Stands Of Pinus Sylvestris Research Articles

Determination of chemical markers affecting the occurrence of Panolis flammea Den. & Shiff.

AbstractThe research conducted so far on the chemical mechanisms of trees' defence against foliophages has not uncovered the chemical compounds biosynthesized by plants that are essential for these mechanisms. The objective of this study was to identify a chemical indicator for the presence of the pine beauty moth in Pinus sylvestris stands. Fresh needled shoots were collected from the crowns of pine trees in stands where the pine beauty moth tends to occur in large numbers, as well as from control stands. Total phenolic contents, total flavonoids contents, total chlorophyll content, terpene compounds, phenolic compound concentration, LMWOAs, sugar content, and colour analysis were conducted. Chlorophyll content, the presence of Panolis flammea in forest stands, and the colour of pine needles were discovered to be related. Variable L* correlated positively with the concentrations of chlorophyll a and b. In pine needles that were not attacked by the pine beauty moth, significantly higher concentrations of 4‐hydroxybenzoic acid, salicylic acid, chlorogenic acid, syringic acid, quercitin, and rutin were found, with the first compound having the most significant effect (4‐hydroxybenzoic acid). Based on the study results, the connected compounds in pine needles make them susceptible to insect attack. In addition, insect repellent programmes were mentioned.

Spatially-explicit effects of small-scale clear-cutting on soil fungal communities in Pinus sylvestris stands

Clear-cutting is a common silvicultural practice. Although temporal changes in the soil fungal community after clear-cutting have been widely investigated, little is known about stand-level variations in the spatial distribution of soil fungi, particularly at the clear-cut edge. We performed spatial soil sampling in three clear-cuts (0.5 ha), edge habitats, and surrounding forests 8 years after clear-cutting to examine the impact of clear-cutting on the soil fungal community (diversity, composition, guilds, and biomass) and soil properties in a managed Pinus sylvestris forest in northern Spain. Our analyses showed small differences in the composition of the soil fungal community between edge, forest, and clear-cut zones, with <4 % of the species strictly associated with one or two zones. The richness, diversity, and evenness of the fungal community in the edge zone was not significantly different to that in the forest or clear-cut zones, although the clear-cut core had approximately a third fewer ectomycorrhizal species than the edge or the forest. Saprotrophic fungi were widespread across the clear-cut–forest gradient. Soil fungal biomass varied significantly between zones, ranging from 4 to 5 mg g−1 dry soil in the forest and at the forest edge to 1.7 mg g−1 dry soil in the clear-cut area. Soil organic matter, pH, nitrogen, and phosphorus did not differ significantly between edge, forest, and clear-cutting zones and were not significantly related to the fungal community composition. Overall, our study showed that small-scale clear-cut treatments are optimal to guarantee, in the medium-term, soil fungal communities within harvested areas and at the forest edge that are comparable to soil fungal communities in the forest, even though the amount of fungal biomass in the clear-cut zone is lower than at the forest edge or in the forest.

Mycobiome of Post-Agricultural Soils 20 Years after Application of Organic Substrates and Planting of Pine Seedlings

