Pinus Halepensis Mill Research Articles

The Pinus halepensis Mill. forests in the central-eastern European Mediterranean basin

The Pinus halepensis Mill. forest vegetation of the central-eastern European Mediterranean basin (France, Italy, Croatia, Albania, Greece) is described here. This study was carried out considering published and unpublished phytosociological data, with the organisation of a systematic classification (syntaxonomic scheme) of the order Pinetalia halepensis according to the principal floristic variations, at multiple spatial scales and according to the physiognomic–structural, floristic, ecological and biogeographical characteristics. Five alliances and 25 associations are recognised.

Variability of Pinus halepensis Mill. Essential Oils and Their Antioxidant Activities Depending on the Stage of Growth During Vegetative Cycle.

The impact of growth stages during vegetative cycle (B0 -B5 ) on chemical composition and antioxidant activities of Pinus halepensis Mill. needles essential oils was investigated for the first time. GC and GC/MS analyses pointed to a quantitative variability of components; terpene hydrocarbons derivatives, represented by α-pinene (8.5-12.9%), myrcene (17.5-21.6%), p-cymene (7.9-11.9%) and (Z)-β-caryophyllene (17.3-21.2%) as major components, decreased from 88.9% at B0 growth stage to 66.9% at B5 growth stage, whereas oxygenated derivatives, represented by caryophyllene oxide (5.4-12.6%) and terpinen-4-ol (0.4-3.3%) as major components, increased from 7% at B0 growth stage to 28.4% at B5 growth stage. Furthermore, our findings showed that essential oil of P.halepensis needles collected at B5 growth stage possess higher antioxidant activities by four different testing systems than those collected at B0 -B4 growth stages. This highlighted variability led to conclude that we should select essential oils to be investigated carefully depending on growth stage, in order to have the highest effectiveness of essential oil in terms of biological activities for human health purposes.

Additive or non-additive effect of mixing oak in pine stands on soil properties depends on the tree species in Mediterranean forests

This study investigated how oak abundance in pine stands (using relative Oak Basal Area %, OBA%) may modulate soil microbial functioning. Forests were composed of sclerophyllous species i.e. Quercus ilex mixed with Pinus halepensis Miller or of Q. pubescens mixed with P. sylvestris. We used a series of plots with OBA% ranging from 0 to 100% in the two types of stand (n=60) and both OLF and A-horizon compartments were analysed. Relations between OBA% and either soil chemical (C and N contents, quality of organic matter via solid-state NMR, pH, CaCO3) or microbial (enzyme activities, basal respiration, biomass and catabolic diversity via BIOLOG) characteristics were described. OBA% increase led to a decrease in the recalcitrant fraction of organic matter (OM) in OLF and promoted microbial growth. Catabolic profiles of microbial communities from A-horizon were significantly modulated in Q. ilex and P. halepensis stand by OBA% and alkyl C to carboxyl C ratio (characteristic of cutin from Q. ilex tissues) and in Q. pubescens and P. sylvestris stands, by OBA% and pH. In A-horizon under Q. ilex and P. halepensis stands, linear regressions were found between catabolic diversity, microbial biomass and OBA% suggesting an additive effect. Conversely, in A-horizon Q. pubescens and P. sylvestris stands, the relationship between OBA% and either cellulase activities, polysaccharides or ammonium contents, suggested a non-additive effect of Q. pubescens and P. sylvestris, enhancing mineralization of the OM labile fraction for plots characterized by an OBA% ranging from 40% to 60%. Mixing oak with pine thus favored microbial dynamics in both type of stands though OBA% print varied with tree species and consequently sustainable soil functioning depend strongly on the composition of mixed stands. Our study indeed revealed that, when evaluating the benefits of forest mixed stand on soil microbial functioning and OM turnover, the identity of tree species has to be considered.

