Effects of heat on the germination of sclerophyllous forest species in the highlands of Madagascar

Abstract

The effects of fire on germination have been extensively studied in many ecosystems. Several studies have shown that plant species in ecosystems frequently exposed to fire can survive through two main mechanisms: vegetative regeneration (re-sprouts) and recruitment of new individuals from a fire-resistant seed bank. In Africa, an increase in temperature can break seed dormancy and stimulate germination of some herbaceous and woody species. In Madagascar, the once widespread highland ecosystems dominated by woody species are now highly fragmented and dominated by anthropic grasslands and fields, with a significantly reduced area occupied by sclerophyllous forests referred to as tapia woodlands'. Six species of this endemic vegetation type were studied: Abrahamia ibityensis (Anacardiaceae), Aphloia theiformis (Aphloiaceae), Carissa edulis (Apocynaceae), Pentachlaena latifolia (Sarcolaenaceae), Uapaca bojeri (Phyllanthaceae) and Vaccinium secundiflorum (Ericaceae). Germination tests were conducted (i) by soaking seeds in water for 24h (imbibition) or (ii) by exposing the seeds to dry heat. Four different temperatures (40, 60, 80 and 120 degrees C) were applied, and seeds were exposed for 10, 30, 60 and 90min. To simulate hotter faster-burning fires, two higher temperatures (100 and 120 degrees C) were also used by exposing seeds to dry heat for 5min. The results did not reveal any significant effect of 24-h water imbibition on germination. For most species, germination decreased with increasing temperature of treatment using dry heat. Uapaca bojeri did not germinate under any treatment. Further studies on the biological and ecological characteristics of tapia woodland species in response to fire are needed to help guide conservation, management and restoration activities focusing on this endemic vegetation type.