Climatic Aridity Shapes Post-Fire Interactions between Ceanothus spp. and Douglas-Fir (Pseudotsuga menziesii) across the Klamath Mountains

Damla Cinoğlu,Jonathan R Thompson,Alan J Tepley,Kristina J Anderson-Teixeira,Howard E Epstein,Steven S Perakis

doi:10.3390/f12111567

Abstract

Climate change is leading to increased drought intensity and fire frequency, creating early-successional landscapes with novel disturbance–recovery dynamics. In the Klamath Mountains of northwestern California and southwestern Oregon, early-successional interactions between nitrogen (N)-fixing shrubs (Ceanothus spp.) and long-lived conifers (Douglas-fir) are especially important determinants of forest development. We sampled post-fire vegetation and soil biogeochemistry in 57 plots along gradients of time since fire (7–28 years) and climatic water deficit (aridity). We found that Ceanothus biomass increased, and Douglas-fir biomass decreased with increasing aridity. High aridity and Ceanothus biomass interacted with lower soil C:N more than either factor alone. Ceanothus biomass was initially high after fire and declined with time, suggesting a large initial pulse of N-fixation that could enhance N availability for establishing Douglas-fir. We conclude that future increases in aridity and wildfire frequency will likely limit post-fire Douglas-fir establishment, though Ceanothus may ameliorate some of these impacts through benefits to microclimate and soils. Results from this study contribute to our understanding of the effects of climate change and wildfires on interspecific interactions and forest dynamics. Management seeking to accelerate forest recovery after high-severity fire should emphasize early-successional conifer establishment while maintaining N-fixing shrubs to enhance soil fertility.

Highlights

Disturbance–recovery dynamics shape the structure and function of forests and are highly sensitive to climate change [1,2]
Douglas-fir biomass was highly variable among plots including near-zero values in at least one plot sampled at each time since fire, which resulted in the lack of a significant linear relationship with time since fire (p = 0.69)
Rapidly declined in biomass within two decades as it became overtopped by taller Douglas-fir and other conifer or broadleaf tree species

Summary

Introduction

Disturbance–recovery dynamics shape the structure and function of forests and are highly sensitive to climate change [1,2]. Harsh abiotic post-disturbance conditions can drastically slow rates of community-level succession and delay recovery [3]. Climate change impacts early-successional dynamics through altered disturbance regimes and a potentially harsher post-disturbance abiotic environment [4]. Combined with exacerbated drought conditions, increased frequency and severity of wildfires can suppress tree regeneration both from slower tree recruitment and growth rates, and enhanced competition due to post-disturbance shrub sprouting [2,5,6]. Empirical evidence shows that climate change strongly influences post-fire recovery dynamics on multiple scales [7]. At broader scales, altered fire regimes due to climate change can influence landscape-level post-fire recovery trajectories [8]. Plant functional types (e.g., shrubs, conifers) might be differentially impacted by climate change, leading to novel assemblage patterns [1]

Methods

Results

Conclusion