Microclimate vulnerability under coupled effects of changing climate and forest structure

Abstract

Understanding how forest structure affects microclimate is crucial amidst global warming, especially in biodiversity hotspots such as the North American Coastal Plain (NACP). We contrasted the effects of forest canopy openness and forest type on key microclimatic variables (daily temperature means, minima, maxima, amplitude) relative to their long-term temporal trends to better understand how forest structure may buffer the effects of changing climate in an important NACP ecosystem (the Long Island Central Pine Barrens). We analyzed 75 years of summer temperature trends (1949–2023) to reveal a dramatic regional warming by 2.3 °C on average, with daily minima increasing much more (by 3.3 °C) than daily maxima (by 1.4 °C), leading to the decline in daily temperature variability (amplitude) by ∼2 °C. We then quantified how late summer temperatures in forest understories (at ∼1 m above ground, in 2020) varied spatially with forest structure to reveal that increasing canopy openness (from ∼0 % to ∼80 %) increased daily maxima (by 2.5 °C) while decreasing daily minima (by -2.7 °C), thus considerably increasing daily temperature amplitude (by 5.1 °C). This effect was particularly pronounced in open-canopy pine-dominated ecosystems. Since forest canopies are expected to become more open under warmer climate due to drought-related tree mortality, lower tree recruitment, and increased fire, future summer daily temperature maxima in forest understories are likely to increase considerably more than predicted from regional temporal trends, while regional changes over time in daily minima (increase) and amplitude (decrease) may be offset in forest understories by changing forest structure.