Department of Botany-Journal Articles

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Open Access
Nitrogen Loss by Burning from Nigerian Grassland Ecosystems
(Royal Swedish Academy of Sciences, 1980) Isichei, A. O.; Sanford, W. W.; Rosswall, T.
Nitrogen loss by burning from natural grassland ecosystems in Western Nigeria was studied over a two-year period in three areas, including sites of Andropogon-Hyparrhenia - Schizachyrium-Brachiaria grassland in derived, Southern Guinea and Northern Guinea savanna. The production of aboveground herbaceous material and litter fall of leaves, wood and fruit/seed was estimated and the nitrogen content just prior to burning determined. Final estimates of from 12 to 15 kg ha-1 yr-1 of nitrogen lost by burning were obtained. it is suggested that such loss may be replaced to a considerable extent by rain and blue-green algal crust fixation.
Open Access
Nitrogen Fixation by Blue-Green Algal Soil Crusts in Nigerian Savanna
(1980) Isichei, A. O.
Blue-green algae, many of which are known to be nitrogen fixers, occur on the surface of the soil as crusts. Crusts are masses of algal filaments that grow on top of each other. These blue-green algal crusts were collected from all of the savanna zones of Nigeria in order to estimate the quantitative role they may play in the nitrogen economy of savanna ecosystems. Algae of the genus Scytonema, which are nitrogen fixers, were dominant in all the crust samples collected. Using the acetylene reduction assay, it was found that the crust samples fixed nitrogen 24 h after rewetting and were affected by pH, temperature, light and moisture variations. If sufficient light were available for near maximum photosynthesis, with an algal cover of the soil surface of about 30 % and mean to maximum-fixation during 70 %of the rainy season of 180 days of 10-hour day-length, from 3.3 to 9.2 kg ha-' yr-' of nitrogen would be fixed. This amount would replace much of the nitrogen lost from the grass standing crop as a result of annual burning of the savanna.
Open Access
Nitrogen in Savanna Grass and Litter
(1982) Isichei, Augustine O.
grasses are low in nitrogen. This is relayed to the low nitrogen content of the soils: there is decreasing nitrogen in the soil northwards and this is reflected in the grasses. Even in the same environment some species are better accumulators than others. Possible reasons are advanced for this. The Andropogon species and Beckeropsis uniseta are the best known accumulators. There is a well marked seasonality in nitrogen concentration in grass. The below-ground parts have their highest concentration in the dry season, while in the above-ground parts the highest concentration is at the beginning of growth. Litter is important because it is a major means of nitrogen re-cycling. Its pattern of fall and decay in the savanna is discussed. It is emphasized that most of the litter fall is after the annual fires. Nitrogen content of litter varies from site to site but does not show significant seasonal difference.
Open Access
Primary Production in the Savanna
(1982) Isichei, Augustine O.
It is emphasized that there is a dearth of information on primary production in the savanna in spite of savanna occupying nearly 80% of the West African land surface. Known values from the literature of annual primary production are presented. Values range from 150 to 1800g m-2. This range is not totally encompassing as primary production is strongly influenced by local conditions. The methods in use for measuring primary production are reviewed and their applicability to the savanna examined. The factors that affect primary production in the savanna are enumerated and discussed.
Open Access
Relationship of Woody Plants to Herbaceous Production in Nigerian Savanna
(1982) Sanford, William W.; Usman, Sugei; Obot, Emmanuel O.; Isichei, Augustine O.; Wari, Musa
Evidence is presented that a light, high tree canopy leads to greater production of grasses in the Nigerian Guinea savanna than either full exposure or dense canopy. Furthermore, some shading provides a microenvironment where such favoured species as the Andropogons replace such undesirable species as Schizachyrium sanguineum and Hyparrhenia species. The role of trees in open rangeland in relation to mineral cycling and soil maintenance is briefly discussed. It is recommended that the common practice of clearing all trees to improve rangeland is stopped and a low density of large trees, preferably legumes, be maintained.
Open Access
Nitrogen Concentration in the Major Grasses of the Derived and Guinea Savanna Zones of Nigeria in Relation to Season and Site
(1983) Isichei, Augustine O.
The concentration of total Kjeldahl N in above- and below-ground grass samples was monitored at five Nigerian savanna sites over 3 years. Significant variation, even in the same species, was found from plot to plot, with the highest concentrations in the samples from early-burnt Derived savanna and the lowest from northern Guinea samples. This may be related to soil N concentrations as a significant positive relationship was found between soil and plant concentrations. Nitrogen concentration in above-ground grass biomass declined almost exponentially from flushing through the dry season, whereas below-ground N concentration increased with the approach of the dry season. Two shade-favouring grasses, Andropogon tectorum and Beckeropsis uniseto were found to have the highest N concentrations above-ground.
