4.1. Image Classification and Accuracy Assessment
The overall accuracy assessment values are good for the classified images of 1987 and 2013 and fair for the image of 2000 compared with the fixed overall accuracy of 80% and an allowable error of 5% set for the calculation of the number of ground-truthing points. These results could be explained by the mix-up in some areas of land categories, such as settlements and croplands. This mix-up could also explain the poor producer’s accuracy for both classes. A similar mix-up was previously reported by Folega, Zhang, Zhao, Wala, Batawila, Huang, Dourma and Akpagana [26
]. The study area is characterized by a cultural landscape defined by smallholder agriculture with a traditional agroforestry system wherein farmers dwell in farmlands and crops are associated with multipurpose trees. The cultural landscape has been described by several studies [21
]. The mixing of trees and houses in this cultural landscape is the source of the misclassification of settlements and croplands. There is even misclassification of settlements with savannas. This latter confusion was also noticed by Badjana et al. [48
Poor producer accuracies with Landsat TM imagery, especially for agricultural land cover types and shrublands, were consistently noted by Smith et al. [49
], although the overall map accuracy was 74%. This result was explained by the fact that agricultural cover types are highly dynamic in their spectral responses, and shrublands can be confused with other forest types [50
]. This almost the same issue in the study area, where there are high heterogeneities in the landscape due to human interventions making it difficult to avoid confusion. On the other hand, the fixed overall accuracy of 80% and an allowable error of 5% were set because of the time and cost to complete this study. This study aims to contribute to sustainable conservation planning, especially for large mammals such as the African savanna elephant. Therefore, the use of moderate-resolution Landsat imagery for this study does not invalidate the results. As stated by Keller and Smith [51
], for larger or wider ranging species, landscape component classification may be more general and may be adequately represented by traditional, broader cover types, such as forest or grassland.
4.2. Land Cover Dynamics
Wetlands are the most important land category found within OKM. This is well in line with the classification of OKM as a Ramsar site [18
]. It is also the most converted land category into others, especially croplands. There is high pressure on wetlands, which are often systematically converted into large paddy fields. Agriculture is the main driver of change in land cover and land use dynamics (LCLU). It is shifting cultivation, such as elsewhere in Togo and in West Africa. This result is in line with previous studies in tropical regions, particularly in West Africa [53
]. Other studies have concluded that agriculture, population growth, and the indirect effects of climate change remain the main factors of land change and the main threats to biodiversity conservation [6
]. Changes in populations’ livelihoods through the implementation of indigenous adaptation strategies [56
] could be considered to be the indirect effects of climate change. The implementation of recessional agriculture as an adaptive strategy in the study area shows that climate change and LCLU change are tightly linked. Pressure is put on wetland because of water availability and high soil moisture.
The increase of settlements could be related to the annual rate of population growth in the study area. In fact, OKM is within a region where the population growth rate is the highest in Togo (3.18%) [60
]. Moreover, the Kpendjal, Oti, and Keran districts are the poorest in Togo [61
]. Therefore, there is high pressure on natural resources from the local population. The intrinsic relationship between natural resource degradation and poverty has been shown by many studies [62
]. On the other hand, there is a particular problem of natural resource management, which increases the pressure on protected areas in Togo after 1990. As described by Folega, Zhang, Zhao, Wala, Batawila, Huang, Dourma and Akpagana [26
], the period from 1990 to 2000 was marked by illegal and anarchic exploitation of protected resources by residents. This situation resulted from the political, economic, and social troubles of 1990 in Togo mainly due to the nascent, uncontrolled democratic process and the semi-military and repressive management system implemented from the colonial period to 1990. These illegal and anarchic anthropogenic activities led to important land conversion. This could explain the increase in croplands from 1987 to 2000. This increment is higher than the reported agricultural expansion on the national scale for the period of 25 years from 1975 to 2000 by United States Geological Survey (USGS [64
]. While this study reported an increase in cropland of about 34% of the total area of OKM from 1987 to 2013, USGS [64
] reported an increase of about 10% at the national level from 1975 to 2000. OKM could be considered to be one of the areas with the highest current agricultural expansion.
As shown by the land cover maps, there is a core area of remaining natural ecosystems (savanna and forest) within OKM (the southeast). This area has been already mentioned by International Union for Conservation of Nature (UICN [16
] as the most conserved area. Periodic visits to this area by savanna elephants coming from bordering countries have been mentioned in several studies [16
]. This relatively conserved area could be explained by the presence of park managers. Their presence is preventing anthropogenic pressure. Thus, better management of the entire OKM is possible if adequate means are provided. This area requires particular conservation attention. Its remaining natural habitats are still under threat from anthropogenic activities such as wood cutting [20
] and charcoal production [22
]. In the center of Benin, Arouna et al. [66
] also found that charcoal production represented the main activity leading to forest destruction and land cover change. Moreover, there are also threats from transhumance, on which no accurate data are currently available. There are a thousand heads of cattle pasturing through this area each year, damaging the crops and invading the protected areas.
