Agustín Merino

Influence of edaphic factors and tree nutritive status on the productivity of Pinus radiata D. Don plantations in northwestern Spain

Relationships among soil parameters, tree nutrition and site index (SI) were examined in Pinus radiata plantations growing on soils developed from different parent materials (acid schist, granitic rocks and basic rocks) in a climatically homogeneous areas of NW Spain. Soil depth, in association with soil water balance and nutrient store, had the greatest influence on the productivity of these plantations. Although foliar N and K were sufficient in every stand studied, widespread deficiencies of P, Mg and, to a lesser extent, Ca were diagnosed. Foliar concentrations of Ca and Mg were positively correlated with soil nutrient concentrations. The main factors affecting site quality were identified with principal component analysis. The SI was positively correlated with foliar P concentrations, soil depth and pH, and negatively correlated with soil total N. Approximately 60% of the observed SI variation was accounted for by these soil properties. The results suggest the importance of site selection and fertilizer treatments in reforestation programmes.

Soil erosion under different harvesting managements in steep forestlands from northern Spain

In spite of the high risk of erosion, highly mechanized operations, in which humus layer removal and down-slope ploughing are practised, are often employed to prepare steep forestlands for planting. The purpose of this study was to evaluate the effect on soil loss of three post-harvesting management systems usually used in a mountainous region of northern Spain. The techniques evaluated were (a) conventional stem-only harvesting, (b) whole-tree harvesting and humus layer removal and (c) whole-tree harvesting and humus layer removal followed by down-slope deep ploughing. Soil erosion was measured in a total of 39 recently clear-felled Pinus radiata plantations over the period between the stand harvesting and establishment of understorey vegetation. They were located on slopes with gradients of between 40 and 50 per cent. For all treatments the associated runoff–rainfall ratios were high, indicating inherent low permeability of the soil. Intense site preparation resulted in considerable decreases in soil organic matter and increases in bulk density, which decreased the hydraulic conductivity and subsequently produced higher runoff. These deteriorations of soil properties delayed the establishment of pioneer vegetation thus extending the period of high erosion. In the ploughed soils, the higher soil erodibility and the removal of slash and vegetation cover resulted in a four-fold increase of soil losses when compared with no mechanical site preparation. The results indicate that, in order to maintain the soil productivity, and for conservation purposes, harvesting management should minimize the soil disturbances and maintain the slash and vegetation cover. Copyright

Soil properties in a hilly area following different harvesting management practices

Abstract In this work, the short-term effects of different forestry practices on soil properties were evaluated. A total of 62 pine (Pinus radiata) plantations from Northern Spain, located in sites with similar climatic conditions on slopes exceeding 35% were studied. In all cases, the soils had similar initial properties and were developed over argillite. The plots studied included mature forest plantations and harvested plots with different management practices for harvesting (stem only or whole tree) and seed-bed preparation (logging slash left on the ground, removal of residues, mixing of horizons or accumulation of soil material from road construction). The study was conducted 5–6 months following harvesting and site preparation and after a period of intense precipitation. In conventionally managed and harvested soils, where the humus layer and abundant logging residues remained on-site, minimal changes in physical and chemical properties were detected. Significant modifications in physical properties and in fertility were evident after whole tree harvesting and intense seed-bed preparation. These practices resulted in increases in bulk density (17%), as well as in decreases in the content of organic matter (65%), total nitrogen (65%), sulphur (39%) and exchangeable calcium (80%) in the upper layer. Decreases in organic matter led to a higher potential for soil erosion. Depletions in effective CEC and exchangeable Mg and K were also found although they were not significant. These alterations were mainly attributed to the mixing of soil layers and soil loss by erosion. Accelerated leaching of nutrient ions may also have occurred because climatic conditions (high moisture and temperature) may favor mineralization, also because of the absence of vegetation, which may have acted as a sink for nutrients. The results of this study showed that, under conditions of the plots studied (high slopes, abundant precipitation and acid, fine textured soils) intense harvesting management affects some soil properties which are important for early growth of later rotations and for conservation of soil and waters.

