tailieunhanh - Springer Old Growth Forests - Chapter 3

Chapter 3 Old Trees and the Meaning of ‘Old’ Fritz Hans Schweingruber and Christian Wirth While the mere presence of ‘old’ trees does not automatically indicate oldgrowth conditions (see Chap. 2 by Wirth et al., this volume), it is fair to say that many old-growth forests contain a high number of trees close to their maximum longevity. | Chapter 3 Old Trees and the Meaning of Old Fritz Hans Schweingruber and Christian Wirth Introduction While the mere presence of old trees does not automatically indicate old-growth conditions see Chap. 2 by Wirth et al. this volume it is fair to say that many old-growth forests contain a high number of trees close to their maximum longevity. Besides definitional aspects tree longevity per se is a key demographic parameter controlling successional dynamics of species replacement stand structure and biogeochemical cycles see Chap. 5 by Wirth et al. this volume . This chapter takes a dendroecological perspective on tree longevity. The first part will explore differences in longevities between different life forms and will ask to what extent trees differ from herbs and shrubs and among each other Sect. . The second part will discuss the mechanisms underlying the death of cells tissues and whole plants Sect. . It will be shown that the concept of death is problematic in the context of clonal plants and that the inevitable presence of external mortality agents may bias our perception of biological limits of longevity. Longevity of Conifers and Angiosperms After an individual becomes established it must persist Weiher et al. 1999 . The question remains for how long Undoubtedly the oldest living beings on our planet are trees. The oldest trees look back on an individual history of almost 5 000 years whereas most herbaceous plants persist for only a few years and some annuals die in the course of weeks. Apparently longevity is highly variable among plants. Reconstructing the age of an old tree is far from trivial because ring formation can be suppressed in stress periods or rings may be doubled in interrupted growing periods. In such cases age determination requires the dendrochronological technique of cross-dating. As shown in Fig. this simple method allows the C. Wirth et al. eds. Old-Growth Forests Ecological Studies 207 35 DOI .