COS 106-9
How mature forests alter the microclimate of forests regenerating after disturbance
The effect that mature forests have on adjacent forest regenerating after disturbance is termed forest influence (FI). FI creates edge effects, since mature forest affects the adjacent regenerating forest’s physical and biotic environment, notably its microclimate. In particular, areas close to a mature forest edge tend to experience microclimate conditions which more strongly resemble mature forest conditions than areas which are further away. A combination of FI microclimatic gradients and distance to source populations of plants and animals will result in distance to a mature forest being a factor in the re-colonisation success of disturbed forest. This study examined whether distance from a mature forest edge is a key determinant of regeneration forest microclimate compared to other environmental factors. Hourly records of temperature and humidity were collected for one year along transects crossing mature forest edges into logging regeneration of varying ages (7-50 years since harvest). We aimed to determine whether the magnitude of FI changed over short and long time scales. We also aimed to examine the changes in magnitude landscape environmental conditions.
Results/Conclusions
We found that distance to a mature forest edge was important in predicting microclimate of regeneration forests, although other factors such as age of regeneration forest and local canopy cover explained a greater proportion of microclimate variation. FI peaked during the middle of the day and was non-existent during the night. It was greatest during the summer months. The magnitude of FI declined with the age of the regeneration forest, but was still present 50 years after disturbance. Landscape level climate conditions had an impact, with the magnitude of FI being greatest on hot, windy days. Thus microclimatic patterns within regeneration forests are influenced by the proximity of mature forests. This knowledge will enable forest managers to manipulate the microclimate of harvested areas by implementing techniques such as aggregated variable retention which result in greater proportions of harvested areas being in close proximity to mature forest. Understanding how the magnitude of forest influence changes over forest succession may allow for targeted management by indentifying which time periods are important to microclimate-sensitive species such as shade-tolerant plants. Determining appropriate rotation lengths and timing of adjacent harvests to facilitate species conservation could also be informed from this research.