Montane Forest In Kenya Research Articles

Variability in tree water uptake determined with stable water isotopes in an African tropical montane forest

AbstractEcohydrological processes in tropical rainforests are insufficiently understood, and existing studies yield contradictory results. We investigated relative contributions of different soil depths to tree water uptake of 83 trees and possible species‐specific differences in a 50 × 50 m forest plot at four dates in a tropical montane forest in Kenya using stable water isotopes and the Bayesian mixing model framework MixSIAR. We found distinct individual tree differences (e.g. Drypetes gerrardii taking 75% of its water from <0.5 m, or a rather large shift in uptake patterns based on the climatic conditions, that is the fourth sampling date), but no consistent species‐specific or small‐scale spatiotemporal patterns in water uptake and depth contributions. Soil water δ18O showed a lateral variation of up to 6‰, which was accounted for by a spatial interpolation of soil water isotopes and enabled us to improve allocations of water uptake sources to individual trees. Our results show that ignoring the lateral variability of water isotope signatures in soils complicates the applicability of a mixing model in this context and might be a widespread constraint reducing the validity and comparability of mixing model results. Further research on underlying processes of water fluxes in forest ecosystems is urgently needed and we point out the need for considering large individual differences in water uptake patterns and small‐scale variability of soil water isotopic composition despite homogeneous soil characteristics.

Zehneria tuberifera (Cucurbitaceae), a new species from Taita Hills, Kenya

A new plant species in the genus Zehneria (Cucurbitaceae) is here described and illustrated. The species was collected at Taita Hills tropical montane forests in Kenya, a fragment of the larger Eastern Arc Mountains biodiversity hotspot. The new species, Zehneria tuberifera, is similar to Z. oligosperma and Z. longiflora, but distinguished by its tuberous rhizome and subcoriaceous leaf blades. Furthermore, it has scattered bristles along the midrib on the adaxial surface of its young leaf blades, a shorter receptacle tube, a trilobed disk in the male flower, solitary or 2-clustered female flowers, and up-to-20-flowered and subumbelliform male inflorescences.

Past and projected rainfall and temperature trends in a sub-humid Montane Forest in Northern Kenya based on the CMIP5 model ensemble

This study presents past and projected temporal changes in mean temperature and rainfall around the Marsabit Forest Reserve (MFR), a sub-humid montane forest in Kenya. Rainfall data for the period 1961–2014 and temperature data for the period 1972–2011 were acquired from the Marsabit meteorological station. Future projections (2006–2100) were based on data from five models that participated in the Coupled Model Intercomparison Project Phase 5 (CMIP5) under Representative Concentration Pathways (RCPs) 4.5 and 8.5. Climate simulations for the 2071–2100 period were compared to the 1961–1990 IPCC baseline period to establish significant change. The MFR recorded a mean rainfall of 784 mm which declined annually at a rate of 6 mm over the period of the study. The long rains (March–May) recorded a mean of 379 mm and decreased annually by 10 mm while the short rains (October–December) recorded a mean of 269 mm and decreased annually by 2 mm between 1961 and 2014, with no statistically significant trend (p > 0.05).The model ensemble reproduced the MFR bimodal rainfall pattern, but overestimated the short rains at 333 mm, compared to the actual mean of 269 mm, and underestimated the long rains at 331 mm, compared to the actual mean of 379 mm. The model ensemble simulated a historical mean rainfall of 651 mm compared to the actual mean of 784 mm. Annual rainfall is projected to increase under both scenarios with higher increases during the OND season compared to the MAM season and under RCP8.5 than under RCP4.5. The mean rainfall in the baseline year was 859 mm while the mean rainfall in the projection period for the RCP4.5 and RCP8.5 scenarios is expected to be 1022 (+19%) and 1105 (+28.7%) mm, respectively; significant enough to be characterized as climate change.Temperatures are projected to increase at a rate of 0.2 °C and 0.5 °C per decade under RCP4.5 and RCP8.5, respectively. Between 2071 and 2100, the MFR is projected to have warmed by between 1.2–1.7 °C and 3.2–4.8 °C under RCP4.5 and RCP8.5, respectively. Extreme rainfall events are projected to increase under the RCP4.5 scenario (severe wetting 13.1%, severe drying 3%) and the RCP8.5 scenario (severe wetting 20.1%, severe drying 3%) compared to the baseline period (severe wetting 6.1%). Our results conform to the ‘East African climate paradox’, where the observed rainfall trends were declining compared to the scenario simulations projecting a wetting anomaly as local temperatures rise. Further studies to better understand the cause of the poor rainfall simulation in the general circulation models (GCMs) in the MFR and the larger East African region will be necessary.

