Abstract:
Teak, Tectona grandis, is an economic tree widely used for timber production,
and its coppice shoot regrowth exploited for pole and firewood. Establishment of Teak
Plantation (TP) is important to reduce the growing gap between the demand and supply
of timber. Natural and anthropogenic factors like Soil Seed Bank (SSB), flora incursion
and grazing could threaten the integrity of TP and its Carbon Stock (CS) capacity.
However, there is dearth of information on how SSB, flora spectrum, and CS could help
in determining the resilience of coppiced-TP in Gambari Forest Reserve (GFR), Ibadan,
Nigeria. Therefore, SSB, flora spectrum and CS were investigated in a coppiced-TP in
GFR.
Thirty 50m x 50m main-quadrats were randomly located for enumeration of tree
species in wet and dry seasons. Within each main-quadrat, five 10m x 10m sub-quadrats
and within each sub-quadrat, five 1m x1m sub-sub-quadrats were laid to enumerate
shrubs/climbers and herbaceous species. Within each main-quadrat, soil samples were
collected from five random spots at 0-5cm (Shallow Topsoil-ST) and 5-10cm (Deep
Topsoil-DT); and were each bulked and air-dried in the laboratory. Soil (1kg) was taken
from each bulked-soil, and spread in 20cm x 20cm x 3cm perforated plastic trays in three
replicates in the screen house to monitor seedling sprouting for five months. In each
main-quadrat, height and girth at breast height of teak plants (girth≥30cm) were
measured. The Relative Importance Value (RIV) for each plant species in TP and SSB
were determined using standard procedures. Community structure indices (Dominance D, Shannon-Wiener-H′ and Jaccard-J) were evaluated. A non-destructive method and
allometric equations were used to evaluate teak CS.
A total of 106 and 79 species belonging to 37 and 34 families were identified in
the coppiced-TP during wet and dry seasons, respectively. The highest RIV in wet and
dry seasons were obtained in Tectona grandis (43.5% and 43.8%; trees), Carpolobia
alba (17.4% and 26.3%; shrubs), Icacinia trichantha (23.7% and 34.1%; climbers) and
Chromolaena odorata (25.1% and 17.0%; herbs), respectively. The D and H′ were: 0.60
and 1.19 (trees), 0.24 and 1.91 (shrubs), 0.15 and 2.17 (climbers) and 0.09 and 2.68
(herbs populations), respectively. The vegetation in both seasons were perfectly similar
for trees (J=100.0%), but less similar for shrubs (J=85.7%), climbers (J=55.6%) and
herbs (J=46.7%). In SSB, 41 species belonging to 17 families, had 20 and 38 species in
wet and dry seasons, respectively. Chromolaena odorata had the highest RIV in wet and
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dry seasons (ST-21.9% and 18.2%; DT-17.1% and 16.3%, respectively). Dominance in
ST and DT were 0.10 and 0.13, while H′ was 2.67 and 2.48, respectively. Similarity was
least (J=36.5%) between ST (wet season) and DT (dry season) and the highest (J=76.3%)
between ST (dry season) and DT (dry season). Jaccard similarity range (SSB/TP) was
0.0-1.8%, 4.2-10.3%, 0.0-3.5% and 25.9-64.7% for SSB/trees, SSB/shrubs,
SSB/climbers and SSB/herbs, respectively. Total CS for teak was 877.8 kg/ha.
There were incursions of Carpolobia alba, Icacinia trichantha and Chromolaena
odorata in the coppiced teak plantation in Gambari Forest Reserve, Ibadan, which
caused low teak carbon stock.
