Mid-Term Effects of Forest Thinning on N Mineralization in a Semi-Arid Aleppo Pine Forest

Abstract

In order to assess the sustainability of silvicultural treatments in semiarid forests, it is necessary to know how they affect the nutrient dynamics in the forest. The objective of this paper is to study the effects of silvicultural treatments on the net N mineralization and the available mineral N content in the soil after 13 years following forest clearings. The treatments were carried out following a randomized block design, with four treatments and two blocks. The distance between the two blocks was less than 3 km; they were located in Chelva (CH) and Tuéjar (TU) in Valencia, Spain. Within each block, four experimental clearing treatments were carried out in 1998: T0 control; and T60, T75 and T100 where 60%, 75% and 100 of basal area was eliminated, respectively. Nitrogen dynamics were measured using the resin tube technique, with disturbed samples due to the high stoniness of the plots. Thirteen years after the experimental clearings, T100, T75 and T60 treatments showed a twofold increase in the net mineralization and nitrification rates with respect to T0 in both blocks (TU and CH). Within the plots, the highest mineralization was found in sites with no plant cover followed by those covered by undergrowth. These results can be explained in terms of the different litterfall qualities, which in turn are the result of the proportion of material originating from Pinus halepensis Mill. vs. more decomposable undergrowth residues.

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

“…It is important to remark that these general results had a high number of sources of variability, and they also considered different data sources. When comparing our results to other studies with similarities in terms of thinning (intensity and time elapsed), forest structure and composition, and environmental conditions, TOC for the 0-10 cm soil depth interval was not significantly enhanced 13 years after thinning (light and heavy thinning interventions) in an Aleppo pine plantation very similar to ours [29]. In addition, other thinning experiments, conducted in the Mediterranean area for Pinus pinaster Ait.…”

“…We obtained mean values of 7094, 4815, and 2650 kg ha −1 (1.71, 1.10, and 0.65%) for the SOC fraction for the 0-10, 10-20, and 20-30 cm soil depth intervals, while a mean value of 35,160 kg ha −1 (4.7%) was found when considering total organic carbon (TOC) for the 0-10 cm soil depth interval. These values are in the range of other studies on Pinus species growing under Mediterranean conditions; for instance, Bautista et al [29] reported a range of 1.1-5.4% for TOC in a Pinus halepensis plantation with different thinning treatments, while a mean value of 4.84% for SOC was reported in a plot with an intermediate forest cover dominated by Pinus pinaster [33]. Thirteen years after thinning, all the organic carbon fractions analyzed decreased with thinning intensity, but significant differences were not observed between the experimental plots.…”

“…In this sense, it is important to highlight the role of thinning may have on improving soil quality and, therefore, on nutrient availability for the remaining trees. Lower C/N ratios for the treated plots in both forest floor and mineral soil, especially when comparing T10 and T100, may indicate a positive effect of thinning in microclimatic conditions and microbial substrate, therefore increasing N mineralization rate [29]. Better conditions, but also better quality (bio-degradability) C, in the leaves of the understorey species, as compared to P. halepensis needles [32], are expected to promote higher microbial activity, thus reducing the C/N ratio.…”

“…Soil moisture was obtained from the mean values for each thinning intensity treatment previously published [23]. MBC was estimated based on the relationship between MBC and basal soil respiration (MBC = 5.605BR 0.6686 ; R 2 = 0.6), as obtained in Aleppo pine experimental plots with very similar forest structure and age to those analyzed in this work [28] (see [29] for more information about this site). Finally, the phosphatase and β-glucosidase activities for our treatments were also obtained from those experimental plots ( [28], unpublished data).…”

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

“…With regard to the latter, forest soils are important carbon (C) stores in different pools; 45% of forest C is found as soil organic matter, and 11% as dead wood and litter [23]. It has been described that forest thinning can affect nutrient mineralisation rates in the forest floor and mineral soil, soil organic carbon (SOC) content, and also labile SOC fractions [24,25]. Many studies have focused on the effects of thinning on SOC [26], but the results are still controversial.…”