by Tom Tidman, Acton Director of Natural Resources

The Arboretum features a broad range of ecologically significant habitats common to the New England landscape. A blending of both glacial remnant features and the influence of over 300 years of farming has transformed the landscape to provide diverse wildlife habitats.

At present, most of the property is in the process of undergoing some tertiary stage of forest succession. Greater than 14 acres were once apple orchards that over time have become overgrown with both native and in some instances non-native vegetation. In addition, approximately 22% of the property can be classified as wetlands, encompassing a variety of habitats, which mesh to form a species rich wildlife mosaic.

Of greatest significance to the development of a "naturalistic" arboretum, is the high degree of emphasis placed upon recognizing wildlife corridors, maintaining edge habitat and in understanding the inter-relationship and dependence of one wildlife habitat region to another. Below, an outline of each of the major wildlife habitat regions will be reviewed.

Wildlife Corridors
Although limited by size and encroached upon on all sides by residential development, the Arboretum provides important habitat for all life functions to an interesting variety of wildlife . In large part, this is a direct function of the abundant habitat diversity found in a relatively diminutive land area, 64 acres. In essence, the Arboretum is an oasis in the heart of residential Acton.

Located within the bounds of the property are:

  • Open grazing/foraging areas for deer, rabbits, voles and mice
  • Extensive wetlands areas for nesting, cover, and water
  • Upland hardwood forests with abundant acorn and hickory nuts and numerous cavity and den trees
  • Several successional stage abandoned orchards providing exceptional wildlife habitat.

Wildlife travel corridors represent a fascinating aspect of the Arboretum seldom noticed by the visitor, as most wildlife travel is done under the cover of darkness. These recognized wildlife travel corridors connect specific feeding, roosting denning, and nesting areas. Daytime travel is done in a way to be concealed from the ever alert senses of predators.

Primary to all life function is the need to procure both food and water. In the Arboretum satisfying these fundamental requirements is most often accomplished in the wetlands areas or along the forest field edge where plant diversity is at its greatest. Reaching these feeding areas presents many species with a daily exercise in staying alive, while giving others an opportunity to hunt.i

One such predator/prey association is the relationship between Red Fox (Vulpus vulpus) and Chipmunk (Tamius stratus). Chipmunks are primarily a ground dwelling member of the squirrel family, utilizing the arboretums grid pattern of stonewalls as travel corridors. In addition to travel, the walls provide shelter and a place to store caches of nuts and other gathered foods hidden within the stones. The Arboretum's fox family is acutely aware of the stonewall thoroughfares. Instead of walking adjacent to the walls, fox stealthily walk along the top of the walls expecting to bewilder an unsuspecting chipmunk.

Wildlife Habitat Inventory

Open Meadow Habitat
Open meadows represent a wildlife habitat quickly becoming a thing of the past in New England. A special effort is made to maintain the grassland habitat found in the Arboretum and not to disturb the wildlife. Meadows are mowed each November after the songbird migration has concluded. Cutting fields back on a yearly schedule is primarily done to remove the uninvited onset of gray dogwood, Japanese multiflora rose and European buckthorn.

For example, gray dogwood masses left unmowed for as little as three consecutive years can encompass entire meadow areas, excluding virtually all other herbaceous growth.

Approximately 5 acres of the Arboretum is actively managed as open meadow habitat. In 1997, the abandoned orchard near the ledge outcropping on the Wood Lane side of the property received some much needed clearing removing two acres of European buckthorn, multiflora rose, and countless saplings. In just one year since the clearing,  many herbaceous plants including meadow grasses, buttercups (Ranuncolos acris), black-eyed Susans (Rudbeckia hirta), and common milkweed (Asclepias incarnata) have returned.

The Arboretum's meadows play host to a wide variety of bird life as well. By maintaining grass fields, we have been able to preserve a healthy population of song sparrows (Melopspiza melodia), chipping sparrows (Spizella passerina), and other ground or herbaceous layer nesting birds.

Over the past two decades, New England has seen a gradual increase in the population of coyotes. The Arboretum is no exception. We have had several reported sightings on the property. While alarming to some, coyotes account for the elimination of more feral cats than any other single predator. With substantially fewer unwanted cats in our meadows, the population of native songbirds continues to rebound.

The meadow next to the rhododendron collection is an excellent place to enjoy the diversity offered by an open meadow habitat.

Meadow/Forest Edge Habitat
Of all habitat regions found in the Arboretum, none is more diverse in species than the forest/meadow edge. A healthy edge habitat ranges from meadow grasses at its most exposed extreme to mature successional forest at its source. Plant species such as staghorn sumac (Rhus typhina), black cherry, various dogwood species, viburnum species, members of the rose and raspberry families, and sapling hardwoods mesh to create the fabric of a diverse forest meadow edge.

