Mink Brook Highlands Area NRI Project 2008-2009
I.
Introduction
The Mink Brook Highlands Area (or MBHA) is a 613-acre tract of land that lies between the
Hanover-Lebanon town line, Route 120 on the west, Etna Road on the east and the north bank
of Mink Brook on the north. In 2008, this land area was designated by the Town of Hanover as
the subject of a comprehensive natural resources inventory, or NRI. The purpose of studying
this tract was summarized in a 5-goal statement published by the Hanover Planning
Department in July:
I.
II.
III.
IV.
V.
To understand how that landscape works to support wildlife;
To identify which are the most important habitat areas in order to guide development in a way to
impact the wildlife support system as minimally as possible;
To understand how unique the eastern bouldery part of the area is in terms of geology and flora
To complement present and future land conservation efforts in Lebanon;
To know if the area is important enough for wildlife and/or unusual enough in terms of geology to
commit to a conservation effort.
Beginning in July 2008, a field-based NRI was conducted on 426 acres of the 613-acre tract
where private property access permission was obtained. This study looked at vertebrate and
invertebrate animals, plants, fungi, rare species, natural and exemplary natural communities,
wildlife habitat, and the level of previous anthropogenic disturbance. A specific focus was the
study of wildlife and their habitat, as well as the geologic uniqueness of the eastern bouldery
part as noted above in Goal #3. The study was mostly carried out on foot, although some
roadside surveys of abutting lands took place on three sides of the tract. Map and literature
references were consulted in advance of the fieldwork, and ongoing assistance was provided by
Vicki Smith of the Hanover Planning Department.
Initial findings were submitted in a series of three short reports, each of which is included in
Appendix C of this report. Presentations to the Hanover Conservation Commission took place in
October and December 2008, and April and November 2009. The following report includes a
descriptive overview of the MBHA, a discussion of methods used in generating the data, and
findings relative to significant ecological areas and wildlife habitat zones. Appendix A contains
the seven maps previously presented as a part of the NRI, Appendix B contains species lists for
the seven principal groups of organisms studied, and Appendix C contains the aforementioned
three short reports on wildlife.
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Mink Brook Highlands Area NRI Project 2008-2009
II.
General Description of the Mink Brook Highland Area
The 613-acre (248-hectare) Mink Brook Highland Area is a rectangular block of land roughly ½
mile wide by 1.8 miles long (800 x 3000 meters). It lies in the central part of the Mink Brook
watershed, which arises on the southern and western slopes of Moose Mountains and drains
westerly towards the Connecticut River. Mink Brook is a fourth-order stream where it flows
along the northern edge of the MBHA, and remains a fourth-order stream until it reaches the
Connecticut River in the southwest part of Hanover. The study area delimited for this NRI
project includes six perennial streams and several intermittent stream drainages that flow in a
general northerly direction before entering Mink Brook. The land therefore slopes mostly north
and is comprised of a series of north-south running ridges and drainageways.
Figure 1. Topographic base map of the Mink Brook Highlands Area (delimited by magenta line)
The MBHA study area spans an elevation of between 520 and 935 feet, with the low point
located beneath Route 120 where Mink Brook flows through an underpass and the high point
being a northwesterly extension of Rix Ledges near the town line. General topographic relief
varies greatly between the eastern and western parts of the MBHA, with everything east of the
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Mink Brook Highlands Area NRI Project 2008-2009
north-running stream that bisects the property in half being comprised of rugged, steep ridges
with ample outcrops and boulders, and everything west of this stream being relatively flat,
boulder-free and smooth. Although the underlying bedrock is of one type – the “Oo1b or late
Ordovician biotite granite of the Oliverian Plutonic Suite – the eastern part of the MBHA was
evidently folded to a greater degree during the period of magmatic upwelling 431 million years
ago (Lyons et al. 1997). Based on outcrop evidence, the western part was also more heavily
metamorphosed during subsequent tectonic activity, as evidenced by the well-foliated, finergrained gneisses and hornblende-rich amphiboles present. The latter was likely responsible for
the higher degree of “richness” – i.e. calcium-rich byproducts of weathered rock, in the western
part as well.
Soils in the MBHA are largely derived
from glacial till materials. Continental
ice sheets during the Wisconsin period
of glaciation 11.5 – 13.5 thousand years
B.P. covered the entire area with ice
greater than one mile thick (Chapman
1974). Since the MBHA includes northfacing slopes of moderate steepness
(i.e. 8 – 25%), the impact of southFigure 2. Bouldery deposits are common in the western part of
the MBHA. These are derived from glacial meltwater over 11.5 K
years B.P. Substrata consist of packed sands and silts.
trending ice created a basal till layer of
compact sands and gravels. Above the
‘hardpan’ lies 12 to 24 inches of loosely sorted fine sandy to fine silty loams, with coarser
materials being found in the eastern part of the MBHA and finer materials found in the western
part. Owing to the proximity of the Connecticut River valley, it is suspected that the source of
the finer materials in the western part came from weathered phyllites and schists that are
common bedrock types in that region. The Bernardston-Pittstown-Stissing series typify the silt
loams of the western part, and the stony phases of Marlow-Peru-Pillsbury series typify the
eastern part. In areas where soils formed in deeper glacial tills such as the lower slopes near
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Mink Brook Highlands Area NRI Project 2008-2009
Mink Brook, Berkshire and Monadnock series soils are found. In the thin soils on ledge and
steep (>35%) slopes, Lyman and Tunbridge soils are found.
