James R. Runkle

Patterns of Disturbance in Some Old-Growth Mesic Forests of Eastern North America

To characterize the disturbance regime of one type of vegetation, study areas in which relatively small-scale disturbance predominates were chosen in several old-growth mesic forests in the eastern United States. Canopy openings covered 9.5% of total land area. New gaps were formed at an average rate of 1% of total land area per year; old gap area closed at a similar rate primarily by sapling height growth. With increased gap size, vegetation within gaps increased in woody species diversity, total basal area, and total number of stems. Stems also showed accelerated growth into larger size classes. As gaps aged, stems grew into larger size classes and basal area increased. Species responses to canopy gaps varied. Some species survived and became established in fairly small gaps (50-100 M2). Although in large gaps (up to 2009 m2 in the present study) these species usually increased in total number of stems and basal area, they declined in importance relative to species which rarely survived in small gaps but grew rapidly in large gaps. The disturbance regimes in the forests studied favored tolerant species but allowed opportunists to persist at low densities.

Treefalls revisited: gap dynamics in the southern Appalachians

In 1976-1977, 284 gaps (canopy-opening sizes 1-1490 M2) were sampled (age, size, species composition) from old-growth mesic forests in Great Smoky Mountains National Park, Joyce Kilmer Wilderness Area and Walker Cove Research Natural Area. In 1983, the woody vegetation (stems - 1 cm dbh) of 273 of these gaps was resampled, rates of gap closure by canopy tree branch growth and sapling height growth were estimated, and incidences of disturbances occurring since 1976-1977 were noted. The average yearly crown extension growth rate was 18 cm/yr, with much variation among species and in- dividuals. Some individual crowns grew into the canopy opening as much as 4 m in the 7 yr. Saplings grew an average of 30 cm/yr in height, again with much variation. Overall, taller saplings grew somewhat faster than smaller ones and saplings in large gaps grew faster than those in small gaps. These two rates of gap closure together suggest that most saplings will require two or more gap episodes to reach the forest canopy. For woody vegetation, basal area per unit gap area was originally highest in small gaps, though it increased between sampling dates most in large gaps. Stem density had been highest in small old gaps, but decreased the most in old gaps. Tsuga canadensis, Fagus grandifolia, Acer saccharum, and Halesia carolina were the most important species in the gaps studied. Most species did not change in relative density or dominance between the two sampling dates and showed no significant correlations between those parameters and gap size and age. Overall, Tsuga and Fagus decreased and Acer saccharum increased in importance. High rates of repeat disturbance favor species able to grow in intermediate light levels and to survive several periods of suppression before reaching the canopy.

CANOPY TREE TURNOVER IN OLD-GROWTH MESIC FORESTS OF EASTERN NORTH AMERICA

I studied the dynamic nature of old-growth, eastern U.S. forests by addressing the following questions: (1) How much do stand density, basal area, and size structure vary over time within several old-growth remnants? (2) How do mortality and growth rates vary with stem size? (3) How much does the importance of individual species vary over time and space? (4) At what rate do snags and stumps form and deteriorate? In 1990–1991, I resampled canopy stems within several old-growth remnants in the southern Appalachians, in Hueston Woods State Park, Ohio, and in the Tionesta Scenic and Research Natural Areas, Pennsylvania. I had previously sampled those sites in 1976–1977 using the point-centered quarter method. I remeasured the same trees and measured new trees if the old ones had died or if a new stem closer to the point than the old stem for that quarter had grown to ≥25 cm in diameter at breast height. Density and basal area changes were small. Density changes equaled −0.33%, −0.52%, and 0.00%/yr for the sou...

