TREE DIVERSITY, USE AND LAND COVER CHANGES IN Mt. OTZI FOREST RESERVE, NORTHERN UGANDA

Transcription

1 TREE DIVERSITY, USE AND LAND COVER CHANGES IN Mt. OTZI FOREST RESERVE, NORTHERN UGANDA By ACANAKWO ERIK FRANCIS BSc. (Forestry) (Mak) A report submitted to the International Leadership and Capacity Building Bursary (ILCB), Royal Geographical Society with IBG as a requirement for the fulfillment of the terms and conditions for the Research Bursary received September 2010

2 1.0 BACKGROUND Forests in Africa have been relied upon as a source of livelihood to provide both wood and non wood forest products, yet their value is gradually declining due to changes in the land cover (Murphy & Lugo, 1986, Dovie et al., 2002, Nampindo et al., 2005). The changes are largely caused by the people living in and around the forests. In arid and semiarid areas, variations in climate as well as human activities have been the primary factors leading to land and environmental degradation. Trends have been observed to be high in tropical dry forests (Murphy & Lugo, 1986). The dry forests are characterized by slower growth rates with more restricted reproductive episodes which make them susceptible to disturbance (Kalacska et al., 2004). The challenge with biodiversity loss is that it corresponds to the irreversible loss of the potentially valuable genetic libraries and existence values. It also affects the local service of the ecosystem (Myers, 1997). In Uganda where the population rate is growing at a rate of 3.2% according to the 2002 census (UBOS, 2002), a high proportion of the vegetation is lost due to burning, settlement and grazing (Winterbottom & Eilu, 2006). The remaining natural vegetation is limited to protected areas where they have some protection from human activities and disturbances. The Northern part of Uganda however had a collapse of the system of governance due to the over two decade long civil strife that led to the abandoning of the forest reserves and the protected areas (Winterbottom & Eilu 2006). The unmonitored and unregulated utilization of the forest reserves might have then resulted in the degradation of the forest reserves in the North of Uganda. 1.1 Statement of the problem Mt. Otzi Forest Reserve is categorized as a prime conservation forest with some unique species of flora and fauna not known in any other protected areas of Uganda (Davenport et al., 1993; Uganda Forest Nature Conservation Master Plan, 2002). However Mt. Otzi Forest Reserve is located in the Northern part of Uganda that suffered civil unrest for over two decades at the hands of rebel outfits that operated within and out of Uganda, in the neighbouring Southern Sudan. The environment of insecurity led to difficulty for managers of the forest reserve to be effective custodians of the forest resource. The failure to ensure patrols and management of the forest reserve resulted in unregulated exploitation of the forest resources. The effect of the local people s utilization of the Mt. Otzi Forest Reserve was not known as no studies had been carried out to assess diversity, use and land cover change. There was need therefore to obtain accurate and reliable information to plan for effective management and monitoring of the forest reserve.

3 1.2 Objectives The general objective of the study was to assess the effect of forest use by the local people on tree species diversity and the resultant land cover change. The specific objectives were; 1. To assess spatial variation in tree diversity, size class distribution and stem density between the Eastern and Western arms of the forest 2. To establish the value and use of the forest reserve to the community 3. To assess land cover changes within and around the forest reserve in Metu Sub-county for the time period between 1986 and Hypotheses H 0 : There is no difference in tree diversity in the two arms of Mt. Otzi Forest Reserve H 1 : The people in and around the forest depend entirely on the forest resource as a source of livelihood. 1.4 Justification The data generated will help in the development of a work plan and management plan for Mt.Otzi Forest Reserve since none has been made before. Information relating to structural characteristics of the woody species as well as the anthropogenic activities could be used as baseline data to monitor changes of the forest eco-system. 2.0 MATERIALS AND METHODS The study was divided into three parts of forest survey, social survey and remote sensing. Mt. Otzi Forest Reserve is situated in Metu County in the North of Moyo District (Figure 1). The forest is located between N and E. The relief of the area is characterized by a rugged terrain with an altitudinal range of m above sea level and rolling hills along the River Nile, rising in a series of hills and peaks in the North and North-east. The reserve is bounded by the international border with Sudan in the North east and overlooks the confluence of the Achwa River and White Nile as it flows into Sudan. The geology of the area is composed of schist, quartzite and marble which occur in the mountains surrounding Metu County (SOME, 1994). There has been evidence of the presence of Chimpanzees (Pan troglodytes) in Metu Sub-county in addition to other smaller animals. The flora of the area is mainly dominated by perennial grass e.g. Andropogon species, while the tree species are represented mainly by a mixture of Butyrospermum, Combretum and Terminalia in the grass land. Rainfall in Moyo is divided into 2 peaks of April and August-October (UPPA, 2000) with a total of mm of rainfall received annually. The dominant agricultural system is the traditional subsistence farming.

