The practice of space-for-time substitution in landscape ecology has provided vital insights for conservation policy, but whether these insights are reliable remains inconclusive. Here, my objective was to test space-for-time substitution using data from the North American Breeding Bird Survey (BBS) and Global Forest Change (GFC) to compare the effects of landscape-level forest cover on bird community metrics over time and space across 31 space-time comparisons in the United States and Canada. Temporal and spatial effects of forest cover on mean bird species richness and mean bird abundance were weakly correlated across the 31 comparisons for both forest and open-habitat species. Bird-forest cover relationships measured over time were more variable and inconsistent than those observed in space. Overall, my study results do not support the use of space-for-time substitution when studying North American birds.