Effects of season and region on sapstain and wood degrade following simulated storm damage in Pinus radiata plantations

Storms causing windthrow are major natural disturbance events and an unpredictable hazard to forest planning. Knowledge of regional and seasonal climatic effects on sapstain and decay fungi will allow forest managers to minimise losses from wood deterioration during salvage operations. A study was conducted monitoring sapstain in trees that were experimentally felled to simulate storm breakage at up to four times during the year in Pinus radiata plantations across six locations in different climatic zones throughout New Zealand. It was found that drying of sapwood and development of sapstain depended more on the season when the storm occurred, rather than the time since felling. Sapstain appeared almost immediately in stems felled during summer, at some locations reaching more than 20% mean cross-sectional cover inside logs within 3 months, whereas in those felled during winter an initial lag phase during the cooler months preceded a more rapid rise during spring and summer. Rates varied substantially between locations with a tendency for faster deterioration where average temperatures were greater. For trees damaged during winter, it was predicted that a P. radiata butt log with a mid-length diameter of c. 16–23 cm will take from 2 to 8 months, depending on climate, to reach an economic damage benchmark threshold of 10% cross-sectional sapstain cover. However, for storms in spring or summer this period reduces to less than 1 month at warmer locations. Development of sapstain was uniform or increased slightly with height along the felled stem, but was greatest close to the felling cut in the basal section that would normally be removed during log retrieval. The results of this study provide new information about the temporal and regional variation in the dynamics of sapstain fungi that will assist forest managers during timber recovery following storms in regions with similar climates and tree species.

► Pinus radiata trees were felled in order to simulate storm damage in forests.
► Sapstain development depended on season when felled rather than period since felling.
► Stain rose quickly if felled in summer but in winter there was an initial lag phase.
► Sapstain tended to develop faster where average temperature was greater.
► Information provided will assist forest managers during log recovery after storms.