4 Figure 1: Location of Mt. Otzi Forest Reserve in Uganda and within West Moyo County

5 2.1 Methods Selection of study area The study was carried out in Mt. Otzi Forest Reserve and in the surrounding areas located within Metu Sub-county. Mt. Otzi Forest Reserve area was divided into 2 parts, the Western and Eastern arms. The Western arm had steep gorges with a highly rugged terrain. The Eastern arm on the other hand has rolling hills rising in a series of hills and peaks. The western arm is not easily accessible due to the rugged terrain, deep and steep gorges, while the Eastern arm is relatively accessible by both animals and humans Forest survey Plot layout The study area in the Forest survey was divided into 4km 2 grid plots using the Hawth s tools, an add-in tool to the ArcGIS version 9.2 software. Three sample plots were selected at the gridline intersection and their Universal Transverse Mercator (UTM) coordinates recorded using a Garmin 12XL GPS Unit. 32 grid intersections were selected, each having 3 sample plots, making a total of 96 sample plots for the forest survey. The sample plots were located in the field using topographic maps and a GPS unit. Plots of 50 X 100m were established for the study within the forest reserve. Tree Variables recorded In each of the identified plots, all the trees with a diameter at breast height (DBH), measured at 1.3m, equal to or greater than 10cm that occurred in the plot were enumerated. For trees that forked below 1.3m, each stem that had a DBH equal to or greater than 10cm was considered as an individual tree. DBH was measured using a tree caliper. Recordings of DBH were organized into diameter size classes with a class interval range of 5.5cm. All trees encountered were identified by their local names after examination of their morphological features such as leaves, fruit, bark, exudates and flowers. Samples of leaves, fruit and flowers from each tree species encountered for the first time were collected tagged and pressed, later taken to the herbarium in Makerere University for confirmation of the plant identities by the curator Social survey The survey was undertaken to assess the local people s utilization of the tree species, frequency of exploitation of the forest resources. Data were collected using a combination of questionnaires, administration of one-to-one interviews, Focus Group Discussions and observational methods. 50 respondents in each of the four parishes were selected through a

6 systematic random sampling of households in the different villages that make up the parish, while groups of 10 people were organized for the Focus Group Discussions Assessment of Land Use/Cover change Data source Data for the assessment of the land use/ cover change was obtained from satellite images downloaded from the internet. Mt. Otzi Forest Reserve occurs within the image path 172 and row 052 of the Landsat grid. Two satellite images; one for 1986 and 2004 were obtained from the Global Land Cover Facility (GLCF), an Earth Science Data Interface, University of Maryland link: A 1995 land use map for the forest reserve was obtained from the National Forestry Authority (NFA). The shape files of Mt. Otzi Forest Reserve, with the different attributes of the area were obtained from the wildlife Conservation Society (WCS) Uganda, Kampala office (Table 1). Table 1 shows details of data source used for the remote sensing assessment. Table 1: Source of Data for Remote Sensing Data type Production date Scale Source Landsat TM m GLCF Landsat ETM m GLCF Land use/cover map :466,792 (View scale) NFA Shape files of the study area - 1:466,792 (View scale) WCS Remote Sensing Data Management The Metu Sub-county vector map was obtained by clipping out Metu Sub-county and its attribute features, producing vector maps of the study area. The downloaded satellite images were then merged to form a false colour composite image. Geo-referencing was done to synchronise the identifiable features on the image with those on the vector map to allow for accurate analysis. The area of study was extracted through the process of square extraction. This helped to make the extent of the image smaller, thus enhancing faster analysis of the image while using the Arc GIS 9.2 software.

