Climate change may alter forest biodiversity and function including plant dynamics such as growth and gas exchange rates and the success of invasive plant species. Boreal Forest Warming at an Ecotone in Danger (B4WarmED) is a manipulative open-air experiment at two sites in northern Minnesota, addressing the potential for climate warming to alter tree function and species composition at the boreal-temperate forest ecotone through effects on juvenile phenology, physiology, and growth. The goal of this study was to compare plant functional traits of tree species from three groups (invasive temperate, native temperate, and native boreal) grown under two temperature regimes (ambient and warmed 3.4 °C belowground and aboveground) to determine whether an aggressive invasive species is differentially sensitive to climate warming than common native species. Here we present data collected over four years (2009-2012) on tree seedling growth, leaf emergence and senescence, leaf gas exchange rates, and leaf nutrients from a subsample of 11,000 seedlings of 11 species planted in 2008.
Results/Conclusions
We found significant effects of warming on growth that differed among species. Native boreal species showed a decline in growth under the warming treatment, while native temperate and the invasive temperate (Rhamnus cathartica) species generally responded positively to warming. However, the invasive R. cathartica showed the largest increase in growth. This growth response to warming by the invasive species does not appear to be driven by differences in growing season length, as all species extended their growing season in the warmed plots (achieved by both earlier leaf out in the spring and later senescence in the fall). Percent leaf nitrogen was also not a driver of growth per se, as this trait was largely unaffected by the warming treatment. However, while specific leaf area (SLA) of both native groups did not vary among treatments, SLA of R. cathartica declined significantly in the warming treatment, causing increased area-based leaf nitrogen concentrations. Area-based photosynthetic rates followed a similar pattern, increasing in the warming treatment for R. cathartica, but remaining stable or declining in the two native groups. Our growth and leaf trait results suggest that invasive R. cathartica may outgrow and outcompete the native species in northern Minnesota under climate change.