|The invasion of Maesopsis eminii in the East Usambara forests of Tanzania|
|Maesopsis eminii is a large African forest tree introduced to many parts of the tropics and grown in monoculture plantations as a fast growing timber tree. Soon after the introduction of Maesopsis to the Amani Botanic Gardens in the East Usambara Mountains in north-eastern Tanzania (which lies outside its native range), it started to spread into the natural forest. The East Usambara forests contain a large number of endemic species and are restricted to a small mountain range. Much of the original forest has been converted or severely degraded as a result of agricultural clearances or forestry operations. Widespread reforestation of logged forest with planted Maesopsis in the 1960s and 1970s and unsustainable logging practices in the 1980s resulted in extensive natural regeneration of Maesopsis in logged areas and natural forest gaps.|
work on the ecology of the Maesopsis invasion includes a review
of the literature, and field research on:
(a) its autecology;
(b) the patterns of invasion into disturbed and undisturbed forests;
(c) its impact on the native forest ecosystem and an assessment of management options.
|The ecological profile of Maesopsis is characteristic of an intermediate "initially shade-tolerant but subsequently light-requiring" species. It has: (a) large (up to 3 cm long) single-seeded fruit dispersed mainly by hornbills; (b) a short-lived (less than one year) soil seed bank; (c) shade-tolerant seedlings (surviving up to c. six months); but (d) shade-intolerant (light-requiring) saplings and mature individuals. Thus, although Maesopsis can germinate and its seedlings survive under forest canopy, it requires full sunlight to grow to maturity and thus can only reach canopy height when growing in large tree-fall gaps. The reduced disturbance regime of the past decade (with reduced levels of logging) has resulted in an apparent slowing down of the rate of spread as fewer sites are being created that are suitable for Maesopsis regeneration. The impact of Maesopsis on the regeneration of common native species is not as important as originally thought, however no data is available on its effect on uncommon and rare endemic species.|
|Maesopsis is only one of a number of the 900 species of woody plants introduced to the Amani Botanic Gardens which are spreading into the remaining natural forest. The incidence of invasions and their impact on endemic species in the East Usambara forests are also affected by heavy human disturbance pressure and climate change observed over the past few decades. These aspects still require careful investigations before final recommendations can be made.|
|Publications and reports available:|
P. & Hamilton, A.C. (1993). Biological invasions by Maesopsis
eminii in the East Usambara forests, Tanzania. Opera Botanica, 121,
Hall, J.B. (1995). Maesopsis eminii and its status at Amani. Report to the East Usambara Catchment Forest Project, pp. 37.
|If you would like a copy of the full report go to the download page.|