Last fall I received a research permit to investigate habitats and measure trees at the Patuxent Wildlife Research Center near Laurel, Maryland. I visited the property several times during the winter. The site is located in Prince George's and Anne Arundel counties and is in the coastal plain physiographic province. Part of why I wanted to visit the site was to investigate reports of old growth forest along the Patuxent River in the refuge. The following is an excerpt of the report I that I wrote based on these investigations. A discussion of old growth is followed by some tree measurement data. I have removed citations and made some edits from the original.
The Maryland Department of Natural Resources defines old growth as the following:
“An old growth forest is a minimum of 2 ha (5 acres) in size with a preponderance of old trees, of which the oldest trees exceed at least half of the projected maximum attainable age for that species, and that exhibits most of the following characteristics:
1. Shade tolerant species are present in all age/size classes.
2. There are randomly distributed canopy gaps.
3. There is a high degree of structural diversity characterized by multiple growth layers (canopy, understory trees, shrub, herbaceous, ground layers) that reflect a broad spectrum of ages.
4. There is an accumulation of dead wood of varying sizes and stages of decomposition, standing and down, accompanied by decadence in live dominant trees.
5. Pit and mound topography can be observed, if the soil conditions permit it.”
A search for old growth forest at the Patuxent Research Refuge was inspired primarily by Mary Byrd Davis’ document, “Old Growth in the East: A Survey” and Matthew C. Perry’s description of large trees at the refuge. Davis’ assessment indicated that there may be as much as several hundred acres of old growth, uncut, or virgin forest at the refuge.
For the purposes of determining the occurrence of old growth forest, both research and in the field reconnaissance was employed. Through a conversation with Dr. Matthew Perry, some areas were identified for investigation, including the site known as Beech Island - located upriver of Duvall Bridge. Aerial photography was also used to determine promising areas for old growth forest. Historical maps and site history were investigated to determine past disturbance on the refuge.
The conclusion derived through this research and site investigation is that it is unlikely that any areas in the north or central tracts of the Patuxent Research Refuge could be considered old growth. Resultantly, it is even less likely that any areas contain primary or virgin forest. Below is a rough review of field observations for the DNR old growth criteria. These observations focus on the Patuxent River floodplain, more specifically around Beech Island. Most other areas in the refuge were clearly young-aged forest.
As no trees were cored as part of this study, tree ages were not recorded. Perry’s description of the big trees of Patuxent is undated, but appears to have been written within the past ten years. It states that based on ring counts done in the past, some trees in the Patuxent floodplain are over 135 years old. Although this is relatively old for the region, for many species it would not meet the DNR criteria for which the oldest trees exceed half the maximum known age for the species. Species found on the refuge which live longer than 270 years include Liriodendron tulipifera, Quercus alba, and Nyssa sylvatica. Although some of the trees in the floodplain are fairly large, one might expect them to be larger if they were old growth. The floodplain consists of rich soils, and moisture is abundant. The large sizes of the trees may be attributable more to growing conditions than exceptionally old age. Tree coring could potentially extend the known ages of the trees in the floodplain. However, many of the largest (assumed oldest) trees are hollow. Dating these trees through tree ring counts would most likely be inconclusive.
Observations of additional DNR criteria may also be inconclusive. Shade tolerant species (beech) were observed in a variety of age classes. However, this is common for many secondary forested areas as well. Canopy gaps were common, but this was primarily a result of the braided river channel. A low degree of structural diversity existed. There was little shrub layer or herbaceous layer, little downed dead wood, and little pit and mound topography. However, each of these attributes could be lacking due to frequent flooding in this area.
Determination of old growth based on observation did not yield a definitive result. There are some old sections of floodplain forest, but they may not be old enough to qualify as old growth. Historic conditions, however, further indicate the unlikelihood of old growth, and particularly primary forest on the refuge.
In 1690, Richard Snowden built Birmingham Manor on a knoll northeast of Brock Bridge. Much of the site is now under the Baltimore Washington Parkway, but some of the remains of the manor still exist. According to at least one source, the brick and oak timbers for the house were transported up the Patuxent River by barge. It is unclear how far up the river barges went, but the same source also indicates that since the time of the manor’s construction, the river has silted in, forming islands and a braided channel.
At least as early as 1734 the Snowden’s had constructed the Patuxent Furnaces iron works along the Little Patuxent River near the bridge just east of the contact station. However, it is likely that some form of iron production was occurring at this or nearby sites, particularly near Brock Bridge, even earlier, and probably shortly after the construction of Birmingham Manor. By 1795 maps show iron works in the area as well as a mill at Duvall Bridge. Churches and farms are also scattered across the landscape. Iron furnaces and forges required a large quantity of wood for the production of charcoal used in fueling the facilities. By 1800, and for many decades before, the land which is now the Patuxent Research Refuge had been under intensive industrial and agricultural use. Another map produced shortly after 1800 shows the area around Brock Bridge and the crossing of the Little Patuxent River. Although trees are shown elsewhere on the map, no trees are shown along the Patuxent River. The Patuxent Furnaces were closed in 1856 due to a lack of wood and iron ore. The other iron works and saw mills in the area probably closed soon after as well.
