Prolifération des fougères dans les érablières du Québec : ampleur du phénomène et moyens de le contrer

L’envahissement des érablières par les fougères est un phénomène de plus en plus fréquent au Québec. Les espèces de fougères envahissantes étudiées ici sont surtout associées à des conditions de drainage imparfait du sol, périodiquement inondé, et à des humus > 14 cm d’épaisseur. L’occurrence de ces espèces de fougères dans les érablières est aussi corrélée à la densité de cerfs de Virginie sur le territoire. Nous avons testé, dans 2 expériences, divers traitements pour favoriser la régénération en érable dans des érablières envahies par Dennstaedtia punctilobula. Seule la combinaison du chaulage et soit de la fauche soit de l’écrasement à répétition des fougères a accru considérablement la densité de semis d’érable après 3 à 5 ans, atteignant 15 à 28 semis/m2. L’écrasement à répétition des fougères ou la pose d’ombrières en sous-bois a aussi réduit de 30 % et plus la densité et la hauteur des fougères. Les observations mettent en lumière la dynamique complexe entre l’ouverture du couvert forestier, l’occurrence de fougères envahissantes, les conditions de fertilité du sol et le broutage par les cerfs, qui influencent l’abondance de la régénération en érable dans les érablières.

Low reproductive success of hay-scented fern (Dennstaedtia punctilobula) regardless of inbreeding level or time since disturbance

Self-fertilization can facilitate the colonization of new habitats because it allows a single individual to found a population. Here we investigated the relationship between mating systems and colonization in hay-scented fern (Dennstaedtia punctilobula (Michx.) T.Moore). Throughout eastern North America, this species has been called a “native invasive” for its tendency to dominate forest understories disturbed by logging, inhibiting tree regeneration. Thus, it is important to understand the mechanisms of its spread. We hypothesized that if populations were founded through selfing, then populations disturbed more recently would retain higher selfing ability; this pattern would demonstrate an important link between mating systems and colonization. For four populations logged at different times in the past, we compared the sporophyte production of gametophytes at different levels of inbreeding (intragametophytic selfing, intergametophytic selfing, and outcrossing) using laboratory crosses. Across all treatments, only 9.8% of gametophytes formed sporophytes (N = 400 gametophytes). Neither inbreeding level nor time since disturbance affected sporophyte production. Selfing ability did not differ across populations logged at different times; there was no interaction between inbreeding level and time since disturbance. The low reproductive success of D. punctilobula, regardless of inbreeding level or time since disturbance, suggests that population establishment and expansion via sexual reproduction may be relatively rare in this clonal species.

Control of Herbaceous Weeds in Allegheny Hardwood Forests with Herbicides

Bromacil (5-bromo-3-sec-butyl-6-methyluracil), glyphosate (N-phosphonomethylglycine), picloram (4-amino-3,5,6-trichloropicolinic acid), simazine [2-chloro-4,6-bis (ethylamino)-s-triazine], and hexazinone [3-cyclohexyl-6-(dimethylamino)-1-methyl-1,3,5-triazine-2,4(1H,3H)-dione] were evaluated at four application rates and five application dates, May 1, June 1, July 1, August 1, and September 1, for their ability to control seven herbaceous, forest ground covers, hayscented fern (Dennstaedtia punctilobula (Michx.) Moore), New York fern (Thelypteris noveboracensis L.), short husk grass (Brachyelytrum erectum Schreb.), bracken fern [Pteridium aquilinum (L.) Kuhn var. latiusculum (Desv.) Underw.], wild oat grass (Danthonia compressa Aust.), rough goldenrod (Solidago rugosa Mill.), and flattop aster (Aster umbellatus Mill.) without residual effects on black cherry (Prunus serotina Ehrh.) seed stored in the forest floor, or on survival and growth of natural or planted black cherry seedlings. Control of most of the target species depended on the date and rate of application. Simazine had no herbicidal effect on these extremely acid (pH 3.9 to 4.4) Allegheny Plateau sites. None of the herbicides interfered with germination of black cherry seed stored in the forest floor or with establishment of seedlings. Bromacil applied at 22.4 kg/ha, picloram, at 9.0 kg/ha, and hexazinone at 13.4 kg/ha reduced survival, or growth, or both, of black cherry seedlings planted in a forest opening. Glyphosate was the most economical herbicide that met the control criteria. Application of 1.1 kg/ha between August 1 and September 1 produced acceptable control of all target species for at least 3 yr.

THE BIOLOGY OF CANADIAN WEEDS.: 26. Dennstaedtia punctilobula (Michx.) Moore

A summary of biological information on Dennstaedtia punctilobula (Michx.) Moore, hay-scented fern, is presented. It has a native perennial herbaceous species of North America which has its center of distribution in the Appalachian region. In Canada it is found from the East Coast to Ontario. It is a weed in native lowbush blueberry fields, upland pastures and roadsides, particularly in the eastern parts of its range, where it forms dense colonies.