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Capsella bursa-pastoris (L.) Medik, shepherd’s purse, is a cosmopolitan summer or winter annual weed species distributed throughout temperate and subtropical regions of the world and is considered one of the most common plants on earth. It is an opportunistic annual that colonizes newly disturbed, open or dry environments and is ubiquitous in cultivated lands in Canada. In annual crops in western Canada, C. bursa-pastoris has been among the 20 most abundant weeds since the first weed surveys in 1970. It is most easily distinguished by its small white four-petalled flowers and its heart-shaped seed-pods, but exhibits considerable variation in leaf shape and flowering time. It has been used for food and medicine by numerous cultures. Its golden-brown seeds are produced in large numbers predominantly through self-pollination and can form a substantial seed bank, with reported values ranging to several hundred thousand seeds m−2. While seeds usually disperse near the mother plant, long-distance dispersal by attaching to vehicles, people and other vectors may be facilitated by its mucilaginous coat. Capsella bursa-pastoris does not produce fertile hybrids with other species of economic or ecological significance. It is generally well controlled by soil-applied and foliar (post-emergence) herbicides although its presence in agricultural fields may result in substantial yield loss, as documented in cole crops in North America and grain crops in Europe. The species can host a wide range of insect, nematode, fungal, viral, and bacterial pests that may damage crop species.

The hybrid knotweed Reynoutria × bohemica Chrtek & Chrtková exhibits greater genetic variation than its parents. We developed methodology for and tested for glyphosate resistance in two Bohemian knotweed populations using rhizome fragments. There was no difference in LD50 (p = 0.3030; F = 1.067) between the populations and no evidence of resistance.

Two related species of Hedera spp. exist throughout Canada: English Ivy (Hedera helix L.) and Irish Ivy [Hedera hibernica (G. Kirchn.) Bean]. These species are difficult to distinguish taxonomically and clear distinctions are not always made in the literature, so we largely discuss them as a single taxon in this account. Ivy is an evergreen perennial with two distinct forms: woody vine (juvenile form) or shrub (adult form). In Canada, Hedera spp. are found naturalized along the southern coast of British Columbia (Vancouver, Vancouver Island, and the Gulf Islands) and in southwestern Ontario. During the past century, ivies have greatly expanded their ranges along the Pacific and Atlantic coasts of North America and in New Zealand, Australia, South Africa, Brazil, and Hawaii. Ivy is physiologically plastic, invading both semi-open and deeply shaded forests. It forms a dense ground cover that can inhibit native vegetation. It grows up on tree trunks and competes for soil nutrients, frequently leading to tree damage or even tree fall. Invasive characteristics include its evergreen habit, persistence, and vegetative reproductive capabilities. Humans have accelerated the spread of ivy by planting it along highway embankments and medians to control soil erosion and through widespread sale as an ornamental plant. There is debate among horticulturalists and ecologists over the destructive and advantageous effects of ivy growth and sale within North America. Various methods of control (chemical, manual, biological, and integrated) may be used to manage this species, but more research is needed to design better control techniques.

Daphne (Daphne laureola L.) is a perennial evergreen shrub native to Eurasia and northern Africa. Introduced to North America as an ornamental shrub, the plant has readily absconded gardens and can now be found throughout suitable habitats on both the east and west coasts of the continent. In Canada, daphne has naturalized in southwestern British Columbia including Vancouver, southern Vancouver Island, and the Gulf Islands. Daphne is of particular concern to the endangered Garry oak (Quercus garryana Douglas ex Hook.) because it invades shady woodland areas, forming dense mono-specific stands that can suppress and inhibit native vegetation. The berries and all other parts of the daphne plant contain a mixture of toxic chemicals that can be fatal to humans or animals if ingested. Removal teams suggest using gloves for elimination and handling of daphne because of its corrosive sap and oil. Widespread planting combined with a lack of public knowledge regarding the species’ invasiveness has created great concern over its potential to spread. Various methods of control (chemical, manual, and biological) have been developed. The most commonly applied approach in Canada is manual control, but care must be taken to avoid contact with skin and follow-up monitoring and control is advised. A promising biocontrol agent is the fungus Phomopsis sp. denovo, which has been observed to cause high levels of mortality in D. laureola under both laboratory and field conditions.

