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The following document is also available for download.
Clickable Table of Contents I. Presettlement Vegetation and Natural Disturbance
II. Postsettlement Vegetation and Historic Land Use III. Management Challenges and Recommendations
Pine barrens (also called pine-oak forest by Westveld et al. 1956, Lull 1968 but herein distinct from red oak-white pine) are characterized by pitch pine (Pinus rigida) and scrub oak (Quercus ilicifolia) with ericaceous groundcover of black huckleberry (Gaylussacia baccata), blueberry (Vaccinium spp.), and wintergreen (Gaultheria procumbens). Sweetfern (Comptonia peregrina) and bracken fern (Dennstaedtia punctiloba) are also important in many areas. Pine barrens typically occur on xeric sand plains of the northeastern coastal plain (Boerner 1981, Forman and Boerner 1981) or on the sandy glacial outwash of major river valleys (Motzkin et al. 1996, Seischab and Bernard 1996, Copenheaver et al. 2000, Howard 2003; Figure 1). Sediment cores taken from lakes near present-day pine barrens ecosystems contain large amounts of pitch pine pollen, indicating that these habitats have been present for thousands of years (Motzkin et al. 2002, Parshall and Foster 2002, Parshall et al. 2003, Copenheaver et al. 2000). The presence of rare obligate Lepidopteran fauna associated with pine barrens vegetation (Patterson and Finton 1996, Wagner et al. 2003) suggests long-term presence of pine barrens throughout at least recent evolutionary time. As pitch pine requires bare mineral soil for establishment from seed, is relatively shade-intolerant, and possesses adaptations to survive fire such as thick bark, epicormic buds, the ability to sprout, and serotinous cones in some areas (Givnish 1981, Burns and Honkala 1990), periodic stand-replacing disturbance is required to perpetuate pine barrens across time scales longer than 100-150 years. Flat expanses of droughty soils where barrens vegetation is usually found contribute to the spread of periodic wildfires, which eliminate competition from shade-tolerant species and prepare the seedbed. Indeed, charcoal is associated with pitch pine pollen in lake sediment cores representing the last 1500-2000 years of fire history (Motzkin et al. 1996, Parshall and Foster 2002). After a half-century of efficient fire suppression and urban development following four centuries of land clearance and timber extraction, the amount of area in northeast pine barrens has declined from historical levels (Patterson and Finton 1996, Parshall and Foster 2002). Conservation and long-term management of these unique ecosystems requires an understanding of the natural communities and their disturbance regimes prior to modification by colonial and contemporary land use (Parshall and Foster 2002, Lorimer and White 2003). Moreover, an understanding of how historical land use has modified species composition and ecological processes over the last 400 years, or an understanding of each area’s “land-use legacy,” is critical to designing appropriate management strategies (Motzkin et al. 1996, Hall et al. 2002, Foster et al 2003).
I. Presettlement Vegetation and Natural Disturbance
There are few satisfactory methods for studying presettlement vegetation and disturbance, but the use of multiple methods paints a more accurate picture of forests of the distant past than the use of just one method. Lorimer and White (2003) list a number of these techniques, including 1) pollen and charcoal from lake sediment cores, 2) land surveys that record witness trees and written descriptions and accounts, and 3) reconstructions from modern old-growth stands.
Palynological records show pine-oak vegetation with associated charcoal deposits in parts of Massachusetts (Motzkin et al. 1996, Motzkin et al. 2002, Parshall and Foster 2002, Parshall et al. 2003), Maine (Copenheaver et al. 2000), New York (Jordan et al. 2003), New Jersey (Lorimer and White 2003) and Delaware (Kirwan and Shugart 2000) for at least the last 1500-2000 years, with associated charcoal deposits. Before settlement (indicated in the sediment cores by a decline in tree pollen associated with a sudden influx of herbaceous pollen such as grass, ragweed, and rumex; Parshall and Foster 2002), pollen on Cape Cod showed a pitch pine forest type on flat sandy outwash (Parshall et al. 2003), characteristic of pine barrens habitat. These cores were associated with more charcoal than cores of other presettlement forest types, indicating higher historical fire frequency and/or intensity. Heath and grass pollen were low, indicating full forest cover. Parshall and Foster (2002), studying pollen from lakes throughout New England , also identified a forest type characterized by pitch pine and oak. This type occurred in coastal areas such as Cape Cod and Long Island , as well as inland river valleys such as the Connecticut Valley of Massachusetts. Grass and herbaceous pollen were rare in presettlement, indicating a forested landscape. Distribution of presettlement forest types and charcoal were broadly related to climate, with pitch pine-oak having the highest associated levels of charcoal. In New England , fire frequency (inferred from charcoal in sediment cores) was higher before 500 AD than it was immediately before settlement, possibly due to climatic changes toward a period that was cooler and wetter (Parshall and Foster 2002, Parshall et al. 2003). However, fire continued to be an important natural disturbance in northeastern pine barrens forests before and after their settlement by Europeans until fire exclusion became widespread in the mid-twentieth century. According to Lorimer and White (2003), pine barrens have the highest incidence of severe disturbance of any northeastern forest type. Fires were most likely frequent and extensive (large areas) in the 1.1 million acre New Jersey Pine Barrens , but less so in other smaller northeastern barrens.
