Modelling of the long-term competition between Typha angustifolia and Typha latifolia in shallow water - effects of eutrophication, latitude and initial advantage of belowground organs.
A dynamic growth model was developed for Typha latifolia and Typha angustifolia that took account of their vertical productive structures, life cycle, shoot height, leaf area and aboveground biomass. The model successfully simulated the seasonal variation of the aboveground and belowground biomass for two monospecific stands at 43°N and 47°N and the total biomass for one competitive stand at 42°N in the USA. Introducing the parameter of nutrient availability for photosynthesis markedly enhanced the agreement of the simulated results with the observation, implying that nutritional limitations of growth influenced the observed results. The long-term competitive analyses show that the competition between T. latifolia and T. angustifolia at 42°N and 56°N depends on the ratio of net production between these two species, and the initial biomass of T. latifolia. T. angustifolia, with its taller shoot height, is capable of dominating T. latifolia under a sufficiently small inferiority of T. angustifolia in net production rate related to the initial biomass of T. latifolia. Therefore, in the higher radiation of lower latitudes, even a 30% nutrient constraint enables the dominance of the invading T. angustifolia over the initial advantage of T. latifolia with 500 g m-2, while in the lower radiation of higher latitudes, a less than 10% nutrient constraint is required. The analyses provide a quantitative background for the observed competition between these two species.