PRUNING TIME CONSUMPTION OF SINGLE BRANCHES OF SCOTS PINE (PINUS SYLVESTRIS L.) TREES

Dieter Franciszek Giefing¹, Łukasz Hubert Łukomski^2
1 Department of Forest Utilization, University of Life Sciences in Poznań, Poland
² Department of Forest Utilisation, August Cieszkowski Agricultural University in Poznan, Poland

ABSTRACT

The purpose of the performed experiments was to determine the time consumption of the removal of single Scots pine branches in relation to their thickness, vitality and height of pruning. Branches were cut with the assistance of special handsaws of the ARS and Buchman type. These saws are characterised by the highest efficiency from all the applied saws which have been subjected to investigations so far. Trees were pruned to the height of 5 meters along consecutive 1 meter-long segments. The test comprised 50 branches for each 1 m long section of the trunk. Measurements comprised the thickness of branches as well as the time needed to remove them.

Key words: tree pruning, time-consumption of pruning, pruning tools, ARS saw, Bushman saw.

INTRODUCTION

The ever growing demand for products of wood industry makes it necessary to supply this branch of economy with considerable quantities of timber raw material. There is increasing demand not only for cheap wood of inferior quality for physico-chemical processing but also for large-size timber raw material of the highest class. Periodically, there are problems with selling defective large-size timber assortments. Therefore, one of the major problems facing forest economy is the question of the quality improvement of produced timber. Knots are one of the main deficiencies considerably worsening the quality of timber raw material.

One of the treatments which can decrease dramatically knottiness of trees is their pruning as this treatment shortens significantly the process of self-cleaning of trunks from branches. This, in turn, allows trees to speed up the process of accumulation of knotless timber which is the most valuable part of the trunk from the user’s point of view. Hence, economically and technically, pruning is the most effective of all tending operations whose aim is to produce timber of the best quality [7, 6, 1, 2].

Pruning operations are performed employing highly specialised tools, primarily saws mounted on special extension arms. These are the basic tools used in pruning operations and they are characterised by very good quality of work and many of them have been tested thoroughly with regard to their pruning effectiveness. The highest pruning efficiency was recorded in the case of the STE-UNI-S web-saw [11, 12] and the Swedish flat saw BUSHMAN [3, 11, 12]. In recent years, saws with parallel toothing have appeared on the market and so far, in the available literature on the subject, only results of experiments on their selective pruning (using the classical method) of pine stands have been published [4].

The purpose of the performed experiments was to analyse the time required to remove individual tree branches employing for this purpose ARS^* saw types with parallel toothing and to compare them with the BUSHMAN type of saw. In the course of experiments the authors examined the effect of the pruning height, branch thickness and healthiness of knots on the obtained results.

AREA, SCOPE AND METHODOLOGICAL ASSUMPTIONS OF THE EXPERIMENT

Investigations were carried out in February 2003 in the Drawsko Forest Division (Szczecinek Regional Directorate of State Forests) in the Studnica Forest Range (Tab. 1).

Tree pruning operations were performed using two saws of the ARS type and two Bushman type saws (zero sample).

The special ARS type saw [2] (Fig. 1A) has flat toothing and is equipped in a plastic handle. It is designed for tree pruning up to the height of 2 m. Another version of this saw is a flat saw designed to be mounted on an extension arm of the STE system [2] (Fig. 1B) and it is equipped in a nib and a de-limbing knife. The length of the saw blade is 470 mm, while its thickness – 1.6 mm. This saw is equipped in a group toothing 4.5 mm high separated by hollows which facilitate the removal of sawdust from the kerf. The extension arm of the STE system (Fig. 3A) consists of sections from 0.6 to 1.7 m long which are joined together by screwing. The extension arm is characterised by considerable rigidity. Thanks to its design, individual elements can be joined together to form an extension arm of any length.

