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Species Richness Decreased (species + richness_decreased)
Selected AbstractsSpecies and structural diversity of church forests in a fragmented Ethiopian Highland landscapeJOURNAL OF VEGETATION SCIENCE, Issue 5 2010Alemayehu Wassie Abstract Question: Thousands of small isolated forest fragments remain around churches ("church forests") in the almost completely deforested Ethiopian Highlands. We questioned how the forest structure and composition varied with altitude, forest area and human influence. Location: South Gondar, Amhara National Regional State, Northern Ethiopia. Methods: The structure and species composition was assessed for 810 plots in 28 church forests. All woody plants were inventoried, identified and measured (stem diameter) in seven to 56 10 m x 10-m plots per forest. Results: In total, 168 woody species were recorded, of which 160 were indigeneous. The basal area decreased with tree harvest intensity; understorey and middle-storey density (<5 cm DBH trees) decreased with grazing; overstorey density (>5 cm DBH trees) increased with altitude. The dominance of a small set of species increased with altitude and grazing intensity. Species richness decreased with altitude, mainly due to variation in the richness of the overstorey community. Moreover, species richness in the understorey decreased with grazing intensity. Conclusions: We show how tree harvesting intensity, grazing intensity and altitude contribute to observed variations in forest structure, composition and species richness. Species richness was, however, not related to forest area. Our study emphasizes the significant role played by the remaining church forests for conservation of woody plant species in North Ethiopian Highlands, and the need to protect these forests for plant species conservation purposes. [source] A 10-year decrease in plant species richness on a neotropical inselberg: detrimental effects of global warming?GLOBAL CHANGE BIOLOGY, Issue 10 2009EMILE FONTY Abstract The census of vascular plants across a 10-year interval (1995,2005) at the fringe of a neotropical rainforest (Nouragues inselberg, French Guiana, South America) revealed that species richness decreased, both at quadrat scale (2 m2) and at the scale of the inselberg (three transects, embracing the whole variation in community composition). Juvenile stages of all tree and shrub species were most severely affected, without any discrimination between life and growth forms, fruit and dispersion types, or seed sizes. Species turnover in time resulted in a net loss of biodiversity, which was inversely related to species occurrence. The most probable cause of the observed species disappearance is global warming, which severely affected northern South America during the last 50 years (+2 °C), with a concomitant increase in the occurrence of aridity. [source] Impact of cocoa farming on vegetation in an agricultural landscape in GhanaAFRICAN JOURNAL OF ECOLOGY, Issue 2 2010Alex Asase Abstract Cocoa production occurs almost wholly within areas identified as biodiversity hotspots in West Africa and it has been noted as a major contributor to deforestation at the forest-agriculture interface. This study investigated the impact of cocoa farming on vegetation in relation to three land-use types of increasing cocoa production intensity from remnant native forest through shaded to unshaded cocoa farmlands in Ghana. The study used transects and forty-two 25 m × 25 m vegetation plots. The overall noncocoa plant species richness decreased significantly (95% CI) from the remnant native forest through shaded to the unshaded cocoa farmlands. Significant differences (P , 0.05) were also found in the mean density and basal area of noncocoa plants per hectare with the remnant native forest recording the highest values and the unshaded cocoa farmlands the lowest. The relative density of about 44.7% out of the 41 most abundant plant species declined in cocoa farmlands. The results of this study showed that cocoa farming could result in a drastic forest plant species loss with subsequent recruitment of nonforest species, forest plant species population decline as well as changes in the structural characteristics of the vegetation. This impact increases with increasing cocoa production intensity. Résumé En Afrique de l'Ouest, le cacao est produit presque entièrement dans des zones identifiées comme des hauts-lieux de la biodiversité et l'on a noté qu'il contribue toujours de façon importante à la déforestation à l'interface entre forêts et terres agricoles. Cette étude a analysé l'impact de la culture de cacao sur la végétation pour une utilisation des terres de trois types caractérisés par des intensités de production de cacao croissantes, allant des restes de forêt native à des exploitations ombragées et non ombragées de cacao, au Ghana. Cette étude a utilisé des transects et 42 parcelles de végétation de 25 m × 25 m. La richesse globale en espèces végétales - hors cacao - diminuait significativement (IC 95%) en passant des restes de forêt native aux exploitations de cacao ombragées et ensuite à celles qui sont exposées au soleil. On a aussi trouvé des différences significatives (P , 0,05) de la densité moyenne et de la surface basale par hectare des plants hors cacao, la forêt native restante donnant les valeurs les plus hautes et les exploitations exposées de cacao, les plus basses. La densité relative de près de 44,7% des 41 espèces végétales les plus abondantes diminuait dans les exploitations de cacao. Les résultats de cette étude ont montré que la production de cacao pouvait entraîner une perte drastique des espèces végétales forestières suivie d'un recrutement d'espèces non forestières, un déclin des populations d'espèces végétales forestières et des changements des caractéristiques structurelles de la végétation. Cette impacts augmentaient avec l'intensification de la production de cacao. [source] Land use affects rodent communities in Kalahari savannah rangelandsAFRICAN JOURNAL OF ECOLOGY, Issue 2 2007Niels Blaum Abstract Shrub encroachment caused by overgrazing has led to dramatic changes of savannah landscapes and is considered one of