William B. Leak

Gap capture in northern hardwoods: patterns of establishment and height growth in four species.

Abstract We sought to determine whether four tree species that commonly coexist—American beech ( Fagus grandifolia Ehrh.), sugar maple ( Acer saccharum Marsh.), red maple ( Acer rubrum L.), and yellow birch ( Betula alleghaniensis Britt.)—differed in their patterns of establishment in gaps and their height growth after gap formation. Fifty-eight canopy trees were sampled in four experimentally created canopy gaps, 44–48 years old, in a northern hardwood forest at the Bartlett Experimental Forest, NH. Using stem analysis, we determined the year of origin of each tree and its pattern of height growth. Over two-thirds of beech and sugar maple canopy trees were advance regeneration, while most yellow birch stems established after gap formation. Red maple was a mixture of the two. Beech had the oldest stems at the time of gap formation (5 out of 18 stems over 20 years of age). No canopy tree established later than four years after gap formation. Species differed in their patterns of height growth, with beech growing more slowly than the others immediately after gap formation. Beech, however, grew at a more constant rate than sugar maple and yellow birch, and approached the heights of these species 30 years after gap formation. Red maple was the tallest and maintained a constant growth rate over the 30-year period. In beech and sugar maple, individuals that established after gap formation eventually grew faster and caught up with those establishing via advance regeneration.

Sixty years of management and natural disturbance in a New England forested landscape

Abstract Changes in species composition of overstory trees (percent of basal area) and size class were monitored over 60 years on 441 cruise plots located on the Bartlett Experimental Forest, a 1052 ha experimental forest in the White Mountains of New Hampshire. The plots were analyzed by elevation class, landtype (deciduous and coniferous), and year (1931–32, 1939–40, and 1991–92) within managed and unmanaged stands. The primary changes in species composition over the 60-year period were due to natural succession, which resulted in marked increases (doubling) of the eastern hemlock ( Tsuga canadensis (L.) Carr.) component, and consistent decreases in paper birch ( Betula papyrifera Marsh.), yellow birch ( B. alleghaniensis Britton) (at medium or low elevations), and aspen ( Populus spp.). Timber management resulted in small decreases in the beech ( Fagus grandifolia Ehrh.) and red spruce ( Picea rubens Sarg.) component and slight increases in sugar maple ( Acer saccharum Marsh.). Natural disturbances (beech-bark disease and hurricane damage) had only minor effects on species occurrence. No consistent evidence of red spruce ( Picea rubens Sarg.) decline was detected. Eastern hemlock, a climatically sensitive species in northern New England with a limited elevational range, increased dramatically at moderate to low elevations, but showed little tendency to invade the highest elevation class; apparently, the warming trend reported elsewhere in New Hampshire is not occurring, or the species are not responding in terms of changes in elevational distribution. The results emphasize the resilience of New England forests and their resistance to exogenous disturbance.

Origin of sigmoid diameter distributions

Diameter distributions--numbers of trees over diameter at breast height (d.b.h.)--were simulated over 20-years using six diameter-growth schedules, six mortality trends, and three initial conditions. The purpose was to determine factors responsible for the short-term development of the arithmetic rotated sigmoid form of diameter distribution characterized by a plateau, near plateau, or bump in the mid-diameter d.b.h. classes. A distinct rotated sigmoid developed when the diameter-growth schedule dropped precipitously in the mid-diameter classes; this might reflect a decadent overstory and thrifty understory. When the initial diameter distribution was distinctly sigmoid, diameter-growth schedules characterized by slow growth in the small-diameter classes tended to maintain sigmoid characteristics. A parabolic growth trend with or without parabolic mortality, also produced moderate rotated sigmoid characteristics. Under most other growth or mortality schedules, the 20-year diameter distribution was J shaped. The results reinforce the concept that diameter distributions tend to maintain or return to the J shape particularly with respect to New England northern hardwoods.

Seed fall in an oldgrowth northern hardwood forest

Seed fall was measured for 11 years in a 200-year-old stand of sugar maple, yellow birch, and beech in New Hampshire. Yellow birch had 5 good seed years, sugar maple had 3, and beech had none. Viable seed fall of yellow birch began in August and continued through autumn and winter. Most of the viable sugar maple seed fell during a short period in October. Beech seed fall occurred slightly later than sugar maple. Seed losses caused by pollination or fertilization failure, abortion, incomplete development, insects, small mammals, and birds averaged about 213 of the total seed fall, but varied widely among years.

