Masresha Fetene

Intra- and inter-specific competition between seedlings of Acacia etbaica and a perennial grass (Hyparrenia hirta)

Intra- and inter-specific competition between seedlings of Acacia etbaica Schweinf. and the grass Hyparrenia hirta (L.) Stapf. was studied to evaluate the influence of the perennial grass on the establishment of the tree seedlings. The experiment was conducted using a replacement series in which plants were grown in a greenhouse at an overall density of six individuals per pot, providing combinations of the two species from 0:6 and 6:0. Indices of intra- and inter- specific competition, relative crowding coefficients and relative yield totals (RYTs) were calculated from the dry weight data. For both shoots and roots, the crowding coefficient of Hyparrenia towards Acacia was five- to ten-fold that of Acacia towards Hyparrenia, which indicated a high competitive strength for the grass species. RYT values of the two species averaged 1.25, indicating some degree of resource complimentarity. Both species had comparable intra-specific competition based on shoot yield. However, based on the root yield, intra-specific competition of Hyparrenia was slightly lower than that of Acacia. Inter-specific competition of Hyparrenia on the root yield of Acacia was more than five times greater than vice versa. With more crowding, shoot/root ratio decreased more in Hyparrenia than in Acacia for pure stands as well as for mixtures which indicated that Hyparrenia could adjust biomass allocation. In general, the results indicated that Hyparrenia was competitively aggressive towards Acacia and may inhibit the growth of tree seedlings when the latter are planted within the grass community. Implications of the findings in terms of land reclamation efforts are discussed.

Comparative characterization of photosynthetic performance and water relations of native trees and exotic plantation trees in an Ethiopian forest

Abstract. Comparative ecophysiological studies by measurements of photosystem II chlorophyll a fluorescence, porometry and stable isotope analyses were performed on regrowth of trees in a plantation of Eucalyptus saligna in Ethiopia. In the Shashemene-Munessa State Forest of the eastern escarpment of the Great Rift Valley, young plants of E. saligna and the native tree Podocarpus falcatus were compared under the canopy of an established E. saligna plantation, and the native tree Bersama abyssinica was also included. For further comparison fully sun-exposed plants of Eucalyptusglobulus in a young newly established plantation, and trees of P. falcatus and the native pioneer tree Croton macrostachys in a remnant natural forest were examined. Photosynthetic yield measurements and light response curves suggested a gradation of sun-adapted to shade-adapted behaviour of E. globulus (exposed) >C. macrostachys >>E. saligna (understorey) ≥ P. falcatus ~ B. abyssinica. As indicated by carbon isotope discrimination, long-term water-use efficiency (WUE) tended to be higher in P. falcatus than in E. saligna in the understorey of the plantation. Transpiration measurements showed that Eucalyptus spp had the highest and P. falcatus the lowest instant leaf conductance for water vapour. Thus, P. falcatus competes well photosynthetically and by a more favourable WUE. These measurements support the expectation that the E. saligna plantation has a nurse effect for regrowth of native trees. With the management practice of regularly coppicing E. saligna in a 7-year rhythm a native P. falcatus forest may regenerate.

Growth and photosynthesis of seedlings of four tree species from a dry tropical afromontane forest

Growth, photosynthesis and carbon allocation pattern were studied in four dry afromontane forest tree species (Olea europea subspecies cuspidata, Podo- carpusfalcatus, Hagenia abyssinica andJuniperus procera) under varied light regimes in a greenhouse. The objective of the study was to assess the potential of the species for growth under forest canopies and to identify their habitat preferences. The light regimes were created using shade cloth and they corresponded with deep forest understoreys (2% of the light in the open gap); moderate shade (10%), slight shade as is found in edges of forest gaps (20%) and 100% representing open gaps. Seedling biomass was significantly influenced by light regimes for all species as were total leaf area and relative growth rate. H. abyssinica had the highest growth rate but the lowest survival rate in shade. There was a consistent trend for higher specific leaf area (SLA) and leaf area ratio (LAR) at lower growth light regimes in 0. europea and P.falcatus. 0. europea and P.falcatus had similar allocation patterns whereby between 20-40% of the total biomass was allocated to stem, 20-30% to roots and 50-60% to leaves. In H. abyssinica up to 80% was allocated to leaves and only a small percentage to stem and to roots. Within species there were significant differences in the light saturated rate of photosynthesis (Amax) per unit area among the plants grown at the lowest light level and in the open. For plants grown in the open there were very little among species differences in Amax per unit area. However, there were significant differ- ences in the Amax of the different species grown at the lowest light level. Chloro- phyll fluorescence measurements indicated that open-grown P. falcatus and 0. europea experienced moderate photoinhibition. From the growth and photosyn- thesis results P. falcatus and 0. europea appeared to be non-pioneer, shade-tolerant species, whileJ. procera and to a larger extent H. abyssinica showed pioneer, light- demanding characteristics. The results are discussed in terms of the occurrence of the species in the mosaic climaxes of afromontane forests.

