Relationships between soil seed banks and above-ground vegetation along a disturbance gradient in the W Park trans-boundary biosphere reserve, West Africa

Aims: Vegetation succession depends on the availability of suitable propagules in the soils, thus knowledge of soil seed banks is essential for formulating effective strategies for restoring the vegetation of degraded sites. The W National Park, the only trans-boundary biosphere reserve in West Africa, is being extensively fragmented and degraded in recent decades. The aims of this study were to assess the reserve’s soil seed banks, their relationships with standing vegetation and bundle of disturbances, and their potential significance for vegetation restoration. Methods: The size and composition of the above-ground species vegetation were assessed in nine plots of 1 ha each representing a range of habitats with differing disturbance severity (low, intermediate and high). A total of 702 soil samples were taken from three layers (0-3, 3-6 and 6-9 cm) and soil seed bank was analyzed using the seedling emergence technique. Important Findings: Generally, seeds of non-woody taxa dominated in samples from all soil depths and habitats of all disturbance severities. The mean soil seed density was 17.8, 24.4 and 26.3 seeds dm-3 in samples from the least, intermediate and most disturbed sites, respectively, and highest in the upper soil layers in all cases. The results indicate that there is limited potential for restoring woody vegetation solely from soil seed banks, and that woody species in the region rely more on recently shed seeds trapped in the standing dead biomass and litter on the ground than soil seed banks for regeneration. Thus, human intervention is needed to accelerate forest recovery, mainly through alleviating anthropogenic impacts on the ecosystem (for instance, avoiding destruction of new seeds by intense fire), and site manipulation to improve environmental conditions for seedling establishment and growth

Relationships between soil seed banks and above-ground vegetation along a disturbance gradient in the W National Park trans-boundary biosphere reserve, West Africa

Aims Vegetation succession depends on the availability of suitable propagules in the soils, thus knowledge of soil seed banks is essential for formulating effective strategies for restoring the vegetation of degraded sites. The W National Park, the only trans-boundary biosphere reserve in West Africa, is being extensively fragmented and degraded in recent decades. The aims of this study were to assess the reserve’s soil seed banks, their relationships with standing vegetation and bundle of disturbances and their potential significance for vegetation restoration. Methods The size and composition of the above-ground species vegetation were assessed in nine plots of 1 ha each representing a range of habitats with differing disturbance severity (low, intermediate and high). A total of 702 soil samples were taken from three layers (0–3, 3–6 and 6–9cm) and soil seed bank was analyzed using the seedling emergence technique. Important Findings Generally, seeds of non-woody taxa dominated in samples from all soil depths and habitats of all disturbance severities. The mean soil seed density was 17.8, 24.4 and 26.3 seeds/dm3 in samples from the least, intermediate and most disturbed sites, respectively, and highest in the upper soil layers in all cases. The results indicate that there is limited potential for restoring woody vegetation solely from soil seed banks, and that woody species in the region rely more on recently shed seeds trapped in the standing dead biomass and litter on the ground than soil seed banks for regeneration. Thus, human intervention is needed to accelerate forest recovery, mainly through alleviating anthropogenic impacts on the ecosystem (for instance, avoiding destruction of new seeds by intense fire), and site manipulation to improve environmental conditions for seedling establishment and growth. Other ways of restoring forests than through the soil seed bank (e.g. sowing seeds collected elsewhere, and planting tree seedlings) could also be relevant

Role of climate and herbivory on native and alien conifer seedling recruitment at and above the Fennoscandian tree line

Questions: We investigated the importance of climate and herbivory on native and alien conifer colonization of the birch-dominated Fennoscandian tree line by addressing the following questions: (a) are tree line and tundra habitats similarly suitable for conifer seedling recruitment; (b) do ungulate and rodent herbivores differentially impact seedling recruitment; and (c) how does the role of habitat and herbivory on seedling recruitment vary across a marked climate gradient? Location: Northern Fennoscandia, Sweden (Vassijaure and Paddus), and Norway (Joatka and Seiland). Methods: We conducted an experiment to assess the emergence rate, survival probability and height development of Norway spruce (Picea abies), Scots pine (Pinus sylvestris) and Siberian larch (Larix sibirica) seedlings. Three experimental plots (i.e., open control, reindeer exclosure and complete vertebrate exclosure) were established in both tree line and tundra habitats at each of the four locations. Seeds of the three conifer species were sown in each plot in June 1999 during three consecutive years. The surviving seedlings were counted in August to September 1999, 2000, 2001, 2002 and 2007. The height of all seedlings was measured in 2007. Results: Our study reveals that Norway spruce, Scots pine and Siberian larch can regenerate from seed at and above the current tree line in northern Fennoscandia. Their performance was generally higher above tree line in tundra than at tree line, but depended on species identity, climate aridity and mammal herbivory, particularly by rodents. These results suggest that the species composition and latitudinal limit of the tree line in the future might depend not only on direct effects of the future climate on the current tree line species, but also on the intensity of alien and native conifer introductions, as well as changes in herbivore populations. Conclusion: If sufficient seeds of Norway spruce, Scots pine and Siberian larch should reach the current tree line, their performances will increase with a warmer and wetter climate, and this effect will be markedly modulated by herbivores (particularly rodents). Further work is required to extend these results to determine the ability of these conifers to become tree line-forming species in the future

