Rates of decay in wood measured by carbon dioxide production

SUMMARY The applicability of two methods of respirometry to measurement of the carbon dioxide output of naturally decaying branches and wood of standing trees was studied. The Warburg respirometer was judged unsuitable for general use on decaying wood. A conductivity respirometer was found satisfactory. Carbon dioxide production was essentially unaffected by fragmentation suggesting that the measurements obtained are likely to be a valuable indication of decay in the intact tree or branch. The carbon dioxide production of samples was fairly stable when conditions were kept constant but responded promptly to increased or decreased moisture. Wood from branches infested with Polyporus tulipiferae in which moisture was increased from approximately 20%–50% (fresh weight basis) increased its carbon dioxide output over a 4‐day period by some seven times. Comparable wood in which the moisture content was reduced from 45 to 20 % showed an almost linear reduction in rate over a similar period to about one‐sixth the original rate. Rate of decay in stained and unstained zones of living trees showed no consistent effect of the stain. However, rates of decay in heart‐rot of poplar caused by Fomes igniarius were only one‐third those reported by Verrall (1937) for decay in culture.