Biomasa arbórea y acumulación de nutrientes en plantaciones de Pinus radiata D. Don en Galicia

Above ground tree biomass and accumulation of nutrients in Pinus radiata plantations from northern Spain In this work the amount of nutrients accumulated in the above ground biomass of nine representative Pinus radiata plantations from NW Spain were studied. From the data of 54 trees, models to estimate the mass of the different tree fractions were developed. The logging residues accumulate the most part of N (60%), as well as substantial amounts of P, K, Ca and Mg (36 to 47%). The accumulations in tree biomass of P, Mg, K and, in some cases, Ca are considerably higher than the available amounts in the soil. The data confirm that the frequent deficiencies of these elements in this type of forest plantations are due to the low nutrient storage in the soils. They also suggest that the nutritional stability of these systems is dependent on the nutrient supply by the decomposition of logging residues. These results, along with those of previous studies, show the need to carry out an appropriate management of logging residues, as well as fertilisation programmes to compensate the nutrient extractions by the clear cutting, especially if whole-tree harvesting is carried out.

Variations in soil carbon sequestration and their determinants along a precipitation gradient in seasonally dry tropical forest ecosystems

The effect of precipitation regime on the C cycle of tropical forests is poorly understood, despite the existence of models that suggest a drier climate may substantially alter the source-sink function of these ecosystems. Along a precipitation regime gradient containing 12 mature seasonally dry tropical forests growing under otherwise similar conditions (similar annual temperature, rainfall seasonality, and geological substrate), we analyzed the influence of variation in annual precipitation (1240 to 642 mm) and duration of seasonal drought on soil C. We investigated litterfall, decomposition in the forest floor, and C storage in the mineral soil, and analyzed the dependence of these processes and pools on precipitation. Litterfall decreased slightly - about 10% - from stands with 1240 mm yr(-1) to those with 642 mm yr(-1), while the decomposition decreased by 56%. Reduced precipitation strongly affected C storage and basal respiration in the mineral soil. Higher soil C storage at the drier sites was also related to the higher chemical recalcitrance of litter (fine roots and forest floor) and the presence of charcoal across sites, suggesting an important indirect influence of climate on C sequestration. Basal respiration was controlled by the amount of recalcitrant organic matter in the mineral soil. We conclude that in these forest ecosystems, the long-term consequences of decreased precipitation would be an increase in organic layer and mineral soil C storage, mainly due to lower decomposition and higher chemical recalcitrance of organic matter, resulting from changes in litter composition and, likely also, wildfire patterns. This could turn these seasonally dry tropical forests into significant soil C sinks under the predicted longer drought periods if primary productivity is maintained.

Carbon balance for different management practices for fast growing tree species planted on former pastureland in southern Europe: a case study using the CO2Fix model

Although it is known that forestry mitigates carbon emissions to some degree, there is still a need to investigate the extent to which changes in forest management regimes affect the carbon cycle. In a climate-change scenario, forest management schemes must be optimized to maximize product supply and minimize environmental impacts. It is difficult to predict the mitigating effects of different silvicultural regimes because of differences in the growth characteristics of each species, destination of products, and industrial efficiencies. The objective of the present study was to use a modeling approach to evaluate the effects of different management regimes for fast growing species in southern temperate Europe in relation to mitigating climate change. A comprehensive study was carried out considering the C sink effect in biomass, soil and wood products, the substitutive effect of bioenergy, and particular conditions of the forest industry in southern Europe. The mechanistic CO2Fix model was parameterized for three species used in fast growing plantations in southern Europe: Eucalyptus globulus, Eucalyptus nitens, and Pinus radiata. Data from 120 plots covering the complete age range observed for each species were used to calculate changes in C stocks in aboveground biomass and organic and mineral soil and to validate the parameterized model for these conditions. Additional information about the efficiency of forest industry processes in the region was also considered. A strong bias in soil organic carbon estimation was observed and attributed to overestimations in the decomposition rates of soil compartments. Slight bias was also observed in the carbon biomass estimation when forest-specific yield models were used to simulate afforestation over former pastureland. As regards the model sensitivity, the Yasso model was strongly robust to turnover of leaves, roots, and branches. The chip wood production alternative yielded higher carbon stock in biomass and products, as well as in bioenergy substitution effect, than the sawn wood production alternative. Nevertheless, the sawn wood alternative was the most effective as regards the C stock in the soil. Site index had an important effect for all species, alternatives, and compartments, and mitigating effects increased with site index. Harvesting of clearcutting and thinning slash for bioenergy use led to a slight decrease in the soil carbon equilibrium but significantly increased the mitigation effect through bioenergy use.

