Scott J. Meiners

The relationship between community diversity and exotic plants: cause or consequence of invasion?

Scott J. Meiners et al. — Thu, 21 Mar 2013 13:27:55 PDT

Invasion ecology has suffered from the artificial separation of invasibility and impact processes in understanding the ationship between diversity and plant invasion. By studying these independently functioning stages of invasion in concert, we can gain great insight into the biological causes and consequences of invasions, and develop crucial information for the generation of adequate management strategies. Our conceptual framework provides a structure to synthesize the current body of research, suggests research needed to fill the gaps in understanding and to organize results from future research. The framework is a powerful tool to guide ecological understanding of the relationship between invasion and diversity across systems, species, and scales. The case studies discussed here clearly show how both the cause and consequence of diversity may operate simultaneously hin an invasion to generate the community associations often noted in static studies. Currently, it is not possible to make generalizations about which mechanism is the most important because of the extreme lack of information for most plant invasions. To understand the nature of the relationship between diversity and invasion, both of these processes must be assessed to determine their relative contribution.

Seed and Seedling Ecology of Acer saccharum and Acer platanoides: A Contrast Between Native and Exotic Congeners

Scott J. Meiners — Wed, 07 Nov 2012 13:47:07 PST

The exotic tree, Acer platanoides, is increasing in forests of northeastern North America, largely within the range of its native congener, Acer saccharum. A combination of field and controlled experiments was used on seeds and seedlings of these congeners to determine species characteristics that may be contributing to these floristic changes. Acer platanoides experienced lower rates of seed predation than A. saccharum in field experiments. Differences in the dispersal and allocation characteristics of the two species were small and not likely to explain the relative success of A. platanoides. Greenhouse- grown seedlings of A. platanoides were much larger than those of A. saccharum because of differences in seed size, not differences in growth rate. These data suggest that preferential seed predation and initial seed size differences may explain greater relative success in Acer platanoides seedlings.

SEASON AND DISTANCE FROM FOREST - OLD FIELD EDGE AFFECT SEED PREDATION BY WHITE-FOOTED MICE

Scott J. Meiners et al. — Wed, 07 Nov 2012 13:44:58 PST

We studied the spatial pattern of seed predation across a forest-old field edge in both fall and winter to assess the potential for seed predators to influence plant spatial patterns. We used a 100 x 100 m grid that began 30 m inside the forest and extended 60 m into the old field. Inside this grid we placed seed stations at regular 10 m intervals and monitored seed removal. Seed predation varied significantly across the edge gradient in both fall and winter with the highest rate of seed removal at the edge in both trials. The spatial pattern of seed predation also differed between seasons. The field portion of the site (³ 30 m from the edge) was characterized by high seed removal rates in winter and low removal rates in fall. This spatial and temporal variation may alter tree establishment, causing long-term changes in plant community composition and structure.

Growth rates, survivorship, and sex ratios of Juniperus virginiana on the New Jersey Piedmont from 1963 to 2000

James A. Quinn et al. — Wed, 07 Nov 2012 13:18:10 PST

Growth rates, survivorship, and sex ratios of Juniperus virginiana on the New Jersey Piedmont from 1963 to 2000. J. Torrey Bot. Soc. XXX:000–000. 20XX.—Studies of the growth, survival, and sex ratios of dioecious species have been predominantly short-term. This research investigated growth rates, survivorship, and sex ratios among cohorts of Juniperus virginiana L. from 1963 through 2000. Males (M) and females (F) in six old-fields of different ages on the New Jersey Piedmont were analyzed, starting with the initial data on height and sex expression collected by John Small on labeled recruits from 1963 through 1976. These plants were relocated and censused during the summer and fall of 2000. No changes in sex expression were recorded between 1976 and 2000. The overall sex ratio was almost 1:1 (333 M, 332 F); only one of the fields showed a significant departure from 1:1. Males grew slightly, but significantly, faster in height than females, but relative growth rates dropped by approximately 50% for both males and females once they became reproductive. Female trees were on average 23 cm taller (and older) than males at first reproduction. Heights in those males and females surviving to 2000 were not significantly different. There was no effect of an individual’s sex on its likelihood of dying, but plants that became established later were shorter, often non-reproductive, and had an increased risk of mortality. These long-term results strongly support genetically-determined sex ratios and a lack of major differences between males and females in growth rates and survival, which had been suggested by single-year studies elsewhere in the species’ range.

