Hydrological Response of Bamboo Plantations on Soil–Water Dynamics in Humid and Semi-Arid Coastal Region of Kenya

Abstract

Soils and water are major resources that drive a country’s economy, and therefore should be conserved and utilized sustainably. However, in Kenya, these two resources are facing huge depletion and degradation due to anthropogenic factors and climate change. Bamboo species, especially on large plantations, can significantly alter ecological, hydrological, and biogeochemical processes in the long term. This study aimed to evaluate the effects of different species of bamboo and tree plantations on important soil–water processes like infiltration, bulk density, runoff, and soil loss in Kenya. The research was conducted at two sites (Gede in Arabuko Sokoke forest and at Baolala, in Kilifi County) managed by the Kenya Forestry Research Institute (KEFRI). The Arabuko Sokoke forest has a hot–humid coastal climate, while Baolala is a hot semi-arid area with little precipitation. The study involved measurement of soil–water infiltration rates using infiltrometers, installing runoff plots to quantify surface runoff and sediment loss, and analyzing soil properties like bulk density for growing periods for different bamboo and tree species. At the Gede forest site, the 30-year-old Thyrsostachys siamensis and Bambusa bambos plantations recorded the highest infiltration rates. Mature bamboo plantations of T. siamensis and B. bambos recorded higher infiltration rates compared to mature plantations of E. camaldulensis and G. arborea. It was observed that the bamboo plantations manifested lower soil bulk density compared to bare land, which recorded the highest bulk density. At Boalala, infiltration rates were significantly higher in the bamboo species compared to grassland and bare land. The painted bamboo (B. vulgaris vittata) had a slightly higher water infiltration rate compared to B. vulgaris. Runoff and erosion patterns reinforced the benefits of more mature bamboo plantations as well. There was a significant correlation between amount of runoff and collected soil loss through erosion. The data showed reductions in surface runoff volumes and sediment loss as the bamboo plantations aged compared to younger species. Therefore, by enhancing infiltration and reducing runoff and erosion, well-managed bamboo plantations can protect valuable soil resources, improve water recharge, and support sustainable land use over the long term. In conclusion, this study showed the strong potential of bamboo as a soil and water conservation tool in Kenya.

1. Introduction

Currently, natural resources are declining across the globe due to climate change and anthropogenic activities [1,2,3]. Soils and water are major resources that drive a country’s economy, and therefore should be conserved and utilized judiciously in a sustainable manner [4]. However, in Kenya, these two resources are facing huge depletion and degradation due to the ever-increasing human and animal population and unsustainable utilization of land for products and services [5]. Over the years, pressure has been exerted upon these resources to meet the demands for industry, food, fiber, wood fuel energy, livestock fodder and other agricultural practices, leading to land degradation and the depletion of water resources [6]. It is estimated that up to 22% of land in Kenya was degraded in the years between 1986 and 2006 [7]. In addition, 30–40% of arid and semi-arid lands are on a rapid declining trend of degradation. This degradation calls for proper management of land resources for sustainable development. The development of the Integrated National Land Use Guidelines to address land restoration issues has contributed to achieving both national and global goals like the UN Millennium Declaration, the UN Millennium Development Goals, and the World Summit for Sustainable Development (WSSD) Implementation Plan [8]. Due to demand for commercial and subsistence farming, much of the watersheds and forests in Kenya have been deforested, leading to land degradation since the 1970s [9]. The overarching deforestation and land degradation have led to increased sediment losses, declining water quality, and reduced capacity of catchment areas to support the flow of rivers, especially in the dry seasons [10,11].

Moreover, anthropogenic activities due to various scales of agricultural practices have also continued to promote nutrient enrichment in streams, rivers, lakes, and coastal oceans worldwide [12,13]. Nutrient load, especially phosphorus, nitrogen, and heavy metals from soil erosion, pollutes rivers and streams, increasing algal blooms, which affect water quality and ecosystem function [14,15,16].

