# The Long-Term Consequences of Forest Fires on the Carbon Fluxes of a Tropical Forest in Africa
## 4 Discussion  
Fires represent an important disturbance type when considering the terrestrial biosphere [14; 57; 58]. In a forest, fire can lead to strong changes, especially in species composition, forest succession, and carbon dynamics [19]. As African forests in particular are strongly affected by fire, it is important to study the different consequences of fire, as this can have an impact on forest dynamics, as well as on the function of tropical forests as a carbon sink. Two different scenarios were investigated in this modelling study. The first scenario analyzed the changes in aboveground biomass, productivity, and carbon balance of a tropical forest at Mt. Kilimanjaro after a large-scale fire. A second scenario analyzed changes after regularly recurring fires. It turned out that the forest needs more than 100 years to recover to its pre-fire state. The climax species lose the largest amount of biomass, as they dominated the forest before the fire. Productivity and respiration are up to 4 times higher after the fire than before the fire. This is mainly due to the regrowing pioneer species. After the fire, trees of fire-tolerant species will dominate a forest stand. This alters the succession in tropical forest, as it is more species-rich after a fire and the fire-tolerant species prolong the succession. This effect also has an influence on the carbon balance in a tropical forest. Please note that the results presented apply specifically to the parameterized forest area at the Mt. Kilimanjaro region. In addition, both the parameters of the forest model and the parameters of the fire model include uncertainties. Although monthly satellite data were available, it is challenging to make statements about the type of fire (ground fire vs. crown fire) and the area of spread. Important in the analysis of the fire model was the consideration of the feedback of a fire event with the vegetation. This means that a fire has an influence on the vegetation, and the vegetation influences the characteristics of a fire. This was implemented in such a way that a fire only breaks out if combustible material is present and the soil or litter layer is relatively dry. Furthermore, a tree burns depending on its fire tolerance and its age. What is not considered are the long-term effects of fire on soil properties, such as nutrient inputs. Since the growth of trees in the forest model has so far been described independent of the nutrient balance in the soil, nutrient inputs have not been considered in this study. Figure 13: Simulated species diversity for different fire frequencies. In each fire scenario, forest fires were simulated with a frequency of 1 to 10 fires per decade. The parameters are the same as in the standard fire scenario (see Table 1). The species diversity is described with the normalized Shannon Index (standard Shannon Index divided by ln(6)). For this index, the relative biomass fraction of each plant functional type is calculated over the last 300 years of simulation (in total, 6 plant functional types). In fact, no real fire experiment was conducted in the study area at Mt. Kilimanjaro. The fire experiments available in the literature often refer to the effects on grasslands [59; 60; 61]. These experiments involve little cost, the time horizon is manageable, and the damage to nature is not so high (compared to a fire experiment in a forest). Experiments concerning forest fires refer mostly to temperate forests or to the tropical forest in the Amazon. The influence of fire on forest structure, biomass, and species composition was investigated in such an experiment [7; 62]. Losses in living biomass after fire ranged from 10% to 90%, depending on how often fire occurred in the area studied. Our simulations indicate that aboveground biomass can be reduced by between 40% and 80%, and thus the results are comparable to the analyses in the Amazon. This is also confirmed by a second study in the Amazon, which found 42% to 57% losses in biomass after a fire [63].