Hemlocks Still Abundant Despite Adelgid Infestation

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edfrank
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Hemlocks Still Abundant Despite Adelgid Infestation

Post by edfrank » Tue Sep 27, 2011 3:48 pm

Hemlocks Still Abundant Despite Adelgid Infestation
September 26, 2011
Zoë Hoyle

http://www.srs.fs.usda.gov/news/485


Click on image to see its original size
Hemlock woolly adelgid infestation. (Photo by USDA Forest Service)

Asheville, NC -- A recent analysis of two decades of USDA Forest Service Forest Inventory and Analysis (FIA) data shows the live volume of hemlocks in the eastern United States still increasing despite spreading infestations of hemlock woolly adelgid. FIA scientists from the Forest Service Southern Research Station (SRS) and Northern Research Station (NRS) published the information as an SRS e-Science Update in early August.

The FIA researchers conducted the analysis for this update on 20 years of data collected across 433 counties that stretch from southern Maine into northern Georgia. “When we started this project we really expected to see large-scale losses of hemlock at the landscape scale,” says Sonja Oswalt, SRS forester and one of four co-authors. “We were surprised to find that, at the broad scale, hemlock loss is nowhere near as dire as expected.”

The researchers actually found an overall increase in live-tree hemlock basal area in both counties infested with hemlock woolly adelgid and those without infestations.

“Even though this is unexpectedly good news about hemlock survival on the larger landscape, we don’t want to downplay the localized effects that many people are aware of,” says Oswalt. “In eastern forests where hemlocks are often the keystone species they can support over 1,000 species birds, animals, and insects. The loss of hemlock stands in many of these areas is nothing less than devastating.”

Two native species of hemlock—eastern and Carolina—grow in the eastern United States. Though a minor component in most of the forests of the eastern United States, high densities of eastern hemlock are found in New England and the mountains of the Southeast and Mid-Atlantic. The Carolina hemlock, similar in appearance to the eastern hemlock, is found only on rocky mountain slopes in the Southern Appalachian region. Stands of hemlocks across the ranges of both species have been decimated by infestations of the hemlock woolly adelgid.

A tiny insect introduced into the United States from East Asia, the hemlock woolly adelgid feeds at the base of hemlock needles, defoliating and eventually killing trees. Since the insect was first noticed in the 1950s, it has expanded its range at between 4.7 and 12.7 miles a year and currently infests about 45 percent of the range of hemlocks in the United States and 41 percent of all hemlock trees.

“The analysis also showed that the general regional trend in the East over the past 50 years has been one of increasing hemlock volume, even with infestation by the hemlock woolly adelgid,” says Randall Morin, NRS FIA research forester and primary author of the update. “Even though the insect has caused substantial negative impacts on hemlock at local scales, analysis of FIA data suggests that infestations have not yet reduced the overall abundance of hemlock, even in states where hemlock woolly adelgid has been active for decades.”

The authors caution that the trend of increasing hemlock volume may not last much longer.

“Despite increasing hemlock volume over the last four decades across most of the eastern United States, the regions with long-established populations of hemlock woolly adelgid are also the regions where hemlock is accumulating slowest,” says Morin. “Net growth rates decrease as years of infestation increase and mortality rates increase, with mortality starting to equal net growth in areas where hemlock woolly adelgid has been present for 10 to 20 years.” As time goes on, the trend of increasing abundance may begin to reverse.

Access the Science Update: http://www.srs.fs.usda.gov/pubs/38492

.
"I love science and it pains me to think that so many are terrified of the subject or feel that choosing science means you cannot also choose compassion, or the arts, or be awe by nature. Science is not meant to cure us of mystery, but to reinvent and revigorate it." by Robert M. Sapolsky

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jamesrobertsmith
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Re: Hemlocks Still Abundant Despite Adelgid Infestation

Post by jamesrobertsmith » Tue Sep 27, 2011 5:24 pm

That's the biggest load of bullshit I've ever read. The hemlocks in virtually every area where I hike and camp are devastated. I can walk for miles and miles and see not one living hemlock tree in places where they used to dominate. Hemlock trees are not spreading...they're being wiped the hell out! This article is completely misleading. I don't know why the author or his sources can claim that the hemlock forests are not in a completely desperate situation. Send his ass into Cataloochee or even just a drive along the Cherohala Skyway. What a bunch of crap!

