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In the world game — football (or soccer) — an own goal is when a player accidentally scores against their team. But own goals are not confined to the football pitch.

Evidence-free policy and management threaten to kick a slew of own goals, via demands to intensively thin native forests. Thinning is where more than half of a forest’s trees are removed in some cases, leaving fewer, more widely spaced stems in what then often becomes a radically altered forest.

Thinning is done by heavy machinery, with the timber typically used for firewood, woodchips or making paper. Because thinning demands such machinery, an extensive, expensive road network is needed. This means it costs money to thin forests, and the government bodies responsible for forest management make losses.

Recent popular books and commentaries have called for the widespread thinning of national parks and state forests. Forestry industry lobby groups also routinely call for forest thinning, especially after wildfires such as the Black Summer of 2019-20.

The logic of such calls is that thinning reduces the risk of wildfires. Yet empirical evidence shows it either has no effect on the severity of wildfires or worsens them in some cases. One study found that thinning operations significantly increased the fuel hazard by adding 24 tonnes per hectare of fuel to the forest floor. This can increase the severity of wildfires, not only endangering the integrity of the forest itself but also putting nearby communities at increased fire risk.

Thinned forests also allow more sunlight through sparser forest canopy, drying out fuel and permitting more wind to blow across it, thereby driving the more rapid spread of a potential fire. Even the government’s forestry guidelines warn of the increased fire dangers posed by thinning.

Further, removing large numbers of trees from forests generates significant amounts of greenhouse gas emissions (up to hundreds of tonnes per hectare), not only during logging operations but also because the trees are used for firewood, woodchips (for export) or for making paper or box liners. These forest products have a short time in the carbon life cycle before they go to landfill and generate yet further emissions.

It is critical to understand that trees are mostly carbon, so thinning forests and turning timber into short-life products liberates much of that carbon to the atmosphere. Importantly, there is a long delay of hundreds if not thousands of years between when carbon emissions from logging first occur and when that carbon is fixed by trees. The more carbon that stays in the atmosphere for longer, the more potent global heating is and the higher the temperatures that result.

Beyond this, thinning forests also impacts biodiversity. A vast number of animal and plant species are strongly dependent on the understorey and other plants that can be lost or badly damaged during industrial thinning operations. It is a critical part of the habitat that is home to critically endangered species such as Victoria’s faunal emblem, the leadbeater’s possum. These animals cannot exist when their habitat is removed. In fact, the more layers of forest that exist, the more species of birds and other animals that can coexist.

The best climate solution for forests is to leave them intact and not log or thin them at all. Forests need to recover from decades of overlogging and gross mismanagement by industry and logging agencies. They need less disturbance, not more. Indeed, other key work indicates that if we were to stop logging native forests in Australia, we would reach our 43% GHG reduction targets by 2030 (and have some margin left over to offset some of our other emissions like those from the transport sector).

The overwhelming conclusion of the body of scientific work done on fire risk, carbon emissions and biodiversity conservation is that thinning forests is a bad idea. Making sure we do not have widespread thinning in forests is a critical way to reduce the risks of yet more evidence-free forest policy management own goals.