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Fire Effects in New Jersey's Pine Barrens by Silas Little
Large forest fires in the New Jersey Pine Barrens frequently take newspaper
headlines in the spring, and sometimes in summer or fall, but hundreds
of small fires throughout the year attract little attention. Fires are
not rare in this section. Indians burned the woods extensively to improve
hunting conditions. Ever since the first white men settled in New Jersey,
fires have been common in the Pine Barrens.
Effects of these fires are all too frequently overlooked or misjudged-partly
because new growth quickly masks the burns, partly because there are many
differences in possible effects. The principal effect of fires has been
on the vegetation, especially on the above-ground parts. On upland sites,
most the root systems are in mineral soil which is heated appreciably
by any type of forest fire. In addition, studies have indicated that forest
fires have relatively little effect on upland soils.
FACTORS MODIFYING FIRE EFFECTS ON UPLAND SITES
Succession
If fires are kept out and there are no other disturbances such as cutting,
the usual forest growth that develops on cleared land in the Barrens follows
this pattern: first, a pine stand develops; then hardwoods, chiefly oaks,
seed under the pines. Later, as the pines mature and die, hardwoods dominate
the stand. The succession from pines to- hardwoods is due to two factors:
(1) hardwoods can live and grow under more shade than pines, and
(2) hardwood seeds, being bigger, can become establishedin the thick cover
of dead leaves that accumulates under unburned stands.
Species Susceptibility
Pines and oaks differ in their susceptibility to fire. Oaks have thinner
bark than the pitch and shortleaf pines of the Barrens, so less heat is
needed to kill their cambium. However, pine crowns are burned far more
frequently than the crowns of oaks because most fires occur when oaks
are leafless. Most of the fire damage to oaks is through killing of the
cambium near the base. When only part of the cambium is killed, the tree
usually lives but an open wound develops. When all of the cambium is killed,
the stem dies but sprouts may start from buds just underground.
On pitch and shortleaf pines, fires usually damage the foliage and well-developed
buds first. More heat is needed to kill the basal cambium, particularly
of. large trees. Thus, these pines may have only their foliage killed
they may also have their major buds and branches killed, yet live through
forming new crown sprouts from dormant buds. If the part above ground
dies but sprouts arise, they usually arise from protected dormant buds.
A tree is completely killed if no sprouts develop.
Tree Size
Large trees have thick bark and crowns farther from the ground so they
tend to suffer less damage than small trees. Certain fires have killed
back all pines 1 to 4 inches in diameter (at breast height), but no pines
with a breast height -diameter of over 13 inches. Less intense fires
have
killed back all oaks 1 to 4 inches in diameter, but only 12 percent of
the oaks larger than 13 inches. (A tree is "killed back" if
the part above ground is dead, but the root is still living and can produce
sprouts . A tree is completely killed if the root, too, is dead.)
Effects of Heat
The temperature of a fire varies within its various sections, its size
and its burning conditions. In some large fires, the head-fires have killed
68 percent of the pine stems 5 to 8 inches in diameter while the less
intense side-fires killed no pines of that size. Small fires are usually
less intense and cause less damage than large ones. When air temperatures
are low, heat is more quickly dissipated and more fire is needed to raise
the temperature of plant tissues to the killing points. Thus, fires do
less damage at low winter temperatures than in spring or summer. The intensity
of a fire is also affected by fuel conditions. When the debris on the
ground is dry only on top, fires may start and spread but they cannot
create as much heat as when all the debris burns. Similarly, where there
is less fuel, the fire will be less intense.
Fire Frequency
Frequent killing fires keep an area covered with small sprouts. Severe
fires at fairly frequent intervals (less than 20 years) eventually eliminate
species that do not bear seed at an early age-the apparent reason why
shortleaf pine and black, white, and chestnut oaks are absent from existing
stands of pitch pine and scrub (bear) oak.
ROLE OF FIRE IN SHAPING UPLAND STANDS
Most of the effect of fire on present forests of the Pine Barrens has
come from large, very hot fires.
