Camel forage variety in the Karamoja sub-region, Uganda

Data analysis

Descriptive statistics were used to summarize the data on the camel forage preference, relative abundance and species richness. Kindt and Coe (2005) observed that one diversity index does not provide sufficient information to order sites from high to low diversity; consequently, both Shannon and Simpson indices were used to compare the plant diversity across the different land cover types and between districts. The inverse of the Simpson dominance (d _s ) was preferred to the Simpson diversity index (D _s ) for the analysis given that the latter provides a good estimate of diversity at relatively small sample sizes (Magurran 2004). The formula used was \( {d}_s=1-\frac{{\displaystyle \sum {n}_i}\left({n}_i-1\right)}{N\left( N-1\right)} \), where, n _i is the abundance of species i and N is the number of all species.

The value of this index ranges between 0 and 1, and the greater the value, the greater the species diversity.

where p is the proportion (n/N) of individuals of one particular species found (n) divided by the total number of individuals found (N). The greater the value of the index, the more diverse the community is.

Species compositional similarities among the land cover types and between the two districts were estimated using the Jaccard similarity index. The Jaccard similarity index uses species presence/absence data for two sample sets (in this case, land cover types and the districts) and is calculated as J = M⁄(M + N), where M is the number of species that occurs in both vegetation types and districts and N is the number of species that occurs in only one of the vegetation types and districts (Asase et al. 2010). Community Analysis Package (CAP-4.1.3) and Species Diversity and Richness (SDR-4.1.2) software were used for diversity analysis. The translation of local species names to scientific names was done with the help of lists generated by Egeru (2014) and Gradé (2008).

Woody species richness in the camel grazing sites

Thirty-eight camel forage species distributed in 20 families were recorded in the study sites. Of these, 28 and 31 camel forage species were recorded in Amudat and Moroto districts respectively. Mimosaceae, Anacardiaceae, Celastraceae and Euphorbiaceae were the most dominant plant families in the study sites (Figure 2). Further, there were differences in species richness across the land cover types. For example, in Amudat, 24 species were recorded in the bushland, 14 in the woodland and 1 species in the farmland. On the other hand, 26, 16, 10 and 3 species were recorded in the bushland, woodland, grassland and farmlands of Moroto district respectively (Figure 3). There was a significant difference in the species richness among the land cover types (P = 0.011); however, there was no significant variation (P = 0.614) in the species richness between the districts.

The most common species in the two districts included the following: Acacia brevispica, Acacia nilotica, Acacia senegal, Acacia seyal, Acacia tortilis and Acacia sieberiana; Balanites rotundifolia, Opuntia cochenillifera, Commiphora africana, Dichrostachys cinerea, Euphorbia candelabrum, Grewia mollis, Maytenus undata, Rhus natalensis and Terminalia brownii; and Zanthoxylum chalybeum, Rhus vulgaris and Lannea species.

Unique to Amudat district were species such as Ficus sur, Acacia drepanolobium, Acalypha fruticosa and Ziziphus abyssinica while Gymnosporia gracilipes, Cadaba farinosa, Acacia hockii, Annona senegalensis, Allophylus africanus, Barleria acanthoides and Gardenia ternifolia were unique to Moroto district.

Relative abundance of woody species among the land cover types

Diversity and plant composition similarity in the camel grazing sites

Camel forage preference

Richness and diversity of woody camel forage species

The study revealed the existence of a significant variety of browse species in the camel grazing sites. Both Moroto and Amudat districts were rich in browse species with the species richness being more-or-less similar between the districts. In Moroto, the richness in woody species was related to the cultural and spiritual values attributed to these species by pastoralists. Traditional shrines in Moroto prohibit tree cutting since trees are believed to be dwelling places for gods (Aleper and Lotyang 2006). The richness of woody plants in Amudat could on the other hand be attributed to the fact that their elders strongly advise against tree cutting. This district is also inhabited by the Pokot, originally from Kenya, who rear camels. The Pokot attach great value to trees, which they use for fodder, food, medicine, shade and as meeting points for elders (Barrow 1988). The sanctions against tree cutting could be to protect the trees that are used as browse by the camels. It was observed in Amudat that a small portion of land is cleared within the vegetation, when setting up homesteads leaving the rest of the environment intact. The homesteads are also sparsely distributed within the landscape as expected of pastoral groupings and settlement patterns.

The inventory of woody flora also revealed variation in richness and diversity across land cover types. A study by Egeru et al. (2015b) similarly reported a high species richness and diversity in Karamoja sub-region. Higher richness and diversity of browse species were recorded in the bushland and woodland land cover types of both districts in comparison to the other land cover types. The differences could be due to varied micro-site factors, namely micro-climate, soil properties, elevation and nutrients, which could be more favourable for woody species growth in the bushland and woodland land cover types. This could be through an effect on regeneration, germination, seed production and phenological events of these plant species. Spatial and environmental heterogeneity govern species richness-diversity gradients (Egeru et al. 2015a; Stein et al. 2014). Human activities, namely tree clearance by pastoralists in a bid to expand cropping land as well as bush burning in grasslands to allow for nutritious grasses to grow for the benefit of the grazing animals, could explain the scarcity of woody species in the farmlands and grasslands of Amudat and Moroto districts. Fire is a traditional tool for prevention of bush encroachment and obtaining an early flush of grass growth (McGahey et al. 2008; Turner 1967). According to Egeru et al. (2014), a rapid increase in croplands in the Karamoja sub-region has been observed over the last decade arising from the ‘chlorophyll syndrome’ - a perception that crop cultivation in the region will assure the Karimojong food security. However, the existence of high diversity and richness of woody species in woodland and bushland land cover types is indicative of how favourable the region is for camel rearing. Camels are predominantly browsers whose forage consists mainly of shrubs, bushes and trees (Iqbal and Khan 2001; Laudadio et al. 2009). Camels are known to prefer the bushland and woodland land cover types because of their shade provision during hot months and their constant rich and varied food supply all year round (Dorges and Heucke 1995, 2003). This implies that camels could have adequate forage even in the face of climate change and variability in Karamoja sub-region, which is often affected by extreme and unpredictable climatic events.

