Lianas buffer tropical forest understories

Lianas are an iconic and important feature of tropical forests. On average, they represent about 24 percent of the woody stems and they contributie significantly to the total leaf area. Their abundance increases with increasing seasonality, and they are able to keep their leaves for a longer period in the dry season. Their abundance in the neotropics has been increasing in the last decades. Lianas have a negative impact on the carbon storage of forests by reducing individual tree growth and increasing tree mortality and turnover. However, their impact on the energy balance of the forest, and the forest understory microclimate in particular, is poorly understood. To fill this gap, we installed two experimental setups in a 12-year, ongoing liana removal experiment on Gigante, Panamá. We installed 180 TOMST TMS-4 microclimate sensors in 8 removal and 8 control plots to monitor the microclimate temperature and soil moisture. Next to that, we installed  ~24 pyranometers and photosynthetic actieve radiation (PAR) sensors in a subset of two removal and two control plots, both horizontally, at 1 meter above the soil, and vertically in the canopy. Our findings revealed that lianas buffer the forest microclimate more than trees, leading to an average midday temperature reduction of 0.2°C at the soil surface (measured 15 cm above the soil). The effect increased at higher temperatures during the dry season (temperature reduction up to 0.35°C on the maximum temperature in the forest). For half of the plots, we were able to account for the impact of forest density and structure on the microclimate using simultaneously collected TLS (terrestrial laser scanning) and ALS (aerial laser scanning) data. Lianas likely reduce soil understory temperatures by reducing the amount of solar radiation that penetrates the forest canopy or by reflecting more light back into the atmosphere.