Open Access
Seasonal Succession in a Small Isolated Rock Dome Plant Community in Western Nigeria
(1984) Isichei, Augustine O; Longe, Peter A.
On the slopes of one of the inselbergs within the Univ. of Ife Campus, Western Nigeria (7o32'N, 4o31'E) are islands of vegetation completely separated from each other by expanses of bare rock. The pattern of seasonal succession in one small vegetation island was studied by weekly estimation of species importance. Species importance was estimated by censusing all individuals and by measurements of cover. At the beginning of the growing season the island is dominated by ephemerals which are later replaced by drought enduring perennials. The number of individuals and species and species diversity and abundance patterns on the island over the growing season show a specific pattern which probably occurs every season.
Open Access
Responses of Savannas to Stress and Disturbance: the Beginning of Desertification
(Federal Ministry of Science and Technology, 1985) Isichei, Augustine O.; Ero, Isaac I.
Stress and disturbance may be natural or caused by man but usually from a combination of extreme values of environmental variables. Their prevalence in the Nigerian Savanna and effect on stability and resilience and, in a sense, desertification has been examined. The stress and disturbance identified include drought, wood cutting and land cultivation, herbivory, annual burning. It is concluded that annual burning does not constitute a destabilizing factor as such since it could be regarded as regular annual phenomenon to which the plant species are adapted, but mainly as a force that accentuates the effects of other destabilizing influences created through improper land use. Effort has been made to place different savanna systems into ranges of stability and resilience. Suggestions have been made for improving grazing system, controlling indiscriminate wood-cutting and ecologically sensitive farming systems. Drought control is distinctly impossible except through irrigation which is not yet extensively practised. Land use and vegetation mapping must be done on a local scale permitting the application of management tools to delineated land units. Parameters of description, evaluation and prediction vary according to land use; intensive or extensive, transformational or conservational. A scheme has been proposed for assessing the phenomena of stress, disturbance/perturbation and their relationship to stability and resilience in the savanna.
Open Access
Changes in a secondary forest in southwestern Nigeria following a ground fire
(1986) Isichei, Augustine O.; Ekeleme, Friday; Jimoh, Bakare A.
In January 1983, two 50 m x 50 m rain forest plots in the University of Ife campus in southwestern Nigeria were demarcated for a baseline study of species composition, litterfall and tree girth increments. By accident, a severe ground fire burnt one of the plots on 31 January, barely two weeks after litter traps had been set and species listing and fist girth measurements completed. The effect of this fire was assessed in the burnt plot after 14 months, in April 1984. The fire affected small trees especially, and there were indications that some species were more sensitive than others. Manihot glaziovii, which was present in the plot and abundant in its vicinity before the fire showed a big increase in density after the fire because it was able to germinate in the openings created by the fie. These observations were related to succession, and it is concluded that the observation by some workers that the initial composition of a regrowth forest may be partly predicted from a knowledge of the seed bank in the soil may be applicable in the present case.
Open Access
Seasonal Cycling of Nitrogen, Phosphorus and Potassium in Isolated Vegetation Mats on an Inselberg in Southwestern Nigeria
(1987) Muoghalu, I.; Isichei, A. O.
On the inselbergs at the University of Ife Campus (7o 31’N, 4o31’E), southwestern Nigeria are mat communities that are completely isolated from each other and have been shown to behave as real islands in their species-area relationships. The amount of nitrogen, phosphorus and potassium in the vegetation and soil of fifteen of these communities on one inselberg were determined bi-monthly through a growing season. These determinations were carried out by randomly selecting three or four mats at a time, clipping all vegetation and excavating the soil on each mat. The excavated soil was sieved to remove subterranean plant material and, after drying, all plant materials and soil were analysed for three elements, nitrogen, phosphorus and potassium. The clippings and excavations were done in March (beginning of rainy season), May, July and September. The concentration of the three elements in the above-ground plant material was highest in May for nitrogen and potassium and in July for phosphorus, and thereafter the concentrations of the three elements declined. Below ground, nitrogen concentration increased continually, phosphorus increased for some time then dropped while potassium was low in May and later increased. The concentration of nitrogen in the soil increased through the season, phosphorus fluctuated while potassium remained more or less constant. The mats could be valuable in understanding nutrient cycling and the relevance of the results obtained from this study is discussed.