7 The extent of extraction was; Maximum X: Maximum Y: Minimum X: Minimum Y: On-screen digitization was done by editing through creation of new polygons on the 1995 land cover map. The process involved studying the satellite images for 1986 and 2004 and creating polygons around the different vegetation types, identified by the different shades and colours. 2.2 Analysis of Data Forest survey data analysis The Shannon-Wiener index was used to assess the tree species diversity. Margalef s index was used to determine the species richness in the different plots of the study area, while Pielou J index of evenness was used to determine the species evenness in the different plots. Species Diversity Richness (SDR) IV software was used to carry out all the above analyses. The independent t-test statistics was used to test if there was a significant difference in the diversity by testing difference in species richness and evenness, stem diversity and basal area in the two arms of the study area Social survey data analysis Forest use data from questionnaires, FGDs and one-to-one interviews were analyzed by using descriptive statistics. Chi-square tests were used to determine whether there was a relationship between distance from the forest and the livelihood option pursued Remote sensing data analysis The overall land cover changes were analysed by adding the 1986 and the 2004 land cover raster maps. The attribute tables of the resulting images were studied to determine the changes in area for the different land use types. 3.0 RESULTS 3.1 Tree species Diversity A total 11,120 individual trees were enumerated belonging to 125 species, 92 genera and 43 families. 20 families were represented by 1 species each, while the rest were represented by 2-11 species. Mimosaceae had the highest number of species (11 species in 6 genera).

8 The species accumulation curve in Figure 2 showed an increasing trend by the 95 th sample plot revealing that there was still an opportunity of adding new species with an increase in sample size. Figure 2: Tree species accumulation curve for sampling in the forest survey At 95% confidence Interval, there was a significant difference (P<0.001) in the stem density of trees located in the Eastern and Western arms of the forest reserve. There were more trees per hectare in the Western arm (247 trees) per hectare than in the Eastern arm (224 trees). Maegalef s index of species richness and Pielous J evenness index both showed higher values in the Western arm than in the Eastern arm of the forest. The independent t-test statistics showed a significant difference P<0.05 and P<0.01 respectively for species richness and evenness for the two arms of the forest reserve. At 17% of the species Importance Value Index (IVI), Combretum binderanum was most abundant species. Two out of the seven unique trees species in Mt. Otzi Forest Reserve were encountered. The Family Importance Value (FIV) also showed the Combretaceae family as being more dominant at 40%. The graph in figure 3 shows the percentage value of each of each family s FIV in the entire forest.

9 Figure 3: Tree families and their corresponding Family Importance Value Indices Diameter Class Distribution The results showed that the diameter size class distributions took an inverse J shape both in the East and Western arms. The highest proportion of the trees encountered was in the lowest diameter size class of cm in the two arms of the forest reserve. The stem count proportion decreased with increasing diameter size class. While both arms had the inverse J shape distribution, the decline in the stem count in the diameter size class in the Western arm from cm to cm was moderate while for the same range of diameter size class change in the Eastern arm, there was a drastic change.

10 Figure 4: Diameter classes and stem count proportions for the trees in the Western arm of Mt. Otzi FR Figure 5: Diameter classes and stem count proportions for the trees in the Eastern arm of Mt. Otzi FR

11 3.2 Utilisation of Mt. Otzi Forest Reserve Out of the 200 questionnaires administered, 184 were completed. The local people considered the reserve as natural store of forest products from which they obtained both woody and nonwoody forest products (Table 2, plates 1 & 2). There was no relationship (P>0.05) between the distance from area of residence and the livelihood activities undertaken. The forest had several values to the local people, but rain formation was the most important value of the forest, while the use of the forest land for farming was the least important value of the forest. The most frequently exploited and used tree species were 78, belonging to 33 families. Butrospermum paradoxum, Vitex doniana, Borassus aethiopum, Anacardium occidentale and Multidentia crassa were among those used as a source of food, Pterolobium stellatum, combretum binderanum, Hoslundia opposita, Rhus natalensis, Combretum gueinzii were among those used for fuel wood, while Sarcocephalus latifolius, Khaya senegalensis, Piliostigma thoningii and Annona senegalensis were used for herbal medicine. Both men and women pointed out similar purposes for most of the exploited tree species. Most men however needed the forest wood products for timber and craft making, while the women needed the woody products for fuel wood and poles. Other tree species such as Tectona grandis, Markhamia lutea, Moringa oliefera, Eucalyptus species, and Azadirachta indica were grown by the local people resident near the forest in the home gardens and compounds. The respondents observed that some important species such as Khaya senegalensis, Afzelia africana were declining in abundance, while Erythrina abyssinica, Acacia hockii, Vitex doniana were reported to be increasing in abundance. Table 2: Importance of Mt. Otzi FR to the community and products obtained (N=184) Importance of Forest reserve Percentage of respondents Products obtained Contributes to rain formation process 22.7% Rain water for agricultural production Source of fuel wood 22.3% Firewood for domestic use, wood for small scale industry such as brick baking, iron works Hunting ground 14.0% Game meat

