Showing papers by "Nikolaos M. Fyllas published in 2013"

On the delineation of tropical vegetation types with an emphasis on forest/savanna transitions

Abstract: Background: There is no generally agreed classification scheme for the many different vegetation formation types occurring in the tropics. This hinders cross-continental comparisons and causes confusion as words such as ‘forest’ and ‘savanna’ have different meanings to different people. Tropical vegetation formations are therefore usually imprecisely and/or ambiguously defined in modelling, remote sensing and ecological studies. Aims: To integrate observed variations in tropical vegetation structure and floristic composition into a single classification scheme. Methods: Using structural and floristic measurements made on three continents, discrete tropical vegetation groupings were defined on the basis of overstorey and understorey structure and species compositions by using clustering techniques. Results: Twelve structural groupings were identified based on height and canopy cover of the dominant upper stratum and the extent of lower-strata woody shrub cover and grass cover. Structural classifications di...

Light inhibition of leaf respiration as soil fertility declines along a post-glacial chronosequence in New Zealand: an analysis using the Kok method

Abstract: Our study quantified variations leaf respiration in darkness (R D) and light (R L), and associated traits along the Franz Josef Glacier soil development chronosequence in New Zealand. At six sites along the chronosequence (soil age: 6, 60, 150, 500, 12,000 and 120,000 years old), we measured rates of leaf R D, R L (using Kok method), light-saturated CO2 assimilation rates (A), leaf mass per unit area (M A), and concentrations of leaf nitrogen ([N]), phosphorus ([P]), soluble sugars and starch. The chronosequence was characterised by decreasing R D, R L and A, reduced [N] and [P] and increasing M A as soil age increased. Light inhibition of R occurred across the chronosequence (mean inhibition = 16 %), resulting in ratios of R L:A being lower than for R D:A. Importantly, the degree of light inhibition differed across the chronosequence, being lowest at young sites and highest at old sites. This resulted in R L:A ratios being relatively constant across the chronosequence, whereas R D:A ratios increased with increasing soil age. Log-log R-A-M A-[N] relationships remained constant along the chronosequence. By contrast, relationships linking rates of leaf R to [P] differed among leaves with low vs high [N]:[P] ratios. Slopes of log-log bivariate relationships linking R L to A, M A, [N] and [P] were steeper than that for R D. Our findings have important implications for predictive models that seek to account for light inhibition of R, and for our understanding of how environmental gradients impact on leaf trait relationships

Ecophysiology of Forest and Savanna Vegetation

Abstract: Ecophysiological characteristics of forest and savanna vegetation are compared in an attempt to understand how physiological differences within and between these vegetation types relate to their geographical distributions. A simple ordination first shows that although precipitation exerts a key effect on Amazonian vegetation distributions, soil characteristics are also important. In particular, it is found that under similar precipitation regimes, deciduous forests tend to occur on more fertile soils than do cerrado vegetation types. A high subsoil clay content is also important in allowing the existence of semievergreen forests at only moderate rainfall. Such observations are consistent with biome specific physiological characteristics. For example, deciduous trees have higher nutrient requirements than do evergreen ones which also tend to have characteristics associated with severe water deficits such as a low specific leaf area. Nutrient contents and photosynthetic rates are lower than for savanna than for forest species with several ecosystem characteristics suggesting a primary limitation of nitrogen on savanna productivity. By contrast, phosphorus seems to constrain the productivity of most Amazonian forest types. Differentiation is made between the fast-growing, high-nutrient-requiring forest types of western Amazonia and their counterparts in eastern Amazonia, which tend to occupy infertile but deeper soils of high water-holding ability. On the basis of observed physiological characteristics of the various vegetation forms, it is argued that, should Amazonian precipitation decline sharply in the future, the slower growing forests of eastern Amazonia will transform directly into an evergreen cerrado type vegetation but with the more fertile western Amazonian forests being replaced by some form of drought-deciduous vegetation.

Viticulture: Climate Relationships in Greece and Impacts of Recent Climate Trends: Sensitivity to “Effective” Growing Season Definitions

Abstract: Recent research has shown significant shifts in the phenological stages of grapevines (Vitis vinifera L.) due to temperature changes. That study investigated the relation between temperature and harvest time in grape growing regions of Greece. Harvest dates were collected on eight different varieties and regions: four island [Muscat of Alexandria (Limnos), White Muscat (Samos), Assyrtiko (Santorini), Athiri (Rodos)] and four inland [Roditis (Anchialos), Agiorgitiko (Nemea), Mavrodafni (Pyrgos), Xinomauro (Naoussa)] areas. In two cases (Limnos, Pyrgos), must sugar concentration (baume degrees) were also collected. Climatic primary (precipitation, mean, maximum and minimum temperature) and secondary (growing degree days, diurnal temperature range and extreme events) data were computed for three periods [calendar year, growing season (April–October) and ripening (according to variety)]. The most frequent significant trends of climatic parameters and crop-climate relationships were observed for island regions compared to inland ones. Calendar year and growing season-based analyses presented the most frequently significant viticulture-climate relationships, with mean, maximum air temperature and growing degree days. The direction and magnitude of harvest time responses were not particularly sensitive to the choice of “effective” growing season definition. A negative harvest response was identified for all variables except for DPrec in three island stations and DTmax > 35°C in Rodos.