Usually, foraging plants are cut down for cattle and the savanna is burnt without any respect to the established fire calendar set by the National Department of Environment. Considering the net change, the increase of forests from 1987 to 2000 could be explained by natural regeneration, because forests are located along rivers and in the well-protected core area (the southeastern part of the study area). However, the decrease in forests from 2000 to 2013 is the result of the combined continuous impact of increasing anthropogenic activities (wood cutting and charcoal production) and climate change. Recent studies have demonstrated that climate change effects in Northern Togo have been expressed by inter-annual fluctuations with the declining tendency of rainfall and the increasing tendency of high temperatures during the period from 1961 to 2010 [56
]. The deficit in rainfall could weaken plant resilience to fire events. Furthermore, one of the most adaptive strategies to climate change implemented in this area by the local population is recessional agriculture. This activity consists of crop cultivation during the dry season on river banks and in wetlands where the crops could benefit from flooding and soil moisture. This practice involves the destruction of gallery forests [48
]. Recessional agriculture is categorized as wetland agriculture and considered to be one of the largest overall agriculture adaptations [68
]. It is described as been highly productive in many tropical regions [69
]. On the other hand, the decrease of forests from 2000 to 2013 reflected the ineffectiveness of the management system of this complex of protected areas and the weakness of the current rehabilitation process.
4.3. Habitat Change Processes
The changes in land cover categories, for the different periods studied, resulted from different transformation processes. These transformation processes implied profound consequences for the landscape structure and functioning [9
]. Here, three main transformations or change processes were identified when considering the period from 1987 to 2013. These were the attrition of forests and savannas, dissection of wetlands, and creation of croplands. However, when this period is decomposed into two parts (1987–2000 and 2000–2013), then four transformation processes can be described. From 1987 to 2000, there was the creation of forests and croplands, dissection of savannas, and attrition of wetlands, whereas from 2000 to 2013, there was the attrition of forests and savannas, dissection of wetlands, and aggregation of croplands. The temporal resolution is essential when designing a study for the identification of transformation processes as suggested Bogaert, Ceulemans and Salvador-Van Eysenrode [9
]. According to these authors, all the identified transformation processes characterize two main changes in the habitat configuration. Attrition and dissection indicate habitat degradation, while creation and aggregation imply the appearance of new habitat units. The process of creation means the formation of new patches of a given land cover or habitat. However, depending on the considered land cover category, the process of creation could have different causes. For instance, from 1987 to 2000, the creation process of forests could be explained by the colonization of bare soil, converting other land cover to forest. Meanwhile, the creation process of croplands is caused by anthropogenic pressure with increasing afforestation. Aggregation indicates the merging of existing patches by physical connection. This explains well what happened to cropland from 2000 to 2013.
Dissection and attrition are considered to represent different steps of the process of fragmentation. Dissection is a subdivision of the area with a minimal area loss associated with the linear structure of disruption, while attrition is the disappearance of patches. There is still a debate over whether to consider the transformation processes to be equally equivalent or steps of the whole process of landscape fragmentation. However, Jaeger [70
] considered attrition to be the last of the six steps of fragmentation. Dissection is considered to be the initial step of fragmentation by Bogaert, Ceulemans and Salvador-Van Eysenrode [9
], and attrition is expected to occur in a patchy landscape, which is the result of another pattern conversion. Considering this sequence, savannas experienced a steady process of fragmentation with a dissection (initial step) from 1987 to 2000 and attrition (last step) from 2000 to 2013. However, the transformation processes were particular in both forests and wetlands. By experiencing creation from 1987 to 2000 and attrition from 2000 to 2013, the fragmentation process was very rapid in forests, especially from 2000 to 2013. This period corresponds to the period of the implementation of the requalification process of protected areas. However, instead of observing a decrease in the pressure on natural resources, it was marked by an increase in anthropogenic pressures. The requalification process in Togo was ineffective in OKM. This complex continues to be pressured by anthropogenic activities, such as illegal logging and the intensification of charcoal production, which have already reported by many studies [20
]. The sequence of the transformation processes of wetlands (attrition from 1987 to 2000 and dissection from 2000 to 2013) indicates that the fragmentation process here is really intensive. This may be linked to the increasing pressure on water resources in the context of climate change.
In summary, there is habitat loss in forests and in savannas (attrition) and habitat fragmentation in wetlands (dissection). These processes are leading to an anthropization process as described by Barima, Barbier, Bamba, Traore, Lejoly and Bogaert [15
] in the forest–savanna transition zone of Côte d’Ivoire. Moreover, in concert with habitat loss, habitat fragmentation is a grave threat to species survival [71