Use of a marsh dominated by the introduced European Lake Sedge, Carex acutiformis, by highly localized native butterflies

To determine whether native butterflies had colonized a marsh in Ottawa that was entirely dominated by the invasive alien European Lake Sedge (Carex acutiformis), we surveyed two adjacent stands of the sedge and surrounding habitats. Dion Skipper (Euphyes dion), Mulberry Wing (Poanes massasoit), Broad-winged Skipper (P. viator), and browns (Lethe spp.) were all abundant in the introduced sedge, but absent from surrounding habitats. This is the first report of the use of invasive-dominated wetland by native Canadian butterflies. Reduced nectar resources because of dominance of the invasive species over native nectar-producing plants did not prevent significant colonization. The known restriction of the butterflies to native Lakebank Sedge (Carex lacustris) as a larval host plant, but its absence in the area, coupled with dominance of its close relative, European Lake Sedge, provides strong circumstantial evidence of the use of the latter as larval food. This report doubles the number of recently localized native butterflies that have been able to increase their distribution by switching to habitat dominated by invasive plants.

Carex lacustris × C. trichocarpa (Cyperaceae), a new natural hybrid

The new natural hybrid Carex lacustris × C. trichocarpa is described from material found in southern Ontario and New York State. The plants are sterile with incompletely developed stamens and distorted pollen that failed to stain with lactophenol. The parentage is confirmed through intermediacy in distinctive morphological characters. The new hybrid possesses unique features of each parent including the red apices of the inner sheath bands of C. trichocarpa and the long ligules of C. lacustris. The flavonoid spectrum of the hybrid was found to be consistent with the proposed parentage. Luteolin glycosides were found only in C. lacustris, whereas tricin glycosides were restricted to C. trichocarpa. Although the hybrid had marker compounds from both putative parents, complementation was incomplete. The occurrence of this hybrid suggests that sedges with quite different chromosome numbers can and do form natural hybrids.

Seasonal changes in carbohydrate levels in tissues of Carex lacustris

Seasonal changes in total nonstructural carbohydrates (TNC) levels in aboveground and belowground tissues of Carex lacustris were determined. TNC concentrations of aboveground tissues averaged 15–20% of the dry weight throughout the year, ranging from 31.3% in newly emerged shoots in September to 3.1% in mostly dead shoots in December. Belowground, TNC concentrations ranged from a low of 16.4% in young rhizomes in midsummer to a high of 44.9% in late October.TNC content of shoots was 68.5 g/m2 on May 5, increasing to a peak of 224.5 g/m2on August 5. Levels declined to a low of 31.6 g/m2 by December 5, of which 74% was found in young shoots about to overwinter. Belowground TNC was 107.5 g/m2 on May 8, declined somewhat into June, then increased to a maximum of 240 g/m2 on October 24. The data indicate these belowground reserves are important for the species to overwinter successfully.The difference between the minimum TNC content of the sedge biomass in late May and the peak in October represented a gain over the summer of approximately 205 g/m2.

Nutrient cycling in a Carex lacustris wetland

Seasonal changes in aboveground and belowground life history of Carex lacustris were determined and used to study primary production and nutrient cycling in the ecosystem. Seasonal aboveground production was estimated to be about 965 g/m2 per year, with a peak rate of 20.9 g/m2 per day reached in late July. Belowground production was estimated to be 208 g/m2 per year for a total production estimate of 1173 g/m2 per year.Nitrogen, phosphorus, and potassium begin the season with high percentage concentrations in green overwintering shoots but the percentages decline to only about one-third of the original at death in December. Early growth in spring is characterized by a redistribution of these nutrients in the shoots, some translocation from belowground tissues, and uptake from the soil. Calciumand magnesium do not show any important translocation patterns during the year.The yearly budget of uptake and loss of nutrients during a year is estimated to be 15.9 g/m2 nitrogen, 1.9 g/m2 phosphorus, 16.6 g/m2 potassium, 2.9 g/m2 calcium, and 1.5 g/m2 magnesium.

The life history of shoots of Carex lacustris

Most shoots of Carex lacustris live for about 12–14 months, emerging in autumn, overwintering as shoots of up to 50 cm in length, and maturing during the next summer. Others emerge in early spring but both groups die in late autumn. A third class emerges in late July or August, grow to be over 50 cm in length, and die in late autumn, living only 2 or 3 months.Flower initials in this species begin growth in the September–October period and overwinter while about 1.0 cm in length. The shoots that develop inflorescences are in general longer, heavier, and have a greater basal diameter than those shoots which do not flower. More shoots flower if the water level in the marsh was high the previous year.

Primary production and life history of Carex lacustris

Seasonal changes in aboveground and belowground standing crop and primary production in a Carex lacustris wetland were determined and related to the basic life history of this species. There was a seasonal minimum of 180 g/m2 green material aboveground frozen in the ice in winter and a maximum of 1037 g/m2 in summer (early August). Seasonal aboveground production based on quadrat data and based on the difference between maximum and minimum standing crop is estimated to be 857 g/m2 per year, maximum daily production 15 g/m2 per day. A second estimate, also based on quadrat data but taking into account the very high shoot mortality during the growing season, was determined. Seasonal aboveground production then is 1580 g/m2 per year, maximum daily production is 20.3 g/m2 per day. Belowground standing crop was 387 g/m2 in winter but then declined to an average summer low of 226 g/m2. Belowground standing crop increased during autumn and, by October 7, a value equal to the previous winter's value was reached. Shoots of this species live for 1 year or less, emerging in autumn, overwintering, and then dying sometime during the next summer.