Figure 3. Softwood swamp on bench (left) behind Hypertherm; seepage swamp (right) at slope break near Mink Brook
Hydric soils exist at the MBHA wherever water tables exist close enough to the soil surface to
create anaerobic conditions in the upper part during one or more weeks during the growing
season. Since much of the study site contained a compact till layer at depths ranging from a few
inches to two feet, water tables were found to be high enough to create hydric coil conditions
in many areas. The wetlands map in Appendix A-2 illustrates the known locations of hydric soils
in the MBHA. Most of the hydric soils were poorly drained compact tills comprised of silt loam
in the western part and fine sandy loam or loamy fine sand in the eastern part. Some of the wet
terraces in the latter area contained very poorly drained soils that have formed in deep organic
material. The most notable area with histosols of this nature is the ‘Bottomless Pit,’ where soil
depths exceeded the length of my five-foot auger.1 In all, a total of 74 acres of hydric soils were
found in the study area, or roughly 17% of the area of coverage.2
Wetlands in the MBHA were found to occur along drainageways, on flat benches, and at slope
breaks above Mink Brook. The six perennial stream drainageways noted above were the
principal areas where stony phase Pillsbury soils were found to support a prevalence of wetland
plants, although at least a dozen other areas were found where intermittent drainageways
1
Estimates of the “bottomless” nature of this peatland area range between 6 feet (2 meters) and 35 feet (10.7 m).
Some lands adjacent to the parcels where property access was granted were included in the final tally based on
aerial photography and visual inspection at a distance.
2
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Mink Brook Highlands Area NRI Project 2008-2009
were also characterized by hydric soils and hydrophytic plants. Nearly all of these drainageway
wetlands were forested, with a mix of hardwoods and softwoods in the canopy. Wetlands on
benches were mostly found in the eastern part, notably at the Bottomless Pit and the softwood
swamps adjacent to it. Benches along Mink Brook also contained wet soils and wetland plants
owing to their regular inundation by floodwaters and characteristically layered (aka somewhat
impervious) soils. Slope break wetlands largely occurred in the northwestern part of the MBHA,
where sharp declinations in slope allowed subsurface groundwater to break out and saturate
the soils above Mink Brook. These very unstable soil sites also contained several man-made
spring and wells.
Figure 4. Old cistern (left) on a very gradual slope; black ash seepage swamp (right) above Mink Brook
GPS-based field reconnaissance produced the cover type and natural communities map in
Appendix A. A total of 32 distinct cover types were found to be present in the MBHA, with 19 of
them being recognizable according to the Natural Communities of New Hampshire (Sperduto
and Nichols 2004). The 13 cover types that were not discernible as to natural community type
were either heavily disturbed (e.g. Phragmites fill pile) or of such a young age (e.g. old field –
upland) that it was not possible to predict what the mature, self-replicating state would be. In
most areas these cover types or natural communities were quite distinct and definable,
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Mink Brook Highlands Area NRI Project 2008-2009
particularly in the eastern part where the boulder-laden ridges or drainageways were neatly
separated from adjacent basins or mixed woodlands. In the western part of the MBHA,
however, there were several “pole” stands (i.e. trees in the pole size class of roughly 10 – 12
inches dbh) where the landscape and flora indicated a gradual boundary from one type to
another. This was particularly true for the semi-rich sugar maple-white ash forest and the
adjacent hemlock-beech-oak pine forest. Slightly elevated mounds tended to be more acidic
and support pines and oaks, whereas the slightly wetter and nutrient rich hollows tended to
support white ash and sugar maple. In this case, the natural community line was approximated
where the percentage of hollows exceeded the percent cover of mounds or vice versa.
Within the 32 cover types and natural
communities differing levels of prior
human disturbance were noted.
Whereas most of the MBHA had been
cleared for agriculture in the early
1800’s, the eastern part was never tilled
and likely did not support grazing
animals for very long. This was not true
for the western part, where stone walls,
Figure 5. Semi-rich forest near edge of more acidic woods, where
sugar maple and ash give way to white birch and hemlock
barbed wire fence lines, and plowed
soils indicated a long history of use.
Wildlife species varied according to the habitat types that are currently present on the MBHA.