Bamboo resources play critical roles in environmental conservation and improving livelihoods. In Kenya, the development of the bamboo sector is greatly supporting the achievement of Kenya’s Vision 2030, especially for manufacturing and the rehabilitation of degraded lands. The classification of bamboo as a cash crop in 2020 and the development of the National Bamboo Policy in 2022 has supported the development of the bamboo sector in Kenya. Its adoption in environment conservation is incorporated into various legal frameworks and strategies, including MTP IV, 2023–20227; the Forest Conservation and Management Act, 2016; the Kenya Climate Change Framework Policy, 2016; the Kenya Green Economy Strategy and Implementation Plan, among others [17]. Kenya aims to increase the area under bamboo by planting 255,000 ha on private, public, and degraded lands by 2031 [17]. The increased bamboo cover will contribute significantly to the National Strategy for Achieving and Maintaining 10% Tree Cover by 2032, Kenya’s Forest and Landscape Restoration targets, and even global targets like the Bonn Challenge.

Large-scale plantations of fast-growing bamboo can significantly alter terrestrial water and nutrient cycles [18], leading to direct impacts on ecological, hydrological, and biogeochemical processes in the long term. Dense rhizome and fibrous root networks that effectively bind the soil and enhance water infiltration [19] characterize bamboo species, particularly on degraded soils.

Different bamboo species exhibit diverse physiological, anatomical, and biological characteristics. Therefore, it is crucial to identify their hydro-soil infiltration properties, estimate transpiration rates, analyze their impact on runoff and soil erosion [20], and assess their influence on soil–water content [21]. Some of the hydrological factors like soil–water infiltration and moisture dictate nutrient availability and uptake by plants [22] and determine the development of surface runoff.

The great potential of bamboo in securing the hydrological functions of catchments and its contribution to social, economic, and rural development have led to an increasing interest to develop and promote bamboo production in Kenya [23]. However, few studies have systematically evaluated the hydrological efficiency of different bamboo species. There is a lack of information for farmers on bamboo propagation, germ plasm sources, and the performance of different bamboo species across different agro-ecological zones. To ensure bamboo growing is a competitive land use, it is necessary for investors to be assured of its viability and efficiency. In this regard, the International Bamboo and Rattan Organisation (INBAR), an intergovernmental organization that promotes the use of bamboo and rattan for sustainable development, has been implementing the Dutch-Sino East Africa Bamboo Development Programme—Phase II. The overall program goal is to enhance climate change mitigation and adaptation benefits by developing inclusive and sustainable industrial and SME bamboo value chains, resulting in enhanced livelihood opportunities, food security, and environmental management in East Africa. Specifically, on hydrology, the present study investigated the spatial–temporal effects of long-term field plantations of different bamboo species on soil–water infiltration, surface runoff, and sedimentation. The novelty of the present study demonstrates the hydrological response of different bamboo species at different climatic conditions of Kenya. As per the authors’ knowledge, this type of the study has not been conducted before for the given Kenyan coastal region.

2. Materials and Methods

2.1. Experimental Sites

The study was carried out on established bamboo plantations within the KEFRI Coast Eco-Region Research Programme. The experiment was set up in rainfed trial plots at Gede, Arabuko Sokoke forest (latitude 3°17′45.9″ S, longitude 39°59′26.3″ E, and at Baolala (latitude 3°11′35″ S, longitude 39°47′54″ E), in Kilifi County along the Kenyan Coast, Kenya. The choice of the sites was influenced by the differences in climate and edaphic factors.

2.2. Soils and Climate

The soils of the Gede forest site are predominantly characterized by highly drained and bleached sandy cambic arenosols; the Baolala site has ferralic arenosols changing to ferralsols in some areas as per the FAO soil classification (Figure 1). Arenosols are generally sandy soils developed from the weathering of old rock, i.e., quartz or recently deposited sands in dry desert-like conditions or beaches with a loamy sand or sandy texture. Ferralic arenosols refer to arenosols with a ferralic horizon starting within 170 cm of the surface, irrespective of the texture of the overlying horizon [24]. The Gede site in Arabuko Sokoke forest is a humid area classified under semi-humid Zone IV of the agro-climatic zones of Kenya [25], with a mean annual temperature ranging from 27 to 31 °C and rainfall of 900–1000 mm per year. The rainfall is bimodal, with long rains occurring in April–June and short rains in November–December. Baolala is a semi-arid area classified under semi-arid Zone V id [25]; it is a tropical dry savanna with precipitation of below 500 mm annually and annual temperatures of 27–34 °C [26].

