I'm a professor at U Michigan and lead a course on climate change problem solving. These articles often come from and contribute to the course.
By: Dr. Ricky Rood , 03:33 AM GMT on Travanj 11, 2012
A Hot Day’s Night: The Beetles -
The semester is almost over here in Michigan, and I am looking forward to more regularity in writing these blogs. Sorry for the recent infrequency, and the occasional excursions into the arcane. I am looking for well posed, interesting, new questions to focus on, and you know how to find me if you have a good idea. In this entry I want to build of the recent heat and the early spring.
The thread I made through the last blog ended up with Plant Hardiness Zones, which are those maps that gardeners and farmers use to decide when to plant seeds. Over the last 20 – 30 years the warming of the planet has caused the northern migration of these zones. The Washington Post has an excellent graphic that shows the changes between 1990 and 2012. Since I am not so facile, I have taken from this graphic the two extremes, 1990 and 2012.
Figure 1: 1990 U.S. Plant Hardiness Zones. (From Washington Post)
Figure 2: 2012 U.S. Plant Hardiness Zones. (From Washington Post)
What I want to look at here are the very coldest temperatures, the purples. If you look at Zone 2b, the zone below -40 degrees F, it essentially disappears between 1990 and 2012. Zone 3a, which is between -35 degrees F and – 40 degrees F becomes much smaller.
So this past winter, and especially March 2012, was extraordinarily warm in the 48 contiguous states. In fact, I, who fly too much, had one of the easiest winters of travel. Based on Jeff Master’s blogs, I chose several times to go through Chicago, and for the most part I have landed with splendid views of a blue Lake Michigan. There was an interesting piece on Talk of the Nation, noting the relation between a warm winter and the lack of flu. So what is the problem? It’s not below -40 degrees anymore. Air travel is easier. We might have less flu. Does anyone besides me, planting potatoes on a dry 80 degree day in March, worry about this?
I have been spending a lot of time with beetle-killed wood this year. You might recall a couple of blogs back in 2009 where I talked about the pine beetles which are killing millions of acres of pine trees in the western U.S. and Canada. (Climate Change and the Forest, Climate and the Beetle) It is beautiful wood, often with a light blue tint. I am using it to restore a couple of 100 year old out buildings. There is a LOT of it; in fact, more than one can imagine managing. There is some lumber being made, some fire wood being made, but for the most part there are millions of acres of dead trees. I have talked to a couple of people who wonder why there is not more outrage about these massive forest kills. That’s fodder for the comments.
Back up to the maps. The pine beetle responsible for killing the pines in the Rockies is itself killed, controlled, by temperatures less the -40 degrees F. This is at the edge of the coldest temperatures normally seen in the U.S., and these cold extremes have largely disappeared since 1990. In the map below, I have used the interactive version of the map from the US Department of Agriculture to extract the State of Colorado. There are only very small areas of Zone 3a remaining.
Figure 3: Plant hardiness zones in Colorado for 2012. From US Department of Agriculture.
We adapt to climate change – or we will. Now, one of the most effective adapters seems to be the Mountain Pine Beetle. In The American Naturalist there is a pre-publication posting of an article on the Unprecedented Summer Generation of the Mountain Pine Beetle. That is, rather than there being one generation of Mountain Pine Beetle during the year, in Colorado, in recent years there have been two broods. The paper is by Mitton and Ferrenberg. There is a press release of the paper here.
They noted in 2008 pine beetles flying and attacking pines more than a month earlier than the historic norm. They set up experiments to test three hypotheses: 1) That temperature had not changed; 2) That the length and timing of the flight season had not changed; and 3) the life cycle of the beetle had not changed. Their results found that there had been significant warming, with spring coming earlier. They found that the behavior of the pine beetle was explained by earlier emergence of the beetles, followed by a second brood of the beetles in the summer. Figure 4 shows this schematically. It is striking to see the move to earlier springs in the figure – as with the hardiness zones.
Figure 4: The historical mountain pine beetle (MPB) univoltine life cycle (above calendar arrows and linked by black arrows) and the observed MPB bivoltine life cycle (below calendar arrows and linked by red arrows). Univoltine means one brood per year, and bivoltine means two broods per year. Calendar arrow colors represent monthly temperature regimes: blue for <0°C, yellow for 0°–4.99°C, orange for 5°–9.99°C, and red for 10°C and higher. From Mitton and Ferrenberg, Mountain Pine Beetle Develops an Unprecedented Summer Generation in Response to Climate Warming.
This research took place in an area that in the 1970s was judged to be “climatically unsuitable for Mountain Pine Beetle development … .” The study is convincing that the devastation of the forest due to the pine beetle is directly related to the warming planet. It points out the vulnerability of the tree populations, as the trees that are being impacted now have not developed a historical resistance to the pine beetle. Since most of the beetles that are born live, this impact is not incremental, as that second generation is enormous.
So, yes, this warm winter has had its advantages - less fuel oil was needed. But in the western forest we are seeing this case study of wide ranging ecological disruption. The consequences of the disruption will unfold in the next decades. Questions of fire and soil erosion will emerge. The impact on tourism will be realized - and, of course, water quality and the change in the ecosystems of the western forests. The Mountain Pine Beetle is adapting rapidly to global warming, what are our strategies to adapt to the Pine Beetle?
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