Assessing vulnerability of two Mediterranean conifers to support genetic conservation management in the face of climate change

AbstractAimTo integrate two major components of vulnerability to climate change: adaptive capacity (approached by genetic groups) and exposure (approached by risk of habitat loss) illustrated with the maritime (Pinus pinaster Ait.) and Aleppo (Pinus halepensis Mill.) pines. To integrate such information in the selection of conservation strategies (ex situ vs. in situ) and to evaluate current European efforts in the conservation of forest genetic resources.LocationMediterranean Basin and European Atlantic coast.MethodsWith the objective of preserving the overall genetic diversity of our two target species, we individually assess each of their genetic groups. We fit a species distribution model and project it to current climate and 42 different future climatic predictions. We create future suitability maps to assess risk of habitat loss based on the number of future climate projections that predict suitability. According to this assessment on the risk of habitat loss, we propose suitable conservation strategies.ResultsWe found areas suitable for in situ conservation for most of the genetic groups, the exception being the central–eastern–southern Iberian genetic groups of maritime pine and the Moroccan genetic group of Aleppo pine which required ex situ conservation. In the current European conservation network, three genetic groups for maritime pine and two for Aleppo pine remain unrepresented, and the representation of the rest is unbalanced.Main conclusionsWe provide a tool to support conservation management of forest trees, an increasingly important task given the negative impact of climate change on forest ecosystems. We also provide a framework to increase the efficiency of the European conservation network: (i) exposure assessment should be considered as a requirement for a population to become a dynamic conservation unit (DCU); and (ii) as illustrated with our two target species, the selection of DCUs should represent all existing genetic groups.

Influence of raw material composition of Mediterranean pinewood on pellet quality

The lack of management and economic value of forest ecosystems in Mediterranean areas, mainly dominated by pines (Pinus halepensis Mill. and Pinus pinaster Ait.), together with a continuous growing of forests on marginal agricultural land have leaded to an increased forest fire risk and devaluation of natural resources in less favoured rural regions. The use of residual forest-based biomass as value added biofuels like pellets can reverse this situation. Nevertheless, there is an industrial need of knowledge of the influence of raw material composition on pellet manufacturing quality for the main Mediterranean softwood species. In this research influencing pellet quality variables such as contents of moisture, ash, fine particles, chlorine and sulphate, but also mechanical durability, bulk density and net calorific value have been analysed following EN standards. The obtained results demonstrate that it is possible to obtain high quality pellets from barked and debarked logs as well as from branches from P. halepensis and P. pinaster. This implies that the abundant forest biomass residues in the western Mediterranean region of Europe can be transformed into high added value solid biofuels, opening new opportunities for local industries.

Sap flow, leaf-level gas exchange and spectral responses to drought in Pinus sylvestris, Pinus pinea and Pinus halepensis

Abstract: In a climate change scenario, Mediterranean forest species such as pines may be endangered by rising temperatures and reduced precipitation, thus calling for studies on the transpiration and water balance in pines. In this paper, the response of young plants of Pinus sylvestris L., Pinus pinea L. and Pinus halepensis Mill. to different irrigation treatments has been studied. Significant differences were found in water potential, sap flow, leaf-level gas exchange and spectral variables. P. sylvestris had higher pre-dawn and midday water potentials, sap flow rates and leaf-level gas exchange rates compared to the other two species in well-watered conditions. Vapor pressure gradient correlated with stomatal conductance, net assimilation and transpiration, but the association between stomatal conductance and sap flow was weak. The environmental variables more strongly associated with sap flow were solar radiation and reference evapo-transpiration, especially in the well-watered plants, but those associations were weaker in the stressed plants. All three pine species showed the isohydric, drought-avoiding strategy common in the genus Pinus, maintaining relatively high water potentials in dry conditions. Nevertheless, P. halepensis showed a water-saving strategy, with a stomatal closure behavior under drought. Stomatal regulation was less strict in P. sylvestris, closer to a water-spending pattern, while P. pinea showed an intermediate behavior. Significant differences were recorded among species in spectral reflectance in the visible and infra-red regions. Photochemical Reflectance Index, Normalized Difference Vegetation Index and combinations of other ratios permitted the discrimination among the three pine species. These spectral variables showed association with sap flow rate, water potential and leaf-level gas exchange variables. Both cluster analysis and k-means classification discriminated Scots pine and Aleppo pine in two different groups. On the other hand, Stone pine showed differences in spectral behavior depending on the hydric status of the plants. Well-watered Stone pine plants had the same spectral behavior as Scots pine, while the plants subjected to drought stress were closer to Aleppo pine plants in spectral response. These findings may help to quantify the impacts of early and mid-summer water deficit on Mediterranean pines in future climate regimes.

