Lumber Recovery Rate of Cupressus lusitanica in Arsi Forest Enterprise, Ethiopia

Abstract

In Ethiopia, sawmills have poor capacity utilization primarily due to the outdated equipment that resulted in a low recovery rate and the production of a high amount of wastage. The lumber recovery rate is the output (lumber) of a log in the sawing process. In Ethiopia, Cupressus lusitanica is significantly used for lumber, for furniture production, construction, poles and posts. Sampled logs were processed according to the normal production rate and standard lumber dimension of the sawmill for the purpose of estimating the lumber recovery rate. The present study aimed to investigate the lumber recovery rate of C. lusitanica and the factors affecting it. A total of 26.93 m³ of lumber was produced by the sawmilling operation, representing 72.86% of the overall lumber recovery rate. Furthermore, the sawdust and slabs were recorded as 2.92 m³ (7.90%) of sawdust and 7.11 m³ (19.24%) of slabs, respectively. There were a number of factors that decreased the magnitude of the lumber recovery rate. It was observed that cutting using a wider saw kerf caused a reduction in the rate of lumber recovery owing to the generation of an increased quantity of sawdust. The lumbers were air-seasoned in the sawmill yard. Maximizing the volume of the lumber recovered from the logs can increase the sawmill profitability, lessen the effects of climate change, ensure the sustainable use of natural resources, enhance the energy efficiency and manage wood waste (e.g., recycling and prevention) for green economic development and industrial transformation. This species has a great demand in the wood industry of Ethiopia; hence, the plantation and yield of C. lusitanica must be expanded in order to provide sustainable forestry, protect valuable forest resources and safeguard the biodiversity in the country.

1. Introduction

Sawmilling is the process of converting a wood log into sizable and merchantable lumber employed in making furniture and other wood-based products [1]. Lumber as a solid wood product is made from a lengthwise sawing of logs. Sawmilling is a manufacturing setting equipped with machines, equipment, transporters and handling mechanisms for the conversion of logs into lumber and other wood products [2]. The recovery rate is the quantity of the wood utilized for manufacturing products divided by the quantity of the products generated. In most cases of sawmills in Ethiopia, 20–40% of the wood logs become wastage, resulting in a low recovery rate. The volume of the lumber produced from a certain volume of logs is affected by different factors; these are the characteristics of the log, sawing pattern, saw kerf, decision making by the sawmill personnel and skill of the saw machine operator [3]. An enhanced lumber recovery rate, a reduction in the factors that affect the lumber recovery and an inclusive development approach are needed to ensure the sustainable use of natural resources, improving the energy efficiency, and wood waste management (e.g., recycling, reuse and prevention) for green economic development and an industrial transformation in Ethiopia [4,5,6].

There are currently about 300 medium and large sawmills operating nationwide, both government owned and privately owned [2]. There are enormous gaps between the demand and supply of wood in Ethiopia due to the rapidly increasing human population and accelerated deforestation. In Ethiopia, there has been extensive deforestation and forest degradation [5,7,8]. The conversion of land, timbering, fuelwood collection and charcoal production have caused forest degradation [9,10]. As a result, the current forest area is only about 15.5% of the total land area of the country [11,12,13]. In Ethiopia, the total capacity of the sawmills is relatively low and declining, in part because the country’s raw material supply is running out and because of antiquated, poorly maintained equipment that frequently breaks down, resulting in low lumber recovery rates and significant waste [5]. Furthermore, the majority of enterprises mainly produce for the local market and use modified tools and equipment [14].

Most of the sawmills in Ethiopia are located in the vicinity of forest resources; however, market centers such as Addis Ababa are distantly located for the products to be available and supplied [2]. It is also evident that old sawmills need replacements with that of modern ones to increase the efficiency and effectiveness in order to achieve green economic development and industrial transformation [5,6]. Almost all mills cut lumber using the through-and-through or live sawing methods to minimize the log rotation and handling on carriages and feeding mechanisms; however, each flitch that is sawn off the log requires more edging [15]. The live sawing of logs is primarily practiced in the country [2]. The recovery rate could be greatly increased by the employment of chainsaws during the logging and sawmilling processes [16]. Small-scale and appropriate kiln-dry technologies such as dehumidification and solar kilns technology should be promoted to improve the quality of the lumber [2,5]. In Ethiopia, the system for grading lumber is mostly disregarded; instead, procedures are based on the dimension (thickness and length) and species are utilized frequently. Lumber grading must be implemented to control the quality and increase the yield and profitability in the sawmills, thereby reducing the import of primary forest products and contributing to the green economic development and industrial transformation of the country [12,13].

