Abstract
The persistence and distribution of species under changing climates can be affected by both direct effects of the environment and indirect effects via biotic interactions. However, the relative importance of direct and indirect climate effects on recruitment stages is poorly understood. We conducted a manipulative experiment to test the multiway interaction of direct and competition-mediated effects of climate change on vegetation dynamics. Following stand-replacing fire in California mixed-conifer forest, we seeded two conifer species, Pinus ponderosa and Abies concolor, in two consecutive years, one relatively normal and the other with an unusually wet and snowy winter followed by a hot summer. We additionally manipulated snow amount and competitive environment for both years. We found the effects of the snowpack treatment were contingent upon other abiotic factors (year of seeding) and biotic factors (shrub competition). Under ambient snowpack, shrubs reduced recruitment of P. ponderosa seedlings, but this negative effect disappeared with reduced snowpack. Additionally, the effects of shrubs on seedlings differed between cohorts and by life stage. In a warmer future, decreased snowpack may increase seedling emergence, but hotter and drier summers will decrease seedling survival; the effects of shrubs on conifers may become less negative as temperatures increase.
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Acknowledgements
This work was funded by Henry A. Jastro Graduate Research Awards, a University of California Davis Department of Plant Sciences MacDonald Fellowship, and a National Science Foundation Graduate Research Fellowship (to CW). Site location and research permissions were obtained with the help of Dana Walsh of the US Forest Service, and herbicide application was conducted under the supervision of Kurt Vaughn. We are grateful to University of California Davis students who assisted with fieldwork. Finally, we thank two anonymous reviewers and editor Kendi Davies for their detailed feedback on this manuscript.
Funding
This work was funded by Henry A. Jastro Graduate Research Awards, a University of California Davis Department of Plant Sciences MacDonald Fellowship, and a National Science Foundation Graduate Research Fellowship (to CW).
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CW, HS, and TY conceived the ideas and designed methodology; CW collected the data; CW and DY analyzed the data; CW led the writing of the manuscript. All authors contributed critically to the drafts and gave final approval for publication.
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Data and R code are available in a figshare repository, https://doi.org/10.6084/m9.figshare.3172468.
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Communicated by Kendi Davies.
Climate change has the potential to shift the balance between species regenerating after fire. We experimentally tested the effects of climate change on post-fire regeneration and shifts in species interactions. We found that the effects of climate manipulation on conifer regeneration differ depending on year of planting and interactions with neighboring plants. This demonstrates the importance of experiments initiated across multiple years in teasing apart abiotic and biotic components of climate change impacts.
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Werner, C.M., Young, D.J.N., Safford, H.D. et al. Decreased snowpack and warmer temperatures reduce the negative effects of interspecific competitors on regenerating conifers. Oecologia 191, 731–743 (2019). https://doi.org/10.1007/s00442-019-04536-4
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DOI: https://doi.org/10.1007/s00442-019-04536-4