Comments on: North American Upper Treeline #1

By: bender

bender — Fri, 06 Apr 2007 21:12:49 +0000

Re #5 Look carefully at the graphic, esp. considering perspective. The increase in RW wrt Temp plateaus at ~15°C for all snow levels above 200cm. It is for snow depth l.t. 200cm where there is an increase from 15°C to 10°C, and it is only a small increase. (Note: Between 400 and 600 cm the temperature response is zero. Below 400cm most of the positive response to Temp is from 20°C to 15°C.)

A July temp of 10°-15° sounds cool, and it is. But the growing seasons there are relatively long, compared to more continental locations.

Also note: this response function is based on only 40 years of data, 1954-94. That’s not alot.

But I’m happy to report that the 2001 CJFR paper (http://www.geog.uvic.ca/dept/uvtrl/hemlock.pdf) uses bootstrap response-function significance-testing (Guiot 1991).

By: Steve Sadlov

Steve Sadlov — Fri, 06 Apr 2007 19:26:25 +0000

Looks like there may also be some sort of delayed-by-1 year signal from the 1813 – 1815 cold event (or the event hit a year later on the West Coast than it did in the Eastern US). That one was a reponse to a volcanic explosion, IIRC.

By: Steve Sadlov

Steve Sadlov — Fri, 06 Apr 2007 19:23:39 +0000

RE: #10 – Pretty interesting sequence of events of some sort, affecting Cascadian and more coastal sites, between 1830 and 1850.

By: Steve McIntyre

Steve McIntyre — Fri, 06 Apr 2007 19:13:41 +0000

Here is the graph on the 10 chronologies from the article that bender referenced. I'm inclined to say that it doesn't show a strong HS pattern.

By: bender

bender — Fri, 06 Apr 2007 18:45:03 +0000

That 1998 “paper” with the response surface was not peer reviewed (note: data points not plotted & surface fit statistics not reported). This one was, however: http://www.geog.uvic.ca/dept/uvtrl/hemlock.pdf
This paper reports on 10 locations, not just one. And there, the authors point out that warm, dry years are years when cone production goes up, thus limiting how much photosynthate gets allocated to radial growth. So don’t be too quick to judge the degree of nonlinearity in the response function.

jae: like a young grad student, you leap to conclusions too quickly. You’re impossible to police! Try to read more.

By: Steve Sadlov

Steve Sadlov — Fri, 06 Apr 2007 17:56:56 +0000

Personally, I’d imagine trees on Vancouver Island probably can be in growth mode clear down to freezing. Also, a year in which the mean temp hovers around or below 10 C, at that location, may correspond to a year where the snow pack survives longer into the summer. While certainly Vancouver Island does not have an outright summer dry season as do areas from Central Oregon south, there is a summer precipitation minimum there.

By: Paul Zrimsek

Paul Zrimsek — Fri, 06 Apr 2007 17:32:36 +0000

Thanks, Steve. I should be clear that I’m not suggesting there’s anything questionable about it; it’s interesting, that’s all.

By: Steve Sadlov

Steve Sadlov — Fri, 06 Apr 2007 17:24:41 +0000

RE: #5 – Certainly, the latitudinal tree line roughly follows the 10 C mean annual isotherm. (Or is it 5 C? – a bit rusty of the top of my head). In any case, that isotherm is determined by a number of factors, which also, in and of themselves, affect growth. Two I can think of straight away are sun light / sun angle and north winds. It could be that the latitudinal tree line may be more a reflection of those factors than it is a reflection of mean temperature per se.

By: Paul Zrimsek

Paul Zrimsek — Fri, 06 Apr 2007 16:51:49 +0000

As one who’s studied general climatology but not dendro I find it fascinating that ring widths are still trending upward with decreasing July temperature as the latter reaches 10C. I’m used to thinking of that as the (approximate) temperature below which trees won’t grow at all.

By: jae

jae — Thu, 05 Apr 2007 22:20:57 +0000

Followup to 1: One would think that one of the a-priori site selection criteria would be to pick a site that did not have such high summer temperatures!