Abstract:
Protected Areas (PAs) such as Old Oyo National Park (OONP) are created to conserve
biodiversity. In Nigeria, unregulated anthropogenic activities in PAs cause changes in
Land Use/Land Cover (LU/LC) thereby, disrupting their ecological functions. Although,
surveys have been conducted to assess forest resources in Marguba Range (MR) of
OONP, effects of changes in LU/LC in MR have not been adequately documented.
Therefore, flora diversity and shift, Carbon Stock (CS), LU/LC Changes (LU/LCC) and
their ecological implications in MR of OONP were investigated.
Buffer Zone (BZ-1.44 ha) and Core Zone (CZ-2.88 ha) of the MR were studied from
2017 to 2019 in two consecutive Dry Seasons (DS) and Wet Seasons (WS). Five
hundred and forty quadrats (BZ-180; CZ-360) were laid in 108 plots (BZ-36; CZ-72) on
36 perpendicular transects (BZ-12; CZ-24) along three baseline transects (BZ-1; CZ-2)
to assess flora composition and diversity in Standing Vegetation (SV) following
systematic sampling procedures. Soil samples were collected at 0-15 cm depth from five
points within each plot and bulked to assess Soil Seed Bank (SSB) composition and
diversity following standard procedures. The CS was estimated using non-destructive
allometric equation. The LU/LCC (ha/year) was evaluated with GIS and remote sensing
techniques on Landsat imageries of 1990, 2000, 2010 and 2019. Supervised image
classification was used to identify the LU/LC classes. Data were analysed using
descriptive statistics, Relative Importance Value (RIV, %), diversity indices, and
Jaccard similarity index (%).
Standing vegetation composition of individuals/ha, families and species were BZ: 2,305,
6 and 12 (DS), 6,613, 25 and 70 (WS); CZ: 2,523, 6 and 11 (DS), 8,493, 24 and 73
(WS), respectively. The SSB composition of individuals/ha, families and species were
BZ: 741, 15 and 30 (DS), 452, 13 and 27 (WS); CZ: 330, 16 and 34 (DS), 171, 14, 27
(WS), respectively. Most prevalent floras as indicated by RIV were Chromolaena
odorata: 12.2 (BZ); 13.3 (CZ) and Aspilia bussei: 6.9 (BZ); 8.2 (CZ). More species
were present in the SSB in DS: 370.5/ha (BZ); 165.0/ha (CZ) than WS: 226.0/ha (BZ);
85.5/ha (CZ). Dominance and Shannon-Wiener were: 0.31 and 1.58 (DS); 0.07 and 3.25
(WS) in BZ; 0.26 and 1.64 (DS); 0.07 and 3.18 (WS) in CZ, for herbaceous species,
respectively. For trees, Dominance and Shannon-Wiener were 0.07 and 3.13 in CZ;
while BZ had 0.06 and 3.02, respectively. The SV and SSB compositions had low
similarity with 22.7 (DS) and 7.9 (WS). Carbon stock was 3.41 t C/ha (BZ) and 7.53 t
C/ha (CZ). The LU/LCC showed that bare surface and forest land use types gained
543.10 and 122.41, respectively, while shrublands lost 724.83.
There was a shift in species composition of standing vegetation and soil seed bank in
Marguba Range. Invasion by Aspilia bussei caused ecological erosion of native species.
Carbon stock of 7.53 t C/ha from woody species was adequate for a woodland savanna
ecosystem. Changes in land use degraded the land cover, thereby threatening ecological
functions of Marguba Range of Old Oyo National Park.