Typical uplands furbearers such as moose, deer, coyote, fox, fisher, bear, and porcupine were
found in the forested upland areas of the MBHA. Riparian and wetland-associated species such
as raccoon, mink, otter, and beaver were found along drainageways and Mink Brook. Upland
passerine birds such as red-eyed vireo, ovenbird, black-throated green warbler, black-capped
chickadee and blue jay were common in mixed woods of all areas of the MBHA, while riparian
species such as kingfisher, alder flycatcher, red-winged blackbird, and song sparrow were
confined to wetland and streamside thickets along or near Mink Brook. Redback salamanders
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and eft stage red-spotted newts were abundant in most areas of the MBHA, while two-lined
and dusky salamanders were localized along perennial streams. Arched hooktip (Drepana
arcuata) and unadorned carpet moth (Hydrelia inornata) were frequent in mixed upland woods,
whereas the harvester butterfly (Feniseca tarquinius) and beaverpond clubtail (Gomphus
adelphus) were restricted to riparian wetlands.
Figure 6. Unadorned carpet moth (left) on pine bark; harvester butterfly (right) on alder
Each zone of the Mink Brook Highlands Area had varying degrees of habitat value, largely based
on the degree of past human impacts and the successional state of the forest that has
regenerated from the previous agricultural landscape. Although a wide variety of wildlife
species can be found in the MBHA, most of them can be regularly found in disturbed
landscapes. Only a handful of species, such as black bear, fisher, bobcat, red-shouldered hawk,
and Canada warbler, tend to be less tolerant of active human presence or at least require it
during a part of their life cycle. It was the observations of the latter species, as well as the
degree of past human disturbance on the landscape that dictated the value of certain areas for
wildlife habitat. Reflecting the pattern of prior agricultural activity noted above, the higher
value wildlife habitat areas tended to be found in the eastern part of the MBHA and along the
immediate Mink Brook corridor. The specific data that supports the map of the three-tiered
wildlife habitat areas, as well as the other significant ecological areas noted in a separate map
in Appendix A can be found in the further section of this report.
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Mink Brook Highlands Area NRI Project 2008-2009
III.
Methods
A) Task 1 – Base Map Development
The study area was initially delimited by the Town of Hanover Planning Department. It included
all of the lands south of the north bank of Mink Brook and its principal tributary that runs
through Hypertherm Corporation, east of Route 120, west of Great Hollow (Etna) Road, and
north of the Hanover-Lebanon town boundary. Property access permission was sought in
written form from all private and public property owners. The latter included Dartmouth
College, which had an easement conveyed to the Town in the Bottomless Pit area. All but two
of the private property owners gave written permission to cross their land in the preparation of
the NRI. The subsequent map of the study area that was derived came from GPS-based ground
confirmation of the Hanover-Lebanon town line, the edge of the two private parcels that were
considered “Out Lots,” and from aerial photograph interpretation of the course of Mink Brook
and its principal tributary near Hypertherm. GPS-based precision for this project was estimated
at 3.3 to 7.8 meters, or 10.8 to 25.6 feet.
The following includes the list of data layers that were referenced during the preparation of the
initial base maps for the project. Each of these were supplied or purchased from NH GRANIT,
the statewide repository of GIS (Geographic Information System) data for the state of New
Hampshire, housed by Complex Systems Research Center at UNH, Durham.
Resource Layer
aerial photos, leaf off, B&W
aerial photos, leaf on, Color
aquifers, limit, material, capacity, WT
bedrock geology
conservation land
contours - 20-foot
digital raster graphics (DRG's)
drinking water, WPA's
elevation - tagged vector contours (TVC''s)
forest matrix blocks
groundwater
groundwater threats
historic and cultural features inventory
hydrography
NH land cover assessment
NH wildlife action plan data
pesticides - agricultural
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Source(s) (Date) / Comments
DOQ's (NHGRANIT, 1998)
NAIP's (NHGRANIT, 2003)
USGS (2000)
Lyons et al. 1997, NHGRANIT (1998)
SPNHF (2008)
NH GRANIT (2007)
USGS (1987)
NHDES (1999)
USGS (1988)
TNC (2006)
NHDES (1997)
NHDES (1997, non-point, point)
NHDHR, Towns (1996)
NHGRANIT (Jan 2006)
Landsat TM, NHGRANIT (2001)
NHFG (2005)
NHDA (1998)
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Mink Brook Highlands Area NRI Project 2008-2009
pipelines
political boundaries - DLG's
railroads
roads
soils - Grafton Co.
wetlands
USGS (1983)
USGS (1996)
USGS (1993)
NH DOT/NHGRANIT (Nov 2005)
NHDES/NRCS (1999)
Landsat TM (2001), NWI (1998), USGS (1987)
The above data layers were used to create the initial maps provided for the town, namely the
base map that served to illustrate the area of GPS-based coverage (Appendix A-1), water
resource base map (Appendix A-2), and the initial cover type map (Appendix A-3). Whereas
there some discrepancies noted (i.e. especially along the town line), these maps provided a
good basis with which to conduct the ensuing field reconnaissance.