A 20-year study of a pine stand on post-agricultural land showed that woody debris in the form of organic matter can be successfully used to restore symbiotic mycorrhizal communities, as is the case with forest soils. Woody substrates restored organic matter in soils altered by long agricultural use and had a positive effect on the composition of mycobiota antagonistic to pathogens, especially to Heterobasidion annosum, the causal agent of the dangerous disease root and stump rot of many forest tree species, including stands of Pinus sylvestris (L.). In a study that started in 2001 in the forest district of Czarne Człuchowskie (northern Poland), the following organic materials were used: wood residues (W), sawdust (S), bark compost (B), and compost applied to the root zone during planting (G). The organic materials were spread in the form of mulch over the entire area during planting. After twenty years, it was found that the substrates used provided suitable growth conditions for mycobiome useful for pines. The addition of organic matter did not change the alpha biodiversity of the soil, but in the long term led to significant changes in the composition of mycobiota (beta biodiversity). The changes in the soil after the addition of organic material naturally accelerated the formation of the forest habitat. A number of fungi evolved that degraded added lignin and cellulose while being antagonists of H. annosum and other pine pathogens. In particular, the well-known hyperpathogens of the genus Trichoderma played an important role by promoting resistance of the soil environment to pathogens. Soil enrichment by bark compost and wood residues increased the relative abundance of Trichoderma more than fourfold.Mycorrhizal fungi became dominant in soil enriched with organic matter. After enriching the soil with bark compost, the relative abundance of Amphinema and Inocybe increased to 5%. The relative abundance of Russula in soil enriched with wood residues and sawdust increased to 9% and 5%, respectively. Mycorrhizal fungi, e.g., of the genus Ąmanita, Rusula, which formed root mycorrhizae, not only increased the root receiving area many times over, but also protected the roots (mechanically and chemically from pathogens). Altogether, the observed positive changes increase the chances that the first generation of pines will survive on the ground.

Threshold Response to Extreme Drought Shifts Inter-Tree Growth Dominance in Pinus sylvestris

Many studies quantify short-term drought impact on tree growth relative to pre-drought growth averages. However, fewer studies examine the extent to which droughts of differing severity differentially impact tree growth or shape stand dynamics. Focusing on three droughts in high and low density stands of Pinus sylvestris in Scotland, we calculated pre-drought growth averages using climatically standardized antecedent growth years to assess tree level drought and post-drought growth performance as percentage growth change (PGC). We then used mixed-effects models to understand how droughts of differing severity impact tree growth and calculated indices of growth dominance (Gd), size inequality (Si), and size asymmetry (Sa) to detect changes in stand structure. Mixed-effects model results indicate that the magnitude and duration of the growth reduction during and following the more extreme drought was significantly larger compared to less severe droughts, for which we found limited evidence of drought impact. While no changes in Si or Sa were noted following any drought, we found evidence of a difference in Gd after the most extreme drought in both stand densities indicative of a threshold response, with smaller trees contributing proportionally more to stand growth relative to their size. Under less severe droughts, inter-tree variability may have partially buffered against stand-level growth change, however, a small increase in drought severity was associated with a significant reduction in average tree growth, an increase in the number of trees growing at &amp;gt;2SD below pre-drought levels and a shift in Gd toward smaller trees, indicating that a drought severity threshold in P. sylvestris may have been exceeded.

Pine Forest Management and Disturbance in Northern Poland: Combining High-Resolution 100-Year-Old Paleoecological and Remote Sensing Data

Global warming has compelled to strengthen the resilience of European forests. Due to repeated droughts and heatwaves, weakened trees become vulnerable to insect outbreaks, pathogen invasions, and strong winds. This study combines high-resolution analysis of a 100-year-old high-resolution peat archive synthesized from the Martwe peatland in Poland with remote sensing data. We present the first REVEALS based vegetation reconstruction in a tornado-hit area from Poland on the background of previous forest management in monocultural even-aged stands – Tuchola Pinewoods. During the 20th century, the pine monocultures surrounding the peatland were affected by clear-cutting and insect outbreaks. In 2012, a tornado, destroyed ca. 550 ha of pine forest around the peatland. The palynological record reflects these major events of the past 100 years as well as changes in forest practices. Our study showed the strong relationships between the decrease of Pinus sylvestris (Scots pine) in palynological record as well as planting patterns after the tornado. Moreover, past forestry practices [such as domination of Pinus sylvestris, the collapse of Picea abies (Norway spruce), low share of Betula spec. (birch) due to Pinus sylvestris promotion and probable also to a lesser by removal of Betula as a “forest weed,” and low plant coverage of tree species due to clear-cutting and cutting after insect outbreaks] were well identified in the proxy record. In monocultures managed over decades, the reconstruction of vegetation may be challenging due to changes in the age composition of the Pinus sylvestris stands. We found that through historical, remote sensing, and paleoecological data, the dynamics of disturbances such as insect outbreaks and tornadoes, as well as the changing perceptions of local society about forests, can be determined.

