Search

The survival of the extensive livestock system, the practice for most farmers in the livestock industry in Ghana depends heavily on the natural pastures as forage resource. To efficiently use the rangelands, knowledge of the species composition, especially that of poisonous plants is essential. Documented knowledge in Ghana is scanty; documentation and dissemination of the knowledge resource would enable a wider access and wider benefit to stakeholders. A study was conducted in Ghana on poisonous plants with the aim to discover the existence and diversity of poisonous plants and associated antidotes affecting livestock for documentation and preservation of knowledge. 70 different items were cited; 22 were poisonous plants for which antidotes were not cited, 28 were poisonous plants with known antidotes and 32 antidotes. There were 575 citations of plants from 194 reported cases of suspected plant poisoning, categorized as poisonous plants for which no antidotes were cited (146), poisonous plants with cited antidotes (147) and antidotes (282). 50 plants species were identified and belonged to 29 plant families. Some plants were known only by local names. There was an extensive knowledge of the diversity of poisonous plants and antidotes within the ecological zones along with possible antidotes. [ABSTRACT FROM AUTHOR]

1. In upland semi-natural oakwoods the natural regeneration of oak Qucicuspetraca and Q. robur is frequently lacking. This threatens the long-term persistence of a habitat of considerable conservation importance. 2. In the absence of excessive grazing pressure, large openings in the woodland canopy can provide suitable sites for regeneration. But these are often dominated by dense stands of bracken Pteridium equilinum which is thought to restrict woody growth severely. 3. In this paper we describe experiments carried out in a semi-natural oakwood in north-eastern Scotland, which tested the hypothesis that shading by a Pteridium, canopy in summer and smothering by the dying fronds in winter exert a detrimental effect on the growth of oak seedlings. 4. Two separate types of Pterideium stand were selected: the first and more dense growing in relatively large gaps in the oak canopy the second and less dense growing in smaller gaps. In the large gaps. three treatments were used: Pteridium cut continuously all year cut in winter only and uncut all year in the small gaps only the first and second treatments were used. The effects of a Pteridium canopy on photosynthetically active radiation (PAR) during the growing season were also measured. 5. The presence of a Pteridium canopy during the growing season reduced PAR to 5.9% of full sunlight in the larger canopy gaps and to 11.4% in the small gaps. Over two growing seasons significant reductions in accumulated oak seedling biomass were recorded in both large and small canopy gaps. Significant increases in specific leaf area. leaf area ratio, and a decrease in root:shoot ratio were also recorded. 6. Smothering by dying Peteridium fronds in winter significantly reduced seedling biomass but had no effect on biomass partitioning or seedling morphology. 7. These results suggest that effective control of dense Pteridium stands is necessary to promote the successful regeneration of oak. However, this should he done in conjunction with measures to ensure the continued supply of early successional woodland habitats. [ABSTRACT FROM AUTHOR]

1. Defoliation of oak trees and seedlings (Quercus petraea and Q. robur × Q. petraea putative hybrids) by various lepidopteran species was investigated in two upland semi-natural oakwoods (Dinnet and Ariundle National Nature Reserves) within contrasting climatic zones in the Scottish Highlands. 2. Experiments were designed to test four hypotheses: (i) the failure of oak to regenerate naturally is partly attributable to defoliation of seedlings by insects. (ii) seedling defoliation is linked to canopy density and composition: (iii) the degree of seedling defoliation is linked to the extent of canopy defoliation: and (iv) defoliation is positively correlated with insect population density in the canopy. 3. The extent of canopy defoliation of oak was significantly different between the two woods with trees at Ariundle, located within a wetter climatic zone, more defoliated than those at Dinnet which is in a drier climatic zone. Defoliation also varied significantly between individual trees and between years. 4. Defoliation was positively correlated with degree of infestation by the larvae of several lepidopteran species. Leaf samples at Dinnet were dominated by Operophtera brumata, and those at Ariundle by Erranis, defoliaria. The degree of infestation was higher at Ariundle. 5. Experimental seedlings were significantly more defoliated under oak canopy than in the open or under a Betula spp. canopy. Canopy defoliation was positively correlated with defoliation of seedlings growing directly beneath, but seedling defoliation was negatively correlated with oak canopy density. 6. Defoliation of oak seedlings by insects poses more of a threat to the natural regeneration of oak at Ariundle than at Dinnet possibly due to climatic differences between these two woods. 7. A group-felling system using coupe sizes of over 0.5 ha is recommended for encouraging oak regeneration in woods such as Ariundle. where seedlings need to be kept free from the influence of an overhead oak canopy. Shelterwood systems, where seed trees are retained after extensive thinning are not recommended. In woods similar to Dinnet both group-fell and shelterwood systems are appropriate management options. 8. Woodland managers should be aware of defoliation problems within their woods before deciding on which silvicultural option to choose. [ABSTRACT FROM AUTHOR]

We studied hemiparasitism in Okoubaka aubrevillei Pellegr. & Normand (Santalaceae), an uncommon West African rainforest tree of widespread distribution (Ivory Coast to Zaire) which attains heights of up to 40 m. It has a very large seed (mean fresh mass of 101 g), and slow accumulation of biomass characteristic of seedlings of shade-tolerant rainforest trees. O. aubrevillei seedlings became hemiparasitic within 6 months when grown next to seedlings of the tree species Entandrophragma angolense (Wel.) DC., Pericopsis elata (Harms) Van Meeuwen, Pterygota macrocarpa K. Schum., and Tieghemella heckelii Pierre ex Chev. P. macrocarpa, and the nitrogen-fixing legume, P. elata were most infected. Characteristically for hemiparasites, midday leaf water potentials in O. aubrevillei were at -2 MPa lower than those of the host seedlings. Stomatal conductance, however, was low, with a maximum of 111 mmol m² s-1. After 1 yr, no significant effects of the hemiparasitism were observed on the growth of O. aubrevillei or on its nutrient status as measured by foliar element concentrations. By contrast, the two most infected host species showed increased mortality and/or reduced growth. Foliar element concentrations were not, however, affected in host plants of the surviving species. Although the resources of a large seed might enable seedlings of O. aubrevillei to grow independently from hosts for prolonged periods, their simultaneous strong effect on the mortality and growth of host seedlings might point to an alternative competitive function of hemiparasitism. [ABSTRACT FROM AUTHOR]