When Europeans first arrived in the northeastern United States at ~1600 AD, they recorded the presence of pine barrens in descriptive accounts and survey records. Detailed accounts are largely unavailable, and surveys including witness trees are far less common in pine barrens than other forest types found inland and colonized later, probably because pine barrens soil was sandy, nutrient-poor, and not conducive to agriculture. Early accounts of pine barrens are non-quantitative but provide evidence for the existence of extensive pine plains on the northeastern coast and major river valleys (Motzkin et al. 1996, Parshall and Foster 2002, Lorimer and White 2003). Fire disturbance in presettlement times undoubtedly occurred, but there is much debate as to what extent natural fire was enhanced by Native Americans. Day (1953) recounted ecological effects of Indians on presettlement forests by studying anecdotal accounts made by settlers and explorers. Early accounts asserted that Native Americans fired the land near their settlements to clear fields for planting, aid hunting by improving visibility or actively driving game, to repel reptiles and insects, increase berries and seeds, and to improve defense in war. Fire cleared out the “underwood,” creating park-like forests throughout coastal New England. Native Americans burned the New Jersey Pine Barrens deliberately in the spring and fall, and accidentally at other times. No early witness accounts were found for fire north of Massachusetts or in northern New England or the Adirondacks, but descriptions of park-like forests in other places in coastal Maine and the Champlain Valley do exist. Morton (1634) summarized his understanding of Native American use of fire near Quincy, MA:
According to Morton (1634), Native Americans ignited fires with “certaine mineral stones,” which they traded for with a southern tribe called the Piquenteenes. Burning of grass killed the understories and scorched the bases of larger trees. Native Americans known to Morton told him that their custom of burning “hath bin continued from the beginninge” of tribal memory. Europeans like Morton regarded the firing as dangerous to their settlements and buildings, so they backfired the areas around their habitations to reduce the fuel loads and prevent forest fires from coming in. According to Morton, forest fires started by Native Americans would spread and burn, with or against the wind, until a rain shower put them out. Burning the country made it passable, and trees grew in a park-like forest, making the country “beautifull and commodious.” The active use of fire by Native Americans to burn large tracts of forest was contested by Russell (1983), who studied 35 first-hand accounts written before 1700. Of these, 14 referred to forest openness often attributed to burning, but only 6 referred to frequent fires as the cause of park-like physiognomy in early forests. Presettlement vegetation was often described as large trees with open understories, but there were also conflicting accounts of colonists having to manually rip out roots and shrubs to plow their new land. Russell (1983) concluded that there was not a lot of evidence in the contact literature supporting purposeful widespread burning because there were no first hand descriptions of Native Americans setting surface fires. Fires were probably frequently set in areas with grassy ground cover, but where fires were said to be the custom, frequency ranged from twice a year to annually to “frequently.” Reasons for setting fires varied by author, indicating only a poor understanding of Native American culture and practices by the European settlers. Most often, the actual fires that were described in European accounts were scattered and of limited extent, not the large broadcast burning of eastern forests that many have imagined. Russell (1983) pointed out that there are other reasons why the forest understory could be open: Many documents were admittedly written to convince colonists to come to the new world; park-like openness would be viewed as favorable by potential farmers. If forests were park-like, shading by dense canopies could have caused this condition, and firewood collection by Native Americans around their villages would also clear out the understories. Russell (1983) admitted that areas of higher fire frequency would most likely be near Native American villages, and that “fires accidentally caused by Indians merely augmented the number of natural fires” in the northeast. Native American villages were most common in coastal and riverine areas where pine barrens were most common (Parshall and Foster 2002); however, Parshall and Foster (2002) concluded that climate and vegetation alone were enough to explain the regional variation in presettlement fire (highest in pitch pine and low in northern hardwoods), and that it was not necessary to invoke Native Americans as an ignition source. As in modern times, landforms and variation in vegetation would have also modified fire frequency and intensity at local spatial scales. According to early sources cited in Day (1953), Native American villages had localized impacts on the forest in addition to possibly increasing fire frequency. The longer a village existed in one place, the “farther the forest receded from it” due to firewood cutting and, in southern New England, agriculture. Maize was grown at a small scale along the northeastern coast south of the Saco River in Maine, into New Hampshire, Massachusetts, New York, and New Jersey, and up the Connecticut and Hudson River valleys, the Champlain Valley, and in the Alleghenies. Villages were most numerous along the coast and major waterways (Parshall and Foster 2002), so the so-called “primeval” forests first encountered by Europeans along the coast in the 16-1700s may have been heavily utilized if not ecologically modified by Native Americans in precolonial times. Native Americans occupied coastal areas such as Cape Cod throughout the Holocene, but were highly mobile populations that farmed but heavily depended on fishing; there were no permanent settlements (Parshall et al. 2003). According to Day (1953), “fields were abandoned as they wore out or as white settlements came close,” or more likely because of the disease epidemics that wiped out ~90% of the Native American populations in some areas. In general, areas succeeded to white pine when abandoned (Day 1953), foreshadowing the effects of European farm abandonment centuries later.
