Vulnerability of riparian ecosystems to elevated CO₂ and climate change in arid and semiarid western North America

Abstract

Riparian ecosystems, already greatly altered by water management, land development, and biological invasion, are being further altered by increasing atmospheric CO 2 concentrations ([CO 2 ]) and climate change, particularly in arid and semiarid (dryland) regions. In this literature review, we (1) summarize expected changes in [CO 2 ], climate, hydrology, and water management in dryland western North America, (2) consider likely effects of those changes on riparian ecosystems, and (3) identify critical knowledge gaps. Temperatures in the region are rising and droughts are becoming more frequent and intense. Warmer temperatures in turn are altering river hydrology: advancing the timing of spring snow melt floods, altering flood magnitudes, and reducing summer and base flows. Direct effects of increased [CO 2 ] and climate change on riparian ecosystems may be similar to effects in uplands, including increased heat and water stress, altered phenology and species geographic distributions, and disrupted trophic and symbiotic interactions. Indirect effects due to climate-driven changes in streamflow, however, may exacerbate the direct effects of warming and increase the relative importance of moisture and fluvial disturbance as drivers of riparian ecosystem response to global change. Together, climate change and climate-driven changes in streamflow are likely to reduce abundance of dominant, native, early-successional tree species, favor herbaceous species and both drought-tolerant and late-successional woody species (including many introduced species), reduce habitat quality for many riparian animals, and slow litter decomposition and nutrient cycling. Climate-driven changes in human water demand and associated water management may intensify these effects. On some regulated rivers, however, reservoir releases could be managed to protect riparian ecosystem. Immediate research priorities include determining riparian species' environmental requirements and monitoring riparian ecosystems to allow rapid detection and response to undesirable ecological change.

Effects of climatic variability and change on forest ecosystems: a comprehensive science synthesis for the U.S

“…In a review of the literature on the effects of climate change in semiarid riparian ecosystems, Perry et al (2012) noted that climate-driven changes in streamflow are expected to reduce the abundance of dominant, native, early-successional tree species and increase herbaceous, drought-tolerant, and late-successional woody species (including nonnative species), leading to reduced habitat quality for riparian fauna. Riparian systems will be especially important locations on which to focus monitoring for the early effects of climate change.…”

Tree growth, cambial phenology, and wood anatomy of limber pine at a Great Basin (USA) mountain observatory

“…The effects of climate change on tree phenology have been investigated mostly in temperate and boreal ecosystems, for which an extension of the growing season is usually expected as a consequence of warming, because of earlier onset in the spring (Menzel and Fabian 1999) or delayed cessation in autumn . In arid and semi-arid regions, including the southwest USA (Perry et al 2012), there are difficulties in predicting the balance between increased evapotranspiration, changes in water-use efficiency, and photosynthesis (Le Houérou 1996). Since phenological responses to climate depend on local conditions (Nord and Lynch 2009), a wide range of responses may be expected (Cleland et al 2007), and in situ observations are crucial to improve the predictive quality of phenological models (Richardson et al 2012).…”

Using CASIMIR-VEGETATION Model in the context of modeling riparian woods and fish species to support a holistic approach for environmental flows to be used on river management and conservation

“…The riparian ecosystem ensures the connection between the aquatic and terrestrial ecosystems having an obvious influence in the improvement of the aquatic systems habitat (Naiman and Décamps 1997;Naiman et al 2005) and biological conservation (Broadmeadow and Nisbet 2004;Van Looy et al 2013). The riparian vegetation is especially vulnerable to flow regime changes (Perry et al 2012) because its adaptations and life-histories are synchronized according to the variable conditions of the river dynamics (Stella et al 2006). This interaction between fluvial geomorphic processes and riparian vegetation dynamics can be traced on the topographic diversity, soil moisture gradients and fluvial disturbance patches (Bornette et al 1998).…”