1. Introduction
A typical approach for depicting the relationship between human activity and the environment is landuse/cover (LULC) change [
1,
2]. Over the decades, LULC has been rapidly exacerbating across the globe, most especially in developing countries [
3,
4,
5] than in developed countries [
6]. Anthropogenic activities are postulated to be the main driving force of LULC change [
6,
7], and these major activities necessitating the changes are population growth, socio-economic conditions, urbanization, changes in lifestyle, agriculture expansion, increasing energy and wood demand, and economic growth [
1,
3,
8]. The conversion of LULC classes, such as vegetation (forests), land, and water bodies negatively affects biodiversity, conservation, ecosystem services, carbon storage, hydrological processes, and sustainable environment management [
2,
8,
9].
Globally, the forest is an indispensable natural resource to many countries and has been used by millions of people over the decades [
10], for instance, communities tend to focus on forests since they are endowed with myriad resources, such as minerals, timber, and food [
11,
12]. This instance calls for sustainable forest management. The question of how communities can sustainably utilize forest resources to meet their needs without adversely affecting the forest cover has been a major concern of environmental advocates, land-use planners, natural resource managers, and other stakeholders [
1,
11,
12,
13,
14,
15]. Sustainable forest management is the systematic approach employed to ensure both judicious utilization of forests and continuous growth of forests without harming other dependent organisms [
12]. Furthermore, sustainable forest management includes environmental benefits, such as ecosystem sustainability, carbon storage and sequestration, improved water and air quality, habitat for endangered species and wildlife, and protects forest health in addition to the social and economic benefits [
10,
12,
16].
Remote sensing data has been broadly utilized in monitoring and assessing environmental changes, such as LULC at the global, regional, and local scales [
8,
17]. Moreover, under the direction of the LULC change project of the International Geosphere-Biosphere Programme (IGBP) and International Human Dimensions Programme on Global Environmental Change (IHDP), several researchers have improved measurements of land-cover change, the understanding of the causes of landuse change, and predictive models of LULC change over the last few decades [4, 18. 19]. Again, many studies have explored time-series mapping of LULC change globally using multispectral satellite images in fields, such as forestry, agriculture, and natural resources.
Mikeladze et al. [
20] used Sentinel-2 multispectral imagery to detect forest cover change in Georgia (the Caucasus). Forest cover estimates were fitted to Sentinel-2A spectral band data that had been altered using various topographic correction techniques using generalized additive models (GAMs). When Sentinel-2 spectral data were topographically adjusted using the Minnaert Correction (R2 = 0.882), the best forest cover metric that could be accounted for was canopy closure, which was computed from upward-looking fisheye pictures obtained beneath the forest canopy. Band 3 (green), Band 8 (NIR), and Band 12 (SWIR) were the spectral bands that best explained canopy closure.
In addition, Housman et al. [
21] evaluated forest health insect and disease survey data and satellite-based remote sensing forest change detection methods and assessed them over Southern New England and the Rio Grande National Forest in the US. They compared the performances of the three products employed, namely Insect and Disease Survey (IDS), Modis Real-Time Forest Disturbance (RTFD), and Operational Remote Sensing (ORS) in the analysis. The ORS uses Modis and Landsat data to identify disturbances in the forest. They found that their models performed better in the Southern New England study area, with overall accuracies ranging from 71.63% to 92.55% than in the Rio Grande National Forest area 63.48% to 79.13%. They argued that while many ORS products were as accurate as or more accurate than IDS and RTFD products overall, the differences were not statistically significant at the 95% confidence range. This shows that the data provided by the existing ORS implementation is adequate to supplement IDS data.
Wang et al. [
22] explored the use of remote sensing data in analyzing forest health. The results of their review showed that, when cost, bands, temporal and spatial resolutions were taken into account, the majority of the studies concluded that Moderate Resolution Imaging Spectroradiometer satellite data (MODIS) are more suitable than other current satellite data for most remote sensing applications for forest health. However, Landsat images have a better spatial resolution, which aids in detecting smaller changes in the earth’s surface, as well as it is cost-free and can provide historical information than MODIS [
23,
24].
Furthermore, Vogelmann et al. [
25] employed time-series Landsat data to map forest degradation in Lam Dong Province, Vietnam between 1973 and 2014. Based on their results, the province of Lam Dong has seen numerous land-use changes, including slow shifts from forest to non-forest areas. The interfaces between forest and agricultural areas that are quite small and occur closer to the province’s borders are where the most notable recent changes can be seen. A noteworthy finding was that during the Landsat era (1972–present), there has been minimal change in the region’s most heavily protected national reserves.
