Physiognomic and chemical characters in wood as palaeoclimate proxies

Abstract

Fossil wood is both abundant and ubiquitous through geological time and space. During growth the parent plant was directly influenced by the biotic and abiotic (including climatic-) factors in the surrounding environment. The climate affects wood production in a number of ways and it is the resulting physiognomic and chemical characters that can help retrodict palaeoclimate. Physiognomic characters include those morphological and anatomical characters that in turn have enabled the use of wood characters, tree ring characters and statistical parameters (Mean Sensitivity) to determine seasonality, length and favourability of growing season, growth rates and forest productivity. Potential chemical characters discussed include (i)␣the preservation of wood-derived compounds (e.g. guaiacyl, syringyl p-hydroxyphenyl and resins); (ii)␣degree of lignin degradation to determine climate induced environmental changes; and (iii) stable isotopes (δD, δ13C and δ18O) to help determine aspects of past climates as derived from environmental changes. The feasibility and methodology of these characters, in both angiosperm and conifer wood, are reviewed in order to establish certain safe guards, or prerequisites, such that interpretations of palaeoclimate can be as unbiased, and thus as reliable, as possible.