Evaluating the impact of private land conservation with synthetic control design.

Private protected areas are increasingly being used to protect biodiversity around the world. To understand the efficacy of these programs, it's important to be able to measure their impact: the difference between the program's outcome and what would have happened without the program. Typically, these programs are evaluated by estimating the average program-level impact, which readily allows comparisons between programs or regions, but masks important heterogeneity in impact across the individual conservation interventions. Here, we present a transparent and robust workflow incorporating synthetic control design combined with statistical matching and time series data to provide an estimate of impact for individual protected areas over time. We also show how individual level impacts can be combined to estimate program-level impact using a meta-analytic approach. We demonstrate our workflow for private protected areas by examining the impact of conservation covenants (legally binding on-title agreements to protect biodiversity) on improving woody vegetation cover in the Goldfields region of Victoria, Australia. Our analysis shows an overall program level impact comprising a 0.3-0.8 % increase in woody vegetation cover per year. However, there is significant heterogeneity in the temporal pattern of impact for individual covenants ranging between -4 to +7% change in woody vegetation cover per year. We compare our results to traditional approaches to estimating program level impact using a subset of covenants that are the same age and find them consistent. This article is protected by copyright. All rights reserved.