12 Importance of Forest reserve Percentage of respondents Products obtained Source of medicine 8.4% Variety of tree parts used to treat several ailments Source of flowing water 8.0% Water for domestic use, water for animals Source of construction materials 8.0% Timber, poles, fibre, thatch Provide wind breaking service 6.2% Protection of crops and other assets against destructive winds Source of wild food 4.1% Edible fruits, vegetables Habitat for wild animals 4.0% Game meat Provide fertile farming land 2.3% Fertile soils especially near streams, increased agricultural yields Table 3: Frequency of extraction of forest products from Mt. Otzi FR Forest Product Weekly Once every 1-6 months As often as necessary Water 167 (90.8%) 0 (0%) 17 (9.2%) Fuel wood 161 (87.5%) 23 (12.5%) 0 (0%) Food 86 (46.7%) 24 (13%) 74 (40.2%) Fodder 66 (35.9%) 66 (35.9%) 32 (28.2%) Craft making raw material 52 (28.3%) 53 (28.8%) 79 (42.9%) Construction material 18 (9.8%) 33 (17.9%) 133 (72.3%) Medicine 12 (6.5%) 58 (31.5%) 114 (61.9%) Timber 0 (0%) 86 (46.7%) 98 (53.3%)

13 Plate 1: Preparing a meal of game meat Plate 2: Honey from a stingless bee hive Plate 3: Woodland cover conversion to Plate 4: Tree destruction from fire Farmland 3.3 Land Cover changes Land Cover distribution The result showed that in 1986 woodland was the dominant land cover of Metu Sub-county covering ha (43%) of the Sub-county, while land covered by water was least, covering 3.51ha (0.01%) of the Sub-county (Table 4, Figure 6). In 2004, woodland was still the dominant land cover type covering ha (33.3%) of the Sub-county, while water was still covered the least area of the Sub-county (Table 4, Figure 7).

14 Table 4: The distribution of the different Land cover types and their values of change in Metu Sub-county between 1986 and 2004 Class Name Change in Area Percentage Area (ha) % Area (ha) % ha change (ha) area area Woodland Bushland Grassland Farmland Settlement Water TOTAL

15 Figure 6: Land cover map of Metu Sub county derived from the satellite image of 1986 showing the different land cover types

16 Figure 7: Land cover map of Metu Sub county derived from the satellite images of 2004 showing the different land cover types

17 Trends in Land cover change Between 1986 and 2004, there were changes in all the different land cover types. The land use/ cover changes were all above 10%. The biggest changes were from woodland cover, and to grassland cover (Table 5). Table 6 shows the changes that occurred and the magnitude of change for individual land cover types, while table 7 shows the acreage of some areas that did not change in land cover between 1986 and The map in Figures 7 shows the areas from which land cover changed, irrespective of what it changed into, while figure 8 shows what the land cover changed into, irrespective of what it was before. Table 5: Amount of vegetation cover loss by each vegetation type (change from) and amount of vegetation cover gain by each vegetation cover type (changed to). Change from 1986 land cover type (ha) Land cover changed to in 2004 (ha) Change from woodland Changed to woodland Change from bushland Changed to bushland Change from farmland Changed to farmland Change from grassland Changed to grassland Change from settlement Changed to settlement Change from water 2.07 Changed to water 2.70