Flexibility of Crassulacean Acid Metabolism in Kalanchoe pinnata (Lam.) Pers. I. Response to Irradiance and Supply of Nitrogen and Water

Summary Plants of Kalanchoe pinnata (Lam.) Pers. were grown in the glass chamber of a phytotron in high-light (16-23 mol photons m -2 day -1 ) and in the shade (0.8-2.1 mol photons m -2 day -1 ) respectively, without or with nitrogen nutrition (12 mol m -3 NO 3 - in irrigation solution) and well watered or droughted for 18-22 days (high-light) and 26 to 32 days (shade) respectively, prior to measurements and analyses. Part of the high-light plants were transferred to the shade and part of the shade plants to high-light before measurements. Gas-exchange (H 2 O-vapour, CO 2 ) was measured and contents of total leaf nitrogen, chlorophyll a and b and carotenoids were analysed. Both high-light and low-light grown plants showed typical CAM gas exchange. When high-light plants were transferred to the shade under all conditions diurnal net CO 2 -balance was negative. Shade plants transferred to high-light greatly increased their daily net CO 2 -uptake, particularly by extended CO 2 -fixation at high rates in the light period, if supplied with H 2 O and N. Thus, shade plants were very successful in high-light provided N and H 2 O were not limiting. Shade adaptation of shade-plants as compared to high-light plants was indicated by higher absolute chlorophyll and carotenoid contents and lower chlorophyll a/b as well as lower CO 2 -uptake to chlorophyll (a + b) ratios. The results show, that the factors irradiance, nitrogen-nutrition and water-availability interact in eliciting flexible responses of the photosynthetic mechanism in the constitutive CAM-plant K. pinnata . Highlight plants were not shade tolerant; low-light plants were shade tolerant but not shade demanding.

Tending for Cattle: Traditional Fire Management in Ethiopian Montane Heathlands

Fire has long been a principal tool for manipulating ecosystems, notably for pastoralist cultures, but in modern times, fire use has often been a source of conflicts with state bureaucracies. Despite this, traditional fire management practices have rarely been examined from a perspective of fire behavior and fire effects, which hampers dialogue on management options. In order to analyze the rationale for fire use, its practical handling, and ecological effects in high-elevation ericaceous heathlands in Ethiopia, we used three different information sources: interviews with pastoralists, field observations of fires, and analysis of vegetation age structure at the landscape level. The interviews revealed three primary reasons for burning: increasing the grazing value, controlling a toxic caterpillar, and reducing predator attacks. Informants were well aware of critical factors governing fire behavior, such as slope, wind, vertical and horizontal fuel structure, and fuel moisture. Recent burns (1-4 years since fire) were used as firebreaks to control the size of individual burns, which resulted in a mosaic of vegetation of different ages. The age structure indicated an average fire return interval of ~10 years. At these elevations (> 3500 m), the dry period is unreliable, with occasional rains. Of all observed fires, 83% were ignited during very high Fire Weather Index levels, reached during only 11% of all days of the year. Burning is illegal, but if this ban was respected, our data suggest that the Erica shrubs would grow out of reach of cattle within a few years only, creating a dense and continuous canopy. This would also create a risk of large high-intensity wildfires since the landscape is virtually devoid of natural fuel breaks. Under the present management regime, this heathland ecosystem should be quite resilient to degradation by fire due to a relatively slow fuel buildup (limiting fire intervals) and an effective regrowth of Erica shoots. Nevertheless, if burning is done during severe drought, there may be a risk of smoldering fires killing the lignotubers. Given the intimate knowledge of fire behavior and fire effects among these pastoralists, it should be possible to develop a fire management plan that can sustain the present land use and ecosystem, and be sanctioned by both authorities and the local community.

