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Stand Development (stand + development)
Selected AbstractsAssociations among symptoms of dieback in even-aged stands of ash (Fraxinus excelsior L.)FOREST PATHOLOGY, Issue 1 2010J. P. Skovsgaard Summary The objective of this study was to establish statistically based associations among macroscopic symptoms of crown dieback, cankers due to Chalara fraxinea, and symptoms caused by other pathogens and pests on Fraxinus excelsior. A total of 454 trees were observed in two plots of a 15-year-old experimental stand. The symptoms included: (i) overall extent of crown dieback; (ii) dieback of upper parts of the crown; (iii) canker in upper parts of the crown; (iv) wilting foliage; (v) cankers and bark proliferations at the lower part of the stem; and (vi) discolouration at stump or stem base. The analysis suggested that the observed symptoms of crown dieback are caused by a primary disease. The macroscopic symptoms attributed to dieback and canker in the crown were strongly associated. Moreover, the disease was associated with symptoms of Armillaria gallica, but no associations were found for symptoms of Neonectria galligena, Pseudomonas syringae subsp. savastanoi pv. fraxini, Hylesinus fraxini or H. varius when considered collectively. Dieback was more frequent on trees of average or below-average size, suggesting that individual tree resistance decreased with decreasing growth potential or tree vigour. The extent of canker in the crown depended on site conditions and possibly on silvicultural practices. The development of phytosanitary prescriptions for silviculture should primarily be targeted towards young stands as these represent the most critical phases of stand development. [source] Tree rings show competition dynamics in abandoned Castanea sativa coppices after land-use changesJOURNAL OF VEGETATION SCIENCE, Issue 1 2006Patrick Fonti Abstract Questions: As a consequence of socio-economic changes, many Castanea sativa coppices have been abandoned and are now developing past their usual rotation length. Do we have to expect changes in stand structure and composition of abandoned Castanea sativa coppice invaded by other species? Is a tree ring-based approach adequate to early recognise changes in inter-specific competitive interaction? Location: Lowest alpine forest belt of the southern Swiss Alps. Methods: We selected a 60-year old abandoned Castanea sativa coppice stand with sporadic Fagus sylvatica and Quercus cerris mixed in. Using tree-ring based indices we analysed differences in the species-specific response to competition. Analyses were performed by comparing how subject dominant trees (10 Castanea, 5 Fagus, 5 Quercus) have differently faced competition from their immediate Castanea coppice neighbourhood, taking into account the changes over time and space. Results: Although no species appears yet to have made a difference in the surrounding coppice mortality, there are species-specific differences in growth dominance, which indicate potential successional processes. Castanea sativa growth dominated in the early stages of stand development. However, after approximately 30,35 yr Fagus sylvatica and Quercus cerris became much more dominant, indicating a change in competitive potential that does not favour Castanea sativa. Conclusions: Without interventions this coppice will develop into a mixed stand. A tree-ring based approach allows an early recognition of forthcoming changes in stand composition and structure and is likely to be an important tool for forest landscape management. [source] Hydraulic adjustment of Scots pine across EuropeNEW PHYTOLOGIST, Issue 2 2009J. Martínez-Vilalta Summary ,,The variability of branch-level hydraulic properties was assessed across 12 Scots pine populations covering a wide range of environmental conditions, including some of the southernmost populations of the species. The aims were to relate this variability to differences in climate, and to study the potential tradeoffs between traits. ,,Traits measured included wood density, radial growth, xylem anatomy, sapwood- and leaf-specific hydraulic conductivity (KS and KL), vulnerability to embolism, leaf-to-sapwood area ratio (AL : AS), needle carbon isotope discrimination (,13C) and nitrogen content, and specific leaf area. ,,Between-population variability was high for most of the hydraulic traits studied, but it was directly associated with climate dryness (defined as a combination of atmospheric moisture demand and availability) only for AL : AS, KL and ,13C. Shoot radial growth and AL : AS declined with stand development, which is consistent with a strategy to avoid exceedingly low water potentials as tree size increases. In addition, we did not find evidence at the intraspecific level of some associations between hydraulic traits that have been commonly reported across species. ,,The adjustment of Scots pine's hydraulic system to local climatic conditions occurred primarily through modifications of AL : AS and direct stomatal control, whereas intraspecific variation in vulnerability to embolism and leaf physiology appears to be limited. [source] Ectomycorrhizal fungal succession in mixed temperate forestsNEW PHYTOLOGIST, Issue 2 2007Brendan