Annual kelp canopy changes showed no clear mean synchrony shift at 34 coastal cells between 2002–2013 and 2014–2025

We tested whether annual kelp canopy changes became more synchronized in a later period that includes the 2014–2016 marine heatwave. We used the SBC LTER Landsat record and 34 fixed 0.25-degree cells in six regions from Baja California to Washington. Each cell had at least 90% pixel coverage in Q3 of every year in 2002–2025 and at least 10 ha of earlier mean canopy. We calculated pairwise correlations of annual log canopy changes within 2002–2013 and within 2014–2025. Regions had equal weights. Mean correlation was 0.388 earlier and 0.389 later. The difference was +0.001, with a shared-time block resampling interval of −0.189 to +0.160. Planned checks and a further check that includes the 2014 transition did not give a clear mean change. Later mean canopy area was 33–75% of the earlier mean in the five selected California and Baja regions, but 102% in Washington. These area ratios apply to selected cells only. The data do not establish equal synchrony or unchanged spatial insurance. Each period has only 11 annual changes. Northern California and Oregon lacked enough cells under the main rules and are outside the tested scope. The package preserves input tables, pixel extraction code, all estimates and resampling draws, source hashes, figures, and reproduction instructions.

kelp · spatial synchrony · Landsat · marine heatwave · fixed cells · reproducible ecology