Showing papers by "Nikolaos M. Fyllas published in 2014"

Analysing Amazonian forest productivity using a new individual and trait-based model (TFS v.1)

Abstract: . Repeated long-term censuses have revealed large-scale spatial patterns in Amazon basin forest structure and dynamism, with some forests in the west of the basin having up to a twice as high rate of aboveground biomass production and tree recruitment as forests in the east. Possible causes for this variation could be the climatic and edaphic gradients across the basin and/or the spatial distribution of tree species composition. To help understand causes of this variation a new individual-based model of tropical forest growth, designed to take full advantage of the forest census data available from the Amazonian Forest Inventory Network (RAINFOR), has been developed. The model allows for within-stand variations in tree size distribution and key functional traits and between-stand differences in climate and soil physical and chemical properties. It runs at the stand level with four functional traits – leaf dry mass per area (Ma), leaf nitrogen (NL) and phosphorus (PL) content and wood density (DW) varying from tree to tree – in a way that replicates the observed continua found within each stand. We first applied the model to validate canopy-level water fluxes at three eddy covariance flux measurement sites. For all three sites the canopy-level water fluxes were adequately simulated. We then applied the model at seven plots, where intensive measurements of carbon allocation are available. Tree-by-tree multi-annual growth rates generally agreed well with observations for small trees, but with deviations identified for larger trees. At the stand level, simulations at 40 plots were used to explore the influence of climate and soil nutrient availability on the gross (ΠG) and net (ΠN) primary production rates as well as the carbon use efficiency (CU). Simulated ΠG, ΠN and CU were not associated with temperature. On the other hand, all three measures of stand level productivity were positively related to both mean annual precipitation and soil nutrient status. Sensitivity studies showed a clear importance of an accurate parameterisation of within- and between-stand trait variability on the fidelity of model predictions. For example, when functional tree diversity was not included in the model (i.e. with just a single plant functional type with mean basin-wide trait values) the predictive ability of the model was reduced. This was also the case when basin-wide (as opposed to site-specific) trait distributions were applied within each stand. We conclude that models of tropical forest carbon, energy and water cycling should strive to accurately represent observed variations in functionally important traits across the range of relevant scales.

Viticulture–climate relationships in Greece: the impacts of recent climate trends on harvest date variation

Abstract: Climate characteristics and relationships with indigenous varieties in Greece are examined to better understand how these varieties perform in their native climate and assess the impact regional climate change has on the Greek wine industry. Thus, harvest dates (� H) for eight indigenous varieties and regions, along with climate data, were gathered and systematically explored using linear regression models and principal component analysis for three 'effective' growing season time period definitions (calendar year, growing season and ripening period). The eight study regions had marked differences in their general climatic characteristics, mainly between mainland and island areas. � H response was not particularly sensitive to time period definition. In five out of eight regions, a systematic shift ofH was identified (earlier harvest), mainly driven by changes in maximum and minimum temperatures. Significant trends in climate parameters and viticulture-climate relationships were more evident for island regions when compared to mainland locations. Moreover, areas with late ripening varieties were shown to be less sensitive to climate changes. Only in one region harvest was delayed, possibly due to non-climate factors. The identification of up-to-date climate and grapevine phenology relationships could be an important step for broader and more confident future assessments of climate suitability for viticulture and climate change impacts in Greece, and provide insights into how lesser known varieties might perform in other regions.

Species adaptive strategies and leaf economic relationships across serpentine and non-serpentine habitats on Lesbos, eastern Mediterranean.

Abstract: Shifts in species' traits across contrasting environments have the potential to influence ecosystem functioning. Plant communities on unusually harsh soils may have unique responses to environmental change, through the mediating role of functional plant traits. We conducted a field study comparing eight functional leaf traits of seventeen common species located on both serpentine and non-serpentine environments on Lesbos Island, in the eastern Mediterranean. We focused on species' adaptive strategies across the two contrasting environments and investigated the effect of trait variation on the robustness of core ‘leaf economic’ relationships across local environmental variability. Our results showed that the same species followed a conservative strategy on serpentine substrates and an exploitative strategy on non-serpentine ones, consistent with the leaf economic spectrum predictions. Although considerable species-specific trait variability emerged, the single-trait responses across contrasting environments were generally consistent. However, multivariate-trait responses were diverse. Finally, we found that the strength of relationships between core ‘leaf economic’ traits altered across local environmental variability. Our results highlight the divergent trait evolution on serpentine and non-serpentine communities and reinforce other findings presenting species-specific responses to environmental variation.