In Ethiopia, a large number of sawmills are functional [2]. Cupressus lusitanica is a tree species that is widely planted in Ethiopia, next to Eucalyptus [17]. The majority of sawmills produce lumber from the C. lusitanica species, which is mostly used for construction, furniture, poles and posts [18]. Additionally, it can be used for light flooring, ship and boat building, vehicle bodywork, agricultural implements, boxes and crates, interior trim, joinery, toys and novelty items, turnery, draining boards, veneer and plywood, hardboard and particle board. This type of wood saw works well and is easy to work with, either by hand tools or machines. It has good nail-holding properties and a beautiful finish, but drilling a clean hole into it is challenging. It works nicely to stain and shine. The wood can be used for peeling and molding [17,18].

Lumber recovery is the quantity and type of lumber that is recovered from a given number of logs [15]. Meanwhile, the lumber recovery ratio refers to the volume of lumber generated during conversion in relation to the volume of logs converted [19]. Wood recovery can be defined as the quantity of wood utilized for manufacturing products divided by the quantity of products generated in a year [20], while the yield is an efficiency metric of wood-converting operations by dividing useful wood parts to rough sawn timber [21]. In mill applications, wood recovery is frequently described as a ratio between the lumber output and input [15]. The wood recovery rate of a wood processing company depends on how the wood is processed to maximize the product quantity and quality [22]. The most widely used efficiency metric in sawmilling and converting processes is the wood recovery rate [23]. The percentage of recovered lumber dropped as the log taper increased. There was a negative relationship between the lumber recovery percentage and the log taper [14]. The major factors that affect the lumber recovery are the log specification (e.g., log taper and log defect), kerf-width sawing variation, sawing methods, decision making, age and type of the sawmills and lack of training for sawmill operators and co-workers. Moreover, the decisions of a sawmill operator significantly affect the lumber recovery [2,14]. The lumber recovery depends on various tree characteristics, e.g., the DBH (diameter at breast height) and total tree height, geometry of the tree (e.g., taper and stem deformations) and internal log quality (e.g., knot size/number and decay) [24]. Hence, the present study has dealt with the lumber recovery rate of C. lusitanica and the challenges and prospects of sawmilling in Arsi Forest Enterprises, Ethiopia.

2. Methods

2.1. Description of the Study Area

The present study was carried out at the Arsi Forest Enterprise, the Oromia Forest and Wildlife Enterprises, located 240 km to the south of Addis Ababa, between latitudes 6°50′ and 7°38′ north and 38°30′ and 39°06′ east (Figure 1). This region, which is part of the Rift Valley and the south-eastern highlands of the Ethiopian plateau, is a forested part, administered by the Arsi administrative zone, with a tiny portion of it is also being under the purview of the Shoa administrative zone [25]. It is estimated that the enterprise’s total concession area, formerly known as Munessa Shashemene Forest, is 21,384 ha, of which 6230 ha is plantation forest and the remaining 15,154 ha is natural forest [26]. Three sizable forest districts, namely Degaga, Gambo and Shashemene forest districts, make up the entire forest area held by Arsi Forest Enterprise. C. lusitanica plantation forest of the Degaga forest district was the site of the present study. The study site is located between 2100 and 2600 m asl.

In 1997, the sawmill was established, and currently, it employs 186 seasonal workers who are working at the sawmill, among which 152 are male and 34 are female. These workers assist with all aspects of the sawmill’s operations. The study found that there is a consistent supply of raw materials for lumber production that comes from the plantation area. The lumbers were air-seasoned in the sawmill yard while being used lumber by lumber in stacking. They also welcome customers’ complaints and suggestions that assist them to improve the quality of their lumber production. Likewise, they mostly practice the live sawing method to maximize their productivity.

