Intra-Annual Density Fluctuations in Tree Rings: How, When, Where, and Why?

Abstract

Intra-annual density fluctuations (IADFs) in tree rings are generally considered structural anomalies caused by deviations from the “normal course” of xylogenesis during the growing season. This definition is based on the bias that, under “normal conditions”, cambial activity stops once a year. Each tree ring can thus be dated to one calendar year, which is one of the principles of dendrochronology. The formation of IADFs can be triggered directly by environmental changes, especially in precipitation and temperature, that affect cambial activity and cell differentiation. It can also be the result of limited photosynthesis, due to defoliation induced by biotic or abiotic constraints.Often indicated with alternative terms, IADFs were first described in the 1930s, and recently reported for many trees and shrubs from different ecosystems throughout the world, particularly for Mediterranean species. Different types of IADFs have been detected; their formation and structural properties depend on many factors including tree genotype, age, size, rooting depth, habitat, soil, climate, photosynthetic activity, and allocation strategies. Whether IADFs affect the adaptive capability of plants remains, however, unclear.We provide an overview of the main anatomical features of IADFs and their occurrence in tree rings from various environments and climatic regimes. We propose a simplified way of classifying them and discuss the hypotheses about their functional role and the factors triggering their formation. To understand the ecological role of IADFs better, we recommend a multidisciplinary approach, involving wood anatomy, dendroecology, and stable isotopes, which has already been applied for Mediterranean species. We conclude by considering that IADFs appear to be the “rule” rather than “anomalies” in some ecosystems where they help plants cope with fluctuating environmental conditions. Moreover, their anatomical structure represents a valuable proxy of past climatic conditions at a sub-seasonal resolution and may be relevant to adapt hydraulic functioning of living trees to changing climatic conditions.

Relationships between Wood Formation and Cambium Phenology on the Tibetan Plateau during 1960–2014

“…For example, tree-ring width is also a function of the rate of radial increment, and the size of the cells formed [16,46]. The effect of a longer growing season on the formation of wood can be biased by a decreased formation rate or reduced cell size [15,47,48]. The different allocation strategies of absorbed carbon by a tree probably result in more complex relationships between wood formation and cambium phenology [7,49].…”

Water potential control of turgor‐driven tracheid enlargement in Scots pine at its xeric distribution edge

“…Among the environmental drivers of conduit dimensions, water availability has a pervasive effect, as drier conditions generally lead to the formation of narrower conduits within the ring, from year to year, as well as between individual trees and species (Deleuze & Houllier, 1998;Fonti et al, 2010;De Micco et al, 2016;Pfautsch et al, 2016). Plant cell expansion is the result of wall relaxation under the action of turgor pressure (P) above a yield threshold (c P ), which is typically formalized using Lockhart's equation (1965) (see Materials and Methods) and which has been shown to apply to numerous plants and cell types (Green & Cummins, 1974;Cosgrove, 1986).…”

Značilnosti zgradbe lesa sadik bora (Pinus sylvestris) in bukve (Fagus sylvatica) izpostavljenih trem različnim okoljskim razmeram / Characteristics of wood structure of pine (Pinus sylvestris) and beech (Fagus sylvatica) seedlings exposed to ...

“…Gostotne fluktuacije se pojavljajo tudi pri drevesih, ki rastejo v zmerni in hladni klimi, in sicer bodisi zaradi sušnega stresa v poletnih mesecih ali pa nadpovprečno vlažnih in hladnih razmer na višku rastne sezone (De Micco et al 2016c). Poleg tega je pogostost gostotnih fluktuacij pri mladih drevesih z mladostnim lesom večja (Wimmer 2002).…”

“…Nenazadnje gostotne fluktuacije lahko nastanejo tudi zaradi zmanjšanja fotosintetske aktivnosti v primeru poškodbe krošnje zaradi abiotskih dejavnikov (npr. požar, zmrzal) ali/in patogenov (Panshin & de Zeeuw 1980, De Luis et al 2011, zato je razlog za njihov nastanek navadno težko določiti brez dodatnih kemijskih, morfoloških, ekoloških, geografskih ali zgodovinskih informacij (De Micco et al 2016c). So pa gostotne fluktuacije zelo koristne za ugotavljanje (nenadnih) sprememb rastnih razmer pri posamezni drevesni vrsti v nekem okolju.…”