Hemlock regeneration

[Lee Frelich]

ENTS:

My recent trip to the Porcupine Mountains yielded some good pictures that show how the regeneration niche of hemlock works.

First, notice that in areas with high winter deer density, all hemlock seedlings are eaten, and there are no young hemlocks to replace old ones that die, as shown in this photo of a 500 year hemlock that fell several weeks ago (same tree as in the earlier post a week ago, but from a different perspective), notice that several saplings near the base of the old hemlock are maples (photo by George Schlaghamersky).

               

                       

                                       

               

This picture of a severely browsed hemlock seedling, which still has some live foliage, was taken during May 2011. A picture of the same seedling appeared in a paper I published in 1985, Current and predicted long-term effects of deer browsing in hemlock forests in Michigan USA, Biological Conservation  34: 99-120. Unfortunately, the pdf of these older papers are very low quality, so I can't show you the 1985 picture--but I believe the live part is actually a few inches shorter now than it was in 1985--a slowly shrinking bonsai created by deer. The live part is the light green foliage in the center of the photo (photo by George S.).

               

                       

                                       

               

Next, is a picture of a hemlock tree that died in 1981, and I took a slab from it in 1982, when the log was still solid, and it had 513 rings, about 15 feet above the ground. We estimated that the tree was around 540 years old(moss-covered log on the ground, photo by George S.). The trees in the gap that formed in 1981 in the background of the picture are now pole-sized trees, but they are all maple, which shows that the deer have been preventing hemlock from replacing itself at least that long--in fact we know from this type of reconstruction that hemlock has not replaced itself since the 1940s when Aldo Leopold wrote an article about the irruption of deer populations in the area.  

               

                       

                                       

               

However, a visit to nearby areas without deer in the winter, shows that even without deer, hemlock seedlings still only survive in a certain small subset of the forest floor. Germinating hemlock seedlings cannot grow on thick duff or compete with large herbs, so they occur on rocky terrain, tip up mounds and rotting wood.

Hemlock saplings growing on talus at base of cliff (photo by George S.).

               

                       

                                       

               

Hemlock seedlings growing on mineral soil of a tip up mound (photo by George S.)

               

                       

                                       

               

Hemlock seedling growing on rotted conifer log (they rarely appear on rotted hardwood logs, photo by Kristi Teppo).

               

                       

                                       

               

Lee

[jamesrobertsmith]

I'm always amazed at how humans are so adept at killing virtually everything that moves and that grows. But when it comes to a small subset of animals the excuse is always "we can't control them". I know this to be total bullshit. Man can exterminate or control anything he damned well pleases to destroy or control. I would think something as easily killed and decimated as white-tail deer would not be a problem. Same with feral hogs. It's not a matter of "can" but a matter of cash.

[KoutaR]

Lee,

Great to read your reports on this outstanding park. I visited it in 2004 and share the opinions with your Estonian friends: of European parks, only Białowieża can perhaps be comparable, but it has limited access for guided groups only.

You wrote hemlock seedlings cannot grow on thick duff or compete with large herbs. Do sugar maple seedlings tolerate better those conditions? What does exclude deer from the areas in your last photos?

Kouta

[Lee Frelich]

Kouta:

Sugar maple seedlings have the opposite niche as hemlock seedlings--they are much more likely to survive on thick duff. This is because the seed is larger and has enough energy to grow a more vigorous root that can penetrate the duff. They can compete somewhat better with herbs because they get larger in the first year than hemlock or other conifer seedlings.  

Furthermore, (although we know relatively about this), there are apparently mycorrhizas that form relationships with sugar maple that are very abundant in the older leaf litter at the base of the duff. Also, duff formed by hardwood leaves has a relatively high pH and N and P supply, while tip up mounds, rotted and conifer logs are low in nitrogen, creating even more differentiation in survival between maple and hemlock seedlings, since maple requires higher pH and nutrients than hemlock. Also, hardwood leaves can land on top of hemlock seedlings in the fall, and then they are crushed by the snow on top of the leaves. It is important to note, however, hemlock seedlings are not successful in either maple or hemlock duff--they just don't get through to the mineral soil quickly enough and a few days without rain kills them if the leaf litter dries out.

And, of course, the earthworm invasion is changing all of these 'neighborhood effects' that have maintained separate maple and hemlock stands for the last 3,000 years. Fortunately, the park still a large area free of earthworms.