2.2. Topography and Soil

Geographically, the Wonji belt of faults and craters, which runs roughly NNE–SSW, is substantially connected to the research region. The rocks are classified as volcanic, primarily ignimbrite but also including basalt in the north and lava close to the southernmost point of the forest [27]. The soils are ferrisols type, medium in texture, radish in color, freely draining and comprised of large quantities of readily available chemical nutrients, except for phosphorus, which is noticeably low.

2.3. Climate

The study area receives heavy rainfall throughout the rainy season owing to the Woyina Dega and Dega climatic zone of the country [28]. The enterprise areas have a bimodal distribution of rainfall, with the main wet season falling from July to October and a less well-defined rainy period typically occurring between March and June. The dry season, which lasts from November to February, with December being the driest month, falls between these two seasons. The average annual rainfall was estimated to be 1250 mm in the study area. The maximum temperature occurs in the month of May, is about 25 °C and the mean annual minimum is about 7 °C [25,28].

2.4. Vegetation and Wildlife Resources

There is a significant amount of both plantation and natural forest vegetation in the Arsi Forest Enterprise region. The dominant trees in the natural forest were Podocarpus falcutus, Celits africana and Olea hochstetteri, while Prunus africana.-Angeria adolfi-friedic, Apodytes dimidiata, Ficus sur, Schefferelra abyssinca and Syzygium guinease were among the less common trees. In the 1950s, the first plantation was established around the sawmills. The main plantation species for the enterprise at hand are C. lusitanica, P. patula, Eucalyptus globulus, E. saligna, E. grandis and E. riminalis, respectively. C. lusitanica is a main timber tree in the plantation of the enterprise for lumber production. The main vegetation types include high forest, which can be found between 2100 and 2450 m, asl bamboo coppice, which can be found between 2450 and 2650 m, asl and low forest and woodland, which can be found on plains and at the edges of steep slopes where bamboo grows [26,28].

The study area is located in a rich wildlife zone of the Arsi-Bale Mountain. As a result, a variety of wild animals, including endemic species, can be found there. Additionally, it is common to see a variety of bird species in various locations. The three most common wild animals are Tragelaphus scriptus Meneliki (Menelik’s bushback), Panthera pardus (Leop-ard) and Tragelaphus buxtoni (Mountain Nyala). There are also some common species, including warthogs, hyenas and various monkeys.

2.5. Survey and Sampling

Present study was carried out at the Arsi Forest Enterprise sawmill, the Oromia Forest and Wildlife Enterprises. This circular sawmill was established in 1997 as a government enterprise. However, it was upgraded in the year 2019 with modern equipment/machineries to increase the sawmill efficiency, enhance the recovery rate and make it profitable along with the green economic development and industrial transformation in the country. The rationale behind the sawmill selection was the sawmill productivity and efficiency. The circular saw had the following specifications: a diameter of 55 cm, a rotational speed of 3200 rpm, 40 saw blade teeth and a kerf width of 3 mm. The use of a saw blade varied based on the diameter classes of the logs. The qualitative and quantitative types of data were used for present study. The surveys were carried out to collect the data, using questionnaires and structured interviews on challenges, prospects, management and the sawmill history. The questionnaires were administered, and field interviews were conducted to use a combination of both (Closed-ended and Open-ended questionnaires) with fixed response questions used in order to collect the information from the respondents. The data obtained were analyzed for the challenges and prospects of sawmills in Ethiopia. In addition, the factors that affect lumber recovery rates and sawmill production flows were examined to achieve the green economic development and industrial transformation. Likewise, the log sawing practices and recovery rates of lumbers were also measured.

Log attributes including length, diameter, sweep, taper and ellipticity were measured in sawmills, and the US Department of Agriculture Forest Service grading procedures were used to determine log scale and grade. During the measuring process, the features of the sawing equipment, such as headrig type, headrig kerf width and sawing thickness variation, were recorded.

