^{3}
) were 3.06, 5.69, and 6.81 €/m
^{3}
in TLM, LLM, and SLM, respectively, and the most economical alternative depending on DL, SD and WD was a TLM. Furthermore, the results of simulated models suggest that as long as the diameter of the felled trees is less than 40 cm, the cut-to-length system is not an economical alternative. The cut-to-length method can be applied for trees with larger diameter (more than 40 cm), and in short skidding distance SLM is preferable to LLM but in cases of long skidding distance, LLM is more economical than SLM.

Nowadays, due to technological evolution, evaluation of machine productivity and calculation of the average cost of skidding for each hour and each cubic meter is necessary to compare their efficiency (

An important research tool which is common to compare the productivity of forest harvesting systems across varying conditions is time studies (
^{3}
;
^{3};
^{3}
;
^{3}
;
^{3}
(13.9 $/m
^{3}
);
^{3}
;
^{3}
;
^{3}
(1.1 $/m
^{3}
);
^{3}
and 3.3 €/m
^{3}
. Also,

In a comparison of whole tree harvesting system cut-to-length involves the high initial cost of investment, repair and maintenance of the machine's complex computerized system, and the inability of the felling-processing machine to handle stems with stump diameter larger than 60 cm. However, whole tree harvesting requires more woods workers, supervision, and support than cut-to-length harvesting. In addition, the hourly machine rate for the whole tree method system has also been higher than for the cut-to-length (
^{3}
and 12.4 €/m
^{3}
in the Black Sea and Aegean regions, respectively, and cost for whole tree system by using four sawyers, a grapple skidder, and a loader was 8.2 €/m
^{3}
in the Mediterranean region. Also,

The main objective of this investigation is comparison cost and productivity of three logging alternatives (1- TLM, 2- LLMand 3-short SLM) depending on the DL, SD, and WD in ground-based cable skidders system in a mixed broadleaved mountainous forest.

This study was conducted in the compartments 46, 107 and 41 of Jo Jadeh district in the Wood Industry of Farim forests (a part of the Hyrcanian forests). Some characteristics of study compartments and harvesting alternatives in case study can be seen in

To estimate productivity and cost a continuous time-study technique was applied. Time for each work element and accumulated time were measured by a deci-minute stopwatch in minutes and seconds. A work cycle and time elements were same for TLM, LLM and SLM which broken down in seven phases (traveling unloaded, releasing, hooking, winching, traveling loaded, unhooking, pilling and delays). For each trip, important variables of the time consumption such as the size of logs (DL and length (LL) of logs), the number of logs (NL), terrain slope gradient in the loaded direction (SL), SD and WD were recorded.

Normally scientific who use time study in forest harvesting operations predict a time consumption model by using the original times which are gathered by time studies in the field. But in this paper, all time study numerical data were transformed to their logarithmic data based on 10 and the time consumption model was developed on the basis of logarithmic time data.

Logarithm modeling is indeed the most reliable method for predicting the consumption of woodworking time. Today's concept of logarithms might make it seem strange that logarithms were really developed out of comparing velocities of arithmetically and geometrically moving points (

The logarithmic time prediction models were developed on the basis of linear regression in SPSS software (SPSS, Tulsa, USA, Version 19, 2011). But only influencing factors with significant correlation coefficients at the level of significance α = 0.05 were used to develop the logarithm models. Subsequently, by used logarithmic models, we simulated unit cost for 11 skidding cycles depending on DL, SD, and WD in TLM, LLM, and SLM. In order to estimate cost depending on DL, DL, NL, and LL were considered as inuencing variables. The value of DL and NL were variable between 11 cycles and LL was variable between the alternatives (TLM, LLM, and SLM).However, other parameter values (such as SL, SD and WD) were same between 11 skidding turns which was set to the mean value. To estimate the cost depending on SD, SD and LL were considered as influencing parameters, and the value of SD was variable between cycles and LL was variable between alternatives, and the other parameters were set to the mean value. In order to estimate the cost depending on WD, WD and LL were considered as influencing parameters, which variable parameter between cycles was WD and LL was variable parameter between alternatives and the other parameters were set to the mean value in all 11 skidding turns in TLM, LLM, and SLM. Delay time of time consumption (DT) by prediction model in TLM, LLM, and SLM was measured as following (

The estimated time by the logarithmic models and the measured time on the field (real time) by time study techniques in TLM, LLM, and SLM are shown in

The ratio between the estimated time by logarithmic models and the measured time by the time study was 93% for TLM, 91% for LLM and 92% for SLM, as well as, values of geometric means are less than the time study numeric data (

TLM prediction model (

LLM prediction model (

SLM prediction model (

Ŷ is time consumption by model (min), LD is loading distance, TU is traveling unloaded, R is releasing, H is hooking, W is winching, TL is traveling loaded, UH is unhooking, P is pilling.

The most important affected factors in TLM were SD, WD, NL, and DL (

The simulated cost models show that the mean net cost depending on DL (volume), SD and WD were 3.06, 5.69 and 6.81 €/m
^{3}
, respectively. In TLM the maximum net cost was 3.23 €/m
^{3}
, mean 3.06 €/m
^{3}
and the minimum was 2.94 €/m
^{3}
; in LLM maximum cost reached 5.76 €/m
^{3}
, mean cost 5.69 €/m
^{3}
and minimum of cost 5.63 €/m
^{3}
. And in SLM the queue was 6.97 €/m
^{3}
, 6.81 €/m
^{3}
and 6.67 €/m
^{3}
depending on the winching distance (

On average, 11, 12 and 15 % of the gross effective time of the time study was DT in TLM, LLM, and SLM, respectively. As mentioned in the methodological part, the DT to the prediction model was estimated by using the average of DT in time study in TLM, LLM, and SLM: DT = (11+12+15)/3 = 12.7%.

According to our assumption all values of estimated time (geometric means) by logarithmic formulas were lower than the time study numerical data (lying between two means). Also, estimated time consumption by the developed models and real time were at a close ratio, on average it was more than 91% (

Knowing the factors affecting the production and costs of skidding has an important role in planning and organizing consumed budgeting, as well as, arranging expenditures to raise profitability (

On average, the net cost for extraction of 1-m
^{3}
of wood was 3.06, 5.69 and 6.81 €/m
^{3}
in TLM, LLM, and SLM. These results are consistent with former studies about cost of ground-based skidders system (such as

The range of costs depending on skidding distances was significantly different in SLM (

In time study, numerical data produces unsolvable contradictions and problems (

The most important part of the harvesting operation is the logging operation. In this context, from an economical point of view, we could suggest suitable harvesting methods in ground-based cable skidders system in a mixed broadleaved mountainous forest. Our finding implies that TLM can apply for trees, whose diameters are less than 40 cm, if a tree's diameter is bigger than 40 cm suitable alternative can be LLM absolutely in longer skidding distance but for trees with the biggest diameter in short skidding distances, suitable harvesting method can be SLM.