2.3. Description of Bamboo Plantations and Species

At the Gede site, four bamboo species were selected for the study: Oxytenanthera abyssinica, Dendrocalamus asper, Bambusa vulgaris vittata (Painted bamboo), and Bambusa vulgaris (green). Oxytenanthera abyssinica is native to Ethiopia, and Bambusa vulgaris and Dendrocalamus asper are becoming more common on Kenyan farms and grow in varied ecological conditions.

Each species was planted in a plot size measuring 20 m × 25 m (500 m²) at a spacing of 5 m × 5 m in completely randomized blocks (RCBD) replicated thrice. The plots were spaced at 10 m to allow enough space for the installation of runoff plots and to record other observations. Each plot had 20 bamboo plants. A guard row around the whole experiment consisting of Bambusa vulgaris was established. At the Baolala site, three species were planted, i.e., Oxytenanthera abyssinica, Bambusa vulgaris vittata, and Bambusa vulgaris (green). An area of 2 ha was manually cleared, and three bamboo species—Bambusa vulgaris vittata (yellow-green), Bambusa vulgaris (green), and Oxytenanthera abyssinica—were planted at a spacing of 6 m × 6 m in June 2020 in a randomized complete block design (RCBD). The experimental layout had three blocks, with the three species for treatment having 35 bamboo seedlings per plot. A buffer of 7 m planted with Bambusa vulgaris was left between the block rows. The plantation, soil characteristics, and soil moisture level at field capacity (%) of the study sites are given in

Table 1. Plantation and soil characteristics of the study site at Gede forest.

Plantation	Age (years)	Height (m)	Canopy Cover	Field Capacity (%)	Soil Texture	Soil pH
D. strictus	30	13.5	13.4	25	Sandy loam	7.5
B. bambos	30	13.5	13.4	20	Sandy loam	7.7
T. siamensis	30	15	4.4	20	Sandy loam	7.7
E. camaldulensis	15	21.3	3	27	Sandy loam	7.8
B. vulgaris	1.5	4.5	4	28	Sandy loam	7.9
G. arborea	9	14	3.5	28	Sandy loam	7.5
E. urophylla	3.5	10.8	2.6	25	Sandy loam	7.8
Indigenous forest	30	13	4.2	20	Sandy loam	7.7
Bare land/grass	-	-	-	20	Sandy loam	7.7

and

Table 2. Plantation and soil characteristics of the study site at Baolala.

Plantation	Age (years)	Height (m)	Canopy Cover	Field Capacity (%)	Soil Texture	Soil pH
B. vulgaris	3.5	13.5	7.3	35%	Loam	7.8
B. vulgaris vittata	3.5	13.5	5.1	35%	Loam	7.7
O. abyssinica	3.5	12	5	33%	Loam	7.6
Grassland	0.5	0.4	closed	30%	Loam	7.7
Bareland/grass				24%	Loam	7.7

.

2.4. Measurement of Water Infiltration in Soils under Bamboo Plantations

Infiltration is a process by which surface groundwater enters the soil. In this study, soil–water infiltration was determined as the rate at which water enters the soil and is absorbed simultaneously using double ring infiltrometers. The infiltrometer used in this study was made up of double concentric rings measuring 50 cm in height and 30 cm and 60 cm in diameter for the inner and outer rings, respectively. Infiltration rates of water in soils under different bamboo and other tree plantations were measured. In addition, infiltration on other tree plantations (E. camaldulensis, E. urophylla, and G. arborea) and in natural forests comprising Combretum schumannii, Brachylaena huillensis, and Grewia sp. were also measured. Finally, accumulated infiltration was computed from the infiltration rates of water into the soil in centimeters. The following baseline data were collected during the infiltration measurements: plantation species and age, height and canopy cover of the plantation, soil type, moisture content, and bulk density. Soil moisture content was estimated on site using a digital meter and gravimetrically by oven drying the sample at 105 °C for constant weight. The moisture content and bulk density of the soil were determined following the standard published methods [27,28,29].