Covering just 2000 ha, Garry oak ecosystems (GOEs) in western Canada contain about 10% of the Species at Risk Act listed species at risk in Canada, including 30 plants listed by Committee on the Status of Endangered Wildlife in Canada as endangered. Since European settlement ca. 1840, GOE sites have been largely degraded by human disturbance, habitat fragmentation, invasive species, overgrazing, and fire suppression. A key strategy to mitigate this loss of biodiversity is to translocate rare plants to GOE restoration sites. The Garry Oak Ecosystem Recovery Team provides advice on proposed translocations but strongly encourages restoration practitioners to focus on plant populations already present on a site. There is a need for a closer look at challenges and opportunities afforded by translocation. If the approach taken is too precautionary, some rare species in this highly threatened ecosystem may be jeopardized. Current translocation efforts are being spearheaded by Parks Canada for golden paintbrush (Castilleja levisecta Greenm.), seaside birds-foot lotus (Lotus formossimus Greene), and white-top aster (Aster curtus Cronq.). Translocations like these together with further research on the genetics and ecology of rare plant species are critical to species recovery efforts within GOE and other similarly compromised ecosystems.

Clements, D. R. and DiTommaso, A. 2012. Predicting weed invasion in Canada under climate change: Evaluating evolutionary potential. Can. J. Plant Sci. 92: 1013–1020. Many weed species have already advanced northward from the United States into Canada, and their number threatens to increase with warming trends under climate change. For many weed species, this range expansion can be attributed to evolutionary adaptation by northern populations occurring in areas experiencing warmer climates and longer growing seasons in recent decades. In this paper, we examine the potential for invasive plant species to be selected for one or more of 10 character traits: (1) high growth rate, (2) wide climatic or environmental tolerance, (3) short generation time, (4) prolific or consistent reproduction, (5) small seed size, (6) effective dispersal, (7) uniparental reproduction capacity, (8) no specialized germination requirements, (9) high competitive ability, and (10) effective defenses against natural enemies. If any one of these traits is selected for in an invasive species, it would provide the affected species with the potential for a more expansive invasion range than anticipated by models that assume a static genotype. Four weed species of interest exhibiting potential northward range expansion within North America were evaluated: an obligatory outcrossing annual dicot, Himalayan balsam (Impatiens glandilifera Royle), a mostly selfing annual dicot, velvetleaf (Abutilon theophrasti Medic.), a perennial dicot that reproduces via rhizomes but forms fertile hybrids, Japanese knotweed [Fallopia japonica (Houtt.) Ronse Decr.], and a primarily selfing perennial grass, johnsongrass [Sorghum halapense (L.) Pers.]. Evidence for potential evolutionary responses to climate change was observed among particular traits for each of the four species, despite population genetic differences. The population genetics of invasive plants are difficult to model, as is climate change itself, but consideration of weed evolution to whatever degree possible should lead to improved predictive power of such models.

Darbyshire, S. J., Francis, A., DiTommaso, A. and Clements, D. R. 2012. The Biology of Canadian weeds. 150 Erechtites hieraciifolius (L.) Raf. ex DC. Can. J. Plant Sci. 92: 729–746. Erechtites hieraciifolius, American burnweed, is a herbaceous annual in the Asteraceae native to forest zones of eastern North America, but introduced to parts of Europe and the Pacific region. Confusion sometimes arises in distinguishing it from other weedy rayless composites in Canada, such as Senecio vulgaris (common groundsel) and Conyza canadensis (Canada fleabane). A pioneer therophyte species of forest zones, it occurs in large numbers when associated with major disturbances such as forest fires, but is also common in areas of smaller scale disturbance such as shores, forest edges and wind-throws. Soil conditions may vary greatly in nutrient content, moisture content, pH and salinity. In Canada, it is generally considered a minor garden and agricultural weed. It is most common in crops such as lowbush blueberry (Vaccinium spp.), cranberry (Vaccinium macrocarpon), strawberry (Fragaria×ananassa) and vegetable crops; however, it occasionally occurs in other field and forage crops. Impacts include a variety of problems contributing to increased production costs or crop yield losses, including herbicide resistance, resource competition, and as a reservoir harbouring crop pathogens. It has been valued as a medicinal herb for treating a variety of ailments. Populations may grow rapidly in response to disturbances typical of managed landscapes, but E. hieraciifolius can usually be effectively controlled by chemical, cultural or manual weed control tactics.

