Sardans J., Peñuelas J., Coll M., Vayreda J., Rivas-Ubach A. (2012) Stoichiometry of potassium is largely determined by water availability and growth in Catalonian forests. Functional Ecology. 26: 1077-1089.EnllaçDoi: 10.1111/j.1365-2435.2012.02023.x
The study of the relationships between organisms and environmental elemental stoichiometry and ecosystem structure and function has recently received increasing attention. Some elements, however, have been less studied or have even been neglected. One of these elements is K, despite its critical importance in the water economy of plants. We hypothesized that K concentrations and especially K contents (concentrations × biomass), their stoichiometries with respect to C, N, and P contents, and their relative allocations to foliar and woody compartments would be linked to climatic gradients in the availability of water, forest type and growth. We tested this hypothesis by analysing the data set of the Catalan Forest Inventory. Evergreens, the type of tree with the slowest growth, showed the highest K contents, especially in wood, and the lowest plasticity to change the stoichiometry of K within and between foliar and woody biomasses along climatic gradients. The allocation of K to leaves in relation to the allocation of C, N and P increased with mean annual precipitation (MAP) and was concomitant with decreases in the allocation of K to wood in relation to the allocation of C, N and P (higher K:C L/W, K:N L/W and K:P L/W). In summer, the driest period, higher K:C, K:N and K:P content ratios in leaves were accompanied by lower K:C, K:N and K:P content ratios in wood, mainly in the species at the driest sites. Higher K:C and K:N content ratios in leaves and above-ground biomass in all forest types, and higher K:C L/W and K:N L/W in conifers and deciduous trees were related to higher growth. K contents of leaves were better correlated with tree growth than were K concentrations of leaves in all forest types. These results show that the stoichiometry of K is strongly related to the availability of water and that the uptake of K is more related to the uptake of water than the uptake of N and P. Stoichiometric differences involving K are related to both the response of plants to drought and to plant growth. K thus plays a key role, together with N and P, in the response of plants to climatic gradients for improving the capacities for growth and adaptation to water stress along environmental gradients and through time (seasons). Moreover, these results show that the differences in stoichiometric composition and plasticity involving K contents can underlie the long-term adaptation of trees to different ecological styles of life. K should thus be considered in ecological stoichiometric studies of terrestrial plants. © 2012 The Authors. Functional Ecology © 2012 British Ecological Society.
Vayreda J., Gracia M., Canadell J.G., Retana J. (2012) Spatial Patterns and Predictors of Forest Carbon Stocks in Western Mediterranean. Ecosystems. 15: 1258-1270.EnllaçDoi: 10.1007/s10021-012-9582-7
Mediterranean semi-arid forest ecosystems are especially sensitive to external forcing. An understanding of the relationship between forest carbon (C) stock, and environmental conditions and forest structure enable prediction of the impacts of climate change on C stocks and help to define management strategies that maximize the value of forests for C mitigation. Based on the national forest inventory of Spain (1997-2008 with 70,912 plots), we estimated the forest C stock and spatial variability in Peninsular Spain and, we determined the extent to which the observed patterns of stand C stock can be explained by structural and species richness, climate and disturbances. Spain has an average stand C stock of 45.1 Mg C/ha. Total C stock in living biomass is 621 Tg C (7.8% of the C stock of European forests). The statistical models show that structural richness, which is driven by past land use and life forest history including age, development stage, management activities, and disturbance regime, is the main predictor of stand tree C stock with larger C stocks in structurally richer stands. Richness of broadleaf species has a positive effect on both conifer and broadleaf forests, whereas richness of conifer species shows no significant or even a negative effect on C stock. Climate variables have mainly an indirect effect through structural richness but a smaller direct predictive ability when all predictors are considered. To achieve a greater standing C stock, our results suggest promoting high structural richness by managing for uneven-aged stands and favoring broadleaf over conifer species. © 2012 Springer Science+Business Media, LLC.
Vayreda J., Martinez-Vilalta J., Gracia M., Retana J. (2012) Recent climate changes interact with stand structure and management to determine changes in tree carbon stocks in Spanish forests. Global Change Biology. 18: 1028-1041.EnllaçDoi: 10.1111/j.1365-2486.2011.02606.x
Most temperate forests are accumulating carbon (C) and may continue to do so in the near future. However, the situation may be different in water-limited ecosystems, where the potentially positive effects of C and N fertilization and rising temperatures interact with water availability. In this study, we use the extensive network of plots of two consecutive Spanish national forest inventories to identify the factors that determine the spatial variation of the C stock change, growth, and mortality rate of forests in Peninsular Spain (below- and aboveground). We fitted general linear models to assess the response of C stock change and its components to the spatial variability of climate (in terms of water availability), forest structure (tree density and C stock), previous forest management, and the recent warming trend. Our results show that undisturbed forests in Peninsular Spain are accumulating C at a rate of ~1.4 Mg C ha -1 yr -1, and that forest structural variables are the main determinants of forest growth and C stock change. Water availability was positively related to growth and C accumulation. On the other hand, recent warming has reduced growth rate and C accumulation, especially in wet areas. Spatial variation in mortality (in terms of C loss) was mostly driven by differences in growth rate across plots, and was consistent with 'natural', self-thinning dynamics related to the recent abandonment of forest management over large areas of Spain, with the consequent increase in tree density and competition. Interestingly, the negative effect of warming on forest C accumulation disappears if only managed stands are considered, emphasizing the potential of forest management to mitigate the effects of climate change. However, the effect of forest management was weak and, in some cases, not significant, implying the need of further research on its impact. © 2011 Blackwell Publishing Ltd.