2.5. Collection and Quantification of Runoff and Soil Loss on Bamboo Plantations

A gauging system consisting of multi-slot divisors was used to quantify runoff generated during the individual rain events on a 20 m × 20 m runoff plot within the D. asper experimental plot (Figure 2 and Figure 3). Runoff data from experimental treatments were recorded manually at 8:00 a.m. (local time) after each rainfall event by measuring the depth of water collected in the runoff collection tanks from July 2022 and May 2024. Annual runoff was calculated as the percent of the total annual rainfall. The collected runoff water was thoroughly stirred, and 1 L was taken from each tank to determine the accumulated sediment in each plot’s runoff tank. The resultant suspensions were filtered using Whatman 42 filter paper with a pore size of 2.5 µm. The sediment in the filter paper was oven-dried for 24 h at 105 °C and weighed to obtain soil loss data [27,28]. Daily rainfall data were collected from the nearby rain gauge installed in the nearby open area near the established bamboo experimental plot.

3. Results

3.1. Water Infiltration in Bamboo and other Tree Plantation Soils

The rate of water infiltration in the soil varied significantly among bamboo species and sites. Generally, the older bamboo species D. Strictus, T. siamensis, and B. Bambos had a higher infiltration rate compared to younger species. For the site in Gede forest, T. siamensis plantations of 30 years recorded the highest water infiltration rates (216.44 cm/h) followed by B. bambos (126.45 cm/h) and B. strictus (62.31 cm/h) of the same age (

Table 3. Means of soil–water infiltration rates at Gede forest. Mean values followed by the same letter do not differ significantly as per Turkey’s honest significant difference (HSD^a,b,c) test.

Species	Infiltration Rate (cm/h)
Bare land/grass	46.95 a
B. vulgaris 1.5 years	53.38 a
B. vulgaris vittata 1.5 years	54.14 a
O. abyssinica 1.5 years	54.6 a
D. asper 1.5 years	56.06 a
D. strictus 30 years	62.31 a
E. camaldulensis 15 years	66.96 a
G. arborea 9 years	109.34 b
E. urophylla 3.5 years	112.07 b
B. bambos 30 years	126.45 b
Indigenous forest 30 years	171.45 c
T. siamensis 30 years	216.44 d
Mean	94.200

, Figure 4). The 1.5-year-old B. vulgaris plantations recorded the lowest rates, nearly equal to those of mature B. strictus and the bare virgin land nearby (Table 3, Figure 4 and Figure 5). The bare land exhibited a prolonged steady-state infiltration rate attributed to high bulk density and absence of plant roots and litter to modify the soil structure. The younger species (B. vulgaris) did not differ significantly from the bare land, suggesting that bamboo needs to grow to maturity and accumulate the required amounts of organic matter for soil modification or rehabilitation.

The comparison between bamboo and other tree species yielded the following: Mature bamboo plantations of T. siamensis (216.44 cm/h) and B. bambos (126.45 cm/h) recorded high soil–water infiltration rates compared to mature plantations of E. camaldulensis (66.96 cm/h) and G. arborea (109 cm/h) (Table 3, Figure 6). However, soils in indigenous forest (171.45 cm/h) consisting of Combretum schumannii, Brachylaena huillensis, and Grewia sp. had significantly higher infiltration rates than mature plantations of B. bambos, E. camaldulensis, and G. arborea. Soil–water infiltration in the mature B. strictus (62.31 cm/h) bamboo plantation was low and not significantly different from mature E. camaldulensis and young B. vulgaris of 1.5 years (Table 3, Figure 5 and Figure 6).

In terms of accumulated water during infiltration, T. siamensis (93.3) and indigenous forest (79.3 cm) accumulated significantly higher amounts of water than all the other plantations studied (Figure 7 and Figure 8). The bare land, as expected, portrayed the lowest accumulation, with a longer time lag. Just like in the infiltration rates, there was no significant difference between B. bambos (30 years) and G. arborea (9 years) or E. urophylla (3.5 years) (Table 3, Figure 9). The E. camaldulensis, D. strictus, B. vulgaris, and bare land all had significantly lower accumulated infiltration compared to other plantations.

