03/06/2021
The State of Alaska has grants available to eradicate bird cherries. These are unfortunate, misguided grants. The reasons for the war on bird cherries (Prunus padus) that have been promoted is that this invasive species kills moose and salmon. Both of these conclusions are misrepresentations of the data. Bird cherries are useful trees. In addition to the beauty, the bees love the early blooming flowers. Birds love the fruit (and spread the seed everywhere). The wood is very strong and useful. The berries are still processed into flour in Siberia (it is delicious used in baked good to give a chocolate flavor). As global warming continues, spruce trees will likely become extinct. Bird cherries may be an important part of replacements for tree species that can no longer survive here.
The two juvenile moose found dead and examined by ADF&G had essentially empty stomachs with the exception of the noted bird cherries, which contains potentially toxic cyanogenic glycosides. These moose were clearly starving, which unfortunately happens during our harsh winters. Most of the time moose avoid plant containing cyanogenic glycosides, such as bird cherries and our native elderberries. If we want to reduce the deaths of moose, consider how many are killed or maimed by cars, reduce speed limits.
If we want to protect salmon fry, a well-documented problem is road runoff, which contains a chemical from tires that kills salmon (https://www.sciencemag.org/news/2020/12/common-tire-chemical-implicated-mysterious-deaths-risk-salmon). Roadway waste runoff in Anchorage is dumped, untreated, into our creeks and waterways.
The studies that supposedly show harm to salmon by bird cherries don’t. David Roon and his collaborators1 noted decreased terrestrial prey subsidies along riparian corridors where European bird cherry has become the dominant stream bank species. They state simply there may be fewer insects falling out of the trees/shrubs for coho fry to eat. The streams were shown to be unaffected at the current level of cover on the weight or biomass of the sampled coho salmon and the ground litter insect populations were similar. Here is where the story gets more complicated. The most prominent leaf associated biomass that contributed much of the greater abundance of insect mass was a sawfly larvae occurring at a high level in thin leaf alder. The specific species of sawfly was not noted, and there was no discussion that this source of biomass could be from another invasive species. This was around the time that an invasive European green alder sawfly was becoming established.
The same author, David Roon et al. 20182 , in a subsequent paper, noted that the invasive sawfly were decreasing the availability of native terrestrial species and devastating leaf cover but again no impact on the coho was detected. The somewhat unusual, and seemly unsupported conclusion of the two papers is that bird cherry is a problem but invasive sawfly is not when in both cases no impact was detected on urban coho of our riparian streams. This has a somewhat political feel to the conclusion, in the absence of evidence. It also turns out that coho share the opinion of my ducks that sawfly larvae are too nasty to eat.
The point of this discussion is that we have a changing ecosystem with climate change and the introduction of non-native species. Reductionist approaches to single factor changes may miss the complexity and can be “cherry-picked” to support actions. The “evidence” presented is hardly a support for single minded notion of poisoning of bird cherries or green alder saw fly. Invasive insects can open opportunities for less susceptible species, and bird cherries are formidable opportunist. Bird cherries are here to stay and the products of Monsanto are not an answer unless the goal is more product sales—which leads to more issues with non-natives.
Invasive European bird cherry (Prunus padus) reduces terrestrial prey subsidies to urban Alaskan salmon streams
DA Roon, MS Wipfli, TL Wurtz… - Canadian Journal of …, 2016 -
1. Riparian defoliation by the invasive green alder sawfly influences terrestrial prey subsidies to salmon streams
DA Roon, MS Wipfli, JJ Kruse - Ecology of Freshwater Fish, 2018 - Wiley Online Library