2.6. Sawn Logs Selection and Sample Size

A total population of 150 sawn logs were selected from the log yard and measured using a caliper and a tape rule, then recorded on the data sheet. The rationale behind the selection of a larger sample size is to maintain the accuracy in the data and deliver a crystal-clear picture of sawmill recovery rate. In the present study, the logs were used from a ≥25 year old C. lusitanica plantation for lumber production. The sampling size is determined by the availability of the sawn logs in the yard. The sample logs were selected after they were delivered to the log yard. First inventory of sawn logs in the log yard were developed. The logs were classified into different diameters classes as ≤20 cm, >20 to ≤25 cm, >25 to ≤30 cm, >30 to ≤35 and >35 cm. These were the common categories that were utilized to produce lumber and were used to determine which category had the highest lumber recovery.

2.7. Data Collection, Processing and Analysis

Data were collected by measuring the volume of logs before conversion and lumber volume after conversion using the metric system. Smalian equations were used in order to compute the log volume. Each log was processed according to normal production rate and standard lumber dimension of the sawmill. All necessary data were collected and recorded in data sheets prepared for the purpose of this study. The quantity, skill and adequacy of the sawmill personnel at the site of operation were also determined and recorded. Both ends and the length were also measured with the use of a caliper. The logs delivered to the sawmill were first selected based on their size and diameter classes. Each log was marked and coded with visible paint or a marker. The lumber recovery percent was also measured and analyzed. Microsoft Office Excel and a standard statistical package were used to calculate the lumber recovery.

The log volume was calculated following Smalian equation

$$\mathrm{V}=\frac{\mathrm{l}\ast \mathsf{\pi }\ast ({\mathrm{D}}_{\mathrm{l}}{}^2+{ \mathrm{D}}_{\mathrm{s}}{}^2)}{8}$$

where

V = Log volume (in m³);

D_l = Large end diameter of the log (in m.);

D_s = Small end diameter of the log (in m.);

l = Length of the log (in m.).

Determination of green volume of sawn timber was calculated as

V_g = L × T × W

where

V_g = green volume of sawn timber in m³;

L = length of sawn timber in m;

T = thickness of sawn timber in m;

W = width of sawn timber in m.

Determination of Lumber Recovery Percentage

The percentage of lumber recovered was estimated by

$$\mathrm{LRP} [\%]=\frac{{{\displaystyle \sum }}^{ }\mathrm{VL}}{{{\displaystyle \sum }}^{ }\mathrm{VT}}=\frac{\left({\mathrm{VL}}_1+{ \mathrm{VL}}_2+{ \mathrm{VL}}_3+\dots +{ \mathrm{VL}}_{\mathrm{n}}\right)}{\left({\mathrm{VL}}_1+{ \mathrm{VL}}_2+{ \mathrm{VL}}_3+\dots +{ \mathrm{VT}}_{\mathrm{logs}}\right)}$$

$$\mathrm{LRP} [\%]=\frac{{{\displaystyle \sum }}^{ }\mathrm{VL}}{{{\displaystyle \sum }}^{ }\mathrm{VT}} \times 100\%$$

where

${{\displaystyle \sum }}^{ }\mathrm{VL}$ = (VL₁ + VL₂ + VL₃ + … + VL_n) or total volume of lumber recovered (m³);

${{\displaystyle \sum }}^{ }\mathrm{VT}$ = (VT₁ + VT₂ + VT₃ + … + VT_logs) or total volume of all logs processed (m³).

The volume of sawdust from each log was estimated by

$${\mathrm{V}}_{\mathrm{sd}}=\mathrm{b}*{{\displaystyle \int }}_{\mathrm{l}}^{\mathrm{n}}\mathrm{w}$$

where

V_sd = volume of lumber turned to sawdust, m³.

b = kerf of the saw blade mm.

l = length of the log, m.

w = width of each plank at the point of cut, m.

The volume of wood slab produced during the log conversion process was estimated by

$${\mathrm{V}}_{\mathrm{S}\mathrm{l}\mathrm{a}\mathrm{b}} = {\mathrm{V}}_{\mathrm{l}\mathrm{o}\mathrm{g}} - ({\mathrm{V}}_{\mathrm{s}\mathrm{d}} + {\mathrm{V}}_{\mathrm{s}\mathrm{t}})$$

where

V_Slab = volume of slab.

V_log = volume of log.

V_sd = volume of sawdust.