3) Reconstruction of Vegetation and Disturbance from Contemporary Stands
Lorimer and White’s (2003) recommendation of using modern old-growth stands to approximate presettlement forest conditions may be inappropriate for the pine barrens forest type, as pine barrens are naturally transitional and perpetuated by frequent disturbances. Presettlement pine barrens were probably even-aged stands that were initiated by large-scale disturbances and did not exhibit typical old-growth characteristics such as gap dynamics unless they were in decline. An example of a declining pine barrens is the Ossipee Pine Barrens of New Hampshire, which has some of the oldest stands of pitch pine in the northeast, with trees from 100 to more than 150 years old (Howard 2003). These forests were undergoing succession to white pine and hardwoods during a 50-100 year absence of fire, and have mean stem densities of white pine (35%), pitch pine (20%), red maple (20%), and red oak (7%) in the mixed pine-hardwoods community type as opposed to > 80% pitch pine in the pitch pine community type. Succession out of pitch pine dominance is consistent with Lorimer and White’s (2003) statement that pine-oak forests in other parts of the northeast succeed to oak in the absence of fire. In New Hampshire, pitch pines were not recruiting beneath dense canopies, while understories of hardwoods such as red maple, red oak, and beech were forming in older pine stands. Not unexpectedly, red maple and beech were also correlated with low charcoal in a study by Kirwan and Shugart (2000) in Delmarva pine lands. In the New Hampshire study, fuel and brush had accumulated, creating a major fire hazard for nearby residential areas (Howard 2003, Patterson 2003). Functioning contemporary pine barrens where fire returns at intervals < 40 years, such as the New Jersey Pine Barrens, may provide a more accurate study of what presettlement pine barrens may have looked like. Where fire is frequent it favors communities of fire-adapted or fire-promoting species (Boerner 1982). Such species have adaptations to withstand fire, such as thick bark, or have the ability to resprout prolifically after being top-killed by fire. In a major surface fire, adult pitch pines are immune because of their thick protective bark (Popp 1987). Dormant buds of top-killed young pitch pine and scrub oak survive beneath the soil surface and are quick to sprout, and within a short time the green of blueberry and other deep-rooted groundcover returns. Prolific postfire sprouting by pitch pines and scrub oaks may tend to increase future fire intensity and frequency by 1) creating a continuous canopy, 2) concentrating the biomass into a single layer, and 3) creating more surface area per unit biomass because of high stem number (Buchholz 1983). Following fire in the dwarf pine plains of the New Jersey Pine Barrens (where fire return interval is 6-8 years; Givnish 1981), surface area of multiple sprouts from the same root systems became twice as high as before the fire, and 12 times as high as non-dwarfed pitch pines on Long Island (Buchholz 1983). Seed banks in the upper soil surface and leaf litter are relatively unimportant to the revegetation of a burned site, as pine barrens seed banks are naturally species poor (Matlack and Good 1990). In the New Jersey Pine Barrens, areas subject to periodic fire (prescribed since ca. 1930) but not clearcut or tilled for more than 100 years, had seed banks that contained a mean of 4.4 species, as opposed to 15.3 species in the aboveground communities. Samples contained no Pinus or Quercus seeds, and were entirely made of disturbance-adapted, short-lived herbs that were not present in the aboveground community. The lack of an important seed bank component in pine barrens ecology is not surprising, as extremely hot stand-replacing burns that kill adult trees also combust the leaf litter, killing any dormant seeds and exposing the mineral soil surface. These burns favor the redevelopment of pine barrens vegetation through recruitment from sprouts and new seeds. Pitch pines on the coastal plain, especially the New Jersey Pine Barrens, can have serotinous cones that release their seeds after being scorched (Givnish 1981). Pitch pine seeds cannot establish through an intact litter layer (Burns and Honkala 1990), so require soil disturbance for successful establishment. The degree of fire intensity at a given area depends on fuel load (aboveground biomass + detritus), fuel moisture, weather conditions, and topography (Boerner 1982); therefore there is much spatial variation in fire intensity on the burned landscape (Boerner 1982, Jordan et al 2003). This variation would translate into spatial heterogeneity and physiognomic diversity in the forest patches that eventually recolonize a large burned area. Central areas of large outwash plains, such as the central pine plains of New Jersey’s pine barrens, are prone to burn more often than peripheral areas, as fire can burn into the center from many directions (Givnish 1981). Lee sides of landforms such as eskers, rivers, and other natural firebreaks may burn less frequently than flat outwash plains, creating differentials in species composition as well as age distributions of the existing forests (Givnish 1981, Howard 2003). Such regional variation in fire frequency causes complexity and heterogeneity at the landscape level as well as genetic heterogeneity within species. As an example of the latter, incidence of cone serotiny in pitch pine increases to 100% toward the center of the New Jersey pine plains, where fire is most frequent (Givnish 1981).
II. Postsettlement Vegetation and Historic Land Use
European colonists had a tremendous influence on the character, composition, and amount of forest vegetation. The earliest colonies in what was to become the northeastern United States were established in the early 1600s in coastal New York , Massachusetts , and New Hampshire , and spread progressively inland. Population size in rural areas and associated activities peaked around 1850 but was followed by a mass exodus to the cities and to the more fertile farmland of the Midwest . The effects of European land use in pine barrens can be summarized in two major categories: 1) agriculture and forest clearing followed by abandonment and revegetation, and 2) an initial increase in fire frequency followed by effective fire exclusion.