Alvarez A, Gracia M, Vayreda J, Retana J (2011) Patterns of fuel types and crown fire potential in Pinus halepensis forests in the Western Mediterranean Basin. Forest Ecology and Management doi:10.1016/j.foreco.2011.01.039.
Vayreda J, Martínez-Vilalta J, Gracia M, Retana J (2011) Forest structure and management interact with recent changes in climate to determine the current forest carbon stock in Peninsular Spain. Global Change Biology doi: 10.1111/j.1365-2486.2011.02606.x.
Otero I., Boada M., Badia A., Pla E., Vayreda J., Sabaté S., Gracia C.A., Peñuelas J. (2011) Loss of water availability and stream biodiversity under land abandonment and climate change in a Mediterranean catchment (Olzinelles, NE Spain). Land Use Policy. 28: 207-218.EnllaçDoi: 10.1016/j.landusepol.2010.06.002
In the north rim of the Mediterranean region, where forest cover is increasing as a result of land abandonment and temperatures are rising as a result of climate change, there is increasing interest for the effects of such changes on the runoff of water courses. This is a paramount issue for the conservation of many freshwater habitats and species. In this work we studied the effects of both an increase in forest cover after depopulation and land abandonment and an increase in temperature on the runoff of a Mediterranean catchment and on the aquatic and semi-aquatic fauna species of the stream (Olzinelles valley, NE Spain). Although in our simulation no decreasing trend in runoff is detected, the monthly runoff-rainfall ratio is now 15% lower than 30 years ago, a fact that may be attributed to a drier period rather than to the small afforestation experienced by the catchment in the last decades. Other factors such as increasing temperatures, changing rainfall patterns and increasing canopy cover are discussed. The observed decrease in the water flow has caused the disappearance of white-clawed crayfish (Austropotamobius pallipes), Mediterranean barbel (Barbus meridionalis), chub (Squalius cephalus), European eel (Anguilla anguilla), and southern water vole (Arvicola sapidus). Our results suggest that in a progressively warmer climate, and especially after land abandonment processes, management of Mediterranean mountain areas should be oriented towards an appropriate distribution of agrarian and forest land-covers in terms of water availability. Down to the stream scale, the pools that keep water throughout the year should be conserved and extended to enhance its potential to maintain aquatic and semi-aquatic species populations. © 2010 Elsevier Ltd.
Vila-Cabrera A., Martinez-Vilalta J., Vayreda J., Retana J. (2011) Structural and climatic determinants of demographic rates of Scots pine forests across the Iberian Peninsula. Ecological Applications. 21: 1162-1172.EnllaçDoi: 10.1890/10-0647.1
The demographic rates of tree species typically show large spatial variation across their range. Understanding the environmental factors underlying this variation is a key topic in forest ecology, with far-reaching management implications. Scots pine (Pinus sylvestris L.) covers large areas of the Northern Hemisphere, the Iberian Peninsula being its southwestern distribution limit. In recent decades, an increase in severe droughts and a densification of forests as a result of changes in forest uses have occurred in this region. Our aim was to use climate and stand structure data to explain mortality and growth patterns of Scots pine forests across the Iberian Peninsula. We used data from 2392 plots dominated by Scots pine, sampled for the National Forest Inventory of Spain. Plots were sampled from 1986 to 1996 (IFN2) and were resampled from 1997 to 2007 (IFN3), allowing for the calculation of growth and mortality rates. We fitted linear models to assess the response of growth and mortality rates to the spatial variability of climate, climatic anomalies, and forest structure. Over the period of;10 years between the IFN2 and IFN3, the amount of standing dead trees increased 11-fold. Higher mortality rates were related to dryness, and growth was reduced with increasing dryness and temperature, but results also suggested that effects of climatic stressors were not restricted to dry sites only. Forest structure was strongly related to demographic rates, suggesting that stand development and competition are the main factors associated with demography. In the case of mortality, forest structure interacted with climate, suggesting that competition for water resources induces tree mortality in dry sites. A slight negative relationship was found between mortality and growth, indicating that both rates are likely to be affected by the same stress factors. Additionally, regeneration tended to be lower in plots with higher mortality. Taken together, our results suggest a large-scale self-thinning related to the recent densification of Scots pine forests. This process appears to be enhanced by dry conditions and may lead to a mismatch in forest turnover. Forest management may be an essential adaptive tool under the drier conditions predicted by most climate models. © 2011 by the Ecological Society of America.
Vilà-Cabrera A, Martínez-Vilalta J, Vayreda J, Retana J (2010) Structural and climatic determinants of demographic rates of Scots pine forests across the Iberian Peninsula. Ecological Applications 21: 1162-1172, doi: 10.1890/10-0647.1.
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.
Gracia M, Comas L, Vayreda J, Ibàñez JJ, Batlles C, Regalado I (2009) Inventario de bosques singulares de Catalunya. V congreso forestal Español.
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