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Project ID:

24-1-01-27

Year:

2024

Date Started:

07/01/2024

Date Completed:

Title:

Drivers of conifer regeneration in successively burned areas in the central Sierra Nevada

Project Proposal Abstract:

1. Problem Statement
Increasing fire activity and burned areas in the North American West due to climate change and historical fire suppression (Westerling et al. 2016, Abatzoglou et al. 2021) has numerous impacts on coniferous forest structure and successional pathways. Repeat fires in quick succession, or short interval reburns, can lead to risk of recruitment failure since the trees that regenerated from the first fire may not have time to reach maturity and provide a seed source for the next generation. Recruitment failure is one of the avenues of eroding forest resilience, as conifer forests experiencing short interval reburns may convert to shrublands or grasslands over time (Coop et al. 2020, Falk et al. 2022). Research into short interval reburns and the natural conifer regeneration that may or may not follow is lacking and is critical to help managers locate areas that are at risk of type conversion.
2. Objectives
We intend to examine the drivers of conifer regeneration in successively burned areas in the central Sierra Nevada by looking at reburned areas within the 2021 Caldor Fire. We will do this by taking advantage of data already collected for a Caldor post-fire monitoring project, as the monitoring plots cover a broad gradient of forest types, elevations, slopes, and aspects. In addition, the existing plot network covers several previous fires: the 2004 Freds fire, the 2011 Long Fire, and the 2019 Caples Fire. We will use Poisson regression models to estimate seedling density (by species) as a function of time since initial fire, burn severity of initial and subsequent fire, as well as overstory species and other biophysical variables. We hypothesize that the strongest driver of recruitment will be time since initial fire and the existing conifer species density and age or size, and that topoclimatic variables such as slope and climatic water deficit will play more minor roles. In addition to a manuscript, we will communicate our findings via a webinar with the California Fire Science Consortium, as well as produce a Fire Science briefing for JFSP. Lastly, we will produce a decision support module for the existing POSCRPT tool (a previous product of the Safford Lab; Stewart et al. 2021) that helps managers identify areas at risk of recruitment failure due to interactions between multiple burns and environmental variables.
3. Benefits
Forest health and wildfire resilience is at the forefront of multiple government agency priorities, as evidenced by the 2014 National Wildland Fire Management Strategy and the 2022 California Wildfire and Forest Resilience Strategy. The proposed research directly addresses the Secretary of Interiors priorities to conserve land and reduce the impacts of catastrophic wildfire as it will help identify potential mechanisms behind recruitment failure as a result of successive fires. Short-interval reburns are increasing by virtue of increased fire frequency and burned areas, and this novel research will contribute to improving underlying scientific understanding of their ecological impacts. We will make our models publicly available on GitHub so modeling and prediction can be replicated in different ecoregions. We will distribute our decision support tool to managers and scientists at national forests and national/state parks who seek to identify forested areas that have enough biological legacies to persist short interval reburns.

Principal Investigator:

Hugh D. Safford

Agency/Organization:

Forest Service

Branch or Dept:

PSW-Univ of CA-Davis

Other Project Collaborators

Type	Name	Agency/Organization	Branch or Dept
Agreements Contact	Adriane M Boykin	University of California-Davis	Department of Environmental Science and Policy
Budget Contact	Adriane M Boykin	University of California-Davis	Department of Environmental Science and Policy
Student Investigator	Saba J Saberi	University of California-Davis	Department of Environmental Science and Policy