V_st = volume of sawn timber (lumber).

3. Results and Discussion

3.1. Lumber Recovery Rate

The relationships between the input (log) and output (lumber), lumber recovery percentage and percentage of sawmill by-products for all log classes are presented in

Table 1. The lumber recovery of Cupressus lusitanica at Arsi Forest Enterprise sawmill, Ethiopia.

Log Classification	Number of Logs	Mean Log Taper (cm)	Mean Diameter in cm	Log Volume in m3	Recoveries
					Lumber Recovery		Sawdust		Slabs
					Volume (m3)	(%)	Volume (m3)	(%)	Volume (m3)	(%)
≤20 cm in diameter	30	0.39	26.83	2.89	1.79	61.94	0.19	6.57	0.91	31.49
>20 to ≤25 cm in diameter	30	0.34	34.02	4.70	3.18	67.66	0.35	7.45	1.17	24.89
>25 to ≤30 cm in diameter	30	0.27	38.87	6.25	4.32	69.12	0.47	7.52	1.46	23.36
>30 to ≤35 cm in diameter	30	0.24	49.72	10.16	7.50	73.82	0.81	7.97	1.85	18.21
>35 cm in diameter	30	0.19	55.85	12.96	10.14	78.24	1.10	8.49	1.72	13.27
Overall and Mean	150	0.29	41.06	36.96	26.93	72.86	2.92	7.90	7.11	19.24

. The study on the rate of lumber recovery of C. lusitanica clearly demonstrated that different sizes of logs were used for lumber production in the Arsi area. The lumber produced was readily available for the construction and furniture industry [2,14,29]. As a product from a fast growing plantation of softwood species, C. lusitanica lumber has lessened the burden on forest product imports while also relieving pressure on natural forests [5]. It has created green jobs and improved the livelihoods of the local people [12,13]. The lumber of this species was widely used in the wood industry due to its fine quality [11]. The demand of this species has increased over the period of time in the wood industry; hence, the plantation and yield of C. lusitanica needs to be increased in order to meet the demand, securing sustainable forestry and protecting valuable forest resources and biodiversity in the country. Currently, C. lusitanica accounts for ≥31% of the commercially softwood planted timber species after Eucalyptus (60%) as a hardwood timber species in the Oromia region of the country. Because C. lusitanica is a non-coppicing softwood species, the old stands are declining; however, young stands of the species are increasing as a result of new plantations [5]. Table 1 shows that the rate of lumber recovery has increased as the diameter classes increased. In comparison to small diameter sizes, larger diameter classes have contributed more to lumber recovery.

However, for lumber production, both bigger and smaller diameters were utilized. If sawmills are to remain efficient and competent, they must maximize their lumber recovery rate and obtain a higher quality of lumber [14]. The sawing process uses energy to produce lumber; thus, it is important to reduce any negative effects it has on the environment. Therefore, it is important to use and encourage energy-efficient machinery, equipment and resources in the sawmilling process [5].

In Arsi Forest Enterprises, Oromia Forest and Wildlife Enterprises at the sawmill, the total volume of processed C. lusitanica logs was 36.96 m³, while the output in terms of the obtained volume of lumber was 26.93 m³ (Table 1; Figure 2). As a result, the lumber recovery rate for C. lusitanica at the Arsi sawmill using a circular saw, rip saw, radial arm saw and re-saw was 72.86%, which is higher than the results reported by Rongrong et al. [30] using the through-and-through sawing method. The lumber recovery rate was high due to a newly established sawmill, upgraded in the year 2019 with modern equipment. Thus, in order to maintain the efficiency of a sawmill, the availability of the spare parts, regular monitoring and maintenance is required. In addition, the lumber recovery rate also depends on the straightness of the logs and having no defects [29]. Log straightness is recognized as an important quality characteristic and has featured prominently in both the log grading rules and lumber recovery [31], because swept logs give rise to product recovery when straight [29]. Alternatively, sustainable forestry practices (e.g., silviculture management) are critical for the straight and defects-free logs correspondence to maximize the lumber recovery rate [11]. The lumber recovery rate was higher than in Muthike et al. [32] who used a chain saw, bench saw and pit-saw-appropriate technology. It is also higher than the results reported for other hardwood species by UNECE [33] for Canada, France and Norway; however, it is comparable to the results for mixed hardwood species obtained in Ireland and Spain. On the other hand, this result is higher than that Christensen et al. [34] obtained for softwoods (Sitka spruce, Picea sitchensis, Bong. Carr.) and western hemlock (Tsuga heterophyla, Raf.). The C. lusitanica lumber recovery results were higher than the findings of Gligoras and Borz [35] who evaluated the lumber recovery rate using an FBO-02 Cut Mobile Band Saw and found a mean value of about 66% of yield. It implies that sustainable forestry practices and defect-free and quality logs (e.g., straightness) contributed to the optimum lumber recovery rate [2,11,14]. Maximizing the rate of lumber recovery results of C. lusitanica has multiple benefits, such as proper log utilization and off-setting carbon footprints, increasing the profitability and mitigating climate change impacts and thereby contributing to green economic development and industrial transformation [5].

