COS 51-1 - Measuring the impacts of insect outbreaks, fire, and moose on carbon stocks in the boreal forests of Newfoundland, Canada

Abstract: Forest fires and insect outbreaks (e.g., spruce budworm (Choristoneura fumiferana)) are natural disturbance agents that create canopy openings and drive eastern North American boreal forest cycles. These openings support natural forest regeneraƟon, with highly palatable, fast-growing, deciduous, and coniferous trees growing into the canopy. Moose (Alces alces) were introduced to the boreal forests on
the island of Newfoundland, Canada more than a century ago. Since their introducƟon, moose have impacted forests on the island through selecƟve browsing of shrubs and young trees, as well as trampling and defecaƟng. Under high moose densiƟes, moose herbivory following natural disturbances can slow or disrupt natural forest regeneraƟon with potenƟal impacts on carbon sequestraƟon. Moose effects have been parƟcularly problemaƟc in protected areas such as naƟonal parks, where hunƟng is oŌen restricted. Our objecƟve was to experimentally evaluate how moose herbivory following natural disturbance impacts the storage of carbon in Newfoundland boreal forests and soils.

We measured carbon stocks under different moose densiƟes and natural disturbance histories in 23 plots in Gros Morne (GMNP) and Terra Nova (TNNP) NaƟonal Parks (n=46 plots total). Twenty of these plots were located in paired long-term moose exclosure-controls (i.e., fenced for ~25 years; n=10 ex; 10 ctrl). At each plot, we measured traits of trees, deadwood, shrubs, saplings, herbaceous vegetaƟon, and ground vegetaƟon and then we fit published allometric models to these data to esƟmate carbon stocks in each pool. We also collected samples of forest liƩer and organic soil to measure carbon stocks in the soils at each plot. We fit generalized linear models (GLMs) to analyze how natural disturbances, moose herbivory, and their interacƟon impact i) aboveground, ii) belowground, and iii) total carbon stocks across our study area. We also fit GLMs to the paired exclosure-control data to further parƟƟon moose effects on the different carbon pools. Our analysis shows that insect outbreaks and forest fires have, on average, 2.6 and 2.1 x less total carbon stored compared to mature forests. Our data show that natural disturbances are the major driver of carbon sequestraƟon in our boreal system, but moose densiƟes are negaƟvely affecƟng carbon storage. Moose may parƟcularly impact carbon sequestraƟon over longer periods if their populaƟons are maintained at high densiƟes, thereby slowing forest regeneraƟon. We did not observe evidence of moose exclusion or natural disturbance effects on paired exclosure-controls however, understanding the impact of spaƟal variability on carbon dynamics will be key to future research. .