The abundance and variety of fruiting plants attracts numerous species of songbirds such as yellow warblers (Dendroica petechia), mockingbirds (Mimus polyglottos), catbirds (Dimetella carolinensis), cardinals (Cardinalis carninalis), and goldfinches (Carduelis tristis). All species nest in the Arboretum, and some feed on the berries and seeds. Wharblers and swallows enjoy the abundant insects that pollinate the flowers, herbs, and other plants.

Edge habitat ranges in age from yearly mowed areas, exhibiting perennials such as the aster family, goldenrods, and vervian to woody shrubs mowed on a three-to-five year cycle allowing for taller denser stands. Many bird nests are found in this dense mass of honeysuckle, multiflora rose, and dogwood.

Travel corridors are less noticeable and generally hidden within the shrub layer of the edge habitat. Starting in late February with the first hint of spring, raccoons and skunks begin a nightly pilgrimage exploring the meadow edge, as omnivorous opportunists consuming a wide range of foods.

The dense stands of gray dogwood left to grow for five years provide the structural support for catbird and cardinal nests. Much older successional growth nearer the forest edge provides support for wild grapes to climb. Catbirds remove the exfoliating bark from the wild grape vines to mold the interior lining of their nests.

Once the nesting season has ended and the frosts of autumn have blanketed the meadow, white-footed mice utilize the abandoned catbirds' nests to store swamp rose and multi-flora rose hips in. The mice leave their warm winter homes deep within the aging apple trees each evening to reclaim their winter supply of food stored in the edge habitat nests. Barred owls watch the meadow shrub edge intently, waiting for mice and voles to come out and feed each evening.

Orchard Habitat
While the shallow, rocky till made farming nearly impossible, it did provide sufficient depth, nutrient availability and gently rolling slopes upon which to grow apples. In fact, 12 acres of the Arboretum were productive orchards as recently as the 1960s. The entire area off Taylor Road is where much of the Arboretum's development has been focused in part of the abandoned apple orchard. Several other orchards in various states of forest succession can be found on the property. In this section, the orchards will be classified in one of three ways:

  • Maintained
  • Early succession
  • Late successionii

Maintained Orchards can be found in the Taylor Road region as well as at the end of Wood Lane in the eastern most region of the property. Our definition of maintained orchard does not mean sprayed and heavily pruned; in fact, quite the opposite. Meadows around the sixty year-old apples are kept open, and poison ivy and multiflora rose is routinely removed from the aging trees. Eastern kingbirds (Tyrannus tyrannus) and robins (Turdus migratorius) frequently nest in these trees. As old trees die some are left standing for Woodpeckers (Picidae) to mine. The dead and peeling bark provides narrow, dark crevices for little brown bats to escape the light of day.

Early Succession in the Arboretum can be observed in two areas: just beyond the southern end of the Rhododendron trail and meadow on the left side of the Wildflower trail, and in the northeast corner of the property near the easement in from Wood Lane. Early stage succession is rich in plant and animal diversity, in many ways quite similar to forest/meadow edge habitat, except that no open meadow borders the orchard. The transition from dense shrub sapling growth to mature forest is unbroken. In the case of the first example referred to above, the abandoned orchard is bordered by a red maple swamp.

Many of the apple trees have died but are still standing, providing denning areas for raccoons, red and gray squirrels, deer mice, and white-footed mice. These areas are densely overgrown with honeysuckle and multi-flora rose providing nesting habitat for many of the same species found in the edge habitat. Blue jays (Uanolitia cristata) and yellow-billed cuckoos (Loccyzus americanos) nest in this protected environment.

A wide variety of songbirds are attracted to early succession orchards to feed on the abundant insect and berry crop found there. Sharp-shinned hawks (Accipiter striatus) feeding on the songbirds spend much of their hunting time motionless in trees along the forest orchard edge waiting for an opportunity for a surprise attack.

Only one example of Late Succession Orchard can be observed in the Arboretum. The 2-acre area is located on the west side of the Highlands/Bog Loop trail as you come up the hill from the bog, near the Wood Lane trail intersection. You have to really search just to find the remains of the apples that have all died and fallen to decay. This unmanaged landscape features 20 to 30 year old red oak (Querius rubra) and white ash (Fraxinos americana), with red maple making up the orchard's southern border. The dense canopy reduces shrub and herbaceous growth on the young forest floor.

With the established growth of red oak, leaf litter covers the ground in this successional stage orchard, providing habitat for ruffed grouse (Bonasa umbellus) to forage in. The western edge of this orchard is bounded by the esker, with spring runoff following the base of the slope. Larger wildlife such as deer, fox, and coyotes travel along a wildlife corridor leading to the bog and wetlands at the south end of the property.