3.2. Percentage Volume of the By-Products of Sawdust and Slabs

By-products (i.e., sawdust and slabs) were recorded as 2.92 m³ (7.90%) of sawdust and 7.11 m³ (19.24%) of slabs, respectively (Table 1; Figure 3). In comparison to sawdust, the slab was discovered more frequently [29]. The by-products generation could be minimized by increasing the sawmill efficiency and the operators. Alternatively, the sawmill by-products produced during processing could be recycled and reused for various forest products development [5]. It is worth noting that the log diameter classes ≤ 20 cm had the highest percentage of slab and the lowest percentage of lumber recovery. The sawmill does not use the <12 cm diameter classes of the logs for lumber production; it is used as firewood [29].

In this study, the volume and percentage of the sawdust produced in each set of the logs were estimated. The log diameter classes ≤ 20 cm produced less sawdust, while the sawdust produced in other logs diameter classes were in ascending order, respectively (Table 1; Figure 3). This is similar to the effectiveness of the lumber recovery among selected sawmills in Nigeria’s Akure metropolis [36]. The amount of sawdust produced in this study was less than that found in a study by Fonseca [37] in Medford, Oregon. The amount of sawdust produced during conversion is determined by the blade thickness and the number of times the saw blade passes through the log during the process [3,29,38,39]. Additionally, it depends on how well the sawmill is maintained and the setting of the saw teeth [32,40].

The slab is a by-product of the logs that have reached the mills but have not been converted into lumber or sawdust; it contains slab, trims, edged wanes, rots and other items. The number of slabs generated during the process was higher in the log diameter classes ≤ 20, while less slabs were produced as the diameter classes of the logs increased, respectively (Table 1; Figure 3). The lowest slab was found in the >35 cm diameter classes of the logs while this diameter class had the highest recovery rate [29]. It was believed that the uses of slab and sawdust may be further improved if the remnants in the form of a slab were channeled into more valuable products [36]. The sawdust and slabs produced during the process were used to make briquettes and as mulch for food crops and gardens, while slabs were used as firewood [29]. Sawdust and slabs could also be collected from a few sawmills to be used in the production of particle boards for local sale.

3.3. Factors That Affect the Lumber Recovery Rate

3.3.1. Log Taper

Tapering is the variation in the diameter of logs from the large end to the small end along a particular length of the logs (unit less ratio) [2,14,29,41]. For this species, as the diameter of the logs increases, the taper-to-volume ratio decreases. The tapering of logs was observed to be more significant in the ≤20 cm diameter classes (Table 1; Figure 4). It shows that the taper declined as the diameter classes increased [29]. The same was shown to hold true by Missanjo and Magodi [14], wherein the lumber recovery decreased as the magnitude of the taper increased. The correlation analysis demonstrates that the log taper (r² = −0. 972; p < 0.001) had a negative relationship with the percentage of the lumber recovery (output) and a positive correlation with the volume of the slabs (r² = 0.971; p < 0.001), implying that processing logs with more taper produces more slabs and less lumber (

Table 2. Correlation among the variables in conversion of C. lusitanica logs at Arsi Forest Enterprise sawmill.