B) Task 2 – Field Assessment of Natural Resources
1. Wetlands and Waterways
As noted above, wetlands were delineated in the field according to the three-parameter
approach of the US Army Corps of Engineers (Wetlands Delineation Manual 1987). These
wetlands were not marked or surveyed in any way, and therefore the map should not be used
for survey or other legal purposes. Field testing of soils was completed using a tile spade and/or
Dutch soil auger, a Munsell soil color book, and Version 3 of the Field Identification of Hydric
Soils of New England (NEIWPCC 2003). Hydrophytic plant prevalence was based on full leaf-on
condition regardless of the time of year. Hydrology was based on primary and/or secondary
indicators appropriate to the time of year. Wetland cover class was initially determined using
the state and federal standard of NWI types (Cowardin et al. 1979), but was converted to
natural community or cover type during subsequent field visits. No attempt was to estimate the
adjacent wetlands on the north side of Mink Brook, nor of the accurate coverage of wetlands in
the ‘Out Lots’ described above. Inferences on the location of wetlands in the latter area were
made on the basis of visual inspection from the boundary and from aerial photography. Surface
water bodies were derived from USGS data except where field analysis suggested a change in
alignment. Formatting for perennial versus intermittent streams followed USGS guidance.
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Mink Brook Highlands Area NRI Project 2008-2009
2. Cover Types and Natural Communities
Cover types were assigned on the basis of field inspection of all locations of the study area, and
delimited using both GPS point data and aerial photograph interpretation. The leaf-on 2003
NAIP aerial photographs were used for the latter. As discussed above, in certain areas of the
MBHA the current cover type was not discernible as a specific natural community, and
therefore left as an artificially named type on the basis of dominant features, such as “Built
Landscape” or “Invasive Scrub-shrubs” or “WP (= white pine) sapling/pole forest.” A clear trend
in mapping natural communities arose from the repeated observations of relatively unaltered
landscapes in the eastern part, wherein forest ages in excess of 135 – 140 years allowed for a
fairly easy determination according to the standards in Sperduto and Nichols (2004). As with
the wetlands and surface water bodies mapping, no attempt was made to derive specific cover
types for the properties where access was denied, with the exception of some aerial photo
interpretation of floodplains along Mink Brook.
3. Wildlife Observations and Habitat Mapping
Wildlife observations took place during all field outings. Observations included direct sightings,
aural observations, tracks, browse, scat, urine, feathers, bark rubbings, claw marks, chewed
acorns or nuts, scent marks, kill sites, caches, dens, forms, dams, and lodges. Point data were
gathered by GPS for significant areas of wildlife concentration such as game trails and scent
posts. Point data was also gathered for any observations of rare or uncommon species such as
bobcat, bear, wood turtle, and American harvester. Every attempt was made to maximize
species detection by visiting the property at all times of year and all times of day. Active
searches were conducted while searching for amphibians, notably stream salamanders and
terrestrial salamanders. Digital photographs were taken of all significant invertebrates for later
identification in the office. Samples were taken of several fungi species in order to confirm their
identification in the office using microscopic techniques. Beyond the active search method,
there was an attempt made to gather quantitative data on the frequency of mammal tracks in
snow, however, snow conditions were not conducive for this effort.
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Mink Brook Highlands Area NRI Project 2008-2009
During the latter two months of the field season, there was a successful effort to conduct
repetitive breeding bird surveys (BBS) of nine different locales in the MBHA. Using standards
developed by Cornell Laboratory and the US Fish & Wildlife Service and utilized in the Breeding
Bird Atlas of New Hampshire (Foss 1994), I conducted a series of point counts at representative
locales of the MBHA. The following locales were used in this effort:
Table 1. Breeding Bird Survey Station Roster
STA.#
STATION
NAME
LOCATION
1
Bottomless Pit
Bottomless Pit near E edge of open fen
2
Pine-oak Knoll
3
4
Drainageway
Mink Bk
Orchard
Top of sharp pine-oak knoll above (W of) Bottomless Pit
Behind Hypertherm along hemlock-yellow birch
drainageway
5
Beaver Pond
Near beaver pond behind moving company
6
HPW slope
Behind Hanover Public Works at edge drop-off
7
Jesse's seep
Behind Jesse's restaurant near large tip-up at seepage
8
Astronics
Just behind Astronics along trail down to Mink Bk
9
Mink Bk Trail
350 m behind Astronics along trail down to Mink Bk
Near bend in Mink Bk just above old orchard
PRINCIPAL HABITAT TYPE
1
Softwood swamp and fen, with associated cool-air boulder talus slopes
2
Pine-oak forest/woodland on granite sill rib; steep slopes
3
Yellow birch-hemlock stony drainageway; int. stream
4
Old field in riparian zone; mixed forest adjacent
5
Beaver pond & marsh; scrub-shrub marsh; riparian zone
6
Open disturbed land above Mink Brook; industrial zone
7
Old pasture pines on wet silty soils, some red maple sensitive fern areas
8
Semi-rich mixed woods near parking lot
9
Rich woods, sub-mature, hardwood dominant
The point count consisted of ten-minute observation periods taken once at each station each
day on May 30 and June 26, 2009. Stations were randomized on the second day so as not to
repeat the sequence. All vocalizing males heard and/or seen from the point station were
recorded in one of three categories: a) stationary males vocalizing within optimal habitat; b)
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Mink Brook Highlands Area NRI Project 2008-2009
same as a) but within a 30 m radius from station center; and c) fly over. Females, non-vocalizing
males, and incidental sign of other birds were noted as well (e.g. migrants). Data from the BBS
was uploaded into Excel worksheets and calculated for relative frequency (see Appendix B).
