Ji Kinyamario

Observations and modeling of biomass and soil organic matter dynamics for the grassland biome worldwide

Century is a model of terrestrial biogeochemistry based on relationships between climate, human management (fire, grazing), soil properties, plant productivity, and decomposition. The grassland version of the Century model was tested using observed data from 11 temperate and tropical grasslands around the world. The results show that soil C and N levels can be simulated to within ±25% of the observed values (100 and 75% of the time, respectively) for a diverse set of soils. Peak live biomass and plant production can be simulated within ± 25% of the observed values (57 and 60% of the time, respectively) for burned, fertilized, and irrigated grassland sites where precipitation ranged from 22 to over 150 cm. Live biomass can be generally predicted to within ±50% of the observed values (57% of the time). The model underestimated the live biomass in extremely high plant production years at two of the Russian sites. A comparison of Century model results with statistical models showed that the Century model had slightly higher r2 values than the statistical models. Data and calibrated model results from this study are useful for analysis and description of grassland carbon dynamics, and as a reference point for testing more physiologically based models predictions of net primary production and biomass. Results indicate that prediction of plant and soil organic matter (C and N) dynamics requires knowledge of climate, soil texture, and N inputs.

Nutritive value of papyrus (Cyperus papyrus, Cyperaceae), a tropical emergent macrophyte

Papyrus (Cyperus papyrus, Cyperaceae) covers large areas in tropical African wetlands. Analysis of its nutritive value has revealed that crude protein is higher in umbels than culms. Ruminai dry matter digestibility of papyrus is, however, higher in culms than umbels. Both the crude protein and ruminai dry matter digestibility decrease with increasing age of the plant. Values for crude protein and ruminai dry matter digestibility are similar to those reported for the range grasses that constitute the greatest percentage of forage in East Africa. In general, papyrus has some grazing potential and could be used as fodder especially in the dry season when other forage is scarce and of low nutritive value.ZusammenfassungDer Futterwert von Papyrus (Cyperus papyrus),einem tropischen Macrophyten. Papyrus (Cyperus papyrus,) bedeckt im tropischen Afrika grosse Feuchtgebiete. Futterwertanalysen ergaben, dass der Gehalt an Rohprotein in den Dolden höher als in den Sprossen ist. Der verdaubare Anteil der Trockenmasse von Papyrus ist für Wiederkäuer jedoch in den Sprossen höher als in den Dolden. Die Verdaubarkeit von Rohprotein wie auch der Trockenmasse sinkt mit steigendem Alter der Pflanze. Die Werte für Rohprotein und verdaubare Trockenmasse sind ähnlich denen, die für die Hauptfuttergräser semiarider Gebiete in Ostafrika angegeben werden. Insgesamt besitzt Papyrus einiges Potential für Beweidung und könnte, besonders in der Trockezeit, wenn anderes Futter rar und von geringem Nährwert ist, verfüttert werden.

Abiotic and herbaceous vegetational characteristics of an arid rangeland in Kenya