Deer are excluded from a large portion of the Porcupine Mountains, and actually a large surrounding landscape, by deep snow. Last winter, for example, a nearby weather station had 25 feet (7.6 m) of snowfall. This is mostly lake effect snow, when arctic air masses cross Lake Superior, they pick up moisture, which then condenses and precipitates out as snow when the air cools when it reaches land. However, the first mile or so along the lake shore, gets little snow, since the air masses get some distance inland before the snow reaches the ground. There is usually a wall of snow 2-3 m deep a certain distance from the lake. Deer migrate out of the deep snow area and go to the lakeshore during winter, and therefore we have a naturally occurring winter deer exclosure, with contrasting areas of high and low deer browsing during winter. During summer, deer do return to these areas, but at that time they usually eat herbs, and relatively little woody material.

Lee

[KoutaR]

Lee,

Thanks for your thoroughgoing answer!

Kouta

[Joe]

sugar maple requires rich soils

in Berkshire County of western Mass. where limestone is a major bedrock, and with higher hills than surrounding areas, with higher soil mositure, sugar maple is abundant

but once I moved to north central Mass., where the bedrock is mostly granite and the soils mostly gravel, sugar maple is much less common, regardless of how much duff there is....

I've noticed many forests where hemlock doesn't seem to regenerate itself- I think part of the problem may be deer, but part of the problem may simply be that it's not a great hemlock site, in the sense that other species are more competetive on that site--- the fact that hemlock at some point in time is abundant on that site may be due to various reason- perhaps the stand was high graded and they left the hemlock, or when the site was allowed to grow back to forest, for some reason it was an excellent year for hemlock seed so that species grabbed the site

I'm just speculating here, each site is different as to what's going on---
Joe

[Lee Frelich]

Joe,
Another phenomenon with hemlock regeneration is related to stage of stand development.  Even-aged hemlock stands (stem exclusion stage of development) are so dark at the forest floor, that some of them have no seedlings of any sort, not even hemlock. Some of them have only about 1% of full sunlight at the forest floor. Then, when stands undergo transition to uneven-aged stage of development, at say 130 or 150 years, gaps form and suddenly regeneration appears if the deer allow it. With numerous gaps throughout the stand, light levels go up to 2-5%, even in areas not directly under gaps, and then the understory becomes quite different.

Lee

[Joe]

Joe,
Another phenomenon with hemlock regeneration is related to stage of stand development.  Even-aged hemlock stands (stem exclusion stage of development) are so dark at the forest floor, that some of them have no seedlings of any sort, not even hemlock. Some of them have only about 1% of full sunlight at the forest floor. Then, when stands undergo transition to uneven-aged stage of development, at say 130 or 150 years, gaps form and suddenly regeneration appears if the deer allow it. With numerous gaps throughout the stand, light levels go up to 2-5%, even in areas not directly under gaps, and then the understory becomes quite different.

Lee

I guess I never see such natural development of old hemlock stands but I do come across many that have been "managed" or "mismanaged". It's always a challenge to try to figue out what happened- what the stand was like before that harvesting, what they did, try to determine why the stand progressed the way it did from that entry, try to determine how it will develop now, and how I can eventually change it for management purposes.

I understand that  most of ENTS people don't think of the management side of forests, often thinking of it in a negative way- but trying to think about it in a constructive way is quite fascinating, as if the forest is my canvas and I'm an artist, while also thinking about the economics and aesthetics.
Joe

[edfrank]

Lee, ENTS,

I took a series of photos showing some hemlock regeneration at Cook Forest SP during the last ENTS Rendezvous there in October 2009.  This seemed a good place to post some of that series.

               

                       

                       

Several small hemlock trees growing on a turn-up mound along the Seneca Trail

               

               

               

                       

                       

Hemlocks growing among some log segments along the Mohawk Trail inside of the loop of the Fire Tower road.  Likely the presence of the large logs limit the deer browse.  White pines are also sprouting.

               

               

               

                       

                       

Overview of the surroundings of a fallen log inside of the loop of the Fire Tower road.

               

               

               

                       

                       

Panorama of the fallen log inside of the loop of the Fire Tower road shown above.  White pine and birch trees are also sprouting on the surface of the fallen log.  Click on the image to see a larger version.

               

               

               

                       

                       

Detail of a section of the fallen log inside of the loop of the Fire Tower road.

               

               

               

                       

                       

Detail of an another section of the fallen log inside of the loop of the Fire Tower road.

               

               

               

                       

                       

A different fallen log with some hemlock growth.

               

               

.

[dbhguru]

Lee, Ed, et al,

 Did you all notice the hemlock regeneration in the images of Hull Woods. The mix of mountain laurel and young hemlocks creates a shrub layer that is most compelling when combined with the large, limbless trunks of the big pines and hemlocks.

Bob