An integrative review of the impact of ungulates on wetland carbon storage and greenhouse gas emissions

Wetlands, spanning freshwater to saline ecosystems, are seasonally or permanently inundated and store over 30% of the worlds carbon within their soils. Ungulates can remove vegetation, disturb soils, and degrade habitats. Although site-level studies exist, broad evaluations of ungulate impacts on carbon stocks and greenhouse gas emissions remain scarce. We assessed how ungulate presence influences aboveground and soil carbon stocks and greenhouse gas emissions in wetlands. Aboveground carbon stocks declined from 36.9 to 3.70 Mg C per ha in the presence of ungulates. Soil carbon stocks were higher in the absence of ungulates (257 Mg C per ha) than in their presence (112 Mg C per ha). CO2 equivalent emissions were higher in the presence of non-native ungulates (38.4 Mg CO2 eq per ha per yr) than in the presence of native ungulates (27.2 Mg CO2 per ha per yr), and higher in freshwater wetlands of warm temperate dry regions when ungulates were present (27.2 Mg CO2 eq per ha per yr) compared to when ungulates were absent (13.2 Mg CO2 eq per ha per yr). Our findings emphasize the importance of expanding research across different climate regions and soil types to support the development of ungulate management strategies that maintain wetland carbon stocks and reduce greenhouse gas emissions.