Stand structural drivers of microclimate in mature temperate mixed forests

- Air temperature and humidity correlated negatively, diffuse light was independent.
- Air temperature and humidity were mainly influenced by subcanopy and shrub layer.
- Variance of microclimate was lowered by litter cover, and stand heterogeneity.
- Diffuse light was decreased by diameter, basal area and tree size diversity.

The complex interactions between stand characteristics and forest site variables result in specific understory microclimate conditions, which are essential for many forest-dwelling organism groups.The main aim of our study was to evaluate the relative importance of stand structure variables and landscape elements that account for the microclimate in closed, managed, mature forest stands. The relationships between different microclimatic variables were also analyzed. 35, 70-100 year-old deciduous-coniferous mixed forest stands were selected in Western Hungary. Air temperature, relative humidity, and relative diffuse light were measured at eight sampling periods between 2009 and 2011.Below-canopy air temperature and humidity showed a strong negative correlation, but diffuse light was independent. The mean values of air temperature and humidity depended on stand structure elements, chiefly on the subcanopy and shrub layer, while their variance was lowered by litter cover. The amount of diffuse light was negatively affected by tree diameter, basal area and tree size diversity.Our results suggest that structural elements have a stronger influence on microclimate conditions than tree species composition of the overstory. The midstory and the shrub layer play key roles in maintaining the special microclimate of forests with continuous canopy-cover. Our results can provide adoptable aspects for forest management and nature conservation for the maintenance of the specific conditions favorable to sensitive forest specialist taxa (e.g. forest herbs, forest-dwelling ground beetles, epiphytic bryophytes, and lichens).

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