Selective Predation on the Seeds of Woody Plants

Scott J. Meiners et al. — Wed, 07 Nov 2012 13:15:14 PST

Selective predation on the seeds of woody plants. J. Torrey Bot. Soc. 124: 67-70). 1997.-Seed predation may be an important factor influencing the structure of successional plant communities. We used a cafeteria-style experiment, placed in an old field and an early successional forest, to determine predator preferences for seeds of nine species of woody plants. Intensity of seed predation was equivalent in both sites. Seed predators preferred Acer saccharum, flex vertic illata, and Viburnum dentatum, but this was not related to seed mass. Predation intensity was more variable in the old field than in the forest, possibly related to the higher ground-layer heterogeneity of the old field site. We conclude that predator choice will allow some species to escape seed predation, potentially altering future plant community composition.

Survival of and Herbivore Damage to a Cohort of Quercus rubra Planted Across a Forest-Old-field Edge

Scott J. Meiners et al. — Wed, 07 Nov 2012 07:50:12 PST

Forest edges are known to affect plant community composition and habitat use by animals. However, the direct influence of edges in determining patterns of tree regeneration is poorly understood. Survival of and herbivore damage to Quercus ruln-a seedlings were experimentally determined for seedlings planted across a forest--old-field edge gradient. Seedling survival was lowest inside the forest ( 1%), intermediate at the edge (25%) and highest within the old-field portion of the gradient (49%). Deer herbivory decreased with increasing distance into the old field. Seedling survival increased under Rosa multiflora and decreased in plots with mammalian herbivory. Seedling height was significantly affected by distance from the edge but was unaffected by mammalian herbivory. Based on our results, herbivore effects on Quercus ruln-a growth and survivorship appear secondary to influences of distance from the forest edge.

Effects of Distance to Juniperus virginiana on the Establishment of Fraxinus and Acer Seedlings in Old Fields

Scott J. Meiners et al. — Wed, 07 Nov 2012 07:36:42 PST

It has been hypothesized that Juniperus virginiana facilitates tree seedling establishment in secondary succession. To test this hypothesis, we sampled four old fields in southwestern Ohio and monitored experimentally planted seeds and seedlings of Acer saccharum and Fraxinus americana for two years. Seeds and seedlings were placed into herbivore exclosures placed 0.3 and 3.0 m from J virginiana trees in an old field in Ohio. We found a significant positive spatial association between juniperus virginiana and tree seedling densities in all four old fields. Soil temperature, soil moisture, evaporative demand and light level in the 0.3 m treatment were significantly reduced, whereas litter depth was increased. Germination of A. saccharum, but not F americana, was reduced in the 0.3 m treatment, whereas seedling survival was unaffected in either species. Growth ofF americana seedlings was reduced by proximity to J virginiana but A. saccharum growth was not affected. Stomatal conductance was reduced in the 0.3 m treatment for F americana but unaffected in A. saccharum. Although there was a positive spatial association between J virginiana and tree seedlings in the old fields sampled, experimental seedlings did not exhibit an early demographic response that indicated facilitation.

Fungal Spore Dispersal by the Eastern Box Turtle (Terrapene carolina carolina)

S. C. Jones et al. — Wed, 07 Nov 2012 07:31:25 PST

Although spores from most macrofungi are wind- or water-dispersed, dispersal may also occur via biotic vectors. The Eastern box turtle (Terrapene carolina carolina) is a facultative mycovore that may play an important role in fungal spore dispersal although, to date, no information exists on fungi occurring in fecal samples of box turtles or on the ecological significance of box turtles as spore dispersal vectors. Consequently, a study of the potential for Eastern box turtles to act as vectors for spore dispersal was initiated by capturing wild turtles and collecting fecal samples. Serial dilutions from fecal samples were made to enumerate spores, quantify the number of spores per gram of fecal material and to isolate and identify fungi. Fungal spores were found to be extremely abundant throughout all samples. Fecal samples from 36 turtles yielded a total of 23 different fungal taxa in the Zygomycota, Ascomycota and Basidiomycota. Two yeasts that were isolated, Cryptococcus albidus and Rhodotorula mucilaginosa, are reported to naturally occur on Trifolium seeds found in fecal samples. A mold previously unreported from fecal material, Aspergillus wentii, was also found in fecal samples. Data collected suggests Eastern box turtles influence fungal spore dispersal by browsing on plant materials and defecating large numbers of fungal spores within their home ranges.