Stopps, G. J., White, S. N., Clements, D. R. and Upadhyaya, M. K. 2011. The Biology of Canadian weeds. 149. Rumex acetosella L. Can. J. Plant Sci. 91: 1037–1052. Rumex acetosella L., sheep sorrel, is a perennial herb originating from Europe and southwestern Asia, now found in at least 70 countries worldwide. A common weed, it appears in grasslands, pastures, rangelands, waste areas, and along roadsides across North America. It frequently occurs as a weed in lowbush blueberry fields in Atlantic Canada, particularly in Nova Scotia. Rumex acetosella thrives on poor, acidic, and disturbed soils across a broad range of climatic conditions. A persistent seed bank and vegetative reproduction from creeping roots contribute to the ability of R. acetosella to tolerate various methods of control including certain herbicides, fire, and tillage. Tart-tasting leaves, rich in vitamin C have led to the use of R. acetosella in European and North American cultures as both a source of food and a component of herbal medicines. Excessive consumption of the leaves, which contain oxalic acid, can be poisonous to horses and sheep. In addition, R. acetosella is a possible host of the tomato spotted wilt virus, which is detrimental to a variety of vegetable crops.

Francis, A., Darbyshire, S. J., Clements, D. R. and DiTommaso, A. 2011. The Biology of Canadian Weeds. 146.Lapsana communis L. Can. J. Plant Sci. 91: 553–569. Nipplewort, Lapsana communis, is an annual weed of the Asteraceae native to Europe and western Asia, first detected in northeastern and Pacific northwestern regions of North America in the 19th century. It appears to have been introduced as a contaminant of imported garden material and seeds, but may also have been deliberately introduced as a medicinal herb. After a century of remaining close to its original points of introduction in gardens and ruderal habitats, it spread to neighbouring areas, and now occurs across southern Canada and in many areas of the United States. Possible reasons for this range expansion include forest clearance and changing crop management practices as was observed in Europe, where this plant has become an important weed in grain, forage and vegetable crops. In Ontario, L. communis has recently emerged as a weed in wheat ...

Hemp dogbane, Apocynum cannabinum (Apocynaceae), is a perennial herb with white to greenish flowers in terminal clusters that produces pencil-like pods 12-20 cm long. A highly variable plant, A. cannabinum may be distinguished from spreading dogbane (Apocynum androsaemifolium) by its shorter corolla (2-6 mm compared with 5-10 mm), erect greenish-white petals (compared with recurved or spreading pinkish petals), seeds more than 3 mm long (compared with seeds less than 3 mm), and more erect leaves (compared with spreading or drooping leaves), although frequent hybridization between the two species obscures the identity of some individuals. Hemp dogbane is native to the United States and southern Canada, but most abundant in the upper Mississippi River Valley and east to the Atlantic coast. It has been increasing in other areas, and becoming more of a problem where conservation tillage is adopted. It infests crops such as corn (Zea mays), soybeans (Glycine max), wheat (Triticum aestivum), sorghum (Sorghum bicolor) and forages, and may cause livestock poisoning due to cardiac glycosides within its milky sap (but livestock generally avoid it). Potential medicinal uses of these compounds have been investigated, and the roots are a source of fibre. Control of A. cannabinum with various herbicides is difficult due to a thick cuticle, and one solution may be to target susceptible stages, such as seedlings or early spring growth. Cultivation may also control A. cannabinum, but care must be taken not to promote the proliferation of the plant through regrowth from fragmented roots and rhizomes. Rotation with alfalfa also reduces populations of A. cannabinum.Key words: Hemp dogbane, APCCA, Apocynum cannabinum, Apocynaceae, weed biology

