ABSTRACT
The African cherry (Prunus africana (Hook.f.) Kalkm.) regenerates poorly both naturally and artificially because of its recalcitrant seed. There is therefore a great need to conserve this species to ensure it does not become extinct. This study evaluated regeneration potential of the African cherry, identified the appropriate stage of collecting seeds for propagation and suitable sowing media that gives optimum germination and sought to identify other tree species with potential commercial uses which could be used as alternative to P. africana and hence ease the exploitation pressure that it currently faces. An experiment was set to evaluate the regeneration potentials of P. africana Vis a Vis Olea capensis and Croton megalocarpus. It also identified the best stage of seed collection and sowing media that can give good germination results. The experimental design used was randomized complete block design (RCBD) in split plot arrangement with the main plots as the stage of seed collection while the subplots as the different media type replicated three times. Seeds were collected at two stages: when fruits are green and mature and when ripe. These seeds were prepared, germinated under the different media types and germination percent monitored. The media used included: {(soil: sand), (soil: sawdust), (sand: sawdust) in ratio 1:1}, {(soil only), (sand only), (sawdust only)} and the normal nursery media of (sand: soil) in the ratio 1:3 was used as a control. The study also identified the effects of site on natural regeneration where by a sample of 10 trees per species was identified and deliberate vegetative disturbance underneath was carried out, and regeneration monitored and compared to undisturbed sites. The data was collected on mean germination percent and statistical analyses conducted at 95% significant level. The results indicated that There was significant difference in the timing of the collection of seeds for C. megalocarpus (F 2, 60, f=24.47, P<0.001). A post-hoc test (Tukey test) showed that germination rate was lower in mature green seeds compared to the other two seed collection stages – mature ripe and stored seeds. There was significant seed timing effect (Chi-square test = 32.90, d. f= 2, p < 0.001) for P. africana. Germination rate was significantly lower in stored seeds compared to the other two seed collection stages i.e. mature green seeds and mature ripe. There was a significant ‘medium’ effect on the germination of C. megalocarpus (F6, 62, f=4.84, p<0.001), Prunus africana (Chi- square test = 14.10, d. f= 6, p = 0.029) and O. capensis (Chi –square test = 18.33, d. f= 6, p = 0.005). Seeds in sand &sawdust 1:1 and sand had higher germination rate compared to those in sawdust. Soil sand 3:1 and soil had moderate germination rate. There was a significant site effect on C. megalocarpus, (F1, 18, f=10.09, p=0.005), P. africana (F1, 18, f=53.42, p=0.001) and O. capensis (W=155, p<0.001) among the three species. Disturbed sites had a higher wildling regeneration compared to non-disturbed site. From the results, it was concluded that the best seed for propagation of P. africana is seed freshly harvested; mature and ripe even without any pre- treatment, while O. capensis and C. megalocarpus seed need to be harvested and dried well before sowing. It is therefore recommended that P. africana seed should be sown using this medium-sand: sawdust 1:1 immediately after harvesting without pre-treatment for optimum germination per cent. The best medium recommended for optimum germination of seed of all the three species is sand: sawdust in the ratio 1:1. It is also recommended that more P. africana seedlings should be used to rehabilitate degraded areas of the natural forests due to its shade intolerance nature. Proper tending of the seedlings after germination should be advocated as well as protection of mature P. africana trees in the wild.
CHAPTER ONE
INTRODUCTION
Background Information
The African cherry (Prunus africana) belongs to the subfamily Prunoideae of the Rosaceae family, it attains highest diversity in temperate regions (Clemente et al., 2006). It is an evergreen hardwood tree with dark-brown longitudinal fissured bark and simple, thick, leathery, oval, leaves with pointed ends. It grows at 700-3000 m above sea level, up to a height of 40 m. It has creamy white flowers and produces black fleshy fruits resembling a cherry when ripe, which are eaten and dispersed by monkeys, birds and squirrels. Flowering occurs between November and February although sporadic flowering all over the year may be found in Kakamega Forest of Kenya (Orwa et al., 2009). Therefore, seeds can be collected between March and August. It is long lived - up to 100 years. The unit for sowing is the depulped fruit (the stone). Germination normally takes place within 30-50 days (Orwa et al., 2009). The seeds are desiccation sensitive (recalcitrant) and therefore only short-term storage is recommended in damp sawdust in a cool dry environment (Luke et al., 2013).
