Effects of Sika Deer (Cervus nippon) and Dwarf Bamboo (Sasa senanensis) on Trillium Populations in Akan National Park,Eastern Hokkaido,Japan

The competition between Trillium spp. and other species could modify the utility of Trillium spp. as indicators of the impact of deer on forest vegetation. To evaluate whether Trillium spp. (T. camschatcense and T. tschonoskii) are appropriate indicators of the impact of sika deer (Cervus nippon) in the presence of dwarf bamboo (Sasa senanensis), which competes with Trillium populations, we examined the size class of large‐growth‐stage Trillium plants, the frequency of the presence of deer pellets and the coverage of S. senanensis in deer‐excluded sites (where deer have been eliminated since 1995) and unfenced control sites in Akan National Park, eastern Hokkaido, Japan. The result of a cumulative link mixed model (CLMM) suggests that size class at deer‐excluded sites is influenced by competitive understory species, even without deer grazing. The CLMM result for unfenced control sites suggests that C. nippon negatively influences the size class of Trillium populations; however, the negative effect weakened with increasing S. senanensis coverage. Thus, S. senanensis can function as an unpalatable neighbor that makes it difficult for C. nippon to detect Trillium plants. We conclude that the size class structure of Trillium spp. can be a useful index of C. nippon usage under sparse or medium S. senanensis understories; however, it is difficult to use these indices under dense S. senanensis understories because of the weakened negative effect of C. nippon grazing.     

THE CYTO-ECOLOGY OF FOUR SPECIES OF TRILLIUM FROM WESTERN NORTH CAROLINA

The major center of variability in the genus Trillium occurs in the southern Appalachian mountains of the eastern United States. The karyotypic variation existing within T. cuneatum Raf., T. grandiflorum (Michx.) Salisb., T. erectum L., and T. gleasoni Fern., the four most abundant Trillium species in western North Carolina, was analyzed and compared with the variation in gross morphology and the ecological associations of the respective species. The number of types of each kind of chromosome (A-E), as exhibited following “nucleic acid starvation” by cold treatment, varied widely from species to species. Chromosome types varied within each species and within populations in the numbers, sizes, and positions of euchromatic and heterochromatic segments. No 10-chromosome karyotype and only one 5-chromosome complement was found to be duplicated in any two plants which belonged to different species. Trillium cuneatum with eight chromosome types was morphologically stable and occurred in a limited geographic area. Trillium gleasoni, characteristically adapted to elevations near 2,000 feet, contained 32 chromosome types and exhibited a high morphological variability. Trillium erectum (25 types) and T. grandiflorum (23 types) were also intermediate in morphological variability. These two species had the widest geographical range. Karyotypes were analyzed from pure stands of each of the four species and for each species from mixed stands of two or more of the species growing in close association. These Trillium species are maintaining a high level of karyotypic and gross morphological variability within comparatively limited geographical areas. None of the observed karyotypes in any species is likely to have arisen by recent interspecific hybridization. The composite karyotype of each species could be used as an aid to classification in the genus Trillium.     

Dispersal by cattle of salt-marsh and dune species into salt-marsh and dune communities

We investigated the spatial cohort structure of Trillium populations in old-growth cove forests in Great Smoky Mountains National Park (TN, USA). We mapped the locations of all Trillium erectum L., Trillium grandiflorum (Michaux) Salisbury, and Trillium vaseyi Harbison occurring within two 10 × 10 m sample plots at each of three old-growth sites—Anthony Creek, Cove Mountain, and Kalanu Prong. The height and life stage of each individual were recorded and a randomly selected subset was excavated for age determination. Our results suggest that Trillium populations in cove forests of the southern Appalachians display a high degree of spatial aggregation and are relatively stable, spatially, over long time periods (i.e., decades). Individual patches (aggregations of plants) within populations were typically multi-aged and no clear spatial cohort structure was observed. Surprisingly, more isolated plants (distal from large aggregations) were among the oldest plants in the population, rather than recent colonists dispersing away from parent populations. Individual species were less mingled than expected given that they share a common dispersal agent (ants). This study provides a double-baseline for Trillium population structure in old, primary forests with low browse pressure.     