Contrasting Effects of Fire Severity on the Regeneration of Pinus halepensis Mill. and Resprouter Species in Recently Thinned Thickets

Many studies have outlined the benefits for growth and reproduction resulting from thinning extremely crowded young forests regenerating after stand replacing wildfires (“thickets”). However, scarce information is available on how thinning may influence fire severity and vegetation regeneration in case a new fire occurs. We investigated the relationship between thinning and fire severity in P. halepensis thickets, and the effects on the establishment of pine seedlings and resprouting vigour in resprouter species the year after the fire. Our results show a positive relationship between forest basal area and fire severity, and thus reserved pines in thinned stands suffered less fire damage than those in un‐thinned sites (respectively, 2.02 ± 0.13 vs. 2.93 ± 0.15 in a scale from 0 to 4). Ultimately, differences in fire severity influenced post‐fire regeneration. Resprouting vigour varied depending on the species and the size of individuals but it was consistently higher in thinned stands. Concerning P. halepensis, the proportion of cones surviving the fire decreased with fire severity. However, this could not compensate the much lower pine density in thinned stands and thus the overall seed crop was higher in un‐thinned areas. Establishment of pine seedlings was negatively affected by the slope and positively driven by the number of cones and thus it was higher in un‐thinned than in thinned stands (respectively, 2581 ± 649 vs. 898 ± 325 seedlings∙ha-1). Thinning decreases fire intensity, and thus it may facilitate fire suppression tasks, but retaining a higher density of pines would be necessary to ensure P. halepensis regeneration after a new fire event.

Springtime ecosystem-scale monoterpene fluxes from Mediterranean pine forests across a precipitation gradient

We quantified springtime ecosystem-scale monoterpene fluxes from two similar Aleppo pine (Pinus halepensis Mill.) forests, located in Israel, that differed in the amount of received precipitation: Yatir in the arid south and Birya in the northern part of Israel (291 and 755mm annual average rainfall, respectively). In addition to the lower water availability, during our measurement campaign the Yatir site suffered from a heat wave with temperatures up to 35°C, which made the campaign-average net CO2 assimilation to occur in the morning (1μmolm−2s−1), with the rest of the daytime hours mainly dominated by net release of CO2. The milder conditions at Birya favored a higher net CO2 assimilation during all daytime hours (with average peaks higher than 10μmolm−2s−1). Despite these large differences in ambient conditions and CO2 net assimilation, daytime monoterpene emission capacities at both sites were comparable. While observed monoterpene fluxes were lower at Yatir than at Birya (hourly averages up to 0.4 and 1mgm−2h−1, respectively), the standardized hourly fluxes, after accounting for the differences in light, temperature and stand density between both sites, were comparable (0–1.3mgm−2h−1). The approach typically used by biogenic emission models overestimated monoterpene fluxes at Yatir when temperatures rose during the heat wave. This result, together with complementary leaf-level measurements showing that summertime monoterpene fluxes almost completely ceased at Yatir while being enhanced at Birya, highlight the interaction of water scarcity and high temperatures that drive monoterpene emissions from vegetation in such extreme climate zones and the need to further improve model performance.

Site factors as predictors for Pinus halepensis Mill. productivity in Spanish plantations

This work presents a discriminant model to predict Pinus halepensis forest productivity using parameters related to water availability (Annual Hydric Index, soil porosity and slope) and information about the N immobilization by soil microorganisms (microbial biomass N). Pinus halepensis is a circum-Mediterranean species that has been widely used for afforestation of poor and degraded soils in water-limited regions. Determining forest and stand productivity is very useful for forest managers as it supports decision making. The aim of this study was to develop a model to predict Pinus halepensis productivity using environmental parameters. A set of 57 soil, climatic and physiographic parameters were determined in 32 Pinus halepensis plots, which were categorized into three site index classes. Principal component analysis (PCA) was used to select the 14 environmental variables that accounted for the highest data variability. Discriminant models with three, four and five environmental variables as predictors were studied. The selected discriminant model included three parameters related to water availability (Annual Hydric Index, soil porosity and slope), which is the main driver of forest productivity in Mediterranean ecosystems, and one nutrient-related parameter known as microbial biomass N, by which microorganisms inform about N immobilization. The model correctly classified 62.5% of the plots. This model may be a very useful tool for supporting decision making in forestry practices aimed at sustainable stand management.

