The effects of time of emergence and plant density on hemp-nettle growth (Galeopsis tetrahit) were measured in natural field populations from the Québec City region and in a greenhouse experiment. In the field, more than 80% of the plants emerged during a peak period of about 2 wk in early May. Few hemp-nettle plants emerged after this peak period. Late-emerging plants produced relatively little biomass compared to plants that had emerged during the early emergence flush. Total biomass accumulation increased with density on three out of four sites. Stands from the lowest density (80 plants m−2) generally produced less biomass than stands of higher plant densities. Average plant biomass production decreased with increasing density. Plants from low density stands displayed a bushy profile compared to the etiolated, single-stemmed plants from high density stands. Mature hemp-nettle stands did not develop strong hierarchical population structures such as found for other annual broadleaf species. Hemp-nettle plants within a stand were distributed rather evenly over a number of height classes. A large proportion of the total biomass was produced by a relatively considerable number of plants 45–59 cm in height rather than by a few dominating individuals.Key words: Hemp-nettle, Galeopsis tetrahit, weed populations, emergence pattern, population density, population structure
Analysis of atmospheric ammonia concentration from four sites in Quebec City region over 2010–2013