Estimation of dieback process caused by herbivory in an endangered root-sprouting shrub species,Paliurus ramosissimus (Lour.) Poir., using a shoot-dynamics matrix model

Mortality, a critical parameter for population dynamics, is difficult to measure in long-lived trees or clonal herbaceous species because of the extremely low frequency of deaths. A model based on shoot recruitment would be helpful to estimate the population fate of species without a sufficient number of observed deaths. Existing matrix models are applicable to the dynamics of physiologically independent shoots, but not to physiologically dependent ones. We developed a shoot-dynamics model for plants with physiologically-dependent shoots, and used the model to estimate the effects of herbivory and conservation measures on the dynamics of a long-lived, shoot-sprouting shrub species, Paliurus ramosissimus (Rhamnaceae). Two populations of the endangered shrub have been severely damaged by herbivory by sika deer. The damage was mainly to new sprouting shoots. No deaths of individual plants were observed during an 8-year survey, and we could not estimate mortality. Thus, prediction of population dynamics based on births and deaths of individuals was impossible. Because P. ramosissimus is a shoot-sprouting species, we instead estimated the decline of individuals using a shoot-dynamics model. Using this model, we estimated the time to an 80 % decrease in shoot number per individual in the two populations at 37.8 and 37.2 years. These lengths suggest an immediate need for conservation measures to prevent herbivory even though no death of any individual was observed in the field survey. The estimated recovery times from the herbivory damage were 28.7 and 29.2 years if herbivory of new shoots is completely prevented by conservation measure.     

A field study of seed germination in the endangered Trillium reliquum Freeman (Trilliaceae)

Previous studies examining the seeds of most Trillium species have reported double dormancy, a type of seed dormancy where two cold periods and one warm period are needed for complete germination. In the present paper, we describe a field study examining the federally endangered Trillium reliquum Freeman (Trilliaceae) in which moderate to high numbers of seeds germinated after one winter following seed production. Sixteen baskets with seeds were placed in four T. reliquum populations (four baskets in each population) in Georgia, USA, in June 2005. In spring 2006, all seed baskets contained seedlings. Germination percentages ranged from 33.3 to 83.3% across sites with a mean of 56.9 ± 3.9%. Trillium reliquum had higher germination percentages compared with other field‐based germination studies with other Trillium species. Our findings will inform future demographic studies of T. reliquum and suggest that double dormancy in seeds may not be as widespread as previously reported within the genus Trillium.     

Effects of herbivory and its timing across populations of Trillium grandiflorum (Liliaceae)

The goal of this study was to identify the degree to which the frequency and timing of herbivory by white-tailed deer (Odocoileus virginianus) and subsequent plant response varied across 12 populations of the perennial herb Trillium grandiflorum. Effects of natural and experimental herbivory on the stage and size of reproductive plants were measured. Both the frequency and timing of herbivory varied across T. grandiflorum populations. Reproductive plants were more likely to regress to nonreproductive stages in the next growing season when (1) reproductive plants were consumed by deer (vs. intact reproductive plants); (2) reproductive plants were consumed early in the growing season (vs. reproductive plants consumed late in the growing season); (3) reproductive plants were smaller in size. Clipped plants that remained reproductive were smaller in the following season than unclipped controls. Plant size was positively correlated with the number of ovules, suggesting that reductions in the growth rate of reproductive plants diminish their future reproductive success. Populations with high levels of natural herbivory had a greater proportion of reproductive plants that regressed to nonreproductive stages, probably because reproductive plants in these populations were smaller in size. However, the plant response to herbivory was similar across populations.     

Size-dependent gender modification in a hermaphroditic perennial herb

The size-advantage model predicts that hermaphroditic organisms adjust sex allocation depending on their resource status. We investigated the relationship between size and sex allocation in the co-sexual perennial herbs Trillium erectum and Trillium grandiflorum at two sites in southern Ontario, Canada by measuring pollen and ovule production and biomass allocation at flowering and fruiting. In both species, there was a strong relationship between size and gender; larger plants allocated proportionately more biomass to female reproduction and produced fewer pollen grains relative to ovules than smaller plants. Variation in gender was better explained by size than age, although age and size were correlated. While the relationship between size and gender was similar between species, T. erectum allocated proportionately more to female reproduction than T. grandiflorum, independent of size. In the absence of pollen limitation, there was no evidence of secondary adjustment of gender at fruiting. The results are discussed in the context of models predicting size-dependent gender modification in animal-pollinated plants. Evidence about the pollination and seed dispersal biology of Trillium spp. suggests that the relative effects of local mate and resource competition may be important in driving size-dependent sex allocation in these species.     

