10 research outputs found

    Analysis of ecological thresholds in a temperate forest undergoing dieback.

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    Positive feedbacks in drivers of degradation can cause threshold responses in natural ecosystems. Though threshold responses have received much attention in studies of aquatic ecosystems, they have been neglected in terrestrial systems, such as forests, where the long time-scales required for monitoring have impeded research. In this study we explored the role of positive feedbacks in a temperate forest that has been monitored for 50 years and is undergoing dieback, largely as a result of death of the canopy dominant species (Fagus sylvatica, beech). Statistical analyses showed strong non-linear losses in basal area for some plots, while others showed relatively gradual change. Beech seedling density was positively related to canopy openness, but a similar relationship was not observed for saplings, suggesting a feedback whereby mortality in areas with high canopy openness was elevated. We combined this observation with empirical data on size- and growth-mediated mortality of trees to produce an individual-based model of forest dynamics. We used this model to simulate changes in the structure of the forest over 100 years under scenarios with different juvenile and mature mortality probabilities, as well as a positive feedback between seedling and mature tree mortality. This model produced declines in forest basal area when critical juvenile and mature mortality probabilities were exceeded. Feedbacks in juvenile mortality caused a greater reduction in basal area relative to scenarios with no feedback. Non-linear, concave declines of basal area occurred only when mature tree mortality was 3-5 times higher than rates observed in the field. Our results indicate that the longevity of trees may help to buffer forests against environmental change and that the maintenance of old, large trees may aid the resilience of forest stands. In addition, our work suggests that dieback of forests may be avoidable providing pressures on mature and juvenile trees do not pass critical thresholds

    Seasonal shifts in clutch size and egg size in the side-blotched lizard, Uta stansburiana Baird and Girard

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    There is evidence that the side-blotched lizard, Uta stansburiana , and some other organisms of temperate latitudes produce fewer and larger eggs as the reproductive season progresses. There are at least two models that could explain this phenomenon.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47737/1/442_2004_Article_BF00376891.pd

    Uluru (Ayers Rock) and Kata Tjuta (The Olgas): Inselbergs of Central Australia

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    Uluru and Kata Tjuta are inselbergs standing in isolation in the desert plains of central Australia. Uluru is a beveled bornhardt shaped steeply dipping Cambrian arkose. Kata Tjuta is a complex of domes, each developed by fracture-controlled weathering and erosion of a mass of gently dipping conglomerate, also of Cambrian age. The sedimentary formations strike northwest to southeast and the compartments on which the residuals are formed were compressed as a result of either cross- or interference folding. They were exposed as low hills by the latest Cretaceous and possibly as early as the Triassic, since which time the detailed morphology of the forms shows that they have come to stand higher and higher in the relief as a result of the episodic lowering of the surrounding plains. Their persistence is attributed to reinforcement effects.C. R. Twidalehttp://www.springer.com/earth+sciences+and+geography/geography/book/978-90-481-3054-

    Estimation of the Mortalities of the Immature Stages and Adults

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    A Second bibliography on semi-Markov processes

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    Recent technological advancements in stem cell research for targeted therapeutics

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