Suitability of vegetation condition metrics as surrogates for bird biodiversity

Surrogate metrics offer a practical means to simplify biodiversity assessments and evaluate responses to environmental change, thereby guiding important management decisions. However, the effectiveness of these surrogates depends on their ability to represent the biodiversity values for which they stand, making rigorous evaluation essential. The Vegetation Integrity metric was developed to quantify biodiversity offset losses and gains in New South Wales, Australia under the Biodiversity Assessment Method. This metric combines multiple vegetation attributes into a single site condition score as a surrogate for broader biodiversity at a site. The underlying assumption is that gains in the Vegetation Integrity metric scores correspond to gains in the species richness and abundance of native plants and animals. We tested this assumption using woodland bird richness, abundance and community condition as indicators of other biodiversity values. Vegetation condition and woodland birds were surveyed at 77 sites, and statistical analyses examined relationships between Vegetation Integrity scores and bird diversity metrics. The Vegetation Integrity metric did not correlate with the richness and abundance of all woodland birds or of threatened woodland birds. It correlated weakly with the richness and abundance of species characteristic of an intact woodland bird community, and with a metric of woodland bird community condition. These weak relationships suggest that the Vegetation Integrity metric is not an adequate surrogate for woodland birds, likely because fauna-specific threats are not reflected in vegetation condition scores. Consequently, decisions based solely on vegetation or habitat data may be inappropriate where management objectives target other aspects of biodiversity. • Vegetation condition metrics are used as surrogates to inform decisions. • It is crucial to test the assumptions of these surrogates. • No correlation with vegetation condition and richness or abundance of woodland birds. • Vegetation condition had a weak correlation with woodland bird condition metrics. • The vegetation condition metric may not be an adequate surrogate for fauna.