Thresholds for adding degraded tropical forest to the conservation estate
Authors: Ewers Robert M. , Orme C. David L. , Pearse William D. , Zulkifli Nursyamin , Yvon-Durocher Genevieve , Yusah Kalsum M. , Yoh Natalie , Yeo Darren C. J. , Wong Anna , Williamson Joseph , Wilkinson Clare L. , Wiederkehr Fabienne , Webber Bruce L. , Wearn Oliver R. , Wai Leona , Vollans Maisie , Twining Joshua P. , Turner Edgar C. , Tobias Joseph A. , Thorley Jack , Telford Elizabeth M. , Teh Yit Arn , Tan Heok Hui , Swinfield Tom , Svátek Martin , Struebig Matthew , Stork Nigel , Sleutel Jani , Slade Eleanor M. , Sharp Adam , Shabrani Adi , Sethi Sarab S. , Seaman Dave J. I. , Sawang Anati , Roxby Gabrielle Briana , Rowcliffe J. Marcus , Rossiter Stephen J. , Riutta Terhi , Rahman Homathevi , Qie Lan , Psomas Elizabeth , Prairie Aaron , Poznansky Frederica , Pillay Rajeev , Picinali Lorenzo , Pianzin Annabel , Pfeifer Marion , Parrett Jonathan M. , Noble Ciar D. , Nilus Reuben , Mustaffa Nazirah , Mullin Katherine E. , Mitchell Simon , Mckinlay Amelia R. , Maunsell Sarah , Matula Radim , Massam Michael , Martin Stephanie , Malhi Yadvinder , Majalap Noreen , Maclean Catherine S. , Mackintosh Emma , Luke Sarah H. , Lewis Owen T. , Layfield Harry J. , Lane-Shaw Isolde , Kueh Boon Hee , Kratina Pavel , Konopik Oliver , Kitching Roger , Kinneen Lois , Kemp Victoria A. , Jotan Palasiah , Jones Nick , Jebrail Evyen W. , Hroneš Michal , Heon Sui Peng , Hemprich-Bennett David R. , Haysom Jessica K. , Harianja Martina F. , Hardwick Jane , Gregory Nichar , Gray Ryan , Gray Ross E. J. , Granville Natasha , Gill Richard , Fraser Adam , Foster William A. , Folkard-Tapp Hollie , Fletcher Robert J. , Fikri Arman Hadi , Fayle Tom M. , Faruk Aisyah , Eggleton Paul , Edwards David P. , Drinkwater Rosie , Dow Rory A. , Döbert Timm F. , Didham Raphael K. , Dickinson Katharine J. M. , Deere Nicolas J. , de Lorm Tijmen , Dawood Mahadimenakbar M. , Davison Charles W. , Davies Zoe G. , Davies Richard G. , Dančák Martin , Cusack Jeremy , Clare Elizabeth L. , Chung Arthur , Chey Vun Khen , Chapman Philip M. , Cator Lauren , Carpenter Daniel , Carbone Chris , Calloway Kerry , Bush Emma R. , Burslem David F. R. P. , Brown Keiron D. , Brooks Stephen J. , Brasington Ella , Brant Hayley , Boyle Michael J. W. , Both Sabine , Blackman Joshua , Bishop Tom R. , Bicknell Jake E. , Bernard Henry , Basrur Saloni , Barclay Maxwell V. L. , Barclay Holly , Atton Georgina , Ancrenaz Marc , Aldridge David C. , Daniel Olivia Z. , Reynolds Glen , Banks-Leite Cristina 
Published: July 2024

Logged and disturbed forests are often viewed as degraded and depauperate environments compared with primary forest. However, they are dynamic ecosystems1 that provide refugia for large amounts of biodiversity2,3, so we cannot afford to underestimate their conservation value4. Here we present empirically defined thresholds for categorizing the conservation value of logged forests, using one of the most comprehensive assessments of taxon responses to habitat degradation in any tropical forest environment. We analysed the impact of logging intensity on the individual occurrence patterns of 1,681 taxa belonging to 86 taxonomic orders and 126 functional groups in Sabah, Malaysia. Our results demonstrate the existence of two conservation-relevant thresholds. First, lightly logged forests (<29% biomass removal) retain high conservation value and a largely intact functional composition, and are therefore likely to recover their pre-logging values if allowed to undergo natural regeneration. Second, the most extreme impacts occur in heavily degraded forests with more than two-thirds (>68%) of their biomass removed, and these are likely to require more expensive measures to recover their biodiversity value. Overall, our data confirm that primary forests are irreplaceable5, but they also reinforce the message that logged forests retain considerable conservation value that should not be overlooked.