Plain Grove Fen, Lawrence County, PA

June 09, 2009.  Carl Harting and I (Ed Frank) visited three sites in western Pennsylvania on Tuesday.  These were Wolf Creek Narrows Natural Area, Hogg Woods, and Plain Grove Fen.  I will post each portion of the trip separately   to better organize the information.

The third site we visited on this day was one called Plain Grove Fen.  It was certainly the most spectacular site and the one where we spent the most time.  The location was one told to Carl by a local forester.  On a previous trip Carl told me he had found a number of large oaks, so I was psyched for the excursion.  This site is located just a few miles west of the others in adjacent Lawrence County.  I consists of a hilltop and hillside forest growing above a wetland area. 

After returning home I looked up the Lawrence County Natural Heritage Inventory document prepared by the Western Pennsylvania Conservancy.  http://www.naturalheritage.state.pa.us/CNAI_PDFs/Lawrence%20County%20NAI%202002.pdf This document (31 MB)  contained a brief description of the wetland: 

Plain Grove Wetlands BDA

Plain Grove wetland rates as one of the most significant wetlands in Lawrence County

both in terms of its rarity and overall quality. The wetland area hosts a complex of

seepages and fens with fourteen plant species of special concern, including a globally rare plant species….Surrounding uplands feature young forests with canopy species typically including white oak (Quercus alba) and red oak (Quercus rubra) with young black cherry (Prunus serotina), hawthorn (Crataegus spp.) and an understory of American hornbeam (Carpinuscaroliniana) and dogwood (Cornus florida). Other low abundance species present are red maple (Acer rubrum), black gum (Nyssa sylvatica) and green ash (Fraxinus pensylvanica). 

 

 

This was not exactly what we found.  Instead of a young forest with smaller trees, the site contains a large number of large oaks and sugar maples of some age. 

The area we visited is located in the upper portion of this aerial photo of the overall site.  We parked near the outlet of the mine haul road and headed into the woods from along the road a few hundred yards west of where we parked.  Immediately we encountered a large tree.  It was a white oak snag still standing 81 feet tall with a girth of 13 feet, just below the roadway.  It was one of several large white oaks and a black oak we measured in that immediate area.  The rest or these trees seemed to be in good health. A short distance farther down the slope we encountered another semi-snag. This time it was a sugar maple with a pom-pom of leaves still growing on its uppermost limb.  The tree was 10 feet in girth, and 85 feet tall.   There were swampy areas near the base of the slope filled with black mud and skunk cabbage.  We worked our way through stepping on downed branches and dryer areas until we reached the stream at the bottom of the hill.

Shagbark Hickory, 7.9 feet girth, 87 feet tall.  There is a colony of bees living in a knot hole about 15 feet up this tree. – photo by Edward Frank

Carl Harting measuring a large oak – photo by Edward Frank

This was a shallow free flowing stream perhaps 20 feet wide with a cobble bottom.  It  flows to the south into a larger stream and its adjacent wetland.  There was a modest sized American beech growing along the stream banks and leaning over the stream itself.  I straddled it to measure a girth, and Carl waded into the stream to get a height.  He said it was the first time he had ever measured a tree while standing in a stream. 

 

Looking up large sugar maple at top of stream bank – photo by Edward Frank

On the far side of the stream on the edge of the stream bank was the first of many large sugar maples we encountered.  This was a magnificent specimen standing 92 feet tall with a girth of 10.8 feet.  The trunk of the tree showed a high degree of balding and had numerous bumps.    From this tree we could see many more large trees extending up the slope and to both the left and right.  Carl said the forest did not extend very much farther to the right (west) so we headed that way.  We kept encountering large sugar maples as we kept working westward.  I measured a modest sized black cherry here, the largest we had encountered, yet as a precaution in case those in the rest of the site we smaller.  Little did I know that I did not need that precaution.  Eventually we reached the end of most of the big trees and headed farther upslope and back to the east.  Up at the top I could see a large tree with a different kind of bark pattern.  Once we reached the tree it could be seen that is was a large double trunk elm.  Neither Carl not I am sure what species.  It was located at the edge of the open patch filed that can be seen in the west central portion of the aerial photo of the site.  One trunk was 9.2 feet in girth, the other was 7.1 feet in girth.  The best height we could get was 81.5 feet.