Increased fire frequency promotes stronger spatial genetic structure and natural selection at regional and local scales in Pinus halepensis Mill.

The recurrence of wildfires is predicted to increase due to global climate change, resulting in severe impacts on biodiversity and ecosystem functioning. Recurrent fires can drive plant adaptation and reduce genetic diversity; however, the underlying population genetic processes have not been studied in detail. In this study, the neutral and adaptive evolutionary effects of contrasting fire regimes were examined in the keystone tree species Pinus halepensis Mill. (Aleppo pine), a fire-adapted conifer. The genetic diversity, demographic history and spatial genetic structure were assessed at local (within-population) and regional scales for populations exposed to different crown fire frequencies. Eight natural P. halepensis stands were sampled in the east of the Iberian Peninsula, five of them in a region exposed to frequent crown fires (HiFi) and three of them in an adjacent region with a low frequency of crown fires (LoFi). Samples were genotyped at nine neutral simple sequence repeats (SSRs) and at 251 single nucleotide polymorphisms (SNPs) from coding regions, some of them potentially important for fire adaptation. Fire regime had no effects on genetic diversity or demographic history. Three high-differentiation outlier SNPs were identified between HiFi and LoFi stands, suggesting fire-related selection at the regional scale. At the local scale, fine-scale spatial genetic structure (SGS) was overall weak as expected for a wind-pollinated and wind-dispersed tree species. HiFi stands displayed a stronger SGS than LoFi stands at SNPs, which probably reflected the simultaneous post-fire recruitment of co-dispersed related seeds. SNPs with exceptionally strong SGS, a proxy for microenvironmental selection, were only reliably identified under the HiFi regime. An increasing fire frequency as predicted due to global change can promote increased SGS with stronger family structures and alter natural selection in P. halepensis and in plants with similar life history traits.

EFFECT OF FUEL TREATMENTS ON CROWN FIRE BEHAVIOR IN ALEPPO PINE FORESTS OF GREECE: A SIMULATION STUDY

This study models the potential effect of various fuel treatments on crown fire behavior by using two crown fire simulation models in Aleppo pine (Pinus halepensis Mill.) stands. Fuel complex characteristics that influence fire behavior were measured in a representative Aleppo pine stand in northern Greece, using standard surface and canopy fuel inventory methods. Nine different fuel treatments (control, prescribed burning, controlled grazing, thinning without slash removal, thinning with slash removal, thinning and prescribed burning with slash removal, thinning and controlled grazing with slash removal, thinning and prescribed burning without slash removal, thinning and controlled grazing without slash removal) were simulated by adjusting surface fuels (total load, load-by-size class, depth) and canopy fuels (available canopy fuel load, canopy base height, canopy bulk density) under dry and normal fuel moisture conditions. Under normal conditions, stand thinning followed by prescribed burning and/or controlled grazing with slash removal prevented crown fire initiation in most cases. Under dry fuel moisture conditions, the simulation showed that the proposed fuel treatments did not appear to be effective in averting crown fire initiation and spread. Combinations of prescribed fire and/or controlled grazing can be used to reduce wildfire hazard in Aleppo pine forests. Management of Aleppo pine forests should include an analysis of how the proposed actions (logging, thinning, etc.) may affect fuel complex properties. Fuel treatment plans should be an essential component of forest management in Aleppo pine forests in Greece, in order to reduce fire hazard.

