Martínez-Vilalta J., Mencuccini M., Vayreda J., Retana J. (2010) Interspecific variation in functional traits, not climatic differences among species ranges, determines demographic rates across 44 temperate and Mediterranean tree species. Journal of Ecology. 98: 1462-1475.EnllaçDoi: 10.1111/j.1365-2745.2010.01718.x
Surprisingly little is known about the relationship between functional traits and demographic rates of tree species under field conditions, particularly for non-tropical species. We studied the interspecific relationship between key functional traits (wood density (WD), maximum tree height, specific leaf area, nitrogen (N) content of leaves, leaf size and seed mass), demographic rates (relative growth rate (RGR) and mortality rate (MR)) and climatic niche for the 44 most abundant tree species in Spain. Demographic data were derived from the Spanish Forest Inventory, a repeated-measures scheme including c. 90 000 permanent plots spread over a territory of c. 500 000 km[TD-SUP-OPEN]2. Functional traits data came primarily from a more detailed forest inventory carried out in Catalonia, NE Spain. Our study region covers a wide range of climatic conditions and, not surprisingly, the studied species differed markedly in their climatic niche. Despite that fact, our results showed that the variability in demographic rates across species was much more related to differences in functional traits than to differences in the average climate among species. Maximum tree height and, particularly, WD, emerged as key functional traits, and were the best predictors of demographic rates in our study. These two variables also mediated the marginally significant relationship between RGR and MR, suggestive of a weak trade-off between growth and survival. The main aspects of our results were not altered by the explicit incorporation of phylogenetic effects, suggesting that the observed relationships are not due to divergences between a few major clades. Synthesis. Our study gives support to the notion that variation in functional traits across species allows them to perform largely independently of climatic conditions along environmental gradients. © 2010 The Authors. Journal compilation © 2010 British Ecological Society.
Mencuccini M., Martinez-Vilalta J., Piñol J., Loepfe L., Mireia B., Alvarez X., Camacho J., Gil D. (2010) A quantitative and statistically robust method for the determination of xylem conduit spatial distribution. American Journal of Botany. 97: 1247-1259.EnllaçDoi: 10.3732/ajb.0900289
Premise of the study: Because of their limited length, xylem conduits need to connect to each other to maintain water transport from roots to leaves. Conduit spatial distribution in a cross section plays an important role in aiding this connectivity. While indices of conduit spatial distribution already exist, they are not well defi ned statistically. Methods: We used point pattern analysis to derive new spatial indices. One hundred and fi ve cross-sectional images from different species were transformed into binary images. The resulting point patterns, based on the locations of the conduit centersof-area, were analyzed to determine whether they departed from randomness. Conduit distribution was then modeled using a spatially explicit stochastic model. Key results: The presence of conduit randomness, uniformity, or aggregation depended on the spatial scale of the analysis. The large majority of the images showed patterns signifi cantly different from randomness at least at one spatial scale. A strong phylogenetic signal was detected in the spatial variables. Conclusions: Conduit spatial arrangement has been largely conserved during evolution, especially at small spatial scales. Species in which conduits were aggregated in clusters had a lower conduit density compared to those with uniform distribution. Statistically sound spatial indices must be employed as an aid in the characterization of distributional patterns across species and in models of xylem water transport. Point pattern analysis is a very useful tool in identifying spatial patterns. © 2010 Botanical Society of America.
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