• Red Rocks with water in front of them in the desert.
  • Clouds behind Joshua Tree and bushes.
  • Desert flowers blooming in bushes in front of mountains in the desert.
  • Setting sun reflecting of clouds of orange and blue behind a joshua tree.
  • Hoover Dam intake towers with water behind the dam showing that it is not full.


Modeling woody plant regeneration and debris accumulation under future streamflow and wildfire scenarios in the Desert LCC

Science Need(s)

Interactions between ecosystems and hydrology; Impacts of climate change and land/resource management to watersheds and associated hydrogeologic resources

Grantee: Grassland, Shrubland, and Desert Ecosystem Science Program, USDA Forest Service Rocky Mountain Research Station
Principle Investigators: Max Smith, Deborah Finch
Cooperative Agreement: $25,920 in funding per year
Project Duration: 2012-2014

Project Goal(s)

Our project objective is to expand cottonwood population models, which we are constructing with data from the Middle Rio Grande, into an applied science tool to predict long-term changes in density of woody vegetation, snags, and woody debris under future streamflow and wildfire scenarios. Agencies will use our results to incorporate future wildfire risk, native plant persistence, and conservation of wildlife habitat into decisions regarding water storage and delivery.   

Brief Project Description

Perennial streams in the Desert LCC support riparian trees such as cottonwood (Populus spp) and boxelder (Acer negundo) that are critical components of habitat for riparian obligate birds and other wildlife species (Webb et al. 2007). Trees, snags, and fallen woody debris provide nesting and foraging sites for a variety of riparian animals (Bateman et al. 2008, Smith et al. 2012). Riparian trees require occasional floods to create space suitable for germination and are dependent on accessible groundwater for growth and survival (Lytle and Merritt 2004). Studies along the Middle Rio Grande in New Mexico have shown that rates of woody debris accumulation are also influenced by hydrology because floods physically remove debris or accelerate its decay (Molles et al. 1998). Changes in streamflow, resulting from increased water demand or climate change, could therefore influence the availability of trees, snags, and woody debris for birds and other wildlife species.

In addition to flooding, wildfire influences the structure of riparian forests. Along flow-restricted streams such as the Middle Rio Grande in central New Mexico, high-severity wildfires are fueled by an understory of abundant woody debris and vegetative growth. Following high-severity fire, cottonwoods and other trees are topkilled, but up to 80% resprout. Post-wildfire forests are thus characterized by numerous snags, resprouted woody plants, and, after snags fall to the ground, large amounts of woody debris (Smith et al. 2009).

Rivers in the Desert LCC differ from one another in flow characteristics, levels of regulation, and vulnerability to wildfire; characteristics that will be influenced by climate change (Seager et al. 2007, Mortiz et al. 2012). An understanding of how changes in streamflow and wildfire frequency will affect structure of live and dead woody vegetation is needed to for managers assess the vulnerability of riparian obligate species to climate change. We are developing stochastic transition models for cottonwood trees and snags along the Middle Rio Grande by modifying Lytle and Merritt’s (2004) stage-structured cottonwood population model (Figure 1). By incorporating influences of flood and wildfire into stage transition rates, we can project future tree and snag density under current conditions and under climate change scenarios. We propose further modifications of this model to create an applied science tool that can be used to model vegetation structure, wildlife habitat, and wildfire risk along streams throughout the Southern Rockies LCC.  

Project Location

The southern stretch of the Middle Rio Grande

Project Tasks

  • Collect and analyze woody debris data in 2013.
  • Add woody debris accumulation rates to the model (2014).
  • Complete a user-friendly version for dissemination.
  • Complete final report.

Project Deliverables

  • Model, coded in R, which can be easily implemented by anyone with data such as streamflow characteristics, current vegetative conditions, and future climate and fire scenarios. Model output will include changes in tree density, snag density, and amounts of woody debris over time.
  • Organize symposia, such the species special session for the 5th International Fire Ecology Congress
  • Produce series of webinars for regional managers and other interested parties, using venues such as the Southwest Fire Consortia
  • Manuscripts including (1) a state of the knowledge summary of riparian drought, flood, and wildfire issues, (2) results from analyses of woody debris accumulation, and (3) model-derived projections of riparian forest structure under various climate and fire scenarios
  • Journal articles

Documents Available for Download