Continuing generally southeastward we continued to encounter good sized trees.  We found some larger black cherry trees, more sugar maples, a triumvirate of bigtooth aspen, and even a stray spruce tree that had escaped into the wood.  One tree that piqued my curiosity was a sugar maple with pronounced ribs extending along the length of the trunk.  I am not sure why this feature develops.  It is as if the surface root bases extend up the side of the tree.

Sugar Maple with ribs – photo by Edward Frank

This maple was growing at the edge of a small opening formed by a fallen tree.  Below this area at the flood plain level was a cluster of smaller trees.  It was an easily recognizable patch of hawthorn tree.  We hadn’t measured any yet, so we headed down to look at the patch.  Growing among the hawthorns were several overgrown apple trees.  I often see this association between the two species.  I am not sure if it just a coincidence because hawthorns frequently colonize old fields or if there is something more that promotes this association. 

From here we headed back up the hill and farther into the site looking for the large oaks Carl remembered from the previous trip.  One strange aspect of the forest here were the species in the understory.  There were cherries, some beech sugar maples, a few oaks, hickory, and cucumber tree.  Of these trees hickory of any kind was very uncommon in the canopy compared to the  numbers that were shrub sized.  Even though I was watching for it, and Carl was also, I could not find any cucumbertrees in the canopy.  They have a very distinctive look and should jump out at you if you are looking for them.  We did find more oaks and some respectable shagbark hickories farther into the site.   We eventually came to an area where the large tress were absent and headed back.  The lower slope of the valley wall was brushy in this area father downstream so we walked along the valley rim exploring this new section. 

 

Black Cherry, 10.1 feet girth, 102 feet tall - photo by Edward Frank

One of the best finds here was a large black cherry, 10.1 feet in girth and 102 feet tall.  At last one to match the oak and sugar maple we had found.  We measured a couple more large oaks in the region, off in the distance I could see a tree with large leaves.  Was this a big cucumbertree as I had been searching for?  As we approached, it turned out that this was a double trunked basswood.   The larger of the two twin trunks was 6.2 feet in girth; the other was 5.9 feet in girth.  The tree was 83 feet tall.  This is not as great of a height as an earlier basswood measured, but it was overall a much bigger tree.

Soon we were back in an area we had previously explored, we headed down slope and decided to cross the stream farther downstream near the hawthorn patch.  This was a chance to see a slightly different area of the woods.  Along the stream bank was a lone black willow.  It was not a species we had encountered anywhere else.  I was measuring its height from across the stream, when I heard a splashing.  Carl was wading across the shallow stream to measure a girth.  Well we had to cross the stream there anyway.   From here it was a short distance across the valley floor and up the other side to reach the road where we had started.  It turned out the beech we measured when first crossing the stream was the largest we encountered on the trip.  The safety black cherry I measured turned out not to be needed.  Walking along the road back to the vehicles there were a couple of cucumbertrees on the north side of the highway and some shingle oaks.  The latter were not found in the area we explored.

