Responses of riparian trees to interannual variation in ground water depth in a semi‐arid river basin

Abstract

We investigated the physiological and growth responses of native (Populus fremontii S. Wats. and Salix gooddingii Ball) and exotic (Tamarix chinensis Lour.) riparian trees to ground water availability at the free-flowing Hassayampa River, Arizona, during dry (1997) and wet (1998) years. In the drier year, all species experienced considerable water stress, as evidenced by low shoot water potentials, low leaf gas exchange rates and large amounts of canopy dieback. These parameters were significantly related to depth of ground water (DGW) in the native species, but not in T. chinensis, in 1997. Canopy dieback was greater in the native species than in T. chinensis when ground water was deep in 1997, and dieback increased rapidly at DGW > 2·5-3·0 m for the native species. Analysis of combined data from wet and dry years for T. chinensis tentatively suggests a similar physiological sensitivity to water availability and a similar DGW threshold for canopy dieback. In 1998, shoot water potential and leaf gas exchange rates were higher and canopy dieback was lower for all species because of increased water availability. However, T. chinensis showed a much larger increase in leaf gas exchange rates in the wet year than the native species. High leaf gas exchange rates, growth when water is abundant, drought tolerance and the maintenance of a viable canopy under dry conditions are characteristics that help explain the ability of T. chinensis to thrive in riparian ecosystems in the south-western United States.

Groundwater-dependent ecosystems: recent insights from satellite and field-based studies

“…Wood formed during drought is enriched in 13 C, reflecting decreases in stomatal conductance relative to photosynthesis and the consequential ratio of [CO 2 ] within and outside of the leaf (C i /C a ) (McCarroll and Loader, 2004;Cocozza et al, 2011;Horton et al, 2001;Maguas et al, 2011). Interpretation of δ 13 C in tree rings can be complicated by the effects of phloem loading (Gessler et al, 2009) and by photosynthetic re-fixation in the bark (Cernusak et al, 2001), although with independent confirmation, xylem δ 13 C can explain differences in groundwater use and water stress in groundwaterdependent trees.…”

“…Similarly, increased Huber value, (Table 3). Consequently, response functions for individual traits are readily apparent; examples include changes with depth-to-groundwater in rates of photosynthesis (Horton et al, 2001), plant cover (Elmore et al, 2006), NDVI (Lv et al, 2012) and crown dieback (Horton et al, 2001). However, few studies have examined multiple traits across multiple scales and then provided an integrated "ecosystem-scale" response function to differences in groundwater availability.…”

Adaptation of Colophospermum mopane to extra-seasonal drought conditions: site-vegetation relations in dry-deciduous forests of Zambezi region (Namibia)

“…Tyree and Hammel 1972;Ritchie and Hinckley 1975;Richter 1997). In line with Horton et al (2001aHorton et al ( , 2001b, Mitlöhner (1995Mitlöhner ( , 1998, Teskey andHinckley (1986), andHennessey andDougherty (1984), the predawn water potential is understood to reflect the soil water potential of the rhizosphere, which affects the assessed trees. The water potential assessed at midday describes the strongest negative water potential applied by the sample species to access soil water at the given measuring time.…”

An Empirical Algorithm for Estimating Agricultural and Riparian Evapotranspiration Using MODIS Enhanced Vegetation Index and Ground Measurements of ET. I. Description of Method

“…Peak E L at Slitherin was at 1,200 hrs, whereas plants at Diablo East had peak E L at 0800 hours and the other sites were intermediate. Other studies have also noted midday depression of saltcedar ET actual [31,[58][59][60].…”