Antonio DiTommaso

Resource manipulations in natural vegetation: a review

This paper reviews the effects that resource manipulations, especially nutrient additions, have on productivity, diversity, species interactions and succession in natural and semi-natural low-growth-form terrestrial restrial vegetation. In most studies, fertilization has resulted in an increase in productivity with a concomitant decrease in species diversity. Plant community productivity in nutrient-poor habitats (e.g. arctic tundra) however, has been relatively little affected by nutrient additions. Results from several fertilization experiments in nutrient-poor habitats indicate that competition may be an important component of community dynamics. Resource additions generally do not affect co-occurring species equally. In many cases, this results from an alteration of the relative competitive abilities of species. Several short-term fertilization studies have suggested that the rate of succession is increased by the addition of nutrients. Opposite trends however, have been reported in long-term studies. Contradictory results among some resource manipulation studies appear to stem largely from design limitations (e.g. only one resource was manipulated). Variability in habitat fertility, the type of resource added and the duration of enrichment also contribute to the difficulties involved in interpreting and comparing field experiments. A pluralistic approach combining glasshouse studies with both neighbour and resource manipulations in the field can be expected to lead to a greater depth of understanding of current controversies over the effects of habitat fertility on the intensity of competition and the relationship between competitive ability and tolerance of resource impoverishment.

Germination behavior of common ragweed (Ambrosia artemisiifolia) populations across a range of salinities

Abstract Common ragweed is a native annual that colonizes disturbed habitats including agricultural fields and roadsides. It is especially abundant along roadways receiving regular applications of deicing salt. Anecdotal evidence has suggested that the emergence of common ragweed seedlings often occurs before the emergence of other roadside species and at salinity concentrations as high as 400 mM L−1, a level that can be found in roadside soils in early spring. However, the extent of this tolerance to salinity in common ragweed populations has not been quantified. The objective of this study was to assess the germination behavior of common ragweed seeds collected from three roadside and two agricultural populations across a salinity gradient. Seed germination of these five populations was monitored daily for 21 d across a sodium chloride gradient [0, 100, 200, 300, and 400 mM L−1] under controlled conditions. Seeds from roadside populations showed consistently greater total germination and rate of germination than seeds from agricultural populations. Germination differences were most evident at the 300 and 400 mM L−1 salinity concentrations. Average germination at the 400 mM L−1 sodium chloride concentration was 31% for two roadside populations and only 3% for two agricultural populations. Germination of seeds placed in distilled water after the 21-d salinity exposure treatments (i.e., recovery rates) was also greater for the roadside vs. agricultural populations. Findings indicate that the germination behavior of common ragweed seeds to salinity for roadside populations may be locally adaptive and allows common ragweed to emerge relatively early in spring thus providing a competitive advantage over later emerging roadside plants. Nomenclature: Common ragweed, Ambrosia artemisiifolia L., AMBEL.

The Biology of Invasive Alien Plants in Canada. 2. Cynanchum rossicum (Kleopow) Borhidi [= Vincetoxicum rossicum (Kleopow) Barbar.] and Cynanchum louiseae (L.) Kartesz & Gandhi [= Vincetoxicum nigrum (L.) Moench]

Cynanchum rossicum (dog-strangling vine) and C. louiseae (black dog-strangling vine) are introduced, perennial herbs or small twining vines in the Milkweed family (Asclepiadaceae). Generic placement of these two species has been problematic, but are here treated as members of Cynanchum subgenus Vincetoxicum. The species occur primarily in natural upland areas, including understories of woodlands, pastures, old fields, shores, flood plains and ruderal areas of southern Ontario and Quebec and the northeastern United States. Ecosystems on well-drained, stony soils are often densely colonized, but both species can tolerate a wide moisture regime. Plants establish in full sun or under forest canopies and may form monospecific stands in all light conditions. They often form dense colonies which smother other vegetation and reduce invertebrate and vertebrate biodiversity. Reproduction is by polyembryonic, wind-dispersed seeds. Effective control is primarily by herbicides, since mechanical control is difficult an...