The Soil Seed Pool of Huffman Prairie, a Degraded Ohio Prairie, and its Potential in Restoration

Scott J. Meiners et al. — Tue, 06 Nov 2012 11:29:46 PST

The germinable seeds in the soil of a relict Ohio prairie were investigated to determine the composition and density of dicots of potential value in restoration. Soil samples were collected from three areas of the prairie with distinctive species compositions: swale, north upland, and south upland. Seed density and species composition were based on seedling emergence over 90 days. North upland and south upland samples yielded similar total seedling densities (5,902 and 5,109 m·2 ) while that of the swale was greater ( 15,262 m·2 ). Thirteen introduced and 18 native dicot species were present; seven of the latter were common in pre-settlement prairies. Sixty percent of the dicot seedlings were of native species. Swale samples contained fewer prairie species and were less diverse than those from the upland areas. Six species common in pre-settlement prairies had greater frequencies of germinable seeds than the vegetation; however, no seeds of prairie species were found that were not in the vegetation. This indicates that the seed pool may be useful in increasing densities of species already present but not in reestablishing species absent in the above-ground vegetation.

ADDITIVE AND NONADDITIVE EFFECTS OF HERBIVORY AND COMPETITION ON TREE SEEDLING MORTALITY, GROWTH, AND ALLOCATION

Scott J. Meiners et al. — Tue, 06 Nov 2012 09:43:20 PST

The interaction between simulated cotyledon herbivory and interspecific competition was studied in a greenhouse experiment using two species of trees, Acer rubrum and Quercus palustris, which commonly invade abandoned agricultural fields. Herbivory treatments were applied as a gradient of cotyledon removal for A. rubrum with 0, 25, 50, 75, and 100% of cotyledon tissue removed. Cotyledons from Q. palustris were clipped and removed (control, early, and late removal) to create a gradient of seed reserve availability. The competition treatment consisted of plugs of old-field vegetation that filled the pots with perennial cover. Mortality of seedlings was higher with competition. There was a significant interaction between herbivory and competition with the highest mortality occurring with competition at the highest intensity of herbivory in both species. Herbivory reduced biomass for Q. palustris only, while competition reduced biomass in both species. Neither species showed an interaction between herbivory and competition for growth. There was a significant interaction between herbivory and competition on allocation patterns for both species, with greater allocation to roots with competition at the highest intensity of herbivory. This study demonstrates the potential for cotyledon herbivory and competition to interact, altering the invasion of tree seedlings into abandoned agricultural land.

PROBABILITY OF TREE SEEDLING ESTABLISHMENT CHANGES ACROSS A FOREST–OLD FIELD EDGE GRADIENT

Scott J. Meiners et al. — Tue, 06 Nov 2012 09:08:57 PST

Forest edges affect many aspects of plant communities, causing changes in microclimate, species composition, and community structure. However, the direct role of edges in regulating forest regeneration is relatively unknown. The pattern of tree establishment across a forest–old field edge was experimentally examined to determine the response of three tree species to the edge gradient. We placed 100 1-m2 plots in a 90 3 90 m grid that began 30 m inside the forest, extended across the edge, and ended at 60 m into the old field. Into each plot, we planted seeds of Acer rubrum, Acer saccharum, and Quercus palustris. Emergence increased with distance into the field for both A. saccharum and Q. palustris. Emergence for A. rubrum increased from forest to field, reaching a maximum near 20 m into the field, and then declined with further distance. Nearly all A. rubrum seedlings died shortly after emergence. Survival of A. saccharum increased with distance into the old field, while survivorship of Q. palustris did not respond to the edge gradient. Establishment probabilities increased with distance into the old field for both A. saccharum and Q. palustris. Growth of Q. palustris and allocation patterns of A. saccharum also varied across the edge gradient. These results suggest that edges have complex, speciesspecific effects on tree establishment and growth that can influence the spatial pattern and species composition of regenerating forests.

NATIVE AND EXOTIC PLANT SPECIES EXHIBIT SIMILAR POPULATION DYNAMICS DURING SUCCESSION

Scott J. Meiners — Tue, 06 Nov 2012 08:47:42 PST

A growing body of literature has led to the debate in invasion biology whether exotic species perform within communities differently than native taxa due to inherent advantages. To address this issue, the population dynamics of native and exotic plant species were assessed from a 48-year record of permanent plot data from the Hutcheson Memorial Forest Center (New Jersey, USA) to determine rate of increase, lag time, maximum frequency, and the year of peak frequency. Overall, native and exotic species exhibited very similar population dynamics. Rates of increase and length of lag times were similar between native and exotic taxa but were strongly influenced by plant life form. Short-lived species were characterized by rapid population growth rates and short lag times. Growth rates decreased and lag times increased with species longevity. Overall, correlations between population metrics were the same in native and exotic taxa, suggesting similar trade-offs in life history patterns. The one difference observed was that, in native species, peak frequency was negatively associated with the year of peak frequency (i.e., early-successional species tended to become more abundant), while there was no relationship in exotic species. These analyses show that exotic species behave in essentially the same way as native taxa within dynamic communities. This suggests that abundant native and exotic plant species are exploiting the same range of ecological strategies resulting in similar roles within communities.