Herbivory and pollen limitation at the upper elevational range limit of two forest understory plants of eastern North America

Studies of species' range limits focus most often on abiotic factors, although the strength of biotic interactions might also vary along environmental gradients and have strong demographic effects. For example, pollinator abundance might decrease at range limits due to harsh environmental conditions, and reduced plant density can reduce attractiveness to pollinators and increase or decrease herbivory. We tested for variation in the strength of pollen limitation and herbivory by ungulates along a gradient leading to the upper elevational range limits of Trillium erectum (Melanthiaceae) and Erythronium americanum (Liliaceae) in Mont Mégantic National Park, Québec, Canada. In T. erectum, pollen limitation was higher at the range limit, but seed set decreased only slightly with elevation and only in one of two years. In contrast, herbivory of T. erectum increased from <10% at low elevations to >60% at the upper elevational range limit. In E. americanum, we found no evidence of pollen limitation despite a significant decrease in seed set with elevation, and herbivory was low across the entire gradient. Overall, our results demonstrate the potential for relatively strong negative interactions (herbivory) and weak positive interactions (pollination) at plant range edges, although this was clearly species specific. To the extent that these interactions have important demographic consequences—highly likely for herbivory on Trillium, based on previous studies—such interactions might play a role in determining plant species' range limits along putatively climatic gradients.     

Species‐Specific Barriers to Tree Regeneration in High Elevation Habitats of West Virginia

Herbaceous competition and herbivory have been identified as critical barriers to restoration of native tree species in degraded landscapes around the world; however, the combined effects of competition and herbivory are poorly understood. We experimentally manipulated levels of herbivory and herbaceous competition and analyzed the response of tree seedling performance over three growing seasons as a function of species and habitat in north‐central West Virginia. Four native tree species were planted in old field and forest experimental plots: Castanea dentata (American chestnut), Quercus rubra (red oak), Acer saccharum (sugar maple), and Picea rubens (red spruce). Red spruce demonstrated the highest growth increment and greatest survival (64%) and most consistent results among treatments and habitats. Red spruce survival was not reduced in the presence of Odocoileus virginianus (white‐tailed deer) browse and herbaceous competition; however, growth was improved by suppression of herbaceous competition. We suspect that this deciduous forest landscape would regenerate to a red spruce dominated forest if seed source was available. In contrast, the other three species tested had very low survival when exposed to deer and were more responsive to competing vegetation and habitat type. American chestnut had low survival and growth across all treatments, suggesting basic climate limitations. Vigorous natural regeneration of Prunus serotina (black cherry) occurred in forest plots where both competing herbs and deer were excluded. Our results demonstrated the importance of testing multiple potential recruitment barriers and species at once and the need for species and habitat‐specific restoration treatments.     

Impact of growth form and carbohydrate reserves on tolerance to simulated deer herbivory and subsequent recovery in Liliaceae

? Premise of the study: Over-browsing of the understory vegetation by white-tailed deer has been a cause of decline in many plant populations. Liliaceae are particularly sensitive, yet individual species differ in their tolerance to deer herbivory. In this paper, we examine whether differences in clonal habit, carbon allocation patterns, and phenology influence the capacity of a species to tolerate and recover from repeated herbivory. ? Methods: Flowering ramets of Clintonia borealis, Maianthemum canadense, and Trillium erectum were subjected to total defoliation for one or two springs. ? Key results: Survival was highest in the nonclonal species, T. erectum, most probably due to its very large carbohydrate reserves. Nutrient reserves were less affected than carbohydrate reserves by defoliation, confirming the importance of carbohydrate reserves for survival. However, faster recovery following episodes of defoliation was observed not in the species that sprouted the earliest, T. erectum, but in the clonal species, M. canadense, which had the smallest carbohydrate reserves but also a lower shoot to root ratio than the other clonal species, C. borealis. All plants that were defoliated for 2 years only partially recovered in terms of leaf area, plant biomass, and carbohydrate and nutrient reserves, confirming the overall sensitivity of these species to simulated deer herbivory. ? Conclusions: High carbohydrate reserves and consequently low shoot to root ratios appear to increase tolerance to herbivory, whereas clonal species recover faster than nonclonal species. The role played by carbohydrates reserves suggests that these species could benefit from slightly higher light conditions in areas subjected to high deer pressure.     

A new Trillium (Liliaceae) from the northwestern United States

A new species,Trillium parviflorum, is described inTrillium subgen.Phyllantherum Raf.Trillium parviflorum is easily distinguished fromT. albidum Freeman, which it superficially resembles, by its overall smaller size, much smaller linear-lanceolate petals, clove-like fragrance, and dark maroon fruit.     