Activity of 137Cs and 40K Isotopes in Pine (Pinus sylvestris L.) and Birch (Betula pendula Roth) Stands of Different Ages in a Selected Area of Eastern Poland

Research Highlights: a forest is an ecosystem that allows for the assessment of radioactive contamination of the environment over several decades. (1) Background and Objectives: measurements of the activity of the 137Cs isotope in various elements of a forest ecosystem are one of the most important parameters in the assessment of radioisotope contamination. The translocation of 137Cs in the environment is determined by the activity of the natural 40K isotope in soil. The activities of 137Cs and 40K isotopes were assessed in two stands of Betula pendula and Pinus sylvestris, differing in age (30, 50, and 80 years old); (2) Materials and Methods: the research was conducted in one of the forest districts of eastern Poland. Wood, litter, and soil were collected for the tests from the sampling sites. The activity of 137Cs and 40K was determined using the γ-spectrometric method. Based on the activity of these isotopes in wood and soil, the values of translocation factors (TF) were determined; (3) Results: the highest activity of 137Cs was recorded in the wood of the oldest stands, the growth period of which coincided with the time period of intensive testing with nuclear weapons. With the growing age of the stand, the value of TF 137Cs increased, while the value of TF 40K was not dependent on the age of the stands. Birch wood accumulated more 137Cs and 40K isotopes than pine wood. (4) Conclusions: the results show a much greater radioactive contamination of the environment in eastern Poland during the testing with nuclear weapons than after the Chernobyl nuclear reactor explosion. The greater accumulation of radiocesium in birch wood than in pine wood predisposes this species to be more useful when assessing the radioactive contamination of the environment from the past.

The advancing mycelial frontier of ectomycorrhizal fungi.

This article is a Commentary on Hagenbo et al. (2021), 230: 1609–1622.

The effect of stand structure on litter decomposition in Pinus sylvestris L. stands in Turkey

• Key message Canopy closure and stand age significantly affected the litter decomposition. Therefore, stand-specific decomposition constants (k) should be calculated in forest carbon models for more accurate carbon budget estimation. Furthermore, to reduce the carbon release from decomposing litter, regeneration cutting should be carried out at later ages, and heavy thinning should not be implemented in mature as well as overmature stands. • Context Decomposition of litter has an important role in primary production with its influence on nutrient release for plant uptake and carbon flux in forest ecosystems. Thus, understanding the effects of the intervention on litter decomposition is crucial for carbon management in forestry. • Aims The effects of stand structure and exposure on litter decomposition rate in Pinus sylvestris stands were investigated. • Methods Samples were taken from young to overmature stands with open to dense canopy. The litterbag method was used to measure the mass loss of the litter. The k values were calculated from the mass loss of decaying litter. Carbon and nitrogen contents of the litter were determined. • Results Cutting caused the decomposition to accelerate at a rate of up to 58% depending on its intensity. The k values were found to fluctuate over time from 0.189 in moderately dense-canopied stands to 0.317 in open-canopied overmature stands. Stand basal area, incubation time, and remaining carbon concentration of the litter accounted for 75% of the variation in the k value. • Conclusion Changes in the stand structure affect the litter decomposition rate in forest ecosystems. Heavy thinning can alter the litter decomposition process drastically, while moderate thinning may not have a clear effect in the long run.