European buckthorn, Rhamnus cathartica L., is an introduced shrub or small tree of forests, thickets, open pastures, hedgerows, roadsides, and riparian habitats. In Canada, it is found from Alberta east to the Maritimes, but is absent from Newfoundland. It is particularly abundant in southern Ontario. Problems arise from its status as an alternate host for the fungi Puccinia coronata Corda. f. sp. avenae Eriks., which causes crown rust and leaf rust of oats and for Puccinia coronata var. hordei Jin & Steff., which causes crown rust of barley. It is also the overwintering host for the recently invasive soybean aphid, Aphis glycines Matsumura, which has been described as a serious threat to soybean production in North America. Prolific fruit production, in combination with extensive seedling establishment and shade tolerance, allows R. cathartica to dominate an understorey quickly. Its ability to tolerate a wide range of conditions, at least in fairly moist areas, may lead to further expansion of its Canadian range. Control strategies should focus on reducing populations in close proximity to oats, soybeans or barley and to reduce its abundance in areas of ecological importance. Key words: Rhamnus cathartica, European buckthorn, Puccinia coronata, soybean aphid, weed biology

Impatiens glandulifera Royle (Himalayan balsam) is an invasive alien annual up to 3 m in height with showy flowers that are generally pink or purplish. Native to the Himalayan region, I. glandulifera was first recorded in Canada in 1901 in Ottawa, and is now found in eight Canadian provinces: British Columbia, Manitoba, Ontario, Quebec, Nova Scotia, New Brunswick, Prince Edward Island and Newfoundland. Impatiens glandulifera is typically found in riparian habitats and may spread rapidly because its seeds are readily transported via waterways. Up to 2500 seeds are produced per plant and dispersed explosively up to 5 m from the parent plant. This can result in dense monotypic stands which prevent establishment of native plants and make stream banks vulnerable to erosion when the shallow-rooted plants die back. Impatiens glandulifera is susceptible to glyphosate but because herbicide use in riparian areas is not advised, other control methods such as hand weeding, mowing or flaming have been used. Methods for eradication are most successful when upstream populations are controlled first, as the plants spread downstream. Removal of I. glandulifera should be managed synchronously with non-native control measures and ideally be accompanied by planting native species to ensure the restoration of native species composition. The prognosis for curbing its spread in Canada seems poor as it has quite rapidly become established along waterways in many regions, following a pattern seen over the past two centuries in Europe. Key words: Impatiens glandulifera, Impatiens roylei, Himalayan balsam, impatiente glanduleuse, policeman's helmet riparian, invasive plant, weed biology

The field of invasive species biology has been growing rapidly in the past decade, spurred on by the US Executive Order on invasive species in 1999. Despite calls to deal with invasive alien species under the International Convention on Biological Diversity in 1992, Canada has been slow to act. Part of the difficulty in managing alien invasive species effectively lies in the lack of ecological knowledge. The Canadian strategy on invasive alien terrestrial plants developed recently by the Canadian Food Inspection Agency sees research as a critical component of the strategy, including study of the biology and ecology of invasive plants. A symposium on ecology and invasive plant species at the Plant Canada meeting in 2007 in Saskatoon served to explore some emerging research in Canada, particularly focusing on Canada’s prairie region. Papers derived from five of the presentations are presented here and illustrate well the continuing challenge of applying ecological principles to the complex issues surrounding invasive plants. Canadian ecologists have made a significant contribution, but much remains to be done along the lines of the simple studies provided in this symposium. Key words: Invasive alien species, prairie region, biodiversity, ecological research

Panicum capillare L., witch grass, is an annual grass native to North America that infests field crops, small grains, grasslands, and a variety of other habitats. High seed production, a persistent seed bank, a tumble-weed seed-dispersing mechanism, and the ability to tolerate some herbicides contribute to the success of P. capillare in these habitats. Despite the widespread presence of P. capillare in crops, its actual impact on crop yield is not well documented. It is an additional host for several insect pests (e.g., cereal aphids) and diseases attacking crop species. Key words: Panicum capillare, witch grass, panic capillaire, weed biology, native weed species