Recruitment of trees at tropical alpine treelines: Erica in Africa versus Polylepis in South America

Background: Constraints on tree regeneration have been described from several temperate treeline sites, however data from tropical mountains are few. Aim: We test the hypothesis that high altitude treelines are caused by constraints on tree regeneration. We report the results of recent studies on climatic variables and on the reproduction of Erica spp. in east Africa, and compare those with similar studies on treeline stands of Polylepis spp. in Ecuador and Bolivia. Methods: We established altitudinal and horizontal transects comprising sampling plots from forests to surrounding grasslands. Data on microclimate, vegetation structure and reproductive activity were collected in the field, and supplemented by tests on germination requirements in the field in permanent exclosures and in the laboratory. Results: Our measurements demonstrated that the number and severity of frost events and potential water stress were higher near the soil surface (0.5 m) than in free air (2.0 m). Seeds of Erica trimera did not germinate, as the necessary climatic requirements (high diurnal temperature range, but no frost) were rarely fulfilled in the field. Most studied species were capable of clonal growth, and the relative importance of vegetative persistence tended to increase with altitude. These effects were independent of the intensity of land use. Conclusions: The harsh microclimate near the soil surface at tropical treelines may be one reason why recruitment from seed is limited for treeline-forming species. This is important for restoration or conservation schemes as well as predictions of treeline dynamics under global change.

SOCIO-ECONOMIC IMPORTANCE OF GUM AND RESIN RESOURCES IN THE DRY WOODLANDS OF BORANA, SOUTHERN ETHIOPIA

ABSTRACT Drylands of Borana Zone, southern Ethiopia, are endowed with different woody species that produce commercial gums and resins, which support the Livelihoods of pastoral and agro-pastoral communities. The objectives of this study were to: (i) assess the role of gum and resin production and marketing in the livelihoods of the pastoral and agro-pastoral communities; (ii) identify major challenges and constraints that hinder sustainable production; (iii) analyze the existing opportunities related to future gum and resin production and commercialization; and (iv) understand the perception of the local communities and the overall future prospects of sustainable gum and resin development, production and commercialization. A semi-structured questionnaire was administered to a total of 80 households, randomly selected from two representative Districts (Arero and Yabello) in the Borana Zone. Group disscussions were also held with 12 key informants. Additional information was also collected from District and Zonal officials, local merchants and enterprises engaged in businesses involving gums and resins. The results revealed that the pastoral and agro-pastoral communities in Borana Zone have intimate attachments with the woody species that provide gums and resins, and that collection and marketing of gums and resins are among the three major sources of livelihoods of local communities, along with livestock and crop production. The average annual household income generated from the sale of gums and resins was estimated at about 2,674 and 2,403 Ethiopian Birr (about 311.00 and 279.00 USD) at Arero and Yabello, respectively. Collection and sale of gums and resins represented the sole source of income for the disadvantaged groups in the local communities, i.e. women, school children and poor households with neither livestock nor land resources. The majority of respondents identified the income generated from the sale of gums and resins as a safety-net safeguarding the communities during recurrent drought periods. Gums and resins are also sources of food, chewing gum, traditional medicine, fodder, traditional soap, insect repellents, fragrance for smoking houses and other cultural practices. Several challenges and constraints are discussed, which affect the sustainable use of the vast woodlands for enhanced livelihoods and reduced household vulnerability in Borana.

