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The frequent lack of rain in spring and summer associated with climate change, along with longer periods of heat, affect German and European forest stocks. Presently, the risks for planting tree seedlings are heightened by frequent soil water shortage and temperature increases. Drought-related failures after planting compromise the efficiency, predictability, and economic viability of forestry.

Current planting methods heavily rely on rainfall distribution and extended periods of extremely high daytime temperatures in the year following planting, especially in locations with low soil water retention capacity. It is inevitable that this problem will worsen with the expected long-term climate change.

Scientists from the Department of Urban Plant Ecophysiology at Humboldt University in Berlin, in collaboration with WaldWieseHolz GmbH (WWH) and the State Competence Center for Forestry in Eberswalde, conducted an FNR project under practical conditions at the end of 2021. The project focused on developing an innovative cultivation method for oaks to improve root development through compostable root sleeves. The project was successfully completed.

The key innovation involved cultivating trees in tubular root sleeves (RWH) until they were ready for planting, and then transplanting them into the ground with robust roots protected and nourished by the RWH. The RWH is a biodegradable planting tube about 30cm long and 5cm thick, containing a fertilized water-retaining substrate. It was found that Sphagnum biomass produced in paludiculture is particularly suitable as a water-retaining substrate in the RWH. Sphagnum Biomass (SBM) is produced as a peat substitute for garden soils in several European countries in CO2-neutral conditions on rewetted peatlands.

The results showed that using a biodegradable tubular root sleeve (RWH) in forestry can increase the success of establishment, promote the development of a deep-rooted system, and prevent or alleviate water stress and planting shock after tree planting. This offers a significant solution potential for problems in forestry.

At the end of the project, Truplast Sonneberg GmbH & Co. KG was brought in as a partner for the production of biodegradable planting tubes.

Truplast has been a specialist in the production of stable suction hoses for decades. In recent years, the company has been researching the properties and processing of various biobased and biodegradable materials to offer tailored solutions for use in agriculture, forestry, and horticulture.

Truplast applied this knowledge to the RWH and acquired the protective rights for the patents submitted by WWH and HU. The planting tube has now been brought to series production. Truplast is thus able to offer a solution for the dilemma of establishing stands in areas damaged by forests, especially in establishing on drought-prone sites, in collaboration with selected forestry nurseries and with further support from HU Berlin.

Seedlings of various oak species (sessile oak, pedunculate oak, red oak), and some other species with large seeds (e.g., sweet chestnut or black walnut), produced in tubular root sleeves (RWH) consisting of a water-resistant, biodegradable planting tube and Sphagnum biomass from paludiculture as a water-retaining substrate, are suitable for forestry in drought-prone locations during the growing season. The roots can reach deep soil horizons already in the planting year.

A significant portion of tree species suitable for stand establishment under climate warming conditions, including species from the genera Abies, Pinus, Pseudotsuga, Tilia, and Carpinus, will soon be prepared and tested for planting using RWH, using examples such as fir, Douglas fir, and pine.

The success of planting depends crucially on the root absorption function regenerating through growth in depth and the formation of new lateral roots during the first growing season after planting.  To secure the water balance, the significant increase in water consumption by the shoot until summer must be compensated by leaching from the soil.

The survival of planted trees is highly dependent on rainfall in spring and summer because root expansion into the depth and the formation of new lateral roots require a moist soil and only begin after the rise in soil temperature in spring. Prolonged dry periods in conjunction with high daytime temperatures, which are becoming more frequent due to climate change, not only lead to forest damage but also significantly hinder the reforestation of areas damaged by forests.