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We analysed the role of topography, tree stand characteristics and management on the susceptibility of forest stands to abiotic natural disturbances. In 1996, stands of Börzsöny Mts, Hungary were hit by a severe ice storm, then by strong winds three years later. Affected areas were mapped on aerial photos, and we built a GIS database containing variables describing topography and tree stand characteristics. The role of variables in predicting ice break and windfall was investigated by non-parametric statistical tests and by a series of C&RT (Classification and Regression Tree) analyses. Elevation, aspect and slope proved to have strong statistical relationships with the distribution of both ice break and windfall, with misclassification error (MER) of 18% and 15%, respectively, if studied without stand descriptors. Mixing ratio and age of beech were the most important stand descriptors to explain the distribution of ice break (MER=15%), whereas that of windfall was best described by the age and height of the two dominant tree species (MER=11%). The explanatory power could be increased if all variables (topographic + stand descriptors) were considered, though the increase in explanatory power was higher in the case of ice break (MER decreased from 15% to 11%) than for windfall (MER decreased from 11% to 10%). Since management related stand variables (beech mixture ratio, age, height, amount of recently felled stock, slenderness) and susceptibility to disturbance events seemed to be related, our results suggest that the sensitivity of tree stands could be decreased by increasing compositional and structural heterogeneity.
Landscape complexity in the boreal forest is a function of physiographic complexity (spatial processes) and post-fire successional (temporal) processes operating across scales. In this study we examine the role of succession and topographic complexity in determining the landscape complexity of Riding Mountain National Park, Manitoba, Canada. Landscape complexity is assessed by using multifractal analysis to quantify landscape patterns from Landsat TM imagery. To determine whether complexity changes with age, . young. sites (post-fire stand ages = 11 and 30 years) were matched with adjacent . old. sites (post-fire stand ages ≯ 95 years). The influence of physiography on landscape complexity is examined by comparing sites having . simple. and . complex. physiographies (as determined by fractal surface analysis). The scaling properties of landscape complexity are determined by calculating the multifractal spectrum (Dq) for each site. Landscape complexity increases during early succession; multifractal profiles of 11 year old sites are lower than those of adjacent older stands. However, the multifractal profiles of 30 year old and adjacent older stands are indistinguishable, suggesting that change in landscape complexity occurs within 30 years following fire. Physiographically . complex. sites have consistently greater landscape complexity than adjacent . simple. sites. We conclude that landscape complexity increases over time as succession proceeds, and in space along a gradient from . simple. to . complex. physiographies. It follows that landscape complexity is lowest in early-successional, physiographically . simple. sites and highest in late-successional, physiographically . complex. sites.
Markesbery, W. R. (1997) Neuropathological criteria for the diagnosis of Alzheimer's disease. Neurobiol. Aging 18 , S13-S19. Neuropathological criteria for the diagnosis of Alzheimer
Carney, J. M., Strake-Reed, P. E., Oliver, C. N., Landum, R. W., Chang, M. S., Wu, J. F., Floyd, R. A. (1991) Reversal of age-related increase in brain protein oxidation, decrease in enzyme activity and loss in temporal and spatial memory by chronic
The concentration (in mg kg–1 fresh weight) of two main hydroxamates, 2,4-dihydroxy- 7-methoxy-1,4-benzoxazin-3-one (DIMBOA) and 2,4-dihydroxy-1,4-benzoxazin-3-one (DIBOA), and their temporal changes were simultaneously investigated using HPLC analysis in the leaves and roots of five Pioneer® maize (Zea mays L.) hybrids to select hybrids with higher hydroxamate contents. Although significant differences were found among hybrids in leaves, youngest leaves and roots, none of them showed unambiguously higher hydroxamate contents. However, the age of the organs and the plants significantly affected hydroxamate content. DIMBOA content of leaves decreased with increasing organ and plant age. DIBOA content varied among the hybrids, but generally decreased in the initial phase and then increased. In the roots, DIMBOA content decreased during the 21-day study and although DIBOA content did not show a clear temporal tendency, differences among hybrids were detected. According to current results, hydroxamate content temporally decreases in hybridspecific patterns, which should be considered when establishing a proper sampling time frame.
