Species-Site Suitability Assessment of Bamboo and Its Detailed Study in Different Agroecological Zones of Kenya

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Introduction
Bamboo is an imperishable product that belongs to the lawn family.It is popularly known as "the poor man's timber," denoting its fashionability among poor populations as a cover for precious wood from trees [1].Tere are more than 1,600 species of bamboo comprising 75-107 subfamilies growing across the world [2][3][4].Most of them grow naturally in the tropical and subtropical regions nearly 4,000 m a.s.l.[5,6].Tey are substantially set up in Asia, Africa, and Latin America and cover a total area of 37 million hectares, which accounts 1% of the global timber area [7].Global bamboo product and consumption is valued at 60 b$, with a transnational trade of 2.5 b$ per annum, supporting 1.5 billion people [8].In eastern Africa, 2.8 million hectares of area is covered with bamboo across Ethiopia, Uganda, Tanzania, and Kenya [9].Bamboo is a highly versatile plant in its adaptability and utility with a great potential for economic development, wealth creation, and environmental resilience [10], providing opportunity to rural communities to strengthen their livelihood, food security, and environmental resilience eforts [9].Tere are over 10,000 proved bamboo uses and products [11].Tese include timber backups, fber and cloth, plastic mixes, food and libation, energy, health, and cosmetics.It has also a proven eventuality in the recuperation of demoralized lands, watershed protection, and climate change mitigation and adaption [12].On account of its expansive shallow rhizome-root system and accumulation of splint mulch, bamboo serves as an efective agent in precluding soil erosion, conserving humidity, and underpinning of embankments and drainage channels [13,14].With its fast growth rate and high periodic development after harvesting, major carbon emission control strategies are needed, especially when the congregated culms are used as sturdy products [15].
In Kenya, bamboo has been an integral part of indigenous timbers.Te country's only indigenous bamboo species Oldeania alpina (K.Schum.)Stapleton grows naturally in the highlands in Mt.Kenya, Aberdares, Mau escarpment, Cherangani hills, and Mt.Elgon at an elevation of between 2300 and 3200 m a.s.l.[16].It covers about 131,040 hectare (ha) distributed in mountain ranges and forest areas managed by the national government [17].It grows in single clumps attaining a mean culm height of 10 m and a diameter at breast height (DBH) of 7.5 cm with a mean culm stocking density of 21,000 culms/ha.Te bamboo species is estimated to yield 100 tons per ha (approximately, 9.6 kg of dry weight per culm).It is mainly used for construction and residential fencing and for making handcraft, furniture, baskets, tooth picks, and match sticks [18].Twenty-two bamboo species were introduced from Asia [9].Some of the introduced bamboo species include Bambusa brandisii, Bambusa vulgaris var.vittata, Bambusa vulgaris var.vulgaris, Bambusa bambos, Bambusa tulda, Dendrocalamus membranaceus, Dendrocalamus strictus, Dendrocalamus asper, Gigantochloa aspera, Oxytenanthera abyssinica, and Tyrsostachys siamensis [19].Since then, bamboo growing has taken root in many counties within the country, similar as Migori, Vihiga, Busia, Homa Bay, Uasin Gishu, Elgeyo Marakwet, Kirinyaga, Kitui, Laikipia, Nyandarua, Embu, and Taraka Nithi.In these counties, bamboo is grown as a crop on the granges though not on a large scale.
Bamboo seedlings imported from Asia and planted in Kenya has great eventuality to contribute to proftable and social pillars of Kenya's Vision 2030.Te big four agenda are the Bonn Challenge, AFR100, Sustainable Development Goals (SDGs), the Convention on International Trade in Endangered Species (CITES), the Convention on Conservation of Biological Diversity (CBD), and UN Framework Convention on Climate Change (UNFCCC) through MSMEs that promote manufacturing and product development; recuperation of demoralized geographies, and provision of afordable ecologically friendly scenario [20].Despite having about 22 bamboo species for close to three decades in Kenya and gazetting the same as a cash crop, there is a huge gap between planning and execution.Te country lacks information about the specifc geographic locations of most introductions, their suitability to the ecoclimatic sites where they have been planted and their growth performance and yield.Tis information gap has hindered widespread adoption of the exotic bamboo species, resulting in inadequate supply of quality planting material, inadequate knowhow about bamboo propagation and sustainable management, weak marketing systems and limited information, and decision-making tools.Moreover, the information gap has impeded the country's ability to estimate the existing bamboo resource base and its potential to contribute to environmental resilience and economic development.Terefore, it is important to collate accurate information on the site-suitability matching on adaptation potential and growth performance and yield of all bamboo species planted in diferent AEZs in Kenya [21].Tis information is essential in assisting bamboo growers and prospective investors in the bamboo sectors to accurately project the expected and guaranteed return.Tis research, in turn, provides a strong platform to commercialize the bamboo farming which in due course will support the larger community for their alternative livelihood options.

