| Return to Wildlife-friendly Management Start Page |
Reprinted from the book entitled
Managing Conservation Land: The Stewardship of Conservation Areas, Wildlife Sanctuaries, and Open Space in Massachusetts
by Peter Westover (Belmont MA: Mass. Soc. of Municipal Conservation Professionals, 1994) 224_pp.
Agricultural Management: Fields and Meadows
Many towns own conservation fields--wet meadows, dry upland fields, wet or dry hayfields that are regularly harvested, abandoned fields with successional weed species and woody invaders, corn and grain fields, and pastures. All of those require active management to maintain openness or change the vegetation mix, minimize trampling in sensitive areas, optimize the habitats of rare or declining species of birds, insects, and herbaceous plants, and maintain the scenic value of the fields.
There are by now many valuable precedents to follow in agricultural land management within Massachusetts and elsewhere. On some areas, notably the Daniel Webster Sanctuary in Marshfield, the Mass Audubon Society has recently carried on a scientific evaluation of various field mowing regimes and the effects of each on populations of nesting birds, small mammals, raptors, wildflowers, and butterflies. Various towns have also experimented with a range of field management types, and are becoming more sophisticated in developing goals that emphasize wildlife habitat improvement.
This chapter covers suggested field management goals, state of the art management steps, sample mowing or cutting regimes for specific purposes, and summaries of a few important articles on field management in relation to bird and small mammal populations. Orchards are covered in a separate chapter.
For fields on conservation lands, productivity in hay bales or tons of corn per acre rarely receives as high priority as other field values, especially habitat and scenery. In the statewide scheme of things, fields managed for habitat are in shorter supply than those managed for maximum production.
In most cases, one cannot optimize yield and habitat simultaneously. With hay, in particular, the cutting and removal of two or three crops per season renders a field practically devoid of the thatch that shelters small rodents, reduces the field's floristic species diversity, leaves the field without weed seeds or plant cover for wintering birds and small mammals, and makes the field fairly inhospitable to those species the following spring. Cornfields managed for high yields usually receive high doses of herbicides, which eliminate forbs and most grasses, and often sit idle with little or no winter cover following late fall harvests for feed corn or silage. Pastures managed for a maximum healthy herd size are likely to be low in species diversity and plant cover.
On the other hand, fields cannot be managed in a vacuum. Farmers managing town fields by rental agreements must produce a profit from the crop and usually need considerable encouragement, often in the form of low rental fees, to assist in meeting habitat management objectives. Mowing done directly by town forces may cost more than mowing by rental agreement, but can usually be done to a more demanding schedule, tailored for the advantage of particular plant and wildlife species. In-house mowing can cost $20 or more per acre per year including fuel, vehicle maintenance, and labor.
As a rule for habitat management in open hayfields, cutting or mowing should usually be kept to the minimum that will still prevent woody plants from taking over. In most instances, mowing too often will reduce a field's attractiveness to butterflies, knock out field wildflowers during at least part of the growing season, interfere with bird nesting patterns, and at least partially eliminate cover for voles and other small rodents.
There are exceptions. To encourage upland sandpiper use near the Massachusetts coast, grass should be kept short. To allow maximum ponding on flood prone fields, those fields should be kept mowed at least in spring and fall. And the perpetuation of certain herbaceous species may require frequent mowing.
As another general rule, one should not settle on a cutting regime without the prior monitoring of plant, insect and wildlife species, including invasive exotics that may be expanding to the detriment of native species. Each field should be managed with an eye for the special needs of the important or unique species present.
Management should also reflect an awareness of the balance of open land types within the town and the outlying area. It makes little sense to manage every field in the same way and on the same schedule unless there is a drastic regional shortage of one particular vegetational community.
The following are two examples of organizations with well thought out management goals for open agricultural areas. First, as with certain other British national parks, the Lake District National Park in northern England aims to encourage the continued viability of the family farm as the basic agricultural unit, discourages overgrazing by lowering use fees, manages hay meadows to maximize the number of species present -- to support "a wealth of wildflowers and insects," especially butterflies -- and cares for roadside verges in a similar manner so as to counterbalance the, loss of herb-rich meadows and other wildlife habitats.
Second, the Massachusetts Audubon Society puts a premium on managing for significant populations of rare or declining native species, restoring old fields and reintroducing native species where appropriate, and working to achieve scenic attractiveness and a diversity of seral stages in field communities that have no important native species (Broadmoor Management Plan 1990).
