Vegetative structure, microclimate, and leaf growth of a páramo tussock grass species, in undisturbed, burned and grazed conditions

Abstract

In neotropical alpine grasslands (páramo), the natural tussock grass vegetation is extensively grazed and occasionally burned. The low productivity of the tussock grass seems to be the reason for the disappearance of this growth form in the most frequently intervened areas. The structure, microclimate and leaf elongation rates of new emerging leaves were studied for the dominant tussock grass species Calamagrostis effusa, at an undisturbed, a moderately grazed (7 year after fire) and a heavily grazed (3.5 years after fire) site. In absence of grazing and burning, the tussocks had a high standing crop (1.07±0.09 kg DW · m^-2) and leaf area per projected tussock cover (LAI: 9.6±1.4). Two thirds of the total mass was dead and more than half of the leaves were in horizontal position. The tussock growth form protects the meristems from severe climatic conditions. At midday, the temperature was higher at meristem level than in the rest of the tussock. At this level, photosynthetic irradiance (PI) was almost extinct at 2.9±0.74% of PI above the vegetation. The red/far red ratio (R/FR) was strongly decreased. Initial leaf elongation of new born leaves was 2.3 mm · day^-1, and constant during the year; estimated net annual production was 198±73.8 g m^-2. At the moderately grazed and the heavily grazed study sites, the tussocks were smaller, greener and more erect than those at the undisturbed site. More PI reached the meristems and R/FR was higher at the base of grazed tussocks. Leaf elongation rates were lower. Most of the litter disappeared during the fires. The lower elongation rate of leaves in the grazed areas might be a response to defoliation, resulting in increased tillering and a lack growth associated with poor temperature insulation and more UV-B damage.