Thomas D. Lee

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.

Temporal patterns of vascular plant diversity in southeastern New Hampshire forests

Abstract A chronosequence of 22 sites in Durham, NH, was used to study upland successional patterns of species diversity over a span of 14–209 years of forest development and to test the hypothesis that diversity is maximized at mid-succession. Nested quadrat sampling was used to estimate the relative importance values of vascular plant species in the tree, shrub, and herb strata. The successional status of each site was estimated using two dendrochronological indices: oldest tree index and abandonment index. Four indices of species diversity were calculated for each site and stratum: species richness, the Shannon index, Hurlbert’s probability of interspecific association, and Pielou’s evenness. Within the quadrats of all 22 sites, total richness was 168 species of vascular plants. Richness decreased linearly over the 200-year chronosequence in all strata for both successional indices, from a maximum of 74 species at 14 years to a low of 13 species at 209 years. Evenness showed no evidence of a successional pattern, so the combined indices of diversity (Shannon and Hurlbert) displayed only weak trends. Multiple regression showed that successional age was always a significant predictor of species richness in every stratum (except the shrub stratum when using the abandonment index), and that stem density (i.e., the “sample size effect”) was not significant in the tree stratum when using the oldest tree index. Age indices held comparable or lower P -values than stem density in most strata. It is likely that richness increased from a low value immediately following farm abandonment to a peak around the age of the youngest sites sampled (over a span of 15–30 years), the rate of increase being governed by the availability of dispersing seeds. The observed decline in richness over the rest of succession was probably caused in part by a decrease in available light. The rate of decline was apparently determined by the rate of competitive elimination of shade-intolerant species.

INTERACTIONS OF LOCAL AND REGIONAL PROCESSES: SPECIES RICHNESS IN TUSSOCK SEDGE COMMUNITIES

Grimes model of plant species richness was used as a basis for examining how local and regional processes interact in the regulation of the species richness of vascular plants growing on individual Carex stricta (tussock sedge) tussocks in New Hampshire, USA. We first used a correlational study of 71 tussocks in five marshes to examine the relationships between species richness and standing crop + leaf litter biomass. We found humped (unimodal) relationships with a wide variation in peak species richness per tussock among sites. Then, using a factorial design involving 167 tussocks in three marshes, we performed Carex stricta standing crop removals, leaf litter removals, and seed additions to examine how these factors interacted to influence species richness. The results of both studies supported Grimes model, which implies that the magnitude of local competitive effects on plant species richness is dependent on regional propagule availability.

POTENTIAL IMPACTS OF THE INVASIVE EXOTIC SHRUB RHAMNUS FRANGULA L. (GLOSSY BUCKTHORN) ON FORESTS OF SOUTHERN NEW HAMPSHIRE

Abstract This paper investigated the potential for the exotic shrub Rhamnus frangula L. (glossy buckthorn) to alter native plant community composition in southeastern New Hampshire. Stratified random sampling was performed with 2 m × 2 m plots randomly located in 5 m intervals along three 50 m transects in four even-aged Pinus-mixed hardwood forests, three of which were managed stands. The associations between R. frangula and the measured species abundances and environmental variables were investigated using linear, least-squares multiple regression and Non-metric Multidimensional Scaling Ordination. Plot basal area of R. frangula was inversely related to woody seedling density (p < 0.001), herb cover (p < 0.05), and species richness (p < 0.01). The relative contribution of R. frangula to explaining variance in seedling density was greater than canopy openness, soil pH, soil clay, or soil sand. Abundance of R. frangula was a statistically significant predictor (p < 0.05) of individual herb species abundances for all study sites. This evidence supports the hypothesis that R. frangula causes a decline in seedling density and alters native ground level plant species abundances. Furthermore, the patterns agree with the suppression of ground level plant species abundances by R. frangula found in removal experiments.

