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Species Tolerant (species + tolerant)

Distribution by Scientific Domains

Life Sciences	50%
Earth and Environmental Science	50%

Selected Abstracts

The influence of tree canopies and elephants on sub-canopy vegetation in a savannah

AFRICAN JOURNAL OF ECOLOGY, Issue 1 2010
Robert Guldemond
Abstract The apparent influence of elephants on the structure of savannahs in Africa may be enhanced by management activities, fire and other herbivores. We separated the effect elephants have on grasses, woody seedlings (<0.5 m) and saplings (0.5,2 m) from the effect of tree canopies (canopy effect), and herbivory (park effect). We defined the canopy effect as the differences between plant abundances and diversity indices under tree canopies and 20 m away from these. Our testing of the park effect relied on the differences in the sub-canopy plant indices inside and outside a protected area that supported a range of herbivores. We based our assessment of the elephant effect on sub-canopy vegetation indices associated with elephant induced reductions in tree canopies. The park and canopy effects were more pronounced than the elephant effect. The park effect suppressed the development of woody seedlings into saplings. Conditions associated with tree canopies benefited woody plants, but not the grasses, as their indices were lower under trees. Elephants reducing canopies facilitated grass species tolerant of direct solar radiation. We concluded that management should consider other agents operating in the system when deciding on reducing the impact that elephants may have on vegetation. Résumé L'influence apparente des éléphants sur la structure des savanes africaines pourrait bien être accentuée par les activités de gestion, les feux et les autres herbivores. Nous avons séparé l'effet que les éléphants ont sur les herbes, les jeunes plants ligneux (<0,5 m) et les arbustes (0,5,2 m) de ceux de la canopée des arbres (effet canopée) et de la présence d'herbivores (effet parc). Nous avons défini l'effet canopée comme la différence entre les indices d'abondance et de diversité des plantes sous la canopée des arbres et à 20 m de ceux-ci. Notre expérimentation de l'effet parc se basait sur la différence des indices de végétation sous canopée à l'intérieur et à l'extérieur d'une aire protégée qui accueille toute une gamme d'herbivores. Nous avons fondé notre évaluation de l'effet éléphants sur les indices de végétation sous canopée, associés aux réductions induites par les éléphants dans la canopée des arbres. Les effets parc et canopée étaient plus prononcés que l'effet éléphants. L'effet parc supprimait le développement des jeunes plants ligneux en arbustes. Les conditions liées à la canopée des arbres bénéficiaient aux plantes ligneuses mais pas aux herbes, car leurs indices étaient inférieurs sous les arbres. Les canopées réduites par les éléphants favorisaient les espèces d'herbes tolérantes à la lumière directe du soleil. Nous en avons conclu que toute gestion devrait considérer l'impact d'autres agents dans le système lorsqu'il s'agit de réduire l'impact que les éléphants peuvent avoir sur la végétation. [source]

Oscillating vegetation dynamics in a wet heathland

JOURNAL OF VEGETATION SCIENCE, Issue 1 2005
Katharina E. Urban
Abstract. Question: The significance of disturbances caused by periodical inundation was investigated with respect to its effects on vegetation dynamics, species richness and fluctuations, and to the relevance of certain plant properties. Location and Method: At a sod-cut stand within nutrient-poor inland sand dunes, permanent plots along a transect were surveyed over a period of up to nine years after sod cutting. Results: In contrast to never inundated plots, periodically inundated plots were characterized by low vegetation cover and by high numbers of species belonging to many different communities, each of them with a low cover. Periodical inundations favoured the presence of pioneers, species tolerant of disturbances, species adapted to wet conditions and stoloni-ferous species. Furthermore, annual fluctuations of species within each plot were higher and most species occurred only sporadically. Discussion: A comprehensive model is presented describing the relevant processes identified in the littoral zone. Changing water tables result in the creation of gaps. The re-colonization of these gaps follows mainly from vegetative regeneration and less to the dispersion of diaspores. Highest species numbers in the zone of moderate disturbances result from a high rate of re-colonization in spite of local extinctions following each disturbance event. It is suggested that colonization abilities are among the most important features for species occurrence at a site rich in disturbances (more important than competitive abilities and more important than a slow rate of displacement). For nature conservation such sites are very important, because they allow (rare) pioneer species to survive for longer periods of time. [source]

Changes in plant communities over three decades on two disturbed bogs in southeastern Québec