Uplands Hardwood Forest Habitat
Deciduous forests represent 17 acres of the Arboretum landscape. Hardwood forests represent a complex ecosystem stratified into canopy, understory, and forest floor dwellers. The largest region of hardwood forest can be found on the east side of the old farm ponds running along the ridge in a north/south orientation.

This is an excellent place to observe warblers and other insect eating songbirds on their northern migration each April and May. Many of these warblers have just returned after having wintered in Central and South America living high in the canopy of tropical rain forests. These behavioral characteristics continue during the northern migration making observation difficult without binoculars and a lot of patience. Warblers such as chestnut sided (Dendroica pensylvanica), Canada (Vilsonia canadensis), black and white (Mniotilta varia), and blackburnian (Pendrolla fusia) spend several days each spring in the hardwood uplands at the Arboretum.

The red-eyed vireo (vireo olivaceus), a member of the warbler family, remains in the Arboretum throughout the summer breeding season and nests on sapling understory hardwoods 10 to 30 feet above the forest floor. Both wood (hylochia mustelina) and hermit thrushes (catharus guttatus) nest in the Arboretum's hardwood forests. Their distinct songs can be heard while walking along the Wildlfower Trail near the native New England wildflower collection.

Far fewer shrub species exist in the partial sunlight of the dry hardwood floor. With fewer shrubs providing food and camouflage, far fewer species of both small birds and rodents live in this region in comparison to the forest/meadow edge habitat. There is much less protection from the keen observation of forest hawks such as the sharp-shinned (Accipter striatus) and broad-winged (Buteo platypterus).

Great-crested flycatchers (Myiarchus crinitus) nest in abandoned woodpecker cavities near the wildflower collection and on the esker, in both instances utilizing dry uplands hardwood forests for nesting. In each case, the flycatchers nest in woodlands bordering significant wetlands areas where insect life is abundant.

White Pine Forest Habitat
White Pine forest Habitat represents 8 acres of the property. The largest stand borders the esker's ridge by a hardwood forest and its westerly side by a red maple swamp. A second dense white pine (Pinus strobus) stand can be found at the end of Wood Lane.

The Wood Lane pine stand provides the isolation necessary to attract roosting great horned owls (Bubo virninianus). Numerous owl pellets have been found in the dense pine needle litter. Crows find privacy high up in these pine stands as well, sometimes building nests on abandoned gray squirrel nests.

The pine stand found along the western boundary of the property adjacent to the esker provides shelter for a pair of red-tailed hawks (Buteo samailensis) that have returned each year to nest. Flying squirrels occupy abandoned downy woodpecker (Picoides pubescens) holes in dead white pine trees shadowed below the 75 year-old white pine canopy.

The dense shade and thick acidic decomposing needle litter on the forest floor limits shrub growth. Few songbirds find the pine stand to be a safe place to nest. An exception can be found along the telephone easement running through the property where sapling black birch (Betula lenta) and red maple (Acer rubrum) grow in profusion. For large animals such as white-tailed deer, red fox and coyotes, the unmaintained telephone easement provides an important east/west travel corridor through the Arboretum.

Red Maple Swamp / Farm Ditch Corridor Habitat
As discussed in the hydrology section and again in describing the wetlands communities found in the Arboretum, water tends to flow from north to south through the property. In a very simplistic way, so does wildlife. The most clearly defined wildlife travel corridors follow the drainage ditches. This is certainly true for both raccoon and skunks that seek crustaceans, frogs, and whatever else may be found in and around the flowing ditches.iii

When designing the first plantings in 1986 along the drainage ditch near the Taylor Road entrance, special attention was given to use native shrubs having a benefit to wildlife, in some instances bearing fruit, with other species providing cover. This was our first attempt to create a wildlife travel corridor in an otherwise intensely developed portion of the property. Our efforts have been rewarded as each spring warblers feed on the first hatch of black flies and midge flies along the corridor.

The Arboretum has a modest population of white-tailed deer, a small herd of approximately three to five family members that utilize red maple swamps as travel corridors. This herd ranges between the Nashoba Brook floodplain marshes to the east, through the Woodlawn Cemetery to the Arboretum, and to the south to the open meadow grasses and clover growing on the town landfill. To the west beyond the Arboretum, they encounter a wall of residential development.

Farm Pond Habitat
In 1990, permits were obtained under the Wetlands Protection Act to excavate a 1600 sq. Ft. area of marsh and create a wildlife beneficial farm pond. The criteria in selecting the location focused on the pond's proximity to the handicapped trail system then under construction, visibility, and its full-sun orientation. At that time the only existing open bodies of water on the property were the two very old man-made farm ponds, both shallow and densely shaded.

