A recent study published in Forest Systems journal discusses the interest of innovative planting techniques (soil conditioners and mulches) to improve the early performance of forestation in mountain conditions. The authors conducted a field experiment in upper montane conditions (1,400 m) in the southern Pyrenees (NE Spain), planted with mountain ash (Fraxinus excelsior L.).
Some of the main technical challenges faced by forestation managers in these conditions are related to water and nutrient deficits resulting from the low soil water and nutrient storage capacity (high stoniness, coarse textures, steep slopes) and to the competition by extant vegetation. The generally poor accessibility of these sites poses further difficulties to the application of tending operations. Soil conditioners and mulches are planting techniques applied at the time of planting that can help young seedlings withstanding the post-planting stress induced by water and nutrients shortage and competing vegetation, respectively.
This work assessed the effectiveness for improving early seedling performance of the individual and combined application of (i) various doses of an innovative soil conditioner including polyacrylamide-free super-absorbent polymers, fertilizers, root precursors and humic acids; and (ii) innovative mulches based on renewable-biodegradable or recycled raw materials. The assessment was carried out in comparison with reference (commercial) soil conditioners and mulches.
The results after two growing seasons showed a positive effect of the application of soil conditioners in tree diameter (+90%) and height (+70%) growth, tree water status and tree nutrient status. The most cost-effective dose of application was 40 g seedling-1, which led to results superior to 20 g seedling-1 dose, but not different to 80 g seedling-1 dose. The new soil conditioner resulted in outcomes superior (diameter growth, tree nutrient status) or similar (rest of variables) than the commercial formulation. This positive performance of the new soil conditioner is beyond the prevalent observations in most previous works, which according to the authors “emphasizes the importance of a correct application (well mixed with the soil of the planting pit, in coarse-textured soil, with a sufficient and precise dosage) of a high quality soil conditioner”.
The effect of mulching was, however, weak, and limited to small gains in height growth. This result contrasts with most references using this planting technique. However, Jaime Coello, main author of this study, states that “the results are in line with previous works where small mulches are used (40×40 cm in this study) and where the competition by extant vegetation is poor during the first growing seasons”.
The authors conclude that “a correct choice and application of soil conditioner can improve the early success of mountain forestation in conditions limited by soils with poor water and nutrients storage capacity”, which “opens the door to more widespread use of this type of product”.
This paper is published in Forest Systems:
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