The aim of the study was to describe the morphology and the development of the extraocular muscles (EOMs) in the pre-hatchling and post-hatchling African black ostrich. The study involved 50 birds aged between 28 days and 3 years. The EOMs were analyzed morphologically with respect to the location and length of the straight and oblique muscles and the third eyelid muscles, the length and breadth of their tendons as well as the distance and shape of the muscle tendon insertions at the corneal limbus. A histological and histometric analysis were also carried out. The greatest increase in the length of the EOMs was noted in groups III–V. A marked increase in the length of the tendons of the dorsal straight muscle was found in groups II and III, in the tendons of the nasal straight muscle in groups IV and V, in the tendons of the dorsal oblique muscle in groups III to V and in the tendons of the ventral oblique muscle in groups IV and V. There was a significant increase in the breadth of the dorsal straight and ventral oblique muscle tendons in groups IV and V and the tendons of the pyramidal muscle in groups III and V. The distance of the distal insertion of the tendon at the corneal limbus increased steadily with age in all the examined groups. The number of fascicles and muscle fibres, their diameter and length in all the studied EOMs were different in the different groups.
Studies of functional diversity can help to understand processes that determine the presence of species in different habitats. Measurement of functional diversity in silviculture areas is important because different functional traits can show different responses to this landscape alteration, and therefore ecological functions can be affected. This study evaluated functional and taxonomic differences in bird assemblages in a native forest and eucalyptus plantations, and also assessed the functional nestedness of the bird species. We censused birds in eucalyptus plantations of four different ages, and also in a native forest. The results showed higher functional and taxonomic diversity of birds in the native forest than in plantations and higher similarity of functional traits between plantations of different ages. The high functional diversity in the native forest indicates a greater variety of functional traits, resulting in greater functional complementarity than in plantations. The association of some traits with the native forest, such as nectarivory and foraging in air, indicates the importance of native habitats in maintaining species and functions related to such traits. Already, species traits in eucalyptus plantations represent a subset of those that were recorded in the native forest, indicating that some functions are maintained in plantations. Our results demonstrate that the species occurrence in the plantations and native forest is determined by species traits. Thus, the maintenance of some functions in plantations is provided, although there is a higher functional diversity in native forest.
., Nowicki, S., Aperia, A. (2000) Arachidonic acid metabolic pathways regulating activity of renal Na(+)-K(+)-ATPase are age dependent. Am. J. Physiol. 278 , 823–829. Aperia A. Arachidonic
Oak woods are the most important forest types growing on 570,700 hectares in Hungary that is about 32% of total forested lands. This paper reports results about the regeneration succession on clearings of sessile oak-Turkey oak forests, following successive clear-cut harvesting practice. Phytosociological relevés were taken, according to the space for time substitution model, covering stand ages from 2 to 28 years old. Major steps of the forest regeneration were analysed by multivariate methods and four stages were determined: I = 1–3 years, II = 4–11, III = 12–21(–25) and IV = (22–)26–28 years. Light climate of the four stages were characterised by measuring relative irradiation under clear sky conditions (RI) at four elevations (0, 20, 40 and 80 cm above ground). Herb layer phytomass was studied by the harvesting method in the same stands where RI was determined.Considering statistically significant differences in the studied variables among stages, two main stress periods were distinguished. The most drastic stress event appears during the transition from the mature forest stage to stage I. It is associated with a great and sudden increase in RI at the herb layer level (at 80 cm above ground RI was 95.5%). Also the amount of total herb layer phytomass of stage I increases considerably reaching more than three times higher values than that found under cutting age mature stands.The second stress period occurs in stage III. Significant decline of light intensity occurs during the transition from stage II to III, resulting an RI of 2–2.5%. Herb layer phytomass also becomes significantly reduced in this stage, amounting only 4 g DW/sqm. During this rather unfavourable period the majority of typical sessile oak-Turkey oak species disappear from the stands. A strong correlation between log(RI) and the herb layer aboveground phytomass was also established.The described two stress phases may lead to forest degradation, since the species able to survive the first stress phase with high RI probably cannot tolerate the very low illumination level in stage III. To prevent losses from the flora and vegetation, or at least to mitigate the damage, more frequent thinning in the thin pole phase (stage III) is recommended. Another solution would be the cultivation of uneven-aged forests, with selection cutting or single-tree selection.
S10 Finkel, T., Holbrook, N. J. (2000) Oxidants, oxidative stress and the biology of ageing. Nature 408 , 239–247. Holbrook N. J