Taitaia, a novel lichenicolous fungus in tropical montane forests in Kenya (East Africa)

AbstractDuring lichenological explorations of tropical montane forests in Kenya, a remarkable new lichenicolous fungus was repeatedly found growing on thalli of the epiphytic tripartite cyanolichen Crocodia cf. clathrata. Molecular phylogenetic analyses placed the fungus within Gomphillaceae (Ostropales, Lecanoromycetes), a family mainly of lichen-symbiotic species in the tropics. The anatomical features (unitunicate, non-amyloid asci and simple, septate paraphyses) as well as the hemiangiocarpic ascoma development confirm its taxonomic affinity. DNA sequence data showed the closest relationship was with Gyalidea fritzei, followed by Corticifraga peltigerae. A monotypic genus, Taitaia, is introduced to incorporate a single species, T. aurea. The new fungus is characterized by aggregated ascomata with yellow margins and salmon red discs developing from a single base.

Harvesting fodder trees in montane forests in Kenya: species, techniques used and impacts

There has been an increasing interest in fodder trees and their potential to help the rural poor. However, few studies have addressed the ecological impacts of fodder tree harvesting. We investigated the species harvested and the techniques used, and the effects of fodder harvesting on (1) species’ populations and (2) forest carbon stocks in three montane forests in Kenya. Focus-group discussions were organized in 36 villages to determine which species were harvested and with which techniques. Field observations were made on vegetation plots: stem diameter, tree height, species and extent of harvest were recorded. Carbon stocks were calculated using an allometric equation with (1) observed height of harvested trees, and (2) potential height estimated with a power model, and results were compared. Eight tree species were commonly harvested for fodder using different techniques (some branches, main stem, most branches except stem apex). Fodder harvesting (together with other uses for some species) negatively affected one species populations (Olea europaea), it did not negatively affect four (Drypetes gerrardii, Gymnosporia heterophylla, Pavetta gardeniifolia, Xymalos monospora), and more information is needed for three species (Olea capensis, Prunus africana, Rinorea convallarioides). Fodder harvesting did not significantly reduce forest carbon stocks, suggesting that local communities could continue using these fodder trees if a carbon project is established. Among the fodder species studied, X. monospora could be used in reforestation programs, as it has multiple uses and can withstand severe pruning. Although our study is only a snapshot, it is a baseline which can be used to monitor changes in fodder harvesting and its impacts related to increasing droughts in northern Kenya and increasing human populations.

Diversity and Altitudinal Distribution of Understorey Corticolous Lichens in a Tropical Montane Forest in Kenya (East Africa)

Lichens constitute an important component of tropical forest biodiversity. This study inventoried corticolous lichens and examined their variation in various forest types with varying climatic conditions in Mt. Kenya, East Africa. Specifically we evaluated variation of lichen assemblages in relation to forest types and tree diversity along an altitudinal gradient (1800-3100m). Ten study sites were established on two contrasting sides of Mt. Kenya in the indigenous forest: six of them at Chogoria which is on the humid southeastern windward side of the mountain and four sites on the Sirimon side located on the drier northwestern leeward side. Overall 242 lichen taxa were documented; with Chogoria and Sirimon forests having 148 and 94 species that translated to an adequate sampling effort of 74 % and 68 %, respectively. The two contrasting forest types (Chogoria and Sirimon) supported slightly different lichens assemblages. Meanwhile lichen assemblages were found to significantly vary with elevation (or forest types) and with tree host. Posterior analyses showed that the differences were significant among sampling sites (or forest types) on the Chogoria side and insignificant on the Sirimon side. Similarly the number of lichens differed significantly among the host tree species. This study stresses the urgent need to upscale the sustainable management of the presently threatened tropical forests in order to preserve their structural heterogeneity.