Diversity, regeneration status, and population structures of gum and resin producing woody species in Borana, Southern Ethiopia

Severe drought and large-scale ecosystem degradation are the two major threats exacerbating livelihood vulnerability of the pastoral and agropastoral communities in Borana Zone, southern Ethiopia. Strategic integration and sustainable management of the vast gum and resin bearing dry forests offer significant socioeconomic and ecological opportunities to enhance adaptation of these communities to adverse climatic variability, while enhancing ecosystem resilience. This study was carried out to investigate the diversity, abundance, distribution, and population structure of gum and resin bearing species in Borana drylands. Surveys were carried out in two districts: Arero and Yabello. Seventy-five (20 × 20 m) quadrats were established at 500 m intervals along transects in seven localities. Forty-six woody species distributed in 16 families and 25 genera were encountered. Gum and resin producing species comprised about 42 and 61% of the total number of species, 49 and 68% of the density ha-1, and 73 and 84% of the total basal area at Arero and Yabello, respectively. Regeneration and diameter class distribution showed clear signs of healthy populations, except for a small number of species, which exhibited bell-shaped diameter class distribution patterns. The results revealed that Borana Zone hosts more diverse commercial gum and resin bearing species compared to the northern part of the country, where organized production and marketing of gum and resin are well developed, and other relatively similar places, such as Middle Rift Valley and the neighbouring Somali region in Ethiopia. Such diversity, abundance, and the overall positive regeneration status of most of the gum and resin bearing species in Borana make up a solid and healthy basis for promoting the sustainable management of woodland resources through organized production and commercialization of high value oleo-gum resins.

The Impact of Fire on the Soil Seed Bank and Regeneration of Harenna Forest, Southeastern Ethiopia

Abstract The composition and density of soil seed banks was studied at Harenna Forest after a major fire in the year 2000. Soil samples were collected from burned and unburned portions of the forest using quadrants 15 × 15 cm and 9 cm deep, laid along line transects. Forest recovery was also monitored on burned sites using permanent plots of 0.1 ha. One hundred fifty-five seedlings germinated from the soil samples, of which 140 and 15 were from the unburned and burned sites, respectively. The proportion of woody species found on the unburned site was 47%, while on the burned site only one woody species was recorded. Overall mean densities were 621 ± 15 and 66 ± 2 seeds per m2 on the unburned and burned sites, respectively. The greatest diversity was found in the upper soil layer, followed by the middle, litter, and lower soil layers collected from the unburned site. Eighteen months after the fire, the burned site was covered with 32 species of dense vegetation, which attained a height of 3.5 m. Our results revealed that although the fire exhausted the soil seed bank, the vegetation could regenerate quickly with pioneer species, which differed in composition from the neighboring unburned stand. This implies that most species in Harenna Forest are sensitive to fire and could be eliminated easily from the area unless they are properly protected. Therefore, an appropriate management plan should be developed and implemented for the remaining forest, including protection from fire.

Analysis of the “shelter tree-effect” of natural and exotic forest canopies on the growth of young Podocarpus falcatus trees in southern Ethiopia

Plantations of exotic trees on areas where tropical forest has been clear-felled have been reported to facilitate regrowth of indigenous tree species. This so-called nurse- or shelter tree effect was investigated in a montane semihumid site in southern Ethiopia where plantations of Pinus patula and Eucalyptus saligna grow in close vicinity to the natural Podocarpus falcatus mixed forest. Physiological performance of P. falcatus saplings growing in the exotic and the natural forests was investigated over the year. Compared with the natural forest, photosynthetic carbon gain and growth of the saplings were significantly enhanced under Pinus patula while likewise retarded under Eucalyptus saligna. Diverging effects of the differently dense shelter canopies on the saplings could be traced to differences in the sub-canopy microclimates and particularly to the intensities and temporal distribution of photosynthetic active radiation (PAR). Moisture also played an important role for photosynthetic carbon gain: while the morning patterns of CO2 uptake were significantly correlated with the patterns of sunflecks, stomatal conductance was the determinant factor in the afternoon. Analysis of the photosynthetic efficiency of sunflecks revealed a lower quantum yield than the basic diffuse PAR intensity. Compared with a theoretically even distribution of the daily PAR, CO2 uptake under the real light climate was 70% under Pinus and in the natural forest, and 59% under Eucalyptus. Relating growth rates of Podocarpus saplings to photosynthesis the microclimate under Pinus was 2.5 times as effective as that in the natural forest and five times more effective than under Eucalyptus.