Many of those goals make good sense for towns that manage fields on conservation lands. Starting with that framework, subsequent field-by-field inventories allow towns to set more specific goals that can be achieved by planned management.
The following are examples of schedules for mowing or brush cutting upland fields for specific wildlife or floristic purposes. It will be obvious that these schedules in general do not maximize hay production. It is also important that fields under any of the proposed schedules be periodically monitored to measure the effects of management on wildlife and plant species.
1. Frequent mowing. In the few coastal areas where upland sandpipers need encouragement, fields should be kept in short grass from April through September. Where fields are managed for maximum hay production, a third or fall cutting is often made, but can leave fields with grass too short for any late fall or winter cover.
2. Two to four cuttings per season. Where noxious weeds like knapweed and burdock must be controlled, two mowings each season will help, and some have found that four or more mowings each growing season for several years in a row may be necessary. Multiple mowings within a growing season are also probably needed to discourage the spread of woody invaders like European buckthorn and staghorn sumac.
3. One early spring mowing per season. If the field is dry and firm enough to support tractor mowing in the spring, an early mowing will allow good regrowth during the summer and fall and will leave cover and seeds for wildlife foraging during the winter months. This cannot be recommended for fields with grassland nesting birds.
4. One early summer mowing per season. One cutting in late May or early June will allow small mammals to return by fall for winter raptors and, as at the Canoe Meadows Audubon Sanctuary, will encourage certain butterflies like the veined white (west of the Connecticut River) and great spangled fritillary without harming other butterfly species. Limiting mowing to once per season or less will encourage many butterflies.
5. One or more cuttings delayed until at least July [4-15]. Delaying mowing until after early July in the southeast or after July 15 in other parts of the state will allow bobolinks to, complete their nesting activities.
6. One cutting delayed until late fall. Mowing or prescribed burning in the late fall after herbaceous plants have gone to seed will suppress thickets of shrubs and small trees but will leave fields bare of winter seeds and cover. An annual, late fall cut will help maintain a predominantly grassy field. Note that the Mass Department of Environmental Protection generally restricts agricultural burning permits to the period January 15 through April 30.
7. One mowing every three years. Unless woody vegetation becomes a problem, mowing no more than once each three years without removing the hay will allow the thatch buildup necessary to support small mammals. Mowing intervals of three or more years will benefit small mammal communities of sites known to include white-footed mice and meadow voles. More frequent mowing changes the microhabitats important to small mammals and prevents population recovery to pre-mowing levels. To keep woody islands within the fields under control, hand cutting may be necessary.
8. One mowing every 3-5 years. A 3-5 year mowing regime, where the exact time between mowings depends on the amount of woody invasion, can maximize the species richness of native wildflowers and favor forbs like milkweeds and asters - nectaring resources for many common species of butterflies - over grasses. A spread of goldenrod species may make it necessary to target areas dominated by those species for more frequent mowing. Areas of goldenrod should be mowed yearly in late summer before the plants have set seed and after most of the plant reserves have been used U. Anderson pers comm. re MAS Broadmoor Wildlife Sanctuary). After it appears that the goldenrod is under control, the field can be mowed as a single unit. If scattered woody invasion occurs between mowing years, it can be controlled by hand cutting.
9. Create periodic, small-scale disturbances. To maintain populations of unusual plant species, special treatment may be necessary. To encourage fringed gentian, for example, the creation of bare soil patches allows for gentian seed germination, and hand-cutting larger trees every three years maintains enough light to perpetuate the species. Note that some species may be favored by prescribed burning, which effectively contains woody vegetation and maintains the open habitat required by certain rare species. Intentional burning, if allowed by local open-burning laws, also reduces the accumulation of organic litter, lowers the threat of catastrophic wildfires, releases nutrients into the soil, and can rejuvenate grassland habitat.
10. Maintenance in shrubby, semi-open condition. To encourage field sparrows, other fruit-eating birds, and certain butterflies and small mammals, fields may be maintained in a shrubby state by intermittent hand cutting or selective brush mowing. Structural diversity can be maintained by mowing around islands of rocks and trees, leaving shrubs associated with the taller remaining trees.
Note that land managers should observe state and local permitting requirements in mowing wet meadows.
