Specific leaf area and leaf area index in developing stands of Fagus sylvatica L. and Picea abies Karst

European beech (Fagus sylvatica L.) and Norway spruce (Picea abies Karst.) are two of the most ecologically and economically important forest tree species in Europe. These two species co-occur in many locations in Europe, leading to direct competition for canopy space. Foliage characteristics of two naturally regenerated pure stands of beech and spruce with fully closed canopies were contrasted to assess the dynamic relationship between foliage adaptability to shading, stand LAI and tree growth. We found that individual leaf size is far more conservative in spruce than in beech. Individual leaf and needle area was larger at the top than at the bottom of the canopy in both species. Inverse relationship was found for specific leaf area (SLA), highest SLA values were found at lowest light availability under the canopy. There was no difference in leaf area index (LAI) between the two stands, however LAI increased from 10.8 to 14.6 m2m-2 between 2009 and 2011. Dominant trees of both species were more efficient in converting foliage mass or area to produce stem biomass, although this relationship changed with age and was species-specific. Overall, we found larger foliage plasticity in beech than in spruce in relation to light conditions, indicating larger capacity to exploit niche openings

Contrasting effects of environmental change factors on the radial growth of co-occurring European beech and fir trees across Europe

Under predicted climate change, silver fir (Abies alba) and European beech (Fagus sylvatica) are the most likely replacement species for the more heat- and drought-sensitive monocultures of Norway spruce (Picea abies) planted across large parts of continental Europe. Our current understanding of the climate-related adaptation potential of fir and beech mixtures is, however, limited. Here we compile and analyse 2855 tree-ring width (TRW) series from 17 mixed beech-fir forest sites in five European countries. Dendroecological techniques that combine various detrending methods with an application of documented environmental change trends reveal wide variation of radial growth between fir and beech across space and time. Coincidental with peak SO2 emissions, the growth of silver fir declined between 1950 and 1980 at most sites, whereas beech growth increased during this period. Correspondent to a significant warming trend from 1990–2010, average beech growth declined, but silver fir growth increased. Our observations of long-term growth trends support the replacement of spruce monocultures with multi-species mixtures that have demonstrated a higher tolerance of environmental changes

Impact of soil compaction heterogeneity and moisture on maize (Zea mays L.) root and shoot development

International audienceSoil compaction heterogeneity and water content are supposed to be decisive factors influencing plant growth. Our experiment focused on simulation of two soil moisture levels (0.16 and 0.19 g/g) plus two levels of clod proportion (30 and 60% volume) and their effects on root and leaf variables of maize (Zea mays L.). We studied number of primary and lateral roots as well as primary root length at the particular soil depths. Statistical tests showed that the decrease rate of the number of roots versus depth was significantly affected by the two studied factors (P < 0.01). Soil moisture and clod occurrence, interactively, affected leaf biomass (P = 0.02). Presence of clods modified root morphological features. Particularly, the diameter of primary roots in the clods was significantly higher than of those grown in fine soil (P < 0.01). For primary roots, which penetrated clods, branching density decreased considerably for the root segments located just after the clods (P = 0.01). Regarding their avoidance to clods and tortuosity, large differences were found between primary roots grown in the contrasting soil environment

Parallel algorithms for finding a suboptimal fundamental-cycle set in a graph

An NP-complete problem of finding a fundamental-cycle set of a graph G with minimum total length is considered. Two parallel algorithms of O(n/p + n log n log p) and O(m + n/p + n log(n/p) + n log p) costs to find a suboptimal solution to this problem are presented (p is a number of processors, n is a number of vertices, and m is a number of edges of G). The algorithms partition an edge and vertex set of G among processors, respectively, and use a new heuristic method to solve the problem. A message-based tree-connected MIMD computer is assumed as a model of parallel computations. The algorithms were implemented for a binary tree of 15 transputers, and the experiments were conducted on a wide range of random graphs. The results show that the vertex set partition algorithm with inferior theoretical cost gives better speedups and finds the fundamental-cycle sets of shorter total lenghts as compared to the edge set partition algorithm