Executive Summary: Riparian ecosystems are vital components of the semi-arid landscape because woody riparian plants provide resources that are absent in adjacent vegetation types. Historically, flood played a key role in shaping the composition and structure of riparian forests. In recent decades, however, the frequency and magnitude of floods has decreased and the timing of peak discharge has been altered. In addition, wildfire has increased in importance as an agent of disturbance along many streams. We initiated this study to increase our understanding of fire, flood, and drought processes at our Middle Rio Grande study sites and develop tools that managers of other systems can use to project the response of riparian trees to future changes in flood and fire dynamics. Specifically, our objectives were to:
1. Identify the mechanisms and measure the success of post-fire recovery of riparian trees along the Middle Rio Grande.
2. Use these data to complete the development of a stochastic cottonwood population model.
3. Measure condition of post-wildfire snags and deposition of woody debris in Middle Rio Grande wildfire sites to expand the cottonwood model to include these dynamics.
4. Develop a model platform for projecting tree dynamics in semiarid riparian ecosystems throughout the Desert LCC and the Southern Rockies LCC.
To meet our first objective, we visited three wildfire sites along the Middle Rio Grande to quantify production of basal sprouts, epicormic sprouts, root suckers, and seedlings by native and nonnative trees top-killed by fire. Greater percentages of top-killed saltcedars (Tamarix spp) and Russian olives (Elaeagnus angustifolia) had live basal sprouts than did native Rio Grande cottonwoods (Populus deltoides ssp. wislizenii). Several cottonwoods produced epicormic canopy sprouts at one plot, but these trees represented less than 2% of all cottonwoods observed. Cottonwood seedlings germinated near the river at a site that had burned and flooded in 2008, indicating that wildfire stimulates cottonwood reproduction under favorable hydrological conditions. Our results show that woody riparian plants are capable of recovering or reproducing following fire, but the mechanisms to do so vary among species and sites.
This product was co-funded by multiple Landscape Conservation Cooperatives: Desert LCC and the Southern Rockies LCC.
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“Using the Riparian Plant Population Model Platform”
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