The Swedish flat saw Bushman – 147 [2] (Fig. 2A) is intended for tree branch pruning up to the height of 2 m. The saw has a bent beech-wood handle. Another type of the saw is the Swedish flat saw Bushman – 146 [2] (Fig. 2B) equipped in a nib and a de-limbing knife intended for tree pruning up to the height of 6 m. It can be mounted on the Sandvik extension arm [2]. The saw is equipped in a triangular blade to which a cylindrical steel grip of 27.5 mm diameter is fixed allowing mounting of the extension arm. The telescope Sandvik extension arm (Fig. 3B) consists of two parts and its length can be regulated from 200 to 380 cm. The small diameter of this extension arm makes it very light but is also affects its rigidity and makes work with it a little more difficult.

A

B

A

B

A

B

The thickest trees of good biosocial position (l and ll Kraft class), well developed stems and without shape defects or injuries were selected for pruning. The performed experiments included the determination of the time needed to remove individual branches depending on their thickness and height of pruning (1 m segments up to the height of 5 m). It was also indicated whether the pruned branch was live or not using for this purpose Henman’s definition according to which a branch is considered alive if at least one needle on it remains alive [8]. The sample included 50 branches for each 1 m long segment of the stem. The time was measured using an electronic stopwatch with 0.5 sec. accuracy and the thickness of branch was determined with 1 mm accuracy using slide callipers.

The polynomial regression analysis was employed in order to determine correlations between the thickness of branches (mm) and the time needed for their removal (s) on the 5 m long butt end part of the stem. Next, using the single factor analysis of variance and the Tukey’s procedure, it was verified if mean branch thicknesses and mean times of removal of individual branches on successive 1 m long segments of pruned trunks differed statistically significantly between one another. In order to determine the significance of differences concerning the mean thickness of branches and the mean time of removal of individual branches on the consecutive 1 m long sections of pruned trunks between the examined tools, the t-Student test was employed.

RESEARCH RESULTS

Investigations carried out with the assistance of the analysis of polynomial regression (in this instance – square) to examine the effect of the branch thickness on the time of their cutting on the 5 m long trunk segment using the ARS saw revealed a fairly strong regression between the examined traits (Fig. 4). The square regression curve (described by the function: y = 0.0069x² – 0.1037x + 0.8496) possesses the determination coefficient (R² = 0.73) indicating a strong correlation between the dependent and independent traits. The run of the regression curve shows that if the branch thickness did not exceed 11 mm, the time needed to cut it off was very short ranging from half to one second. A marked increase of the time consumption of the operation was recorded when the pruned branches measured 27 to 47 mm in diameter and this referred both to dead and live branches. It should be emphasised that the time needed to remove single branches was very short (from 0.5 to 10.5 seconds), indicating high effectiveness of the ARS saw (the saw with the parallel toothing).

The square regression analysis of the time required to cut off a single branch in relation to its thickness using the specialised Bushman saw revealed a fairly strong regression with over 66% determination of the dependant variable on the independent variable (Fig. 5). The run of the regression curve (described by the function: y = 0.0315x² – 0.7279x + 5.0653) showed that the cutting time of one branch of up to 12 mm thick was short ranging from half to one second. The time consumption of pruning increased rapidly when branches 20 to 39 mm thick were cut. The recorded time consumption of the pruning operations using the Bushman saw ranged from 0.5 to 29 seconds and was distinctly higher in comparison with the ARS saw.

The comparison of the two examined types of saws showed that the time necessary to cut branches using the Bushman saw was almost three times longer in comparison with the ARS saw, despite the fact that the thickness of the pruned branches for both types of saws was similar.

The applied single factorial analysis of variance revealed statistically significant differences between mean thicknesses of branches in the consecutive 1 m long sections of pruned tree trunks. Also mean times needed to cut individual branches for the ARS and Bushman saws showed statistically significant differences.

Verification of the significance of differences using the Tuckey’s procedure revealed that the pruning times of single branches up to the height of 2 m, for both tested saws, did not differ between the individual sections of the tree trunk, irrespective of differences in the branch thickness.

