Do we need more trees to achieve carbon neutrality on livestock farms? Accounting for the negative emissions on small tropical livestock farms in Ecuador

<p>Ecuador, as a signatory to the United Nations Framework Convention on Climate Change, in its Nationally Determined Contribution, has expressed its intention to reduce greenhouse gas emissions (GHG), with a focus on the energy and forest sectors. Despite the socio-economic importance and the growing pressure of agricultural and livestock activities on land use change, this sector is not explicitly considered in the national mitigation goals. Currently, grasslands occupy 57% of agricultural land in Ecuador and cattle, being the main livestock activity, is responsible for at least 46% of agricultural emissions, the third largest source of GHG emissions, after land use change and energy. The foot and mouth disease national eradication campaign carried out in 2016, shows that the cattle population is distributed over approximately 275000 farms, where 80% of these farms can be considered as subsistence systems (<20 animals/farm). Due to the heterogeneity of these systems, mitigation strategies focused on reducing methane from enteric fermentation can be difficult to apply, measure, and report. Another possibility for cattle livestock systems is to focus the mitigation opportunities on maintaining carbon stocks and enhancing carbon sequestration through the management of trees on farms. This study analyses the contribution of trees in pasture areas and forests on small livestock systems for offsetting GHG emissions from cattle activities. In 2018, a survey was performed on 101 farms distributed across the Amazon and coastal region in Ecuador, where herd characteristics and management were recorded.  Farmers were asked to draw the boundaries of the farm on a Google Earth map, identifying the extent of primary and secondary forest areas. Trees in pasture areas were measured on plots of 1000m<sup>2</sup>, with two plots per farm. A UAV survey was performed using a DJI Mavic Pro quadcopter, equipped with an RGB camera, over plots off 125m<sup>2</sup>, and at a flying altitude of 70m. For this work, 37 farms were selected (13 in the Amazon region and 24 in the Coastal region) and GHG emissions calculated from cattle livestock activities using IPCC Tier 1 equations. The aboveground biomass for pasture areas was estimated using the Jucker et al., 2017 equation, with tree characteristics derived from the UAV survey. Average results were extrapolated to the total pasture area reported by farmers in the survey. Primary and secondary forest areas were identified from satellite images. Forest state (degradation level) was estimated using NIR data from SENTINEL-2/LANDSAT 8/PlanetScope. Aboveground biomass estimates for forests were obtained from published data using similar site conditions. Emissions from cattle activities are expressed as carbon equivalent. Biomass carbon was estimated as 0.47 of total biomass.</p>