Traditional ecological knowledge is defined as a cumulative body of knowledge, practice and belief. It is a mutual relationship between living beings (including humans) and its environment which evolves by adaptive processes and are handed down through generations by cultural transmission (Berkes 1999). Such knowledge has contributed to conservation of biodiversity (Gadgil, Berkes & Folke 1993), rare species (Colding 1998) and protected areas (Johannes 1998) as well as to sustainable resource use (Berkes 1999) from one area to another. In Africa, there are important elements to take into account regarding indigenous or traditional spirituality towards the nature. The value of traditional knowledge of natural resources is widely recognised among indigenous people because it was accumulated and transferred orally across generations. According to Charnley, Paige and Jones (2007) and Berkes, Colding and Folke (2000), the integral success of the traditional ecological knowledge into biodiversity conservation depends on active participation of the knowledge holders, such as indigenous communities and institutions. To avoid loss of biodiversity, traditional rules play an important role when developing conservation strategies for rare species by limiting illegal activities such as selective trees felling (Ormsby 2013). Some sacred species constitute excellent totems. Totems are often plants or animals that are a stand-in of its owner and their presence dissuade from illegal access to sacred areas. Furthermore, these sacred species contribute significantly in conservation by acting as umbrella species to the overall ecosystem (Ndimukaga 2009). Sacred place functions under the principle of faith and fear of god and other supernatural forces. This principle requires honesty, respect of ancestors and observation of moral values (Kamga-Kamdem 2008).

In many sub-Saharan African societies, the traditional ecological knowledge among indigenous people is synonymous with spirituality, which contributed to sustain the sacred forests. Rwanda, one of the smallest countries in the world with only 26, 338 km², has a rich forest heritage. The value of Rwandan culture is based on oral history, ecology and nature, geographical sites and by igitaramo. Igitaramo constitutes a gathering of families, communities and friends with songs and dances. During pre-colonial time, Rwandan society was inherently linked to forest, which hides great lessons concerning rites, ancestral customs, taboos, arts, crafts, music, dance and many more. Such integral links led to the emergence of traditional medicine (Karangwa 1997). The Rwandese are aware of the existence of these traditional healers who provide home-based healthcare. Locally, they are known as abavuzi gakondo or abapfumu. The former denotes traditional healers involved in the use of plants and the latter denotes those who are involved especially in the ritual component of traditional medicine (Rwangabo 1993). But it has been said that sometimes abapfumu use leaves, roots or barks of plants to protect their clients in exchange for money (Adenkule 2007). As a matter of fact, traditional ecological knowledge is still very much alive in Rwanda because it contributes significantly to solve health problems. In Rwanda, cutting of certain tree species is seen as a taboo as well as killing of indigenous animal such as primates, elephants, leopards, birds, etc. According to Kimenyi (1989), this conservation emphasised the symbiotic and interdependence relationship between people, plants and animals. It is for these reasons that cultural values are an essential component of every society and they act as checks and balances in the management of natural resources (Verschuuren et al. 2010).

Buhanga sacred forest is a relict forest of tremendous ecological importance to Rwandan’s society for cultural purposes. It lies in volcanic belt and has one of the highest population density in Rwanda and Africa, with up to 500–700 people per km² (NISR 2012; Plumptre, Masozera & Vedder 2001). Buhanga relict forest contains sacred water-spring, marshland, medicinal plants, native trees and even a last refuge for arboreal, migratory birds. For example, African Pitta Pitta angolensis is a migrant bird that breeds in central Tanzania, Malawi, southeast Democratic Republic of Congo, eastern Zambia, Zimbabwe and possibly northern South Africa that was sighted in Buhanga sacred forest (BirdLife International Africa Partnership e-bulletin 2008). Unfortunately, reports indicate that this relict forest is facing many threats as a result of human interference on the environment in various ways, such as harvesting of firewood and agriculture (MINITERE & CGIS-NUR 2007; REMA 2009). In fact, high pressure of disturbance of natural reserves in Rwanda was noticed until the resettlement of refugees after the genocide during the year 1997–1998 where people both settled and farmed within many natural reserves (Plumptre et al. 2001). It should be mentioned that in most cases natural resources are still viewed as limitless in the mind of the resource-poor local communities in Rwanda as a source of income. However, it should be seen furthermore that without any practical actions for sustainable utilisation of so-called ‘limitless resources’ and usage of traditional ecological knowledge, there is a risk of genetic loss and lack of traditional information from generation with time.

To address the issue of loss of this critical cultural forest in Rwanda, the goal of this study is to document the traditional ecological knowledge and belief in the utilisation of some important plant species of Buhanga sacred forest. Hence, there is a need for such information and documentation with the help of local communities to develop comprehensive and useful strategies for public awareness but also to formulate recommendations for monitoring natural resources for better future (Figure 1).