Management intensity controls soil N2O fluxes in an Afromontane ecosystem

Studies that quantify nitrous oxide (N2O) fluxes from African tropical forests and adjacent managed land uses are scarce. The expansion of smallholder agriculture and commercial agriculture into the Mau forest, the largest montane forest in Kenya, has caused large-scale land use change over the last decades. We measured annual soil N2O fluxes between August 2015 and July 2016 from natural forests and compared them to the N2O fluxes from land either managed by smallholder farmers for grazing and tea production, or commercial tea and eucalyptus plantations (n=18). Air samples from 5 pooled static chambers were collected between 8:00am and 11:30am and used within each plot to calculate the gas flux rates. Annual soil N2O fluxes ranged between 0.2 and 2.9kgNha−1yr−1 at smallholder sites and 0.6–1.7kgNha−1yr−1 at the commercial agriculture sites, with no difference between land uses (p=0.98 and p=0.18, respectively). There was marked variation within land uses and, in particular, within those managed by smallholder farmers where management was also highly variable. Plots receiving fertilizer applications and those with high densities of livestock showed the highest N2O fluxes (1.6±0.3kgN2O-Nha−1yr−1, n=7) followed by natural forests (1.1±0.1kgN2O-Nha−1yr−1, n=6); although these were not significantly different (p=0.19). Significantly lower fluxes (0.5±0.1kgNha−1yr−1, p<0.01, n=5) were found on plots that received little or no inputs. Daily soil N2O flux rates were not correlated with concurrent measurements of water filled pore space (WFPS), soil temperature or inorganic nitrogen (IN) concentrations. However, IN intensity, a measure of exposure of soil microbes (in both time and magnitude) to IN concentrations was strongly correlated with annual soil N2O fluxes.

Soil organic carbon changes following degradation and conversion to cypress and tea plantations in a tropical mountain forest in Kenya

This study investigates, in a montane forest in Kenya, the changes in amount and stability of soil organic carbon (SOC) as a consequence of: a) forest degradation, by comparing primary and degraded forests; b) the replacement of degraded forests with cypress and tea plantations, by considering sites installed at different time in the past. The SOC concentrations and stocks were determined in different layers to 1 m depth, and the SOC turnover time (TT) derived by measuring the 14C concentration in the layers within the 0–30 cm depth. A significant SOC decline was evident in the 0–5 and 5–15 cm layers of degraded forest while, on the long term, both plantations induced a significant SOC increase in the 0–30 cm depth. The longer TT’s and lower SOC concentrations in the upper layers of degraded rather than primary forests imply an impact of forest degradation on the decomposition of the fast cycling SOC. Similarly, the shorter TT with increasing plantations age implies differences in SOC stabilization mechanisms between plantations and forests. Cypress and tea plantations established on degraded forests stimulate a long term SOC accrual but at the same time decrease the stability of the SOC pool.