- Griffith map from 1795 depicting an iron forge on the Little Patuxent River, an iron furnace on the Patuxent River near what is now Brock Bridge and a mill near what is now Duvall Bridge.
- Moore travel map from 1802. The map on the right depicts the crossing of the Little Patuxent River. The lefthand map shows the crossing of the Patuxent River near what is now Brock Bridge. The Snowden Iron works are marked near this crossing. Trees are not shown within either river valley.
Prior to the creation of Fort Meade in 1917 and subsequently the Patuxent Research Refuge in 1936, the north and central tracts had experienced over 225 years of disturbance. Over 120 of these years were intense disturbance, including repeated cutting of trees for lumber and charcoal production. It is likely that trees unsuitable for lumber were also cut, because they could be used for charcoal production for use in the iron works. Considering that wood was eventually in short supply, it is likely that any tree of significance was cut, even if access was not particularly easy.
Mining for iron ore consisted mostly of open pits. Tobacco farming and other forms of farming also occurred in the area. The heavy impacts of tree cutting, iron mining, and farming most likely generated a large quantity of sediment, both in the refuge and upstream of the refuge. Slash from tree cutting was historically thrown into rivers which would have also increased sediment deposition in the Patuxent. The islands and braided channels existing along the Patuxent River in the refuge today are likely a result of siltation from this sediment. It is unlikely that the currently existing islands occurred in their present form or locations 320 years ago when Birmingham Manor was built.
For these reasons as well as the lack of conclusive field observation evidence, it is very unlikely that there is any old growth on the Patuxent Research Refuge north or central tracts. However, it is probable that some trees on the refuge are over 150 years old, which corresponds to previous tree ring counts and also to the end of intensive use of the site. By some definitions, some areas on the refuge might be considered old growth. Additionally, the refuge also provides very good potential for future old growth, but it can be said with a relatively high level of certainty, that the refuge does not include any primary or virgin forest.
- The Martenent map from 1860 has Patuxent Forge labeled along the Little Patuxent River. A blacksmith shop and saw mill are shown near Work’s Bridge, the approximate present location of Brock Bridge. A grist and saw mill are shown near the present location of Duvall Bridge.
As part of field investigations for old growth forest , some trees were measured on the refuge. These were typically examples of the species which were particularly large. Circumference at breast height (CBH) was measured with a tape at 4.5 feet above the ground at mid-slope. Heights were measured using the Eastern Native Tree Society methodology which uses laser range finders, clinometers, and sine calculations to determine height. This is the most accurate method of height measurements commonly available. The included table provides documentation of these measurements.
Species - CBH - Height - Notes
Carpinus caroliniana - 3' 10" - 55' - fallen, on ground, height measured with tape
Carpinus caroliniana - 3' 8" - 56.5'
Fagus grandifolia - 14' 5" - 110.8' - appears trunk may be hollow at base
Fraxinus americana - 10' 8" - 114.8'
Fraxinus pensylvanica - 9' 9.5" - 120.5'
Fraxinus pensylvanica - 10' 9" - 126.4'
Liriodendron tulipifera - 13' 0" - 137.1'
Liriodendron tulipifera - 15' 0" - 127.5' - bark is balding near base
Magnolia virginiana - 2' 10" - NA - measured at 2' from ground, hollowed out trunk
Magnolia virginiana - 1' 9" - NA
Magnolia virginiana - 1' 9" - 55.7'
Pinus virginiana - 3' 6" - 112.3'
Platanus occidentalis - 20' 5" - 119.0'
Quercus lyrata - 10' 5.5" - 113.6'
Quercus michauxii - 10' 4" - 107.6'
Quercus michauxii - 13' 8" - 118.8'
Quercus palustris - 11' 8" - 111.6'
Toxicodendron vernix - 11.5" - 24.3'
Trees of note include the following:
Carpinus caroliniana (American hornbeam): Two large trees of this species were measured, but one of them had recently fallen. The tree which was still standing was large, but is not larger than the current state champion. However, it is quite a bit taller than the current champion, and as such is note worthy. It is very likely that larger trees of the species exist in the refuge elsewhere along the Patuxent River.
Platanus occidentalis (sycamore): This tree is not large enough to qualify for state champion status. However, it is a particularly nice specimen of the species. The habit is uniform, the trunk does not appear to be hollow, and the tree is very large. This tree grows along the Little Patuxent River, but is easily accessible from the nearby road.
- Large sycamore in the floodplain of the Little Patuxent River, near the past location of Patuxent Forge.
Quercus lyrata (overcup oak): There were several trees of this species occurring in an area of the Patuxent floodplain. The example measured appeared to be the largest, but others were similar in size and exploration over a broader area might lead to discovery of a larger tree. One dead tree of very similar size had fallen nearby. Overcup oak is an uncommon species in Maryland. The tree measured is much larger than that of the current state champion, and as such should easily be able to become the new state champion if nominated.
The Patuxent Wildlife Research Center is a fairly large site. I measured relatively few trees and would like to measure more. I am hoping to renew my research permit for this winter and make more extensive measurements of the trees on the property.
Darian