1) Agriculture and Abandonment
Hall et al. (2002) documented changes in land use in Massachusetts over 400 years, illustrating patterns that applied to most of New England and the northeast. Using colonial land surveys, 19 th century maps showing forested lands, and agricultural censuses, Hall et al. (2002) documented changes in the composition, structure, distribution of forests at the statewide level. Agricultural land use in Massachusetts peaked between 1830 and 1885 when 50% of the land was in pasture, hay, or agricultural fields, and sheep and cattle exceeded 650,000. In 1830, forest blocks were small, averaging 119-204 ha on the mainland, but were somewhat more on Cape Cod and the islands (490 ha). At the peak of agricultural development, forests were relegated to poor lands such as mountains, swamps, and dry sand plains. At the time of settlement, pine-oak vegetation dominated Cape Cod, and much of the Cape was not settled until the better inland soils had first been claimed. In Massachusetts, pine barrens were often farmed (Motzkin et al. 1996, Hall et al. 2002); however, in New Jersey and in the northern barrens of New Hampshire and Maine, pine barrens were very rarely plowed (Copenheaver et al. 2000, Howard 2003). In fact, most pine barrens fueled a healthy forest products industry, as pitch pine was cut for firewood, fuel, fence posts, railroad ties, barrels and boxes, and early shipbuilding (Hall et al. 2002, Howard 2003). After 1850, many northeastern farms were abandoned with the discovery of productive agricultural lands in the west, the development of railroads, and the lure of the industrial revolution in the major cities (Foster 1999, Hall et al. 2002). Farms on rocky uplands and coastal sand plains were abandoned first, and relatively fertile river valleys last. Forests increased statewide as agricultural land decreased; only 7% of the land in Massachusetts is in agriculture today. The effects of the deforestation and reforestation of the northeastern United States reverberated through centuries after the original land uses had ceased. Modern vegetation patterns on the northeastern landscape still reflect 19 th century land use practices (Foster et al. 2003). The age and size structure of modern forests are often unimodal as a result of old-field abandonment or a clearing event. Many forests were cleared or cut repeatedly for firewood, producing even-age stands and multistemmed trees that remain today (Hall et al. 2002). For example, in 1885, only 30% of the forest lands in Massachusetts had trees greater than 12.2 m tall; by 1971 the percentage had grown to 77% as trees grew taller and sawtimber increased (Hall et al. 2002). However, even with this increase, eastern forests currently lack structural elements such as large trees, coarse woody debris, tip-up mounds, pits, and standing dead trees (Foster et al. 2003). Though the lack of structural elements such as those listed above may not be as important in naturally even-aged pine barrens ecosystems as they are in other northeastern forest types, agriculture had other lasting effects in barrens. Plow horizons in soils persist for centuries after sites are reforested, and physical, chemical, and microbial changes in soils may affect vegetation hundreds of years later (Foster et al. 2003). The physical effects of plowing, a process that destroys the root systems of native vegetation in favor of the new crop, had direct and lasting effects on the vegetation. In the Montague pine barrens of the Connecticut River Valley, some understory and groundcover species were geographically restricted to areas of the barrens that had never been plowed, even though soil chemistry was not appreciably different between plowed and unplowed areas (Motzkin et al. 1996, Compton et al. 1998, Donohue et al. 2000, Foster et al. 2003). For example, wintergreen (Gaultheria procumbens) was absent on sites that were formerly plowed, and only present on sites that were never plowed. Seeding experiments showed that Gaultheria sown in plowed areas grew as well if not better than in unplowed areas. Donohue et al. (2000) concluded that wintergreen was not restricted by environmental differences, but rather by its intrinsic low recruitment from seed and slow clonal growth rate that kept it from arriving at unplowed sites (wintergreen grew laterally at only 43 cm/year over the last 100 years). Life history limitations, in combination with former agricultural land use, determined the modern range of this species in the pine barrens, and at its present slow rate of expansion, it would take thousands of years for wintergreen to recolonize its former range. In the same pine barrens, historical plowing and land use affected overstory species as well. 97% of pitch pine-dominated stands were found on formerly plowed areas, whereas 89% of scrub oak-dominated sites existed on unplowed areas (Motzkin et al. 1996). Historical land use explained more variation in vegetation than environmental variables. Scrub oak stands formed by repeated cutting of pitch pine and burning (a process that also formed a scrub oak barrens on Martha’s Vineyard; Foster et al. 2002), or they formed on former pastures (the latter a common pattern in coastal New England; Motzkin et al 1996). In plowed areas, scrub oak recolonized only as scattered understory individuals, unlike the dense thickets that are found in unplowed areas today. Pitch pine trees, on the other hand, nearly all belonged to the post-abandonment cohort, because abandoned fields provided an excellent litter-free seedbed for their establishment (Mozkin et al. 1996, 1999); modern closed pitch pine stands in Montague were a reliable indicator of former agricultural activity. In other former pine barrens areas, such as Martha’s Vineyard (Foster et al 2002) and Cape Cod (Motzkin et al. 2002), agricultural abandonment had not so predictably affected present day forest composition, but rather obscured presettlement relationships of forest species to environmental variables such as soil texture and landform. Over much of New England plow layers are still present; however, land uses such as cutting, land abandonment, and fire suppression have homogenized tree species composition (Foster et al. 2003).
