Plant Ecology 159: 211–239, 2002.
© 2002 Kluwer Academic Publishers. Printed in the Netherlands.
Ecology of the pteridophytes on the southern slopes of Mt. Kilimanjaro
I. Altitudinal distribution
Lehrstuhl für Pﬂanzenphysiologie, Universität Bayreuth, Universitätsstr. 30, 95440 Bayreuth, Germany (e-mail:
Received 26 October 1999; accepted 4 June 2001
Key words: Altitudinal zonation, Mt. Kilimanjaro, Pteridophytes, Tropical mountains
140 taxa of 61 genera in 24 families of pteridophytes were recorded on the southern slopes of Mt. Kilimanjaro.
These represent about one third of the entire pteridophyte ﬂora of Tanzania. The families richest in species are the
Aspleniaceae, the Adiantaceae, the Dryopteridaceae, the Thelypteridaceae and the Hymenophyllaceae. Due to its
luxuriant montane rain forest, which receives a precipitation of up to over 3000 mm, Mt. Kilimanjaro is distinctly
richer in pteridophyte species than other volcanoes in East Africa. However, compared with the mountains of the
Eastern Arc, the number of pteridophytes on Mt. Kilimanjaro is smaller. This can be explained by the widely
destroyed submontane (intermediate) forest rather than by the higher age of the Eastern Arc Mts.
The altitudinal distribution of all ferns was investigated in 24 transects. On the southern slopes of Mt. Kiliman-
jaro they were found in an altitudinal range of 3640 m. Cyclosorus quadrangularis, Azolla nilotica, Azolla africana
and Marsilea minuta are restricted to the foothills, while Polystichum wilsonii, Cystopteris nivalis and Asplenium
adiantum-nigrum are species found in the highest altitudes.
Based on unidimensionally constrained clustering and on the analysis of the lowermost and uppermost oc-
currence of species, ﬂoristic discontinuities within the transects were determined. From these data and from an
evaluation of the distribution of ecological groups and life forms, 11 altitudinal zones could be distinguished: a
colline zone (−900 m asl), a submontane zone (900–1600 m asl) with lower and upper subzones, a montane zone
(1600-2800 m asl) divided into 4 subzones, a subalpine zone (2800–3900 m asl) with lower, middle and upper
subzones, and ﬁnally a (lower) alpine zone above 3900 m. The highest species numbers were observed in the lower
montane forest belt between 1600 and 2000 m altitude. The zonation of ferns found at Mt. Kilimanjaro corresponds
well with the vegetational zonation described by other authors using bryophytes as indicators in different parts of
the humid tropics.
Tropical mountains produce an enormous wealth of
pteridophyte species. From the South American An-
des e. g. about 2000 pteridophyte species are known
(Moran 1995). However, the causes of this phe-
nomenon are not well understood. Only few studies
address the change of pteridophyte diversity with in-
creasing elevation (Lellinger 1985; Panama, Jacobsen
& Jacobsen 1989; East and South Africa, Parris et al.
1992; Mt. Kinabalu, Mehltreter 1995; Costa Rica and
Kessler 2000; Bolivia). Mt. Kilimanjaro, the highest
free-standing mountain of the world (750 to 5895 m
asl), overtopping its foothills by more than 5000 m,
provides an excellent model for the investigation of the
altitudinal distribution and habitat demands of tropical
Frahm & Gradstein (1991) pointed out that
bryophytes are excellent tools for recognising the al-
titudinal zonation of tropical mountains as they: (i) are
indicators of climatic factors such as temperature and
humidity; (ii) have much wider ranges than most vas-
cular plants, and; (iii) are fewer in species than those.
These reasons also apply to the pteridophytes, plus