A two-year study was conducted with an overall objective of characterising the structure and function of an arid rangeland in Kenya. A plot measuring 100 × 100m was used for this study. Data on rainfall and temperature were recorded at the plot site whereas data on evaporation rates and relative humidity were obtained from the meteorological office near the study site. Herbaceous aboveground material was sampled at monthly intervals using a rectangular 0.25m2 quadrat frame. Clipped material was separated by species and classified dead or live by physical examination. A 5cm diameter metal soil corer was used to sample belowground plant material, at monthly intervals. The sampled material was washed with running water over 2mm sieves and classified dead or live using the vital staining technique. All weights and calculations were based on organic weight. Total aboveground standing crop ranged from 84.6g m−2 to 295.4g m−2, with a mean of 162.3 ± 60.6g m−2. Mean monthly aboveground standing crop for 1992 and 1993 was 142.8 ± 53.8 and 178.5 ± 63.3g m−2 respectively. The two values were significantly different (p<0.10). Aboveground biomass yield ranged from 17.7g m−2 to 242.7g m−2, with a mean of 104.3 ± 58g m−2 and a coefficient of variation of 58%. Mean aboveground standing crop was 59 ± 24g m−2 Monthly values ranged from 28.8g m−2 to 120g m−2, with a 38% coefficient of variation. The range for total belowground standing crop was from 83.3g m−2 to 232.7g m−2, and a mean of 155.2 ± 46g m−2. The values had a coefficient of variation of 30%. Mean total monthly belowground plant material yield for 1992 and 1993 was 137.6 ± 41g m−2 and 169.9 ± 46g m−2 The coefficients of variation were 59% and 28% respectively. The mean monthly belowground biomass yield was 51.6 ± 33g m−2 with a coefficient of variation of 64%. Mean monthly yield for belowground dead material was 103.7 ± 32g m−2, with a coefficient of variation of 31%. There was no significant difference (p>0.01) in the mean belowground dead material yield between 1992 and 1993. In 1992, annual NPP was 439.2g m−2, giving a net primary productivity of 1.22g m−2day−l. Monthly NPP ranged from 17.2g m−2 to 90.1g m−2 In 1993, annual NPP was 944.5g m−2, equivalent to a net primary productivity of 2.62g m−2 day−1. Monthly NPP was between 27.4g m−2 and 548.6g m−2. Over the 1992–1993 period, NPP was 1 383.7g m−2, equivalent to a productivity of 1.92g m−2day−1. Trends in monthly NPP closely followed the trend in rainfall. On the whole, herbaceous vegetation production and productivity were episodic in nature and closely linked to rainfall. The high primary productivity puts arid and semi-arid rangelands under sharp focus as CO2 sinks, whose role in the amelioration of greenhouse effect could be more important than is currently appreciated.

Production and decomposition of plant litter in an arid rangeland of Kenya

Data on litter production and decomposition in an arid rangeland in Kenya was collected over a two-year period. Utter sampling was carried out at monthly intervals using a rectangular 0.25m−2 quadrat frame. Utter within the quadrats was handpicked and washed with running water to get rid of soli particles, dried, and weighed. Weights were expressed on organic matter basis. Monthly litter production ranged from 31.4g m−2 to 130.0g m−2. Mean monthly yield was 92.5 ± 26g m−2, with a 28% coefficient of variation. There was no significant difference (p>0.01) in litter yield between 1992 and 1993. Rate of decomposition for aboveground material ranged from 0.005g g−1 day−1 to 0.084g g−1 day−1. The mean annual rate of decomposition was 0.026g g−1 day−1. Belowground plant material rates of decomposition spread from 0.009g g−1 day−1 to 0.062g g−1 day−1. with a mean annual rate of 0.041g g−1 day&minus1. Belowground material consistently decomposed faster than aboveground material. Peaks in both aboveground and belowground material decomposition rates coincided with rainfall peaks. Overall, in this arid environment, litter production and decomposition is pursed in nature, and trends are closely related to rainfall occurrence. Moisture is thus a limiting factor both to the production and decomposition of litter. Belowground litter plays a significant role in nutrient cycling.

Patterns of seed dispersal and establishment of the invader Prosopis juliflora in the upper floodplain of Tana River, Kenya

Invasive species in Africa have important impacts on food security and biodiversity conservation. African floodplains in arid areas are critical wildlife habitats in addition to crop production and dry season livestock grazing. The study aimed to understand the patterns of spread of the invader Prosopis juliflora in a typical African floodplain characterised by both multiple dispersers and habitats. Data was collected on faecal seed density, establishment and vegetation composition, and subjected to non-parametric tests and regression analysis. The results showed that both livestock and wildlife species played a critical role in dispersal of Prosopis juliflora, especially yellow baboons (Papio cynocephalus), bush pigs (Potamochoerus larvatus), donkeys and goats. Habitat preference of wildlife dispersers and livestock herding patterns influenced the spatial pattern of invader seed influx. Establishment of Prosopis juliflora was enhanced by ecological disturbance such as in rested crop fields and habitats outside conservation areas as compared to those inside. Establishment was also higher inside the floodplain than outside probably due to higher seasonal soil resources. Lastly, indigenous woody species diversity declined significantly as the density of Prosopis juliflora increased. We conclude that patterns of spread of Prosopis juliflora were related to ecological disturbances, type of disperser and flooplain effect.