2) Modification of Fire Frequency
When Europeans arrived in North America and began to clear forests and build settlements, they elevated fire frequency above the level found in presettlement forests. Palynological studies comparing presettlement to postsettlement vegetation found a dramatic increase in the amount of charcoal deposits in lakes at times that corresponded to the influx of grass and herbaceous pollen, lower organic content, and higher sedimentation associated with European land clearance (Parshall and Foster 2002, Parshall et al. 2003). Increased fire frequency may have resulted from the use of fire in land clearing and an increase in accidental ignitions as the European population grew. Later, the development of railroads further increased fire frequency as cinders from steam locomotives ignited nearby brush (Howard 2003, Parshall et al. 2003). The effects of increased fire frequency are not exactly clear, as other land uses such as cutting were also affecting the vegetation at the same time. Lake sediment cores showed a decline in oak pollen and an increase in pitch pine pollen in areas that were formerly pine-oak (Parshall and Foster 2002, Parshall et al. 2003). This change could be interpreted as a reduction in oak and other hardwoods due to logging, or as an increase in pitch pine due to increased fire frequency, but most likely a combination of the two. In both the Connecticut Valley and coastal areas of Massachusetts, pitch pine establishment also occurred as a result of old-field abandonment on former pine barrens (Motzkin et al. 1996, 2002). Some pine barrens on former agricultural sites have been since modified by, but do not owe their original establishment to, historically recorded fires. Since the late 1940s, the technology has existed to fight large fires and exclude them from many forests in the United States that historically had burned. Pine barrens subject to this policy have slowly and subtly changed over the last 50 years to the point where ecological threats are now being recognized. Most northeastern barrens are thought to be in decline as a result of fire suppression (Copenheaver et al. 2000, Howard 2003), as evidenced from barrens across the region. The Waterboro Pine Barrens in Maine experienced a large fire in 1947 and has not burned since that time. The Waterboro barrens had not been plowed for agriculture, but was utilized for timber. Copenheaver et al. (2000) used aerial photographs dating back to 1940 to track changes in plant communities over the last 60 years, and found that the mixed deciduous cover type doubled in area. Pitch pine-scrub oak increased, but open canopy pitch pine declined by 93% and scrub oak cover declined by 67%. Copenheaver et al. (2000) concluded that fire disturbance was necessary for the exclusion of fire-intolerant species and long-term perpetuation of the pine barrens ecosystem. In the Ossipee Pine Barrens of New Hampshire, Howard (2003) found a similar situation where shade-tolerant, fire-intolerant hardwoods and white pine substantially increased over the last 50 years. Sites classified in pitch pine forest declined from 2/3 of the study area to less than 40% of the study area between 1952 and 2002, with pitch pine sites converting into the mixed pine-hardwood community type. Hardwoods such as red maple, red oak, and beech, already established in the current forest understories of many sites, were predicted to dominate 50% of the study area by the time the current understory replaces the current canopy (Howard 2003). Sites most at risk of successional replacement had longer time intervals since the last stand-replacing fire. These included sites at long distances from known historical ignition sources (such as the railroad) and in the shadow of natural firebreaks, where hardwood seed sources are most abundant. Pitch pine was not successfully recruiting in the Ossipee Barrens, though a seed source for it was present throughout. In the Montague Plains Barrens of Massachusetts in 1939, the landscape was 49% grassland or shrub-heath, 29% open canopy forest, and 15% scrub oak shrublands (Motzkin et al. 1996). By 1985, pitch pine forest occurred across 40% of the barrens, hardwood forests in 12%, and mixed forests occupied 21%. Open canopy forest (9%) and grass/shrub/heath (3%) declined substantially. Not surprisingly, fires since 1939 have been restricted to small localized burns, quickly contained and extinguished, and no meaningful regeneration of pitch pine has occurred because of the lack of severe fires or plowing. In all pine barrens in the Connecticut Valley, accidental fires, when the do occur, usually happen during the late winter or spring when the soil is wet, and they are controlled before they can consume the litter layer (Motzkin et al. 1999). Severe summer burns of the type that probably occurred naturally are less common and commonly suppressed when they do start. As a result, shade-tolerant hardwoods have established in most stands (Motzkin et al. 1999). White pine and hardwoods may predominate in the future in the absence of future disturbance. A similar situation occurred on Long Island, New York, from 1938 to 1994 (Jordan et al. 2003). After intense, frequent wildfires in 1938, 90% of the barrens was classified in open canopy woodland or shrubland, but by 1994 this cover type had diminished to 45% of the study area. No fires occurred over 70% of the study area, and where fires did occur they were small due to increased forest fragmentation and effective firefighting. Even though a severe summer wildfire burned 810 ha of forest in 1994, Jordan et al. (2003) predicted that conversion to closed canopy forest and loss of pine barrens vegetation is inevitable in the absence of wildfire or an equivalent management practice. On the Delmarva Peninsula in 1937, fire had historically returned every 10-40 years, supporting a landscape of oak-pine or pine woodland (50%) or open savanna (50%). The study area had experienced cutting in the 1800s but no agriculture (Arabas 2000). Between 1937 and 1993, 25% of the barrens converted to hardwood forest, with 50% converting to closed canopy oak-pine or pine, at the expense of 50% of savanna area. Both landscape- and stand-level changes have taken place, as areas now classified as hardwood forest have not seen fire over the last 50 years.