Open Access
The Reversibility of Changes in Species Composition, Production and Soil Properties Following Defoliation, Trampling and Application of Excreta
(RSSD Australia, 1988) Isichei, A. O.; Walker, Brian H.; Menaut, Jean-Claude
An important notion underlying the experimental hypotheses is that it is not the direct effects of herbivory on the vegetation, but rather the indirect effects on soil properties which increase the irreversibility of changes to vegetation properties.
Open Access
Nutrient Content and Performance of the Herbaceous Legume Tephrosia Bracteolata in Relation to the Grass Andropogon Tectorum in both Natural Habitat and Pot Culture in Southwestern Nigeria.
(International Society for Tropical Ecology, 1990) Isichei, Augustine O.; Awodoyin, Rasheed Olufemi
Tephrosia bracteoluta, an annual herbaceous legume (sub-family Papilioniodeae), occurs extensively in the savanna zone of West Africa. It is palatable to livestock. Its accumulation of nitrogen, phosphorus and potassium over a growing season (in natural habitat in Southwestern Nigeria) was measured and compared with that of Andropogon tectorum, another palatable grass in the same habitat. Crude protein concentration in Tephrosia throughout the growing season is enough to meet the recommended livestock requirements, whereas the concentration in Andropogon meets this requirement only when the grass is young. Tephrosia and Andropogon were positively associated in natural habitat Competition between Tephrosia and Andropogon in pot culture was investigated. Both species showed a decrease in yield with increasing density, a pattern also shown for number of tillers of Andropogon and girths and heights of both plants at maturity. In the mixture the yield port plant of Andropogon was higher than in its monoculture.
Open Access
Ecology of Piliostigma Thonningii in Early Successional Plot in Northwestern Nigeria
(1990) Mbaekwe, E. I.; Isichei, A. O.
In the Kainji Basin, Mokwa and Yelwa areas of northwestern Nigeria early successional plots are usually dominated in terms of number of stems by the Caesalpinioid shrub Piliostigma thonningii. An ecological study of 17 sample plots from the areas was carried out in order to define the niche of Piliostigma because of its potential in providing soil cover and rehabilitation of degraded lands. In the plots studied it was found that Piliostigma abundance was associated with a high soil sand: clay ratio, open vegetation canopy and low species diversity. These characteristics identify Piliostigma as an early successful species.
Open Access
Emissions of Carbon, Nitrogen, and Sulfur from Biomass Burning in Nigeria
(1990) Akeredolu, Funso; Isichel, A. O.
There are as yet no reported direct measurements of emissions of carbon, nitrogen, and sulphur in the Nigerian environment. Extrapolations here have been based on the composition of the sources before burning. The accuracy of the analysis of the chemical compositions of the vegetations is, however, not in doubt, so that at their face value, the estimates are fairly reliable. Most estimates have been pantropical and therefore involve extreme generalizations. The present estimates will help in arriving at better global estimates. There are however, some assumptions made which would need to be validated through further experimentation.
Open Access
Mineral Nutrient Flow from an Inselberg in South-Western Nigeria
(1990) Isichei, Augustine O.; Morton, Alan J.; Ekeleme, Friday
In a study carried out to find out if inselbergs enrich their surroundings with nutrients via drainage, amounts of total nitrogen, nitrate-nitrogen and potassium in rainfall, drainage from bare rock patches and vegetation mats on an inselberg in South-western Nigeria were measured over one year. 43.3 kg ha-1 total nitrogen, 4.8 kg ha-1 nitrate-nitrogen and 10.7 kg ha-' potassium were recorded in rainfall for the year of study. The amount of total nitrogen in drainage from bare rock was 79% of that in rainfall whilst that in drainage from vegetation mats was 29% of the rainfall amount. The respective values for nitrate-nitrogen were 57% and 13%; for potassium they were 90% and 38%. It was assumed that the loss of nutrients as water drains through vegetation mats and over bare patches was due to absorption by plants and soil in the mats and lichens in the bare patches. It was therefore concluded that there was no net enrichment of rainwater with nutrients as it flows over inselberg slopes. There is, however, a funneling of water along with contained nutrients from the inselberg to the surrounding areas. This funneling is additional to the nutrients and rainfall incident on these surrounding areas and may account for the vegetation around inselbergs being more lush than vegetation in the same area but further away from the inselbergs. A simple modeling approach was used to assess potential nutrient outflow from inselbergs. The model shows that discharge of nutrients from the edges of inselbergs increases linearly with inselberg diameter. The model further shows that if nutrient funneling only affects an area near to the edge of the inselberg then nutrient addition is several times higher than would be expected from rainfall deposition alone.
Open Access
Yield and Nitrogen Accumulation by Andropogon gayanus and Schizachyrium sanguineum Grown under Four Nitrogen and Water Application Regimes in Gravel and Sand Pot Culture
(1990) Oke, Samson O.; Isichei, Augustine O.