Overyielding in mixed pine forests with belowground complementarity: impacts on understory

The impact of biodiversity loss on the functioning of forest ecosystems has become a central issue in ecology. Most reports of the positive effects of tree mixture on the biodiversity–productivity relationship focus on mixtures that combine tree species with contrasting traits. Nevertheless, little is known about how coniferous mixtures of the same genus affect forest productivity, what mechanisms are involved, and how the understory is affected. Here, we assessed the effect of mixed versus monospecific stands of Pinus sylvestris L. and P. pinaster Ait. on productivity, its impact on the understory, and its relationship with soil water and fertility, based on research with six triplets (6 triplets × 3 forest stands × 1 plot = 18 plots) in North-Central Spain. Each triplet consisted of two plots dominated either by P. sylvestris or P. pinaster and of one mixed plot that contained both species. Productivity, at the stand and neighborhood levels, and the understory richness, and soil water and fertility at the stand level were analyzed. A positive effect of pine mixture on productivity was observed at the smaller spatial scale, and it had no negative effect on the understory richness. The greater space-use efficiency (higher tree density and basal area) of both Pinus species in the admixtures was related to soil water and fertility niche complementarity. The fundamental role of scale in determining the relationship between species richness and ecosystem functioning in forests is highlighted.

Spatio-temporal distribution of Hylobius abietis in Scots pine stands \u2013 implications for pest monitoring

The protection of reforested areas against the large pine weevil Hylobius abietis is one of the greatest forest management challenges in many European countries. No information exists on the spatial distribution of this pest, which is necessary to assess its abundance and, consequently, to precisely estimate its threat to reforested sites. The aim of this study was to assess the spatio-temporal changes in the number of H. abietis beetles in reforested clear-cut areas (reforestations) and neighbouring Pinus sylvestris stands, from which these beetles are assumed to migrate to the reforestations. In this two-year study, baited traps were used to catch H. abietis beetles in the reforestations and neighbouring stands. The results revealed significantly more beetles in the neighbouring old stands (61–69 years) than in the young stands (5–11 years). The distribution of the beetles in both the old and young stands was inversely dependent on the distance from the stand edge. The large pine weevil migration to the reforestations was most intense in mid-May and early June. In May, most beetles were collected along the edges of the reforestations; in June, their distribution was more regular; and in July, the beetles were more abundant in the central part of the reforestations. These results allow H. abietis monitoring improvement, which is an important element of integrated forest protection.

Are pine-oak mixed stands in Mediterranean mountains more resilient to drought than their monospecific counterparts?

Climate change projections point to an increase in the intensity and frequency of extreme drought events with important negative impacts on forest functioning. Predicting these impacts constitutes a crucial challenge for forest managers and for the maintenance of ecosystem services supply. Promoting mixed stands seems a promising strategy for adapting forest ecosystems to ongoing climate change. However, some uncertainty exists regarding whether admixture can improve growth resilience to extreme drought events. Here, we aim to assess tree growth response to drought in mixed and monospecific stands of Pinus sylvestris L. and Quercus pyrenaica Willd. in central Spain. We built tree-ring chronologies and evaluated tree growth sensitivity to water availability and growth resilience components to extreme droughts using linear mixed models. We found contrasting species- and climate-specific responses to admixture. Q. pyrenaica growth was significantly higher in mixed than in monospecific stands, especially in years without water limitations, while P. sylvestris showed higher growth in mixed stands under dry conditions. However, our results showed a species-specific trade-off between resistance and recovery. While P. sylvestris showed higher resistance but lower recovery to drought events in mixed than monospecific stands, Q. pyrenaica showed higher recovery but lower resistance. This trade-off might explain the absence of admixture effects on species resilience. Our results highlight the importance of considering species-specific responses to water availability and associated trade-offs when evaluating admixture effects on drought vulnerability. Overall, we show a positive effect of admixture on the long-term growth stability in response to average climate conditions, but no effects in short-term resilience capacity to increasingly common extreme dry conditions. Consequently, admixture can promote forest productivity stability but should be carefully considered as a management solution for promoting the resilience of Mediterranean mountain forests to increasing aridity.

