## 1 Introduction  
Plantation forests are forests established by planting or deliberate seeding to achieve principally economic goals [1] such as timber, energy, fiber, and non-woody forest products [2]. They are also established for soil and water conservation and carbon sequestration in the process of afforestation and reforestation [3]. According to the FAO [2] report, plantation forests cover about 131 million ha worldwide and account for 3% of the global forest. Between 1990 and 2020, their area increased by 55.8 million ha, with the biggest jump (21.2 million ha) recorded between 2000 and 2010. The impact of plantation forests on the environment will depend on what land use they replace [4]. If they are established on frequently cultivated land for a long time or degraded lands, they may provide substantial opportunities for biodiversity conservation [5] and deliver vigorous ecosystem service [6], but plantations converted from the natural forest have adverse impacts on biodiversity [7]. Plantation forests are essentially significant in fragmented landscapes, where they may account for a large amount of remaining forest habitat [8] and can serve as corridors between habitats [4]. Small-scale plantation forests initiated by farmers on degraded lands have become important in Ethiopia, particularly since the mid-1990s [9]. An estimated area of 754,900 ha of the country is covered by small-scale plantation forests, and of this, 84.7% (639,400 ha) is found in the Amhara Region [9]. Critical levels of land degradation and reduced productivity forced farmers to start planting trees, often with predominantly exotic and fast-growing species at the expense of crop production [10; 11; 12]. In the Northwestern Highlands of Ethiopia, specifically in the Fagita Lekoma District, the study site and one of the districts in the Amhara Region, growing Acacia _decurrens_ plantations on small-size farmlands have been rapidly increasing and are widely planted because of the economic and environmental benefits. This species is preferable due to its advantages of a fast-growing rate and adaptability to degraded and acidic soil conditions [13]. Additional reasons that motivate farmers to plant this species are its use as fuel and construction wood, animal fodder, charcoal production and availability of market, and soil fertility maintenance [14]. It also creates job opportunities for landless community parts and supports local livelihoods and rural developments, especially when managed by smallholders [13; 15]. Land-use change from cultivated land and grassland into Acacia _decurrens_ plantation has been common in the district in the past three decades and resulted in an increase in the forest cover of the district by more than 250% between 1887 and 2015 [16], and around 400% between 2006 and 2017 [17]. A range of ecosystem services can be obtained from plantation forests established on degraded lands that require restoration [18]. New plantation forests generated from former agricultural land can improve ecosystem service [19]. The rapid expansion of plantation forests significantly affects climate, hydrology, biodiversity, and the terrestrial carbon cycle. The expansion of plantation forests can amend the understory climate condition and soil properties [20], and water quality [21]. These changes occur as a result of changes in temperature, rainfall, land use type, and storm frequency and magnitude [4]. In addition, plantation forests can contribute strongly to regulating the environment, biodiversity, and socioeconomic functions, especially carbon sequestration [22]. To monitor such dynamics, remote sensing is an essential and effective source of data [23]. Remote sensing technologies drive developments in forest resource assessments and monitoring at various scales. They enable the provision of airborne and spaceborne data with a higher spatial resolution, frequent coverage, and expanded spectral coverage [24].