Notations were made on rare or uncommon species that are known to be sensitive to human
disturbance. Notes were also kept on confirmed breeders.
Figure 7. Left: BBS #7 behind Jesse's restaurant; right: young raven calling for food from the Astronics roof
C) Task 3 – Data Assessment and Category Impact Mapping
1. Significant Ecological Areas
Significant ecological areas (SEA’s) were derived directly from the natural community mapping
effort. These were identified on the basis of uniqueness, rarity, and sensitivity to anthropogenic
disturbance. Uniqueness was determined on the basis of natural community type, its condition
(i.e. exemplary or not), and the salient characteristics of its landscape position. The author’s
familiarity with the local and regional setting was used in this estimation. Guidance from the NH
Natural Heritage Bureau’s list of rare natural communities was used in the derivation of rarity.
A particular natural community was deemed rare when it was listed as either S1 (from 1 to 5
occurrences in the state), S2 (6 to 10 occurrences in the state), or S3 (from 20 to 100
occurrences in the state). Sensitivity was based on the author’s experience with degraded
landscapes and the apparent loss of species that often accompanies such degradation.
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2. Potential Wildlife Impacts Map
This map was prepared at the request of the Hanover Planning Department and Conservation
Commission for the purpose of guiding development in this 613-acre area. The three categories
of habitat were identified as follows:
1. No-disturb areas with high habitat value
2. Minimal disturbance areas with moderate habitat value
3. Previously disturbed areas with low habitat value
Designation of the previously disturbed areas was relatively straightforward in that they were
quite visible from both the roadside and the aerial photographs. Sites that contained a
continuous forest cover were mostly identified as Zone 1 or 2, although there were a few areas
where anthropogenic disturbance prior to forest regeneration was severe enough to warrant a
low habitat value assignment. Late successional natural communities that contained above
average wildlife observations were deemed to be a part of Zone 1. Often these areas were
immediately adjacent to Zone 3 areas where previous development had taken up high quality
wildlife habitat. Zone 2 areas were lands largely devoid of abundant wildlife sign, or contained
sign that reflected tolerant wildlife species (such as white-tailed deer), and contained strong
evidence of prior agricultural activities (plowing, stone walls, etc.). The boundaries between
these areas and Zone 1 areas were usually distinct, although the boundaries of these areas with
Zone 1 areas were not always easily discerned.
Figure 8. Often the boundary between high wildlife habitat value areas and ones with much lower habitat value was quite
distinct, as evidenced in this view of the edge of a talus boulder woodland behind Hypertherm. Just a few feet off of this
large boulder ridge was a forest of typical mixed hardwoods and softwoods with unremarkable ground topography or relief.
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Mink Brook Highlands Area NRI Project 2008-2009
IV.
Findings
As noted above, previous reports have summarized the salient attributes of the Mink Brook
Highlands Area in terms of east versus west, prior land use activities and disturbance, wildlife
habitat and natural community types, and wildlife crossings.3 These points have also been
made during one or more of the public presentations offered to the Hanover Planning
Department and the Hanover Conservation Commission. What remains is a description of the
significant ecological areas as they pertain to wildlife habitat, some of the salient wildlife
species that added insight to the derivation of sensitive wildlife habitat zones, and the
recommended wildlife management and conservation practices that may be implemented to
help protect these attributes. The first part below contains a discussion of the findings relative
to significant ecological areas and sensitive wildlife habitat areas, and the final part is contained
in the next section (V.).
A) Description of MBHA Natural Resources Under Task 3
1. Significant Ecological Areas and Wildlife Habitat
A total of 36 separate ecological areas among 11 different types were deemed to be significant
in terms of their uniqueness, rarity, and sensitivity. This equaled 96 acres in the MBHA, or
roughly 16% of the total area. It should be noted that while some of the SEA’s were mapped on
‘Out Lot’ properties as a result of boundary edge viewing or roadside surveys, most of the
interior of the central block was ‘off-limits’ and did not receive an adequate review. Based on
the topography and land use history, it appears that least the eastern part of this unvisited area
contains some of the same SEA types as found in the eastern part of the MBHA. Among other
types, this likely includes Dry Oak-Pine Forest, Talus Forest/Woodland, and Vernal Woodland
Pools. Along Mink Brook there are very likely other floodplain forests and streamside seepage
swamps that could be added to the SEA acreage. On the western part of the unvisited area, the
rich seepage swamp extends across the boundary wall in a limited way.
3
MBHA attributes regarding east versus west as well as past land use was described in the November 2008 report;
wildlife habitat and natural community types were summarized in the April 2009 report and presentation; and
wildlife crossings data on each of the 12 major game trails leading into and out of the MBHA was provided in the
June 2009 report. See Appendix C for these reports.