Moisture content variation of ground vegetation fuels in boreal mesic and sub-xeric mineral soil forests in Finland

Forest fire risk in Finland is estimated with the Finnish Forest Fire Index (FFI), which predicts the fuel moisture content (FMC) of the forest floor. We studied the FMC variation of four typical ground vegetation fuels, Pleurozium schreberi, Hylocomium splendens, Dicranum spp., and Cladonia spp., and raw humus in mature and recently clear-cut stands. Of these, six were sub-xeric Pinus sylvestris stands, and six mesic Picea abies stands. We analysed the ability of the FFI to predict FMC and compared it with the widely applied Canadian Fire Weather Index (FWI). We found that in addition to stand characteristics, ground layer FMC was highly dependent on the species so that Dicranum was the moistest, and Cladonia the driest. In the humus layer, the differences among species were small. Overall, the FWI was a slightly better predictor of FMC than the FFI. While the FFI generally predicted ground layer FMC well, the shape of the relationship varied among the four species. The use of auxiliary variables thus has potential in improving predictions of ignitions and forest fire risk. Knowledge of FMC variation could also benefit planning and timing of prescribed burns.

Response of ecological stoichiometry and stoichiometric homeostasis in the plant-litter-soil system to re-vegetation type in arid mining subsidence areas

Mining restoration is a key in ecological sustainable development. Ecological stoichiometry and homeostasis in the plant-litter-soil system remain largely unknown but are vital for developing guidelines for vegetation restoration in mining subsidence areas in arid northwest China. Six re-vegetation types comprising stands of Amorpha fruticosa, Hippophae rhamnoides, Xanthoceras sorbifolium, Cerasus humilis, Cerasus szechuanica and Pinus sylvestris were selected for study. We investigated changes in the contents and stoichiometry of C, N and P in roots, stems, leaves, litter and soil in order to understand stoichiometric homeostasis and the factors driving nutrient cycling. The stoichiometry of the plant-soil system varied markedly with different re-vegetation types. The coupling of plant and soil N:P ratios indicates that the concentrations of C, N and P are usually equilibrated. Leave N:P ratios in all re-vegetation types studies indicate that plant growth was N-limited. 1/H only in H. rhamnoides and A. fruticosa (nitrogen-fixing plants) was simultaneously categorized as 'homeostatic' and this might mitigate the N-limitation. Soil easily-extractable glomalin, hyphal density and available phosphorus were key factors shifting the ecological stoichiometry. The study demonstrates that nitrogen-fixing re-vegetation species can promote stoichiometric homeostasis and the results contribute to guidance for vegetation restoration practices in mining subsidence areas.

Lichens of Pinus sylvestris stands in Makedonia and Thraki, Northern Greece

Christensen, S. N. 2020. Lichens of Pinus sylvestris stands in Makedonia and Thraki, Northern Greece. – Herzogia 33: 75 – 89.The species composition and phytogeography of 66 species recorded from Pinus sylvestris stands are briefly discussed. Bryoria furcellata, Cliostomum griffithii, Fuscidea cyathoides and Lecidea nylanderi are new to Greece, nine species are new to the province of Makedonia and eleven are new to Thraki.

Crown plasticity of five pine species in response to competition along an aridity gradient

Crown dimensions such as diameter or crown projection area are important indicators for tree vigour, growing stage or production efficiency and can be used as proxies for the assessment of wood quality, leaf area and leaf biomass, biodiversity, wildlife habitat and disturbance risk to forest stability. Crown allometry can vary with site and competition conditions, but variation patterns are not still well understood.The main aim of this study was to analyze this allometry variation in the most common pine species along the aridity gradient of the Iberian Peninsula, studying the crown response to aridity and to competition, and determining whether the presence of inter-specific competition modifies crown allometry.A set of 40,402 sample trees from 12,283 sample plots, along with the Martonne aridity index as an indicator of climatic conditions, were used to develop allometric models, the parameters of which were generalized by including aridity and competition indicators. The plots were located in monospecific or mixed stands of Pinus sylvestris, Pinus nigra, Pinus pinaster, Pinus pinea and Pinus halepensis.According to our results, both aridity conditions and competition status are important factors modifying the crown allometry of the studied species. Moreover, we found that both size-symmetric competition and size-asymmetric competition should be taken into account when modelling the crown size, both types leading to smaller crown diameter. The crown plasticity of the studied pine species in response to competition presented a low range of variation, the greatest being that of maritime pine, while Scots pine and black pine showed the smallest. The way in which aridity and competition influence crown size differs among the studied species, indicating differences in crown plasticity patterns. Moreover, in humid sites, where competition for light is more important, the crown allometry response to changes in competition is greater, being most evident in P. pinea and P. halepensis.The species mixing effects had less influence on pine crown allometry than the total competition effect, although the effect was always significant. The effect of size-symmetric competition from admixed species was positive or neutral, except for the effect of P. sylvestris on P. nigra crowns. Size-asymmetric competition also plays an important role in the species mixing effects, these effects on intermediate or suppressed trees varying depending on the species mixture. The models developed reveal significant species-specific effects on crown allometry, pointing to the ability of pine species to adapt their crowns to different growing conditions.