CHANGES IN SOUTHERN APPALACHIAN CANOPY TREE GAPS SAMPLED THRICE

Species responses to disturbance (mortality of dominant individuals within a community) influence many aspects of that ecological community. To trace the responses of vegetation to one particular type of disturbance, I sampled vegetation in 250 canopy gaps in 1976/1977, 1983, and 1990/1991. These gaps were located in three sites in the southern Appalachians of eastern North America: Great Smoky Mountains National Park, Walker Cove Research Natural Area, and Joyce Kilmer Wilderness Area. Each gap was sampled thrice for sapling composition (stems ≥1 cm in diameter at breast height). Additional measurements included the extension growth of border trees into the gap, recent mortality rates of border trees, deterioration rates of gap makers that had been standing dead in earlier samples, and the composition of understory plots. The mean extension (branch) growth of border trees was 12 cm/yr, with slower growth by longer branches. Gap makers that had been tall stumps tended to deteriorate, although 35% stayed intact over the 14 yr of the study. Border-tree mortality averaged 0.60%/yr, with higher rates for larger stems and with much interspecific variation. Stem density of saplings in gaps increased during the first sampling interval and decreased during the second as self-thinning counteracted increased establishment. Basal area increased during both sampling intervals. The death of border trees increased basal area per unit gap area. The four main species (Acer saccharum, Tsuga canadensis, Fagus grandifolia, and Halesia carolina) showed different patterns of correlation to gap size and age. Species in general showed more correlations with gap age for the first sample than afterwards; gap size was more consistently related to species importance. Species patterns also were affected by the presence or absence of border-tree mortality. The stands studied seem nearly at equilibrium. Some small changes are likely to occur, but the species present dominated all size classes: gap saplings, border trees, other canopy trees not related to gaps, and understory saplings. Species differed in their relative growth rates in the understory and in gaps of different sizes. Species also differed in their survival rates in the understory and in the canopy.

Edge versus Age Effects in the Development of a Beech-Maple Forest

Differences in the species composition of plots on the edge and the interior of a disturbed second-growth stand and an undisturbed old-growth beech-maple stand in Ohio, USA, were studied. Differences attributed to position (edge versus interior) were more pronounced than differences due to the age of the stand (interior of second-growth versus interior of old growth). The marginal plots of the old-growth stand are characterized by increased densities of saplings and trees of Carpinus carolina, Fraxinus americana, Ostrya virginiana, Quercus rubra, and Tilia americana. Conversion of much of the Midwestern portion of the US to small fragmented woodlots or habitat islands suggests that small but continuous environmental differences associated with the forest edge may have a greater impact on stand composition than brief but large scale disturbances associated with logging.

Mortality and replacement patterns of an old-growth Acer-Fagus woods in the Holden Arboretum, northeastern Ohio.

Abstract The objective of this study was to establish baseline data for the structure and dynamics of an old-growth beech (Fagus grandifolia)-sugar maple (Acer saccharum) woods in northeastern Ohio before the anticipated future impacts of disturbances such as beech bark disease. Several parameters were selected for study based on their likelihood of being influenced by these disturbances including: (1) species composition; (2) mortality and growth rates of trees, overall, by species and by size class; (3) canopy replacement patterns; (4) coarse woody debris (CWD) characteristics; and (5) the understory response to existing openings and its implications for change in the forest under present conditions. This study extends our understanding of beech-sugar maple old growth because our site is, perhaps, the most northeasterly one not yet affected by beech bark disease and because it is the only studied site influenced by weather conditions generated by Lake Erie. The overall annual mortality rate (from 1992 to 1997) of 2.3% was higher than that reported for other old-growth woods (1%). Mortality was highest for the large canopy stems (≥50 cm dbh) of beech and the subcanopy stems (10–25 cm dbh) of sugar maple. Growth rates decreased with stem size for beech, but increased with stem size for sugar maple. Over the 5 y period beech decreased in relative basal area and relative density whereas sugar maple increased in both measures. CWD mass (35.9 Mg ha−1) was similar to other old-growth deciduous forests. Beech mortality has been greater than sugar maple mortality for several years. Sugar maple and beech were dominant in the understory although few stems <1 cm dbh were found near treefall gaps. Older gaps had more numerous and larger stems. Currently, the structure and dynamics of the woods are very similar to other old-growth beech-sugar maple forests of the region. Beech is present in all size classes. However, the number of large beech stems has been declining steadily even though beech bark disease has not yet reached the area.

