Comments on: Almagre: the Graybill Photos

By: Jonde

Jonde — Sat, 20 Oct 2007 12:20:11 +0000

40 Geoff:

I say you are right and if I should make a bet I would bet precipitation. It is just funny that Mann reconstruct air temperatures that do not have any influence on radial growth (annual means). If Mann insist to use BCPs to reconstruct any temperatures it should be early summer, not any 12 month means.

By: jae

jae — Sat, 20 Oct 2007 02:40:07 +0000

Mr. Pete:

As I recall, tree #30 has a very slight lean overall. Not enough that we recorded it. Wed have to go back up and stare at these trees a bit to record a better set of lean/reaction wood data

Slight leans make no significant difference. Reaction wood is only significant at fairly extreme leans, like maybe 20 degrees. I would not worry much about leans less than that.

By: Geoff Sherrington

Geoff Sherrington — Sat, 20 Oct 2007 01:10:05 +0000

Re 39 Jonde

You might be right. But remember, a tree cannot grow in the absence of water. Water is needed to take nutrients from earth to roots. So there is some water and there is some water variability (plausibly) over time. Which is more important, spring air temperatures or water supply variablilty, I have no idea, but I would not place all bets on just one horse. And of course, there could be a correlation between spring air temperatures and water supply, just to confuse the experiment – an experiment dealing with CO2 effects on hypothesised global warming.

By: Jonde

Jonde — Fri, 19 Oct 2007 01:21:56 +0000

Steve you are right and, in fact, this was my point. Most of the radial growth will take place during the first month of the summer and is dependant on winter precipitation (snow). Positive response of ring width to winter precipitation is clearly seen in Siberian larch forests. I dare to say that the same rule apply to BCP.

I was just hypothesising that if someone use BRCs to reconstruct past air temperatures, those reconstructed temperatures are most probably defined by spring air temperatures.

By: Steve Sadlov

Steve Sadlov — Thu, 18 Oct 2007 17:13:24 +0000

I would add that for White Mountain BCPs, the only liquid precip even experienced at the sites is due to very infrequent and unreliable local convective or imported monsoon showers. Most of these occur, when they occur, at the very end of the growing season, the peak being Aug and Sept. Very rarely, these will start earlier, say, in July or June. Even more rarely is a freak occurence of a late May monsoon, but that is so rare it is not worth discussing. Bottom line is, for all intents and purposes, White Mtn BCPs depend on snow pack for moisture.

By: Steve Sadlov

Steve Sadlov — Thu, 18 Oct 2007 17:08:05 +0000

I disagree with #36. I doubt that at an elevation above 10K feet in such an inland part of California (e.g. Continental Climate), that even a 2 deg C higher than normal “average” temperature for a given spring is going to make any difference with when the snow pack is gone or the soil thaws. The controlling factor will be both the amount of winter (frozen) precip and how late it fell in the season. Ironically, these same factors will also control available moisture in July and August. A big, late snow pack means good moisture during July and August. (The “normal” begining of climatic Spring in that location is essentially late June.) The winter of 2006 – 2007 is a classic case of the worst case scenario in terms of moisture. Total precip was low, and, the normal big dumps of Feb and March did not happen. There was a slight recovery in April, but not enough to result in a decent snow pack. The meagre snowpack was gone by early June, and with the soil mositure already low due to the overall lack of precip (plus lots of wind) it was bone dry by the end of June.

By: Jonde

Jonde — Thu, 18 Oct 2007 02:43:52 +0000

In fact there are “threshold temperatures” for different plants. I think this was mentioned previously. If the temperatures are between the lower and upper limits, the growth is not affected by the temperature, at least not in any significant way. Because of this, 1-2C differences in annual temperature are not easily visible in tree rings unless the changing temperatures are strongly influencing the periods of growing season when the temperatures are in the upper or lower thresholds. Even then I would say that only change in temperatures that can be seen in bristlecone ring widths is the change in spring temperatures (earlier snow melt date – earlier melting of soil and higher soil temperatures – earlier start of root activity, thus roots can absorb more soil moisture during the early wood cell development at early summer if there is water what to absorb).

By: SteveSadlov

SteveSadlov — Thu, 18 Oct 2007 02:33:00 +0000

RE: #26 – Lassen certainly gets more direct weather from the Pacific than the Whites. Also, during times like right now, with the rain line moving between 36 and 38 N, Lassen is getting much more rain, in general, than we are down here in the upper 30s N. Lassen also experiences a type of cold damp, which you see when the snow level is down around 2K at that latitude, which you would never get in the Whites. Finally, big difference in exposure to monsoonal moisture – the Whites are more prone to it (but given that its really May and June early monsoons that would matter, Lassen is far enough north as to expect standard Pacific storm rain that late in the season … 6 of one, half dozen of the other). Soils and bedrock obviously completely different.

By: Geoff Sherrington

Geoff Sherrington — Thu, 18 Oct 2007 01:42:56 +0000

Just read the Abebnah Ph.D. posts. Simple fact explained again by her. If you have drought, trees don’t grow fast. If you have lots of water, trees grow faster. That’s why we water gardens. As to how this correlates with temperature, or even dominates it…..
Geoff.

By: MrPete

MrPete — Thu, 18 Oct 2007 01:31:29 +0000

By the way, re reaction wood on tree #30 / 84-55… the “matched” photo above is not particularly helpful for understanding the angle of the tree. That photo was rotated a bit to match the Graybill version, and seriously cropped as well.

In general, I don’t know that these photos can be relied on to understand absolute lean. The terrain was often quite rough, and the camera did not have a built-in level …

You can see whether a trunk contains bends or twists of course. Below you’ll find the whole photo. (As usual, click to see in the gallery…)

As I recall, tree #30 has a very slight lean overall. Not enough that we recorded it. We’d have to go back up and stare at these trees a bit to record a better set of lean/reaction wood data.