tailieunhanh - Springer Old Growth Forests - Chapter 4

Chapter 4 vEcophysiological Characteristics of Mature Trees and Stands – Consequences for Old-Growth Forest Productivity Trees increase their relative fitness to competing trees or to other life forms both directly and indirectly, by growing tall, as increased light interception increases photosynthesis (direct) and simultaneously making this resource unavailable to competitors (indirect). | Chapter 4 Ecophysiological Characteristics of Mature Trees and Stands - Consequences for Old-Growth Forest Productivity Werner L. Kutsch Christian Wirth Jens Kattge Stefanie Nollert Matthias Herbst and Ludger Kappen Introduction Trees increase their relative fitness to competing trees or to other life forms both directly and indirectly by growing tall as increased light interception increases photosynthesis direct and simultaneously making this resource unavailable to competitors indirect . Consequently trees that grow taller larger or have greater shading power may dominate smaller trees with less shading power. However as trees become older and grow taller they face constraints that differ drastically from those experienced by smaller species or early ontogenetic stages. Falster and Westoby 2003 who used game-theoretic models to learn about the evolutionary background of tree height summarised thus height increases costs as past investment in stems for support as continuing maintenance costs for the stems and vasculature as disadvantages in the transport of water to height and as increased risk of breakage . No wonder that trees do not grow infinitely high. In general absolute and relative growth rates tend to decrease with age and height. This decline in productivity observed at both the tree and stand level has been attributed to a range of processes . increasing respiratory demand and limitation of photosynthesis on the tree level and on the stand level increasing sequestration of nutrients in slow-decomposing litter and ecophysiological differences between early- mid- and late-successional canopies. This chapter will review these current hypotheses first on the tree level then the stand level as well as in the context of successional changes of community composition. Increased Respiratory Demand A widespread hypothesis about the decrease in growth with tree age is based on the idea that higher respiratory demand limits resources for wood growth. .