Exploring the role of water in tree growth and what trees can tell us about the hydroclimate of the past

Abstract

Here, we revisit the role of water potential in tree growth control using a field-based approach to exploring the role of soil moisture supply and atmospheric moisture demand on tree water potential and subsequently, growth. We explore how limitation in tree radial growth can be well predicted by local hydrometeorlogical conditions and associated tree water potentials, and observe that such limitation occurs under conditions that are considerably more mesic than those associated with the onset of photosynthetic limitation resulting from stomatal regulation (Martin et al., 2017). While direct observation of tree xylem growth and growth limitation remains a very challenging problem, our findings provide strong evidence for the role of Psi x in the regulation of tree radial growth in dry environments...Because one of the most prominent features of observed climate change in the American West has been an advancement in the timing of spring conditions (Cayan et al., 2001; Stewart et al., 2005), developing a better understanding of how the timing of moisture delivery and tree growth relate is an important research goal. Using a field-based study carried out over three years in western Montana, we quantified the timing and magnitude of moisture delivery to a forest ecosystem, and coupled this to isotope-based observations of where in the soil profile trees sourced water from as well as the seasonal evolution of radial growth. This allowed us to estimate the importance of winter precipitation relative to summer rains for growth in trees over the growing season. This work establishes a baseline understanding of how temporal dynamics of moisture delivery to forests and tree growth relate in time and can help guide our understanding of how ongoing changes to climate conditions may affect tree growth in the future...In order to better understand the hydroclimatic dynamics of the Missouri river, we developed a network of tree ring based reconstructions of streamflow spanning 1200 years for every major tributary across the mountain headwaters of the Missouri river. We examined the history of basin-wide drought events evident in the tree ring record in the context of reconstructed temperature and explored how the relationship between temperature and streamflow has changed over time. As a result, it is evident that rising temperatures create new challenges for water managers and users in the Upper Missouri River Basin that are likely to increase as temperatures warm in the future.