Invasive capacity of Tamarix ramosissima in a Mojave Desert floodplain: the role of drought

Abstract

Tamarix ramosissima (Tamaricaceae) is a woody phreatophyte that has invaded thousands of hectares of floodplain habitat in the southwestern U.S. In this study, we examined the response of gas exchange and stem sap flow of Tamarix and three co-occurring native phreatophytes (Pluchea sericea (Asteraceae), Prosopis pubescens (Fabaceae) and Salix exigua (Salicaceae)) to drought conditions in an early successional floodplain community in the Mojave Desert of southern Nevada. In an analysis of a size/age series of each species across the whole floodplain (both mature and successional stands), stem growth rate was lowest for Tamarix. However, along the same successional chronosequence, Tamarix came to dominate the 50+ year old stands with dense thickets of high stem density. Xylem sap flow, when expressed on a sapwood area basis, was highest in Tamarix under early drought conditions, but comparable between the four species toward the end of the summer dry season. Multivariate analysis of the gas exchange data indicated that the four species differentiated based on water use under early drought conditions and separated based on plant water potential and leaf temperature (indices of drought effects) at the end of the summer dry season. This analysis suggests that the invasive Tamarix is the most drought tolerant of the four species, whereas Salix transpires the most water per unit leaf surface area and is the least tolerant of seasonal water stress. Therefore, Salix appears to be well adapted to early successional communities. However, as floodplains in this arid region become more desiccated with age, Tamarix assumes greater dominance due to its superior drought tolerance relative to native phreatophytes and its ability to produce high density stands and high leaf area.

Water uptake from different soil depths for halophytic shrubs grown in Northern area of Ningxia plain (China) in contrasted water regimes

“…No irrigation effect was found on its Pn, gs, Tr, c pre , c mid of uncovering some physiological bases in relation to its phreatophytic nature (Cleverly et al 1997;Xu & Li 2006). Compared with the 20-year-old T. ramosissima, the threeyear-old T. ramosissima depended heavily on soil water in the middle profile (80Á140 cm), implying the age effect on water use strategy of this species.…”

Multiple states in river and lake ecosystems

“…Local reductions in the groundwater level may be caused by species that effectively exploit groundwater. Saltcedar can reach a lower water table and use more water per unit sapwood than several native species (Sala et al 1996;Cleverly et al 1997;Horton & Clark 2001). Shafroth et al (2000) found that saltcedar saplings were significantly less vulnerable than indigenous species to groundwater depletion.…”

“…Shafroth et al (2000) found that saltcedar saplings were significantly less vulnerable than indigenous species to groundwater depletion. This competitive advantage could lead to increased establishment of saltcedar, lowering the water table further and causing the loss of more native trees (Cleverly et al 1997). Saltcedar is also salt tolerant and excretes salts that may reduce the germination of salt-sensitive species (Busch & Smith 1995).…”

Riparian trees and aridland streams of the southwestern United States: An assessment of the past, present, and future

“…Following decreasing reproduction and increasing mortality of native trees, drought-tolerant species such as saltcedar (Tamarisk spp.) and Russian olive (Elaeagnus angustifolia) may be released from competition, increasing their invasive capacity (Cleverly et al, 1997;Katz and Shafroth, 2003). A combination of increased frequency of heavy rains and decreased magnitude of spring floods, predicted by other climate change studies, may benefit late-successional species such as Arizona Walnut (Juglans major), mesquites (Prosopis spp.…”