Integrated logging can be defined as combined harvesting of sawlogs and pulp/woodchips, of which the latter comprise approximately 90% of the trees felled in integrated logging operations. The following points summarise the effects of this practice.
In south-east Australia mature forests are complex biological systems. They are rich in plant species, ranging from mosses and ferns, many species of herbs and shrubs to mixtures of tree species, including a uniquely diverse assemblage of eucalypts. Similarly, animals range from tiny soil organisms through a myriad of insect and other invertebrate species to amphibians, reptiles, birds and mammals, the whole forming a network of interdependent organisms. The massive disturbance involved in integrated logging totally destroys this state of complex interaction, removing major elements and altering the very basis of soils and microclimates on which it depends. Years after integrated logging, trees may have regenerated, but habitat has not. The structure of herbs, understorey shrubs and trees of various species and ages ranging from seedlings to huge old giants with dead branches and hollows has been replaced by dense even-aged regrowth, often dominated by Silver-top Ash, which is the species best adapted to disturbance and fire. Little is known about the effects on invertebrates, but many observations on birds and mammals indicate a drastic reduction in the number of species present in these altered forests. Particularly affected are the tree-dwelling possums and gliders and the large owls that prey on them. The cycle of tree harvesting for woodchips can be as short as 15 years, and the estimated time for a eucalypt to develop nesting hollows is about 150 years. Some habitat trees are left in logged areas but they are too few, isolated and vulnerable when stripped of their surrounding buffer.
The practice of integrated logging produces a massive amount of soil disturbance. When combined with post-logging fire the soil surface is exposed to a degree that makes large scale sheet and gully erosion inevitable. The removal of the forest canopy allows high intensity rain to bombard the exposed soil and cause run-off loaded with silt.
Snig tracks and roading all contribute to the disturbance. Streamlines in and below logged areas have shown increased turbidity. Beds for streams and estuarine lakes in catchments with integrated logging are filling with sediment at a rate far exceeding that where the forests have remained relatively undisturbed.
Integrated logging operations remove the litter from which recycling of nutrients by fungi, worms, insects and the like normally proceeds. Regrowth forest has consistently shown a decrease in vigour compared to the forest it replaces, implying a loss of fertility.
The hydrology of forest ecosystems is profoundly altered by integrated logging. The removal of vegetative cover and litter lowers infiltration, thereby increasing surface run-off. This is further increased by heavy machinery compacting the soil. Baring the soil surface causes evaporative losses in the upper layer, which forms a dry crust resistant to wetting. Catchment studies have shown that immediately after logging, discharge increases. At 4 years post logging, dense even-aged regrowth eucalypts use far more water than mature forest and discharge is reduced for many years. Given the dependence of coastal communities on hinterland catchments for water, this aspect of integrated logging has significant implications for the maintenance of water supplies.
Aesthetic, wilderness and recreational value.
The aesthetic impact of integrated logging immediately following harvesting is devastating and for many years afterwards the monotony of even-aged regrowth and lack of diversity detract from the enjoyment of the forest by recreational users. The effect on wilderness values is self-evident.
By Dane Wimbush