Hydraulic responses to extreme drought conditions in three co-dominant tree species in shallow soil over bedrock

Abstract

An important component of the hydrological niche involves the partitioning of water sources, but in landscapes characterized by shallow soils over fractured bedrock, root growth is highly constrained. We conducted a study to determine how physical constraints in the root zone affected the water use of three tree species that commonly coexist on the Edwards Plateau of central Texas; cedar elm (Ulmus crassifolia), live oak (Quercus fusiformis), and Ashe juniper (Juniperus ashei). The year of the study was unusually dry; minimum predawn water potentials measured in August were -8 MPa in juniper, less than -8 MPa in elm, and -5 MPa in oak. All year long, species used nearly identical water sources, based on stable isotope analysis of stem water. Sap flow velocities began to decline simultaneously in May, but the rate of decline was fastest for oak and slowest for juniper. Thus, species partitioned water by time when they could not partition water by source. Juniper lost 15-30 % of its stem hydraulic conductivity, while percent loss for oak was 70-75 %, and 90 % for elm. There was no tree mortality in the year of the study, but 2 years later, after an even more severe drought in 2011, we recorded 34, 14, 6, and 1 % mortality among oak, elm, juniper, and Texas persimmon (Diospyros texana), respectively. Among the study species, mortality rates ranked in the same order as the rate of sap flow decline in 2009. Among the angiosperms, mortality rates correlated with wood density, lending further support to the hypothesis that species with more cavitation-resistant xylem are more susceptible to catastrophic hydraulic failure under acute drought.

Spatiotemporal variation in range‐wide Golden‐cheeked Warbler breeding habitat

“…However, it should be noted that each of these warbler habitat maps (including the one presented here) is based off imagery that can be considered somewhat outdated. The Diamond et al (2010) (Kukowski et al 2013). Thus, current warbler habitat maps may have large errors of commission (i.e., false positives), and should be updated, when feasible, for more reliable large-scale warbler conservation planning to take place.…”

Lagged mortality among tree species four years after an exceptional drought in east Texas

“…Following this, Schwantes et al (2017) developed drought-related canopy loss estimates for 2012 across a statewide climate gradient and noted, again, the highest loss in central Texas with east Texas least affected. Localized studies within central and western portions of the state highlighted variability in drought-related mortality among species (Kukowski et al 2013, Poulos 2014, soil types (Twidwell et al 2014), and elevation (Waring and Schwilk 2014). However, these studies were focused on initial mortality, and used independent stratified or remotely sensed estimates, and may have missed the extent of mortality from this event, or later, continued mortality from physiological stress or insects and diseases.…”

Prolonged experimental drought reduces plant hydraulic conductance and transpiration and increases mortality in a piñon–juniper woodland

“…2013; Kukowski et al. 2013). Recent modeling efforts utilizing long-term tree ring records and estimates of future drought severity (Seager et al.…”