Plain Grove Fen
Species	CBH (ft)	Height
White Oak	12.5	81	dead snag
Shagbark Hickory	7.9	87
Black Oak	9.9	75
White Oak	12	90.5
White Oak	11.7	95.5
Sugar Maple	7.3	50
Sugar Maple	10	85	snag- almost dead
Hophornbeam	1.6	50
Bitternut Hickory	6.1	87
Black Oak	9.5	90
Hornbeam	1.4	35
American Beech	5.8	61.9	along stream
Sugar Maple	10.8	92
Basswood	4.1	83.5
Sugar Maple	10.6	84
Sugar Maple	8.4	97
Black Cherry	4.7	81
Sugar Maple	9.1	92
Red Oak	7	98
Elm	9.2	81.5	double second girth 7.1 ft.
Black Cherry	5.9	100
Red Oak	8.9	105
Red Oak	8.6	102
Black Cherry	8.3	101
Black Cherry	8.4	109.5
Sugar Maple	8.4	105
Red Maple	6.9	96
Apple	4.5	40
Hawthorn (sp)	2.5	25
Black Cherry	8.6	97
Aspen, Bigtooth	3.2	90
Aspen, Bigtooth	2.7	88
Aspen, Bigtooth	3.4	90
Sugar Maple	9.8	80.5
Black Oak	9.8	104
Red Oak	10.8	114
White Oak	8	114.5
Red Oak	9.9	110.5
Shagbark Hickory	5.7	105
White Oak	6.2	101
Red Oak	10.5	113
White Oak	8	114
Shagbark Hickory	6.3	98
Basswood	3.8	90.5
White Oak	6.3	96
Black Cherry	10.1	102
Black Oak	11.9	102
Red Oak	11.4	110
Shagbark Hickory	6.6	108
Red Oak	13	108.5
Basswood	6.2	83	double second girth 5.9 ft.
Black Cherry	9.9	102
Red Maple	7.3	92
Black Willow	4.1	44.6	along stream

 

Looking at the data we measured 17 different species of tree.  We measured 12 trees over 10 feet in girth, representing five different species, with several more trees and species just short of the 10 foot barrier.

Plain Grove Fen
Species	CBH (ft)	Height
Red Oak	13	108.5
White Oak	12.5	81	dead snag
White Oak	12	90.5
Black Oak	11.9	102
White Oak	11.7	95.5
Red Oak	11.4	110
Sugar Maple	10.8	92
Red Oak	10.8	114
Sugar Maple	10.6	84
Red Oak	10.5	113
Black Cherry	10.1	102
Sugar Maple	10	85	snag- almost dead

 

The Rucker Height Index for the site was not that high at 101.85.  Given the large numbers of fat trees I also calculated a Rucker Girth Index of 9.5

Plain Grove Fen
Species	CBH (ft)	Height
White Oak	8	114.5
Red Oak	10.8	114
Black Cherry	8.4	109.5
Shagbark Hickory	6.6	108
Sugar Maple	8.4	105
Black Oak	9.8	104
Red Maple	6.9	96
Basswood	3.8	90.5
Aspen, Bigtooth	3.4	90
Bitternut Hickory	6.1	87
Rucker Height Index		101.85
Elm	9.2	81.5	double second girth 7.1 ft.
American Beech	5.8	61.9	along stream
Hophornbeam	1.6	50
Black Willow	4.1	44.6	along stream
Apple	4.5	40
Hornbeam	1.4	35
Hawthorn (sp)	2.5	25
Plain Grove Fen
Species	CBH (ft)	Height
Red Oak	13	108.5
White Oak	12.5	81	dead snag
Black Oak	11.9	102
Sugar Maple	10.8	92
Black Cherry	10.1	102
Elm	9.2	81.5	double second girth 7.1 ft.
Shagbark Hickory	7.9	87
Red Maple	7.3	92
Basswood	6.2	83	double second girth 5.9 ft.
Bitternut Hickory	6.1	87
Rucker Girth Index	9.5
American Beech	5.8	61.9	along stream
Apple	4.5	40
Black Willow	4.1	44.6	along stream
Aspen, Bigtooth	3.4	90
Hawthorn (sp)	2.5	25
Hophornbeam	1.6	50
Hornbeam	1.4	35

 

We had only had a handful of RGI’s calculated so I have little with which to compare this number.  Still is seems to me that it is a good number for this single site.

Edward Frank

Bees in knothole in large Shagbark Hickory

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