Dendrosenecio woodlands on Mt. Kilimanjaro

East African volcanoes – islands of temperate ecosystems

The highest free-standing volcano of the world (above the sea) is Mount Kilimanjaro which rises 5,895 m above sea level and 5,100 m above the surroundings. The plains around the mountain are dry and hot, covered with savannah and semi-desert vegetation but on the hillsides of Kilimanjaro grow lush tropical forests. Mountain is that high that it has several distinct altitudinal zones, with diminishing glaciers on the top.

Kilimanjaro massif started to form some 3 million years ago and the last major eruptions took place some 350,000 years ago. This is a long time enough for the development of unique species on this isolated mountain.

In Eastern Africa are located several such biodiversity "islands" – free standing mountains with unique plants and animals – Mount Meru, Mount Kenya, Mount Elgon, and others. Mount Kilimanjaro though is the highest and one of the oldest ones.

Giant groundsels and lobelias

First Europeans reached the upper part of Kilimanjaro in the second half of the 19th century. When they passed through the dense forest, they were surprised to find groves of weird, alien looking plants.

Most impressive of these plants is Dendrosenecio johnstonii, first described by H.H.Johnston in 1884. This plant grows up to 10 m tall, it forms a woody stem (diameter up to 40 cm) with large leaf rosettes on the top. These stems are branching after the flowering and over the time grow similar to giant candilabres. Mature trees can have up to 80 branches.

These plants grow in wet moorland at the height of 2,7 – 3,35 km and are found only on Mount Kilimanjaro. Further up in the mountain grows another endemic species of giant groundsel – Dendrosenecio kilimanjari (subspecies cotonii), although there is subspecies (kilimanjari) which grows lower, in mist forest. This plant also grows tall, up to 9 m high.

Groundsels have evolved specific adaptation to the frost which occurs almost every night here – the amazing leaf rosettes close inwards during the night, thus protecting the young shoots and flowers.

Third giant plant of Kilimanjaro moorlands is Lobelia deckenii – giant lobelia which grows up to 2.5 m tall when flowering and is found near the summits of other African mountains as well. This plant protects itself from the frost in a very unusual way: leaf rosettes around the stem have small stores of water, which freezes into numerous ice cubicles every night. This layer of ice protects the core of the plant.

Fairly recently (in 2005) there was discovered a frog – Kilimanjaro Stream Frog (Strongylopus kilimanjaro) – which lives at the height of some 3230 m in ice cold streams. Unfortunately the existence of this amphibian is endangered by the melting of glacier.

Natural laboratories

The tallest Eastern African mountains (Afromontane sky islands) serve as amazing natural laboratories, where in similar conditions have evolved similar but nevertheless differing species of plants.

Thus 11 species of Dendrosenecio have evolved near the summits of these mountains:

• Dendrosenecio adnivalis – Ruwenzori
• Dendrosenecio battiscombei – Mount Kenya, Aberdare Mountains
• Dendrosenecio brassiciformes – Aberdare Mountains
• Dendrosenecio cheranganiensis – Cherangani Hills
• Dendrosenecio elgonensis – Mount Elgon
• Dendrosenecio erici-rosenii – Virunga Mountains
• Dendrosenecio johnstonii – Mount Kilimanjaro
• Dendrosenecio kilimanjari – Mount Kilimanjaro
• Dendrosenecio keniensis – Mount Kenya
• Dendrosenecio keniodendron – Mount Kenya, Aberdare Mountains
• Dendrosenecio meruensis – Mount Meru, most likely the newest species

These "sky islands" contain also 21 species of giant lobelias.

References

1. World Wildlife Fund. The Guinean Montane Forest. Accessed in the 21st April 2013.