Spring-to-autumn timing intervals crossed zero in four eastern US camera samples in 2008-2023

We tested whether later spring canopy greening predicts later autumn decline after summer temperature and rain controls. We used 190 camera-years at 28 eastern US cameras in two regions and two periods in 2008-2023. Spring slopes were -0.388 and -0.142 autumn days per spring day in North, and +0.876 and +0.133 in South. All four ordinary and four-test confidence intervals included zero. All fitted sensitivity intervals also included zero. Conditional autumn date ranges permitted both slope signs in all four samples. These data do not establish a repeated positive seasonal link or its absence. The early southern model has only three spatial clusters and four residual degrees of freedom. Selected views, missing seasons, changing cameras, spring date error and omitted weather limit inference. This is an exploratory association test, not a test of physiological mechanism, pollution or a causal climate effect. Code, source hashes, aggregate results and reproduction instructions are included. Source records remain external.