Effects of Thinning Intensity on Forest Floor and Soil Biochemical Properties in an Aleppo Pine Plantation after 13 Years: Quantity but Also Quality Matters

Abstract

In order to quantify the impacts of silvicultural treatments in semiarid forests, it is necessary to know how they affect key aboveground processes and also properties characterizing the forest floor and mineral soil compartments. The general objective of this work is to study the mid-term effects of thinning intensity on forest floor and soil properties after 13 years following the intervention. The experimental design consisted of a randomized block design with four thinning treatments (3 thinning intensity plots plus a control or unmanaged plot) and three blocks or replicates. Several determinations, such as total organic carbon, dissolved organic carbon, or basal respiration, were performed for characterizing forest floor and mineral soil by considering three random sampling points per experimental plot. Thirteen years after thinning, total organic content, the different organic carbon fractions studied, and basal respiration were higher in the forest floor of the unmanaged plot. These results, however, were contrasted to those obtained for the mineral soil, where significant differences between the treatments were only observed in basal respiration and C/N ratio, while the different organic carbon fractions were not affected by thinning intensity. Our results suggest better soil quality where biological activity is enhanced as a consequence of improved environmental conditions and also litterfall input. The latter is especially important in forests with tree leaves of low biodegradability, where new understorey species promoted by thinning can provide higher nutrient availability for the remaining trees and, therefore, better forest resilience.

Seasonal Variation and Soil Texture-Related Thinning Effects on Soil Microbial and Enzymatic Properties in a Semi-Arid Pine Forest

“…However, as SOC and WSOC are dependent on many factors, unpredictable results are usually found in different studies. In fact, mineral soils showed less variation in organic C than forest soils, which in most cases was not significant and dependent mainly on species composition, soil taxonomic order and time since thinning [26,33,80]. Our results were mixed, as no significant difference was found under clayey soils (Blocks I and II), but a positive significant effect was found under sandier soils (Block III).…”

“…Also, a larger canopy (i.e., broadleaved and mixed forests) correlates with a high input of organic matter to the forest floor, but coniferous forests produced the most recalcitrant litter of low quality (i.e., in terms of organic matter supply) [26]. The decomposition of organic matter in these latter situations (including Aleppo pine) is greatly influenced by abiotic factors, such as solar radiation or precipitation, conditioned by the intensity of thinning [33]. It was observed that the clayey soils (Blocks I and II) have higher SOC and WSOC levels than Block III, which is attributed to a higher organic matter storage capacity due to the different texture (i.e., the following correlation was found: Clay (%) = 5.43 SOC (%) + 5.24, R 2 = 0.93).…”

“…Thinning also affects soil labile carbon pools, and also controversial results have been obtained [24]. Different studies have found that thinning increased labile organic carbon [32], decreased it [33], or produced no effect [34]. Chen et al [24] also found different results depending on the fraction of labile organic carbon in the soil examined.…”

Enhancing Forest Sustainability: A Comprehensive Exploration of Thinning Practices and their Effects on Soil Chemical and Biochemical Properties

“…Molina et al studied the middle-time influence of thinning intensity on forest floor and soil properties 13 years after thinning, in a Pinus Aleppo plantation [46]. The survey was conducted on plots managed under 3 thinning intensities: high thinning intensity (16% of forest cover, 178 trees ha−1), moderate thinning intensity (46% of forest cover, 478 trees ha−1), and low thinning intensity (64% of forest cover, 689 trees ha−1).…”

Effects of Thinning Intensity on Litterfall Production, Soil Chemical Properties, and Fine Root Distribution in Pinus koraiensis Plantation in Republic of Korea

“…The thinning-induced increase in the amount of litter is generally followed by changes in soil physicochemical properties and nutrient cycling [15,16]. Thinning allows more sunlight to penetrate the canopy and reach the forest floor, increasing the amount of organic materials, which has a substantial impact on soil physicochemical qualities [17]. As a short-term effect of thinning, a reduction in tree density decreases litterfall production and carbon content in the forest floor [18], and the extent may vary depending on soil depth [19].…”