Land use affects total dissolved nitrogen and nitrate concentrations in tropical montane streams in Kenya

African tropical montane forests are facing fast and dynamic changes in land use. However, the impacts of these changes on stream water quality are understudied. This paper aims at assessing the effect of land use and physical catchment characteristics on stream water concentrations of dissolved organic carbon (DOC), total dissolved nitrogen (TDN), nitrate (NO3-N) and dissolved organic nitrogen (DON) in the Mau Forest, the largest tropical montane forest in Kenya. We conducted five synoptic stream water sampling campaigns at the outlets of 13–16 catchments dominated by either natural forest, smallholder agriculture or commercial tea and tree plantations. Our data show a strong effect of land use on TDN and NO3-N, with highest concentrations in stream water of catchments dominated by tea plantations (1.80±0.50 and 1.62±0.60mgNl−1, respectively), and lowest values in forested catchments (0.55±0.15 and 0.30±0.08mgNl−1, respectively). NO3-N concentration increased with stream temperature and specific discharge, but decreased with increasing catchment area. DOC concentrations increased with catchment area and precipitation and decreased with specific discharge, drainage density and topographic wetness index. Precipitation and specific discharge were also strong predictors for DON concentrations, with an additional small positive effect of tree cover. In summary, land use affects TDN and NO3-N concentrations in stream water in the Mau Forest region in Kenya, while DOC and DON were more related to hydrologic regimes and catchment properties. The importance of land use for NO3-N and TDN concentrations emphasizes the risk of increased nitrogen export along hydrological pathways caused by intensified land use and conversion of land to agricultural uses, which might result in deterioration of drinking water quality and eutrophication in surface water in tropical Africa.

Spatial variability of soil N2O and CO2 fluxes in different topographic positions in a tropical montane forest in Kenya

AbstractQuantifying and understanding the small‐scale variability of nitrous oxide (N2O) and carbon dioxide (CO2) emission are essential for reporting accurate ecosystem greenhouse gas budgets. The objective of this study was to evaluate the spatial pattern of soil CO2 and N2O emissions and their relation to topography in a tropical montane forest. We measured fluxes of N2O and CO2 from 810 sampling locations across valley bottom, midslope, and ridgetop positions under controlled laboratory conditions. We further calculated the minimum number of samples necessary to provide best estimates of soil N2O and CO2 fluxes at the plot level. Topography exhibited a major influence on N2O emissions, with soils at midslope position emitting significantly less than at ridgetops and valley bottoms, but no consistent effect of topography on soil CO2 emissions was found. The high spatial variation of N2O and CO2 fluxes was further increased by changes in vegetation and soil properties resulting from human disturbance associated with charcoal production. Soil N2O and CO2 fluxes showed no spatial pattern at the plot level, with “hot spots” strongly contributing to the total emissions (10% of the soil cores represented 73 and 50% of the total N2O and CO2 emissions, respectively). Thus, a large number of samples are needed to obtain robust estimates of N2O and CO2 fluxes. Our results highlight the complex biogeochemical cycling in tropical montane forests, and the need to carefully address it in research experiments to robustly estimate soil CO2 and N2O fluxes at the ecosystem scale.

Habitat selection by a rare forest antelope: A multi-scale approach combining field data and imagery from three sensors

It can be difficult to further scientific understanding of rare or endangered species that live in inaccessible habitat using traditional methods, such as probabilistic modeling based on field data collection. Remote sensing (RS) can be an important source of information for the study of these animals. A key advantage of RS is its ability to provide information over an animal's complete range, but models incorporating RS data are limited by RS's ability to detect important habitat features. In this study, we focus on the rare, poorly-understood mountain bongo antelope (Tragelaphus euryceros isaaci) which survives in the wild in isolated pockets of montane forest in Kenya. We hypothesize that mountain bongo habitat is multi-scaled. We analyzed field and RS data (derived from SPOT, ASTER, and MODIS) ranging in scale from 0.02–85.93 ha to test our hypothesis. Important microhabitat features were identified through logistic regression models of vegetation structure data collected in plots (0.04 ha) of bongo presence (n=36) and absence (n=90). Models were selected using an information theoretic approach. We analyzed the correlations between microhabitat (four canopy and four understorey structure measures) and RS variables derived using spectral mixture (SMA) and texture analysis; most ASTER and SPOT variables were significantly related with canopy structure variables (max|r|=0.56), but correlations between understorey structure and all but two RS variables were insignificant. Further logistic regression modeling showed that combining field microhabitat (primarily understorey structure variables) and larger-scaled RS measures (ASTER spectral mixture analysis variables aggregated to 450 m (20.25 ha)) provided superior models of bongo habitat selection than those based on field or RS data only. The results demonstrate that: 1) forest canopy characteristics at scales of ~20 ha and understorey structural conditions at the micro-scale of 0.04 ha were the most important features influencing bongo habitat selection; 2) models for predicting bongo habitat distribution must incorporate both micro- and macro-habitat variables; 3) optical RS data may characterize important micro-scale canopy variables with reasonable accuracy, but are ineffective for detecting understorey features (unless alternative techniques such as forest structural indices can be successfully applied); 4) RS and field data are both essential for understanding bongo habitat selection. The technique employed here for understanding this rare antelope's habitat selection may also be applied in studies of other large herbivores.