11. Annual mowing for vernal pools. Mowing very wet areas annually can allow better ponding in fields for resting areas for spring and fall migrating waterfowl. Permits are required.
12. Annual mowing for hay or mulch. Mowing wet meadows, for example stands of tall grass like reed canary, can encourage their use by bobolinks if done each year after mid-July. Bobolinks prefer a minimum of
thatch, and removal of the hay crop will keep that heavy thatch from developing.
13. Cutting (not haying) once every three years. Mowing wet meadows once every three years and leaving the crop in place encourages more forbs for butterflies and other invertebrates. The thatch left in grassier areas favors small mammals. Although adjacent wetland areas with stands of sedges or cattails can be dry enough to mow in the occasional dry summer, it is important to protect them from cutting, especially if species like marsh or sedge wren or least bittern are using them for nesting.
14. Intermittent cutting as needed. In very poorly drained meadows, intermittent cuttings will reduce woody growth and allow sporadic flooding in spring and fall for waterfowl.
16. Grazing of wet meadows. Wet meadows are especially favorable for grassland birds in spring, but can be easily damaged early in the season by the trampling of cattle or the use of hay equipment.
In general, many creatures cannot survive mowings, done even every 2 to 3 years, so that unless high productivity or serious removal of woody invaders is necessary, it is helpful to extend the time between mowing seasons as much as possible. The mowing of field edges helps eliminate shade from the field and keeps invading plant species from encroaching, but may have detrimental effects on small creatures.
Cornfields attract various birds and mammals, although the heavy use of herbicides normally associated with corn crops can deter many species. Pheasants, doves, starlings, raccoons, deer and others will visit cornfields in the late summer and fall, depending on when the crop is harvested and how thoroughly the harvesting process removes the grain. It may be helpful to leave some uncut rows of corn at the edge of the field to provide winter feed and cover for Canada geese, other migrants, and resident wildlife, although corn harvesting often leaves considerable corn debris for winter feeding anyway. It can also help to sow a winter cover crop immediately after harvesting the corn rather than chopping the field clean and leaving it bare. Where herbicides have been used on corn, an extra year will probably be necessary before putting the field into an alternate crop. Where cornfields are rented out, it is important to ensure that at the end of the field's use for corn it is re-harrowed to remove deep furrows and, preferably, planted to a good hay or other cover crop.
When harvesting wheat or other grain crops, using flushing bars on cutting equipment can reduce the killing and injuring of field birds (D. Snyder, pers com). Combines tend to leave little grain debris for food or cover, whereas smaller pickers leave more stalks and leftover grain. As with corn, a winter cover crop is better than a bare field in preventing winter erosion and windblown soil loss and in providing at least minimum wildlife cover.
It is usually best for wildlife habitat, erosion control and windbreaking to leave wide brush rows along fence lines and along streams adjacent to fields. As with the delaying of hay cutting to avoid interfering with bird nesting, there are tradeoffs: the more brush one leaves along the edges, the more the east, South, and west edges of fields will be shaded and the more the brushy edge will send weed seeds out into the field. Also, the more difficulty the farmer will have with woodchucks, raccoons and other animal pests, as hedgerows provide shelter for those creatures. Eliminating hedgerows, altogether is usually detrimental, although for bobolinks, a large unbroken expanse of field is optimal.
[Photo caption: If mowed after July 15, large hayfields can attract nesting bobolinks and meadowlarks. A barn owl nest box has been installed in the barn at the edge of this field. ]
Grassland nesters -- meadowlarks, bobolinks, savannah sparrows, Henslow's sparrows, grasshopper sparrows, upland sandpipers, red winged blackbirds and others -- have become the targets of research and state-of-the-art management practices on many refuges. Some of those species are in a state of recent population decline due to the loss of agricultural fields and changes in hayfield management methods. The intentional management of fields to help reverse those declines is a worthy goal.
One of the most thorough papers dealing with field nesting birds is a 1988 Cornell doctoral dissertation by E.K. Bollinger entitled "Breeding dispersion and reproductive success of bobolinks in an agrarian landscape. " Bollinger examined the preferences of several species of field-nesting birds for different conditions on hayfields in New York state. His results offer clues to the type of management that may help reverse population drops in certain of those species, particularly bobolinks, which have declined dramatically in the eastern United States since 1900, especially in the last 20 years.