Materials and Methods
2.1.Area under Study.Kenya spreads over an area of 582,647 km 2 , of which over 10620 km 2 consists of natural lakes.Te country is located in Eastern Africa, lapping the ambit between latitudes 40 N and 40 S and longitudes 340 E and 410 E, bounded by Ethiopia and Sudan on the north, Somalia and the Indian Ocean in the east, Uganda in the south, and by Tanzania towards the west.Te country geographically is divided into two larger corridors; one conforming 1/3 rd of the elevated lands forming the southwestern of the country and the remaining 2/3 rd forming a bow of low mesas and plains.Te land rises gradationally westward from a narrow littoral plain in a series of mesas, terminating in an upland area that crosses by the Great Rift Valley and includes the country's loftiest point, Mount Kenya (5199 m a.s.l.).Te northern and northeastern regions of the country correspond substantially of thirsty plains.Te rainfall varies unpredictably, but utmost of the corridor of the country enjoys two wet and two dry seasons.Its mounds are temperate and its littoral zones are hot and sticky; low lying areas are generally hot.Te rainfall throughout the country ranges from 250 mm in the northern areas to about 2,000 mm in the western region with an average periodic rainfall of 680 mm.Te high rainfall zone, which receives more than 1,000 mm annually, is the productive agrarian land (Figure 1).
Te assessment was conducted in twelve sites where both indigenous and exotic bamboo species had been planted.Te sites were clustered in nine counties representing nine diferent AEZs.Te counties included Migori, Busia, and Kakamega in western Kenya; Nyeri, Muranga, and Kiambu in the central highlands of Kenya, Makueni, in the semiarid eastern zone, and Kilif and Kwale in the coastal lowlands (Figure 1).

Study Design.
Te fow diagram of the entire process has been presented in Figure 2. A sample of nine representative counties was selected for the species-site suitability assessment of the introduced bamboo species.Representative sites were selected in each county.Te selection criteria involved picking a site with the most diverse bamboo species.Bamboo clumps that were at least fve years in age were assessed (Figure 3).

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International Journal of Forestry Research International Journal of Forestry Research 3 Tis was done in order to accurately capture the growth yield.For each bamboo species, three clumps were randomly selected for assessment.Within a clump, three culms were selected for in-depth analysis of growth parameters with a view to providing data on growth performance and yield.From the sampled culms, insect pest and disease infestation were assessed through the direct observation method.

