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Mortality rate is thought to show a U-shape relationship to tree size. This shape could result from a decrease of competition-related mortality as diameter increases, followed by an increase of senescence and disturbance-related mortality for large trees. Modeling mortality rate as a function of diameter is nevertheless difficult, first because this relationship is strongly nonlinear, and second because data can be unbalanced, with few observations for large trees. Parametric functions, which are inflexible and sensitive to the distribution of observations, tend to introduce biases in mortality rate estimates. In this study we use mortality data for Abies alba Mill. and Picea abies (L.) Karst. to demonstrate that mortality rate estimates for extreme diameters were biased when using classical parametric functions. We then propose a semiparametric approach allowing a more flexible relationship between mortality and diameter. We show that the relatively shadetolerant A. alba has a lower annual mortality rate (2.75%) than P. abies (3.78%) for small trees (DBH La relation entre taux de mortalite et taille des arbres presente une forme en U. Cette forme serait associee a une diminution de la mortalite due a la competition pour les faibles diametres, suivie d'une augmentation de la mortalite due a la senescence et aux perturbations. La modelisation du taux de mortalite en fonction du diametre est difficile, car la relation est fortement non-lineaire et car les donnees sont desequilibrees, avec peu d'observations pour les gros arbres. Les fonctions parametriques habituellement utilisees sont peu flexibles et sensibles a la repartition des donnees. Nous avons etudie la mortalite d'Abies alba Mill. et de Picea abies (L.) Karst. pour demontrer que l'estimation du taux de mortalite pour des diametres extremes etait biaisee lorsque fon utilisait des fonctions parametriques. Nous proposons une approche semi-parametrique plus flexible pour representer la relation entre mortalite et diametre. Nous montrons qu'A. alba, (espece la plus tolerante a (ombre, a un taux de mortalite annuel plus faible (2,75 %) que P. abies (3,78 %) pour de faibles DBH ( [Traduit par la Redaction], Introduction Understanding how mortality risk is influenced by tree size is frustrated by the fact that tree death is rarely observed, especially for large trees. The relationship between size and [...]

To authenticate to the full-text of this article, please visit this link: http://dx.doi.org/10.1111/j.1365-2745.2009.01507.x Byline: David A. Coomes (1,2), Georges Kunstler (1,3), Charles D. Canham (4), Elaine Wright (5) Keywords: coexistence; forest dynamics; light transmission; niche differentiation; richness-productivity relationships; shade tolerance Abstract: Summary A central concept in forest ecology is that differences in the growth rates and shade tolerances of tree species determine patterns of secondary succession. The most shade-tolerant tree species are the competitive dominants in late-successional forests, while species with fast growth rates persist through rapid establishment after disturbance. There is ample support for niche differentiation along the shade-tolerance axis, at least for temperate forests, but less thought has been given to the range of shade tolerances and growth rates encountered within a community and to how it might vary along environmental gradients. We hypothesized that a wider range of growth rates and shade tolerances are found on nutrient-rich soils, because such soils not only support fast-growing species with high metabolic rates, but also species capable of tolerating the very deep shade cast by forest canopies growing where nutrients are plentiful. We test our hypothesis by quantifying light transmission through two neighbouring forests in southern New Zealand, one on phosphorus-rich alluvial soil and one on phosphorus-depleted marine-terrace soil, and comparing the growth rates of saplings on these contrasting sites. Less light was transmitted to the forest floor on alluvial sites than on marine terraces (2.5% vs. 7.5% daylight, on average) and neighbourhood analyses within mapped stands indicated that large-leaved subcanopy species were responsible for intercepting that extra light. Sapling growth was strongly inhibited by shade in the understorey of the alluvial forests, but was less inhibited under the terrace forests. Fast-growing subcanopy species were common on the alluvial sites and these species had characteristically soft leaves and high foliar-nutrient concentrations. Slow-growing shade-tolerant species were also abundant on these sites. Therefore, the interspecific variance in growth rates was greater on nutrient-rich sites, supporting our hypothesis of a greater range of shade tolerance niches on better soils. Of the five species found on both forest sites, all five had greater high-light growth rate on the alluvial sites. Synthesis: A wider range of growth rates was observed in the nutrient-rich forests. This wider range may translate into a greater number of shade tolerance niches and thereby provides an explanation for the greater numbers of species commonly found on nutrient-rich soils when compared with neighbouring nutrient-poor sites. Author Affiliation: (1)Forest Ecology and Conservation Group, Department of Plant Sciences, University of Cambridge, Downing Street, Cambridge CB3 2EA, UK (2)Landcare Research, PO Box 40 Lincoln 7640, New Zealand (3)Cemagref - U.R. Mountain Ecosystems, 2, rue de la Papeterie, BP 76, 38402 St-Martin d'Heres Cedex, France (4)Cary Institute of Ecosystem Studies, Box AB, Millbrook, NY 12545, USA (5)Department of Conservation, PO Box 13049, 3/137 Kilmore Street, Christchurch, New Zealand Article History: Received 2 November 2008; Accepted 20 March 2009Handling Editor: John Lee Article note: (*) Correspondence author. E-mail: dac18@cam.ac.uk