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AndrewJoslin
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Re: Hemlocks Still Abundant Despite Adelgid Infestation

Post by AndrewJoslin » Tue Sep 27, 2011 7:24 pm

Their data includes northeast states where extreme low temps in winter are suppressing adelgids, that's why they can say that areas that have had adelgids for decades are increasing hemlock volume. For example far eastern Massachusetts is on the verge of a total hemlock wipeout whereas in western Mass. some areas are adelgid free and other areas only have chronic low-level adelgid activity.
-AJ

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Re: Hemlocks Still Abundant Despite Adelgid Infestation

Post by TN_Tree_Man » Tue Sep 27, 2011 7:50 pm

Ed,

This is an interesting find, but as I give more consideration, perhaps it should not be too surprising after all. The adelgid is an exotic insect pest with limiting factors contrasting a soil-born pathogen (think chestnut blight).

I know that hemlock is a viable species in regards to regeneration. Seed germinates fairly easily. We (Tennessee side of the Great Smoky Mountains National Park), like most of the ENTS roll regions, have a lot of large, standing, dead hemlocks. I have noticed some seedlings popping up within some of the dying/dead stands though.

While most of the larger, older trees will be lost, hope for the species remains. Perhaps the species will be able to "wait out" the adelgid pandemic.


p.s. I'm afraid that the recently discovered Thousand Cankers Disease effecting Black walnuts will wreck more havoc in the end than the hemlock wooly adelgid.


Steve Springer
"One can always identify a dogwood tree by it's bark."

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dbhguru
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Re: Hemlocks Still Abundant Despite Adelgid Infestation

Post by dbhguru » Wed Sep 28, 2011 9:21 am

Ed, Robert, Andrew, Steve, et al,

All though I'm reluctant to express my opinion of the article in such crystal clear terms as you have Robert, I'm trying to correlate what I recently saw in the southern Appalachians this past July with the thrust of the article, and that dog don't hunt. I'm not much interested in the hemlock as a shrub. Maybe that is what is being described and foreseen as the future of the species. Seedy regeneration and then dieback repeated ad infinitum. Yuk!

Bob
Robert T. Leverett
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Co-founder and President
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Joe

Re: Hemlocks Still Abundant Despite Adelgid Infestation

Post by Joe » Thu Sep 29, 2011 5:02 am

FIA data is attrociously poor. The late Karl Davies studied how they come up with the data and it's not very good! Here in Mass., something like one acre in 5,000 is studied, yet state officials and others use the FIA data as if it came from God, offering up the data to countless decimal places as if it's real information.

One acre in 5,000! Any statisticians out there? Would you bet much of your money on such data! I fully understand it's expensive to get such data- to get accurate info would cost billions, but at least acknowledge that the data is not good, if the state guys pointed that out, I'd respect them a lot more for having real intelligence. I've seen no sign of adelgid in W. Mass. though others have- at least here, it's not taken hold, IMHO. As a forester, I don't get thrilled by hemlock because it's a low value species, economically speaking- but after attending a few of Llynn Rogers' field trips on black bears, I like them very much so I often don't mark for harvest some hemlock that I'd otherwise mark. Lynn (sp?) said that old, rough barked hemlock are great for bears because the momma bear knows that her cubs can climb them.
Joe

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mdavie
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Re: Hemlocks Still Abundant Despite Adelgid Infestation

Post by mdavie » Thu Sep 29, 2011 10:25 am

I saw that synopsis the other day; from what I can tell, it was looking at data over the last 20 years? All I can think is that there must be a great deal of recent data that was not really taken into account. To be honest, I don't know why that was reported in the manner it was without some huge caveats, and as it is, it is a bunch of nonsense.

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dbhguru
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Re: Hemlocks Still Abundant Despite Adelgid Infestation

Post by dbhguru » Fri Sep 30, 2011 7:35 am

Mike,

I think most Ents who get out in the field a lot and read this analysis of Tsuga are saying: What? I'm suspicious of the analysis on several levels, but I'll hold off commenting further until I see reports from others. Maybe I have missed something, but I don't see how.

Joe's analysis of the FIA data is spot on. It isn't very good. At least not here in Massachusetts. I've seen lots of the plots and I'd hate to have to draw many specific conclusions from the CFI plots.

Bob
Robert T. Leverett
Co-founder, Native Native Tree Society
Co-founder and President
Friends of Mohawk Trail State Forest
Co-founder, National Cadre

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James Parton
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Re: Hemlocks Still Abundant Despite Adelgid Infestation

Post by James Parton » Fri Sep 30, 2011 9:32 am

Hemlocks may be abundant, but at least here in NC they are infected and dead ones! Generally speaking, the only healthy ones are treated ones.
James E Parton
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New Order of Druids

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Joe

Re: Hemlocks Still Abundant Despite Adelgid Infestation

Post by Joe » Fri Sep 30, 2011 9:39 am

I just watched a National Geographic Video, "Six Degrees Could Change the World". It's rather frightening. Many critics say it's over done- a worse case scenario- but, we already have major environmental disturbances such as diseases infecting many tree species- yet, that's NOTHING compared to the drastic changes that are in store for us if global warming contines, according to this video.
Joe

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