Seasonal nutrient retranslocation in reforested Pinus halepensis Mill. stands in Southeast Spain

Retranslocation, resorption and relocation of nutrients are important adaptive mechanisms developed by plants to acquire the amount of the nutrients required for growth. They are usual mechanisms in deciduous and conifer trees that occur in Mediterranean regions where drought periods are usual. Soil factors, environmental characteristics and species factors are key drivers of nutrient retranslocation in conifers but is not well understood how soil fertility or intraspecific competition influences the process. We studied retranslocation in Pinus halepensis Mill. stands showing different site quality (differences in climate and intraspecific competition) occurring in Southeast Spain. We monitored reforested mature Aleppo pine forests in stands with differences in site quality, climate and intraspecific competition. Stands were characterised, the content of nutrients of soil and green samples (twigs and pine needles) were recorded, and seasonal nutrient retranslocation was obtained. Site characteristics were related to growth rate and nutrient content of foliage and soil. We evaluated whether the retranslocation of nutrients from older to younger foliage was related to the current-year growth rate and to the nutritional status of the plant as influenced by intraspecific competition. Foliar macronutrient concentrations and the amount of retranslocated macronutrients were seasonal, with differences related to site quality and tree density. As a general trend, nutrient concentrations increased after drought (autumn) and decreased during the growth period (spring). However, some micronutrients (mainly Na and Fe) decreased during both periods. The retranslocation pattern in Aleppo pine reinforced the hypothesis that pine adaptations to drought- and fire-prone habitats are linked to the resilience of these forest types. We developed scientific knowledge to assist decision making in adaptive forest management; e.g. fertilizer recommendations or reforestation programmes.

MODELO INDIVIDUAL PRELIMINAR DE CRESCIMENTO DE ÁRVORE, MODELO DE ÍNDICE DE LOCAL E MODELO DE "MORTALIDADE" PARA PINHEIRO-DE-ALEPO (<i>Pinus halepensis</i> MILL.) EM CHALKIDIKI (NORTE DA GRÉCIA)

Modelos preliminares de altura, modelo de volume, modelo de índice de local e análise de "sobrevivência” para Pinus halepensis Mill., em Chalkidiki (Norte da Grécia ) foram preliminarmente desenvolvidos baseados em medidas de 20 parcelas experimentais estabelecidas em 2010. Os dados para altura, volume e modelos de "mortalidade" consistiram em 790 observações obtidas de 40 árvores (20 dominantes e 20 codominantes). Uma equação derivada da função hiperbólica foi selecionada para modelar altura dominante e volume de desenvolvimento. O modelo de crescimento em altura foi usado como uma curva-guia para desenvolver duas curvas de índice de local. A altura média dominante e codominante foi estimada em 10 m (Local I) e 7 m (Local II) (idade-base de 17 anos). A sobrevivência de Kaplan-Meier e as funções de risco aplicadas para a análise de "sobrevivência", confirmaram as curvas de índice de local desenvolvidas pelo modelo de altura (SI10 e SI7).

Comparison of height-diameter models based on geographically weighted regressions and linear mixed modelling applied to large scale forest inventory data

Aim of the study: The main objective of this study was to test Geographically Weighted Regression (GWR) for developing height-diameter curves for forests on a large scale and to compare it with Linear Mixed Models (LMM).Area of study: Monospecific stands of Pinus halepensis Mill. located in the region of Murcia (Southeast Spain).Materials and Methods: The dataset consisted of 230 sample plots (2582 trees) from the Third Spanish National Forest Inventory (SNFI) randomly split into training data (152 plots) and validation data (78 plots). Two different methodologies were used for modelling local (Petterson) and generalized height-diameter relationships (Cañadas I): GWR, with different bandwidths, and linear mixed models. Finally, the quality of the estimated models was compared throughout statistical analysis. Main results: In general, both LMM and GWR provide better prediction capability when applied to a generalized height-diameter function than when applied to a local one, with R2 values increasing from around 0.6 to 0.7 in the model validation. Bias and RMSE were also lower for the generalized function. However, error analysis showed that there were no large differences between these two methodologies, evidencing that GWR provides results which are as good as the more frequently used LMM methodology, at least when no additional measurements are available for calibrating.Research highlights: GWR is a type of spatial analysis for exploring spatially heterogeneous processes. GWR can model spatial variation in tree height-diameter relationship and its regression quality is comparable to LMM. The advantage of GWR over LMM is the possibility to determine the spatial location of every parameter without additional measurements. Keywords: Spatial analysis; Pinus halepensis Mill; forest modelling.Abbreviations: GWR (Geographically Weighted Regression); LMM (Linear Mixed Model); SNFI (Spanish National Forest Inventory).