At the Boalala site, soil–water infiltration was studied in five land uses, i.e., three bamboo species—B. vulgaris (green), Oxytenanthera abyssinica, and B. vulgaris vittata—were compared with bare eroded land and a short-term virgin grassland. The results indicated that the infiltration rate was significantly higher in the bamboo species than in the grassland and bare land (

Table 4. Means of soil–water infiltration rates at Baolala Mean values followed by the same letter do not differ significantly as per Turkey’s honest significant difference (HSD^a,b,c) test.

Bamboo Species	Infiltration Rate (cm/h)
Bare eroded land	11.26 a
Grassland	33.95 b
O. abyssinica 3.5 years	35.35 b
B. vulgaris green 3.5 years	55.01 c
B. vulgaris vittata 3.5 years	71.75 c
Mean	41.46

). Painted bamboo (B. vulgaris vittata) had a slightly higher soil–water infiltration (71.75 cm/h) compared to B. vulgaris (55.01 cm/h), with both plantations recording a statistically significant difference over Oxytenanthera abyssinica (35.35 cm/h) of the same age of 3.5 years (Table 4, Figure 10). There was no significant difference in water infiltration between cultivated land left fallow for 6 months and covered with grass (33.95 cm/h) and Oxytenanthera abyssinica (35.35 cm/h). Soil–water infiltration on bare land was extremely low, with initial maximum rates of 0.4 cm/min to 0.1 cm/min after nearly 2 h (Figure 10, Figure 11 and Figure 12). The bare eroded land portrayed a significantly lower infiltration rate compared to the other land uses. These results were attributed to the accumulation of organic carbon through litter fall and root development in the land uses with vegetation as opposed to bare land, leading to change in soil structure, soil texture, and porosity, as illustrated in the soil bulk densities (Figure 13). A similar trend was also observed for water accumulated during infiltration in the soils of the studied land uses and plantations (Figure 11).

3.2. Soil Bulk Density of Bamboo Plantations

Soil bulk density varied significantly among bamboo species. For the Gede forest site, soil bulk density across different bamboo and tree plantations ranged between 1.05 g/cm³ and 1.36 g/cm³, with bare land as the control recording the highest (Figure 13). The bulk density of the B. strictus (1.09 g/cm³) and T. siamensis (1.05 g/cm³) soils was statistically significant compared to the soils of B. bambos plantations (1.17 g/cm³) of the same age (Figure 13). The differences within the bamboo species alluded to the root structure and litter fall since B. strictus and T. siamensis have a higher root density, as evidenced by the numerous rootlets during sampling of the soils. Mature bamboo plantations recorded lower soil bulk density compared to mature E. camaldulensis and G. arborea, indicating that bamboo has a more positive effect on soil properties compared to trees. Generally, soils within young bamboo plantations had higher bulk densities compared to mature bamboos (Figure 14).

For the site in Baolala, the trend was similar to the Gede site, where soil bulk density across different bamboo and tree plantations ranged between 1.28 g/cm³ and 1.4 g/cm³, with bare land as the control recording the highest. There was no statistical difference between B. vulgaris (1.29 g/cm³) and vittata (1.28 g/cm³), with both bamboo species recording lower bulk densities compared to O. abyssinica (1.31 g/cm³) and grassland (1.32 g/cm³) (Figure 15). The differences in bulk densities between the Gede forest and Baolala sites was largely attributed to the differences in land uses, especially for the tree species and less in terms of soil type, as both sites had arenosols, which are typically sandy in texture, i.e., cambic arenosols and ferralic arenosols.

Soil bulk density is influenced by several factors in plantations, i.e., soil type, plantation species and age, and organic matter content, among other factors. According to the literature, most sandy soils have soil bulk densities of 1.3–1.7 g/cm³, with sands having 1.65 g/cm³, loamy sand 1.6 g/cm³, sandy loam 1.5 g/cm³, loams 1.5 g/cm³, clays 1.35 g/cm³, and silts 1.6 g/cm³. The hydrological properties of sandy soils allow them to hold more available water for plants at low pressures compared to fine-textured soils. Depending on the texture analysis of the particle sizes and the presence of organic matter content, available water capacity for plant use may be between 3 and 17%. These parameters are crucial to understanding the effective survival of bamboo in rain-deficit regions.