Leucanthemum vulgare Lam. (Asteraceae), known as ox-eye daisy, is a familiar perennial herb with white ray florets and yellow disc florets. It commonly inhabits roadside ver ges, pastures and old fields from Newfoundland to British Columbia, and also as far north as the Yukon Territory. Introduced from Europe, L. vulgare was well established in North America by 1800. The Canadian distribution of L. vulgare has expanded in many areas recently, particularly in western Canada. It can form dense populations that may reduce diversity of natural vegetation or pasture quality, and also serves as a host and reservoir for several species of polyphagous gall-forming Meloidogyne nematodes that feed on crops. It is considered a noxious weed under provincial legislation in Quebec, Manitoba, Alberta and British Columbia, as well as under the Canada Seeds Act. Control efforts are sometimes complicated by difficulties in distinguishing ox-eye daisy from some forms of the commercially available Shasta daisy ( L. × superbum).

Three years ago, we published a revised format for the series on the Biology of Canadian Weeds, as well as instructions for the preparation of Updates of Previous Accounts (Cavers and Warwick 2000). This led to renewed interest in the series with 15 new accounts and two updates being published from April 2000 to October 2003. In addition, four new accounts and two updates have been accepted for publication, pending revision. There have also been many changes in the list of manuscripts in preparation. Since there are also a number of changes that need to be made in the Format and the Instructions to Authors, we are reprinting all of this information here. The term “weed”, as used in this series, refers to any vascular plant that perpetuates itself in habitats where it is not wanted. Individual contributions should contain accounts of a single weed species or a group of related species. Prospective authors should note that a new series, the Biology of Invasive Alien Plants in Canada, is being launched in this journal issue (Warwick et al. 2003). Before submitting an offer of contribution, authors should consider carefully the status and history of their species in Canada and then select the appropriate series. The Biology of Canadian Weeds series addresses undeniable problematic weeds in Canada, whereas the new series is designed to cover aliens in Canada that have demonstratable potential risk. In cases where the assignment to a particular series is not clear, the editors of both series may be called upon to make a judgment call. Please consult the new series (Warwick et al. 2003) for further information. If you wish to write an account on a weed species, you must first check to ensure that the species has not been assigned to someone else. This involves sending an “offer of contribution” to Dr P. Cavers. After approval of your offer, you may proceed with writing the paper. The completed paper is to be submitted directly to the Canadian Journal of Plant Science (see below). Offers of contributions by individuals or groups should be made to Dr. Paul B. Cavers, Department of Biology, University of Western Ontario, London, Ontario, N6A 5B7, e-mail pcavers@uwo.ca. These offers of contributions will be subject to approval by a committee of the Canadian Weed Science Society (CWSS). Approved offers will be subject to re-approval after three years if the article has not been completed during that period. Any inquiries about the format to be used or advice on preliminary drafts should be directed to Dr. Cavers. He can also supply blank maps of Canada and will suggest specialists or institutions that will provide various types of services for authors. The Canadian Weed Science Society has a web site [http://cwss-scm.ca/] with on-line references to common English and French names, links to provincial and federal legislation and current lists of species published and in preparation for this series. The finished manuscript should be submitted to: Canadian Journal of Plant Science; Mr. T. Fenton, Head, Journals Section, Agricultural Institute of Canada, 141 Laurier Ave. W., Suite 1112, Ottawa, Ontario, Canada K1P 5J3. All contributions must comply with the format of this journal. Accounts on a single species, including all maps, drawings, diagrams and photographs, should not exceed 50 pages [12 point font, double-spaced with numbered lines]. Of course, accounts on more than one species can be longer. The authors should also provide the names and addresses [including phone numbers and e-mails if available] of three potential referees.