Carbon sequestration potential and physicochemical properties differ between wildfire charcoals and slow-pyrolysis biochars

Pyrogenic carbon (PyC), produced naturally (wildfire charcoal) and anthropogenically (biochar), is extensively studied due to its importance in several disciplines, including global climate dynamics, agronomy and paleosciences. Charcoal and biochar are commonly used as analogues for each other to infer respective carbon sequestration potentials, production conditions, and environmental roles and fates. The direct comparability of corresponding natural and anthropogenic PyC, however, has never been tested. Here we compared key physicochemical properties (elemental composition, δ13C and PAHs signatures, chemical recalcitrance, density and porosity) and carbon sequestration potentials of PyC materials formed from two identical feedstocks (pine forest floor and wood) under wildfire charring- and slow-pyrolysis conditions. Wildfire charcoals were formed under higher maximum temperatures and oxygen availabilities, but much shorter heating durations than slow-pyrolysis biochars, resulting in differing physicochemical properties. These differences are particularly relevant regarding their respective roles as carbon sinks, as even the wildfire charcoals formed at the highest temperatures had lower carbon sequestration potentials than most slow-pyrolysis biochars. Our results challenge the common notion that natural charcoal and biochar are well suited as proxies for each other, and suggest that biochar’s environmental residence time may be underestimated when based on natural charcoal as a proxy, and vice versa.

Effects of Ash Applications on Soil Status, Nutrition, and Growth of Pinus radiata D. Don Plantations

The aim of this study was to evaluate the effectiveness of multiple applications of biomass ash to acid soils. The study was carried out in two stands of Pinus radiata D. Don, aged 13 and 15 years, in the province of Lugo (northwest Spain). The soils in the stands were developed on lutites and migmatites. Experimental plots (each 1,225 m2) were established, and the experimental treatments were as follows: control (untreated), ash (addition of 4.5 Mg dry matter ha−1 year−1 in 2003, 2004, and 2005) and ash plus P (addition of ash plus phosphate fertilizer in 2003).

Respuesta inicial del aporte de cenizas de biomasa arbórea en el estado nutricional de una plantación joven de Pinus radiata D. Don

El objetivo del presente ensayo fue evaluar la respuesta del empleo de cenizas de corteza de madera como enmendante y fertilizante de una plantacion joven de Pinus radiata que se desarrolla sobre un suelo forestal acido. El trabajo consistio en un ensayo de campo, con aporte de dos dosis de cenizas en cobertera (5.000 kg ha-1 y 10.000 kg ha-1) y una dosis de fertilizante mineral NPK 8:24:16 (200 g en hoyo) en el momento del establecimiento de la plantacion. Durante 28 meses se evaluo la respuesta de la fraccion solida del suelo y de la composicion quimica de las aciculas. El aporte de cenizas derivo en aumentos temporales del pH y de la concentracion de Ca, Mg, P y K disponible en el suelo. Esta mejora de las propiedades quimicas del suelo se tradujo en incrementos temporales en la concentracion de Ca y, en menor medida, de Mg en las aciculas. Como posible diagnostico, el analisis de vectores de los contenidos y concentraciones de nutrientes foliares mostro que estos dos elementos limitaban el crecimiento de la especie.

Response of some soils of Galicia (NW Spain) to H2SO4 acidification

This paper presents the results of an acidification experiment, consisting of seven consecutive equilibrations of repesentative soils of Galicia with a H2SO4 solution (pH 3). Different responses to soil acidification, such as SO4 retention and cation release, were evaluated. In soils derived from gabbro and amphibolite, SO4 retention and Al release were the principal acid neutralization mechanisms, whereas in soils derived from granite, schist, shale and sandstone Al release was the main process. The SO4 retention was significantly correlated with Al and Fe extracted with dihionite-citrate-bicarbonate and crystalline Fe. The released base cations came mainly from exchange sites, though sometimes also from other sources, probably by mineral weathering. The major sources of Al in these soils were metalorganic complexes and weatherable minerals. Solutions with pHs close to 4 are in equilibrium with gibbsite, kaolinite, jurbanite and alunite; at lower pH values, with jurbanite and alunite.