GIANT SENECIOS AND ALPINE VEGETATION OF MOUNT KENYA

1. Quantitative patterns of alpine plant community structure throughout the upper Teleki Valley on Mount Kenya are described. Data on the frequency of all (61) vascular plant species found in 45 transects were analysed using canonical correspondence analysis (CCA) and an agglomerative cluster analysis. Data on the density and size of giant senecios at these transects were also analysed. 2. Senecio keniodendron (high) and S. keniensis (low) separate along an altitudinal gradient, with a distinct hybrid zone in areas of sympatry. Senecio keniodendron occurs in stands of even-sized trees, which may be even-aged. 3. Vegetation analyses revealed a continuum of plant community composition. Mid- and lower-altitude ridges were floristically more similar to wet valley bottoms than to dry slopes, a finding with conservation and management implications. 4. Eleven environmental factors were measured at each transect and included in the canonical correspondence analysis. Included among these measurements was the average tree height of even-sized stands of Senecio keniodendron. The first three axes identified by CCA were associated with percentage vegetation cover (soil moisture), altitude, and mean S. keniodendron stand height, respectively. 5. An analysis of mid-altitude slope transects revealed that the mean height of S. keniodendron trees was the dominant environmental determinant of community composition in these sites. There appears to be considerable variation in plant community composition associated with a natural cycle of establishment, growth and senescence of even-sized S. keniodendron stands.