To authenticate to the full-text of this article, please visit this link: http://dx.doi.org/10.1111/j.1365-2745.2009.01482.x Byline: Georges Kunstler (1,2), David A. Coomes (1), Charles D. Canham (3) Keywords: growth; growth-survival trade-off; mortality; saplings; seedlings; shade tolerance; size effect; SORTIE/NZ Abstract: Summary A trade-off between growth in high-light and survival in low-light of species is often proposed as a key mechanism underpinning the dynamics of trees in forest communities. Yet, growth and survival are known to depend on plant size and few studies have analysed how this trade-off can vary between juvenile life stages and the potential consequences of the trade-off for the differences in regeneration rate between species in mixed forests. We quantified growth and mortality for two different juvenile life stages - seedlings and saplings - of seven tree species common in temperate rain forests in New Zealand using data from field studies. We found strong evidence that the ranking of species for survival in shade and growth in full light was affected by size. There was a trade-off between seedling survival in low light and sapling height growth in high light, but no trade-offs were observed when considering other combinations of life stages (seedling growth vs. seedling survival, seedling growth vs. sapling survival, or sapling growth vs. sapling survival). We ran simulations with an individual-based forest dynamics model - SORTIE/NZ - to explore how the trade-off drives the differences in tree species regeneration success in gaps vs. under closed forest conditions. These simulations indicate that because species' ranks in shade tolerance varied with life stage, regeneration success was not predicted from knowledge of tree performance at a single life stage. For instance, high-light sapling growth was a strong determinant of regeneration success in forest gaps, but seedling growth was also influential. Under closed forest, regeneration success was primarily limited by low-light mortality at the seedling stage, but seedling growth and sapling survival were also influential. Synthesis. Growth-survival trade-offs can be strongly affected by the size of the individual analysed, resulting in completely different rankings of the shade tolerance of species across different juvenile life stages. Performance of both seedlings and saplings influenced regeneration success, highlighting the need to consider growth-survival trade-offs and the shade-tolerance strategies of tree species over a large range of juvenile sizes. Author Affiliation: (1)Department of Plant Sciences, University of Cambridge, Downing Street, Cambridge CB3 2EA, UK (2)Cemagref, U.R. Ecosystemes Montagnards, 2 rue de la Papeterie, BP 76 38402 St-Martin-d'Heres, Cedex, France (3)Cary Institute of Ecosystem Studies, Box AB, Millbrook, NY 12545, USA Article History: Received 8 July 2008; accepted 12 January 2009Handling Editor: Jason Fridley Article note: (*) Correspondence author. E-mail: georges.kunstler@cemagref.fr

To purchase or authenticate to the full-text of this article, please visit this link: http://dx.doi.org/10.1111/j.1365-2745.2007.01261.x Byline: JENNIE N. BEE (*), GEORGES KUNSTLER (*[double dagger]), DAVID A. COOMES (*[dagger]) Keywords: herbivory; invasive species; plant growth; plant-herbivore interactions; red deer; simulated browsing Abstract: Summary A prominent idea in the literature on plant-herbivore interactions is that fast-growing species have low resistance but high resilience to herbivory. In other words, fast-growing species are selectively eaten by herbivores but recover quickly following damage. Many studies have challenged the generality of this theory, but little attention has been paid to plant species that have evolved in the absence of major groups of herbivores. Here we analyse whether this resistance-resilience trade-off applies to New Zealand woody species, which evolved without exposure to mammalian herbivores until their introduction in 19th century. We simulated deer browse by clipping saplings of 12 tree species to varying extents (0, 20, 40, 80 and 100% of leaf-bearing branches removed), and quantified the shoot growth, diameter growth and survival of these saplings. The time taken to regrow the removed branches was generally slow, but varied among species. For example, species took between 0.5 and 3 years to recover from removal of 60% of branches. It was the inherently fast-growing species that recovered most quickly. Some species had stimulated shoot growth at moderate levels of clipping (40-60%) but this effect had relatively little effect on recovery time compared with differences in potential growth rates of species. Diameter growth rate fell linearly with increased clipping intensity for all 12 species, and there was no indication of recovery 2 years after the treatment. We speculate that saplings invested in rebuilding their canopies following clipping, and that few resources were left over for diameter growth. Few saplings died as a result of clipping, except when 100% of leaf-bearing shoots were removed, in which case five species died in substantial numbers (> 15%), including all three conifers in the study. Previous work has shown that the most palatable species (i.e. those with low resistance) have leaves with low fibre content. We find that these species are relatively fast growing and recover most rapidly from simulated browsing (i.e. are highly resilient). This provides some support for a resistance-resilience trade-off related to potential growth rates. Deer invasion in New Zealand was associated with the loss of short soft-leaved tree species from the browse layer. Our study suggests that the most palatable species have the potential to grow fast and may be in a relatively strong position to recover if deer are eradicated. Author Affiliation: (*)Department of Plant Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EA, UK, ([dagger])Landcare Research, PO Box 69, Lincoln, New Zealand, and ([double dagger])Cemagref - Unite de Recherche Ecosystemes Montagnards, B.P. 76, 38402 St-Martin-D'Heres cedex, France Article History: Received 13 January 2007; accepted 13 April 2007Handling Editor: Bob Jefferies Article note: Correspondence: D. A. Coomes (tel. 01223 333911; fax 01223 333953; e-mail dac18@cam.ac.uk).

Abstract: Accurate predictions about plant invasions require estimation of demographic and dispersal parameters in low-density, expanding populations. We used inverse modelling on the spatial distribution of seedlings to estimate the [...]

Abstract: Encroachment of trees into low-productivity grasslands is a serious threat to grassland biodiversity throughout Europe. Although the rate of encroachment of trees into grassland is variable and poorly understood, [...]