III. Management Challenges and Recommendations
1) Importance to Regional Biodiversity
Pine barrens are a significant contributor to the biological diversity of the northeastern United States (Noss et al. 1995). Latham (2003) noted that although many species found in barrens are common, a number of regionally and globally rare plants and animals also are dependent on these habitats. The Long Island pine barrens, for example, supports 54 rare plants and 19 rare animals (Edinger and Jordan, personal communication, as cited in Latham 2003). Sperduto et al. (2000) found that most regional- and state-listed rare plants in the Pine River State Forest (a subunit of the Ossipee Pine Barrens in New Hampshire) were associated with numerous bogs and marshes embedded within the pine barrens matrix. Among animals, butterflies and moths are especially dependent on barrens. The importance of pitch pine–scrub oak barrens for rare Lepidoptera is likely a consequence of a variety of abiotic and biotic factors. The most obvious reason for their importance is an obvious dependence of moths and butterflies on specific host plants. Specifically, scrub oak is the sole or principal larval host for 16 (29%) of the 56 Lepidoptera of conservation concern in New England and New York (Wagner et al. 2003). Another 11 rare species feed on pitch pine and eight more rely on lowbush blueberries (Vaccinium angustifolium and V. pallidum; Wagner et al. 2003). Frost pockets found in pitch pine–scrub oak barrens are important habitat for regionally rare or endangered Lepidoptera (Goldstein 1997). Specifically, the importance of frost pockets to rare Lepidoptera that feed on oaks may be the result of delayed leaf phenology. Young, tender leaves are more nutritious than older leaves because of their greater nitrogen and water content (Feeney 1970, Slansky 1993). The delayed spring leaf-out in frost pockets provides highly nutritious food concurrent with sufficiently warm and sunny days, resulting in rapid growth of larvae (Wagner et al. 2003). Within barrens, patches of exposed sand or rock also are the habitat of many ground-dwelling invertebrates that have phylogenetic affinity to taxa reaching greatest diversity in deserts and similar xeric ecosystems (Wagner et al. 2003). Loose, sandy soil is ideal for burrowing and dries and warms readily. As a result, barrens support some southern species near the northern edge of their geographic range ( Kirby 1992). Barrens also are an important habitat for a number of vertebrates. Here, the relationship is based on edaphic and structural features, not host plants. In the northeast, approximately 50% of the bird species and almost 60% of the mammal species rely on a combination of early, mid, and late-successional stands (Scanlon 1992). Although the majority of amphibians and reptiles utilize a range of seral stages (Scanlon 1992), the eastern hognose snake (Heterodon platirhinos) is restricted to xeric, sandy soils that are often dominated by pitch pines or scrub oaks (Michener and Lazell 1989). Some vertebrates are clearly obligates of early-successional forests or shrub-dominated habitats, such as brown thrashers (Toxostoma rufrum ; Askins 1998) and New England cottontails (Sylvilagus transitionalis; Barbour and Litvaitis 1993). Historically, barrens and other native shrublands were likely a reliable habitat for these species and may be key to long-term viability in the Northeast (Litvaitis et al. 1999, Litvaitis 2003).
Sustainable management of northeastern pine barrens ecosystems poses a number of important challenges. The locations and existence of current pitch pine canopies within the presettlement range of pine barrens may be the result of former land use in the late 1800s to early 1900s, including farm abandonment and/or cutting, combined with a subsequent period of increased fire frequency. The current state of many northeastern barrens is that of old stands of pitch pine that have been invaded or are in the process of being successionally replaced by less fire-tolerant species such as white pine, oak, red maple, or other hardwoods. In most cases where fire has been excluded, pitch pine regeneration is lacking due to impenetrable leaf litter on the forest floor. A half-century of fire exclusion and fragmentation has prevented the massive burns that regenerated these stands in presettlement times, though an alarming amount of potential fuel has accumulated since the 1950s. Because pine barrens are successional habitats that require periodic fire to perpetuate them over long time periods, successful long-term management must take this disturbance into account to produce appropriate levels of turnover. Lorimer and White (2003) recommended that managing forests using techniques that approximate the ‘natural range of variability’ in forest habitats. Such techniques are thought to sustain biodiversity of native species by producing landscapes similar to those in which native species evolved. In addition, because the structure and function of nearly all ecosystems depends on site history, policy development and the management of those ecosystems must be designed with an eye to the past (Foster et al. 2003). According to Foster et al. (2003), accurate historical perspectives allow more dependable interpretations of landscape patterns and hence inform the development of realistic management goals and strategies. Ignoring historical land use legacies can lead to faulty management schemes. In pine barrens, an understanding of historic fire regimes is critical to the design of management plans that will both sustain native species and processes and be viable economically (Foster et al. 2003). It is important to note, however, that because of the vegetation patterns and environmental changes imposed on a landscape during 400 years of land use, there is no quick fix to restore current pine barrens forests to presettlement conditions. Also, because each geographically isolated pine barrens has been subject to a unique combination of historical factors and influences, management considerations should be developed on a site-by-site basis. We do not advocate applying a blanket approach to management of all pine barrens, and the methods and recommendations below should be carefully weighed before being tailored to any particular stand.
3) Contemporary Issues and Considerations
Jordan et al. (2003) asserted that the main threats to pine barrens today are development, fragmentation, and fire suppression. Although all three are the product of the last fifty years, the first two have to do with relatively recent urban sprawl. Whereas in the past outwash plains were considered barren for the purposes of farming and therefore almost useless, they now provide flat, well-drained land upon which to build housing developments, businesses, roads, malls, and airports for rapidly expanding urban centers along the coast. The result has been major habitat loss and fragmentation in ecosystems that were historically large and contiguous (Seischab and Bernard 1991, Motzkin et al. 1996, Howard 2003). Motzkin et al. (1999) urgently recommended land protection for the remaining large, undeveloped sand plains in the northeast to prevent further habitat loss and to facilitate having more options for management. This recommendation is currently being implemented by both state and private agencies such as the Nature Conservancy (Howard 2003); however, more protection is still needed as sprawl continues to encroach upon all northeastern pine barrens. Management of the remaining pine barrens will have to contend with the challenges of multiple ownership as well as the ecological effects of parcelization. Fragmentation of pitch pine-scrub oak vegetation on the modern landscape limits the spread of fires, which were once able to spread into large contiguous areas in presettlement times. Catastrophic high-intensity burns characteristic of the presettlement times could affect more than 1000 ha in central Massachusetts (Motzkin et al. 1999), and even more in the vast New Jersey Barrens. Today, most pine barrens fragments in the Connecticut River Valley are less than 10 ha in size. Therefore the incidence and intensity of fire are both lower, leading to prevention of pitch pine recruitment and invasion of fire intolerant species (Motzkin et al. 1999). Additionally, fragmentation prevents the clonal recolonization by species that were extirpated from certain areas by the 19 th century plow (sensu Donohue et al. 2000). To promote fire-tolerant pine barrens vegetation on these small parcels, management will have to find a way to allow pitch pine establishment from seed, and at the same time suppress invading fire-intolerant species. Although burning pine barrens may seem like a likely tool to perpetuate this forest type, it may not be a workable solution in many areas of urban interface because of the deteriorated condition of many barrens. Fuel in the form of live and dead scrub oak, heath, leaf litter, and coarse woody debris has accumulated underneath pine barrens since the last fire, which in many cases (outside of New Jersey) has been since the 1940s or 50s. In the Ossipee Pine Barrens in New Hampshire, mature pine forests date from fires in 1885, 1920, and 1957 (Patterson 2003), and fuel models for the barrens predicted surface flame lengths of 2.3-3.6 m and a rate of spread of 3.1-8.8 m per minute in 16.1 kph (10 mph) winds. Windspeeds of only 24.1-32.2 kph (15-20 mph) would be sufficient to cause catastrophic crown fires with flames higher than 30.5 m (100 ft; Patterson 2003). Such a conflagration would easily jump residential roads that are 15-23 m (50-75 ft) wide and be extremely hazardous to property and human life in a suburban setting, especially if defensible space is not maintained between dwellings and the forest edge (Howard 2003). Likewise, where fire is to be used as a management tool near urban areas, management areas must be enclosed with firebreaks to prevent uncontrolled spreading. For example, in the Ossipee Pine Barrens, the Nature Conservancy is preparing 200 m wide fire breaks at the edges of the West Branch Pine Barrens in preparation for controlled burns (Peter Benson, The New Hampshire Nature Conservancy, pers. comm.). Breaks in thick pine-scrub oak vegetation could be created with bulldozers or brontosauruses (a large shredder/chipper mounted on a back-hoe, often used to clear power line rights-of-way).
