the movement of plant seeds. In my area, free ranging cattle have provided the same movement of plants, with some areas having ‘invasive’ plant species which have been spread by cattle, replacing native plants as a direct result of free ranging.
Plants will propagate in any area where the conditions are right. Climate change can result in increased movement of plant ranges, but in a majority of these situations, it is not the result of AGW but rather the result of people altering the environment directly – building a road through a forest will directly alter the climatic conditions with warmer areas being closest to the roads similar to the Urban Heat Effect. The type of plants which grow there will be directly influenced by plants which are either introduced by humans or animals.
The temperature increase shown for this area is 1 deg C. The dry air lapse rate is 3 deg C per thousand feet. The change of temperature in the study area is 1 deg so the elevation change required to keep the same temperature is 333 ft.
Does the study have sufficient discrimination to tell if the range of any particular species has changed by moving up the hill by 333 ft?
Answer ‘yes’ and I have a once in a lifetime opportunity for you to buy a large bridge in London.
JF
Heh. What you just said: “Critical thinking is so unimportant that it can’t be minimized and ignored enough.”
What you were trying to say: “the importance of critical thinking cannot be overstated.”
I.e., it’s so significant, no emphasis is too great.
The same point mentioned by Latitude and Bill Thompson is bugging me. In what way is an average temperature determining the range?
What was the number of degrees-days different? Consider the article on the corn crop. It is all about total hours factored for sunlight and temperature. The average is basically irrelevant. It is quite possible the increase is elevation for a few species was a reduction in total temperature range with an increase in summertime nightly minima. Before you assert range changes due to climate change you have to first demonstrate that change took place. The average temperature on the valley floor is a poor metric of choice. The average wind speed or direction might be a better indicator.
Further, if you want to demonstrate the ‘chasing plants uphill’ idea you would concentrate on the lower, now ‘unliveable’ region where the plants can no longer subsist. Attracting plants uphill is very different from driving them up. I am not clear what this paper is showing.