Effects of canopy-mediated microclimate and object characteristics on deadwood temperature

Deadwood is a crucial component of forest ecosystems, supporting numerous forest-dwelling species and ecosystem functions, such as water and nutrient cycling. Temperature is a major driver of processes, affecting, inter alia, metabolic rates within deadwood. Deadwood temperature is determined by factors at both the forest stand-scale and individual deadwood object-scale. Yet, the contribution of individual factors within the complex hierarchy of scales that drive temperature in deadwood remains poorly understood. We conducted a real-world experiment to analyze the effects of forest stand canopy cover (open vs. closed canopies), surrounding deadwood amount (high vs. low), deadwood tree species (beech vs. fir), position (soil contact vs. uplifted) and diameter (range: 19-47 cm) of coarse woody debris on within-deadwood daily mean, minimum and maximum temperature at monthly and seasonal level. Stand-scale factors were more important than object-scale factors for explaining the variance in temperature. Canopy cover exhibited the strongest relationship with temperature. Daily mean and maximum temperature were higher and daily minimum temperature was lower in open than in closed canopies during the growing season (May-October). Further, daily minimum was lower in open canopies during winter (November-April). Annual daily mean and maximum temperature were about 1 °C and 5 °C warmer, respectively, and minimum temperature about 2 °C colder in open compared to closed canopies. Effects of deadwood amount, object diameter, position, and tree species on temperature were less important and statistically significant in only a few months. We conclude that canopy cover is more important than deadwood characteristics in determining internal deadwood temperature. An increase of canopy disturbance will hence elevate the temperature in deadwood, which might have important consequences on deadwood-dwelling species and ecological processes, such as heterotrophic respiration. To diversify habitat conditions for multiple species, we recommend enriching deadwood under various canopy conditions.