ECOLOGICAL IMPLICATIONS OF LAND USE / LAND COVER CHANGES IN THE MARGUBA RANGE OF OLD OYO NATIONAL PARK, NIGERIA

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.