ASPECTS REGARDING THE ACCESSIBILITY OF MOUNTAINOUS STANDS SUBJECT TO WINDFALLS

Gheorghita Ionascu¹ and Norocel-Valeriu Nicolescu²

1 Dean, Correspondent Member of the Romanian Academy of Agricultural and Forest Sciences.
² "Transilvania" University, Faculty of Silviculture and Forest Engineering, Brasov, Romania.

Abstract

Different ecological factors, especially of climatic origin, sometimes have very damaging effects on forests. Huge amounts of timber are destroyed, while stands of various sizes are thrown down.

The effects of windfalls that occur on a small scale each year are small on forest sites, logging and wood-processing activities. On the contrary, the consequences are tremendous when the phenomenon is spread over large areas, covered by extremely affected stands. Unfortunately, this situation is quite common in Romania. Large-scale windthrows occurred in counties of Covasna, Harghita and Mures at the end of 1995.

In Romania there is good experience in coping with such situations, but the major difficulties we are now facing are related to the forest road network. The road network is characterized by a low density (less than 7 m/ha) and poor road quality.

The best technical solution to be put into practice in the Romanian mountainous stands subject to windfalls seems to be the use of cable cranes. They are driven either gravitationally or mechanically and allow the lateral collection of fallen trees and their transport from the felling area to the forest road or the stacking place.

Taking into account the complex peculiarities of wind-damaged stands, this paper points out the possibilities of using various Romanian and foreign types of cableways in such difficult conditions.

Keywords: Windfalls, harvesting, accessibility, skyline cable cranes.

Introduction

Different ecological factors, especially of climatic origin, often affect forest stands, causing major disturbance. Unfortunately, such situations are quite common in Romania, a country where windfalls and windbreaks occur on a large scale, especially in Norway spruce (Picea abies L.) monocultures.

At the end of 1995, large areas of forest land, especially in the Covasna, Harghita, and Mures counties (eastern Carpathians), comprising about 2.0 million m³, were thrown down. In such circumstances, the most urgent activity to be carried out in these areas consists of wood harvesting and cleaning of the damaged stands to avoid the risk of insect attacks and to prepare the ground for re-afforestation.

In the case of wood harvesting in areas of windfall stands the following aspects must be considered:

· the establishment of a harvesting and transport network to allow the extraction of large amounts of timber in a short time;

· the choice and utilization of efficient harvesting machinery and technologies;

· the utilization of specialized staff, ready to face difficult working conditions;

· the preparation of stacking places, where non-marketable timber can be stored in good conditions over long periods of time;

· the allotment of funds to purchase performance and ergonomically efficient harvesting machines and installations;

· the cleaning of felling areas and establishment of young plantations.

Skyline cable cranes and their use in harvesting operations

The optimum wood harvesting solution to be put into practice in the Romanian mountainous stands (located especially on long and steep slopes) subject to windfalls seems to be the use of skyline cable cranes. This choice is the result of a thorough analysis of harvesting conditions that has taken into consideration some aspects such as:

· the form and size of the felling area;

· the intensity of windfalls and the spread type of fallen trees;

· the lateral and along-the-slope extraction distances;

· the present and future technical and financial opportunities of private and state-owned harvesting enterprises;

· the density and distribution of the forest road network;

· the form and size of fallen trees.

The solution of using skyline cable cranes is due to the major advantages of their utilization such as:

· possible utilization on different terrain and under different climatic (especially hydrothermal) conditions;

· possibility of wood extraction from any part of the felling area (below the skyline and on both sides of it);

· possibility of de-tensioning of fallen trees in order to provide easy bucking and branch removal, without regard to safety requirements;

· possibility of use along slopes of various lengths and areas;

· easy mounting and dismounting when used on large logging areas with large timber volumes;

· prevention of various damages (to soil or standing trees) when transporting the fallen trees.

Unfortunately, the use of skyline cable cranes is limited because of various disadvantages in their use such as:

· the need of artificial supports (trees located at the end of the long extraction racks) when used in concentrated felling areas;

· the need of purchasing new machines and installations or re-activation of old and possibly unused ones;

· the need of new forest roads and maintenance of old roads in order to provide easy access and safety to extraction lorries.

In Romania the wide variety of skyline cable cranes is due especially to the various harvesting conditions (in terms of slope, terrain, length of extraction racks), as well as to the location of forest lands especially in the mountainous region (over 60 per cent). Some of the most efficient cable cranes used when harvesting windfallen timber are shown in Figure 1. These machines are used in different conditions such as:

· side collection of felled trees using remote-controlled winches (types TCD-1 and TCD-2);

· short-distance (less than 500 m) extraction, on slopes shorter than 500-600 m (models FPU-500 and FUMO-403);

· long-distance (up to 2 000 m) extraction (models FP-2 and FUC-MF 2005, the semi-permanent Maneciu type or the pendular cable crane).

The FPU-500 and FP-2 (gravitational) types can be installed either at the bottom or at the top of the felling area, where the majority of forest roads are located.

These installations can carry loads up to 2 t except for the FUC-MF 2005, which can carry loads up to 5 t (wholly or partially clear of the ground). The second option seems to be the best solution since preparation of the shallow ground (scarification) resulting from the use of such technique allows better conditions for young seedlings when planted following the harvesting operations.

The type of skyline cable crane, as well as the harvesting method, is chosen depending on the size of the felling area and the type of terrain. Usually, the gravitational types are the most used ones due to their low fuel consumption, as well as because in this case forest roads are located at the lower side of the felling area. The extraction racks are mostly installed along the highest slope of the terrain. The distance between two consecutive racks is about twice the possible distance of lateral tree collection (usually less than 100 m, but sometimes more when the working surface to cover and the volume to collect are larger). These distances can be even higher when trees are collected under the skyline by means of independent machinery (winches and tractors) or horses (Figure 2). Usually, the racks are perpendicular to the forest roads (a), with an inclination of 30-45 degrees (b) or, in the case of large and concentrated felling areas they can be of the "fan" type, the changing of their route being eased by the fact that the location of the lower station is constant.

On horizontal terrain, where gravitational cable cranes cannot be used, the universal types such as FUC-MF 2005 or FUMO-403 are the most desirable ones.

After cable crane harvesting, the timber is stacked on roadsides and is quickly transported to avoid both road blocking and creation of large depots of windfelled timber.

In such circumstances, the felled areas could be quickly cleared of trees and the sites prepared for artificial regeneration by planting.

Technical terms

Skyline cable cranes	= harvesting machines comprising two main rope drums; the load is supported by a block running on a tensioned fixed cable, the "skyline".
Terrain	= land used as working surface
Extraction racks	= routes created during different silvicultural operations for extracting felled timber.
Windfalls	= uprooting or breakage of trees caused by strong winds.

Figure 1. Technical characteristics of skyline cable cranes used in Romania

Figure 2. Skyline cable cranes

a. extraction racks perpendicular to the forest road; winch located at the lower limit of the felling area

b. extraction racks at 30°-45° inclination; winch located at the lower limit of the area (universal or gravitational types)

c. establishment and use of skyline cable cranes in a felling area

d. ways of load transport (wholly or partially away from the ground)