In nature, a fruiting tree can produce thousands of seedlings (wildings) that can be collected and transplanted. However, it is often seen that the wildings do not transplant well. In Cameroon the species has been propagated from cuttings. Without the use of hormones, about 10% of the seedlings had rooted after three months (Hall et al., 2000). This therefore indicates the difficulty in propagation. In terms of natural regeneration, this species shows low or sporadic recruitment (Ewusi et al., 1992, Jimu L et al., 2012).
Previous studies on the bark extracts of P. africana showed that they were effective in the treatment of benign prostatic hyperplasia (BPH) (Bombardelli and Morazzoni, 1997). In Kenya,
P. africana is present in most forested areas above 1500m (Hall et al., 2000). Bark is harvested on privately owned forest land when it is converted to tea estates, resettlement lands, and other uses; harvest is forbidden from protected areas (Cunningham et al., 1997). The species is exported as dried bark, chipped bark, and timber. The collection of mature bark for this purpose has resulted in the species becoming endangered (IUCN, 2002). Harvesters remove too much of the bark in an unsustainable manner. Many trees are debarked up to the smallest branches and others felled with negative impact on the limited wild population of this tree species (Ndibi, 1996; Betti, 2008).
In the 1990s it was estimated that 35,000 trees were debarked annually (Cunningham and Mbenkum, 1993). Currently, P. africana bark is entirely collected from the wild, although attempts at cultivation are underway in Kenya (Dawson, 1997; Dawson et al., 2000).
From the beginning, the harvest has been known to be destructive (Ngengwe, 1996; Walter and Rakotonorina, 1995). By 1995, because of the growing international demand for the bark, it was included as an endangered species in Appendix II of CITES at the Ninth Conference of the Parties. It was also listed by IUCN as vulnerable (IUCN, 2002). Despite the protection afforded by these designations, however, P. africana remains Africa’s most intensively exported medicinal plant species by volume (Cunningham et al., 2002).
Olea capensis is often a bushy shrub or a small to medium sized tree up to 10 m in height, but it may be much larger, occasionally reaching 40 m; occurring in bush, littoral scrub and evergreen forest. The fruits take about 6 months to ripen. Seed storage behaviour appears to be orthodox (Albrecht, 1993). Growth is reported fast in young plants but much slower in older ones. It is a shade-tolerant, pioneer species and a dominant forest tree (Orwa et al., 2009).
Croton megalocarpus is a hardy and fast-growing tree that grows to 15-35 m with a distinctive layering of branches and a rather flat crown. It is a pioneer species and it is found growing in cleared parts of natural forests, forest margins or as a canopy tree. The species regenerates well through seedlings, and under favourable climatic conditions may sometimes become invasive (Maroyi, 2010). The seeds are extracted from the shell by cracking with a hammer or a stone. On average there are 1700 seeds/kg. (Maroyi, 2010) noted that after sowing, the seeds germinate within 35-45 days, attaining germination rates of 95% without any pretreatment.
Statement of the Problem
The three species; Prunus africana, Olea capensis and Croton megalocarpus are important multiple-use tree species with both local and international economic and medicinal value. The high demand has led to over-exploitation that has caused serious damage to wild populations leading to concerns on the long-term sustainability of harvesting and conservation of the tree species. Kakamega forest being the easternmost remnant of the Guinea-Congolian rain forest system is an important ecosystem that needs to be maintained. The African cherry (Prunus africana) regenerates poorly both artificially and naturally because of its recalcitrant seed and shade intolerant nature. However, high demand for P. africana has led to its over-exploitation due to its medicinal properties and its valuable timber. Currently, P. africana bark is entirely collected from the wild, although attempts at cultivation are underway in Kenya. The species is therefore facing extinction threat and thus calls for conservation efforts. This is because neither the uncontrolled harvesting of P. africana populations, nor cultivation in people’s farms as one of the alternatives, easy problems to solve. This is because the species takes over 15 years to bloom, bear fruit, and for the bark to attain an adequate thickness for harvesting. This study takes into consideration two other species for comparison purposes i.e. O. capensis and C. megalocarpus. These are multi-purpose trees and thus they have potential commercial importance which can be useful to ease the pressure that is currently faced by P.africana.
Research Objectives
Broad Objective
To document the regeneration potentials of P. africana, Olea capensis and Croton megalocarpus seeds in Kakamega forest and hence contribute to improved seed germination of the three species.