		Log Volume (m3)	Lumber Recovery (%)	Slabs (%)	Sawdust (%)	Taper (cm)	Mean Diameter (cm)
Log volume (m3)	Pearson Correlation	1
	Sig. (two-tailed)
Recovery (%)	Pearson Correlation	0.983 **	1
	Sig. (two-tailed)	0.003
Slabs (%)	Pearson Correlation	−0.980 **	−1.000 **	1
	Sig. (two-tailed)	0.003	0.000
Sawdust (%)	Pearson Correlation	0.952 *	0.992 **	−0.994 **	1
	Sig. (two-tailed)	0.013	0.001	0.001
Taper (cm)	Pearson Correlation	−0.962 **	−0.972 **	0.971 **	−0.957 *	1
	Sig. (two-tailed)	0.009	0.006	0.006	0.011
Mean Diameter (cm)	Pearson Correlation	0.995 **	0.991 **	−0.989 **	0.967 **	−0.976 **	1
	Sig. (two-tailed)	0.000	0.001	0.001	0.007	0.005

**. Correlation is significant at the 0.01 level (two-tailed). *. Correlation is significant at the 0.05 level (two-tailed).

). This shows that there was a negative and significant correlation between the lumber recovery percentage and the log taper [29]. This is corroborated by the findings of Missanjo and Magodi [14] and Ayarkwa and Addae [41], who reported that the log taper has a negative correlation with the lumber recovery rate, while slabs have a positive correlation and negatively affect the lumber recovery rate. The lumber recovery percentage was found to be lower when the taper was reduced during the slabbing and edging operation. In a similar vein, Bennett [42] said that sawing taper logs causes a yield loss at the large end, with the clearest timber on the log often being lost. One solution to offset the effect of tapering on the rate of lumber recovery is decreasing along a length of logs, because in doing so, the volume of the trimmings decreases, thereby increasing the volume of the lumber [29].

3.3.2. Decision Making of Sawmill Operator

The decision-making ability of the sawmill machine operators was another aspect of this study’s findings that affected the rate of the timber recovery [29]. Indeed, different operators have varying levels of decision-making ability, and as a result, they make different decisions and obtain different results from the same logs [43]. According to Bennett [42], sawyers can maximize yields from the same logs if they make rational decisions. Similarly, according to Keegan et al. [44], better sawmill technology and practices employed in log conversion at sawmills are responsible for a significant increase in lumber recovery. Kilborn [38] stated that poor decision making may result in the oversizing of the product when compared to standard products on a market, that producing a greater amount of product size variation affects the lumber recovery and that oversizing the product results in about 2.5% of additional losses. The ITTO [45] stated that training for professionals in administration, operations, maintenance, sales, marketing and logistics and the analysis of raw material resources and product lines is critical for sawmills to maintain long-term profitability. As a result, it will aid in improving the rate of lumber recovery, sawmill maintenance and sawmill operators’ decision-making abilities [2,14,29,41].

A decision of sawmill personnel significantly affects the lumber recovery. A decision could be made in the context of product recovery to achieve specific objectives (e.g., maximum product yield, quality and value) [2,14,41]. A better understanding of the connection between tree characteristics and lumber volume recovery aids the sawmill sector in planning for the supply of the wood needed to produce forest products and the sustainability of the wood industry [5]. The heterogeneous nature of the raw material demands that machine operators make thousands of decisions every day. Fatigue, a lack of knowledge or ability or carelessness can mean poor decisions. In some cases, so many variables must be considered in such a short time that even the best operator finds it impossible to make optimum decisions [46].

3.3.3. Age and Type of the Sawmills

In Ethiopia, sawmills are normally associated with a low utilization capacity and outdated equipment that resulted in a low recovery rate and the generation of a large amount of waste [5]. Most of the mills are old and designed to convert large saw logs of indigenous species [2]. However, this sawmill is comparably a new sawmill and was upgraded recently; hence, the lumber recovery rate obtained was higher and, apart from this, the straightness of the logs also contributed to it. Additionally, what makes it successful is the use of a modern machine and regular maintenance. Similarly, Faruwa et al. [40] and Ogunwusi [47] stated that different types of sawmill machines contribute to the variations in the rate of lumber recovery, but old and outdated machines differ from new ones in terms of productivity. The use of thinner saw blades results in narrower kerfs and produces less sawdust, which improves the rate of lumber recovery [29,38,39]. In a similar manner, Fonseca [37] demonstrated how saw cuts and kerfs impair the lumber recovery by generating around 7–14% more sawdust from the volume of the log. According to Lin et al. [3], saw kerfs had a substantial impact on the volume of lumber recovery. According to Muthike et al. [32], the rate of lumber recovery depends on the type of sawmill machinery employed.

