An assessment of factors leading to the decline of Beclardia macrostachya (orchidaceae) population in Mauritius

Abstract

Clearing of forest land for agriculture and urbanization following colonization have reduced the forest cover in Mauritius to 3% of total land cover. Today exotic species such as Psidium cattleianum (wild guava), Araucaria columnaris , and Ravenala madagascarensis dominate at Pigeon Wood, the only site in Mauritius where Beclardia can be found, leaving little space for very few indigenous tree species like Labourdonnaisia glauca , Apholoia theiformis and Foetida mauritiana . Beclardia macrostachya is an orchid endemic to Mauritius, Madagascar andReunion. Though it is abundant in the latter countries, it is one of the rarest or chids in Mauritius. An assessment of the factors associated with the stability of this orchid was carried out in forests of these three countries to understand the drastic decline of this orchid in Mauritius. Mor phometric and fertility counts carried out at different forests revealed differences in fitness and fertility rates among forests of the same countries and between different countries. Stability of the different Beclardia populations was carried out based on counts of juveniles and adults. Higher fertility rates and most stable populations were observed in the forests of Reunion Island (Bebours) and Madagascar (Ambohitanteley), whereas very low fruit set were observed in Mauritius, unless manual pollination was carried out. Microscopic analysis revealed the presence of pelotons of endomycorrhiza during the early development of the seedlings, in vivo . Based on comparative studies among the different sites, pollinator limitation and absence of suitable hosts were the primary factors that led to the present decline in Mauritius. The high density of wild guava, Psidium cattleianum , which has slowly taken up most of the forest areas inMauritiushas affected the regenerating capacity of Beclardia macrostachya and the density of putative hosts of this orchid. GC-MS/MS analysis of nectar revealed α -D- glucopyranose to be the primary reward of the pollinators and benzyl alcohol, methoxybenzyl alcohol and methoxy methyl phenol to be components floral fragrance.