Echium vulgare L., known as blueweed or viper’s bugloss, is a blue or purple flowered biennial or short-lived monocarpic perennial herb found in every province in Canada. A naturalized weed of European origin, E . vulgare grows in highly disturbed are as, typically in soils of limestone or dolomite parent material. It is not competitive with crops, but serves as an alternate host for fungal pathogens and contains hepatotoxic alkaloids detrimental to livestock when consumed in large amounts. E. vulgare is a noxious weed in Nova Scotia, Québec, Manitoba, Alberta and parts of British Columbia. Beneficial aspects include contributions to honey production and herbal medicine. Key words: Echium vulgare, blueweed, viper's bugloss, weed biology

Gorse (Ulex europaeus L.) is a leguminous shrub native to western Europe and North Africa. During the past century it has greatly expanded its adventive range in Australia, New Zealand, Chile and Europe, and along the Pacific and Atlantic coasts of North America. In Canada, it is found in British Columbia (Vancouver, Vancouver Island, the Gulf Islands and Queen Charlotte Islands) where it is classed as a noxious weed. Gorse is also found from Virginia to Massachusetts on the east coast of North America. The shrub rapidly invades dry and disturbed areas, forming dense thickets that can suppress and inhibit native vegetation, including economically important conifer seedlings. It can occupy the same habitats as Scotch broom [Cytisus scoparius (L.) Link] but usually occurs on drier sites. Both of these legumes threaten native plant communities but U. europaeus persists longer and possesses conspicuous spines. Invasive characteristics of gorse include its evergreen habit, prolific seed production, longevity of seeds in the soil and nitrogen fixation. Human activities such as agriculture and construction of logging roads have accelerated the spread of gorse in British Columbia, but there is still an historic opportunity to restrict the population expansion that this species has exhibited in many other countries. Various methods of control (chemical, manual, biological and integrated) are evaluated. Key words: Ulex europaeus, Cytisus scoparius, exotic plant, biological control, Exapion ulicis

Several types of salsify or goat's-beard, Tragopogon species (Asteraceae), are found in Canada as biennial or monocarpic perennial herbs with yellow or purple flowers. Introduced from Eurasia, T. pratensis and T. dubius have become established in all provinces in Canada except Newfoundland and the territories. Tragopogon porrifolius tends to be more local, but is also found in southern areas of most provinces. Tragopogon species hybridize readily, and the tetraploid species T. mirus and T. miscellus have resulted from crosses among the three diploid Tragopogon species in North America. Salsify species produce relatively large umbrella-like pappuses which promote long-distance dispersal. These species also invade rangeland, and are considered noxious weeds in some parts of Canada. Key words: Tragopogon dubius, Tragopogon pratensis, Tragopogon porrifolius, Tragopogon mirus, Tragopogon miscellus, salsify, goat's-beard, Asteraceae, Compositae, hybridization, weed biology

Yellow toadflax, Linaria vulgaris Mill. (Scrophulariaceae), is a weed of rangelands and agricultural crops. Introduced from Eurasia into North America more than 300 yr ago, it is now naturalized in all provinces and territories up to 60° northern latitude and beyond 2000 m altitude. It became a concern in the middle of this century when it invaded the prairies. Its seriousness as a weed declined in the late 1950s, possibly as a result of biological control. Concern has been renewed recently because the adoption of minimum tillage techniques could lead to greater abundance. Reproduction is vigourous by means of adventitious root buds and by high seed production. Growth forms, vegetative reproduction, flower phenology, and germination are variable. The capability for regrowth from root parts makes L. vulgaris a difficult weed to eradicate and limits the efficacy of cultural control methods. The possibilities for chemical control are limited due to resistance to common herbicides. Biological control projects conducted during the past 50 yr have been partly successful and are on-going. Key words:Linaria vulgaris, toadflax, Scrophulariaceae, weed biology, control, review

