Ecology of Hyparrhenia rufa (Nees) in derived savanna in north-western Costa Rica.
Abstract
H. rufa was the only herbaceous plant to prosper under annual burning in derived savana in N.W. Costa Rica. Under favourable conditions it could be > 4 m tall but on closely grazed areas its height was <0.5 m. In normal stands its canopy coverage was 100% but basal area was only 8%. Tiller connections soon atrophied and bunches consisted of closely crowded independent plants. Rapid elongation of internodes about 4 weeks before anthesis gave the plant a conspicuously banded appearance. Roots had a maximum diameter of about 1.3 mm. Root distribution in five 1-m core samples was 1220, 322, 277, 258 and 177 g/m2 in successive 20-cm layers of soil. When burning the sward, fire breaks only 1-m wide were adequate provided back-firing was practised. Seeds possessed no dormancy and could be stored with unimpaired viability for at least 14 months, but they required light for good germination and were intolerant of heat from grass fires. Plants produced new green shoots after seed dissemination despite lack of water. The regeneration capacity of plants was increased by mowing or grazing. Nutritive value was low; of samples taken between Apr. and Jan. the most favourable chemical composition was found in Apr. : 11.2% ash, 7.4% CP, 3.02% ether extract, 28.8% CF, 49.58% NFE, 0.1575% P. By Jan. the CP content had fallen to 1.4%. RB