Assessment of changes in land cover and forest composition and structure in Okongo community
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Date
2020-01
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Namibia University of Science and Technology
Abstract
Land cover refers to the observed vegetation, structures, or other features that cover the land such as closed forests, open forest, woodland, grasslands, bushland, and settlements. Land cover change is one of the serious threats to the forests and woodlands of Namibia, and it is mainly triggered by forest resource utilization and conversion to agriculture by local communities. As one of the mechanisms to control land cover change, Namibia introduced the Community Forests (CF) programme for local communities to own, manage and use forest resources sustainably. Therefore, this study assessed changes in land cover in Okongo Community Forest (CF) in Namibia for the period 2003 – 2017 by comparing the Okongo CF with the areas outside Okongo CF. The study also monitored major changes (trends) in forest composition of Okongo CF since it was gazetted. The study area is situated in the Okongo constituency in the eastern part of Ohangwena region and includes Okongo CF, Omufitu Wekuta CF, within Okongo Conservancy. The study area was divided into five sub-areas - Okongo CF, Omufitu Wekuta CF, the central buffer zone, the buffer east and the buffer west to compare the land cover change. The study adopted a mixed approach by analysing land cover on satellite images (2003 Landsat 7 satellite imagery and 2017 Landsat 8 satellite imagery) and forest inventory data for 2000 and 2015 derived from the National Forest Inventory database. The satellite image data collected were analysed quantitatively using a GIS and FRAGSTATS technology for landscape metric calculations. The inventory data were entered and organised in Excel. Trees were placed in diameter at breast height (DBH) classes and the stem density, mean DBH, and basal area of all measured trees were determined. DBH distribution was studied for the timber species such as P. angolensis, B. plurijuga, B. africana and G. coleosperma, as well as stem densities and basal area per ha.
The main land cover changes that occurred for the period 2003 – 2017 between Okongo CF and areas outside Okongo CF include a decrease of forest/shrubs land in three of the five sub-areas: the buffer west (-4.7%), Omufitu Wekuta CF (-4.6%), and the central buffer zone (-6.9%). Forest cover remained close to the same in Okongo CF (0.2 %) and the eastern buffer (-0.01%). An increase in bare land was found in the buffer east of the study area (260.1%) and Omufitu Wekuta CF (557.7%). However, the Okongo CF showed more declined in bare land (-98.1%) than other parts of the study area. About 0.67% of the study area was converted to settlements area and this includes part of Okongo, Omufitu Wekuta CF and the central buffer zone. As for human activities, it is agriculture that showed an increase in all areas with much increase experienced in the buffer west (77.3%), Omufitu Wekuta CF (85.1%) and the central buffer zone (113.1%) of the study area. The study found that the eastern part of the study area (includes Okongo CF and the
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buffer east) shows hardly change in forest/shrubs cover and agriculture. The FRAGSTATS analysis of landscape metrics for landscape structure and patterns Spatio-temporal fluctuations showed that patch density generally increased for nearly all land cover classes except for bare soil (80 ha). Largest patch index decreased for forest/shrubland (94.2%) as compared to other land uses and the interspersion and juxtaposition index (IJI) decreased for forests/shrubs land (15%) and bare land (1%) while it increased in agriculture land (9%).
The study found that the mean DBH of all measured tree species in 2000 inventory was significantly higher than the mean DBH of 2015 inventory (p-value = 0.003). There were no significant differences in the distribution of frequencies of timber tree species between the 2000 and 2015 inventories (U=44.5, p=0.684). This study found a significantly lower count of 250 stems per hectare for the 2000 inventory as compared to the 2015 inventory with 300 stems per hectare (p-value = 0.021). The study found that the mean DBH of timber species (P. angolensis, B. plurijuga, B. africana and G. coleosperma) in 2000 and 2015 was not significantly different (p=0.875). There was no significant difference between the basal cover of 2000 and 2015 inventory (p-value = 0.737).
It is concluded that the Okongo CF experienced a positive and favourable decrease in bare land class and area converted to bare land in comparison with the other parts of the study area. The study also concluded that there is a favourable increase in an area that was converted to forest/shrubs land compared to Omufitu Wekuta CF, the buffer west and the central buffer zone. Another small patch of an area of the Okongo CF was converted to agricultural land and settlements whereas the remainder of the area remains forest/shrubs land. This suggests that there has been sustainable land use management in Okongo CF since its gazettement in 2006. Considering the effects of changes in areas outside Okongo CF, it was recommended that the Government must consider extending strategies employed in Okongo CF to Omufitu Wekuta CF to realise positive gains, introducing indigenous forests plantations and educating people to increase awareness on the importance of conserving forests.
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Keywords
Community forest, Forest composition, Land cover, Patch density, Tree inventory, Woodland
Citation
Shikomba, A. (2020). Assessment of changes in land cover and forest composition and structure in Okongo community. [Masters thesis, Namibia University of Science and Technology].