Response of Herb Layer Cover to Experimental Canopy Gaps

Abstract

To monitor response of herb layer species to canopy openings, we created thress single-tree (33-36 m2) and three multitree (51-151 m2) gaps in a northern hardwoods stand. Percent cover of herbs and tree seedlings beneath the gaps and adjacent closed canopy was estimated in late May and July during 1 season before, and 3 seasons after, creation of the gaps. Environmental factor (e.g., light, soil moisture and temperature, and air temperature) were measured beneath gap and canopy. An outbreak of Hydria prunivorata in the 1st 2 postgap seasons opened the remaining canopy during July and August and potentially influenced growth of summergreen understory species. Aster acuminauts, not present on the study area before gap creation, established in two multitree sites by the 3rd postgap season. Early summer herbs, such as Maianthemum canadense and Oxalis acetosella, increased cover over the study period. However, response of these herbs occurred in both gap and canopy locations. Additionally, cover of no herb species correlated significantly with the gap environment. Cover of Prunus serotina seedlings was primarily influenced by moth herbivory in the 1st 2 postgap seasons; however, recovery in the 3rd season was greatest in the largest multitree gap. These results (1) indicate the importance of co-occurring disturbances in the forest and (2) suggest that small gaps are below the threshold for pronounced herb layer response on the Allergy Plateau, USA.