Crop management systems utilizing no-till and legumes for soil improvement and double cropping represent promising systems for the preservation of soil, productivity and sustainability in Ontario agriculture. Field experiments were conducted in 1988 and 1989 to investigate the effect of planting date and tillage system on corn silage and grain yield for corn planted into either an established alfalfa sod or bare soil. There were no differences in grain and total biomass yields between corn planted in May under the no-till treatment and corn planted in May under the fall-plowed treatment, in both years. In 1988, delaying corn planting until after first-cut hay harvest on fall-plowed plots did not result in grain yield reduction compared with May-planted corn under the same tillage regime. Grain yield was reduced significantly in 1989 by a delay in planting. Corn silage yield was equivalent among all systems in 1989, indicating that no-till systems can be used effectively for producing alfalfa hay and silage corn. In 1988, rainfall in June was 7% of the average value, and as a result planting difficulties resulted in low silage yields, particularly in the no-till treatment. However, under conditions of adequate soil moisture, no-till corn following alfalfa should produce yields comparable to those with conventional tillage systems, while enhancing soil properties. Key words: No-till, alfalfa, silage corn, planting date

Helianthus tuberosus L., Jerusalem artichoke, is a native perennial tuber-producing weed. In Canada, its range extends from the Maritimes to the Pacific coast, but it is primarly found in southern Ontario and Manitoba. A cultivated form has been grown commercially in Ontario and western Canada for use as a human food source, for livestock feed and for the production of a variety of chemical products such as ethanol. As a weed, H. tuberosus competes vigorously with grain and field crops, but does not readily invade arable land except as a volunteer crop. The high carbohydrate content of H. tuberosus tubers, coupled with multiple regenerative strategies featuring seeds and tuber-bearing rhizomes, can lead to rapid population increases under favorable conditions.Key words: Helianthus tuberosus, Jerusalem artichoke, weed biology

This paper presents mathematical equations describing the relationships between the amount of stemflow per canopy layer per storm and the amount of gross rain per storm for four different canopy layers in a multi-storied forest community. The curves representing the relationships were curvilinear; for three of the canopy layers stemflow per storm increased at an increasing rate as gross rain per storm increased, approaching a constant rate of increase. Numerical values of the equation coefficients varied with canopy level in the forest stand profile and with variations in vegetal structure within the forest community. The lowest canopy in the vegetal profile, a fern canopy, had the most marked effect on rainfall redistribution.

Young red pine (Pinus resinosa Ait.) trees were grown under three watering treatments from late summer until early fall and under two watering treatments again the next spring. Size of apical buds, date of bud swell and bud burst in the spring, number of needle fascicles on the new shoots, shoot length, and needle-fascicle spacing were related to the first treatments. Most of these plant responses were correlated with bud size, and the correlations were unaffected by the spring watering treatments. The effect of treatments was on magnitude only, i.e. on mean sizes or mean numbers of the plant organs.In all cases in this experiment watering treatments during elongation had no effect on the results. Therefore in a species such as red pine, with determinate height growth, environment during bud formation played an important role in determining later shoot responses by acting on the bud size.Possibly the relationships reported here are genetically characteristic, unalterable by environment or at least by water alone. In this case the effect of environment on the trees was a proportionate increase or decrease in the size or number of plant organs.

This paper presents results of measurements, made separately for each of four canopy layers, of throughfall and stemflow in a multilayered stand of largetooth aspen (Populus grandidentata Michx.). Each canopy layer is identified by the predominant woody or fern species. Equations describe relationships between stemflow, stem size, and storm size, and between throughfall and storm size. In general, stemflow per stem per storm increased as both stem size and storm size increased, the latter having the greater effect. The equations varied with species. General stemflow equations were constructed to calculate stemflow per stem per storm for tree sizes and storm sizes within the measured range. Throughfall per storm increased as storm size increased, but at different rates for different canopy layers. Monthly budgets of interception, stemflow, and net rainfall for the various canopies, separately and together, were computed for the summer months of 1969 using the stemflow and throughfall equations, measured gross rainfall during all summer storms, and data on canopy structure for four plots within the stand. Interception by all canopies together amounted to 22 to 46% of monthly gross rainfall. Interception from the bracken fern canopy alone was 3 to 9%. Stemflow was about 8 to 17% of the monthly gross rainfall. The highest proportion of total stemflow was from bracken fern. Net rainfall was 54 to 78% of the monthly gross rainfall.

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