Bollinger found that bobolinks are much more likely to nest in fields larger than 5 acres. Large fields had greater overall bobolink densities, greater densities of male bobolinks, and greater numbers of bird species than small fields. Bobolinks and savannah sparrows also avoid field margins and wooded edges, where they suffer higher predation and cowbird parasitism.
Bobolink success was also positively correlated with the number of years since the replanting of the field in legumes. The older the field since replanting, the higher is the species richness. The sparser, lower, patchier, and more grass-dominated the vegetation, the better-suited the field is to bobolinks. Younger fields tend to be legume monocultures, which are generally avoided by bobolinks.
[ref: Bollinger, Eric Kenton, 1988, Breeding dispersion and reproductive success of bobolinks in an agrarian landscape. PhD Diss, Cornell University, Ithaca. See, Bollinger and T.A. Gavin, 1992. Eastern Bobolink Populations: ecology and conservation in an agricultural landscape, Pp.47-506 in J.M. Hagan, III, and D.W. Johnson, eds., Ecology and Conservation of Neotropical Migrant Landbirds. Smithsonian Inst Press, Washington DC.]
The trend over the past 40 years or more has been toward earlier replanting of hayfields to legumes. Forty years ago, alfalfa and timothy/clover stands were commonly left for more than 10 years before replanting, but now it is usually 4-5 years.
Bobolinks are also significantly less abundant in fields where woody vegetation has become established.
Bobolinks, Henslow's sparrows and grasshopper sparrows nest late and are highly susceptible to early mowing. The trend toward earlier and earlier hay cutting in recent decades has thus diminished their nesting success. (Although meadowlarks complete their first brood earlier than bobolinks, they tend to have two broods to the one of bobolinks, and the influence of cutting on their nesting success is thus harder to measure.) Harvesting with modern mowing and raking equipment nearly always destroys the nests, sometimes kills the birds themselves, and often attracts predation by ring-billed gulls and crows. Of those bobolinks with nests destroyed by mowing, 42 percent re-nested in adjacent fields but most of those nests were again destroyed by cutting.
Not surprisingly, bobolinks tend not to return to fields where fledgling success has been low.
Two other recent papers, both written for the Daniel Webster Wildlife Sanctuary in Marshfield, also address current grassland management issues. The sanctuary is 444 acres in size and is dominated by seasonally flooded meadows and upland grasslands, making it an excellent site for field management study.
The first, the Ecological Management Plan for the sanctuary (Mass Audubon 1987), discusses several objectives for the sanctuary. Mowing is used to create a mosaic of vegetation on the various meadows to optimize natural diversity. Both upland and seasonally flooded fields are maintained in an open condition for upland sandpiper and winter raptor habitat. Burning and grazing are discussed as future management options, the latter to be used specifically to create structurally different patterns of vegetation. Visitor use is kept to designated trails and human encroachment is prevented in nesting and brood-rearing fields during breeding seasons.
The plan also includes the management recommendations of R.P. White and S.M. Melvin (1985) for the rare grassland birds upland sandpiper, northern harrier and grasshopper sparrow. They recommend no mowing during the period May 1 to July 31 to reduce nest destruction and mortality of incubating adults of flightless chicks, but recommend at least one mowing a year.
The second paper, a study by Nancy Sferra entitled "Field management, small mammals, and wintering raptors at Daniel Webster Wildlife Sanctuary" (MAS, 1990) focuses on the development of an optimum mowing rotation for the continued support of small mammal and winter raptor populations. She notes that meadow voles are the most important prey species at Daniel Webster, and found that July haying brings drastic declines in vole numbers through direct mortality from machinery and through loss of cover resulting in increased vulnerability to predation.
For almost all fields, vole populations were lowest the spring following mowing, with peak vole densities occurring the second summer after mowing. Mowing only every other year allowed small mammal populations to recover to densities high enough to support wintering raptors on the sanctuary. Winter raptors almost universally avoided hayfields, with their very low prey density, in favor of fields with sufficient food and cover for winter populations of small mammals.