4) Effects of Prescribed Fire in Pine Barrens
Prescribed fire has been used in the New Jersey Pine barrens since at least the 1950s to reduce fuel loads and therefore reduce the danger of catastrophic uncontrolled wildfires. Buell and Cantlon (1953) were optimistic about prescribed burning as a silvicultural practice designed to improve New Jersey Pine Barrens forests and return them to higher levels of production. They recognized that “fire judiciously used favors a fire subclimax forest of high pine composition.” At the time of Buell and Cantlon’s (1953) study, controlled burns were done in the winter to ease fire control, at intervals of 1-5 years. Frequent burning (1-2 year intervals) reduced the litter layer, reduced shrub cover by 50%, and increased the number of pine seedlings. Fuel loads also were reduced. Buell and Cantlon (1953) recommended burning followed by harvesting of the overstory to release new pine seedlings, some of which subsequently grew 6 feet in 2 years. Following the harvest, fire exclusion was recommended until the new pines developed thick fire resistant bark. Shrubs and groundcover increased after fire suppression was implemented. The effectiveness of prescribed burning has been variable, however, even within the New Jersey Pine Barrens. Boerner (1981) studied the effects of a prescribed spring burn, which had little effect on community structure except to open the heath-shrub layer for some transient (1-2 year) patches of herbaceous species. Few tree seedlings were observed. The weak effects of the prescribed burn contrasted with the effects of a winter wildfire, which killed all aboveground stems of oaks and the needles of pines, but almost all resprouted to form a dense 1 m canopy only one growing season later. Popp (1987) investigated the effects of 1-3 successive (annual) summer prescribed fires in the Ossipee Pine Barrens in New Hampshire with the goal of reducing hardwood and scrub oak competition with pines. The canopy of pitch pine and white pine received no damage from all three prescribed fires. The subcanopy and understory was made up of white pine and hardwoods (red maple, grey birch), the hardwoods being more numerous. Subcanopy white pine suffered 50% mortality in just one prescribed burn, whereas subcanopy pitch pine was immune. All understory white pine were killed in single fire. Hardwoods had a progressive response: one fire top-killed them, but stimulated vast numbers of sprouts. Successive fires killed their rootstocks or diminished resprouting ability. Three years of summer burns inflicted 25% mortality on subcanopy hardwoods and 40% mortality on understory hardwoods. Top-killed scrub oak rootstocks were immune from all fires, increasing the number of sprouts with each burn. Species diversity of groundcover declined with burning, but blueberry, wintergreen, and bracken fern (all typical groundcover species in pine barrens) remained unaffected. Popp (1987) concluded that light summer fires 1) reduced fuel loads, 2) did not reduce scrub oak density, and 3) progressively reduced red maple and grey birch, killing an increased proportion of the rootstocks. Pitch pine did not regenerate in the light burns, so Popp (1987) recommended a hot spring burn coordinated with heavy pitch pine seedfall, or a cutting to open the canopy followed by burning the slash piles. Popp’s (1987) recommendations for Ossipee were in agreement with those of Howard (2003), who found that sites with evidence of past low-intensity surface fire (i.e, bark charring on large trees) were actually more likely to succeed to mixed pine-hardwoods or red maple than sites with no evidence of fire. Howard (2003) ascribed this propensity to the sprouting ability of red maple and oak, which probably increased in stem density following fires that did not damage their root systems. In pine barrens close to residential areas, the use of prescribed fire may be restricted by law. For example, spring burns are the only type allowed in the Connecticut Valley of Massachusetts because of open burning regulations during dry summer months (Motzkin et al 1999). Less intense spring burns have little effect on roots of hardwood and shrub species that compete with pitch pine, or on the thickness of the litter layer that prevents pitch pine establishment. In the face of these restrictions, Motzkin et al. (1999) recommend a tree-pronged approach by 1) cutting unwanted hardwoods during the growing season, 2) using soil scarification to promote pitch pine regeneration, and 3) controlled burning facilitate and maintain pine barrens vegetation. Scarification using a fire plow dragged behind a tractor favored the regeneration of pitch pine from natural seed sources in the Ossipee Pine Barrens, though at the time of the scarification the emphasis was on direct-seeding of white pine (Peter Pohl, Carroll County UNH Cooperative Extension, pers. comm.). Though reintroduction of burning does not always work to restore plant composition or soil characteristics to historic levels (Motzkin et al. 1996), and it is not always possible to get rid of introduced species (Foster et al. 2003), it is clear that some kind of burning is most likely necessary to perpetuate forests historically composed of fire-adapted species. Where severe summer burns are impractical, annually repeated small-scale burns might slowly eliminate hardwood competition (Popp 1987). Unlike consecutive summer burns, a single spring burn is almost totally ineffective at reducing competing vegetation (Boerner 1981) because it does not deplete much of the photosynthate stored in hardwood root systems from the previous year. However, spring burns are usually much safer and easier to control, and do reduce some of the fuel load (Buell and Cantlon 1953, Patterson 2003). Because of the volatility of some areas, carefully controlled growing season burns during wet weather and/or mechanical treatments have recently been recommended in Massachusetts (Motzkin et al 1999), New Hampshire (Patterson 2003), and New York (Jordan et al. 2003) to reduce fuel loads in pine barrens adjacent to residential development. Jordan et al. (2003) stressed that the development of defensible space around urban interface will make larger burns in the interior more feasible by protecting human life and property. Space could be created mechanically using bulldozers or other heavy equipment, and then followed by small backfires to eliminate litter.