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As with the general mapping of natural communities, the types of SEA’s varied east versus west
in the MBHA. The eastern part had the only softwood swamp examples, as typified by the
Bottomless Pit depicted below. These deep organic soil sites occurred near the drainage divide
behind Hypertherm between Mink Brook and the stream leading southerly along Great Hollow
Road. Shallow slopes and constant supplies of groundwater have allowed organic soils to build
up beneath a canopy of red spruce and eastern hemlock. On a slightly higher landscape position
but also within these flat terraces and basins was the only example of a Lowland Spruce-fir
Forest. Slightly drier than the softwood swamps, this area had balsam fir as the predominant
understory species and red spruce as the dominant canopy species. Both the softwood swamps
and lowland spruce-fir forest had deep layers of moss on the forest floor with scattered
softwood seedlings of spruce, fir and hemlock. The softwood canopy and understory browse
provided excellent cover for wintering moose, deer, snowshoe hare, and porcupine; and with
the adjacent talus boulder slopes, these areas offer prime habitat for fisher, bobcat, and longtailed weasel. All three of these species would not have occurred on the MBHA properties
without this type of habitat support.
Figure 9. Lowland spruce-fir forest (left) and old male fisher (right) behind Hypertherm
Perhaps the second most common SEA in the eastern part of the MBHA is the Talus
Woodland/Forest. These sites are characterized by very steep, ledgy soils that support a thin
veneer of hemlock, oak, pine and spruce atop smooth granite outcrops and boulders. Based on
the folds in the magma domes that formed these ridges, many of them lie on a north-south
axis. Prominently elevated above the surrounding sloping valleys, they have droughty soils that
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Mink Brook Highlands Area NRI Project 2008-2009
support excellent mast-producing trees such as red oak, white oak, and eastern white pine. Red
squirrels are abundant, which in turn support aerial predators such as the red-shouldered hawk
and barred owl that was observed in this part of the MBHA. White-tailed deer and turkey also
rely heavily on the mast provided by oaks; they also eat the fungi (or fungi-supported insects)
that grow in association with oak. The only sign of a deer-kill was also in this area. It was being
fed on by bobcat, coyote and fox. The lowest elevation Talus Woodland/Forest supported the
only Dry Oak-Pine Forest observed in the MBHA. Although similar in vertebrate animal diversity
and value, the variance in plant species likely supported unique and different fungi such as
black-staining polypore (Meripilus sumsteinei), chicken-of-the-woods (Laetiporus sulphureus),
and the invertebrate fauna that these giant mushrooms support.
Figure 10. Dry Oak-Pine Forest on granite ridge (left); chicken-of-the-woods fungus on oak (right)
The third most significant ecological area that characterized the eastern part of the study area
was the forested floodplain along Mink Brook. Also found in patches in the western part, this
floodplain area was different than most small riverine floodplains in that red maple was not
necessarily the dominant species. Owing to the presence of abundant groundwater discharge,
as well as the slightly ‘sweeter’ soils associated with the groundwater, black ash was a common
co-dominant if not dominant member of this natural community. In one instance, it formed an
association with a hawthorn species that was actually tree-sized. This apparently naturally
occurring community had never been previously observed by the author, and was reported to
the state Natural Heritage Bureau. Clearly the most valuable attribute of this natural
community for wildlife was the excellent opportunity (i.e. food and shelter materials) for
beaver. Active beaver lodges and dams were observed all along Mink Brook, and all of the
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typical animals that this keystone species brings forth was represented: mink, otter, muskrat,
heron, ducks and geese, alder flycatcher, gray catbird, yellow warbler, Canada warbler, song
sparrow, and red-winged blackbird. In one area where beaver-induced sapling and shrub stands
were very thick along Mink Brook a female 9-year old wood turtle was found. This state watch
(S3) species was the only one found in the MBHA and is rarely recorded in the watershed. This
floodplain area also supported several butternut trees, which are also consider a state watch
species because of their recent decline from butternut blight.
Figure 11. Song sparrow (left) and black ash
streamside floodplain (right) along Mink Brook
In terms of the western part of the Mink Brook Highlands Area the significant ecological areas
tended to relate to the higher pH silt loam soils. Along the eastern edge of the western study
area a rich seepage swamp was designated on account of the predominance of bitternut
hickory, black ash, white ash, sugar maple, red maple, maidenhair fern, and plantain-leaved
sedge. The water table was elevated to within 12 inches of the surface and virtually all of the
herbaceous plants occuring in the seepage hollows between the tree mounds were
hydrophytes. This unusual occurrence of a rich seepage swamp was brought about by a
combination of agriculture, which disturbed the soil surface and allowed subsurface
groundwater to regularly discharge above the surface, and earthworms, which have helped
eliminate any accumulation of leaf litter that would otherwise acidify the soil. Although wildlife
species that are directly associated with this SEA appeared to be few – such as flying squirrel,
turkey, deer, raccoon, moose, and star-nosed mole, none are rare or intolerant of disturbance.