Specific Objectives
1. To determine the optimal timing of seed collection for propagation of P. africana, O. capensis and C. megalocarpus.
2. To determine the suitable media for optimum germination of P. africana, O. capensis and C. megalocarpus seeds in the nursery.
3. To compare propagation and regeneration of P. africana with that of Olea capensis and
Croton megalocarpus in Kakamega forest.
Null Hypotheses
1. Optimal timing of seed collection has no effect on the germination potential for the seeds of the three species
2. There is no effect of sowing media on germination rate of the seeds.
3. There is no difference in propagation and regeneration of Olea capensis, Croton megalocarpus and P. africana.
Justification
Prunus africana is a hardwood multi-purpose tree. Its timber is excellent for a number of uses including making strong tool handles, making of bridge decks, window and door frames, and good for fuel wood. Its bark provides traditional medicine for both human and domestic animal ailments. It is also exported to Europe for preparation of drugs that treat BPH (Benign Prostatic
Hyperplasia), an increasingly common health problem in older men (Nyamai et al., 2016). However, over-exploitation has led to listing of the species in appendix II of CITES as endangered. This is contrary to Kenya’s journey towards prosperity which involves the building of a just and cohesive society, enjoying equitable social development in a clean and secure environment- Vision 2030. This species also plays an important role in the montane ecosystem and thus tree deaths from debarking affects the integrity of the forest and reduces food resources for rare birds (Cunningham and Mbenkum, 1993 and CITES, 1994). This study takes into consideration two other species for comparison purposes i.e. O. capensis and C. megalocarpus. This is both medium-sized multi-purpose trees and thus they have potential commercial importance. The bark leaves and roots of C. megalocarpus are useful in treatment of whooping cough, pneumonia and stomach problems. It also provides strong timber and building poles. The bark of O. capensis is useful in reduction of fever, treating venereal diseases and stomach problems. It also provides quality timber. The findings of this study therefore will contribute to new knowledge on propagation of P. africana and also help ease the exploitation pressure on P. africana as consumers will utilize alternative tree species. It is also hoped that the outcome of this study will contribute to a balance between exploitation, forest conservation and economic development. This will mean therefore sustainable utilization of the medicinal species.
Scope and limitation of the study
The study was done within the spatial dimensions of Isecheno forest station of kakamega south forest where P. Africana, O. capensis and C. megalocarpus is abundant. This study evaluated regeneration potential of the African cherry, identified the appropriate stage of collecting seeds for propagation and suitable sowing media that gives optimum germination and sought to identify other tree species with potential commercial uses which could be used as alternative to P. africana and hence ease the exploitation pressure that it currently faces. Therefore, experiments were set for P. africana vis avis O. capensis and C. megalocarpus. However, it should be noted that O. capensis did need seed in Kakamega forest during the year of study and therefore posed a challenge I the experiments that involved mature ripe and mature green seeds for propagation. Studies indicate that this species does not seed regularly, (Orwa et al., 2009) observed that flowering of this species takes place only at irregular intervals of up to seven years in the late dry season. For experiments on the natural regeneration, the nature of disturbance underneath selected trees was clearance of vegetative material but no disturbance on the soil.
Only mean germination percent of the seedlings in the different media was studied and therefore, the study did not involve transplanting of the seedlings. Although seeds of P. africana, O. capensis and C. megalocarpus are dispersed in various ways, for instance they are eaten and dispersed by monkeys, birds and squirrels, this study limited itself to natural seed fall.
Definition of Terms
Benign Prostatic Hyperplasia - a condition that affects the prostate gland in men causing the flow of urine to be slower and less forceful.
Conservation - the act of using and protecting resources properly. Proper use of resources and strict compliance with the rules on conservation are the keys to protecting and conserving our limited resources.
Disturbance - forest disturbance is an event that causes changes in the structure and composition of the forest. In this proposal it is used to mean deliberate clearance of vegetation under the selected trees.
Enrichment Planting - is a technique for promoting artificial regeneration of forests in which seedlings of preferred timber trees are planted in the under-storey of existing logged-over forests and then given preferential treatment.
Hyperplasia - enlargement.
Propagation - the production of more plants by seeds, cuttings, grafting or other methods. Prostate - a gland found between the bladder (where urine is stored) and the urethra (the tube urine passes through).
Prostate Cancer - a form of cancer that develops in the prostate.
Regeneration - the process of new trees growing again on land that was formerly wooded, whether naturally or as a result of planting schemes.
Vulnerable - Liable to injury and subject to be affected injuriously.
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