Data Collection.
Bamboo species were identifed by their botanic names.Te number of culms per clump was evaluated, followed by measuring the clump radius in metres.Tree representative culms were harvested from each clump.Te harvested culms were measured for length, DBH, and internode length and wall thickness.Te sampled culms were analysed for signs of disease or pest infestation.
Soil samples were collected to assist in characterizing the specifc site conditions, particularly in regards to soil chemical and physical properties [22].Te samples were randomly collected under diferent clumps of bamboo species.Soil samples of 500 g were collected from a depth of 0-30 cm using an auger.Te Munsell soil colour chart was used to identify the colour of the soil in the feld.Samples were stored in tightly closed plastic containers and transported for physical and chemical analysis.Tey were air dried for 3 days to remove excess moisture, homogenized using pestle and mortar for grinding, and sieved using a 2 mm sieve to remove plant litter and stones.Physical analysis included soil moisture, bulk density, and soil texture.Chemical analysis included pH, electrical conductivity (E.C.), and levels of nitrogen, phosphorus, and potassium [23].
Ten insect pests observed onsite were collected in vials and brought to the laboratory for microscopic analysis.Te type of damage on the bamboo culm was recorded.Disease infestations manifested on foliage and culms was recorded.Labels containing details of bamboo species, county, clump number, number of afected culms, and date of assessment 4 International Journal of Forestry Research were recorded.Te diseases were rated from low (L) to severe (S).

Bamboo Biomass Determination.
Te sampled culms were cut into small pieces, packaged in gunny bags, labelled, and weighed to determine the fresh weight of each culm before transported to the laboratory.Te labels contained details of the bamboo species, county, planting site, clump and culm numbers, date of assessment, and fresh weight.Te bamboo culms were dried in the oven at 72 °C for 36 hours followed by weighing the culms to determine the dry weight [24].

Data Analysis.
Records on the clump radius, culm density, culm length, culm DBH, and internode length, and wall thickness were entered in Microsoft Excel and thereafter transferred to GenStat statistical software version 21 for analysis.Analysis was done using ANOVA, and it entailed assessing variation in growth performance for each bamboo species across planting sites at 5% signifcance level [25].
Post hoc tests were carried out to separate means using the Ryan-Einot-Gabriel-Welsch multiple range test (REGWQ) at 5% signifcance level [26].

Results
Te results cover soil properties across sites, planted bamboo species, morphological identifcation guide of bamboo species encountered during the survey, growth performance of bamboo species, growth yield of bamboo species planted in diferent AEZs and a comparison of results of each species against the growth performance and yield in its native zone, uses of each bamboo species, and identifed insect pests and diseases of bamboo in their native range [27].3).

Planted Bamboo Species in Kenya.
Sixteen bamboo species and two subspecies from nine diferent AEZs were identifed.Te species included one indigenous and ffteen exotic bamboo species (Table 4).Four of the ffteen exotic bamboo species were solid/semisolid bamboos (O.abyssinica, T. siamensis, D. strictus, and B. tulda) while the rest had hollow culms [28].It is worth noting, however, that the country has a few more bamboo species, particularly recently added by the Dutch-Sino Bamboo Project in East Africa since 2017.Some of the notable new introductions include Phyllostachys heteroclada, Cephalostachyum pergracile, Bambusa polymorpha, and Dendrocalamus laonensis.Since those species have not completed their desired age (fve years) for analysis, hence they have not been included (Table 4).

Oldeania alpina. Oldeania alpina was recorded as one of the planted bamboo species in Limuru in Kiambu County
and Ndakaini in Murang'a County (Figure 4).
Summary of species' growth performance in Limuru and Ndakaini is presented in Table 5.
Te results indicated that O. alpina was more productive in Limuru (LH1: tea/dairy zone) than in Ndakaini (UM1: cofee/tea zone).Tis was attributed to the fact that Limuru (2,085 m a.s.l.) was located at relatively higher elevation than Ndakaini (2,056 m a.s.l.).Te higher elevation in Limuru was not very far from the natural range of O. alpina of 2300−3500 m above the sea level.Despite growing much taller and larger in Limuru than Ndakaini, O. alpina's mean height and diameter were still signifcantly lower than the expected situation (height � 20 m and diameter � 5.0-12.5 cm) in its natural range [29] (Table 6).