Plains Stands
Low growth of pitch pine and scrub (bear and blackjack) oaks, such as
that found near the Burlington-Ocean County line along Route 72, is due
chiefly to repeated killing fires that keep sprouts young and small.
These
sprouts' growth is retarded by th e age of the stumps from which they
grow and by competition among large numbers- of sprouts-as many as 249
one-year-old sprouts have been counted in a single clump. Recent studies
indicate that the Plains stands' fire history has favored a race of pitch
pines that is relatively slow-growing, develops a mature form relatively
early and has a crooked form and serotinous cones. (Serotinous cones
are
pitchy enough to stay closed, at least for several years, unless opened
by a fire's heat. By these mechanism s, fire produced the "miniature
forest" that was once considered such a mystery.
Pitch Pine-Scrub Oak Stands
Stands similar in composition to those in the Plains arise from slightly
less frequent or less intense fires which give the pines more growing
time. However, these pines are usually slow-growing for two notable reasons:
(1) many stems probably started as sprouts and (2) many of the pines lived
through one or more fires that killed their crowns.
Oak-Pine Stands
These usually have a dense understory of oak (black, white, chestnut,
etc.) sprouts with some scattered pine sprouts, both having started after
the last severe fire. Over this understory is a scattering of large pines
that survived the last and, often, earlier fires. This composition apparently
results from severe fires at intervals of possibly 30 to 40 years, certainly
at longer
intervals than in the pitch pine-scrub oak areas. In the oak-pine stands,
large pines have usually been deformed by past fires and if any oaks survived
the last fire, they will probably have basal wounds.
FIRE EFFECTS OF SHRUBS AND HERBACEOUS VEGETATION
Just as a history of fire can alter the composition of a forest, it can
also affect the undergrowth. On upland sites, an undergrowth of huckleberries
and low-bush blueberries prevails under climax hardwoods and most oak-pine
stands. Frequent light f ires tend to reduce the shrub cover and favor
herbaceous plants, especially along roads or under open stands. Severe
fires can also reduce the shrub cover, especially of huckleberries. On
sandy sites, severe fires favor such species as golden-heather un til
they are once again crowded out by the spread of blueberries and huckleberries.
Pine Stands
Foresters believe park-like stands of pine prevailed in the original forest,
due to the frequent fires the Indians set, mostly in the fall and winter.
Similar stands with mature trees reaching heights of 65 to 100 feet are
apparently favored by frequent light fires. Prescribed burning, as used
in the Pine Barrens by foresters in recent years, calls for setting light
fires, mostly in the
winter, to reduce accumulation of fuel. Although this is mainly done to
reduce the wildfire hazard, prescribed bu rning tends to create pine stands
of seedling or seedling-sprout origin and to permit trees to develop without
the deformities created by severe
fires.
FIRE'S EFFECTS ON LOWLAND SITES
On lowland
sites -- both the pine stands of poorly drained soils and the white-cedar
stands of the swamps -- the effects of fire are just as varied
as they on upland sites. For example, deep-burning fires the organic
soils of swamps can create (1) ponds, flats with a shallow layer of
water covered
by leatherleaf (2) flats with a shallow layers of water covered by leatherleaf
or
(3) meadows containing a wide variety interesting herbaceous plants. Killing
fires that do not burn deeply enough to create any of the above conditions
can result in forests of white-cedar, of swamp hardwoods, or of a mixture
of cedar and hardwoods.
SUMMARY
On upland sites, all of the various
combinations species occur on a wide variety of soils, so fire history
has been more important in shaping the
present-day forest than soil differences. Though the organic content
and drainage has created difference in the vegetation of the pinelands
and
swamps, her too, fire has been the overriding factor in shaping both
the lowlands and swamps.
Permission to reprint this copyrighted article which
appeared in the Winter 1978 edition of Frontiers magazine was granted by
the Academy of Natural Sciences of Philadelphia. |