A Review of the Biology and Ecology of Three Invasive Perennials in New York State: Japanese Knotweed (Polygonum cuspidatum), Mugwort (Artemisia vulgaris) and Pale Swallow-wort (Vincetoxicum rossicum)

Terrestrial weeds continue to evolve in association with the rapid global changes in our land-use systems, due to their regenerative strategies, their adaptability to change, and their inherent diversity. Currently, invasive weeds are estimated to cost the United States’ economy up to

The Biology of Invasive Alien Plants in Canada. 5. Polygonum cuspidatum Sieb. & Zucc. (= Fallopia japonica (Houtt.) Ronse Decr.)

35 billion per year, and this total is rapidly increasing, as greater numbers of invasive species become naturalized. Several invasive exotic species have more recently established across New York State, creating difficulties for agricultural producers, roadside and natural areas managers, and homeowners and resulting in millions of dollars expended annually for their control. Three perennials that have become particularly problematic in New York State in recent years in both agricultural and roadside settings include Japanese knotweed (Polygonum cuspidatum Sieb. & Zucc.), mugwort (Artemisia vulgaris L.), and pale swallow-wort (Vincetoxicum rossicum (Kleop.) Barbar.). This review describes their history, biology, ecology, and potential for management and focuses on key characteristics contributing to their spread in New York State and adjacent regions.

Effects of canopy shade on the morphology, phenology, and seed characteristics of Powell amaranth (Amaranthus powellii)

Polygonum cuspidatum (Japanese knotweed) is an introduced perennial geophyte in the buckwheat family (Polygonaceae). The phytogeographic distribution of P. cuspidatum in North America suggests a large number of intentional introductions via ornamental plantings from 1870 to 2000, followed by secondary spread from these foci. This species is most pernicious along riparian corridors and road and railroad rights-of-way, reducing visibility, displacing native species, negatively affecting native wildlife, and causing alterations in natural hydrologic processes. Although non-hybrid seed recruitment has not been observed in Europe because of the presence of male-sterile clones only, dispersal of seeds and stem and rhizome fragments by flowing water does occur in North America and populations are readily established from these sources. The primary means of local and regional range expansion is human-mediated transport of rhizome-infested soil. Hybridization is common with the congener P. sachalinense in the intr...

Influence of Market Orientation on Food Plant Diversity of Farms Located on Amazonian Dark Earth in the Region of Manaus, Amazonas, Brazil

Abstract Characterizing the response of weeds to canopy shade is important for improved understanding of crop–weed competition and weed population dynamics. In 2000 and 2001, field studies were conducted in central New York state to examine the influence of three neighbor types (none, broccoli, or broccoli plus winter rye) and two locations (between or within rows of broccoli) on the morphology, phenology, and seed germination characteristics of Powell amaranth. Reductions in light availability and in the ratio of red-to-far red light were associated with increases in (1) partitioning of dry weight to stem tissue, (2) stem elongation, and (3) specific leaf area. Canopy shade also resulted in fewer main leaves at flowering and a reduced rate of leaf appearance but had no effect on the number of days to flowering. The relationship between Powell amaranth fecundity and aboveground dry weight was allometric, with both parameters declining significantly under competition. The weight of seeds produced did not vary significantly according to the competitive environment experienced by the maternal parent. However, the germination percentage of viable seeds was 40 to 50% lower for seeds maturing on plants grown under competition than without competition. Reductions in the number of main leaves at flowering and increased seed dormancy may be adaptive responses to canopy shade. Both mechanistic crop–weed competition models and population dynamic models would benefit from incorporation of data on the phenotypic plasticity of morphology, phenology, and seed germination characteristics of weeds. Nomenclature: Powell amaranth = green pigweed, Amaranthus powellii S. Wats. AMAPO; broccoli, Brassica oleracea L. var. italica PLENCK ‘Marathon’; winter rye, Secale cereale L.