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Mink Brook Highlands Area NRI Project 2008-2009
This may not be the case for the myriad species of invertebrates that likely rely on the unique
combination of herbaceous plants to survive.
Closely associated with the above seepage swamp, but occurring in slightly drier and more
steeply sloped areas was the Rich Mesic Forest. This natural community is ranked S3 by the NH
Natural Heritage Bureau and while not uncommon, is uncommon in the MBHA. This example of
a Rich Mesic Forest appears to be transitional to the Rich Sugar Maple-Oak-Hickory Terrace
Forest that is ranked S1 by NHNHB. The similarities include its presence on old glacial lakebed
sediments (silt loams), the predominance of bitternut hickory in the canopy, and the presence
of a very similar herbaceous flora. The latter included rich site indicators such as sharp-lobed
hepatica, blue cohosh, maidenhair fern, ostrich fern, two-leaved mitrewort, loose-flowereed
sedge, and silvery spleenwort. It also included two less common species found in rich, mesic to
sub-hydric sites, early meadowrue and hairy-leaved sedge (Carex hirtifolia).
Just downhill of this site, where groundwater discharge was more significant, the Rich Mesic
Forest morphed into a Red Maple-Black Ash Seepage
Swamp. The central portion of this swamp was
dominated by a thick carpet of herbaceous plants such
as woodland horsetail, sensitive fern, fowl mannagrass, turtlehead, false hellebore, swamp saxifrage,
and drooping sedge. The lower portion contained a
sufficient amount of alder to attract the state watch
(S3) American harvester butterfly, an arctic skipper,
the moustached clubtail dragonfly, and the eightspotted forester moth. Each of these species tend to
be habitat dependent, and the small, high-quality
seepage wetland offered excellent habitat for their
Figure 12. Rich seepage swamp with red maple,
black ash, and wide variety of herbaceous plants
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occurrence.
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Mink Brook Highlands Area NRI Project 2008-2009
2. Potential Wildlife Impacts Areas by Category
The dreivaton of the MBHA Potential Wildlife Impacts Map in Appendix A arose from the
fieldwork and habitat analysis that preceded it. Natural communities mapping, observation of
wildlife sign, determinations about past land uses and their lasting impacts on habitat quality,
and current land use patterns suggested the three zones as designated on the map. In terms of
causal factors, the most important variable responsible for current habitat condition was
topographic relief, that is, the surface “roughness” that dictated whether or not early settlers
could extract natural resources from the land. The clear prevalence of older forests that mimic
late successional or old growth types in the eastern part of the MBHA resulted from the
inability of settlers to log, farm, build roads, or otherwise develop this area. The abundance of
large surface stones, steep slopes, and very wet soils made this landscape very difficult to
“tame.”
Even the low-lying terraces and benches, while more readily available for logging activities,
were typically too wet or stony to yield to plow or oxen team. The Bottomless Pit has deep
mucky soils, the lowland spruce-fir forest is a bed of mossy stones, and the riverine floodplain is
subject to frequent floods. Although early settlers did manage to clear most of the forests for
sheep pasturage, very little evidence reamins of their tenure, and the general age of the forest
in the eastern part – roughly 135 – 140 years, suggest that this area was vacated early during
the demise of New England agriculture in the mid nineteenth century.
This was clearly not the case in the western part, where smoother slopes, deeper soils and few
stones or boulders provided easy access with ample growing potential for crops and livestock.
In the western part of the MBHA, the only significant restriction was surface and subsurface
water. Water tables had to be managed, and typically were, as evidenced by a number spring
houses, ditches, and short canals. Steep slopes just above Mink Brook prevented much
agricultural activity except for pasturage, although the lands above the 700-foot contour were
relatively easily cleared of stones and plowed. These upper slopes were cropped for hay well
into the 20th century. This very different land use history made it somewhat challenging to draw
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Mink Brook Highlands Area NRI Project 2008-2009
a neat line between the current, highly disturbed landscape, and the former agricultural land
that still has a lasting effect on wildlife habitat quality and condition.
On the basis of land use history, forest cover age and natural community type it was relatively
easy to depict the highest value wildlife habitat in the MBHA. In all, a total of five units
comprising 279 acres were deemed to be Zone 1 wildlife habitat,4 that is, of the best quality
and the most likely to be negatively impacted by future development. Most of the eastern part
of the MBHA fell into this category, as did the entire riparian strip along Mink Brook. In the
western part, the aforementioned rich mesic sites, both upland and wetland, fell into this zone.
In terms of the moderately valuable wildlife habitat that would be slightly affected by increased
human disturbance and development, most of this land was identified from the central western
and upper eastern parts of the MBHA. This zone totaled approximately 173 acres of the study
area. Nearly all of the Zone 3 wildlife habitat – those areas where human disturbance has
already severely impacted the condition and quality of the habitat, fell along roadways such as
along Route 120, along Great Hollow Road , and behind Centerra. It should be noted that most
of this area has already been built upon, and that future expansion opportunities in this zone
are few. This area totaled 77 acres of land.