3.3. Runoff and Soil Loss in Bamboo Plantations

Generally, surface runoff and soil loss through erosion decreased with the age of the bamboo plantation due to increased canopy cover, litter fall, and root density, which improve the soil structure and aggregate stability. There was a significant correlation between amount of runoff and collected soil loss; more soil was lost from high quantities of runoff collected, especially during the onset of rains, when the bamboo plantation had little undergrowth and little cover. The amount of surface runoff and soil loss was influenced by the status of the soil cover, rainfall intensity, and infiltration rates. The seasonality of rainfall patterns influenced the bamboo canopy cover and growth of weeds on the plantations. There were high rates of soil loss immediately after the prolonged periods of dry spells, i.e., January to March, as there was no undergrowth and the bamboo had shed almost all its leaves. Within the 24 months of conducting the experiment, 390 kg of soil in a hectare of land had been collected from 209.85 m³/ha of water as runoff (

Table 5. Cumulative runoff and soil loss from the bamboo experimental plot.

Age of Bamboo (Months)	Cumulative Rainfall (mm)	Cumulative Runoff (m3/ha)	Cumulative Soil Loss (Kg/ha)
2	33	34.8	57
6	89	63.9	101.7
10	158.5	98.7	166.8
18	294	151.5	219.6
19	373	187.95	261
22	380	189.45	295.5
23	413	199.95	352.5
24	443	209.85	390

). The correlation of runoff–soil loss from the bamboo species plots can be seen in Figure 16. Figure 16 reveals that cumulative runoff increased gradually with low sediment, while the soil loss line approached the threshold point of erosion, as seen in the straight line 19 months after plantation establishment. The wide gap between lines of soil loss and runoff after 19 months showed the effectiveness of bamboo growth in reducing both runoff and soil loss. In regard to the rainfall–runoff–soil loss analysis, efforts were made to reflect the scenario of rainfall–runoff–soil loss under the limited dataset availability. The analysis could be improved if the dataset is available for a longer time span. In addition, high soil infiltration rates for the porous sandy soils and elevation played a key role, as the site topography was mostly gently rolling to flat, hence the reduced speed of the runoff.

4. Discussion

Water infiltration has been defined simply as the downward entry of water into the soil, while the velocity at which it enters the soil is termed the infiltration rate. The infiltration rate is measured by the depth of the water layer that can absorb at a particular time. Cumulative infiltration of water in soil is defined as the total amount of water that a given layer of soil is able to absorb from rainfall or irrigation in a given time. Several studies and literature, including [22], have indicated water infiltration into the soil is a function of soil texture, soil mineralogy, management practices, topography, and soil moisture content. Soil moisture stands as a cornerstone among soil parameters crucial for the sustenance of plants, animals, and microorganisms [30]. This parameter, often characterized as the quantity of water within the unsaturated zone, holds significant importance in forecasting plant growth and enhancing the management of water resources. The assessment of soil moisture dynamics emerges as a pivotal agronomic factor that is essential for monitoring and optimizing plant and crop growth [31]. The overall trend depicted in the graphs, illustrating the variation in infiltration rates observed in farmed, forested, and bare soil conditions, presents a notable pattern.

The results from this study show higher infiltration rates in bamboo forests compared to other tree plantations and land uses, which can contribute to groundwater recharge and which in turn improves ecological flow downstream. The role of bamboo root systems in enhancing infiltration is well understood, especially in creating macropores and improving soil structure, thereby facilitating water infiltration. There is huge potential for using bamboo in soil conservation and erosion control measures, thus stabilizing degraded sloping lands as well. In addition, there is an urgent need for the adoption of climate-smart agricultural practices to achieve a sustainable increase in production, adaptation, and the mitigation climate change [32], and bamboo is a suitable candidate for adoption. The effectiveness of bamboo in terms of reducing surface runoff and soil loss is because of its higher infiltration rate. Ref. [3] found that bamboo root systems significantly increased infiltration rates in tropical soils, suggesting their potential role in soil conservation. That study endorses the findings of the present study.