The evaluation of significance of differences with the assistance of the t-Student’s test (Tab. 2) showed that the type of the applied tool had a significant effect on the time required to remove individual branches. The ARS saw was characterised by lower times needed to cut off branches on all trunk segments and this difference increased with the height of pruning. The result of the Student’s test showed lack of significant difference in the time consumption of pruning only on the second meter. This is the height at which this treatment is easiest to perform. In the case of the remaining trunk segments, statistically significant differences were observed which increased with the height of branches to be removed, irrespective of their mean thickness on the consecutive 1 m long trunk sections. These observations are also corroborated by results presented on Figures (Figs. 4 and 5). The maximum time needed to remove individual branches with the ARS saw did not exceed 11 seconds, while the maximum time of removal of the thickest branches with the Bushman saw exceeded 25 seconds.

The obtained research results also allowed determining the effect of branch vitality on the time of their removal. Live branches occurred only in the case of the fifth section of pruned trunks and the time needed to remove them was by about 35% longer in comparison with dead branches (of similar diameter and situated on the same height). This was caused by resin secreted from live branches which accumulated on saw blades and resulted in ineffective ‘slipping’ of the blade in the kerf.

DISCUSSION

The results obtained in the course of this research allow noting a number of important regularities. Firstly, a high efficiency of pruning with saws equipped in parallel toothing must be emphasised (ARS saws). It is worth noting that the application of ARS saws led to better results at all heights of pruning, despite the fact that, up to the height of 4 m, mean diameters of branches cut using the Bushman saw were smaller than those cut by the ARS saw and on the third meter those differences were statistically significant (Tab.2). It should also be mentioned here that the Bushman saw belongs to the group of three saws which allow obtaining the best labour effectiveness form among several tools used for pruning and which have been subjected to tests [3, 5]. This confirms the clear advantage of ARS saws (saws with parallel toothing) over all other tools used in pruning operations up till now.

The experiments carried out so far [11, 5] failed to produce significant differences in the productivity between several of the examined tools used to prune trees up to the height of 2.00 m. It should be mentioned that the investigations referred to above did not include the ARS saw. Our experiments showed significant differences between the times required to cut single branches with the ARS saw in comparison with the Bushman saw occurring already on the first 1 meter-long butt end part of the trunk. Also on the second trunk section, the time consumption of the operation was smaller when branches were cut with the ARS saw, although this time differences were not statistically significant. These results allow concluding that the impact of the applied tools on work efficiency decreased with the ease with which the treatment was carried out. Hence, the results obtained in this study do not contradict opinions presented in the above-quoted literature on the subject. Also in those studies, the authors reported slight, statistically non-significant differences in the time needed to prune branches of lower trunk segments using different tools.

The pruning of the tree trunk at the height of 1 – 2 m is very easy as it corresponds to human anthropometric characteristics and, therefore, the measured differences were statistically non-significant. The first butt end part of the trunk requires bending and is somewhat more difficult for workers. The coefficient recorded here confirmed the significance of the observed variation, but its value was relatively small, smaller than on the 3^rd, 4^th and 5^th meters.

Maćkowiak [11] also found that up to the height of 2.20 m, the diameter of branches did not affect the time required to remove them. This finding was also confirmed by our research results. However, it should be stressed that branch diameters in the lower part of the trunk do not vary significantly and at small variability of this trait in the examined sample, the probability of finding statistical differences is negligible.

The above-quoted results indicate the usefulness of the application for pruning operations of professional tools of the highest quality. This is particularly true when pruned branches are situated at higher levels (2^nd, 3^rd and higher pruning levels) as well as when trees with thick branches are to be pruned.

Our research results obtained for both the ARS and Bushman saws corroborate findings reported by Maćkowiak that the time needed to remove live branches is longer (by approximately 30%) in comparison with the removal of dead branches. In our experiments, the time required to cut off live branches was by about 35% longer than in the case of dead branches.

