Exploring microclimate variability across spatial scales

Forest microclimates play an essential role in biodiversity because they buffer temperature extremes and, thus, the impacts of climate change. Yet, our understanding of the small-scale spatial variation in forest microclimate remains vague. This knowledge gap is mainly caused by existing sampling designs capturing large-scale gradients (e.g. elevation gradients, successional gradients) instead of small-scale variation within a site. To bridge this gap, we established eight 1-hectare intensive measurement sites across a diverse gradient of Central European forests, from Atlantic lowland forests in Belgium to mountain forests in Southern Germany. Each site is stocked with 16 microclimate loggers recording temperature and soil moisture on a regular grid. We further quantified forest structure within each site using terrestrial laser scanning, offering a detailed representation of plant material distribution in all three dimensions. This setup allowed us to thoroughly examine spatial variability in microclimates within and between forest types and how variations in microclimates are linked to forest structure across variable spatial scales. Our initial findings show that logger-specific linear regressions between site-average temperature and microclimate temperature had very good fits (mean R2 = 0.98, ranging from 0.85 to 1.00). The standard deviations of regression slopes per site ranged from 0.03 to 0.11 (mean of 0.06), indicating that all sites experienced substantial variation in microclimates at a spatial scale of 20 m. Higher spatial microclimate variability was thereby correlated with higher variability in forest structure. In the next step, we will predict local microclimate variation from structural predictors (i.e. plant area index, height, canopy complexity) at variable spatial scales (from 1 to 20 m), allowing for a more detailed assessment of how microclimate variability scales across space. Hence, our research provides a new and valuable perspective on forest microclimates by specifically considering small-scale spatial variability.