Early gap successional pathways in a Fagus‐Acer forest preserve: pattern and determinants

. Many theories of forest succession imply that terrestrial plant community composition within a region tends to converge toward a climax community. That is, given similar climatic and edaphic conditions, succession at different sites within an area will lead to comparable species compositions, a pattern referred to as successional convergence. In this study, we examine changes in plant composition within forest canopy gaps over a 17-yr period to identify potential patterns of successional convergence and to ascertain the factors controlling the successional pathway. To do so, we: (1) sampled 36 forest canopy gaps in Hueston Woods Nature Preserve in 1977, 1981, 1985, 1989 and 1993, (2) evaluated changes in the similarity of gap composition over this period, and (3) examined gap composition in each year as a function of variables describing gap habitat, seed source proximity, and disturbance history. Results indicated an initial pattern of successional divergence, with gaps exhibiting increased dissimilarity over the first 10–12 years of succession. We attribute this initial period of divergence to the effects of differential seed inputs from edge individuals and heterogeneity of available light due to differences in gap size. Recent surveys, however, indicated that gap composition has become more similar as competition within gaps has become more intense. In these samples, gap composition is closely linked to site conditions, including slope, soil conditions, and site exposure. Finally, while these patterns may suggest equilibrium-oriented dynamics, non-equilibrium processes such as repeat disturbances are also evident at Hueston Woods and will likely play an important role in determining future successional pathways.

Factors Influencing Species Composition in Canopy Gaps: The Importance of Edge Proximity in Hueston Woods, Ohio

In this research, we attempt to quantify the factors structuring woody species composition within forest gaps in the interior of Hueston Woods Nature Preserve, Ohio. Our results indicate that composition is related not only to factors commonly cited in other studies, including disturbance history, topographic position, and environmental factors (e.g., gap age, soil pH, slope, and aspect), but also to the proximity of forest edge communities. Partitioning of species variation to environmental factors, spatial factors, and spatially structured environmental factors reinforces the importance of both environment and edge proximity in explaining gap composition. These findings underscore the need for a more complete understanding of the potential impacts of edge effects in fragmented landscapes.

Thirty-two years of change in an old-growth Ohio beech–maple forest

Old-growth forests dominated by understory-tolerant tree species are among forest types most likely to be in equilibrium. However, documentation of the degree to which they are in equilibrium over decades-long time periods is lacking. Changes in climate, pathogens, and land use all are likely to impact stand characteristics and species composition, even in these forests. Here, 32 years of vegetation changes in an old-growth beech (Fagus grandifolia)-sugar maple (Acer saccharum) forest in Hueston Woods, southwest Ohio, USA, are summarized. These changes involve canopy composition and structure, turnover in snags, and development of vegetation in treefall gaps. Stand basal area and canopy density have changed little in 32 years. However, beech has decreased in canopy importance (49% to 32%) while sugar maple has increased (32% to 47%). Annual mortality was about 1.3% throughout the study period. Mortality rates increased with stem size, but the fraction of larger stems increased due to ingrowth from smaller size classes. Beech was represented by more very large stems than small canopy stems: over time, death of those larger stems with inadequate replacement has caused the decrease in beech importance. Sugar maple was represented by more small canopy stems whose growth has increased its importance. The changes in beech and sugar maple relative importance are hypothesized to be due to forest fragmentation mostly from the early 1800s with some possible additional effects associated with the formation of the state park. Snag densities (12-16 snags/ha) and formation rates (1-3 snags.ha(-1).yr(-1)) remained consistent. The treefall gaps previously studied are closing, with a few, large stems remaining. Death of gap border trees occurs consistently enough to favor species able to combine growth in gaps and survival in the understory.

Impacts of Beech Bark Disease and Deer Browsing on the Old-growth Forest

ABSTRACT Old-growth stands within the Tionesta Research Natural Area were sampled in 1977, 1990 and 2000. Sapling growth within 25 treefall gaps was sampled all three times. Canopy trees were measured using the point-centered quarter method, with 83 points sampled all three times. Gap regeneration increased significantly in density and basal area from 1977–1990. Beech (Fagus grandifolia) significantly increased its relative gap sapling density from 68% to 91% to 94% over the 3 y. Other species decreased in absolute numbers presumably due to deer browsing. Canopy tree density remained constant and basal area increased 1977–1990 but both decreased 1990–2000. Species relative density and basal area values did not change. Mortality rates almost doubled from 1977–1990 to 1990–2000, increasing especially for smaller canopy trees. Snag densities and formation rates also increased, though not significantly, from the first to the second time interval. Beech, in particular, showed large increases in mortality, probably due to the growing impact of beech bark disease, which reached the stand about 1990. The stand seems changing to a new state with less beech in the canopy and more in the understory. Which species will replace beech in the canopy is difficult to predict.