Glenn R. Matlack

Vegetation dynamics of the forest edge: trends in space and successional time

Forest herbs, shrubs, and tree seedlings were censused at five distances from human-generated edges at 14 sites in south-eastern Pennsylvania and northern Delaware, USA. Forest edges varied in orientation and in the degree of canopy closure, allowing comparisons of vegetation by aspect and successional stage. Soil depth and pH were measured at vegetation sampling points at a subset of sites; microclimate data were available from a parallel study. Edge-related pattern was observed in overall species composition, and in distributions of 15 individual species. At recently created forest edges, species abundances were correlated with steep climatic gradients. Although most edge-orientated species were clustered ≤ 5 m from the edge, some species consistently reached peak densities at distances up to 40 m, the greatest distance surveyed (...)

Spatial distribution and the performance of individual plants in a natural population of Silene dioica

Summary1)A natural population of the perennial herb Silene dioica was mapped at intervals over the course of a year. The ‘space available’ to each plant was estimated by a Thiessen polygon, defined by the position of the plants neighbours.2)Germination and recruitment of seedlings appeared to be unrelated to the position of individuals with respect to their neighbours.3)Various measures of plant growth were strongly correlated with polygon area in some seasons, suggesting that competition was occurring between individuals for spatially distributed resources. Plasticity allowed plants to exploit the available area, regardless of polygon shape or the number of neighbours defining a polygon.4)In the early spring phase of seedling establishment, growth appeared to be enhanced and seedlings lived longer when they were close to neighbours. In late spring this effect was replaced by the more rapid growth of individuals in the larger polygons, i.e. with more distant neighbours. This sequence of events is consistent with the onset of competition for resources in late spring.5)These effects were observed despite heterogeneity in the environment and variation in individual response.

Reassessment of the use of fire as a management tool in deciduous forests of eastern North America

Prescribed burning is increasingly being used in the deciduous forests of eastern North America. Recent work suggests that historical fire frequency has been overestimated east of the prairie-woodland transition zone, and its introduction could potentially reduce forest herb and shrub diversity. Fire-history recreations derived from sedimentary charcoal, tree fire scars, and estimates of Native American burning suggest point-return times ranging from 5-10 years to centuries and millennia. Actual return times were probably longer because such records suffer from selective sampling, small sample sizes, and a probable publication bias toward frequent fire. Archeological evidence shows the environmental effect of fire could be severe in the immediate neighborhood of a Native American village. Population density appears to have been low through most of the Holocene, however, and villages were strongly clustered at a regional scale. Thus, it appears that the majority of forests of the eastern United States were little affected by burning before European settlement. Use of prescribed burning assumes that most forest species are tolerant of fire and that burning will have only a minimal effect on diversity. However, common adaptations such as serotiny, epicormic sprouting, resprouting from rhizomes, and smoke-cued germination are unknown across most of the deciduous region. Experimental studies of burning show vegetation responses similar to other forms of disturbance that remove stems and litter and do not necessarily imply adaptation to fire. The general lack of adaptation could potentially cause a reduction in diversity if burning were introduced. These observations suggest a need for a fine-grained examination of fire history with systematic sampling in which all subregions, landscape positions, and community types are represented. Responses to burning need to be examined in noncommercial and nonwoody species in rigorous manipulative experiments. Until such information is available, it seems prudent to limit the use of prescribed burning east of the prairie-woodland transition zone.

Influence of Fruit Size and Weight on Wind Dispersal in Betula lenta, a Gap-colonizing Tree Species

-The prevailing model of wind-borne seed dispersal assumes that variation in seed size and weight controls patterns of seed distribution by limiting exposure to horizontal airstreams. To test the applicability of this model in a natural dispersal situation, seeds of Betula lenta were collected downwind of a population along transects which trapped seeds (a) after primary dispersal through the air, and (b) after primary aerial dispersal plus secondary dispersal across a snow cover. In order to examine mechanisms of seed flight, weights of 296 seeds were experimentally modified and duration and distance of seed flight measured in laboratory trials. Rate of descent of modified seeds depended strongly on individual seed weight and wing loading, and lateral movement in a horizontal airstream was determined by rate of descent, as predicted. In the field, however, distance traveled by aerial movement was only weakly linked to seed size and weight, and the relationship did not hold during secondary dispersal near the ground. Thus, seed size and weight are not the principal factors controlling seed movement under all conditions. It may be necessary to invoke models based on airstream turbulence.