Long-term species and structural changes after cleaning young even-aged northern hardwoods in New Hampshire, USA

Abstract The effects of four cleaning practices (including a control) on species composition and structural characteristics were studied over a 31-year period following treatment of an even-aged 25-year-old northern-hardwood stand that originated after complete clearcutting in 1933–1935. The treatments consisted of: a heavy and a light crop tree cleaning; a drastic species-cleaning treatment that removed nearly all pin cherry (Prunus pensylvanica L.f.), aspen (Populus tremuloides Michx. and grandidentata Michx.), striped maple (Acer pensylvanicum L.), and red maple (Acer rubrum L.) sprout clumps followed by a crop-tree cleaning; and an uncut control. There were no significant differences among treatments in species and structural characteristics in the 56-year-old stand at the end of the study period, except for the presence of a moderate aspen component in the light cleaning and the control. Although previous research shows that cleaning treatments in young northern hardwoods may have silvicultural and economic benefits, the impact of such treatments on long-term stand development is relatively minor.

Migration of tree species in New England based on elevational and regional analyses

With field measurements of migration patterns, we used two complementary approaches to examine tree-species movement after a documented increase in temperature. The advancing-front theory was used to examine age trends over distance and elevation for both a mountain site in New Hampshire and a regional comparison across the State of Maine. Well-defined stationary fronts were identified for red spruce (Picea rubens) and beech (Fagus grandifolia), while a catastrophic front was depicted for sugar maple (Acer saccharum) and a constant slow-moving advancing front was exhibited by hemlock (Tsuga canadensis). The regional analysis, in Maine, indicated that white pine (Pinus strobus) and balsam fir (Abies balsamea) decreased significantly in average latitude and elevation over a 24-year period. The potential ranges of the major species in terms of elevation and regional position appear stable.

Six-year beechnut production in New Hampshire.

Beechnut production and losses were studied over a 6-year period in 41 northern hardwood stands ranging in age from 10 to 140 years in the White Mountains of New Hampshire. Beechnut production increased consistently with stand age or d.b.h. of dominant trees and percentage of basal area composed of beech. Losses to insects, rodents, and birds before the seed reached the ground ranged from 24 to 100 percent; insects caused the greatest losses. Good seed years occurred about every third year.

Seventy-year record of changes in the composition of overstory species by elevation on the Bartlett Experimental Forest

Remeasurements over a 70-year period (1931-1932 to 2002-2003) on 404 cruise plots on the Bartlett Experimental Forest in New Hampshire provided a record of landscape-level changes in the composition of overstory species over time by elevation and d.b.h. (diameter at breast height) classes. Typically, early to midsuccessional species declined while late successional species, especially hemlock, increased. The exception was at upper elevations (2,000 feet and higher), where natural wind disturbance maintained a variable component of paper and yellow birch. There is no evidence of species decline or migration that is inconsistent with natural succession or natural disturbance.

Regeneration of upper-elevation red oak in the White Mountains of New Hampshire

Northern red oak occurs in limited amounts with a mixture of softwoods on the shallow soils at upper elevations in northern New England. These stands are important for wildlife habitat and forest diversity as well as a modest amount of timber harvesting. Little experience or research is available on how to regenerate upper-elevation oak. However, an examination of a 35-year-old clearcut on an upper slope of the Bartlett Experimental Forest reveals successful oak regeneration. We describe the species mix and tree sizes in the clearcut stand, the species composition and advanced oak regeneration in the adjacent uncut portion of the stand, and suggest methods for regenerating upper-elevation oak.

Tree species migration studies in the White Mountains of New Hampshire

The movement of tree species in either latitude or elevation has attracted increased recent attention due to growing national/international concerns over climate change. However, studies on tree species movements began in the early 1970s in the White Mountains of New Hampshire, mostly due to ecological interests in the episodic behavior of upper-elevation tree species on some of the most scenic mountains. Observations taken while making elevational transects appeared to indicate that regeneration of some species was advancing or retreating in relation to the main stand of mature trees. This process was formalized into a graphical model that would predict rates of movement which was then tested on the Bartlett Experimental Forest located in the White Mountain National Forest. This paper describes the several types of migrational models that were developed as well as long-term remeasured plot evidence against significant recent changes in the species distributions.