Figure 13. Old bailer (left) near Route 120 depicting a
bygone era of agriculture in the western part; right:
common reed (Phragmites) grows on old fill piles near the
DHMC parking lot
4
Note that areas immediately adjacent to the study area were also zoned by category in order to assist in the
planning efforts nearby.
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V.
Recommendations and Next Steps
The Hanover Planning Department and Hanover Conservation Commission is to be commended
on their thoughfulness and forward thinking in terms of “sizing up” the Mink Brook Highlands
Area for wildlife habitat and condition. As I believe this report depicts, there are some
remarkable attributes of this 613-acre area, and some of these are likely unique in the town.
The presence of rich mesic forests, both wet and dry, the absolutely stunning landscape of
boulders, steep ledges, and narrow ridges in the eastern part, and the relatively high diversity
of wildlife species in an otherwise fragmented landscape suggests that there is positive future
for this area if managed appropriately.
Although this study provides ample detail on the presence of various wildlife and plant species
as well as natural community types, it is but one study during a single year’s time. Long-term
trends in wildlife populations were not able to be determined, nor was there an opportunity to
connect this unfragmented tract to other lands nearby. There was a significant gap in coverage
between the study of the eastern and western parts, and there likely remains some outstanding
attributes that may affect the overall conservation initiatives that arise. For that reason, the
following is offered a a short list of suggestions relative to the future of this area:
1) Finalize plans to integrate this NRI with the one conducted on lands to the south in
Lebanon – this step is self-evident in terms of providing a set of seamless management
goals for the entirety of this unfragmented block, and has already been discussed by the
Hanover and Lebanon Conservation Commissions and Planning Departments.
2) Encourage cooperation with the landowners in the MBHA where access was not
previously granted – while this may be difficult for one landowner, the other should be
willing to allow access to the +/- 90 acres they own. This may allow for the resolution of
the ‘east versus west’ debate as to where to draw the line between potential protected
areas.
3) Prioritize conservation efforts in the eastern part where older forests and rough
landscapes dictate long-term protection – initial conversations have already taken
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place to make this a reality. The protection of wildlife habitat, natural forest ecosystems,
alongside recreational opportunities appear to make this a doable objective. The town
should be encouraged to provide incentives for the landowner to secure easements for
the benefit of the public at large.
4) Discourage any through trail along Mink Brook – this idea has been posited by at least
one group and should be unquestionably denied on the basis of the rationale I have
demonstrated in this report, namely, the presence of sensitive and rare wildlife, natural
communities, and an encroaching level of development that has already compromised
the northern shoreland district of Mink Brook.
5) Encourage trail erosion controls among the mountain bike users behind Hypertherm –
even within the twelve month period of this study the number of trails and mountain
bike riders behind Hypertherm has increased substantially. In recent conservations with
Hypertherm employees, a note of caution was expressed in this regard. Although it may
appear that there are other reasons to disallow mountain bikes in this area, on the basis
of wildlife habitat and quality I believe that at present, mountain biking is a compatible
use with the planned conservation efforts. (Night-time riding should be discouraged,
however!)
6) Conduct any timber harvesting in the western part during frozen ground conditions –
as noted above, the sub-hydric to hydric soils in the eastern part are very erosive and
would be subject to degradation from mechanical impact of any kind. Long-term
damage has already been done in many areas by agricultural and silvicultural
equipment. The dramatic blow-down of 2005 demonstrates the instability of the soils,
and any logging activity in this area will have to reckon with such instability. Further, it is
strongly recommended that no mechanical equipment of any kind be allowed below the
steep slope break at the +/- 700-foot elevation contour.
7) Discourage any bridge-building across Mink Brook – further fragmentation by human
recreationists that approach from the north side of Mink Brook will only further
compromise the integrity of the wildlife travel lanes and crossing areas currently known
to be present.
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8) Establish a “front line” of defense against invasive plants in the late succesoinal areas
of the MBHA – this is perhaps the most challenging task ahead in terms of long-term
management, and may ultimately not be successful. The significant difference between
the forest types in the eastern and western parts is also reflected in the amount and
diversity of invasive plant species in each part. Honeysuckle has virtually taken over
every floodplain understory along Mink Brook, and Japanese knotweed has completely
altered the scrub-shrub zone in the larger floodplains of the northeast part. While
barberry, buckthorn, giant helleborine orchid, and winged euonymus can be found
scattered throughout the MBHA, any further inroads by development into this area
could cause a significant increase in these and other species. Any development proposal
for this area should also contain a management and monitoring plan for invasive species
control.
Acknowledgments
I would like to thank Vicki Smith of the Hanover Planning Department for her coordination of
the project, the members of the Hanover
Conservation Commission for their arduous work
in moving the cause of conservation forward in
the town, the private landowners (notably Perry
Seale and the Hypertherm employees) who
facilitated travel onto their lands, and the
members of the interested citizens group that
attended the quarterly presentations and
provided excellent feedback and inquiry
throughout the project.
Figure 14. Conservation-minded folks on Rix Ledges
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