What can assist pine and beech seedlings in growing successfully after they are planted?
The rising frequency of dry spells combined with extreme air temperatures is making it challenging to establish new forest plantings. As a result, foresters are seeking strategies to prevent seedlings from drying out during the handling and planting processes. They are also exploring ways to extend the availability of water for these seedlings after planting.
Photo: Regrowth of small pines on the border between a clearing and mature forest. Author: Jan Řezáč
One effective method for retaining water during periods of higher rainfall, which can then be utilized by seedlings during droughts, is the application of hydrogels. These substances are made from hydrophilic polymers and can absorb a significant amount of water—up to 400 to 1500 times their dry weight—while also binding nutrients.
Due to their unique properties, hydrogels can serve as “artificial humus,” making them valuable soil conditioners and fertilizers. They are particularly beneficial when applied to eroded soils or used in land reclamation and forest nurseries.
Hydrogels have several positive effects on plants, including improved survival during stress periods, protection against dehydration, and increased water absorption. In regions that experience dry spells, hydrogels are an effective tool for prolonging water availability, thus extending the growing season for planting seedlings.
Scientists at the Opočno Research Station, VÚLHM, v. v. i., studied the effects of hydroabsorbents on pine and beech seedlings. Their findings were published in the article titled Indiferentní reakce sazenic borovice lesní a buku lesního ošetřených hydroabsorbenty (Indifferent response of Scots pine and European beech seedlings treated with super-absorbents), which appeared in the journal Reports of Forestry Research in March 2024. This research was conducted as part of a project funded by the LČR Grant Service, s. p.
Photo: Young beech seedlings planted in a hedge, protected against game. Author: Jan Řezáč
The scientists aimed to evaluate the impact of four hydroabsorbents applied during the planting of seedlings in clearings, specifically focusing on the growth of Scots pine and European beech. They anticipated that the application of hydrogels would enhance the attractiveness and growth of the seedlings.
The reason for testing these particular tree species is that European beech is the most common deciduous tree used for melioration and strengthening in the Czech Republic. Scots pine, on the other hand, is a valuable coniferous species often planted in areas with lower rainfall, where significant losses can occur during extended dry periods following afforestation.
Based on the market analysis, the researchers selected four commercial hydrogel preparations for their experiments, which were supplemented by a control group that did not include any hydroabsorbent. They anticipated that testing multiple types of hydrogels would yield different effects.
To assess the impact of the tested preparations, the scientists established a total of 11 research areas. The bare-root planting material was sourced from operational nurseries. For Scots pine, they used either one-year-old or two-year-old seedlings, while for European beech, they employed 2 to 4-year-old seedlings.
Photo: Regrowth of small pines on the border between a clearing and mature forest. Author: Jan Řezáč
During the planting activities conducted in 2020 and 2021, significant emphasis was placed on ensuring the high quality of afforestation efforts and the use of appropriate preparations. Hydroabsorbents were strategically placed near the roots of the seedlings.
The assessed parameters for evaluating the success of the plantings included survival rates, height growth, and the increase in the thickness of the root collar. Additionally, the experiment included an economic analysis comparing the costs associated with implementing different variants of the planting approach.
In conclusion, the researchers summarized their findings as follows:
During experiments conducted under semi-operational conditions in 2020 and 2021, no positive effects were observed from the application of tested water-retaining preparations (hydroabsorbents) on seedling losses after planting or on the growth of Scots pine and European beech seedlings.
The choice of tree species can significantly influence the effectiveness of drought support measures. While adding hydrogel may benefit drought-sensitive species, it is not advantageous for more tolerant species. European beech and Scots pine are not classified as drought-sensitive species, although they can still be affected by extreme climatic conditions.
Photo: Successfully regrowing gap with European beech. Author: Jan Řezáč
The natural resilience of these tree species, combined with the specific climatic conditions in the regions studied, resulted in sufficient hydric properties of the soils in these habitats. Consequently, the influence of hydromeliorants was minimal. The interaction of factors such as the inherent characteristics of the soils, the weather patterns during the relevant years, and the traits of the tested trees did not yield a significant impact from the applied treatments.
Given the mixed results from this research, economic considerations become increasingly important. The use of hydroabsorbents is shown to be an unnecessary expense, leading to
An essential factor influencing the success of artificial regeneration is the quality of the planting material used. This includes both its morphological characteristics and its physiological condition, which depends not only on the growing conditions in the forest nursery but also on the proper handling of the seedlings prior to planting.
The research indicated no significant differences in the relatively high mortality rates of treated and control seedlings planted in clearings. This finding confirmed that adding water-retaining agents to the soil at the time of planting cannot be expected to resolve issues related to the quality of the planting material.
Paper Indiferentní reakce sazenic borovice lesní a buku lesního ošetřených hydroabsorbenty (Indifferent response of Scots pine and European beech seedlings treated with super-absorbents) can be downloaded here.
Authors of the paper: Jan Bartoš, Jan Leugner, Dušan Kacálek, Ondřej Špulák, Jana Hacurová, FGMRI (VÚLHM, v. v. i.), Research Station Opočno (Výzkumná stanice Opočno), e-mail: bartos@vulhmop.cz
Prepared in accordance with the original by Jan Řezáč, FGMRI (VÚLHM, v. v. i.), e-mail: rezac@vulhm.cz