Cumulative effects of spruce budworm and moose herbivory on boreal forest ecosystems

Ungulate herbivory is a key natural disturbance in many ecosystems. In forest ecosystems, ungulate often co-occurs with other disturbances yet there are few studies looking at the cumulative impacts of ungulates and on dynamics. We report an 18-year experiment to investigate combined effects introduced, non-native moose native spruce budworm balsam fir recruitment regeneration. Specifically, we measured inputs into early life-history components dominant boreal ecosystems such as seed density, seedbed quality, seedling sapling height well adult density eight paired exclosure control sites across gradient (i.e. no outbreak, recent old outbreak) that resulted closed, partially open canopies. Piecewise structural equation models (SEMs) revealed strong negative effect indirect this mediated through density. observed similar pattern lowest densities canopy, then closed As expected, SEM showed positive bryophyte cover The support for exclusion saplings were average taller denser than plots these differences most pronounced canopies created by undisturbed or canopy sites. Overall, show evidence interactive all life stages negatively affecting regeneration forests. Human activities creating conditions facilitate expansion increased herbivores ecosystem functioning. A greater understanding how interacts needed improve our predictions dynamics under global change. free Plain Language Summary can be found within Supporting Information article.