5) Prescribed Fire as a Silvicultural Technique
Fire can happen at many intensities; as a crown fire it is a stand-replacing disturbance, equivalent to “regenerating” the stand in forestry terms. This was the way that pine barrens ecosystems were naturally perpetuated, as severe, duff-consuming wildfires usually occurred after prolonged drought, usually in summer (Jordan et al. 2003). There are few situations in which fire can feasibly be used to regenerate a stand in this way because of the danger involved and the lack of control. Surface fire, on the other hand, can be a useful silvicultural tool in the sustainable management of pine barrens. Light fire is not extremely effective at burning away the duff layer to expose mineral soil and facilitate pitch pine seeding (Boerner 1981, Popp 1987, Motzkin et al. 1999); alternatively, mechanical treatments such as dragging a plow could be used to scarify soil and simulate the litter-reducing effects of wildfire (Motzkin et al. 1999, Howard 2003). Prescribed fire could instead be used as a method of cleaning unwanted fire-intolerant understory species from an established pine barrens stand, or to precommercially thin an overcrowded stand of young pitch pine of weak individuals. In the first case, young white pine is killed in a single fire, while hardwoods may persist through several before succumbing (Popp 1987). If a goal of management is to protect white pine for eventual harvest, burning must be delayed until the white pines have grown large enough to withstand the heat, as they are fire-intolerant when young. After exclusion of hardwoods has taken place, perhaps after 3-5 annual burns, it would be necessary to continue burning at intervals similar to presettlement return intervals (~10-40 years; Givnish 1981, Lorimer and White 2003) in order to prevent the recolonization of hardwood species and promote ecological processes and wildlife that would have been associated with frequently burned presettlement barrens. Improvement cutting or girdling may be necessary initially to remove large hardwood trees that survived prescribed burns and continued to act as seed sources within the managed area of the barrens (Howard 2003). An additional benefit of periodic fire would be that the nutrients tied up in the competing vegetation would be released back to the soil for use by the crop trees (Boerner 1982), perhaps increasing their height growth.
In order to create a sustainable yield in an ecologically healthy pine barrens (i.e., not invaded by non-native or late-successional species), the above techniques using prescribed fire could be used until such a time as the crop—in this case, pitch pine—is ready for harvest. Pitch pine is not as commercially valuable as white pine; however, it is not recommended that the entire stand be managed for conversion to white pine because 1) pitch pine is the dominant presettlement tree species naturally associated with this ecosystem, and 2) former attempts to convert to white pine in the Ossipee Pine Barrens in New Hampshire were largely unsuccessful (Peter Pohl, UNH Cooperative Extension Educator, Forest Resources, Carroll Co., NH, pers. comm.; Paul Beck, International Paper Sawmill, Freedom, NH, pers. comm.). However, some white pine grown in the protection of pitch pine may be more resistant to the white pine weevil, which readily attacks and deforms white pine in monocultures. In order that yield be sustainable, harvested areas should be distributed across the barrens landscape in order to simulate periodic stand-replacing disturbances, but at a rotation length where wood in the system is produced at a rate equal to that at which it is extracted. Clearcutting or seed-tree methods followed by soil scarification would best simulate natural disturbance in pine barrens ecosystems, and patch sizes could vary. Logging slash could be lopped or burned on site at an appropriate time to control fuel loads (sensu Patterson 2003). Scarification would allow regeneration seeding from adjacent pitch pine adults. The resulting landscape would be a mosaic of even-aged pitch pine cohorts such as might form following a series of stand-replacing fires. This system would provide structural diversity on the landscape level, economic and ecological sustainability, and reduced threat of uncontrolled wildfires because of active fuel management. It would also mitigate the historical legacy of fire suppression, which threatens modern pine barrens with replacement by fire-intolerant species. Incentives for implementing such a silvicultural program in pine barrens may need to come from conservation or public safety interests, rather than from for-profit organizations. However, it may be possible for conservation groups, state agencies, and/or municipalities to break even over the long term by paying for the cost of management with harvests. The benefit to biodiversity by wisely managing this quickly-disappearing forest type would be priceless.
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