Maesopsis eminii Engler (Rhamnaceae)

A large African tropical forest tree introduced to various parts of the tropics for timber production or as a shade tree. Naturally regenerating in many places and invasive in the rain forests of the East Usambaras (Tanzania).

Species characteristics
Life form, size and lifespan
Large canopy tree reaching a height of up to 43 m and a diameter of 1.2 m. Exceptionally able to live up to 200 years.

Taxonomy, variation and plasticity
The genus Maesopsis is monospecific. On the basis of height and wood quality variation a western African sub-species (M. eminii subsp. berchemoides Hallé) has sometimes been recognized. Tree height increases from about 15 m in western Africa to over 40 m in East Africa. The size and the dentation of the entire leaf exhibit much variation. The species is either deciduous or semi-deciduous depending on local climatic conditions.

Reproductive biology
The sex expression and pollination system is poorly understood but flowers are thought to be hermaphrodite and protogynous and insects are the likely pollinating agent. Flowering and fruiting starts after four to ten years and large seed crops are produced every year often every six months. A number of birds, including hornbills, and monkeys dispersed the large drupe (2-3 cm). Seeds remain dormant for up to at least 200 days. Germination is not triggered by light but appears to be affected by lunar cycles and enhanced soil humidity promotes early germination.

Resilience and resistance
Coppices freely after being cut and is susceptible to fire.

Environmental requirements and successional status
Usually described as a pioneer M. eminii germinate and seedlings survive under forest canopy for a few months. However, to grow and reach canopy height M. eminii requires large canopy gaps. At the forest-savanna boundary it becomes established under shrubby vegetation.

Products and uses
Timber is soft but firm and strong, and widely used in Uganda. However, the wood is not resistant to termites and fungal decay. M. eminii has been used in eastern Tanzania and Fiji in forestry plantation. It is used in India as a shade tree in coffee plantations and elsewhere in Asia as an agroforestry tree.

Status in native range
Range and abundance
M. eminii is widely distributed throughout moist tropical Africa from Liberia to Uganda and south to Angola. Usually an uncommon tree with the exception of the forest-savanna boundary in Uganda where it may be dominant.

Climate
Broad spectrum of climate requirements from per-humid tropics to seasonal tropics.

Site requirements
In moist forests M. eminii becomes established in large forest gaps. In Uganda, it does not regenerate in grassland mainly because of its susceptibility to fire. At these sites the grassland must be colonised by fire resistant species before M. eminii regenerates to form dominant stands. Subsequently succession proceeds to a high forest containing only a small proportion of M. eminii. On Lake Victoria islands succession from grassland to forest is similar except that it normally takes place around anthills. This suggests that higher nutrient status is necessary for tree colonisation to occur.

Weediness
In most of its native range M. eminii has no weedy tendencies, on the contrary it is usually scarce even in secondary forests.

Pests and diseases
Many insects and fungal diseases affect M. eminii causing defoliation, stem breakages and bark cankers.

Status in invaded regions
History of introductions and intensity of invasions
Introduced, probably from the Bukoba regions in western Tanzania, to the Amani Botanic Gardens in the East Usambara (eastern Tanzania) in 1913 when a 1 ha forestry trial plot was set up. Large-scale forestry planting was undertaken during the 1960s and early 1970s. M. eminii is now dominant in secondary forests near the M. eminii plantation and is found in many natural forest treefall gaps.

Natural regeneration and spread observed in Rwanda, Fiji, India and on Pemba Island (Tanzania). In Puerto Rico it regenerates profusely and is likely to become common or abundant in forests within the next century.

Patterns of invasion and time-lag
In the natural forest in the East Usambaras M. eminii becomes established in large treefall gaps and pit-sawing gaps where light levels are high. Seedling establishment occurs on bare humus soil. Less than 15 years lapsed between the introduction of M. eminii until it was first reported as regenerating in the natural forest.

Site and climate
Mountainous area at an altitude of ca. 1000 m. The climate is seasonal and frost-free with two rainy seasons and the annual rainfall varies between 1,000 mm and 2,000 mm.

Floristic region and vegetation types
The East Usambaras are part of the isolated Eastern Arc Mountains of Eastern Africa. Their sub-montane forests contain a number of endemic or near endemic species and have a high conservation value.

Pests and diseases
Little damage occur apart from limited fungal attack on young seedlings and some squirrel seed predation.

Impact on ecosystem
M. eminii becomes dominant in logged forests and regenerates in treefall gaps. It alters soil properties and associated fauna. Impact on tree regeneration probable but evidence inconclusive.

Impact on humans and related activities
In the East Usambaras people have no use for the wood, including as firewood, and do not exploit it. Farmers or foresters do not consider M. eminii as a pest as the tree does not have thorns or any other obvious negative effects on human activities.

Control
As yet no control programme has been initiated. Since the tree coppices readily, felling stands dominated by M. eminii must be accompanied with bark removal of stumps. Ring barking does not lead to crown death unless the cambium and part of the xylem are cut. Trees may be killed using arboricide.

Ecological differences
Existence of ecological equivalent species and competitive interactions in invaded regions
In the East Usambaras no equivalent species exist. A combination of very fast growth rates (in full light), large bird-dispersed fruits and seeds, short-term (few months) shade-tolerance in newly germinated seedlings and shade intolerance thereafter are a unique combination of characteristics in M. eminii.

Differences in status and ecology between invaded and native ranges
In the East Usambaras M. eminii does not appear to suffer from any significant attacks from pests and diseases similar to those reported from Uganda. Regeneration in treefall gaps, common in the East Usambaras, is scarce in the native range. M. eminii dominance in secondary vegetation is never observed in native range.

Selected references
* Beentje, H.J. (1990) Botanical assessment of Ngezi Forest, Pemba Island, Zanzibar. Zanzibar Forestry Devl. Plan, Finnida, Zanzibar.
** Binggeli, P. (1989) The ecology of M. eminii invasion and dynamics of the evergreen forest of the East Usambaras, and their implications for forest conservation and forestry practices. In Hamilton, A.C. & Bensted-Smith, R. (Eds) Forest conservation in the East Usambara Mountains, Tanzania, pp. 269-300. IUCN, Gland.
** Binggeli, P. & Hamilton, A.C. (1993) Biological invasion by Maesopsis eminii in the East Usambara forests, Tanzania. Opera Bot. 121, 229-235.
• • Eggeling, W.J. (1947) Observations on the ecology of the Budongo rain forest, Uganda. J. Ecol. 34, 20-87.
* Hall, J.B. (1995) Maesopsis eminii and its status in the East Usambara Mountains. East Usambara Catchment Forest Project Technical Paper No. 13. Finish Forest & Park Service, Vantaa.
# Johnston, M.C. (1972) Rhamnaceae. In Milne-Readhead, E. & Polhill, R.M. (Eds) Flora of tropical Africa. Crown Agent for Overseas Government & Administration, London.
# Normand, D. (1935) Sur le Maesopsis de l'ouest africain et la bois de nkanguele. Rev. bot. appl. Agric. trop. 15: 164, 252-263.
* Sreenivasan, M.S. & Dharmaraj, P.S. (1991) Maesopsis eminii Engl - a fast growing shade tree for coffee. Indian Coffee 55, 17-20.
• Thomas, A.S. (1941) The vegetation of the Sesse Islands, Uganda. An illustration of edaphic factors in tropical ecology. J. Ecol. 29, 330-353.

Pierre Binggeli

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