The influence of climate and management on transpiration of residential trees during a bark beetle infestation

Abstract

Trees in residential environments are affected by a unique combination of environmental and anthropogenic factors, including occasional insect outbreaks that are increasing in frequency and severity due to climate change. We studied loblolly pine trees infested by bark beetles in a residential backyard in a southeastern US city. We investigated the responses of tree and stand-level transpiration to environmental factors (solar radiation, atmospheric vapor pressure deficit, and soil moisture), severe weather events (strong winds and heavy storms), bark beetle infestation, and human actions (insecticide treatments and tree removals). We used constant heat dissipation probes to make continuous sap flux measurements (J0) in tree boles. Over 22 months of the study, J0 of trees with confirmed infestation decreased from ~90 to ~60 g cm−2 day−1 and J0 of the rest of the trees increased from ~60 to ~80 g cm−2 day−1. One infested tree died, as its J0 steadily declined from 110 g cm−2 day−1 to zero over the course of 2 months, followed by a loss of foliage and visible signs of severe infestation 6 months later. J0 was sensitive to variations in incoming solar radiation and atmospheric vapor pressure deficit. In most trees, J0 linearly responded to soil water content during drought periods. Yet despite complex dynamics of J0 variations, plot-level transpiration at the end of the study was the same as at the beginning due to compensatory increases in tree transpiration rates. This study highlights the intrinsic interplay of environmental, biotic, and anthropogenic factors in residential environments where human actions may directly mediate ecosystem responses to climate.