D. Twieg Summary ,,Ectomycorrhizal (ECM) fungal communities of Douglas-fir (Pseudotsuga menziesii) and paper birch (Betula papyrifera) were studied along a chronosequence of forest development after stand-replacing disturbance. Previous studies of ECM succession did not use molecular techniques for fungal identification or lacked replication, and none examined different host species. ,,Four age classes of mixed forests were sampled: 5-, 26-, 65-, and 100-yr-old, including wildfire-origin stands from all four classes and stands of clearcut origin from the youngest two classes. Morphotyping and DNA sequences were used to identify fungi on ECM root tips. ,,ECM fungal diversities were lower in 5-yr-old than in older stands on Douglas-fir, but were similar among age classes on paper birch. Host-specific fungi dominated in 5-yr-old stands, but host generalists were dominant in the oldest two age classes. ECM fungal community compositions were similar in 65- and 100-yr-old stands but differed among all other pairs of age classes. ,,Within the age range studied, site-level ECM fungal diversity reached a plateau by the 26-yr-old age class, while community composition stabilized by the 65-yr-old class. Simple categories such as ,early stage', ,multi stage', and ,late stage' were insufficient to describe fungal species' successional patterns. Rather, ECM fungal succession may be best described in the context of stand development. [source] Relationship between plant hydraulic and biochemical properties derived from a steady-state coupled water and carbon transport modelPLANT CELL & ENVIRONMENT, Issue 3 2003G. KATUL ABSTRACT There is growing evidence that plant stomata have evolved physiological controls to satisfy the demand for CO2 by photosynthesis while regulating water losses by leaves in a manner that does not cause cavitation in the soil,root,xylem hydraulic system. Whether the hydraulic and biochemical properties of plants evolve independently or whether they are linked at a time scale relevant to plant stand development remains uncertain. To address this question, a steady-state analytical model was developed in which supply of CO2 via the stomata and biochemical demand for CO2 are constrained by the balance between loss of water vapour from the leaf to the atmosphere and supply of water from the soil to the leaf. The model predicts the intercellular CO2 concentration (Ci) for which the maximum demand for CO2 is in equilibrium with the maximum hydraulically permissible supply of water through the soil,root,xylem system. The model was then tested at two forest stands in which simultaneous hydraulic, ecophysiological, and long-term carbon isotope discrimination measurements were available. The model formulation reproduces analytically recent findings on the sensitivity of bulk stomatal conductance (gs) to vapour pressure deficit (D); namely, gs = gref(1 , m × lnD), where m is a sensitivity parameter and gref is a reference conductance defined at D = 1 kPa. An immediate outcome of the model is an explicit relationship between maximum carboxylation capacity (Vcmax) and soil,plant hydraulic properties. It is shown that this relationship is consistent with measurements reported for conifer and rain forest angiosperm species. The analytical model predicts a decline in Vcmax as the hydraulic capacity of the soil,root,xylem decreases with stand development or age. [source] Influence of fire severity on stand development of Araucaria araucana,Nothofagus pumilio stands in the Andean cordillera of south-central ChileAUSTRAL ECOLOGY, Issue 6 2010MAURO E. GONZÁLEZ Abstract Fire is the prevalent disturbance in the Araucaria,Nothofagus forested landscape in south-central Chile. Although both surface and stand-replacing fires are known to characterize these ecosystems, the variability of fire severity in shaping forest structure has not previously been investigated in Araucaria,Nothofagus forests. Age structures of 16 stands, in which the ages of approximately 650 trees were determined, indicate that variability in fire severity and frequency is key to explaining the mosaic of forest patches across the Araucaria,Nothofagus landscape. High levels of tree mortality in moderate- to high-severity fires followed by new establishment of Nothofagus pumilio typically result in stands characterized by one or two cohorts of this species. Large Araucaria trees are highly resistant to fire, and this species typically survives moderate- to high-severity fires either as dispersed individuals or as small groups of multi-aged trees. Small post-fire cohorts of Araucaria may establish, depending on seed availability and the effects of subsequent fires. Araucaria's great longevity (often >700 years) and resistance to fire allow some individuals to survive fires that kill and then trigger new Nothofagus cohorts. Even in relatively mesic habitats, where fires are less frequent, the oldest Araucaria,Nothofagus pumilio stands originated after high-severity fires. Overall, stand development patterns of subalpine Araucaria,N. pumilio forests are largely controlled by moderate- to high-severity fires, and therefore tree regeneration dynamics is strongly dominated by a catastrophic regeneration mode. [source] | ||||||||||