The Bracke concept

Botanical scarification plays a key role in improving the conditions for growth and the chances of survival of a seed or plant. The problems encountered when establishing a new forest are the same, no matter the global location. Just as in agriculture, the greatest risk of harm comes from vermin and competing vegetation in fertile soil. This is the main advantage of scarification: it protects the seed or plant during the start of its life, when it is most exposed to attack by vermin and competing vegetation. In the northern regions of the world, however, improved growth is the more important aspect, as attacks by vermin are not as severe. Naturally, the positive effects of scarification are complex, and it is difficult to rank and compare them. The cumulative advantages of increased survival rates and improved growth are, however, unequivocal. As such, scarification gives the seed or plant a helping hand.

At northern latitudes, the growing season is short, with trees generally growing from May to September. The temperature is seldom high. Proper scarification exposes plants to higher air and ground temperatures, lets in more sunlight, provides more nutrients, and improves the water balance of the soil. All these advantages provide increased growth during the plant’s first year, corresponding to that of plants several degrees further south. Due to the temperature difference, the importance of growth increases as one moves north.

The optimum scarification for planting is known as inverted humus. This provides the components that give plants the greatest chance of survival and the best growth potential.

Increased air and ground temperatures are attained because proper scarification creates a raised planting bed. Cold air is heavier than warm air and consequently the difference in temperature between ground level and a couple of decimeters above ground often amounts to a couple of degrees during the coldest part of the day. The fact that sunlight can more easily reach a raised and cleared surface also provides a higher temperature. The lack of vegetation allows heat loss during the night, providing a lower temperature in scarified areas on clear nights. The extra sunlight provides not only an increased temperature, but even more energy for photosynthesis. Scarification increases nutrients because the humus layer is compressed and imbedded in the mineral soil. The nutrients in the humus and mineral soil must compost if they are to be made available to the plants, and an important factor in rapid composting is warmth. This determines the rate of decay and therefore nutrient availability.

The oxygen and water balances of the soil are also important aspects to consider when reducing the risk of the plant dying young and to optimize growth. A soil with well-balanced moisture content never feels wet or damp to the touch. Practical experience and extensive trials show that a considerably larger number of plants that die do so by drowning rather than drought. An optimum balance between water and oxygen in the soil means reducing the water content for the greater part of the growing season. This is done by scarification, which creates a higher planting bed than if the plant were planted at ground level. In this way, the soil is drained of water, thereby eliminating the risk of the plant drowning. Draining the soil by scarification also creates a flow of rainwater that ensures the soil is oxygenated, allowing the plant’s root system to develop well. The right combination of oxygen and water also helps increase the rate of composting. Composting is slow, for example, in marshlands where the water content is high and on dry soil where the water content is low.

In 1987, Bracke Forecare presented the results of a trial begun twelve years previously by the company SCA Skog AB. The trial, located in an area of poor soil, highlighted the differences between planting in mineral soil patches and inverted humus mounds. While the percentage of plants that survived did not differ between the two, there was a difference in that all plants in the inverted humus were standing upright. About a third of the plants in the mineral patches were leaning or prone. After twelve growing seasons, the plants in the inverted humus had rootage about 35 times that of the plants in the soil patches, and trunk volumes of about five times the size.

Mattson & Bergsten (2003) showed that scarification in areas of low quality soil increased the growth in volume of 18-year-old Lodgepole pines by 200-500 percent compared to planting without scarification. Disc trenching increased growth by 150 percent. In average quality soil, growth increased by 100 percent on mounded and trenched sites compared to unprepared sites.