18 Table 6: Table shows details of all the Land cover changes between 1986 and 2004 Value Changes Description Cell count Area Change m 2 Area Change Ha 101 Settlement 94 84, Woodland to settlement , Bushland to settlement , Farmland to settlement , Water 16 14, Bushland to water 12 10, Farmland to water 18 16, Water to woodland 12 10, Woodland 83,393 75,053,700 7, Bushland to woodland 27,502 24,751,800 2, Grassland to woodland 7,572 6,814, Farmland to woodland 13,102 11,791,800 1, Water to bushland 11 9, Woodland to bushland 37,135 33,421,500 3, Bushland 51,985 46,786,500 4, Grassland to bushland 7,966 7,169, Farmland to bushland 7,084 6,375, Woodland to grassland 26,998 24,298,200 2, Bushland to grassland 25,901 23,310,900 2, Grassland 23,619 21,257,100 2, Farmland to grassland 2,899 2,609, Settlement to farmland , Woodland to farmland 22,234 20,010,600 2,001.06

19 Value Changes Description Cell count Area Change m 2 Area Change Ha 906 Bushland to farmland 18,666 16,799,400 1, Grassland to farmland 2,030 1,827, Farmland 34,732 31,258,800 3, Table 7: Area of each vegetation cover type that remained stable from 1986 to 2004 Land cover category Hectares Settlement 8.46 Water 1.44 Woodland Grassland Bushland Farmland

20 Figure 7: The map shows sections of decrease from each land cover type between 1986 and 2006 irrespective of which land cover type it went to

21 Figure 8: The map shows sections of increase in each land cover type between 1986 and 2006 irrespective of which land cover type it came from 4.0 DISCUSSION

22 4.1 Tree species Diversity The 125 species encountered in the study was less than 247 species encountered during the biodiversity by Lwanga (1996). The difference in the species number could have resulted from the difference in sampling techniques and the relatively smaller extent of the forest reserve studied (Metu Sub-county only). Lwanga studied the whole forest reserve in the two Subcounties of Metu and Dufile. However the Species cumulative curve also showed an increasing trend which implies that new species could still be encountered with the increase in sampling area. The species diversity, stem density and basal area were found to be higher in the Western arm of the forest reserve than in the Eastern arm and this could be attributed to the difference in the terrain of the two arms of the forest reserve. The Western arm had very deep and steep gorges with very rugged terrain. This could have made access to the western arm of the forest difficult, thus less exploitation and disturbance. The area in the west of Metu Sub-county is also relatively gently sloping with fairly well drained and deep soils. This could have facilitated the increase in farming undertaken in the West of Metu Sub-county, leaving the western arm of the forest less disturbed. The Eastern arm has gentle rises on the rolling hills which facilitates relatively easy access to the eastern arm of the forest reserve. This could have made the exploitation of the forest resources easier. On the other hand, the Eastern arm of the forest has fewer options of livelihood options that can be engaged in by many people other than forest exploitation. This could have facilitated increased exploitation of the forest resources as well as causing other disturbances such as fire. The difference in species diversity could have also been due to the difference in the site conditions between the two arms. The difference in conditions such as moisture, humidity and the soils conditions could have influenced different regeneration and growth rates of the tree species in the two arms of the forest reserve. Diameter size class distribution In both arms, the highest proportion of trees was observed in the size class of cm and this was expected because savannah trees and shrubs are mainly characterized by small sizes of their trees. However the higher proportion of trees within the cm diameter size class in the Eastern arm than in the western arm could be attributed to favourable conditions in the East that facilitate higher frequencies of seed germination and growth. The drastic decline in stem count in the eastern arm of the forest reserve from cm to cm could be attributed to the exploitation of the pole-sized trees for subsistence use harnessed by the ease in access to the forest reserve. Obiri et al., 2002 found that local harvesting pressure on small pole sized stems for subsistence use resulted in local extinction of some

