On the deer-grass, trighophorum caespitosum (l.) hartman

Abstract

The species has been examined from an ecological standpoint, by comparing it with Molinia caerulea (L.) Moench, an alternative dominant of Scottish "blanket bog". Of the two recorded subspecies, only ssp. germanicum and intermediates of uncertain status appear to survive in Britain. A floristic description is given of the transition from dominant Trichophorum to dominant Molinia in an area typical of the N-W Highland region. Following "muirburn", both species reproduce from seed. The successful establishment of a Trichophorum seedling eventually produces a single tussock. Edaphic factors appear to control the distribution of the two species. An account is given of a polarographic survey of soil oxygen, and a survey of groundwater movement based on applications of Darcy's law. The transition from Trichophorum to Molinia is accompanied by a striking increase in the rate of horizontal water movement. An hypothesis is advanced whereby the groundwater acts as a vehicle of mineral nutrition. Productivity studies show that the rate of uptake of nutrients by adults is similar in. the two species. A stagnant body of groundwater, supplying nutrients slowly, limits the early development of the relatively large Molinia seedlings, allowing successful establishment of the much smaller seedlings of Trichophorum. Moving groundwater, enhancing the mineral supply, permits luxuriant development of Molinia seedlings, whose shade limits the development of Trichophorum. Ion exchange sites in the peat may form an intermediate nutrient reservoir. Experiments to examine this hypothesis included one in which seedlings of Trichophorum were grown in competition with those of Molinia. The growth of Molinia was limited more by nutrient availability than by plant density. The growth of associated Trichophorum varied inversely with nutrient availability, due apparently to competition from Molinia. Other experiments and observations suggested light as the limiting factor for Trichophorum. The effects of soil aeration were not significant. Some suggestions are included for improving techniques for the in situ estimation of soil oxygen.