Trends in bird diversity over 12 years in response to large-scale eucalypt plantation establishment: Implications for extensive carbon plantings

Abstract

Large-scale plantations established for timber production or for carbon sequestration can dramatically transform landscapes, however little is known about the response of biodiversity. We report on trends in bird diversity during a 12year longitudinal study on three large-scale plantations of locally indigenous eucalypts in northern New South Wales, Australia. The study began in a farmland mosaic and has continued to follow bird occupancy rates after the establishment of eucalypt plantations within the paddock areas. Bird surveys were undertaken at focal trees located in different classes of remnant vegetation, which became embedded within the plantations as well as in the plantation matrix itself. Reference sites were also located in adjacent blocks of forest. We found that species richness increased over time in the plantation matrix, as well as remnant vegetation embedded within the plantation (isolated trees, tree patches and remnants, but not riparian locations). When birds were classified as forest-dependent, forest-associated or mosaic generalist, the species richness of forest-associated birds increased and mosaic generalists decreased over time at selected remnant categories. Richness of forest-dependent birds did not change over time. After plantation establishment, bird composition at remnant locations gradually shifted towards that of forest, although all locations remained distinct from forest even after 11years of plantation growth. The response of 36 individual species was assessed with 47% percent of species increasing over the 11years and 31% of species declining. Notably the noisy miner, a hyper-aggressive species, decreased over time. We suggest a reduction in the occurrence of this species could be an important contributor to the increase in the diversity of smaller bird species. These include species of regional concern, such as the eastern yellow robin and the rufous whistler, which increased over the study period. Our results suggest that large-scale plantations of locally indigenous species contribute to ecological restoration of cleared landscapes. However, the plantation matrix after 11years provided less suitable habitat than nearby forest as it supported fewer species, especially for birds that are characteristic of forest. Retention of remnant vegetation at the time of plantation establishment, including large isolated paddock trees, contributed considerably to the biodiversity present in the plantations and is likely to provide key refuge areas during any subsequent harvesting. Continued collection of longitudinal data are needed to describe changes through the full plantation rotation and harvest, while the extent to which other taxa respond to eucalypt plantation establishment also requires documentation.