Experimental Removal of the Non-indigenous Shrub Rhamnus frangula (Glossy Buckthorn): Effects on Native Herbs and Woody Seedlings

Abstract Effects of the non-indigenous shrub Rhamnus frangula L. (glossy buckthorn) on tree recruitment, herb cover, forest floor plant species richness, and R. frangula recruitment were tested in two southeastern New Hampshire Pinus forests using a randomized complete-block field experiment. The treatment, applied in January of 2000, was the presence of well-established R. frangula populations with three levels: R. frangula absent prior to experiment (“uninvaded”), > 90% R. frangula cover (“Rhamnus present”), and removal of > 90% R. frangula cover (“Rhamnus removed”). After 2 years of measurements, Rhamnus present had significantly lower first-year native tree seedling density than Rhamnus removed and uninvaded plots (0.11, 0.40, and 0.40 seedlings/m2 respectively). First-year native tree seedling density in the Rhamnus removed and uninvaded treatments were similar. Neither percent herb cover nor plant species richness were significantly affected by the removal of R. frangula in the two years following treatment. We believe these results indicate that the presence of dense R. frangula inhibits the establishment of tree seedlings. Rhamnus removed plots sampled one year after removal had five-fold greater first-year R. frangula seedling density than the other treatments. However, after two years first-year R. frangula seedling density was similarly low in all treatments (< 0.5 R. frangula seedlings/m2). Control efforts for R. frangula may need to focus on conspecific seedling emergence for at least two years following initial control.

Forest community analysis and the point-centered quarter method.

The point-centered-quarter (PCQ) method has been applied in community analysis since the publication of the method nearly 50 years ago. This and other distance methods offer increased sampling efficiency over fixed-area plots (FAP), but have long been known to produce biased density estimates when plant distribution deviates from random spatial patterns. Spatial indices have been developed to quantify the direction of this bias when plant distributions are aggregated or evenly distributed. Its continued use, especially in community analysis, requires additional scrutiny in measurements of community structure. We measured 14 forest stands of varying age, elevation and disturbance regime using FAP and PCQ methods. Density estimates were biased, with the point-centered quarter method lower than fixed-area plot estimates when stems were aggregated and higher when stems were evenly spaced. In general the PCQ method underestimated species richness. The efficiency of the PCQ method makes it popular for ordination studies, although comparison of community structure varied from 18% to 90% similarity between the measurements of species basal area in the same stands using the two different methods. The bias observed in calculations of stem density, species abundance and community similarity indicate that use of the PCQ method should be approached with caution when used in community level analysis.

Upland old-field succession in southeastern New Hampshire1

HOWARD, L.F AND T.D. LEE. (Department of Plant Biology, University of New Hampshire, Durham, NH, 03824). Upland old-field succession in southeastern New Hampshire. J. Torrey Bot. Soc. 129: 60-76. 2002.A 22-site chronosequence was used to study old-field successional communities in Transition Hardwood forests of Durham, NH. Sites ranged from recently abandoned fields to hemlock forests greater than 200 years old. Trees, shrubs, and herbs were sampled in nested quadrats, and importance values were calculated. Increment borings were used to determine site ages. Five woody community types were identified using cluster analysis and ordination: 1) Gray Dogwood and 2) Juniper-Blackberry-Sweetfern (both early-successional, 14-23 years since abandonment), 3) White Pine and 4) Oak-Viburnum (both mid-successional, 50-150 years since abandonment), and 5) Hemlock (late-successional, 100-200+years since abandonment). Six herb stratum associations were found: 1) Kentucky Bluegrass and 2) Goldenrod-Dewberry-Buckthorn (both early-successional), and 3) Pennsylvania Sedge, 4) Wild Sarsaparilla, 5) Canada Mayflower, and 6) Canada Yew (all mid-late successional). Photosynthetically active radiation (PAR) declined exponentially over the 200-year chronosequence, and the temporal importance of woody species in the understory was associated with particular forest floor light levels. Actual succession at individual sites with similar soils may also be modified by previous land-use history, differential seed availability, and post-agricultural disturbance.