Assessment of soil seed bank from six different vegetation types in Kakamega forest, Western Kenya

Kakamega forest, the only rainforest in Kenya, has faced extensive fragmentation and degradation over the last decades. Slow recovery of degraded areas is due to slow or no natural regeneration. An assessment was conducted to ascertain the contribution of soil seed bank in forest regeneration within six sites in Kakamega Forest. Sites investigated were the natural forest, plantation, shrubland, secondary grassland, natural glade, and burnt glade. Soil sampling was done from three stratified depths of 0 to 5, 5 to10 and 10 to 15 cm in each site. Soil seed bank was determined by seedling emergence technique and total seed counts. Laboratory experiments on seed viability were done in a germination chamber at 20°C. Soil seed banks in all the six vegetation types were mainly dominated by herbaceous species. There was a high seed density in the upper layers for all the sites except for natural forest and burnt glade. Seed viability tests revealed low seed viability for the seeds from all the sites. It was concluded that natural regeneration is slowed by low woody species which ranged from 5.7 for natural glade to 48.4% for natural forest soil seed bank, and a low seed viability that ranged between 1.3 for plantation to 33.8% for grassland. It is therefore important to consider other ways of forest restoration other than the soil seed bank. Key words : Seed bank, herbaceous species, seed viability, seedling emergence.

Human Population Growth, African Pastoralism, and Rangelands: A Perspective

ABSTRACT Pastoral livestock production systems in Africa that have existed for centuries are now threatened by changing demographics, improved communications, increased availability of modern weapons, open rangeland shrinkage, global warming, and large-scale migration of people from rural areas to rapidly expanding cities. Human population increase coupled with globalization has led to major conflicts over natural resources in several African countries. If current growth rates persist, the population of Africa will double in 33 yr. Land resources available for farming are now fully used in several African countries. There is growing concern about the capability of these countries to feed their future projected populations. Africas three most populous countries (Nigeria, Ethiopia, and Egypt) are all net food importers. Demand for meat and milk in Africa is projected to double by 2050. Roughly one-half of Africa can be classified as rangeland. Some form of pastoral grazing is the most efficient way to use most of these lands and sustain traditional cultures. Because most African rangelands are now stocked at or above grazing capacity, there is little potential to increase livestock production by increasing animal numbers. However, because offtake levels across Africa are much lower than in other parts of the world, considerable potential exists to increase meat and milk production. Local development projects oriented toward keeping people on the land and self-sufficiency have considerable potential to improve living and environmental conditions for small farmers and pastoralists. Improved and equal education opportunities for both genders, family planning assistance, renewable energy development, empowerment of women, improvement of soil and water resources, and wildlife conservation should be areas of development focus. Maintaining migration corridors, providing legal rights to historic grazing lands, and providing support services along migration corridors such as watering points, markets, schools, and health care are important strategies to sustain pastoralism.

Genetic variation between ecotypic populations of Chloris roxburghiana grass detected through RAPD analysis

Chloris roxburghiana is an important rangeland grass in Kenya. In some areas it has disappeared due to land degradation resulting from overgrazing and drought. Efforts to re-introduce the grass through re-seeding using seeds from research stations have had little success. One possible reason for low establishment is attributed to transplanting spatially separated populations that may represent genetically distinct ecotypes. To test this hypothesis, germplasm diversity within and among four populations of C. roxburghiana from four ecologically distinct sites was analysed using random amplified polymorphic DNA (RAPD) markers. A total of 131 polymorphic markers were identified using nine RAPD primers. There was significant variation among populations, with genetic diversity (H) ranging from 0.134 to 0.206. Analysis of molecular variance (AMOVA) revealed most variance within populations (76%). However, the variation among populations was also significant (24%). The UPGMA of the population frequency indicated that the four populations of C. roxburghiana were genetically distinct, probably as a result of variation in soil fertility, geographical isolation and socio-ecological history of the study sites. Although there are differences for neutral genetic markers between the populations, it is difficult to relate this directly to ecotype since correlation does not imply causality. The implication for optimising future seed collection is discussed and potential areas for further studies identified.

