Vincent de Leijster

123 Chronosequence analysis of economic performance of agroforestry coffee farms in Colombia 6 6.2.4.1 Potential revenue We calculated potential additional revenues from the non-marketed products and services that were produced on the farm, namely tree fruits, Musa fruits, timber, and carbon. To calculate the ‘value of non-marketed tree fruits and Musa fruits’, we used the average fruit production of each fruit tree species and their average farm-gate price, which we obtained from the farms that did market these products (see appendix 6). For each fruit species, we multiplied fruit tree or Musa plant density by the average production per tree per year, and by the average price that was paid for the specific fruit. For the ‘value of non-marketed timber’, we extrapolated from the data obtained for the group of farmers that had sold timber on the farm and concluded that every 18 years about 18% of the trees were harvested (appendix). We standardized the actual timber gross revenues by dividing these revenues by the standing timber tree density. Then we assumed that 50% of tree could be sustainably harvested every 18 y, and by adjusting for that we calculated potential timber benefits based on standing timber tree density. For the remaining 50% and the other trees (fruit, legume and native trees) we calculated the ‘value of non-marketed carbon offsets’. For this purpose, we used the diameter at breast height (DBH) and tree height (H) of each tree as measured in the field to calculate the carbon content, using the allometric equation of Chave et al. (2014): AGC = 0.47 · 0.0673 · (ρ · DBH 2 · H) 0.976 (equation 1) The total carbon stock (AGC), was first standardized to ha, and then multiplied by the conversion factor of 3.67 to account for the weight difference between CO 2 and solid carbon. The total sequestered CO 2 was then multiplied by the global average voluntary carbon price of reforestation projects in 2018 (€2.85/tCO 2 ; Hamrick and Gallant, 2017). Then, we annuitized this total carbon value (TCV), using a project life time (t) of 30 years, and a discount rate (r) of 8% (Cacho et al., 2013), to obtain the annual potential benefits from carbon offsets (CV y ), using the following equation: CV y = TCV*(0.1/((1+ r )^ t )-1))+0.1) (equation 2) We also examined amore conservative (minimum) and amore optimistic scenario (maximum) for potential timber and carbon benefits, by varying the timber harvesting regime (18%, 50% or 100% of the standing trees per 18 years), discount rate (6%, 8% or 10%, and carbon price (€2.85 or €13.35 /tCO 2 ). The description of these scenarios and the results are presented in the appendix (appendix 6).