Effects of Invasive Winter Moth Defoliation on Tree Radial Growth in Eastern Massachusetts, USA

Winter moth, Operophtera brumata L. (Lepidoptera: Geometridae), has been defoliating hardwood trees in eastern Massachusetts since the 1990s. Native to Europe, winter moth has also been detected in Rhode Island, Connecticut, eastern Long Island (NY), New Hampshire, and Maine. Individual tree impacts of winter moth defoliation in New England are currently unknown. Using dendroecological techniques, this study related annual radial growth of individual host (Quercus spp. and Acer spp.) trees to detailed defoliation estimates. Winter moth defoliation was associated with up to a 47% reduction in annual radial growth of Quercus trees. Latewood production of Quercus was reduced by up to 67% in the same year as defoliation, while earlywood production was reduced by up to 24% in the year following defoliation. Winter moth defoliation was not a strong predictor of radial growth in Acer species. This study is the first to document impacts of novel invasions of winter moth into New England.

Forest community composition and dynamics of the Ossipee Pine Barrens, New Hampshire1

Abstract In New Hampshire, the Ossipee Pine Barrens is the largest and best example of a Pinus rigida-Quercus ilicifolia dominated ecosystem remaining in the state. Because of long-term fire suppression in the 20th century, we hypothesized that undisturbed stands may be undergoing succession to more shade-tolerant Pinus strobus and hardwoods. To test this hypothesis, we sampled 41 sites within the barrens covering the range of soils, landforms, stand age, and vegetational variation present in the barrens. Current (2002) tree (≥ 10 cm dbh) and sapling (taller than 1 m, < 10 cm dbh) densities were measured by quadrat sampling. Past (1952) vegetation was reconstructed using reverse-growth equations derived from increment cores from trees alive in 2002 and forensic evidence such as stumps. Future (2052) vegetation was estimated using a simple transition model based on 1952–2002 compositional changes. Community types were classified using cluster analysis of 80 communities based on the 2002 and back-casted 1952 tree species abundances at the study sites. Cluster analysis of the 80 communities using tree relative densities produced four community types, dominated by 1) P. rigida, 2) P. rigida and Acer rubrum, 3) P. strobus and A. rubrum, and 4) A. rubrum, respectively. The frequency of the Pinus rigida community type was highest in 1952 and declined with time, with only 8% of sites predicted to support pitch pine canopies by 2052. The Pinus strobus-Acer rubrum community type increased between 1952 and 2002 as the Pinus rigida type declined, and should continue to increase in the future. The other two communities appeared to be transitional. Pinus rigida was even-aged on most sites, where forests averaged 97 ± 42 years (SD) old. Many sites will transition to P. strobus and hardwoods as canopy pitch pines die, because P. rigida recruitment was not occurring in most stands.

Use of waveform lidar and hyperspectral sensors to assess selected spatial and structural patterns associated with recent and repeat disturbance and the abundance of sugar maple (Acer saccharum Marsh.) in a temperate mixed hardwood and conifer forest

Waveform lidar imagery was acquired on September 26, 1999 over the Bartlett Experimental Forest (BEF) in New Hampshire (USA) using NASAs Laser Vegetation Imaging Sensor (LVIS). This flight occurred 20 months after an ice storm damaged millions of hectares of forestland in northeastern North America. Lidar measurements of the amplitude and intensity of ground energy returns appeared to readily detect areas of moderate to severe ice storm damage associated with the worst damage. Southern through eastern aspects on side slopes were particularly susceptible to higher levels of damage, in large part overlapping tracts of forest that had suffered the highest levels of wind damage from the 1938 hurricane and containing the highest levels of sugar maple basal area and biomass. The levels of sugar maple abundance were determined through analysis of the 1997 Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) high resolution spectral imagery and inventory of USFS Northern Research Station field plots. We found a relationship between field measurements of stem volume losses and the LVIS metric of mean canopy height (r2 = 0.66; root mean square errors = 5.7 m3/ha, p < 0.0001) in areas that had been subjected to moderate-to-severe ice storm damage, accurately documenting the short-term outcome of a single disturbance event.