4.4. Riparian Vegetation as an Indicator of Habitat
Persistence
A large base of research points to drought as the major driver of
shrinking vegetated zones in arid and semiarid systems (e.g., Stromberg
et al., 2007; Garssen, Verhoeven, & Soons, 2014; Andersen, 2016);
however, further research indicates the role of ephemeral wetlands in
ecosystem persistence in the face of extreme drought (Leigh, Sheldon,
Kingsford, & Arthington. 2014; Sandi et al., 2020). The presence of
dryland wetlands allows arid or semiarid riverscapes to exist as
isolated refugia during periods of extreme drought, with low flow
channels providing short-term connections between otherwise isolated
sections of the river network. Additionally, the presence of riparian
vegetation reduces the rates of evaporation, contributing to water
retention in dryland systems (Rodrigues, Gomes Costa, Raabe, Medeiros,
& Carlos de Araújo, 2021).
We demonstrated the valley plug and resulting overflow from the main
channel into the valley bottom allowed the riparian zone to increase
substantially over 12 years. Though we cannot make a definitive claim
that this system has experienced increased resilience, visual estimates
and delineation of the riverscape demonstrate the valley plug has
experienced an increased capacity for water retention beyond what is
typical during drying. We observed from imagery collected in 2021 that
the system was retaining overflow inundation well into the expanded
riparian zone through late-August, prior to summer monsoon flooding.
Given what is known about the importance of riparian vegetation, as well
as dryland wetland systems in arid and semiarid regions, it is logical
to suggest that this valley plug is contributing to habitat persistence
in the face of amplified drought in the American Southwest.