The extensive implementation of carved hollows worldwide as part of formal and informal restoration projects highlights a sharp contrast with the nascent data on their effectiveness and long-term suitability for wildlife conservation. Here, we systematically reviewed the available evidence on the use of artificially carved hollows. Our aim was to inform more evidence-based restoration strategies to support hollow-dependent species and guide future research and monitoring. We identified 42 studies published between 1981 and 2025 across eight countries. Over 700 species were documented using artificially carved hollows, primarily invertebrates (176) and fungi (448), but also birds (30), mammals (19), reptiles (7), and amphibians (1). We found that 49 tree species, mainly eucalypts ( Eucalyptus), oaks ( Quercus), and pines ( Pinus), have been used as host trees. Nearly 50% of studies in pine forests focused solely on the red-cockaded woodpecker ( Leuconotopicus borealis). Of studies that reported monitoring, most were relatively short programs (1–3 years). Although almost half of the studies reported on breeding success or individual behavioural responses of species using artificially carved hollows, less than 20% explicitly linked these outcomes to broader population-level benefits, such as a measurable increase in population size or growth rate. Importantly, all population-level studies focused exclusively on the red-cockaded woodpecker. Few studies reported on the time and financial investment of installation. Less than 25% of studies reported on tree-level responses following installation (e.g., changes in tree health or mortality) and most of these were also short-term investigations (less than 3 years). Due to the variability in wildlife species targeted, success rates, methods employed, host tree species used, and paucity of overall available data, we found it difficult to reach meaningful conclusions about the efficacy of artificially carved hollows in general, their impacts on tree health, the functional lifespan of these structures or ongoing maintenance requirements. The limited scope of published literature, averaging fewer than one publication per year, identifies the strong need for more comprehensive research to evaluate the long-term effectiveness and ecological implications of artificially carved hollows for wildlife management and conservation.
Best et al. (Thu,) studied this question.