Download The Rwenzori Mountains straddle the equator along the border

The Rwenzori Mountains straddle the equator along the border between Uganda and the
Democratic Republic of Congo in Africa. The mountains form a complex of huge pre-Cambrian
blocks uplifted to alpine heights later than 2M years BP. The complex has been dissected by
erosion resulting in six separate mountains all rising above 4500m a.s.l. and each consisting of
several peaks. The highest of these peaks is the Margherita on Mt. Stanley. All mountains were
glaciated until historic times but the ice caps have now completely disappeared on Mts. Gessi,
Luigi and Emin. Glacial recession in Rwenzori has affected its landscape including the soils,
vegetation and lakes (Osmaston, 1998; Eggermont et al 2007; Panizzo et al., 2008; Russell et
al., 2008).
Climate data on the range are summarized in Temple (1961) and Osmaston (1965). The
Rwenzori are wetter than other East African mountains, with annual rainfall varying with altitude
from 2000 to 3000 mm, and being heaviest on the eastern slope, which faces the prevailing
winds. On the Uganda side heavy precipitation is strongest from mid-March to May and from
September to mid-December. The equatorial position of the mountain range creates daily air
temperature oscillations between -5 and 20°C in the Alpine and Nival zones, an order of
magnitude greater than the seasonal variation in maximum daytime temperature. Occasional
night-time freezing occurs from ~3000 m altitude (the present-day boundary between Bamboo
and Ericaceous zones); at 4000 m (the Ericaceous-Alpine zone boundary) freezing occurs on
80-90% of the nights.
Vegetation on the Rwenzori is organized in discrete vegetation belts distributed across the
altitudinal gradient, like other tropical mountains. Montane forest extends from about 1,800 m to
2,400 m, and varies from dense forest through bracken or shrub dominated areas with scattered
trees, to grassy glades. The bamboo zone dominated by Sinarundinaria alpina reaches its
upper limit at about 3,000 m, and the Ericaceous zone extends from the end of the bamboo up
to about 3,900 m. Ericaceous vegetation is characterised by broad-leaved trees (Hypericum
spp. or St. John’s Wort, Hagenia abyssinica and Rapanea rhododendroides), arborescent
heathers (Erica spp.), flowering shrubs (typically Helicrysum guilelmii), scattered tree groundsel
(mostly Senecio longeligulatus), and giant lobelias (chiefly Lobelia stuhlmannii). Alpine
vegetation includes Carex runssoroensis tussocks, as well as Helichrysum stuhlmannii,
Alchemilla spp., Senecio and Lobelia. Almost all rock surfaces in the Nival zone, if not overlain
by glaciers, are covered by lichens of the genera Umbilicaria and Usnea and mosses, such as
Rhacocarpus humboldtii forming bright orange carpets.
Classic studies of Afroalpine vegetation changes in response to glacial/interglacial climate
change (e.g. Coetzee, 1964) argue that these vegetation belts migrate through various altitudes
in response to a slowly changing climate. However, we now know that the vegetation response
to climate change is species-specific, and that, at least at low elevation, current, relatively rapid
climate change may produce novel new plant communities (Williams and Jackson, 2007). In
the Rwenzori, the different vegetation zones are not always clearly separated, and transition
zones with mixed types are common throughout the range. Moreover, at a given altitude the
vegetation can vary greatly according to microclimate and edaphic conditions (soil depth,
moisture, stability and fertility) in the different valleys, highlighting the subtle and complex ways
that climate change could influence Rwenzori vegetation.
The general objective is to evaluate the sensitivity of Rwenzoris plant species to future climate
change impacts by analyzing the composition and distribution of plant species in relation to soils
in the Alpine zone of Mt. Rwenzori. Ongoing warming at high altitudes in the tropical
troposphere will cause upslope shifts in the elevation ranges of plants species. To understand
how increasing temperature will affect plant taxa in the Rwenzori, we will investigate plant
species distribution across gradients of climate and in different soil types near the current
Rwenzori treeline. Specifically, we will:
•
Construct a sound GIS database for use in identifying Alpine plant species distribution,
land cover, and edaphic system in the Rwenzori Mountains covering a period between 1960
and 2008
•
Characterize the soils, geomorphic processes and landscape aspects that may influence
plant pattern at the study sites
•
Investigate the changes in the composition and distribution of plants below, at and above
the tree line
•
Model alpine plant species distribution using Species Distribution Model (SDM) along
altitudinal gradients