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Since the United States enacted its first species-at-risk legislation in 1966, many jurisdictions have similarly adopted legislation aimed at conserving biodiversity through the identification of species at risk of extinction, the protection of these species from harm, and the establishment of recovery programs (Ray and Ginsberg 1999; Waples et al. 2013). Although these statutes have successfully thwarted extinction for hundreds of species, they have also failed to recover many at-risk species (Schwartz 2008; Mooers et al. 2010; Evans et al. 2016). As global extinction rates approach those observed during the five mass extinction events in Earth’s history (Barnosky et al. 2011), robust, well-implemented conservation laws are critically needed to slow the loss of biodiversity (Westwood et al. 2019; Leclère et al. 2020).

Pacific salmon (Oncorhynchusspp.) carcasses can fertilize riparian forests with marine-derived nutrients when populations make their annual return to natal streams to spawn; however, the strength of this cross-system linkage likely varies substantially among years due to the interannual fluctuations in abundance that characterize most salmon populations. Here, we used a 36-yr time series (1984–2019) of satellite imagery and salmon abundance estimates to assess spatiotemporal associations between forest greenness (a measure of plant productivity) and adult sockeye salmon (Oncorhynchus nerka) abundance in the lower Adams River, British Columbia, Canada. The Adams River sockeye population displays a quadrennial pattern of abundance, with a dominant cohort that spawns every four years in numbers that are typically two to three orders of magnitude larger than non-dominant cohorts. We found that variation in forest greenness was consistently explained best by models including dominant cohort year, whereas models lacking an index of salmon abundance were the lowest-ranked. Greenness of riparian vegetation increased by an average of 0.015 NDVI units (approximately 1%) in the summer after a dominant cohort return, and this effect on greenness persisted into the subsequent fall (11–13months after spawning). The positive association between quadrennial pulses of salmon and riparian greenness occurred in plots both within 30m of the stream and 95–125m away from the stream, indicating that the spatial extent of fertilization may occur well beyond areas directly adjacent to the riverbank. These results suggest that forests respond to cyclical variation in salmon abundance and that overwinter storage of marine-derived nutrients within catchments allows plants to capitalize on these nutrients in the following growing season. Continued advances in remote sensing technology will enhance our understanding of cross-system resource linkages and can inform the ecosystem-based management of Pacific salmon.

Annual spawning migrations by Pacific salmon can provide substantial subsidies to nutrient‐limited freshwater and riparian ecosystems, which can affect the abundance, diversity, and physical characteristics of plant and animal species in these habitats. Here, we provide the first investigation of how salmon subsidies affect reproductive output in plants, focusing on a common riparian shrub, salmonberry (Rubus spectabilis). We studied 14 streams with a range of spawning salmon densities on the central coast of British Columbia, Canada. We determined the effects of chum (Oncorhynchus keta), pink (O. gorbuscha), and total salmon spawning density on the number of fruits per shrub, number of seeds per fruit, fruit weight, and estimated sugar content (° Brix) of salmonberry fruits. We found that the number of fruits per salmonberry shrub increased with increasing salmon density. However, we found no effect of salmon density on the number of seeds per fruit, fruit weight, or sugar content. The effect of salmon density was species‐dependent; the number of fruits per shrub increased with chum salmon density but was not affected by pink salmon density. This could be because chum salmon occur at higher densities and are transferred from water to land at higher rates than pink salmon in our study area. Higher salmonberry fruit production could lead to a larger input of salmonberry fruits to coastal food webs. These results demonstrate how salmon can cross ecological boundaries and influence reproductive output of terrestrial species.