Almost nothing is known about the presence of annual growth rings in North American perennial herbs and, correspondingly, the age of forbs is also largely unknown. In this study we sampled ...established individuals of dicotyledonous perennial herbs (60 species) in different habitats in lower Michigan (U.S.A.) and analyzed the main roots for the presence of growth rings in the secondary xylem. Two thirds of the species showed clearly or relatively clearly demarcated growth rings in the root xylem that are most likely annual rings. The anatomical patterns contributing to the delineation of growth rings in the root xylem differed widely, particularly among plant families. These included variations in vessel diameter and vessel density and differences in the presence and extent of tangential bands of fibres or lignified parenchyma, respectively. Among introduced species and in disturbed habitats (meadows, ruderal sites), clearly demarcated growth rings were found more frequently than among native species and in semi-natural and natural habitats (old fields, prairie remnants, open sandy vegetation). While most of the sampled plants were young (2 to 3 years old), the age distribution in the whole sample was relatively wide (2- to 16-year-old plants). Older individuals (
6 years old) were mainly found in semi-natural and natural habitats. Results indicate that the analysis of annual rings in the root xylem of perennial herbs (herb-chronology) may be widely used as a reconstructive method in plant ecology over extensive geographic areas with seasonal temperate climate. Research into plant invasions may particularly profit from a high proportion of forb species in disturbed habitats that show clearly demarcated annual rings.Key words: age determination, anatomical patterns, annual rings, perennial herbs, population ecology, secondary root xylem.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Two dendroecological procedures are described. The first involves the radiodensitometric analysis of conifer material from an altitudinal transect between the subalpine and the lower, arid ...timberline. Core samples were taken from selected stands with very differing site conditions at three altitudes, and tree-ring parameters including maximum latewood density, latewood width, and total width were measured. A special type of diagram was developed to assist analysis of the complex relationships between tree-ring growth, weather, and site conditions on a year-for-year basis. This is a departure from the conventional approach of analyzing only mean relationships over long time sequences. An advantage of the elaborated single-year method is that the growth models are allowed to vary with time. Typical cases are illustrated, and the dynamics of the overlapping influences of weather and site conditions are discussed. The second procedure comprises the visual identification and dating of abrupt, persistent changes in the tree-ring pattern and their relation to biotic and abiotic factors. This allows the reconstruction of insect attacks, forest fires, and forest clearing.
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