Annual Variation in Fish Assemblages of Watersheds with Stable and Changing Land Use

Abstract Freshwater fish assemblages are sensitive to changes in land use, but it is unclear how rapidly assemblages respond to such change or how closely they track physical changes in the stream environment. We monitored fish assemblages at the outflow of three watersheds on the outer coastal plain of Mississippi over a period of 8 y. The watersheds differed in patterns of land use, being predominantly forested, rapidly urbanizing, and long-urbanized, respectively. Watersheds were distinct in fish species composition, differing primarily in abundance of Etheostoma lynceum, E. stigmaeum, Luxilus chrysocephalus and Lythrurus roseipinnis. Species richness was consistently greatest at the predominantly forested site and least at the urbanized site. Fish assemblages were distinguishable in terms of substrate preference, water-speed, silt tolerance, and trophic habit. The stream draining the urbanizing watershed showed an increase in richness of species of high silt tolerance and a decrease in richness of those preferring a gravel substrate over the sampling period. Contrary to expectation, annual variation in composition was modest relative to differences among sites. Annual variation in richness and numbers was unrelated to measures of streamflow or seasonal precipitation. Changes in stream character related to land use change appear to have impacted the fish assemblages of these streams, but the transition to an urban fish assemblage in the urbanizing stream occurred before the study period, well before the obvious signs of physical degradation appeared at the site.

Agricultural history drives structure and tree-species composition of second growth forest over 100 years in southeastern Ohio, USA

Questions Most modern forest in eastern North America has recolonized after abandonment from agriculture. Cultivation and pasturing, historically the dominant forms of agriculture, differ in their environmental legacies and potentially influence stand development following abandonment. We ask how the legacy of agriculture plays out in development of second-growth stands, and whether tree community composition and structure differ between sites with contrasting land-use histories. Methods Thirty-five second growth stands were sorted into a replicated chronosequence of formerly cultivated and pastured sites spanning 80 years. Stand age and land-use history were determined from historical aerial photographs and from site characteristics including microtopography and soil profiles. In addition, a control group was selected consisting of long-established forest stands showing no signs of agricultural disturbance. At each site stand composition and structure were described using the point-centered quarter method. Results Stand density declined and basal area increased through the chronosequence but neither pastured nor cultivated sites reached levels observed in the control group. Density decreased most dramatically between the 41-60 and 61-80 year age classes, consistant with competitive stand thinning. Tree community composition changed through time, reflecting a shift away from light-demanding successional species and toward long lived, shade-tolerant species characteristic of long-established forests. Composition and structure did not differ significantly between cultivated and pastured sites, but individual species did show significant differences with the greatest contrast evident shortly after abandonment. Conclusions Stand development following agriculture appears to be a process of convergence in species composition and density. Because most deciduous forest in eastern North America is less than 80 years old, these results suggest that most forest is still accruing biomass and has yet to reach a stable density and composition. This article is protected by copyright. All rights reserved.

Seed longevity and dormancy state suggest management strategies for garlic mustard ( Alliaria petiolata ) and Japanese stiltgrass ( Microstegium vimineum ) in deciduous forest sites