Soil moisture and its role in growth-climate relationships across an aridity gradient in semiarid Pinus halepensis forests

In Mediterranean areas with limited availability of water, an accurate knowledge of growth response to hydrological variables could contribute to improving management and stability of forest resources. The main goal of this study is to assess the temporal dynamic of soil moisture to better understand the water-growth relationship of Pinus halepensis forests in semiarid areas. The estimates of modelled soil moisture and measured tree growth were used at four sites dominated by afforested Pinus halepensis Mill. in south-eastern Spain with 300 to 609mm mean annual precipitation. Firstly, dendrochronological samples were extracted and the widths of annual tree rings were measured to compute basal area increments (BAI). Secondly, soil moisture was estimated over 20 hydrological years (1992–2012) by means of the HYDROBAL ecohydrological model. Finally, the tree growth was linked, to mean monthly and seasonal temperature, precipitation and soil moisture. Results depict the effect of soil moisture on growth (BAI) and explain 69–73% of the variance in semiarid forests, but only 51% in the subhumid forests. This highlights the fact that that soil moisture is a suitable and promising variable to explain growth variations of afforested Pinus halepensis in semiarid conditions and useful for guiding adaptation plans to respond pro-actively to water-related global challenges.

Comparative natural durability of four Mediterranean softwoods against wood decay fungi

Atlas cedar (Cedrus atlantica Manetti), thuya (Tetraclinis articulata (Vahl) Masters), Aleppo pine (Pinus halepensis Mill.), maritime pine (Pinus pinaster var atlantica Ait) are among important Mediterranean coniferous species that provide softwood round timber. Atlas cedar and thuya are well known for their noble timber used in ebinestry and marquetry while those of the two pines are mainly used as wood service. The natural durability is an important property of wood regarding performance and service life. The present work is conducted to assess the natural durability of these woods against wood destroying fungi, in laboratory test, according to the methods described in the European standards, CEN/TS 15083-1 and NF EN 350-1. Mass losses of wood specimens, after 16 weeks of exposure to fungi attack, showed that C. atlantica and T. articulata woods are very durable to durable against wood-decay fungi attack. Such natural durability allows these woods to access the risk classes of biological attacks 4 and 5 (high risk) for end-use without preservative treatment, while P. halepensis and P. pinaster var atlantica woods, classified as less to none durable, must be treated before use at high risk classes circumstances.

A hydroeconomic modeling framework for optimal integrated management of forest and water

Forests play a determinant role in the hydrologic cycle, with water being the most important ecosystem service they provide in semiarid regions. However, this contribution is usually neither quantified nor explicitly valued. The aim of this study is to develop a novel hydro-economic modelling framework for assessing and designing the optimal integrated forest and water management for forested catchments. The optimization model explicitly integrates changes in water yield in the stands (increase in groundwater recharge) induced by forest management, and the value of the additional water provided to the system. The model determines the optimal schedule of silvicultural interventions in the stands of the catchment in order to maximize the total net benefit in the system. Canopy cover and biomass evolution over time were simulated using growth and yield allometric equations specific for the species in Mediterranean conditions. Silvicultural operation costs according to stand density and canopy cover were modelled using local cost databases. Groundwater recharge was simulated using HYDRUS, calibrated and validated with data from the experimental plots. In order to illustrate the presented modelling framework a case study was carried out in a planted pine forest (Pinus halepensis Mill.) located in south-western Valencia province (Spain).The optimized scenario increased groundwater recharge. This novel modelling framework can be used in the design of a “payment for environmental services” scheme in which water beneficiaries could contribute to fund and promote efficient forest management operations. This article is protected by copyright. All rights reserved.

