## 4 Discussion and Conclusions  
This research supports literature that cites the major drivers in savanna systems as climate, namely precipitation, and humans, namely human population densities that are putting pressure on protected areas [2; 32; 33]. From this study, we can conclude that across southern African savanna parks and buffers, where the savanna systems are by their very nature water-limited, increases in precipitation lead to higher NDVI. This study supports that precipitation is important in maintaining healthy vegetation, but under an increasingly changing climate, where there are increasing temperatures and more precipitation variability leading to less available moisture, these systems may become significantly altered [7; 51]. This can potentially have widespread effects given the extent of drylands globally, and is a reason why such studies, and the development of vegetation persistence metrics, are key. An unexpected finding of this research was that park size was not a significant factor of determining higher or lower NDVI. The phrase \"bigger is better\" is often used when describing protected areas because of principles of connectivity in landscape ecology [37], which can be true to a certain threshold, but further nuances in this theory have come about more recently. New information suggests that placement of a protected area is more important than size [38; 52; 53]. However, \"bigger is better\" has remained an influence on policy makers. The \"Convention on Biological Diversity\" and \"World Parks Congress\" have created initiatives to conserve the maximum area of land as possible, but this may not actually be the best way to conserve biodiversity [52; 53]. As [PERSON] et al. (2007) states, \"The relative size and placement of a protected area within the greater ecosystem may be more relevant than absolute size for the ability of a protected area to maintain ecological function\" [38]. Therefore, other factors should also be taken into consideration, and one of these is relative location. Protected areas that exist further away from human populations in remote locations and those that have less human use of natural resources tend to function better [38]. Our research supports these previous findings because areas of higher human population density had lower NDVI values across seasons and time periods. Also linked to the relationship between humans and parks is the existence of buffer zones. Buffer zones exist to mitigate the effects of humans on the landscape and wildlife. However, human populations have often been moved out of national parks and into the buffer zones. Therefore, the landscape in buffer zones is often more affected than in parks [54]. This is supported by our findings when comparing vegetation persistence in and out of parks. Vegetation persistence experienced more positive and less negative pixels inside of parks across seasons, time periods, and park sizes when compared to the buffer zones. This research highlights the importance of the transfrontier conservation areas that have been developed in this century. The principle of transfrontier conservation areas lie in theories of landscape ecology, that being more connected is better [39]. Peace Parks Foundation has begun the effort of creating transfrontier conservation areas across Africa, but several of their pilot sites are in southern Africa and are included in this analysis [43]. Our results further support the validity of setting up these conservation areas across geopolitical borders from the perspective of the positive relationship between the existence of a transfrontier conservation area and higher NDVI values. This research also supports observed global greening trends in vegetation. Greening of the earth has been observed over the last few decades by NASA and NOAA satellites [24]. One of the largest contributing factors to this greening is CO\({}_{2}\) fertilization, but there are other factors, such as nitrogen levels, land use, temperature, and climate [25; 26; 27].