Even a single piece of wood can be damaged before it is produced, as care must be taken before it reaches consumers. According to a recent study, sawmills in Ethiopia are ordinarily portrayed by a low utilization limit and obsolete equipment, bringing about low recovery rates and the production of a lot of wastage [2,14,29]. In addition, the quantity of lumber created from a specific volume of logs is influenced by a few components identified by the attributes of the logs (i.e., species, log diameter, length and defects), innovation, sawing design, stumble measurements, nature of sawmills, preparing and experience of the machine operators [5]. It was discovered that one of the best ideas for increasing sawmill efficiency is the employment of new machinery. These cutting-edge devices boost the efficiency by simultaneously creating vast numbers of high-quality products [29].

3.3.4. Log Defects

Both natural and artificial log defects affect the lumber quality, yield, value and recovery because such defects are not supposed to be included within the lumber [2,14,41]. In this study, a log class on having more defects resulted in a low recovery rate of lumber. Knots are the commonest cause for lowering the value or recovery of lumber [48]. They also affect the working qualities of wood considerably, because they are much more refractory under tools than the wood surrounding them [48]. Defects-free and straight boles that come from better silviculture-managed plantations imply an increase to the lumber recovery rate [5]. A higher lumber recovery rate thus results in the optimum use of resources and helps with climate change mitigation by increasing the carbon sequestration and green economic development [6,12,13].

3.3.5. Capacity Building and Training

High-performance work practices, including empowerment and training, influence the organizational and employee performance. However, for a better performance, employees should be motivated by high-performance work practices. Employee motivation is enhanced through training, capacity building and empowerment, and this increased motivation level leads to a better organizational performance through the higher engaged behavior of employees [49].

To improve the efficacy and competitiveness, investments in sawing and drying technologies vocational trainings are required to enhance the capacity and efficiency of the operators and co-workers [5]. Maurice et al. [50] described that vocational training for workers could increase the efficiency rate of logging operations by 5% and training can avoid the loss of material in processing. Maurice et al. [50] also apportioned the training courses needed for saw millers for technical improvements by allowing the efficient utilization of new technologies.

The major challenges the sawmill is facing is the availability of spare parts. The government should pay attention to make available the spare parts on time. There are sometimes disruptions of development activities in the forests area, which need to be controlled. The efficiency of sawmills could be improved by decreasing the cost of a sawmill, upgrading the equipment, performing routine maintenance and by improving the decision making of the operators [29]. The blade is sharpened by using a saw blade doctor machine. The sawmill is repaired annually to improve the sawmill efficiency. The lack of a packaging system at the sawmill may be necessary to increase the production and efficiency.

4. Conclusions

The optimization of the rate of lumber recovery helps to increase the profitability, enhance the energy efficiency and reduce the burden on forest resources and the import of forest products, thereby contributing to green economic development and protecting valuable forest resources and the biodiversity of the country. The results of the present study show that increasing the logs taper led to the production of more slabs, which resulted in a lower lumber recovery rate. By-products (such as sawdust and slabs) could be used to make briquettes, mulch for food crops, particle boards, etc. Alternatively, an increased plantation area and yield of this tree species and sustainable forestry practices are needed to meet the rising wood-based demand of the industry.

The study found that a number of variables, including the log taper, operator decision making, age and kind of sawmills and log defects, affect the rate of lumber recovery. Adopting new energy-efficient sawmill technology, training, skill development, maintaining the quality of the input logs, increasing the efficacy of sawmill operators, capacity-building training for sawmill operators, as well as routine sawmill maintenance, could increase the recovery rate of lumber and support sustainable forest management and environmental sustainability.