This research assessed the post-fire early successional interactions between Ceanothus spp. and Douglas-fir in the Klamath River Basin of the Pacific Northwest with a focus on time since fire and climatic water deficit (i.e. drought). Climate change is expected to increase drought and induce more frequent and higher severity fires, affecting plant community composition and successional dynamics in the Klamath region. Post-fire communities are predicted to transition from needle-leaf evergreen forest to a shrub-chaparral ecosystem, which will influence the dynamics of energy exchange, water balance, and biogeochemical cycling. In this context, it is important to examine early successional interactions between Ceanothus spp. and Douglas-fir along gradients of time since fire and climatic water deficit, as they will determine the future vegetation constituents of the Klamath forests. These interactions have the potential to be shaped by the nitrogen-fixing capacity of Ceanothus and its effects on soil nitrogen availability.
Results/Conclusions
Our results indicate that plots with higher Ceanothus biomass had lower soil C:N levels, suggesting the effects of N-fixation. Douglas-fir growth rates however remained stable with increases in soil N given time since fire and climatic water deficit. Successional patterns are observed with decreasing Ceanothus and increasing Douglas-fir relative biomass with time since fire and lower climatic water deficit. Interspecific competition is assessed through the interaction of Ceanothus abundances and Douglas-fir growth rates on a gradient of time since fire and climatic water deficit. Plots that have a greater abundance of Ceanothus also have significantly lower relative abundances and biomass values for Douglas-fir. Other studies in the literature additionally show the prominence of soil moisture availability, light, and space on the post-fire regeneration of Douglas-fir in the presence of Ceanothus. Distance to live seed source remains a crucial aspect of the regeneration process. Results from the study presented here contribute to our understanding of the effects of wild fire management on forest community dynamics under climate change scenarios.