Frontier Tanzania Environmental Research REPORT 110 ...

Kazimzumbwi Forest Reserve
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wiithin Kazimzumbwi FR was found to be low. Overall within vegetation plots, the five most
common species accounted for only 25% of all individuals recorded. This figure does however
include all trees of a dbh of 10cm or over; thus it is not confined to canopy trees, and is not
confined to trees within any 1ha block. Calculations based on the number of trees and species per
plot (vegetation and regeneration) in this study revealed the vegetation of Kazimzumbwi FR to
vary greatly in its degree of monospecif ic dominance. Those plots with the highest mono-specific
dominance were dominated by a few species such as Cassia siamea or Lecaniodiscus fischeri.
These figures are based on the number of individuals however and abundance does not
necessarily reflect dominance, especially when considering canopy dominance. Of those species
found to be most abundant within vegetation plots, only Manilkara sansibarensis and Albizia
petersiana are canopy trees whilst Cassia siamea is a plantation species and Rinorea angustifolia
a dominant forest shrub. Calculations based on basal area could possibly yield interesting results,
however qualitative observations of dominance amongst species would appear to provide good,
but possibly subjective, results. These conclude that dominance is spread between 5-7 species
within each vegetaion type and thus a few species do infact dominate most of the vegetation types
encountered.
Many vegetation types were recognised within Kazimzumbwi FR, the various characteristics of
which reflect those of Coastal Forest vegetation types as described by Clarke and Robertson
(2000) fairly well. The Coastal Forest vegetation types of ‘Mixed Dry Forest’, ‘Brachystegia
Forest’ and ‘Swamp Forest’ are all represented within Kazimzumbwi FR. The existence of the
latter of these is particularly important, as freshwater swamp conditions, and thus Swamp Forest,
are rare in Coastal Forests (Clarke & Robertson 2000). The ‘scrub/thicket/bush’ and ‘edge forest’
vegetation types recorded in Kazimzumbwi FR do not correspond well with any of the vegetation
types listed by Clarke and Robertson (2000), and rather contain species from all of them. This can
be explained as variation in plant communities is continual through space (and time) and thus the
strict definition of vegetation types is not always appropriate. Such areas were previously
disturbed by human activity (refer to section 5 for more detail).
Altitude varies little within Coastal Forests and thus factors other than this are important in
determining their vegetation communities (Clarke, Vollesen & Mwasumbi 2000). Climate, soil,
geology, geomorphology, human disturbance, aspect, historical factors and even termites may all
effect forest assemblages. Any number of these factors could be important in determining
vegetation communities within Kazimzumbwi FR, but human disturbance is considered to be
particularly important. Brachystegia forest, scrub forest, wooded grassland, grassland, open areas
and edge forest are all habitats potentially resulting from human activ ities. Brachystegia forest
may result from past clearance and subsequent soil degradation, scrub forest from regeneration
after clearance and/or burning, wooded grassland and grasslands from widespread and frequent
fire-burning by early humans, open areas from selective logging and edge forest through activites
such as railway construction (see Clarke 2000, Clarke and Robertson 2000). Topography is also
considered to be an important determining factor, particularly with regard to the extent of vines,
through its’ link to the availability of water resources.
4.5.2 ‘NEW RECORDS’
Combining the species recorded systematically and through opportunistic collection, 20 species
(12%) recorded within Kazimzumbwi FR have not previously been recorded in Coastal Forests
(based on florulas given by Clarke, Vollesen and Mwasumbi (2000) and Clarke (1995)). All of
these species have widespread distributions and are from families already represented within
Coastal Forests. The botanical collection and study of Coastal Forest is far form complete and
thus these findings are particularly important.
Frontier-TanzaniaCoastal Forest Research Programme