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Herbivores alter plant biodiversity (species richness) in many of the world's ecosystems, but the magnitude and the direction of herbivore effects on biodiversity vary widely within and among ecosystems. One current theory predicts that herbivores enhance plant biodiversity at high productivity but have the opposite effect at low productivity. Yet, empirical support for the importance of site productivity as a mediator of these herbivore impacts is equivocal. Here, we synthesize data from 252 large-herbivore exclusion studies, spanning a 20-fold range in site productivity, to test an alternative hypothesis-that herbivore-induced changes in the competitive environment determine the response of plant biodiversity to herbivory irrespective of productivity. Under this hypothesis, when herbivores reduce the abundance (biomass, cover) of dominant species (for example, because the dominant plant is palatable), additional resources become available to support new species, thereby increasing biodiversity. By contrast, if herbivores promote high dominance by increasing the abundance of herbivory-resistant, unpalatable species, then resource availability for other species decreases reducing biodiversity. We show that herbivore-induced change in dominance, independent of site productivity or precipitation (a proxy for productivity), is the best predictor of herbivore effects on biodiversity in grassland and savannah sites. Given that most herbaceous ecosystems are dominated by one or a few species, altering the competitive environment via herbivores or by other means may be an effective strategy for conserving biodiversity in grasslands and savannahs globally.

Understanding patterns of community structure and the causes for their variation can be furthered by comparative biogeographic analyses of island biotas. We used woody plant data at the local scale to investigate variations in species rarity, alpha, beta, and gamma diversity within and between three islands from the oceanic archipelagoes of Azores, Canaries and Mascarene. We used standardized protocols to sample ten 50 m × 50 m forest plots in each of the three islands with contrasting climate and regional species pools: Terceira (Azores), Tenerife (Canaries), and Reunion (Mascarene Islands). Occupancy frequency distributions and species abundance distributions were used to investigate rarity. The partitioning of beta diversity in a distance-decay framework was used to test for spatial patterns of community composition. Rarity was much more pronounced in the highly diverse islands of Tenerife and Reunion than in the regionally poorer island of Terceira. The number of species rose faster with increasing sample area in both Tenerife and Reunion. The slope of the species rank abundance curve was steeper in Terceira whereas the richer island assemblages approached a lognormal model. Compositional changes according to spatial distance were mostly due to replacement of species in Terceira and Reunion. Our results point to important differences in the community structure of Terceira, which is the less diverse and temperate region in comparison to Tenerife and Reunion which are highly diverse.

With the aim of explaining the role that taxa and island features have in biogeographical patterns, we processed presence–absence matrices of all the Macaronesian native species of ten different taxa (arthropods, birds, bryophytes, fungi, lichens, mammals, mollusks, pteridophytes, reptiles and spermatophytes) through simulated annealing analysis. Distribution patterns among the archipelagos were pinpointed, along with the different biogeographic roles played by islands and species groups. All the networks analysed resulted to be significantly modular and the structure of biogeographic modules reflects known past connections among the archipelagos and the current drivers of species distribution. The role assigned to the species supports some biological (ecological amplitude, degree of endemicity) and functional (long‐distance dispersal and persistence abilities) traits of their respective biota and justifies their position in recent models of biogeographical distribution. Whereas it was expected that the modules identified by the spermatophytes and arthropods would reflect the compartmentalization of archipelagos quite well, this was also the case for much more vagile taxa, such as fungi or lichens. Conversely, results obtained for pteridophytes and bryophytes suggest that for those taxa geographic distance and/or macroclimatic conditions are less important than the size, age and orography of an island to determine the modularity of island groups. On the other hand, dry, species‐poor islets, act as connectors, tending to cluster together for different taxa, independently of their archipelagic adscription, whereas large, high, humid islands tend to form network or module hubs representing regional centers of speciation and dispersal. [ABSTRACT FROM AUTHOR]

Invasion biology is an important element of global environmental change and represents one of the main threats to biodiversity. American species were introduced to Tenerife after the Spanish conquest during the eighteenth century, as is the case for Agave americana and Opuntia dillenii. The long period of naturalization and adaptation of these species has led them to become two of the most dispersed introduced species of the archipelago. We analyzed several eradication management processes in an area intensively invaded by both O. dillenii and A. americana. Three treatments were randomly applied: mechanical removal, use of herbicide (glyphosate at 10% volume), and mechanical and herbicide applied together. Both the effectiveness of the treatments to remove the target exotic species biovolume and the impact of the eradication methods on species richness and species composition of the area were analyzed. We found that the treatments had an impact on species composition but not on species richness. Species composition was mainly affected by mechanical treatment. The effect caused by the mechanical removal of the exotic target species in species composition is minor after 4 years, and is related to a higher dominance of shrub species typical of coastal shrubland and of annual or pioneer species. The control of O. dillenii and A. americana is evident from insignificant recovery 4 years after treatment application. A mechanical and herbicide treatment together, allowed not only the immediate removal of large individuals but also the herbicidal control of smaller ones. [ABSTRACT FROM AUTHOR]

