Biodiversity bottleneck: seedling establishment under changing climatic conditions at the boreal–temperate ecotone
Climate change is increasing global temperatures, severe rainfall events, and the occurrence and severity of drought. Changes in global climate may have negative consequences for particular plant species and for biodiversity overall. In the short term, altered temperature and precipitation regimes may have the most severe effects on plant species near their range limits and in the earliest stages of plant development. To address these issues, we assessed seedling emergence, early survival, and growth of 18 boreal, temperate, and exotic woody species at the boreal–temperate forest ecotone in central Minnesota. We experimentally warmed forest plots to mimic projected warming by the end of the twenty-first century (+ 1.7 °C and + 3.4 °C). We also experimentally removed summer rainfall (~ 42% reduction) to simulate drought conditions in this region. We found that emergence and survival of boreal and exotic species was lower in experimentally warmed plots. This was exacerbated by drought. Temperate species emergence and survival was largely unaffected by climate manipulations (on average). Conversely, temperate seedling growth was greater in warmer conditions, but only when paired with drought. We found that overall seedling species richness was reduced by warming, mostly due to lower boreal and exotic species emergence and survival (conifers were also strongly negatively affected across species-range groups). If temperate seedling emergence and survival does not compensate for loss of boreal species, these forests may experience loss of biodiversity (and associated ecosystem functions) in the future.
KeywordsTemperate Boreal Exotic Invasive Drought Warming Ecotone Seedling Ontogeny
This research was supported by the US Department of Energy, Grant No. DE-FG02-07ER64456; the Wilderness Research Foundation; Minnesota Agricultural Experiment Station, project no. MIN-42-050; and the Maine Timberlands Charitable Trust. We would like to thank the interns and support staff at the Hubachek Wilderness Research Center and the Cloquet Forestry Center.
AJW designed the seedlings study, collected the data, analyzed the data, and wrote the first draft of the manuscript; NAF helped design and conceptualize the seedling study and provided extensive guidance on the manuscript; CB, RR, RM, and PBR conceptualized and designed the B4warmed experiment; and KR and AS collected the data. All authors provided feedback on multiple versions of the manuscript.
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