# The Carbon Dynamics of Dry Tropical Afromontane Forest Ecosystems in the Amhara Region of Ethiopia
## 1 Introduction  
Tropical forests account for 50% of the Earth's total plant biomass [1] and store 40% (428 Gt C) of the terrestrial carbon [2]. Tropical forests are threatened by deforestation due to land use changes. A good example is Ethiopia, which experienced a decline in forest covered land area from 40% to less than 10% during the last century [3]. The removal of the forest cover has resulted in severe soil erosion, species extinction, as well as reduction in productivity and carbon sequestration [4]. The main reasons for the rapid land use change is the expansion of agricultural land associated with the demand for fuelwood for a fast growing population [5]. Ethiopia has a population of about 100 million people and an estimated annual increase of 3% or 3 million people, 73% of them working in the agricultural sector [6]. For the rural population, it is increasingly difficult to cover the supply of fuel wood for heating homes and cooking, since only small forest areas are left, and the remaining forests are largely protected. In most of the cases, these forests remained because they are located next to monasteries and are preserved as \"church forests\". However, these \"church forests\" are not untouched, since we can observe strong evidence for forest management impacts. In order to avoid further deforestation and to promote afforestation, the Ethiopian government has selected the forestry sector as one of the green economic pillars to be developed by 2030 [7]. The key goals of the green economy plan are: (i) avoiding further deforestation, (ii) inducing reforestation programs, and (iii) improving forest management by establishing sustainable forest management plans. Ethiopia already takes part in international reforestation programs [8; 9] and has expanded its national goal for reforestation and afforestation to reach 7 million hectares of forests [10]. The goals of the green economy plan are consistent with the strategy for reducing emissions from deforestation and forest degradation (REDD+), promoting sustainable forest management, conserving forest carbon stocks, and increasing the forest carbon stocks of developing countries [11; 12; 13; 14; 15]. One of the main difficulties in implementing REDD+ activities is measuring and ensuring the sustainability of forest management activities based on consistent and reliable biomass and soil data [12; 16]. Out of three different common approaches for assessing the dynamics of forest ecosystems, (i) repeated forest inventories, (ii) repeated forest cover, NPP and NEE estimates from remote sensing (NPP--Net Primary Production, NEE--Net Ecosystem Exchange), and (iii) the application of ecosystem models e.g., biogeochemical-mechanistic models [17], only the latter is applicable for Amhara region. Repeated forest inventories are not available in many developing countries, including Ethiopia whereas remote sensing technology [18; 19; 20] has strong limitations when it comes to addressing stand density changes (e.g., changes in the number of trees within a given stand due to forest management) if the crown cover--often expressed by the leaf area index--is assumed to remain closed [21; 22; 23; 24]. The third carbon assessment option, the application of biogeochemical-mechanistic ecosystem models (BGC-Models) has several advantages. For a comparison of different BGC-Models, see [25; 26]. BGC-Models address carbon, nitrogen, water and energy flux dynamics (above and below ground) within ecosystems and respond to forest management and climate change effects [27; 28; 29; 30; 31]. The carbon storage of ecosystems can be calculated based on key input data such as daily weather, atmospheric CO\({}_{2}\) concentration, nitrogen deposition, general soil information (soil depth, texture) and an eco-physiological parameter setting characterizing the vegetation type or species. Biome-BGC specifically has the advantage that it is fully prognostic, applicable on large temporal and spatial scales and includes effects of forest management on carbon and nitrogen stocks [27].