23 species. Hall and Rodgers (1986) also report that it is common to encounter removal rates of up to 50% for small sized classes from forests in Africa especially those that are easily accessible. 4.2 Utilization of the forest resources All the respondents depended on the forest reserve in one way or the other, but the forest value in rain formation could have been the most important especially to the residents of Pamoyi and Pameri, because the people depended on rain fed agriculture for crop production. Species abundance variation and utilization The observed increase in the abundance of some species e.g. Erythrina abyssinica, Acacia hockii, Vitex doniana, could be attributed to their ability to establish themselves in large quantities in gaps within the forest. However, some species might have been left unexploited within the forest reserve, because they are considered less valuable for domestic use, for example Daniellia oliveri which has poor strength and structural wood quality. 4.3 Land cover change Farmland increased in the West of the Metu sub-county because of the relatively flat plain with deep well drained soils. This favoured farming as the main land use activity. The increase in woodland cover in 2004 in the Western arm of Mt. Otzi forest Reserve and the decline in the Eastern arm could be attributed to human influence. In the West of Metu Sub-county, farming as a livelihood activity and the good transport network might have caused a shift in land use, from forest exploitation within the Western arm of the forest reserve to farming, carried out in the West of Metu Sub-county. The grassland increase in the Eastern arm was observed to be at the expense of the woodland. The changes could be attributed to the disturbance due to annual fires and land use conversion by inhabitants of the area in search of pasture. The demand for pasture for livestock production could have been a major driving force for the land cover change. This caused the reduction of the woodland and bushes in the eastern arm of the forest reserve and a conversion into grassland. The observations in land use change were consistent with the questionnaire responses which attributed the change in forest structure mainly to anthropogenic action. 5.0 CONCLUSION

24 1. The terrain of the two arms of the forest reserve affected the species diversity within the forest reserve 2. Local people depend on the forest both directly and indirectly 3. Land cover changes are attributed to anthropogenic activities undertaken in the area and the annual fires 4. The terrain has an influence on the pattern of land cover change 5.1 RECOMMENDATION Ensure that people achieve high yields on farm lands out of the forest reserve. This would reduce the incidence of encroaching on the forest reserve. Provide high yielding crop varieties and multiple land use systems through agroforestry. Reduce disturbance through fire and other anthropogenic activities to allow for the forest tree species regeneration and a succession process. Enforce policy measures such as establishment of bylaws at the sub-county and parish level to reduce on the incidences of annual fires in the forest reserve. Study and document the status of all unique tree species in Mt. Otzi Forest Reserve to ensure that advance planning is undertaken by key stake holders to prevent their extinction from the forest reserve. Do restoration and enrichment planting to improve stocking of the Eastern arm Strict policy measures must be undertaken to ensure cultivation is only practiced out of the forest reserve Research studies similar to this one carried out in Mt. Otzi Forest Reserve should be done within the other forests in the dryland region of Northern Uganda to ensure adequate planning is undertaken for conservation of the remaining forest reserves. References

25 Davenport, T.R.B., and Howard,P.C., (1993). Field Reports to commissioner for forestry. Forest Department. Kampala, Uganda. Dovie, D.B.K., Shackleton, C.M., Witkowski, E.T.F., Direct use values of woodland resources consumed and traded in a South Afrfican village. International Journal of Sustainable Development and World Ecology 9 (2002) Kalacska,M., Sanchez Azofeifa, G.A., Calvo Alvarado, J.C., Quesada,M., Rivard, B., Janzen, D.H Species composition, similarity and diversity in three successional stages of a seasonally dry tropical forest. Forest Ecologyand Lwanga, J Trees and Shrubs, Chapter 3 In: Otzi forest reserves, Biodiversity Report; Report No:17 Edited by T. Davenport and P. Howard. Forest Department, Kampala Uganda. Murphy, P.G., and Lugo, A.E., Ecology of Tropical dry forest. Annual Review of Ecology and systematics 17:66 88 Myers, N Biodiversity s genetic library. Pages In G.C., Daily. Nature s services: Societal dependence on natural ecosystems. Island Press, Washington, D.C., USA Nampindo, S., Phillipps, G.P., Plumptre, A The impact of conflict in Northern Uganda on the environment and natural resources management, WCS & USAID. Obiri, J.A.F., Lawes, M.J., Mukolwe, M., The dynamics and sustainable use of high value tree species of the coastal Pondoland forests of the Eastern Cape Province South Africa. Forest Ecology and Management, 166, State of the Environment report for Moyo (SOEM), 1994 Uganda Bureau of Statistics (UBOS), Uganda Population and Housing Census Uganda Forestry Nature Conservation Master Plan (UFNCMP), Ministry of Water Land and Environment Forest Department. Uganda Participatory Poverty Assessment (UPPA), Moyo District Report for the Ministry Finance Planning and Economic Development. January 2000 Winterbottom, B., Eilu, G Uganda Biodiversity and Tropical Forest Assessment, Final Report. A Publication for the United States Agency for International Development