Succession

Scott J. Meiners et al. — Tue, 07 Feb 2012 10:41:27 PST

Succession in a strict sense refers to the recovery and revegetation of an area following a disturbance such as the cessation of agriculture, the retreat of a glacier, or an intense forest fi re. Succession is a special case of vegetation dynamics, although many early ecologists referred to all vegetation change as succession. Succession includes a series of compositional and structural changes, often in a directional manner. The common occurrence of natural disturbances coupled with the extent of human activity on the planet makes succession one of the most ubiquitous ecological processes. Because invasion is a crucial feature of succession, understanding the nature and controls of community dynamics is important for the science and management of invasive species.

Domain and Propositions of Succession Theory

Steward Pickett et al. — Tue, 07 Feb 2012 10:28:00 PST

Succession is perhaps the oldest of ecological concepts, having arisen when ecology was emerging as a self-conscious discipline (Mcintosh 1985). Yet it continues to address many fundamental issues in ecology, to support important applications, and to synthesize the insights and perspectives of other theories. Thus, it fulfills two functions key in assessing the utility of a contemporary ecological theory. First, it exhibits the attributes of a mature, welldeveloped, and intensively tested theory (Glenn-Lewin et al. 1992; Pickett and Cadenasso 2005). Second, it provides a linkage among theories and applications that have usually been considered separately (Walker et al. 2007). For example, the theory of succession or community dynamics has been applied to terrestrial and aquatic habitats (Bazzaz 1979; Stevenson et al. 1991; Biox et al. 2004), and for communities of microbes (Boucher et al. 2005), birds (Keller et al. 2003), soil invertebrates (Yi et al. 2006), and mammals (Schweiger et al. 2000).

Terrestrial Macrofungi of Illinois Old-Growth Prairie Groves

Scott J. Meiners et al. — Tue, 07 Feb 2012 09:36:24 PST

ABSTRACT.—Macrofungi from two old-growth prairie grove remnants in the Midwestern United States (Brownfield and Trelease Woods. Champaign Co., IL ) were surveyed over two summer and fall fruiting periods. Communities of Ascomycetes, Basidiomycetes and Myxomycètes were sampled and compared using multivariate statistical analyses. Standard estimations of species richness were calculated for comparison with other studies of fungal diversity. Environmental factors (rainfall, humidity, air temperature and soil temperature at 10 cm depth) as well as leaf litter composition, and woody plant communities were surveyed to assess their impact on fungal communities. Fungal community structure was found to differ significandy both between and within Brownfield and Trelease Woods. Communities of terrestrial macrofungi were determined to be strongly influenced by seasonality, with soil temperature at 10 cm depth showing the strongest correlation to changes in community composition. Brownfield and Trelease Woods, formerly part of a contiguous prairie grove with likely a single fungal community, are shown to have developed significantly different fungal communities over a period of separation of more than 120 y.

Allelopathic Effects of Goldenrod Species on Turnover in Successional Communities

Nikki Pisula et al. — Tue, 07 Feb 2012 09:33:14 PST

While goldenrod species are often found to be allelopathic in laboratory settings, its importance in controlling plant community dynamics has been much more difficult to assess. We designed a study to determine whether allelopathy is related to the success of goldenrods in abandoned agricultural land. To accomplish this, we conducted laboratory bioassays for six co-occurring goldenrod species and compared these results to the cover and impacts of these species in the field. We determined the germination responses of two target species to a gradient of leaf extract concentrations to assess the allelopathic potential of these goldenrods. We also used long-term successional data to determine the influence of each goldenrod species on community turnover. Germination percentages in the lab were reduced by leaf extracts for most goldenrod species and varied dramatically among species. In the field, influences of goldenrods on their associated communities were weak and opposite expected allelopathic effects, as the number of associated species generally increased with goldenrod cover. The relative strength of allelopathy among goldenrods was not related to the abundance achieved during succession. In this system, we documented the potential for goldenrods to exhibit allelopathic interactions in a controlled situation. However, these effects were not strong enough to alter community structure and turnover.

