The spread of Adelges tsugae (Hemlock Woolly Adelgid) directly threatens the survival of Tsuga canadensis (Eastern Hemlock) and has also triggered pre-emptive and salvage logging. In this study, we took advantage of a 25-year-old accidental experiment involving Eastern Hemlock removal by logging at Smith College's MacLeish Field Station, in western Massachusetts, to investigate how microclimate, ecosystem processes, and forest-floor animal communities might change in the decades following Eastern Hemlock loss. On average, mean understory light levels in summer were 68% higher under young Black Birch (Betula lenta) canopies as compared to adjacent mature Eastern Hemlock forest. Mean daily air temperature, relative humidity, soil temperature, and organic-layer moisture content were similar between young Black Birch and mature Eastern Hemlock plots, although some of these factors were significantly more variable in the former. The soil organic horizon was significantly thicker in Eastern Hemlock plots, but net nitrification rates did not differ substantially between young Black Birch and mature Eastern Hemlock forest plots. We detected significantly greater densities of microarthropods (e.g., mites, collembolans) in the forest floors of Eastern Hemlock plots, possibly linked to the thicker organic horizon. Our results indicate substantial changes in forest structure and microarthropod communities with Eastern Hemlock removal, but little evidence of large changes in key ecosystem processes, like nitrogen cycling. Other sites that represent similar accidental experiments with Eastern Hemlock removal due to past human disturbance likely exist and should be studied before intact reference stands are lost to Hemlock Woolly Adelgid or preemptive salvage logging.