REMARKS AND CONCLUSIONS

1. The type of the tool used to cut branches exerts a strong influence on the time needed to perform this treatment. The mean time of cutting single branches with the ARS saw amounted to 1.65 seconds and was almost half shorter in comparison with the time needed for the same operation using the Bushman saw (3.22 s).

2. The time required to cut individual branches along the 5 m long butt end part of the trunk was correlated with their diameter. The course of this correlation for the ARS saw was characterised by the square regression described by the function: y = 0.0069x² – 0.1037x + 0.8496. In the case of the Bushman saw, the square regression was described by the function: y = 0.0315x² – 0.7279x + 5.0653.

3. The time required to cut individual branches increased with their diameter and height at which the knot (branch) were situated on the trunk.

4. Up to the height of 2.20 m, both in the case of the ARS and Bushman saws, the diameter of pruned branches had no statistically significant influence on the time needed for their removal.

5. The removal of live branches was by 35% more time-consuming than the removal of dead branches.

REFERENCES

1. Aboney E. A. 1981. Zur Wertästung von Nadelhözern mit Handgeräten. [Trees pruning with hand tools]. Göttingen [in German].

2. Giefing. D. F. 1999. Podkrzesywanie drzew w lesie. [Pruning trees in the forest] Wydawnictwo Akademii Rolniczej, Poznań [in Polish].

3. Giefing. D. F., Hołota R. J., Stefański P., Œrednicki J. 1996. Czasochłonnoœć podkrzesywania drzew w lesie. [Time required to prune forest trees] Sylwan 140, 1: 37–44 [in Polish].

4. Giefing D.F., Łukomski Ł.H. 2004. Wydajnoœć podkrzesywania sosny zwyczajnej za pomocš piły ręcznej typu ARS. [Effectiveness of Scots pine pruning using the ARS type hand saw] Technika Rolnicza, Ogrodnicza, Leœna, 11: 22–25 [in Polish].

5. Giefing D. F., Maćkowiak S. 1998. Czasochłonnoœć podkrzesywania sosny zwyczajnej (Pinus sylvestris L.) różnego typu piłami ręcznymi. [Time needed to prune Scots pine (Pinus sylvestris L.) trees using different types of hand saws] Sylwan, CXLII, 12: 33–47 [in Polish].

6. Göler von Ravensburg R. 1970. Die Wertästung der Kiefer in arbeitswirtschaftlicher Sicht [Pine pruning from economic point of view]. Hann. Münden [in German].

7. Häberle S. 1968. Höhere Reinerträge durch Wertästung [High income due to pruning]. Allg. Forst Z. 33: 579 [in German].

8. Heneman D. W. 1963. Pruning conifers for the production of quality timber. For. Commis. Bull. [Edinburgh] 35.

9. Katalog Grube 2000, Ausrüstungen für Wald, Landschaft, Natur und Umwelt [Tolls for forestry, agriculture, nature and environment]. Hützel, s. 227, 236-239 [in German].

10. Kala R. 1999. Elementy wnioskowania parametrycznego dla przyrodników. [Elements of parametric inference for naturalists] Wydawnictwo Akademii Rolniczej, Poznań [in Polish].

11. Maćkowiak S. 1997. Badania czasochłonnoœci i wydajnoœci prac przy podkrzesywaniu sosny zwyczajnej (Pinus sylvestris L.) w zależnoœci od zastosowanych metod i narzędzi. [Time consumption and productivity analysis of Scots pine (Pinus sylvestris L.) pruning in relation to the applied methods and tools – Manuscript] Maszynopis. Katedra Użytkowania Lasu AR, Poznań [in Polish].

12. Maćkowiak S., Giefing D. F. 1999. Time consumption analysis of pine (Pinus sylvestris L.) pruning using the classical and dominant trees methods. Folia Forestalia Polonica, A, 41: 47-58.

* The authors chose to carry out the experiments on ARS type saws because they are the first saws with parallel toothing introduced on the market. Other saws available on the market with the same type of toothing utilize the design first applied in the ARS saws.

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