共查询到20条相似文献，搜索用时 15 毫秒
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Yann Nouvellon Jean-Paul Laclau Daniel Epron Antoine Kinana André Mabiala Olivier Roupsard Jean-Marc Bonnefond Guerric le Maire Claire Marsden Jean-Daniel Bontemps Laurent Saint-André 《Forest Ecology and Management》2010,259(9):1796-1807
Specific leaf area (SLA; m2leaf kg?1leaf) is a key ecophysiological parameter influencing leaf physiology, photosynthesis, and whole plant carbon gain. Both individual tree-based models and other forest process-based models are generally highly sensitive to this parameter, but information on its temporal or within-stand variability is still scarce. In a 2–4-year-old Eucalyptus plantation in Congo, prone to seasonal drought, the within-stand and seasonal variability in SLA were investigated by means of destructive sampling carried out at 2-month intervals, over a 2-year period. Within-crown vertical gradients of SLA were small. Highly significant relationships were found between tree-average SLA (SLAt) and tree size (tree height, Ht, or diameter at breast height, DBH): SLAt ranged from about 9 m2 kg?1 for dominant trees to about 14–15 m2 kg?1 for the smallest trees. The decrease in SLAt with increasing tree size was accurately predicted from DBH using power functions. Stand-average SLA varied by about 20% during the year, with lowest values at the end of the 5-month dry season, and highest values about 2–3 months after the onset of the wet season. Variability in leaf water status according to tree size and season is discussed as a possible determinant of both the within-stand and seasonal variations in SLA. 相似文献
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《Forest Ecology and Management》2005,211(3):356-370
Uneven-aged management using single-tree or group selection has been in practice for many decades, especially in northern hardwood forests. Use of stocking regulation tools is thought to produce and maintain specific stand structures that upon regulation, are sustainable over time. We evaluated stand structures in northern hardwoods in Upper Michigan across three ownerships that practice different approaches toward uneven-aged management. Industry land (MeadWestvaco—MWV) uses primarily diameter limit cutting combined with a sawyer-select harvest method, retaining a maximum diameter of 45.7 cm (18 in.) with a residual basal area of 16.1 m2/ha (70 ft2/ac) and a cutting cycle of 10 years. The Michigan Department of Natural Resources (DNR) uses a crop tree release technique with a residual basal area of 18.4 m2/ha (80 ft2/ac) and a cutting cycle of 20 years. Both ownerships view regeneration of new cohorts as inevitable given the intensity of disturbance and the forest type. The third ownership (the Ford Forestry Center School Forest at Michigan Technological University—FFC) employs strict stocking regulation using the BDq method (residual basal area of 16.1 m2/ha (70 ft2/ac), maximum diameter of 50.8–55.9 cm (20–22 in.), and a q-ratio of 1.3) with a cutting cycle ranging from 12 to 15 years.Stand structure on a total of 25 stands was characterized for these ownerships to assess the impact of management strategy on stand structure and species composition. Differences in species composition and lower diversity indices were found where increasing sugar maple dominance was an objective (FFC ownership). All ownerships showed reduced relative importance values of mid-tolerant species such as yellow birch in their stands as compared to values reported for old-growth or unmanaged stands. Diameter distributions were classified into one of three shape categories (negative exponential, increasing q-ratio, and rotated sigmoid) using the regression of DBH, DBH2, and DBH3 on the log10 of trees per hectare. The best model in terms of adjusted-R2 and root mean square error (RMSE) was selected for each stand. All management strategies resulted in similar occurrences of distribution shapes, despite some evidence of a trend toward a rotated sigmoid distribution. These trends suggest that several different diameter distribution shapes in uneven-aged northern hardwoods in the Lake States are possible following a variety of management approaches, with sugar maple increasing in dominance with strict adherence to certain stocking regulation guidelines. 相似文献
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《Forest Ecology and Management》2005,204(1):131-137
The effects of soil compaction and cultivation on soil mineral N dynamics were investigated through an 18-month, in situ N mineralisation experiment during the inter-rotation and early establishment period of a second rotation (2R) hoop pine (Araucaria cunninghamii Aiton ex A. Cunn) plantation in southeast Queensland, Australia. Treatments were 0, 1 and 16 passes of a fully laden forwarder (gross weight, 40.2 Mg) and cultivation by disc plough (zero cultivation and cultivation). Nitrate N was the dominant form of mineral N throughout the 18-month sampling period in both non-cultivated and cultivated soils, varying between 10 and 40 kg ha−1 whilst ammonium N remained <10 kg ha−1. Compaction had no significant effect on N mineralisation or nitrification. However, the remediation of the effects of compaction on soil through the use of the disc plough had significant impacts on N mineralisation, nitrification and N leaching. On a seasonal basis, the mean net N mineralisation increased from around 30 to 53 kg ha−1, nitrification from 28 to 43 kg ha−1 and nitrate N leaching from around 10 to 73 kg ha−1 following cultivation. 相似文献
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《Fitoterapia》2014
Ginkgolic acids are alkylsalicylic acid derivatives with a thermolabile carboxylic group from Ginkgo biloba L., and they exhibit anticancer activity. Their anticancer effects are closely associated with their thermal stability. In this study, the thermal decomposition of ginkgolic acids was analyzed at temperatures of 30, 50, 70 and 250 °C. The results clearly showed that an obvious slow decarboxylation of the ginkgolic acids was detected at 70 °C. When the temperature increased to 250 °C, the decarboxylation reaction was rapidly completed. The ginkgolic acids were decarboxylated to yield ginkgols. The ginkgols C13:0, C15:1 and C17:1 were separated and definitively identified by IR, NMR and GC-MS. The cytotoxic effects of ginkgols C13:0, C15:1 and C17:1 were tested and compared with those of the corresponding ginkgolic acids. An MTT assay showed that ginkgol C17:1 (48-h IC50 = 8.5 μg · ml- 1) has the strongest inhibition on SMMC-7721 cells in a dose- and time-dependent manner. The anticancer action may occur via the induction of apoptosis by the activation of caspases-3, the upregulation of Bax expression, and the inhibition migration of SMMC7721 cells. The results indicated that ginkgol C17:1 might be useful for the further development of a hepatocellular carcinoma preventive agent. 相似文献
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