Environmental Influences on Density and Height Growth of Natural Ponderosa Pine Regeneration following Wildfires

Darcy H Hammond,Penelope Morgan,Andrew T Hudak,Eva K Strand,Beth A Newingham

doi:10.3390/fire4040080

Abstract

Over the past century the size and severity of wildfires, as well as post-fire recovery processes (e.g., seedling establishment), have been altered from historical levels due to management policies and changing climate. Tree seedling establishment and growth drive future overstory tree dynamics after wildfire. Post-fire tree regeneration can be highly variable depending on burn severity, pre-fire forest condition, tree regeneration strategies, and climate; however, few studies have examined how different abiotic and biotic factors impact seedling density and growth and the interactions among those factors. We measured seedling density and height growth in the period 2015–2016 on three wildfires that burned in ponderosa pine (Pinus ponderosa) forests in the period 2000–2007 across broad environmental and burn severity gradients. Using a non-parametric multiplicative regression model, we found that downed woody fuel load, duff depth, and fall precipitation best explained variation in seedling density, while the distance to nearest seed tree, a soil productivity index, duff depth, and spring precipitation as snow best explained seedling height growth. Overall, results highlight the importance of burn severity and post-fire climate in tree regeneration, although the primary factors influencing seedling density and height growth vary. Drier conditions and changes to precipitation seasonality have the potential to influence tree establishment, survival, and growth in post-fire environments, which could lead to significant impacts for long-term forest recovery.

Highlights

Tree regeneration is a critical aspect of post-wildfire recovery in forested ecosystems, since tree growth is both ecologically and economically valuable
Fine woody fuel load interacted with duff depth, which resulted in a marked peak in seedling density at high fine woody fuel load only when duff depth was around 15 mm (Figure 2B)
We found that 9–15 years post-fire, ponderosa pine seedling density and height growth were generally impacted by different but related factors

Summary

Introduction

Tree regeneration is a critical aspect of post-wildfire recovery in forested ecosystems, since tree growth is both ecologically and economically valuable. In most forested ecosystems, living trees represent one of the largest and most dynamic carbon pools [1], affecting species interactions in a myriad of ways including through changes in the understory light environment and hydrology [2,3]. Following high-severity wildfire, failure of tree regeneration can result in ecosystem type conversion with potential cascading impacts on system-wide species composition and processes [4,5,6]. Due to changing climate as well as changes in fire regimes, conifer regeneration has declined across the western U.S following

Methods

Results

Discussion

Conclusion