Optimistic Scenario. This scenario assumes that there will be a substantial increase in the annual rate of afforestation and reforestation...
Optimistic Scenario. This scenario assumes that there will be a substantial increase in the annual rate of afforestation and reforestation, due to the growing concern to prevent the global average temperature from rising over the next century and the growth of new commodities based on environmental values, such as carbon capture [5,52,53]. The Paris Agreement and the Kyoto Protocol have designed economic instruments that provide Forests 2023, 14, 82 8 of 17 financial incentives for governments to protect the environment using the private sector for strict pollution standards [29].
In this scenario, most of the parameters of the realistic scenario in Table 3 were considered, assuming an afforestation and reforestation rate higher than that of the realistic scenario (β = 0.04). By increasing the rate of afforestation and reforestation, carbon capture will increase, decreasing the greenhouse effect and regulating environmental temperature and humidity patterns. According to [54,55], they showed that trees have a positive effect on relative humidity increase and temperature reduction. Thus, this scenario assumes an increase in ambient relative humidity in the area where P. radiata plantations are concentrated (h = 0.14). On the other hand, the presence of financial incentives would increase the fire prevention budget by 120% (θ = 0.18) in activities such as thinning, which will indirectly contribute positively to individual growth in the long term (ν = 0.42)
and decrease the continuity of fuel susceptible to fire. The optimal trajectories for live biomass are similar for the three scenarios (Figure 2a), however, as expected, in the optimistic scenario there is greater biomass accumulation (the total area under the curve is 12 300) compared to the other scenarios (10 739 in the realistic and 5 125.4 in the pessimistic scenarios, respectively). In general, the minimum biomass volume coincides with the maximum burned area (Figure 2c), although in the pessimistic scenario this occurs at earlier ages as a result of lower ambient humidity and higher fire propensity [56], which shortens the rotation age. It is also observed that in the following plantation rotation cycles the biomass is lower than in the first cycle for the three scenarios. It could be due to the presence of fires in the three scenarios which causes the volatilization of the main soil nutrients [57].
Volatilization of some major soil nutrients, such as nitrogen and phosphorus, can affect tree growth and limit terrestrial carbon sequestration [58,59]. This model does not consider artificial fertilization of the soil and the plantation starts growing when the minimum burned area occurs. In [10], they argue that a higher reforestation rate, together with prolonging the rotation age, are key strategies to maximize carbon capture and mitigate the negative effects of global climate change. The model corroborates the above since the optimistic scenario considers a higher rate of afforestation and reforestation than the realistic scenario, which increases the volume of forest biomass and there is a prolongation of the rotation age to 29 years, as opposed to the earlier rotation ages determined by the pessimistic (23 years) and realistic (27 years) scenarios. The rotation age of the realistic scenario is within the rotation age range reported by [60] in operational plantations of P. radiata in central Chile. In the realistic scenario the model maintains the same rotation age as in [60]
, while for the pessimistic scenario the rotation age was reduced since the forest was affected by the fire, which forces early felling to avoid damage by new fires, with the consequent emission of CO2 to the atmosphere. In the case of the optimistic scenario, the model prolongs the rotation age due to the positive impact of market incentives for environmental protection. Carbon capture and burned area follow the same trend in all three scenarios (Figure 2b,c). As expected, the maximum burned area occurs years after the maximum biomass volume is produced. The realistic scenario shows a small burned area under the curve of 6258.8,
which suggests that the model realistically reflects the current fire prevention and firefighting situation in Chile, which is more efficient [61,62]. It is also observed in the optimistic scenario that the burned area under the curve is 8313.2, which is greater than the realistic scenario. That scenario happens because in the optimistic scenario there is a greater volume of biomass (Figure 2a). However, in the pessimistic scenario, despite a low volume of biomass, there is a greater burned area under the curve of 10,974 compared to the other two scenarios. This situation is because the relative humidity threshold is the lowest of the three scenarios and the forest is more prone to burning, which decreases the biomass. Finally, Figure 2d shows that the intrinsic growth variable is higher in the optimistic scenario, while the pessimistic scenario is lower and with a flat trend due to the negative effect of the higher number of fires, which affects individual plantation growth.
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