Open fields, especially poorly drained meadows, can be rich in botanical species, some of which may require special management attention to perpetuate. A recent list compiled over a 5-month period for a nearly level, poorly drained conservation field typical of those of the Connecticut River Valley, the MacLeod Meadow in Amherst (Johnson and Searcy 1991), included 95 species. Among them were 5 ferns, one Equisetum, 10 species of Carex, 14 other grass and sedge species, 49 herbaceous species (including the orchids Calopogon pulchellus, Platanthera lacera, Rpsycodes, Pogonia ophioglossoides, and Spiranthes cemua), 11 shrub species and 5 tree species.
On the average, that field is mowed once every three years, which -is sufficient to keep woody invaders confined mainly to several small shrub islands and allows sufficient sunlight for a rich variety of nonwoody plants. The wetter side of the meadow is dominated by reed canary grass (Phalaris) and has a much lower species richness than the opposite side, which is a borderline wetland with many facultative species present.
A recent species inventory for a sloping meadow complex one mile to the south (the Atkins Flats Conservation Area), with a greater variety of soil moisture conditions (Slater 1991), included 141 species -- 8 trees, 23 shrubs, and 110 nonwoody species. The fields of Atkins Flats are rented to a local farmer for hay production, and the various mowing regimes in practice have created a mosaic of tall grass, short grass, and grassy shrub-filled areas with an exceptional variety of field-nesting birds and visiting raptors.
Recent work in Massachusetts on barn owls (Davis 1991), bluebirds, and other field-related bird species provide helpful suggestions for the management of open areas, including the most effective placement of nest boxes and artificial perches.
Barn owls are listed as a species of "special concern" in the state, under stress because of the decline of farming and increased urbanization. A ten-year Massachusetts Audubon barn owl nest box program on Martha's Vineyard has been quite successful, with some 28 breeding pairs recorded there in 1993 (versus none from 1960 through 1974). Other nest box programs around the state, especially near the coast, also show promise, with boxes being placed primarily in locations known to have seen nesting barn owls in the past. Boxes are placed inside barns at least 22 feet above the ground with a 6 x 6 inch opening to the outside, and in the vicinity of open grassland with high vole populations (D. Ziomek, pers comm). Kestrels and other cavity nesters may use the boxes if no barn owls show up.
Poles placed in open fields as perches will often be used by raptors, as will natural dead snags. If bobolink or other small bird nesting is of high priority in a given field, however, attracting raptors that may prey on their young during the nesting or fledging season may be a mistake (W. Healy, pers comm).
The following are some additional suggestions:
- *Fields of less than about 3 acres are too small to benefit many species of nesting birds. They have too much edge to attract forest nesting species but not enough area for field nesters, and cowbirds tend to be a problem in small fields.
- *Tile drains in fields allow planting equipment to use the land earlier in the season without damaging the soil and creating ruts. (On the other hand, draining wet meadows artificially can change their plant composition and their habitat characteristics and is is subject to state wetland regulations.)
- * It may be necessary to protect fields from human trampling where uncommon flowers like fringed gentian are found or where there are wildflowers that attract particular insect species (as with Aster umbellatus, the host for Harris checkerspot butterfly).
- * Excessively drained areas chemically treated to get rid of forbs, seeded with grasses and hayed annually become practically devoid of small mammals.
- * The removal of hedgerows can be a mixed blessing for wildlife: the practice can eliminate nesting spots but can also increase the amount of contiguous meadow, eliminate edge, and remove a potential source of woody invasion of the field.
- * Loss of natural vegetation quality can result from fertilizing, draining and leveling the natural topography.
- * Supplementary feeding of grazing animals can keep them on a field too long; they should stay on a site only if they can get adequate nutrition from the pasture vegetation.
- * Dandelion seeds are a common food item for grassland birds; stoutstemmed grasses like orchard grass (Dactylus glomerata) and smooth brome (Bromus inemis) are important for redwing nesting support; bobolinks, savannah sparrows and other ground-nesting species commonly use low forbs as nest cover.
- * Hedgerows, in fields attract harriers and short-eared owls.
- * Neck-high reed canary grass can be too high for raptors in their hunt for rodents.
- * Upland sandpipers prefer grass 6 to 8 inches high and in spring are attracted to fields that were mowed in the previous fall. Grazing can encourage this species.
- * David Ludlow, Daniel Webster Sanctuary manager, reports that knapweed, a problem on the mowed fields at Daniel Webster, is a lesser problem on grazed areas. And on some fields plowing and disking can reduce annual weeds and produce dirt patches used by sparrows.
| Return to Wildlife-friendly Management Start Page |