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Seedling growth recruitment natural regeneration Ceriops tagal Gazi
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Spatial and Temporal Regeneration Dynamics in Ceriops tagal ( Perr.) C.B. Rob. (Rhizophoraceae) Mangrove Forests in Kenya
Abstract
Mangrove forests consist of a mosaic of tree cohorts, each having a regeneration history
that depends on episodic recruitment of seedlings based on the availability of a “regeneration
niche”. The aim of this study was to assess seedling population structure in Ceriops tagal
natural monospecific stands and one eight-year old reforested stand at Gazi Bay, Kenya, to
determine performance in terms of growth and survival over a period of two years. Four natural
monospecific stands (two on the western creek designated as site 1 and 2, and two on the eastern
creek designated as site 4 and 5) were identified with the reforested stand (on the eastern creek) as
site 3. The vegetation structure of these stands and natural regeneration were assessed by Linear
Regeneration Sampling. Regeneration Class I (RCI) seedlings of known age were tagged and their
growth parameters (diameter, height, leaf production and number of nodes) and survival rates
monitored for a period of two years. The reforested stand had the same basal area (2.2 ± 0.1 m2
ha-1) as site 1 (2.1 ± 0.1 m2 ha-1), and the former’s mean height was also similar to that of western
creek sites (1 and 2), but lower than the eastern creek sites (4 and 5). The western creek sites had
the highest seedling mortality (61 % for both) and lowest growth rates recorded over the two year
period compared to a mortality of 45 % for the eastern sites. An analysis of seedling growth over
the two years as a function of measured environmental factors showed a weak interaction, with
height above datum (HAD) and canopy cover showing the highest correlation of only 30 %. The
high mortality on the western creek sites may be attributed to harsh environmental conditions
due to the limited expanse of the intertidal area of the western creek mangroves compounded
with anthropogenic pressure due to its proximity to human settlements. Overall, C. tagal forests
at Gazi Bay seem to be more vulnerable to environmental stress because they occur at the upper
intertidal area, which limits their long-term structural development. Of the four species common
at Gazi, C. tagal is the least structurally developed with very low basal areas and mean heights,
which are both important determinants of wood quality. These upper-shore forests therefore
require management approaches distinct from those of other species to ensure that their natural
regeneration and overall structural development are not unsustainably compromised.
that depends on episodic recruitment of seedlings based on the availability of a “regeneration
niche”. The aim of this study was to assess seedling population structure in Ceriops tagal
natural monospecific stands and one eight-year old reforested stand at Gazi Bay, Kenya, to
determine performance in terms of growth and survival over a period of two years. Four natural
monospecific stands (two on the western creek designated as site 1 and 2, and two on the eastern
creek designated as site 4 and 5) were identified with the reforested stand (on the eastern creek) as
site 3. The vegetation structure of these stands and natural regeneration were assessed by Linear
Regeneration Sampling. Regeneration Class I (RCI) seedlings of known age were tagged and their
growth parameters (diameter, height, leaf production and number of nodes) and survival rates
monitored for a period of two years. The reforested stand had the same basal area (2.2 ± 0.1 m2
ha-1) as site 1 (2.1 ± 0.1 m2 ha-1), and the former’s mean height was also similar to that of western
creek sites (1 and 2), but lower than the eastern creek sites (4 and 5). The western creek sites had
the highest seedling mortality (61 % for both) and lowest growth rates recorded over the two year
period compared to a mortality of 45 % for the eastern sites. An analysis of seedling growth over
the two years as a function of measured environmental factors showed a weak interaction, with
height above datum (HAD) and canopy cover showing the highest correlation of only 30 %. The
high mortality on the western creek sites may be attributed to harsh environmental conditions
due to the limited expanse of the intertidal area of the western creek mangroves compounded
with anthropogenic pressure due to its proximity to human settlements. Overall, C. tagal forests
at Gazi Bay seem to be more vulnerable to environmental stress because they occur at the upper
intertidal area, which limits their long-term structural development. Of the four species common
at Gazi, C. tagal is the least structurally developed with very low basal areas and mean heights,
which are both important determinants of wood quality. These upper-shore forests therefore
require management approaches distinct from those of other species to ensure that their natural
regeneration and overall structural development are not unsustainably compromised.