Andropogon gayanus and Schizachrium sanguineum grass plants were grown in sand and gravel media under two levels each of applied nitrogen and water to study the effect of growth medium texture on yield and nitrogen accumulation in the two species. Nitrogen level was varied by applying the nutrient solution once every other day to one group of experimental plants and once in four days to another group. Water was applied at the same frequency but alternated in time with the nutrient solution. There were on the whole four treatments. Both grasses had their highest yields when grown in sand. Applying nutrient solution every other day and water once in four days resulted in the highest grass yield. Higher nitrogen concentration in both grass tissues was obtained in gravel and – S sanguineum accumulated more nitrogen when the two - grasses are compared. The results obtained in the experiment confirm results obtained from other studies- on yield and nutrient accumulation by grasses in compact and coarse soils and the ways the result could be useful in active savanna management are discussed.
Open Access
Effect of tree canopy cover on the yield, crude protein and fibre content of forb species in Nigerian Guinea savanna
(Kluwer, 1991) Muoghalu, J. I.; Isichei, A. O.
The relationship between tree canopy cover and forb species in savanna was investigated by examining the effect of tree canopy cover on the yield, crude protein, fibre and lignin content of forb species. The yield of some forb species show a tendency of being higher under tree canopy than in the open though no statistical significance can be shown. A higher forb yield is obtained under high tree canopies than under lower ones. No significant differences in mean crude protein, fibre and lignin content were observed between forb species growing under tree canopy and those in the open.
Open Access
Nigerian Man and Biosphere Research Plots in Guinea Savanna: Floristics and Structure of the Vegetation
(1991) Muoghalu, Joseph I.; Isichei, Augustine O.
A study was made of the vegetation of three plots used in the Nigerian Man and Biosphere Research Programme for Savanna Studies. The aim is to provide detailed information on the vegetation of the plots which may possibly contribute to an understanding of factors influencing savanna structure and relative abundances of forbs, grasses and woody species. Results show that there are differences in the species composition of the plots. There are more forb species than grass species in each plot. The woody basal areas and crown areas of the plots do not depend entirely on the density but also on the size of the woody species. There are differences in herbage yield in the plots that could be attributed to differences in soil properties, species composition and level of human and animal activities between the plots.
Open Access
The Effects of Tree Canopy Cover on Soil Fertility in a Nigerian Savanna
(1992) Isichei, Augustine Onwuegbukiwe; Muoghalu, Joseph Ikechukwu
The effect of tree canopy cover on soil properties was studied over three periods: mid-dry season (January), mid-growth period (August) and peak-growth period (October) in three 1 ha plots in savanna of north-west Nigeria. The objective was to find out whether tree canopies change the nutrient status of the soil under them relative to adjacent grasslands. Soils under tree canopies were found to have significantly higher levels of organic matter, calcium, magnesium, potassium, total exchangeable bases, cation exchange capacity and pH than those in open grasslands. Nitrogen and phosphorus were slightly higher in soils under tree canopies than those in the open grasslands. Trees 7m and above had more influence on soil properties than smaller trees. Differences in soil properties among the study plots were due to differences in their soil texture. Seasonal trends were observed in organic matter, carbon, nitrogen ratio, cation exchange capacity, phosphorus, calcium, sodium, total exchangeable cations and percentage base saturation.
Open Access
Seasonal Partitioning of Dry Matter and Nitrogen in Andropogon Tectorum Regenerated from Rhizomes
(1993) Oke, S.O.; Isichei, A. O.
Seasonal partitioning of dry matter and nitrogen over a growing season in Andropogon tectorum regenerated from rhizomes were studied under nutrient and water regimes in sand culture. The dry matter and nitrogen content of Andropogon tectorum was partitioned into leaf, stem, root and rhizoms fractions under both regimes. The leaves constituted the largest component of the biomass under both treatments over the growth period and its contribution ranged from 30.96% to 72.19% while the rhizome constituted more or less the least component of the biomass (3.19% to 38.25%) over the entire growth period except at the early stage and stem and root had intermediate proportions. Percentage total nitrogen in leaf, stem, root and rhizome generally declines from the beginning of growth period to maturity. The total nitrogen concentration of leaves of both treatments was constantly higher than those of other parts monthly throughout the study period. The proportion constituted by the leaves declined from the early stage to maturity whereas in rhizomes the proportion was increasing from the early stage to maturity. At maturity a notable general trend of percentage total nitrogen proportions constituted by different parts of plants is that proportion constituted by belowground parts was higher than those of above-ground parts while reverse was the case with dry matter.