the most threatening forms of rangeland degradation leading to habitat fragmentation. Although changes to plant assemblages are becoming better known, however, our understanding of how shrub encroachment affects rodent communities is low. In this study, we investigated relative abundance of five rodent species in sixteen southern Kalahari rangelands where shrub cover ranged from low (<5%) to high (>25%). Rodent abundance was determined on three trapping grids (40 × 100 m) for each site. Our results show that increasing shrub cover affected rodent species differently. The relative abundance of hairy-footed gerbil, short-tailed gerbil and bushveld gerbil declined with increasing shrub cover, whereas highveld gerbil and striped mouse exhibited hump-shaped relationships with shrub cover. Overall, species richness decreased with increasing shrub cover and a negative impact of high shrub cover above 15% on rodent abundance was congruent for all species. We conclude that our results support the hypothesis that long-term heavy grazing that results in area wide shrub encroachment, threatens the diversity of arid environments. Résumé L'envahissement de buissons dû au surpâturage a conduit à des changements spectaculaires des paysages de savane et on le considère comme une des menaces les plus dangereuses pour la dégradation des pâturages menant à la fragmentation de l'habitat. Bien que l'on connaisse mieux les changements qui touchent les associations de plantes, on comprend moins bien comment l'envahissement des buissons affecte les communautés de rongeurs. Ici, nous avons étudié l'abondance relative de cinq espèces de rongeurs dans seize prairies du sud du Kalahari où le couvert de broussailles allait de faible (<5%) àélevé (>25%). L'abondance des rongeurs était déterminée sur trois grilles-pièges (40 m × 100 m) pour chaque site. Nos résultats montrent que l'augmentation de la couverture des buissons affecte les espèces de rongeurs différemment. L'abondance relative de trois espèces de gerbilles (Hairy-footed gerbil, short-tailed gerbil et bushveld gerbil) diminuait avec l'augmentation du couvert buissonneux, alors que la highveld gerbil et la souris striée présentaient une relation < Responses of subalpine dwarf-shrub heath to irrigation and fertilizationJOURNAL OF VEGETATION SCIENCE, Issue 3 2007Lisa Brancaleoni Aeschimann et al. (2004) for vascular plants with the exceptions of Vaccinium uliginosum ssp. microphyl-lum, henceforth called V. uliginosum (instead of Vaccinium gaultherioides Bigelow) and Festuca rubra L. ssp. commu-tata Gaudin, henceforth called F. rubra (instead of Festuca nigrescens Lam.); Frahm & Frey (1987) for bryophytes with the exception of Polytrichastrum alpinum (Hedw.) G.L. Smith instead of Polytrichum alpinum Hedw Abstract Question: Our study aimed at testing to what extent water and/or nutrients affect community composition in sub-alpine heath. We hypothesized that nutrient addition will have an overall positive effect on heath vegetation but water addition will have greater effects and will probably reinforce the effects of fertilization in drier habitat conditions. Location: Monte Rondinaio, northern Apennines, Italy (44°08' N; 10°35' E, ca. 1850-1930 m a.s.l.). Methods: Nutrients and water were added during five growing seasons in two communities (HV community, moister; EV community, drier) and the biomass of all species was estimated non-destructively by the point-quadrat method. Results: Total above-ground biomass increased in both communities with fertilization due to increased graminoid biomass and decreased moss biomass, but was unaffected by irrigation. In the HV community species richness decreased as an effect of fertilization while in the EV community species richness was raised by irrigation. Conclusions: Our study partly supported our hypothesis since water addition had a stronger effect in the drier community. However, this effect was not revealed by changes in above-ground biomass but rather by differing responses of individual species in the two communities. [source] The relevance of preserving temporary ponds during drought: hydrological and vegetation changes over a 16-year period in the Doñana National Park (south-west Spain)AQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 3 2008Laura Serrano Abstract 1.Although the Doñana National Park is given the highest degree of environmental protection in Spain, it is likely that groundwater discharge to several ponds within the Biological Reserve has been damaged by abstraction to a tourist resort located less than 1 km away. 2.Hydrological changes were monitored over 16 years (1 October 1989 to 30 September 2005) by recording the shallow water table of six temporary ponds at 1,8-week intervals, and the duration of pond wet phase (or hydroperiod) during each hydrological cycle. 3.The average rainfall for the study period was 563.2 mm, and included 6 wet, 5 moderate, and 5 dry years in a seemingly random sequence. The average rainy season extended from October until the end of March, while the dry season occupied the rest of the year. 4.The water table generally oscillated following this alternation of rainy and dry seasons, but this fluctuation was minimal during dry years, and even failed to occur at some ponds. 5.Since 1998/99, the average hydroperiod has shortened by 3 months at Charco del Toro pond, and by almost 2 months at Brezo pond, while the rest of the ponds exhibited a reduction of less than 1 month. 6.Vegetation changed in the ponds between May 1990 and 2005. Total plant cover increased (range of increase: 16,65%), and species richness decreased in all ponds (range of species loss: 4,18). 7.The reduction in the hydroperiod probably enhanced the growth of a few woody plants to the detriment of flooding-dependent species as the cover of Pinus pinea increased nearly fourfold at Brezo pond, while that of Scirpus lacustris was halved at Charco del Toro pond. 8.The pumping area for the nearby tourist resort should be relocated, and a specific management strategy should be developed in order to prevent further damage to the ponds. Copyright © 2007 John Wiley & Sons, Ltd. [source]
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