Trees Tell the Story of 500 Years of NYC Drought History

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#1)  Trees Tell the Story of 500 Years of NYC Drought History

Postby edfrank » Mon May 07, 2012 9:58 pm

Trees Tell the Story of 500 Years of NYC Drought History
Posted on April 29, 2012

http://seaandskyny.com/2012/04/29/trees-tell-the-story-of-500-years-of-nyc-drought-history/

by Neil Pederson

I didn’t see this coming. Yes, winter 2011-2012 has been quite unusual and it is becoming more obvious that almost anything can happen with our weather these days (see October snowstorm followed by days in winter 2012 when my house windows were opened). But, a moderate to severe drought just seven months after many of us were wondering if the rainstorms were going to stop? With the insight that my co-authors and I had looking over the past 500 years of drought history for the Greater NYC region, I didn’t expect this.

Image

In a paper currently in revision with the Journal of Climate, we reconstructed drought history using tree rings back to the year 1531. We were wrapping up the manuscript in Summer 2011 when the march of the tropical storms was beginning. To talk about the drought reconstruction for a hike I was leading on Columbia’s Lamont-Doherty campus, I put together a record of the Palmer Drought Severity Index derived from meteorological measurements. When I first calculated annual and summer drought for the past 110 years, I thought I or the web source used to gather the data made a mistake because it looked odd, unnatural even. It looked like The Hockey Stick, but for moisture, not temperature.


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#2)  Re: Trees Tell the Story of 500 Years of NYC Drought History

Postby Joe » Tue May 08, 2012 8:04 am

I'm no expert on tree rings- but, I'd be careful about the significance of the data. Many things effect tree ring size other than moisture- and this is an issue much more so here in the east than out west- including competition, diseases, age of the trees, etc. No doubt these factors are well understood by the experts- but I'd suggest that such a project should have to measure a great  many trees to have confidence in the data. Maybe they did that, I didn't study that article.
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#3)  Re: Trees Tell the Story of 500 Years of NYC Drought History

Postby Neil » Sat May 12, 2012 4:32 am

Hi Joe,

We do consider as many of the potential factors of tree growth as possible when making climatic reconstructions from tree rings. In the blog post I mentioned that it took a long time to get this paper 'out' because I made three versions of the reconstruction until I was convinced that what I was seeing was not the result of some of these other factors. I reworked the data multiple times to test this idea, especially the idea that a change in competition in recent decades was causing what turns out to be an 'epic' pluvial - the extended, recent wet period. Tree age matters little when it comes to growth rates. Some of the oldest trees in this collection are growing faster than ever. Some of the younger trees might not be growing as fast as one might expect. You are correct, it is more complex in the east.

What wins us over in the end are the statistics. Once we reduce factors like competition and growth releases (the ecology) from the raw ring widths, we conduct multiple tests to ensure the trees are reflecting what is recorded in the instrumental data. In this case, the trees account for 66.2% of the annual change of May-Aug drought from 1895-1981 and pass several verification tests. That isn't too shabby for trees growing in humid environments like the eastern US. We only go to 1981 in this case because this is the common period for all of the trees used in this reconstruction. We tested subsets of the collection between 1981 and 2002. The trees account for 49.3% of the drought variance in 2001 and more than 51% between 1982 and 2000. We cannot go closer to the present with  this collection of tree rings - not enough tree-ring data were collected after 2001 to make a reconstruction.

Finally, this is a well-replicated network of tree rings. We use 32 distinct collections over the 1852-1981 common period. I do not have the final numbers in my head, but I estimate we have at least 450 trees, and likely closer to 500, for the 1852-1981 period. From 1982-2001 we had a minimum of 275 trees and likely have closer to 300-320 trees.

We feel pretty confident with the data and the results. Now, if we could get more trees prior to 1531, man what a cool record this would be!

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#4)  Re: Trees Tell the Story of 500 Years of NYC Drought History

Postby Chris » Sun May 13, 2012 12:30 am

Have there been any attempts to look at fire scars and correlate them to these especially drier times periods? Yes you have issues with Native American set fires and suppression by Europeans, but would some old Pitch Pines on some drier ridge perhaps have escaped most of that and reflect a more "nature" burn regime. How about proxys for rainfall [sedimentation]?
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#5)  Re: Trees Tell the Story of 500 Years of NYC Drought History

Postby Neil » Mon May 14, 2012 7:10 am

hi Chris,

Good question. The science of reconstructing fire history in the eastern US is just beginning in earnest. By just beginning I mean over the last 20 years. Much of the work has been conducted in coniferous forests of the east, though there are some nice exceptions in the midwest. Many records are rather short in the most eastern portion of the eastern US [only about 120-180 yrs], a period that is dominated by burning by European settlers [they burned as much, if not more than first nation people/Indians]. I do not know this part of the literature as well as others, but some good places to look are here:

Google publications in Scholar Google for Richard Guyette and Michael Stambaugh of the Missouri Tree Ring Lab [here is a good intro vid of Mike http://vimeo.com/14515784]. While they have made a massive collection across the eastern US, much of their earlier work is in the midwest - http://web.missouri.edu/~guyetter/pubs.html. Henri Grissino-Mayer of the University of Tennessee and Charles Lafon of Texas A&M are doing some nice work in the Southern Appalachians. Here are two recent publications: http://web.utk.edu/~grissino/downloads/Flatley%20et%20al.%20Landscape%20Ecology.pdf and http://web.utk.edu/~grissino/downloads/Aldrich%20et%20al.%20AVS.pdf. The Minnesota Tree Ring lab, Kurt Kipfmueller and Scott St. George, will start cranking out work from the Boundary Waters and points north: https://sites.google.com/a/umn.edu/umndendro/. A couple of nice papers have started to come out of the West Virginia Tree Ring lab led by Amy Hessl: http://www.geo.wvu.edu/~ahessl/publications.html. The three species paper is nice: http://www.nrs.fs.fed.us/pubs/40520. I am on a paper in preparation with Ryan McEwan looking at fire history since the late-1600s at Lilley Cornett Woods.

My favorite from the WVU group is a look at the causes of fire in the contemporary records collected by the state of West Virginia. From what I recall, it burns a bit more often and the fires are large when it is dry, despite the contemporary use of fire by locals: http://bellwether.metapress.com/content/n232602j6322j3m5/?p=a79f955e00384ea5a0a3f9f3887d284f&pi=2. So, extrapolating that record to long-term drought history would suggest it has burned more in the past due to a more favorable climate for fire (but, that is just speculation by me).

One of my favorite papers on fire in the east was conducted in Vermont red pine. They got a nice long record of fire: http://home.mtholyoke.edu/courses/jbubier/pdf/Mann94QR42.PDF. It shows a slowing of fire in recent decades, as does fire records from the northern range limit of red pine in Canada and thereabouts. These records come from areas where humans have less of an impact on fire. Click on the "Cited by" link for this paper: http://scholar.google.com/scholar?hl=en&q=fire+in+eastern+canada%2C+red+pine+northern+range+limit&btnG=&as_sdt=1%2C33&as_sdtp=. I've seen scattered papers showing wetting in the north. Given what we know about fire and trends in moisture in eastern North America, it might not be too surprising that fires have become less common.

I apologize if I left off other major pieces of contemporary work in the east. I imagine I did. Bud Heinselman did a nice piece in the early 1970s: http://www.frc.state.mn.us/documents/council/landscape/NE%20Landscape/NE_Update_2011/Reich_FirePatterns_NEMN_2012-02-15.pdf and http://www.sciencedirect.com/science/journal/00335894/3/3

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