The constructed wildlife pond fluctuates from a spring maximum depth of approximately four feet to completely dry during dry summers as in 1997. The fluctuating water depth has its advantages for many aquatic insects as well as several amphibian species such as American toads and green frogs, both species found to breed in the shallow pond. Breeding success for both frogs and toads is very high as the occasional drying of the pond eliminates a permanent fish population. The dry, down-cycle also aids the rate of leaf and weed decomposition on the pond bottom, allowing for more oxygen to be present, elevating the rate of aerobic bacteria decomposition.

Native shrubs and trees were successfully planted around the perimeter of the pond increasing species diversity and attracting a variety of insect eating birds. Eastern phoebes (Sayornis phoebe), eastern kingbirds, yellow warblers, and tree swallows (Iridoprocne bicolor) are common visitors to the pond. A resident pair of mallard ducks (Anas platyrhynchos) nests near the pond each year.

Open water is fundamental to a well-balanced wetlands ecosystem. The initial attempt to create this important habitat feature has met with much interest by Arboretum visitors and acceptance by many native species.

Old ponds / vernal pools
Years of accumulated silt and decomposing leaf litter have left the upper farm pond with water depths of less than three feet. During the summer of 1997, the upper pond was completely dry. Even in its current state, the upper pond is frequented by an interesting variety of bird species, especially during the spring migration when the willow trees (Salix nigra) along its shoreline host many species of warblers. Wood ducks (Aix sponsa) frequent the shallow pond; and, in 1993, a wood duck box was placed along the pond's eastern shoreline. Green herons (Botorides striatus) and great blue herons (Ardea herodias) can be observed wading in the water throughout the summer months.

Both farm ponds are bordered by upland hardwood forests along their eastern shorelines, creating sufficient habitat for the ponds to be used by wood frogs and spotted salamanders as breeding areas. Further study may indicate how important these ponds are as active vernal pools.

Bog Habitat
Studying the interesting variety of life on the bog is a difficult proposition. Fortunately, for those visiting the Arboretum's bog, a 220 foot long boardwalk was constructed by two Eagle Scouts in 1989. The elevated deck crossing the southwest corner of the bog allows for a superb opportunity to observe this unique wetlands landscape.

The surface or mat of the 2.5 acre bog consists of a dense layer of sphagnum moss (sphagnum palustre). These chlorophyll enriched "green" leaves grow perpendicularly atop previous years of growth. As the organic layers below the bog surface slowly decompose, a deep bed of peat is assembled. The process of creating peat occurs very slowly, at a rate of about 1 inch of accumulation every 100 years.iv Depth probing of the peat done in March, 1998 indicates a maximum depth of about 16 feet.

Sphagnum moss is able to retain approximately 25 times its own weight in water and acts as the environmental control mechanism for most other life living on the bog. The bog remains cold, even frozen just below the sphagnum surface well into the spring, limiting the ability of plant roots to absorb water. Though the wetlands is completely saturated, very little of the water can be utilized by the plants inhabiting the bog.

Members of the heath family common to the bog, such as Leatherleaf (Chamaedaphne calylulata), retain their leaves for two years with nitrogen stored in second year leaves being made available for the next year's growth; as nitrogen for leaf growth in the bog soils is not found in a complex useful for plant development. The Leatherleaf leaves are thick and do not give up water readily. The plants grow in dense, shrubby masses and provide nesting habitat for mallard ducks and red-wing blackbirds (Agelaius phoeniceus). Ribbon snakes can often be seen from the boardwalk moving through the Leatherleaf tangle.v

The bog's harsh environment has caused some plants to pursue different methods of procuring sufficient nitrogen to survive. In this instance a group of plants has actually become carnivorous in order to augment the limited availability of nutrients. Northern pitcher plants (Sarracenia purpurea) are the Arboretum's only plant carnivore, and can be observed from the boardwalk. These unusual insect-eating plants have evolved in such a way as to consume insects, and occasionally salamanders and even frogs, to provide the protein necessary during the flowering and seed production season. Insects lured by a fragrance emitted from the plant enter the mouth of the pitcher, slip into an enzyme enriched rainwater reservoir, and drown in a bath of digestive juices. It is possible that sundew, another insect eating plant, may also exist in the bog. However no locations have been confirmed.

i Tracking and the Art of Seeing (Paul Rezendes, Camden House Publishing, Inc., 1992)
ii Forest Wildlife of Massachusetts (Richard M. Degraaf, David A. Richard, University of Massachusetts, Cooperative Extension, 1987)
iii Tracking and the Art of Seeing (Paul Rezendes, Camden House Publishing, Inc., 1992)
iv Saving Graces, Sojourns of a Backyard Biologist, (Roger B. Swain, Little, Brown and Company, 1991)
v Bogs of the Northeast, (Charles W. Johnson, University Press of New England, 1985)