Effects of anthropogenic activities on distribution and abundance of epiphytic orchid Polystachya fusiformis (thou.) Lindl. at the Manga range ecosystem in Kisii, Western Kenya

Abstract

Orchid diversity which is a major source of income in Kenya is threatened due to rapid loss and fragmentation of habitats, which accounts for up to 80% of natural habitat lose. Since orchids have complex life histories in which there is a varied display of morphological and anatomical adaptations, which are of interest to scientists, photographers, artists, collectors and economists, their conservation is of a necessity. A lot of effort has to be directed to their conservation, especially the critically endangered epiphytic orchid Polystachya fusiformis (Thou.) Lindl. The present study focused on the factors influencing extermination of the orchid P. fusiformis (Thou.) Lindl.. The study will provide information on the status of the epiphytic orchid P. fusiformis (Thou.) Lindl. its distribution and abundance, and its related symbionts in the Manga range ecosystem. Manga range covers an approximate area of 20 km2. It is situated 5 km to the North-East of Kisii town between 00o33‟ South and 34o57‟ East in Kenya along the Kisii-Nyamira counties‟ common border. The sampling design method was a two-transect based plan that was oriented from the base of the range where there was a continuous baseline at the foot of Manga range to collect data on the distribution and abundance of the epiphytic orchid P. fusiformis (Thou.) Lindl. Transects were initiated at the base of the rocky outcrops on the North and North-Western parts of the Manga range. A total of 88 quadrats each measuring 1m2 was randomly laid along a 30m long line transect. The GPS co-ordinates where orchid clusters were detected were recorded using a Garmin e-Trex vista Global Positioning System (GPS). Roots of healthy orchids were selected from each quadrat to examine for the presence/absence of fungal symbionts. There was significant variation in the abundance and distribution of epiphytic orchid with change in altitude. Forty one 1m x2m quadrats were found to have a density of 3.2 individuals per unit area; 47 quadrats did not have any orchid. Logging, wood collection, and fire were the key factors which influenced the distribution and abundance of orchid. One way ANOVA Levene‟s test xiv for equal variance showed that the density of orchid clusters significantly decreased with increase in altitude (p = 0.00004) at α 0.05. The majority of P. fusiformis (Thou.) Lindl. plants were clustered around the altitude of 1800m to 1850m above sea level. Orchid cluster abundance was calculated to be 31% of the total sampled area at Manga range ecosystem. Fire is a great threat to P. fusiformis (Thou.) Lindl. at the lower altitudes as their aerial roots and exposed pseudobulbs burn easily during the dry season when humidity is relatively low. The orchid is sensitive to fire and as such it was limited to parts of the Manga range with high level of water seepage and relictual stands of host trees where it displays a clustered pattern of distribution. Although these studies did not show host-orchid-specificity, the host trees were identified as follows: Spathodea campanulata, Vangueria infausta, Ficus thonningii, Olea capensis, Croton sp. Terminalia sp. and Protea sp. at the time of study (October 2011-March 2012). A total of 64 standing trees and 160 tree stumps of P. fusiformis (Thou.) Lindl. host trees were detected in the months of October-December 2011. Identification of pure fungal isolates revealed the presence of Rhizoctonia sp. and Fusarium sp. in the roots of orchid roots. A fungal colonization of the orchid roots did not reveal host-fungus specificity.