Discussion
Te soil pH level varies from 5.055 to 6.674.Kairi-ini has the lowest pH value which depicts highly acidic behavior, whereas Kehancha has the highest pH which concludes a neutral soil characteristic [30,31].Neutral soil is most favorable for bamboo plantations and the growth rate as per their quality are the best across Kenya [32].High porous and high permeable soils are considered as the most favorable soil [33] for bamboo plantation.Bamboo plants require a slightly acidic pH soil for the best possible health and growth.pH lying between 4.5 and 6.0 is considered as good for healthy bamboo growth.Te bulk density of soil is lowest in Kakamega (0.61 g/cm 3 ) and highest in Gede (1.632 cm 3 ).Higher bulk density portrays low soil porosity and soil compaction [34].Compact soil restricts deep rooting and ceases the plant growth [35].Kakamega, Kairi-ini, Limuru, Muguga, Kagumo Garden, and Ndakaini are favorable sites International Journal of Forestry Research for bamboo cultivation as far as the density of soil is considered.Regarding the soil texture, sandy soils are better than any other category of soils [36].Locations such as Kakamega, Kehancha, Muvumoni, and Jilore have high soil texture in comparison to the other locations and hence can be considered more advantageous.Bamboo species available in diferent AEZs of Kenya are native; still many species have been imported from other countries/continents. Te exotic bamboos are solid to semisolid in nature which is considered as good to excellent quality [37].Te maximum use of O. alpine has been recorded in the entire country since they are available in plenty and have high quality.Tey are mostly  International Journal of Forestry Research

Conclusion
Te results on bamboo performance and yield strongly show that Kenya has a great potential for bamboo development.
Tus, with focused planting guided by species-site suitability matching, the growth performance and yield are likely to increase signifcantly.Te study found the utilization of bamboo to be still rudimentary in regards to product portfolio.It is an indication that this is an aspect which bamboo sector development needs to prioritize.Some evident facts lie in that in many instances, uses of bamboo remain unexplored.Tese include scafolding (which is a major driver of Eucalyptus planting in Kenya), roof construction using round poles, and fabrication of basic household furniture including tables, benches, and beds.It is expected that the expansion of bamboo planting coupled with training of contractors and carpenters will promote its widespread use in the construction sector.During heavy infestations of insect pests, there is a need for power equipment when spraying systemic chemicals to control thrips, spider mites, and other sap suckers so that material can reach insect pests under webbing.A spreading surfactant, recommended by some labels (including bifenazate), is added to the chemical of choice because bamboo leaves are difcult to wet.Regular control of insect pests and diseases can help avoid invasions as well as infections.Spraying the soil with deltamethrin-based chemicals at 240 g/l can be efective in preventing the invasion of bamboo diseases in prone areas.Research trials tended to register a better yield than farmers' plantations.Bamboo culms in some farms were hardly being harvested.In such cases, farmers feared that harvesting would interfere with research data.Te situation presented a challenge because it resulted in signifcantly larger culms and higher yield compared to the case in farmers' plantations [38].

Figure 1 :Figure 2 :
Figure 1: (a) Map of Kenya in Africa and (b) study area.

Table 2 :
Variation in soil bulk density across AEZs.

Table 3 :
Variation in the soil texture across AEZs.

Table 5 :
Summary of the growth performance of O. alpina planted in Limuru and Ndakaini.

Table 4 :
List of bamboo species that were assessed during the nationwide bamboo-species site suitability assessment in diferent AEZs in Kenya.

Table 6 :
A summary of species-site suitability analysis for diferent bamboo species currently planted in Kenya.
Phyllostachys aurea variety of bamboo grows at a height of 1,000-2,100 m a.s.l. and mostly used by local community as a live hedge.Tey are widely used for fencing purposes by most of the lower income group people and village dwellers.Some of the other varieties of bamboo are used for furniture, roofng of houses, and other miscellaneous purposes.