Preliminary results of the influence of bamboo on the reduction of surface runoff and soil loss rates are encouraging and seem to improve as bamboo plants or plantations mature and the canopy cover increases. Against the backdrop of these findings, bamboo forests can act as natural buffers against erosion and sedimentation, especially of farmlands, and therefore conserve the ecological function of soils, especially soil fertility. Furthermore, complex root structures of both bamboo and indigenous tree species help bind soil particles and stabilize slopes, thereby minimizing erosion risk. The environmental and ecological balance is preserved by maintaining the natural and anthropogenic pressures in the watershed, thus enabling sustainable management in typical rural scenarios where land degradation is predominating at an alarming rate due to anthropogenic activities [33].

While bamboo forests are known for their erosion control properties, exotic tree species like eucalyptus may exhibit different effects on soil stability due to factors such as litter decomposition rates and allelopathic effects on understory vegetation, which causes soil–water repellency, inhibiting infiltration [34]. The dense canopy cover and litter layer of bamboo and indigenous forests intercept rainfall, reducing the amount of water reaching the ground surface and decreasing surface runoff. The fast growth rates of bamboo compared to indigenous forests make it a better choice, if not the only choice, for soil and water conservation; for instance, in this study, infiltration under 1.5-year B. vulgaris was not significantly different from mature naturalized eucalyptus and Gmelina plantations. While both bamboo and exotic trees may mitigate runoff compared to open or degraded landscapes, potential variations in runoff dynamics could be due to differences in canopy structure, litter characteristics, and water uptake patterns.

5. Conclusions

The infiltration rate in the soil varied significantly among bamboo species and locational sites. Generally, the older bamboo species T. siamensis, and B. Bambos had a higher infiltration rate compared to younger species. For the site in Gede forest, T. siamensis and B. bambos plantations of 30 years recorded the highest infiltration rates. The comparison between bamboo and other tree species yielded the following: Mature bamboo plantations of T. siamensis and B. bambos recorded high soil–water infiltration rates compared to mature plantations of E. camaldulensis and G. arborea. However, soils in indigenous forest consisting of Combretum schumannii, Brachylaena huillensis, and Grewia sp had significantly higher infiltration rates than mature plantations of B. bambos, E. camaldulensis, and G. arborea. For the Boalala site. the results indicated that the infiltration rate was significantly higher in the bamboo species than in the grassland and bare land. The painted bamboo (B. vulgaris vittata) had a slightly higher water infiltration rate compared to B. vulgaris, with both plantations recording a statistically significant difference over Oxytenanthera abyssinica of the same age. There was no significant difference in water infiltration between cultivated land left fallow for 6 months and covered with grass and Oxytenanthera abyssinica.

Bamboo plantations and site edaphic conditions influenced soil bulk density greatly compared to other land uses and tree plantations. For the Gede forest site, soil bulk density across different bamboo and tree plantations ranged between 1.05 g/cm³ and 1.36 g/cm³, while bare land as the control recorded the highest. Plantations of B. strictus and T. siamensis recorded a statistically significant reduced bulk density of soils compared to B. bambos of the same age. For the site in Baolala, the trend was similar to the Gede site, where soil bulk density across different bamboo and tree plantations ranged between 1.28 g/cm³ and 1.4 g/cm³, with bare land as the control showing the highest value. There was no statistical difference between B. vulgaris (green) and the painted bamboo (vittata); both species recorded a lower bulk density compared to O. abyssinica and grassland.

Generally, surface runoff and soil loss through erosion reduced with the age of the bamboo plantation due to increased canopy cover, ground litter, and root density, which improve the soil structure and aggregate stability in the long term. There was a significant correlation between amount of runoff and soil loss through erosion. The amount of surface runoff and soil loss was influenced by the status of the soil cover, rainfall intensity, and infiltration rates. The seasonality of rainfall patterns influenced the bamboo canopy cover and the growth of weeds on the plantations. Since the results from this study show higher water infiltration rates in bamboo forests compared to other tree plantations and land uses, this can contribute to groundwater recharge and thus sustain the ecological flow downstream. There is huge potential for using bamboo in soil conservation and erosion control practices due to its ability to enhance water infiltration. This study demonstrates the effectiveness of bamboo in reducing surface runoff and soil erosion, which in turn improve the perenniality downstream and stabilizing eroded sloping lands. Finally, the findings of this study have practical applications in watershed management and the management of various land uses and planning. Promoting bamboo cultivation in vulnerable areas could help reduce sedimentation in rivers and water reservoirs, culminating in improved water quality downstream.