Morphological and RAPD-marker characterization of Melia volkensii (Gürke) in vitro plants regenerated via direct and indirect somatic embryogenesis.

Somaclonal variation induced in vitro during tissue culture can be a problem in clonal micropropagation of elite plants. This study investigated the extent of morphological and genetic similarity or dissimilarity between Melia volkensii in vitro plants (somatic seedlings) obtained via somatic embryogenesis and normal seedlings. Comparisons were made between in vitro plants regenerated directly from cotyledon explants, indirectly from zygotic embryos and normal seedlings of the same parent trees. Regeneration was achieved using half MS medium supplemented with 0.05 mg/l thidiazuron. Shoots were elongated in half MS with 0.1 mg/l BAP plus 0.01 mg/l IAA then rooted in half MS with 0.1 mg/l IBA and 0.1 mg/l NAA. Six morphometric and five meristic characters were used for the morphological characterization. PCR-RAPD markers were used for assessment of genetic similarity or distance. Multivariate analysis using principal coordinates, cluster analysis, analysis of similarities (Anosim) and similarity percentages analysis (SIMPER) revealed significant dissimilarities (p< 0.0001) in morphometric and meristic characters between the in vitro plants and normal seedlings. However, significant similarity (p<0.01) was observed in the RAPD-genic characters of the in vitro plants and normal seedlings. Out of six morphometric traits, taproot length, internode length and shoot height were the most important sources of dissimilarity, cumulatively accounting for 72.37% of overall morphometric dissimilarity. Number of lateral roots was the single most important source of meristic dissimilarity, with 77.02% contribution. Plants regenerated directly from cotyledons were more similar to the normal seedlings in morphological and RAPD-marker characters than those regenerated indirectly from zygotic embryos. This study paves the way for identification of trait-specific RAPD markers for further characterization through sequence-characterized amplified regions (SCARs). Key words : Morphometric, meristic, PCR-RAPD, Melia volkensii, tissue culture, somaclonal variation.

Impact of the invader Ipomoea hildebrandtii on grass biomass, nitrogen mineralisation and determinants of its seedling establishment in Kajiado, Kenya

The invasive coloniser Ipomoea hildebrandtii aggravates the problem of inadequate grass forage in Kajiado district, Kenya. To test its impact on grass biomass, nitrogen (N) mineralisation and seedling establishment, grazing and coloniser density were controlled using experimental exclosures and weeding treatments separately in a factorial design. Grass biomass increased 47% in weeding treatments and 117% with protection from grazing. Ipomoea hildebrandtii removal also led to decline in soil moisture at at a depth of 5 cm and an increase at 30 cm, and lower soil compaction. Grazing lowered soil moisture and increased soil compaction. Mineralisation of N was highest under the dominant grass Chloris roxburghiana followed by I. hildebrandtii and bare ground. Weeding increased N mineralisation whereas grazing lowered it. Multiple regression showed that I. hildebrandtii seedling establishment was significantly higher with low grass biomass, high soil moisture at a depth of 30 cm and higher soil N nitrification. Thus weeding, which caused an increase in the latter two factors, led to increased seedling establishment. Grazing, which lowered soil moisture and mineralisation, led to lower seedling establishment despite reduced competition from lowered grass biomass. This shows invasibility by I. hildebrandtii in rangelands increases when lowered competition is accompanied by an increase in soil resources such as moisture and nitrogen, thus supporting the resource fluctuation theory.