The characteristic shrubland of regenerating temperate mixed hardwood forests provide habitat for many early successional specialist species. The irregular shelterwood is a silvicultural method for regenerating a forest that promotes young complex shrubland landscapes for a period of 15–25 years. In this study, we surveyed bird diversity across an irregular shelterwood chronosequence of a southern New England oak-mixed hardwood forest. We measured the variation in diversity across a chronosequence comprising 31 stands and 30 years of growth as of 2022, with particular focus on nesting guilds. Secondly, we conducted a longitudinal analysis of bird diversity in each stand over a period of 16 years to assess the reliability of the shelterwood chronosequence as a within-year proxy for long-term study. Similar to many prior studies, we found that overall diversity and bird abundance decrease as the regenerating shelterwood ages. Over a 30-year period after harvest, Shannon diversity decreased by over 10 %, species richness decreased by over 20 %, and relative abundance decreased by 50 %. Shrub-nesting birds are particularly sensitive to the loss of young regenerating and shrubland habitat and decrease sharply in abundance as a forest ages, from 51 % of the population to 12 % after 30 years. Ground-nesting birds increase in abundance with young regenerating forests and tree-nesting birds are unaffected by stand age, from 8 % to 40 % over 30 years. However, most importantly, we show these trends occurred both longitudinally and within a single year, indicating that the use of a chronosequence is an effective method of measuring trends in bird abundance and diversity over a period of forest regeneration. This is the first study demonstrating the validity of this method for estimating breeding birds in temperate forests and allows for a more widespread application of its use, particularly where long-term monitoring has not been done.
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