Prevalence of HIV infection among the patients with an avascular necrosis of the femoral head in Ouagadougou, Burkina Faso

Objective: To study the prevalence of HIV infection among the risk factors associated with the avascular necrosis of the femoral head in Ouagadougou, Burkina Faso. Design: Multicenter retrospective study. Setting: Rheumatology consultations and Orthopedic-Traumatology Surgery Department Of The University Hospital Yalgado Ouédraogo, at the Medico-Surgical Private Clinic “Notre Dame de la Paix” and the Medical Center ‘Paul VI’ in Ouagadougou, Burkina Faso. Patients and methods: The study was conducted on recorded cases from January 2007 to December 2009. All patients received during the study period for an avascular necrosis of the femoral head that was confirmed by X-ray and / or CT were included. The search for HIV antibodies was performed for all patients by the ELISA test confirmed by the Western Blot test. Results: There were 79 men (56%) and 62 women (44%). It shows a sex ratio of 1.2. The average age of patients was 43.95 ± 15.36 years with extremes of 7 and 79 years. The average duration of disease before diagnosis was 6 ± 6.5 years with extremes of 1 and 39 years. The affected area involved the left hip in 67 cases (47.5%), the right hip in 48 cases (34%) and was bilateral in 26 cases (18.5%). Among the risk factors, alcohol consumption was reported in 30/67 (44.8%), steroids in 09/67 (13.4%), sickle cell disease in 12/141 (8.5%). Six patients (4.25%) among the 141 had an HIV infection. Conclusion: HIV infection has a place among the risk factors of an avascular necrosis of the femoral head. A HIV serology test should be systematically carried out in all patients with an avascular necrosis of the femoral head in sub-Saharan Africa, particularly in the absence of other risk factors. Key words: Avascular necrosis of the femoral head, HIV, sickle cell disease, sub-Saharan Africa

Early avian functional assemblages after fire, clearcutting, and post-fire salvage logging in North American forests

Abstract Increased demand for timber, the reduction in the available timber resources, and more frequent and severe forest fires under a changing climate have increased the use of salvage logging in North American forests despite concerns regarding impacts on biodiversity and long-term forest productivity. We aimed to complement previous approaches that used bird species richness or individual abundance in salvage-logged habitats to assess the sustainability of this practice. We looked for commonalities in the taxonomic, functional, and phylogenetic components of bird assemblages among these three post-disturbance habitats across a broad geographic range. We compiled six North American datasets selected from primary and grey literature that documented species composition of avian assemblages in habitats after recent fire, post-fire salvage logging, and traditional logging. Our results revealed contrasting patterns of bird trait assemblage among burned, post-fire salvage, and traditionally logged habitats. In salvage-logged habitats, taxonomic diversity, functional diversity, and functional and phylogenetic redundancy were significantly lower than in both burned and traditionally logged habitats. The frequency of insectivores was significantly lower after salvage logging than after both fire and traditional logging. These findings suggest that cumulative disturbances have a negative effect on early assembly of bird communities. The outcomes of this study encourage further assessments, at landscape level, of salvage logging intensity, burn size, and fire severity on bird functional structure to better plan for their conservation. Résumé La demande accrue de bois, la réduction des ressources ligneuses disponibles, les feux de forêt plus sévères et plus fréquents dans le contexte du changement climatique ont favorisé le recours à la coupe de récupération dans les forêts d’Amérique du Nord malgré les inquiétudes en ce qui a trait aux impacts sur la biodiversité et la productivité à long terme de la forêt. Nous avions pour objectif de compléter les approches précédentes qui ont utilisé la richesse ou l’abondance de chaque espèce d’oiseaux dans les habitats engendrés par la coupe de récupération pour évaluer la durabilité de cette pratique. Nous avons cherché des points communs dans les composantes taxonomique, fonctionnelle et phylogénétique des assemblages d’oiseaux entre trois habitats engendrés par cette perturbation à travers une vaste étendue géographique. Nous avons compilé six jeux de données nord-américaines choisies à partir de la littérature primaire ou grise qui a documenté la composition en espèces des assemblages aviaires dans les habitats issus d’un feu récent, d’une coupe de récupération après feu ou d’une coupe traditionnelle. Nos résultats révèlent différentes configurations de caractéristiques des assemblages d’oiseaux parmi les habitats brûlés, récupérés après feu ou exploités de façon traditionnelle. Dans les habitats issus d’une coupe de récupération, la diversité taxonomique, la diversité fonctionnelle, la redondance fonctionnelle et phylogénétique étaient significativement plus faibles que dans les habitats issus d’un feu ou d’une exploitation traditionnelle. La fréquence des insectivores était significativement plus faible après une coupe de récupération qu’après un feu ou une exploitation traditionnelle. Ces résultats indiquent que des perturbations cumulatives ont un effet négatif sur les premiers assemblages des communautés d’oiseaux. Les résultats de cette étude encouragent à poursuivre l’évaluation des effets, à l’échelle du paysage, de l’intensité de la coupe de récupération, de la taille du brûlis et de la sévérité du feu sur la structure fonctionnelle des oiseaux pour mieux planifier leur conservation