The role of reproduction in Glyceria maxima invasion

Abstract

Glyceria maxima (Poaceae) is regarded as one of the most invasive grasses worldwide, but has only recently become naturalised in South Africa after its intentional introduction as a fodder crop in the 1940s. It invades seasonally inundated habitats. The primary reproduction mode of G. maxima within established infestations was studied at two sites in the KwaZulu-Natal Midlands. Glyceria maxima seeds were also collected from three sites (in KwaZulu-Natal) to understand their dormancy and determine viability. No seedlings were found within established G. maxima infestations. Cold stratification (4 °C) and dry storage of seeds at ambient room temperature for eight weeks did not enhance G. maxima seed germination (means: 0.5% and 2.5%, respectively). However, tetrazolium tests revealed that a high proportion of seeds that did not germinate were still viable. After-ripening of seeds for 19 months resulted in very high germination (mean: 92% across the three sites). A combination of high seed viability, physiological dormancy, high germination following after-ripening and substantial vegetative reproduction is likely to contribute to the invasion success of G. maxima in the aquatic ecosystem. Therefore, chemical control should be investigated as a matter of priority as no control recommendations for this species exist in South Africa.

Keywords: after-ripening, grass, invasive weed, propagules, wetland