APPLIED VEGETATION SCIENCE, Issue 1 2009
S. Pellerin
Abstract Questions: Have the natural plant communities of two mined bogs experienced changes in composition and richness over a three-decade period, and are these changes associated with anthropogenic disturbances? Location: Bas-Saint-Laurent region, southeastern Québec, Canada. Methods: We monitored three decades of floristic changes in two disturbed bogs by revisiting 57 plots in 1998, which were previously sampled in 1965 and 1966. Changes in species richness and composition were evaluated using Wilcoxon signed rank tests, principal component analysis and partial redundancy analyses (pRDA). We also used pRDA and an indicator species analysis to determine which species had undergone the greatest changes over time. Variation partitioning was used to evaluate the relative influence of human disturbance in compositional change. Results: The main changes in the vegetation of the two bogs were 1) a decrease of overall species diversity, 2) an increase in the percent cover of trees and of species tolerant of shade or drought, and 3) a decrease in the cover of heliophilous species. Picea mariana, Sphagnum fuscum and Pleurozium schreberi increased in percent cover while Chamaedaphne calyculata and Sphagnum rubellum decreased in percent cover. Variation partitioning suggested that human activities had a significant impact on vegetation composition. Conclusion: The results indicated that substantial changes occurred in the vegetation of the natural fragments of these severely disturbed bogs. Although human activities were partially responsible for the changes, our study suggested that the drying of the peat surface due to drought during the 1960s and 1980s may have contributed to the vegetation changes. [source]

Phylogenetic Age is Positively Correlated with Sensitivity to Timber Harvest in Bornean Mammals

BIOTROPICA, Issue 1 2008
Erik Meijaard
ABSTRACT The reasons that forest vertebrates differ in their response to selective timber extraction in tropical forests remain poorly characterized. Understanding what determines response and sensitivity can indicate how forest management might yield greater conservation benefits, and help us identify which lesser-known species may be especially vulnerable. We assessed the response of 41 Bornean mammals to selective timber harvest and tested eight hypotheses regarding the correlation between those responses and a range of species characteristics. Multivariate analyses show that phylogenetic species age is a key variable determining sensitivity. Older species are less able to cope with the effects of selective timber harvest. Most of these species are endemic to insular southeast Asia, and do not occur on the Asian mainland. These species are more specialized, and appear less able to cope with habitat change. In contrast, species tolerant to logging evolved more recently. This group tends to be omnivorous or herbivorous, to use all vegetation strata, and to be regionally widespread. This finding allows the sensitivity to habitat disturbance of lesser-known species to be predicted, and therefore has important conservation implications. These new insights also help in the design of large-scale forest landscapes that combine sustainable forest management and species conservation requirements. We recognize that these functions can be compatible, but that some species still need completely protected areas for their survival. RINGKASAN Hingga saat ini belum banyak penelitian mengungkapkan bagaimana berbagai vertebrata hutan akan bereaksi ketika dilakukan pembalakan hutan secara selektif. Dengan mempelajari tingkat reaksi dan kepekaan vertebrata, maka dapat diketahui bagaimana pengelolaan hutan dapat memberikan manfaat konservasi yang lebih besar. Penelitian demikian dapat membantu kami mengidentifikasi spesies mana saja yang biologinya sedikit diketahui namun termasuk rentan kepunahan. Kami mengevaluasi tanggapan 41 spesies mamalia Kalimantan/Borneo terhadap pemanenan kayu secara selektif, dan selanjutnya menguji 8 hipotesa berkaitan dengan hubungan atau korelasi antara tanggapan yang terjadi dengan berbagai karakteristik dari masing-masing spesies yang diteliti. Berdasarkan analisis multivarian disimpulkan bahwa umur filogenetik dari masing-masing spesies merupakan penentu kelentingan masing-masing spesies tersebut terhadap dampak pemanenan selektif. Spesies yang berumur lebih tua cenderung kurang dapat mentolerir dampak pemanenan kayu. Kebanyakan spesies ini merupakan endemik kepulauan di Asia Tenggara. Spesies ini cenderung merupakan spesialis (memiliki niche yang lebih sempit), serta tampaknya tidak seberapa kuat menerima dampak perubahan habitat. Sebaliknya spesies yang lebih toleran terhadap pembalakan cenderung baru berevolusi belakangan ini. Kelompok ini cenderung bersifat omnivora atau herbivora, serta mampu menggunakan seluruh lapisan vegetasi yang ada, serta tersebar meluas. Berdasarkan penelitian ini, dimungkinkan dilakukan prakiraan terhadap kepekaan dan dengan demikian terdapat berbagai manfaat praktis dalam hal metodologi. Analisis ini juga dapat membantu perancangan lanskap hutan berskala besar, dengan menggabungkan pengelolaan hutan berkelanjutan serta kebutuhan konservasi spesies. Kami melihat bahwa kedua kebutuhan pengelolaan tersebut dapat dipadu-serasikan, namun untuk beberapa spesies akan mutlak dibutuhkan kawasan yang dilindungi penuh demi kelanjutan spesies-spesies tersebut. [source]