Abstract1. Open-top chambers simulate global warming by passively increasing air temperatures in field experiments. They are commonly used in low-stature alpine and arctic ecosystems, but rarely in taller-stature plant communities because of their limited height.2. We present a modified International Tundra Experiment (ITEX) chamber design for year-round outdoor use in warming taller-stature plant communities up to 1.5 m tall. We report a full year of results for the chambers' effects on air and soil temperature, relative humidity, and soil moisture in a northern hardwood forest clearing and a southern early successional grassland site located in Michigan, USA.Detailed construction plans are also provided.3. The chambers elevated daytime air temperatures at 1 m height by 1.8°C above ambient levels, on average over an entire year, at both the northern and southern site. The chambers did not affect relative humidity at either site. The chambers did not alter average soil temperature or moisture at the northern site and reduced soil temperatures and soil moisture at the southern site. The chambers increased variability in soil freeze/thaw cycles at both sites. K E Y W O R D Sclimate change, open-top chamber, passive warming, plant community ecology, warming experiment

Climate change is expected to favor exotic plant species over native species, because exotics tend to have wider climatic tolerances and greater phenological plasticity, and also because climate change may intensify enemy release. Here, we examine direct effects of warming (+ 1.8 °C above ambient) on plant abundance and phenology, as well as indirect effects of warming propagated through herbivores, in two heavily invaded plant communities in Michigan, USA, separated by approximately three degrees latitude. At the northern site, warming increased exotic plant abundance by 19% but decreased native plant abundance by 31%, indicating that exotic species may be favored in a warmer world. Warming also resulted in earlier spring green-up (1.65 ± 0.77 days), earlier flowering (2.18 ± 0.92 days), and greater damage by herbivores (twofold increase), affecting exotic and native species equally. Contrary to expectations, native and exotic plants experienced similar amounts of herbivory. Warming did not have strong ecological effects at the southern site, only resulting in a delay of flowering time by 2.42 ± 0.83 days for both native and exotic species. Consistent with the enemy release hypothesis, exotic plants experienced less herbivory than native plants at the southern site. Herbivory was lower under warming for both exotic and native species at the southern site. Thus, climate warming may favor exotic over native plant species, but the response is likely to depend on additional environmental and individual species' traits.

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