Stable carbon and nitrogen isotope analysis of human and animal diet in Africa

The stable carbon and nitrogen isotope composition of bone collagen has been determined for 238 modern non-human mammals, comprising 43 species of herbivores and carnivores from grasslands and montane forests in Kenya and Tanzania, and 97 historic and prehistoric humans, representing 12 populations with different dietary adaptations from eastern and southern Africa. Among non-human species carbon isotope ratios separate grazers from browsers in open grasslands, forest floor from forest canopy, and forest floor from open grassland feeders. Nitrogen isotopes separate carnivores from herbivores and forest from savanna-living species. Water-dependent herbivores have lower nitrogen isotope ratios than drought-tolerant ones in the same habitat. Among human populations, carbon isotopes differentiate those who regularly consume grains and/or the protein of browsing animals from those who consume wild plants, non-grain crops and/or the protein of wild animals. Nitrogen isotopes differentiate those dependent on the milk, meat and blood of domestic animals or marine resources from those dependent mainly on plant foods. Combined use of carbon and nitrogen isotopes permits the differentiation of pastoralists from farmers, camel pastoralists from capri-bovine pastoralists, and grain farmers from non-grain farmers. The apparent presence of physiological and climatic influences on nitrogen isotope ratios within trophic levels complicates dietary interpretations of variations in nitrogen isotope ratios but may also offer a new tool of climatic reconstruction. It shoudl nonetheless be possible to use the analysis of the isotopic composition of bone collagen as a quantitative technique for the reconstruction of diet, habitat selection, climate and water balance in prehistoric animal and human communities, and to test models that suggest dietary adaptations were prime movers of hominid biological and cultural evolution.

Leaching Losses of Minerals from Leaves of Trees in Montane Forest in Kenya

The functions of xeromorphic features in plants of dry forests are fairly well understood but the occurrence of some of the same features, e.g. small leaves and thick cuticles, in moist forests is not easily explained. The uniformity of leaf type in Tropical Lowland Rain forests has long been appreciated. Richards (1952) observed that the texture of the leaves is often leathery, the upper surface generally glabrous and polished, with any tomentum confined to the lower surface. The margin is usually entire or finely serrate, leading to an acumen or 'drip-tip'. Richards (1952) also summarized the evidence that leaf size decreases with increase in altitude. The hard texture of the leaves is maintained and the leaves of Tropical Montane forests may appear markedly xeromorphic. It is possible that the thick cuticle of such leaves has an important role in minimizing loss of nutrients by leaching. The significance of foliar leaching has been recognized by ecologists in many studies on mineral cycling. The literature has been reviewed recently by Tukey (1970) and Jordan & Kline (1972). The present study was designed to provide information on foliar leaching phenomena of species restricted to wet or relatively dry climates (given uniform leaching conditions) and on ecotypic variation in leaching properties of species growing in both wet and relatively dry climates. Very little is known about the foliar nutrient contents of the plants in the vegetation types concerned and it was necessary first to discover the levels of the common nutrients in the species investigated.