Population structures and individual performances of <Emphasis Type="Italic">Trillium grandiflorum</Emphasis> in hedgerow and forest habitats

In agricultural landscapes, linear habitats, such as hedgerows at field margins increase structural connectivity among forest patches, potentially providing dispersal corridors for forest herbs. The spatial structure of linear habitats, however, also results in edge effects and perturbations that can influence the individual and population performance of forest plants. This study compares the stage structure and components of growth and reproduction of 14 Trillium grandiflorum populations in hedgerows and forests. Hedgerow Trillium tended to grow faster and, when mature, produced more flowers and more ovules per flowers than forest Trillium, a pattern possibly associated to differences in nutrients and light availability between the two habitats. Seed production and germination rate, however, did not differ between hedgerows and forests. At the population level, seedlings and juveniles were proportionally less abundant in hedgerows than in forests. Although well-established plants can thrive in hedgerows, reduced recruitment may eventually limit the capacity to establish new populations and therefore hamper migration along hedgerow-corridors. Considering the strategies by which plants persist in linear habitats becomes particularly relevant at a time when species are expected to be much in need of dispersal corridors because of climatic stress.     

Restoration of three forest herbs in the Liliaceae family by manipulating deer herbivory and overstorey and understorey vegetation

Background: Research on herbaceous vegetation restoration in forests characterised by overstorey tree harvests, excessive deer herbivory, and a dominant fern understorey is lacking. Most of the plant diversity found in Eastern hardwood forests in the United States is found in the herbaceous understorey layer. Loss of forest herbaceous species is an indicator of declining forest conditions.

Aims: The combined effects of deer herbivory, competitive understorey vegetation removal, and overstorey tree removal on the abundance and reproductive capacity of three understorey herbs in the Liliaceae family were evaluated.

Methods: A split-plot randomised block design was used with three replicates. Treatments included three harvest intensities, fenced/unfenced, herbicide/no herbicide-treated, prescribed burn/no prescribed burn, and all combinations. A generalised linear model was used to compare treatment effects over 8 years.

Results: Both fruit production and cover increased significantly in fenced areas for all three species. There was a significant 6-year recovery period for cover of the three species in response to herbicide. There was a significant 4-year recovery period of fire-treated plots for fruit production of the three species. The most intensively cut, fenced, and herbicide-treated plots had the greatest increases in sapling and Rubus spp. cover. Cover and fruit production of the three herbs were significantly greatest in the moderate-cut treatment.

Conclusions: Restoration of these three liliaceous species is most likely to occur in Eastern deciduous forests and similar forests using a combined fenced and moderate-cut treatment.     

Experimental analyses of the evolutionary processes inTrillium

In the Japanese species ofTrillium examined here, every interspecific cross produced healthy F₁ progeny at the rate of about 50 to 60 per cent of the total inborn ovules except forT. hagae. These figures were not appreciably different from those of self-pollinated or sib-mated examples of these species.Trillium hagae, a putative natural hybrid betweenT. kamtschaticum (2n=10) andT. tschonoskii (2n=20), accepted all foreign sources of pollen grains in manual pollination. These and other crossing experiments suggest that no appreciable barrier has developed that might cause interspecific crossability and that they are habitual inbreeders. Despite theri crossability, a very low rate of actual pollen flow was detected by examining electrophoretic phenotypes of seeds taken from sympatric populations of these species.     

Herbivory and plant competition reduce mountain beech seedling growth and establishment in New Zealand

The effect of herbivory and resource availability on the competitive ability of different plant species has been an area of intense debate amongst plant ecologists for at least two decades, but the interactive effects of herbivory and plant competition between woody and herbaceous plants are rarely studied and theory is poorly developed. This study used experimental manipulations on transplanted and naturally occurring mountain beech (Nothofagus solandri var. cliffortioides) seedlings to show the effects of deer browsing and competition from deer-induced, herbaceous turf communities on mountain beech regeneration in New Zealand. Differences in the species composition of these turfs had little effect on mountain beech seedling establishment, but turf removal increased seedling growth and survivorship, showing that competition with other plants had direct effects on mountain beech regeneration. Deer browsing reduced the establishment and growth of seedlings, but the size of this effect did not vary with light and nutrient availability. There was no immediate compositional response of turf communities following the removal of deer browsing. The addition of nutrients appeared to reduce the intensity of belowground competition (stem growth increased relative to root growth) and increase seedling mortality, but there was no effect of changing levels of light. These results showed simple and direct negative effects of deer browsing on mountain beech regeneration. Indirect negative effects on regeneration were caused by deer-induced turf communities. We found little evidence for interactive effects between herbivory, plant competition and the availability of light or nutrients on seedling regeneration, which suggests that these factors acted independently. Nomenclature: Beever et al. (1992); Parsons et al. (1995); Edgar and Connor (2000); and Brownsey and Smith-Dodsworth (2000). Raukaua simplex is described by Mitchell et al. (1997). Coprosma “taylorae” is referred to by Eagle (1986) and Halocarpus biformis, Phyllocladus alpinus, Podocarpus hallii and Podocarpus nivalis by Wilson and Galloway (1993).     