Kanjin and Alam [
9] quantified LULC changes and estimated the Normalized Difference Vegetation Index (NDVI) in Sundarbans (Bangladesh and India) for six different years, such as 1973, 1980, 1990, 2000, 2013, and 2023. The LULC was done using Landsat data, while Modis data was used to calculate the NDVI. According to their findings, over the twenty years in Sundarbans, there have been significant changes in dense and sparse forest. For instance, dense forest has been rapidly converted to sparse indicating that the mangrove vegetation is getting lost due to climate and anthropogenic activities.
Yang and Lo [
26] estimated LULC changes using time-series satellite images in the Atlanta, Georgia metropolitan area, US over the past 25 years. They used different methods to map the LULC in the study area, such as radiometric normalization, unsupervised classification, a GIS-based reclassification, and post-classification. The post-classification product was compared with the GIS overlay to detect the LULC changes. The findings reveal the loss of forest and urban sprawl as the main issues associated with Atlanta’s rapid urbanization. Also, Moisen et al. [
27] indicated that North Central Georgia has experienced a great deal of forest land and tree cover reduction over the past 30 years. Using remotely sensed observations to supplement standard forest inventory data, their study identified the temporal patterns and thematic shifts associated with this loss.
Despite much research done on LULC changes in the world and most especially in Georgia, US, there is limited knowledge on the extent to which LULC has impacted forest cover and health in Southeast Georgia. Therefore, this study seeks to estimate the impact of LULC on forest cover and forest health in the study area. The study is deemed necessary since the findings will have policy implications on forest management in the study area and also contribute to the body of knowledge on forest cover change estimation. The research specifically addressed four specific questions such as: (1) How much forest cover has been lost from 2005 to 2023? (2) Which LULC class has significantly gained the most area from forest cover over the period? (3) What will be the impact of LULC change on forest cover by 2050? (4) How has LULC change affected forest health between 2005 and 2023?
4. Discussion
Multispectral satellite imagery, particularly Landsat aids in monitoring environmental changes, such as LULC at a 30-meter resolution [
24]. The use of Landsat images for 2005, 2015, and 2023 assisted in estimating LULC changes in Southeast Georgia, US. This study showed that the combination of Landsat imagery and random forest classification algorithm proved to yield a good classification accuracy (83% for 2005 and 85% for 2023), and this supports existing literature [
38,
39,
40].
The LULC classes in the study area have experienced drastic changes across the period. For instance, the forest cover decreased from 65.27% to 63.20% between 2005 and 2023, and this is predicted to decrease to 53.42% by 2050 (
Table 3). The change detection statistics (
Table 6) presented that the forest cover was mostly lost to the urban class. Also, the 2050 LULC projection showed that agriculture might increase by approximately 18.7%. Because Southeast Georgia is mainly driven by manufacturing and agriculture (Georgia Department of Economic Development, 2024), this could explain the reason for the agricultural expansion by 2050. The studies of Moisen et al. [
27] and Yang and Lo [
26] also had a relatable finding, which suggested that forest cover in Atlanta and North Central Georgia has declined over the years. Again, Vogelmann et al. [
25] findings supported that of this current study, which found that the forests are steadily changing to non-forest areas in Lam Dong Province, Vietnam. Furthermore, Hu et al. [
17] unveiled that forest lands in the Southern Punjab Province, Pakistan were converted to urban areas and cropland, which aligned with the results of this study. Moreover,
Table 6 shows that forest cover lost about 111 hectares to water bodies. This could partially be the construction of more irrigation facilities to aid agricultural activities and efforts geared towards the restoration of wetlands, like swamps.
According to Figure 8, the NDVI values gradually changed from 0.992 to 0.866 between 2005 and 2023, suggesting that the health of the vegetation cover, such as forest is dwindling in the study area. For instance, Negative NDVI values (-1 to 0) are associated with areas of bare rock, sand, water, urban areas or snow; low values (0 to 0.2) indicate sparse or stressed vegetation, like sparse grassland/shrubland, and areas with low vegetation cover; moderate values (0.3 to 0.5) represent moderate to dense vegetation, namely forest, croplands, and savanna; and high values indicate dense and vigorous vegetation, including dense forests and highly productive agricultural fields [
5,
17]. This finding corroborates with that of Sarfo et al. [
5], who found that the vegetation health in southeastern Ghana had significantly reduced. The reduction of forest health implies carbon sequestration, wildlife-dependent, other ecosystem services, and revenue generation [
2,
8]. This temporal variation in the NDVI values could partly be due to the annual harvesting of forest products and seasonal variation, such as timbers in the study area.