Oviposition preference and larval performance of monarch butterflies ( Danaus plexippus ) on two invasive swallow-wort species

Homegardens may serve as reservoirs of agro-biodiversity on highly fertile, anthropogenic Amazonian Dark Earth (ADE) soils of the Amazon basin. However, as these soils are used more intensively for market-oriented agriculture, we suspected a decrease in their agro-biodiversity. We present data obtained from surveys on 16 farms where ADE was present in the region of Manaus, Amazonas, Brazil. When farms were separated into two groups by market orientation, species richness on the farms was not significantly influenced by market orientation, but there was less dominance (i.e., more diversity) for homegardens in the low-market orientation group (P < 0.1). The proportion of native species was not affected by market orientation. Hence, while the most market-oriented farms retained high species richness, homegardens located on them contained higher proportions of commercially interesting species.

Corn competition alters the germinability of velvetleaf (Abutilon theophrasti ) seeds

The potential of two invasive herbaceous vines Vincetoxicum nigrum (L.) Moench and Vincetoxicum rossicum (Kleopow) Barbar. (Asclepiadaceae) to reduce monarch butterfly (Danaus plexippus L.) (Lepidoptera: Nymphalidae, Danainae) populations was investigated by evaluating oviposition selection in adult monarch butterflies and larval feeding preference in choice tests comparing the native host plant of monarch butterflies, Asclepias syriaca L. (Asclepiadaceae) and the two non‐indigenous Vincetoxicum species. In both choice and no‐choice tests, no eggs were oviposited on either of the two Vincetoxicum species whereas over 66 eggs per female were oviposited on A. syriaca plants. All first instar larvae allowed to feed on A. syriaca for 48 h survived while a significantly lower proportion survived on V. rossicum (44%) and V. nigrum (14%). Mean weight of larvae that did survive on the Vincetoxicum species was significantly lower than the mean weight of larvae that fed on A. syriaca. The mean weight of surviving larvae, however, did not differ between the two Vincetoxicum species. The mean proportion of leaves consumed by larvae feeding on A. syriaca was significantly greater than the mean proportion of leaves consumed by larvae feeding on either Vincetoxicum species. Findings from this research indicate that V. rossicum and V. nigrum are not viable hosts of monarch butterflies and are likely to pose little direct threat to their populations as oviposition sinks. The ability of these highly aggressive plants, however, to out‐compete and displace the native host of monarchs, A. syriaca, may pose a more serious threat. The potential of monarch populations to adapt to the two Vincetoxicum species as host plants over the long‐term is discussed.

Evolution of an invasive phenotype: shift to belowground dominance and enhanced competitive ability in the introduced range

Abstract Velvetleaf is a troublesome annual weed in many cropping systems of the United States and Canada. Differences in the growing environment of parent plants can influence the number, structure, germinability, and viability of seeds produced. Thus, the effects across a range of competitive environments and corn planting dates on velvetleaf seed production, germination, and seed coat weight were examined under field conditions. Seed production of velvetleaf increased with increasing biomass. Total velvetleaf reproductive output was reduced in competition with corn compared with monoculture stands. Corn planting date had no effect on the dormancy status of seeds, but increased competition from corn resulted in up to a 30% decrease in the proportion of seeds that were dormant. Seed and seed coat weights also decreased for plants of velvetleaf grown in competition with corn compared with those grown in monoculture. These findings suggest that velvetleaf plants growing in relatively noncompetitive environments, such as along field edges or in field areas with poor crop stands, are likely not only to produce a greater number of seeds but also a greater proportion of seeds that are dormant. This alteration in the dormancy status of velvetleaf seeds in the absence or presence of a crop provides unique opportunities for effective long-term management of the soil seedbank in this species, especially for velvetleaf individuals bordering fields or growing in fallow areas that might require more stringent control because of increased seed dormancy. Nomenclature: Velvetleaf, Abutilon theophrasti Medic. ABUTH; corn, Zea mays L. ‘Dekalb 520RR’.