Relative abundance of woody camel forage species

The study revealed a variation in the relative abundance of woody species among the land cover types and across districts. The differences could be attributed to environmental/habitat factors. Variations in habitats are introduced by topography, geology, light intensity, temperature, edaphic factors, humidity and herbivory pressure (Bonkoungou 2001). These environmental gradients with their complex interactions influence the composition, structure, distribution and abundance of woody species (Tadesse et al. 2008). Also, human-induced factors such as selective tree cutting, expansion of farming land and induced fires could explain the difference in the relative abundances among the land cover types. The relative abundance was dominated by species, namely A. brevispica, G. mollis, E. candelabrum, G. gracilipes and R. vulgaris. These species could perhaps be among those that are least preferred by the locals as construction materials or firewood. However, some of these species such as A. brevispica are particularly known for invasive characteristics (Angassa and Oba 2008, 2010); as such, their high relative abundance could be arising from their rapid spread and colonizing effect on the landscapes in Karamoja sub-region. Further, Nalule (2010) has shown that the relative abundance of different tree species in Karamoja sub-region is related to preference by local communities so certain species dominate because they are less frequently harvested by local people. The dominance of these species in all the vegetation types could also be explained by the fact that as camels and other livestock graze, they transfer seeds of these plants from one grazing land cover to another, thus explaining why these species are common and dominant. These species could also be invasive in nature, thus out-competing other species. Studies by Egeru et al. (2014) and Nalule (2010) also reported these species as common in Karamoja sub-region. These species also feature among those that are preferred by camels as browse in southern Ethiopia (Tolera and Abebe 2007). Meanwhile, the limited relative abundance of species, such as E. tirucalli, could be a result of an unexpected foraging of the woody species, as this has emerged as dry season forage for camels (Kagunyu and Wanjohi 2015).

Similarity of plant community among land cover types

The plant communities were found to be more similar in the bushlands and woodlands of both Amudat and Moroto districts. These communities could have similar soil conditions, for instance soil texture, saturation, pH and organic matter. Camels are also known to prefer grazing in these two habitat types (Dorges and Heucke 1995, 2003). Thus, it can be argued that camels transfer species between and within the bushland and woodland land cover types as they browse, thereby creating a pool of similar plant species between them. However, the plant communities in the bushland and woodlands were found to be dissimilar to those in the farmlands and grasslands. The differences could be attributed to variations in disturbance levels, microclimate and edaphic factors as well as observed transitions in land use and cover in the region over the last three decades (Egeru et al. 2014). Land clearance for crop production has intensified, especially the production of sorghum, an adaptable staple that occupies 80% of the total cultivated land area in the sub-region. At 1500 kg/ha, sorghum yields are low (Levine 2010). Consequently, households expand land area in order to increase production. This practice has left huge tracts of land open without traditional trees and shrubs but also exposes these lands to rapidly multiplying tree species such as Acacia oerfota that quickly form bushlands once cultivated lands are abandoned and their productivity declines.

Camel forage species preference as revealed by pastoralists

A wide range of plant species were reported to be preferred by camels. Camels graze on a broad spectrum of plant species including those that are avoided by other domestic herbivores (El-Keblawy et al. 2009). This is because of their unique anatomical and digestive characteristics (Laudadio et al. 2009). These characteristics come as an adaptation to harsh environments to which camels have been accustomed.The majority of the species reported as preferred by camels were trees and shrubs. Camels’ inclination towards these woody plants stems from their anatomical traits such as the mobile and prehensile split upper lips, the long tongue, the stretched neck and extended heads (Amin et al. 2011). These make them preferentially browsers than grazers. The woody plants are also less affected by inter-seasonal variations due to their extensive and deep root system and longer life spans (Abel at al. 1997) and are consequently available all year round. Furthermore, most of the large woody trees are evergreen with high-quality forage throughout the seasons (Schwartz et al. 2012). Their forage preferences and unique traits enable them to efficiently use rangelands that are prone to drought, with a degraded herbaceous layer, and those undergoing bush encroachment (Schwartz et al. 2012). Camels are consequently resilient to drought and can subsequently build the resilience of pastoralists who depend on them.

The species reported as preferred by camels also matched those that were recorded from field assessments as the most abundant in the study sites. Camel herders were in a position to cite preferred camel forage species owing to their accumulated traditional ecological knowledge, especially on livestock forage species and landscape condition, as a result of them having observed their animals feed over time. Two key issues arise from this finding; first, there is correlation between traditional observations of livestock feeding habits and abundant forage species; thus, preference of particular forage-browse species could be related to their availability at the landscape level. Secondly, traditional observations of tree abundance coincide with scientific observations, suggesting that traditional deductions are not mere coincidence. Similar findings have been recorded by a number of researchers among the Borana, Turkana and Rendile in Ethiopia and Kenya (Oba 2012; Oba and Kaitira 2006; Roba and Oba 2008). Further, those forage species observed here to be preferred by camels have also been identified as such in previous studies (Chimsa et al. 2013; Desalegn and Mohammed 2012; Kuria et al. 2012; Rutagwenda et al. 1990; Schwartz et al. 2012).