Taking consideration the size of Buhanga sacred forest, there is a high percentage of plants being naturally harvested in the forest by local communities. The fact that more than a half of remedies were prepared from herbs in natural habitat than cultivated or home gardens indicates that the natural area of Buhanga sacred forest is very important for local communities to satisfy their home-based healthcare. Our finding is similar to the finding of Edwards (2004) reporting that 2/3 of medicinal plants used worldwide are harvested from the natural environment. During interview, traditional healers reported that more medicinal plants were harvested previously than now in Buhanga sacred forest and some species formerly forest-habiting species are now rarely encountered in the area. This is the case of the species P. africana that became extinct in the natural forest while C. cylindrica still existed occasionally due to overharvesting in the past. Studies involving Rwanda on medicinal plants reveal decline of these resources (Stewart 2003).

Our research findings revealed that the poison vomiting, mental diseases and Kilondatumbo in human health problems were the most cited diseases in our study area because remedies against these three predominant health problems were mostly prepared. In a situation where several drugs in one area are required, this indicates a prepotency of a particular disease (Dawit & Ahadu 1993). The potential of medicinal plants recorded in this study were also confirmed by other research conducted elsewhere in Rwanda (Dessouter 1991; Kamagaju et al. 2013; Kayonga & Habiyaremye 1987; Mbarubukeye & Niang 1996; Rwangabo 1993). As per the ethnoveterinary medicine represented mostly by tick-borne diseases, suggests that these diseases were very important in the area. According to Byavu et al. (2000), Mbarubukeye (1991) and Van Puyvelde et al. (1985), the East Coast fever (theileriosis) played a vital role in cattle mortality in Rwanda, particularly in exotic pure breed crossing with the Ankole breed while anaplasmosis and babesiosis represented an enormous cost in term of time and money. Also study conducted by Nshimiyimana and Mutandwa (2010) indicates that damages attributable to ticks borne diseases in Rwanda were considered as the first economic damage of bovine production transmitting sucking blood parasites diseases such as theileriosis, anaplasmosis and babesiosis.

With more than 70% of leaves use as ingredient in making of medicinal concoction indicates that leaves are more required to solve the health problem in our study area. In reference to Dawit and Ahadu (1993) and Poffenberger et al. (1992), the normal harvesting leaves estimated of up to 50% does not significantly affect the growth of plant species or does not cause a great danger to existence of individual plant when compared to the collection of underground part, stem or whole plant from both ecological points of view and survival of species. The extinction of P. africana as reported by the healers is due to overutilisation of both its leaves and barks as ingredients and was replaced by agricultural activities. The same were reported by Sayer, Harcourt and Collins (1992) Stewart (2003) and MINITERE (2003). In general there was no really threat of overharvesting of plant in Buhanga sacred forest as it used to be in the past because the remedies are prepared and used locally, and therefore harvested in small quantities. Traditional healers reported that they do not store remedies for a prolonged period of time because when the need comes, they go out to collect plants, prepare the remedies and use it for treatment. However the importance of Buhanga were known a long time ago, this sacred forest has acquired since 2005 a status of protected area as a part of the Volcanoes National Park from the former Rwanda Office of Tourism and National Parks (ORTPN), now Rwanda Development Board (RDB) (REMA 2009). In the same context, culture and spiritual beliefs plays an important aspect in the conservation of Buhanga sacred forest. Recently, water springs from Buhanga are still used as source of clean water for local people in the area and caves and some tree species (Dracaena steudneri, Erythrina abyssinica and Ficus thonningii) are important for their ritual and ceremonies.

This study has revealed the importance of traditional ecological knowledge in Buhanga sacred forest plays a vital role in our heritage. The high plant diversity used in traditional medicine to treat different ailments was localised mostly in the natural habitat and does not really present threat of overharvesting because remedies are prepared on a need-to-need basis. Also this study has shown how cultural values and beliefs are crucial tools for conservation and should therefore be incorporated in all management plans of Buhanga sacred forest.

In light of this research finding, we recommended that traditional healers should be trained on how to domesticate natural plant species as some of them has becoming rare or extinct in the surrounding area due to past anthropogenic activities. Among others 15 species were documented and reported in our study area as priority species for preservation of stored grains for their medicinal importance uses. These include: B. cicatricose, S. septemtrionalis, T. rhynchocarpum, S. terminale, Zanthoxylum sp., R. abyssinicus, P. africana, R. multifidus, T. brevipes, U. massaica, A. alba, C. opulifolium, C. cylindrica, S. aculeastrum and S. mannii.