Spatiotemporal dynamics of lianas during 50 years of succession to temperate forest

Laura Ladwig et al. — Tue, 07 Feb 2012 09:28:49 PST

Although they are important components of forest communities, the general ecology and spatiotemporal patterns of temperate lianas during forest regeneration are largely unknown. The dependence of lianas on other plants for physical support makes them a potentially important driver of community dynamics. We examined 50 years of vegetation data from an old-field succession study to determine the dynamics and community controls on liana expansion within the Piedmont region of New Jersey, USA. Four lianas, Lonicera japonica, Parthenocissus quinquefolia, Toxicodendron radicans, and Vitis spp., occurred in enough abundance for detailed analyses. In general, liana cover peaked during mid-succession (20–30 years post-abandonment) when community composition was mostly herbaceous with scattered trees and shrubs. Liana cover began to decrease as trees became dominant and the canopy closed. Temporal patterns of cover dynamics of abundant species indicated three early- and one late-successional liana species within the community. In contrast to cover, frequency of lianas increased throughout succession, indicating that liana populations persisted despite dramatic declines in cover for the three early-successional species. Temporal dynamics between native and nonnative lianas were similar but spatially distinct as cover of native species dispersed and expanded near the forest edge while the nonnative species preferentially grew far from the forest. These dynamics indicate that successional processes may ultimately lead to the decline of most lianas. However, the persistence of lianas as high numbers of suppressed individuals suggests that they may rebound quickly following canopy disturbance.

Relative allelopathic potential of invasive plant species in a young disturbed woodland

Nikki Pisula et al. — Tue, 07 Feb 2012 08:22:20 PST

Invasive plant species are often more successful within introduced areas when compared to their natural ranges. Allelopathy has been suggested as a potential mechanism for this success because invasive plants frequently establish monocultures and may produce allelochemicals evolutionarily novel to the recipient community. However, species are typically tested in isolation making the relative strength of allelopathy difficult to assess. We conducted laboratory bioassays for 10 co-occurring non-native species to determine the relative strength of their allelopathic potential. These species represented a suite of successful invaders within a young forest and were from a variety of plant life forms: trees, lianas, shrubs, and herbs. We determined the germination responses of a target species to a gradient of leaf extract concentrations to assess relative allelopathic potential. The relative strength of germination inhibition was quantified by the slope (b) of the germination response to plant extract concentration. Ailanthus altissima extract had the greatest inhibitory effect on target species germination out of all 10 species (b 5 20.55) while the other tree species, Acer platanoides extract, had small effects on germination (b 5 20.14). For lianas, Celastrus orbiculatus extract inhibited the target species (b 5 20.28) more than Lonicera japonica extract (b 5 20.06). All invasive shrub extracts had very small effects on seed germination (b value 20.03 to 20.19). Extracts of the two herbaceous species, Alliaria petiolata and Microstegium vimineum, had very large inhibitory effects (b520.37 and 20.38, respectively). In this system, we screened a suite of invasive species for allelopathic potential and determined the relative strength of germination inhibition. Most species, particularly invasive shrubs, did not exhibit sufficient allelopathic potential to suggest allelopathy would occur in the field. Four species, Ailanthus altissima, Alliaria petiolata, C. orbiculatus, and M. vimineum all exhibited strong germination inhibition and warrant additional study in the field.

Liana host preference and implications for deciduous forest regeneration

Laura M. Ladwig et al. — Tue, 07 Feb 2012 07:49:05 PST

Lianas have the potential to shape forest communities and alter forest regeneration. However, impacts of lianas on forest regeneration, particularly in temperate forests, are largely unstudied. To understand potential liana impacts on the community we need to first know the location and intensity of liana burdens on host trees. We examined liana-tree host references within a series of young regenerating deciduous forests in the Piedmont region of New Jersey, USA. Established trees ($ 5 cm dbh) and the lianas associated with each tree were surveyed in 2008. The five most abundant liana species were Celastrus orbiculatus, Lonicera japonica, Parthenocissus quinquefolia, Toxicodendron radicans, and Vitis species. Host preference for each liana species was measured in two ways, as colonization on tree trunks and coverage in the canopy. Host preferences based on tree species and tree size were compared among liana species. A total of 798 trees were measured and lianas occurred on 64% of them. Host preferences were generally consistent between colonization and canopy expansion, suggesting the same factors that regulate establishment also regulate liana growth. Most liana species had higher colonization and greater canopy cover on early successional trees, particularly Juniperus virginiana. In contrast, Vitis spp. were more abundant on canopy hardwood trees. Slight preferences based on tree size were seen for some species. The preference of lianas for early successional trees may make lianas a contributing factor to the acceleration of succession within this eastern deciduous forest. However, the continued expansion of some lianas at the site, particularly Vitis spp. and C. orbiculatus, may alter future liana-tree associations and forest trajectories.