Changes in soil organic carbon over 20 years after afforestation in semiarid SE Spain

This paper analyses the changes on SOC in semiarid abandoned farmland located in SE Spain partially afforested with Pinus halepensis Mill. in winter 1995–1996. The study tests the effects that 10 soil-preparation treatments before planting exerted on SOC, evaluates the effects of land-use change on SOC, and simulates SOC dynamics using the RothC model. The land-use changes studied were from cereal crops to abandoned croplands and from cereal crops to afforestation, in comparison to a native forest in equilibrium (maximum SOC reached). The results show that there were no differences in SOC among the soil-preparation treatments applied 20years ago. An increasing mean SOC was recorded in the afforestation subplots. These increases were not always significant from one sampling period to another and were related to silvicultural practices and climate. SOC in the afforested land was influenced by the soil carbonate content (+), pH (−), and pine density (+). After 20years, the mean SOC values in the afforested land were higher than in abandoned croplands and cereal crops (12.23MgCha−1, 9.52MgCha−1 and 8.02MgCha−1, respectively) though no statistical differences were registered among these land uses. In all cases SOC differed with respect to the native pine forest, which showed 40.59MgCha−1. Our results indicated that not enough time had elapsed to detect significant cumulative effects in SOC due to slow dynamics of carbon in the soil in the semiarid climate, the low inputs of organic matter to the soil and, probably, the low soil clay content in the study area. At the end of this study, the SOC in the afforested area was 69.9% less than in the native pine forest, indicating a clear potential for SOC sequestration in the following years. The RothC model was able to simulate the measured SOC increases due to the abandonment of agriculture and the afforestation of the cereal crops. In a 20-year model, we found a fit for the time course of SOC in abandoned croplands of RMSE<10%, and a RMSE=33% for the afforested area. Although the model in all cases overestimated the SOC measured, our results could be used as general indicators for predictions of the time course of SOC and potential carbon sequestration in semiarid afforested areas.

Root rot and damping-off of Aleppo pine seedlings caused by Pythium spp. in Algerian forest nurseries

Aleppo pine (Pinus halepensis Miller) is a common forest tree in the Mediterranean Region. Production of Aleppo pine seedlings is hindered by damping off and root rot diseases in cooler conditions of north-western Algeria, which significantly reduces the seedling emergence. This work was carried out to evaluate the pathogenicity of different Pythium Pringsheim species on Aleppo pine seedlings. Seventeen isolates of Pythium spp. were isolated from diseased seedlings, identified to the species level based on DNA sequence from the internal transcribed spacer region and their identity was confirmed on morphological basis. The obtained isolates were pathologically characterized in Petri dish and pot assays. Germination was significantly inhibited by the different Pythium spp. isolates. The highest inhibition was observed with Pythium ultimum Trow in Petri dish and pot assays. The reduction in root growth differed significantly between different isolates. The maximum reduction in root growth (92.2%) was observed for P. ultimum in Petri dish assay. The various isolates of Pythium showed a significant influence on root length, shoot length and vigour index. The maximum disease incidence (89.7%) was caused by P. ultimum. Our results indicated that Pythium spp. is commonly found on diseased seedlings, in most containers and bare-root nurseries.

MISSING AND DARK RINGS ASSOCIATED WITH DROUGHT IN PINUS HALEPENSIS

The responses of the vascular cambium and tracheid differentiation to extreme drought in Aleppo pine (Pinus halepensis Mill.) were investigated. The research focused on the drought year of 2005, in the primary study area at Maigmo (MAI) in southeastern Spain, with comparisons in Jarafuel (JAL) and Guardamar (GUA). The climate in this region is typically warm and dry with hot summers. Wood formation throughout the 2005 growing season was studied in transverse microtome sections and integrated with a retrospective dendrochronological analysis of crossdated increment cores collected in 2009. For most anatomical sections collected throughout the growing season at MAI, the vascular cambium appeared to be dormant as indicated by the low number of cells per radial file. Occasionally, immature xylem derivatives were observed during the growing season but without production of an annual ring. In increment cores collected at MAI, the 2005 position in the annual ring series contained either a narrow ring of both earlywood and latewood (47% of samples), a narrow ring of apparent latewood with no earlywood (13%), or a missing ring (50%). We introduce the term “dark ring” to refer to those annual rings of apparent latewood with no earlywood. For trees at JAL, the 2005 ring had below-average width and contained both earlywood and latewood. At GUA, the trees produced the widest 2005 ring of all three sites and mainly contained an intra-annual density fluctuation (IADF). The IADF was formed after cambial reactivation in the autumn. Although dark rings, IADFs, and especially missing rings complicate dendrochronological analysis, these anatomical features may provide an additional proxy record from which to infer climate variability and change in the past.