An effective management plan for invasive herb populations must consider the potential for regeneration from the soil seedbank. To test this potential, we examined two species, Japanese stiltgrass and garlic mustard, at deciduous forest sites in southeastern Ohio. Seeds were buried in nylon mesh bags and recovered at regular intervals over 24 mo. Recovered seeds were tested for germination and viability. Burial was replicated on north- and south-facing slopes to test for environmental control of dormancy state. Stiltgrass seeds experienced severe mortality in the soil, rarely surviving the full 24 mo. Stiltgrass showed fractional germination in the lab ranging from 86% to 89% of viable seeds in late spring (the season of natural seedling emergence) to complete nongermination in winter. Most garlic mustard seeds survived through the experimental period (82% and 88% survival across 24 mo) with consistently low mortality (0% to 13%) unrelated to season. Slope aspect had no significant effect on survival or dormancy state in either species. Extrapolation of garlic mustard mortality implies that reproduction would need to be suppressed for a substantial period (perhaps >10 yr) to ensure eradication of a population. In stiltgrass, rapid seed mortality suggests that control can be achieved in 2 to 4 yr. Nomenclature: Garlic mustard, Alliaria petiolata (Bieb.) Cavara and Grande; Japanese stiltgrass, Microstegium vimineum (Trin) A. Camus.

Do deer and raccoons defecate in the right place? Fitness consequences of vertebrate seed dispersal for a deciduous forest herb

Precision of seed placement in a heterogeneous environment is often assumed to select for the evolution of animal-mediated dispersal systems, but this hypothesis has rarely been tested in a multivariate sense. We quantify the microsite fitness benefits of dispersal by white-tailed deer (Odocoileus virginianus) and raccoons (Procyon lotor) for mayapple (Podophyllum peltatum), a shade-tolerant perennial herb, in deciduous forests of southeastern Ohio, USA. Micro-environmental variables were recorded at dung-deposition microsites, at rooting points of mayapple shoots, and at random (control) points in the forest. Fitness was assessed as the degree of overlap in ordinations of microsites by environmental variables. Mayapple occupied a broad sector (56%) of environment space corresponding to low and mid-slope positions, ravines, and proximity to trees. Deer and raccoon defecation placed dung in 71–74 and 86–95% of environment space, respectively, reaching mayapple microsites in 57–60 and 53–54% of cases. Deer placed dung in mayapple environment space 7–9% more often than predicted by random distribution, and raccoons placed dung in mayapple space 0–5% more often, consistent with only a modest degree of directed dispersal. Thus, the precision hypothesis is only weakly supported. The greatest fitness benefit of vertebrate dispersal appears to be the broad distribution of seeds, thereby increasing the probability of randomly reaching a suitable microsite. Imprecise dispersal suggests that secondary mechanisms of seed movement need to be explored in deciduous forest communities.

Seed longevity and dormancy state in a disturbance-dependent forest herb, Ageratina altissima

Does seed dormancy allow disturbance-oriented forest herbs such as Ageratina altissima to persist in heterogeneous natural communities? To document seed longevity and dormancy state, Ageratina seeds were buried in nylon mesh bags in second-growth forest stands in south-eastern Ohio, USA. Bags were recovered at 2-month intervals, and seeds were tested for viability and germinability in the lab. Live seed numbers declined rapidly, with seed banks exhausted in an estimated 33–37 months. Seeds showed a strong dormancy polymorphism, with 71–84% of live seeds germinable between March and July, the season of natural seedling emergence. At other dates, most seeds appeared to be in a state of induced dormancy, allowing little (0–21%) germination. The slope aspect of the burial site, an important factor controlling aboveground vegetation, had no effect on seed longevity or dormancy condition. Dormancy in Ageratina appears to be adapted to allow opportunistic germination in late spring–early summer, but to prevent germination in less benign periods. Seed longevity is shorter than the natural frequency of gaps in mesophytic forest. We conclude that a long-term dispersal/dormancy trade-off is probably an oversimplification of the spatial ecology of this species. The primary function of dormancy appears to be short-term tracking of seasonal variation.

Managing fire in the mesic deciduous forest when fire history is unknown: response to Stambaugh et al.

Thanks to Stambaugh et al. (2015) for their close reading of my review (Matlack 2013) and thoughtful comments, criticisms, and suggestions. I hope this exchange is the beginning of a much-needed discussion on the use of fire in moist and mesic deciduous forests of the eastern United States (hereafter, MDF). The purpose of Matlack (2013) is to emphasize the fine-grained nature of fire as an ecosystem process and to call attention to gaps in our understanding. My concern is that we are rushing to subcontinent scale generalization on the basis of sparse and idiosyncratic data.