THE GENUS CYRTANDRA (GESNERIACEAE): ITS INDICATIVE POTENTIAL FOR ASSESSING HISTORICAL AND ACTUAL DISTURBANCE OF ISLANDS FOREST SYSTEMS

Michael Kiehn

Institute of Botany and Botanical Garden, University of Vienna, Rennweg 14, A-l030 Vienna, Austria

With more than 600 species of perennial herbs, shrubs or (rarely) small trees Cyrtandra is by far the largest genus of the Gesneriaceae. Distributed throughout the Pacific Ocean islands and adjacent continents, Cyrtandra species are frequent and prominent elements of the understorey of forest systems in altitudes between 200m and 1500m. First studies on the life-cycle of Hawaiian Cyrtandra have shown that individual plants need between two to six years from germination to first flower set. Seedlings and young plants of Pacific Cyrtandra species are very sensible even to short droughts. After such events only adult plants can (to some extend) recover. Thus changes in the microclimate (e.g., due to alterations in the composition of the covering tree layer) are likely to have strong impacts on the establishment of seedlings. Especially in addition to other disturbances (e.g., by introduced animals destroying the fruits or the seedlings) this drastically influences the age structure of populations, finally leading to the disappearance of species even under only slightly altered environmental conditions. The comparison of historical collections of Cyrtandra in a given area with the actual situation thus has indicative value for estimating degrees and processes of forest disturbance in the past. Age structure analyses of Cyrtandra populations are likely to help assessing the actual situation of forest systems monitored in the framework of the PABITRA project. Due to a relatively short generation time of Cyrtandra species, also positive effects of management measures (e.g., of fencing, the removal of feral pigs or of invasive plant species) can be documented on the basis of age structure studies of Cyrtandra populations. Because of the abundance of Cyrtandra in the Pacific, comparison of data obtained for different study sites should be possible.

 

Abstract from: 43rd Symposium of the International Association for Vegetation Science, July 23-28, 2000, Nagano, Japan.


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