OOS 3-2 - Using zoogeochemistry research to inform natural carbon capture initiatives: a case study of moose density in Newfoundland

Four moose were introduced to Newfoundland from mainland Canada about 120 years ago, to supply the burgeoning population with meat and the tourism industry with sport hunting. Without a predator to restrict its growth, the island’s moose population grew exponentially until the late 1900s, and today is one of the densest in the world.

While moose have become an integral part of Newfoundland’s cultural fabric, their high density threatens the boreal forest there. Boreal forests are historically a carbon sink, taking up more atmospheric carbon dioxide than they emit. When a canopy gap forms (from disturbances like insect outbreaks and commercial timber extraction), boreal tree seedlings grow to fill the gap. This creates hotspots of high-quality forage for moose, whose preferential browsing on these seedlings impedes regeneration. This positive feedback results in sustained canopy gaps; we posited that these gaps would also produce local changes to carbon cycling dynamics.

We measured soil carbon content and cycling in these gaps and in mature forest. We hypothesized that historically high moose herbivory would interact with canopy disturbance to produce gaps with lower soil carbon storage and greater carbon emissions to the atmosphere (e.g. soil carbon flux), caused by accelerated microbial activity and soil carbon turnover. We hypothesized that disturbance type would also moderate effects on carbon dynamics, with timber extraction gaps having greater negative effects compared to insect outbreak gaps due to the removal of hardwood material.

We found that flux was generally higher, and more heterogeneous, in gaps compared to mature forest, with more frequent instances of “hotspots” of high flux reflecting hotspots of soil carbon mineralization. These differences are likely driven by a combination of increased soil temperature at the soil’s surface, and differences in the litter input of organic carbon and nitrogen, as gaps’ plant communities are dominated by fast-growing shrubs and forbs. The interaction of moose density with the creation of canopy gaps threatens the forests’ ability to sequester soil carbon in the long term by accelerating the rate of its consumption as organic matter, a feedback loop sustained by continued moose browsing and the replacement of the closed canopy’s understory with fast-growing meadow species. These data can inform existing moose population management and hunting license strategies to both successfully manage moose population density as well as encourage natural carbon dioxide capture via improved boreal tree species’ regeneration on the island.