Characterization of six microsatellite markers in Trillium camschatcense using a dual‐suppression‐polymerase chain reaction technique

Trillium camschatcense is a herbaceous perennial plant distributed in Hokkaido and northern Honshu, Japan. Geographical variations in the breeding system (partial selfing or obligate outcrossing) are reported in the populations of Hokkaido. We isolated six polymorphic microsatellite loci from this species. The number of allele per locus ranged from four to 12, whereas the expected heterozygosities ranged from 0.69 to 0.83. These markers may allow further investigations to reveal the evolutionary and ecological processes of mating system in T. camschatcense.     

Species-specific herbivore–herbivore interactions and plant responses to sequential attack by multiple herbivores on a perennial woody plant

When plants are sequentially attacked by multiple herbivores, herbivore identity and host specialization can greatly influence the patterns of herbivore–herbivore and plant–herbivore interactions. However, how prior herbivory and the resulting induced plant responses potentially affect subsequent herbivores deserves further investigation. In this study, we conducted a common-garden experiment that manipulated sequential herbivory by the specialist caterpillar Gadirtha fusca Pogue (Lepidoptera: Nolidae) and the generalist caterpillar Spodoptera litura (Fabricius) (Lepidoptera: Noctuidae) on Chinese tallow, Triadica sebifera (L.) Small (Euphorbiaceae). We tested how prior exposure to herbivores with different levels of host specialization affected the performance of subsequently arriving con- and heterospecifics, as well as plant growth and defense responses under subsequent herbivory. We found that prior exposure to the specialist G. fusca facilitated the performance of subsequent conspecifics, resulting in a significant decrease in the growth (height and stem diameter at ground level) of tallow plants. However, prior exposure to the generalist S. litura did not affect the feeding of subsequent con- or heterospecifics or the growth of tallow plants. Sequential herbivory by specialist and generalist conspecifics resulted in lower levels of tannins and flavonoids, respectively, in leaves of tallow plants, whereas sequential herbivory by the two species did not affect the levels of tannins or flavonoids, compared to a single damage event. We conclude that herbivore species-specific plant responses appear to be more important than herbivore identity or specialization in determining herbivore–herbivore interactions and plant responses to sequential herbivore attack.     

A comparative study of floral development inTrillium apetalon andT. kamtschaticum (Liliaceae)

Trillium apetalon Makino is unique amongTrillium in having apetalous flowers. Using scanning electron microscope, the early floral development was observed in comparison with that ofT. kamtschaticum Pallas ex Pursh having petalous flowers. Morphologically petal primordia closely resemble stamen primordia in their more or less narrow and radially symmetric shape and are clearly distinct from sepal primordia with broad bases. Early in floral development sepal primordia are first initiated and subsequently two whorls of three primordia each are formed in rapid sequence, the first three at the corners and the second three at the sides of the triangular floral apex. Based on comparison in position and early developmental processes of their primordia, petals and outer stamens ofTrillium kamtschaticum are equivalent to outer stamens and inner stamens ofT. apetalon. The replacement of petals by outer stamens apparently leads to the loss of petals inTrillium apetalon flowers. Such a replacement can be interpreted in terms of homeosis. The replacement of the petal whorl leads to the serial replacement of the subsequent whorls: outer stamens by inner stamens, and inner stamens by gynoecium inTrillium apetalon. The term ‘serial homeosis’ is introduced for this serial replacement.     

Exotic consumers interact with exotic plants to mediate native plant survival in a Midwestern forest herb layer

Consumer-facilitated invasions have been proposed as an alternative mechanism to direct competitive exclusion to explain the replacement of native plants by exotics. In a factorial field experiment manipulating competition from the exotic plant Alliaria petiolata and herbivory by exotic mollusks, we documented that mollusk herbivory significantly reduced the survival of two species of native palatable plants, but found minimal direct herbivore effects on less palatable species, including the invasive A. petiolata. These effects were evident after one growing season on younger juvenile plants of Aster cordifolius, but only after two growing seasons on older transplants of the same species, suggesting a greater vulnerability of young plants. In contrast to our expectations, A. petiolata competition alone had no effect on any of the six native species we tested. However, competition from A. petiolata did affect the survival of the most palatable native plant when mollusks were also present. While not significant for any other single species, this same pattern was observed for three of the five remaining native species tested. The selective grazing on palatable plants that we document provides novel evidence contributing to our understanding of observed shifts in the forest herbaceous layer towards the dominance of exotic plants and unpalatable species. More broadly, our results highlight the importance of the interactive effect of consumers and inter-specific competition in forest understories via its contribution to differential survival among regenerating species.