Copyright of Silva Lusitana is the property of Unidade de Investigacao de Silvicultura e Productos Florestais and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Silva Lusitana is the property of Unidade de Investigacao de Silvicultura e Productos Florestais and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Historically, fire has played a dominant role in shaping many forest plant communities. Mediterranean-type vegetation is one of the world's major fire-prone biomes, with conifer forests among the most flammable ecosystems in the Mediterranean region. Prescribed fires are a powerful tool for reducing fire hazards by decreasing amounts of fuel. The main objective of this work is to analyse the effects of prescribed burning on the understory vegetation composition and species richness in a reforested stand of Pinus canariensis. Nine 900 m2 plots were settled in areas were prescribed burning had been applied in the last 5 years; their respective control plots were established in nearby unburnt areas of similar environmental conditions. In each plot, we systematically selected 10 points in which we sampled the presence of species in 1m2 quadrats and analysed for species richness and species composition. No significant changes in the number of species richness were found medium term after prescribed burning. Also, when we analysed species composition, no discrimination among the control and burnt plots was detected. From an ecological point of view, prescribed fire is a good practice to reduce biomass accumulation in P. canariensis reforested stands, resulting in low effects in species composition and richness. However, it would be necessary long-term studies to evaluate the effects of prescribed burning intensity, season and frequency, as well as positive effects on the naturalization of these artificial stands. [ABSTRACT FROM AUTHOR]

Global warming can be mitigated by carbon sequestration through forestry and agroforestry. For countries with low industrial development, carbon sequestration also represents an opportunity to fund sustainable development. In the Canary Islands, CO2 emissions are above the average for Spain, in fact, they are estimated to be three times higher. Authorities have been working in recent years to reduce these emissions and increase carbon sequestration. Afforestation on the island of Tenerife has been carried out mainly using an endemic pine species (Pinus canariensis), the dominant species of native pine forest stands. However, the exotic Pinus radiata has also been introduced in some areas. The success of exotic invasive species is often attributed to their capacity for fast growth, particularly when resources are not limited and can continue to increase. In this situation, exotic species are more competitive compared to native ones. We evaluated the capacity to absorb CO2 of P. radiata vs. P. canariensis under similar environmental conditions and planted during the same period. Through allometric equations for above ground biomass, we estimated the amount of biomass and carbon content in individuals and extrapolated these results to the rest of the mass (in the the Corona Forestal Natural Park in Tenerife). Our preliminary results revealed that P. radiata and P. canariensis sequester different amounts of carbon under similar environmental conditions. The carbon capture strategy of a species is strongly associated with disturbance, with species from disturbed sites having traits that confer capacity for fast growth. We suggest that P. radiata has a higher carbon sequestration capability per individual than the native species P. canariensis. However, the much larger extensions and density of P. canariensis make this species the main carbon sink on the island. [ABSTRACT FROM AUTHOR]

Prescribed fires are a powerful tool for reducing fire hazards by decreasing amounts of fuel. The main objective is to analyze the effects of prescribed burning on the understory vegetation composition as well as on the soil characteristics of a reforested stand of Pinus canariensis. The study attempts to identify the effects of the preburning treatment of cutting understory vegetation on the floristic parameters of the vegetation community. This study was carried out for two years following a prescribed fire in a Canarian pine stand. Cutting and burning treatment affected species composition and increased diversity. Burnt and cut plots were characterized by a diverse array of herbaceous species and by a lower abundance of Teline microphylla (endemic legume), although burning apparently induced its germination. Cut treatment was more consistently differentiated from the control plots than burnt treatment. Soil K decreased after both treatments, pH slightly decreased after cutting, while P and Ca increased after fire. From an ecological point of view, prescribed burning is a better management practice than cutting the woody species of the understory. However, long-term studies would be necessary to evaluate the effects of fire intensity, season and frequency in which the prescribed burning is applied. [ABSTRACT FROM AUTHOR]

Prescribed fires are a powerful tool for reducing fire hazards by decreasing amounts of fuel. The main objective is to analyze the effects of prescribed burning on the understory vegetation composition as well as on the soil characteristics of a reforested stand of Pinus canariensis. The study attempts to identify the effects of the preburning treatment of cutting understory vegetation on the floristic parameters of the vegetation community. This study was carried out for two years following a prescribed fire in a Canarian pine stand. Cutting and burning treatment affected species composition and increased diversity. Burnt and cut plots were characterized by a diverse array of herbaceous species and by a lower abundance of Teline microphylla (endemic legume), although burning apparently induced its germination. Cut treatment was more consistently differentiated from the control plots than burnt treatment. Soil K decreased after both treatments, pH slightly decreased after cutting, while P and Ca increased after fire. From an ecological point of view, prescribed burning is a better management practice than cutting the woody species of the understory. However, long-term studies would be necessary to evaluate the effects of fire intensity, season and frequency in which the prescribed burning is applied.