Can mixed pine forests conserve understory richness by improving the establishment of understory species typical of native oak forests?

A positive effect of mixed pine forests ( Pinus sylvestris L. and Pinus pinaster Ait.) on the understory richness and tree regeneration was observed with respect to monospecific stands. Understory species typical of the native Pyrenean oak forests in the Iberian Peninsula contribute to maintaining high understory richness in such mixed pine forests. The influence of stands characteristics on the understory in mixtures that combine coniferous tree species of the same genus deserves more study since they are frequent in Spain. To assess the effect of mixed versus monospecific stands of Pinus sylvestris L. and Pinus pinaster Ait. on the main tree species regeneration and understory species composition. Tree regeneration and understory species composition were inventoried in eighteen forest plots (6 triplets) in North-Central Spain. Each triplet consisted of two plots dominated either by Scots pine or Maritime pine and one mixed plot that contained both species. The basal area (%) of both Pinus species was the only characteristic of the stands that significantly influenced the understory composition and tree regeneration. Characteristic species of humid and temperate zones, including P. sylvestris regeneration, dominated in Scots pine stands, and typical species of well-drained Mediterranean areas, including P. pinaster regeneration, dominated in Maritime pine stands. In mixed stands, the highest regeneration of the native Pyrenean oak with respect to monospecific stands was accompanied by understory species typical of native oak forests that share the same regeneration niche. Mixed pine forests allow the development of understory species better than monospecific forests.

Cone and seeds variability in seed orchards and seed stands of Pinus sylvestris L.

Seeds from seed orchards and seed stands may differ in morphology and quality, both determined during the seed assessment. The study aims at the comparison of phenotypic characters of cones and seeds originating from economic seed stands and seed orchards of Scots pine from western Poland. The study was conducted in 5 seed stands and 5 clonal seed orchards, representing five Scots pine populations. The analyses included the following measurements: length and width of cones, the number of empty and full seeds in the cone and the weight of 1,000 seeds. Moreover, the measurements of the length and width of the seed surface were carried out.&#x0D; The analysed seed stands and orchards were characterized by high variability in terms of the size and weight of cones and the amount of seeds. An ANOVA treatment showed that seed stands and orchards significantly differed in length and width of cones and seeds. Both seeds and cones from the seed orchards were characterized by higher values of analyzed traits than ones from the economic seed stands. Differences in mass of cones and 1000 seed weigh were of low significance (p = 0.022 ÷ 0.037). Significant differences between the length of seeds and seed area among all of the examined populations were demonstrated. The percentage contribution of empty seeds for all of the analysed sites of origin was not statistically significant.&#x0D; &#x0D; &#x0D; &#x0D; Keywords: Scots pine, population, seed orchards, variation, seeds, cones

Understory response to overstory and soil gradients in mixed versus monospecific Mediterranean pine forests

Many studies highlight the role of mixed versus monospecific forests to provide numerous ecosystem services. Most reports of the positive effects of tree mixture on biodiversity focus on coniferous–deciduous combinations, but little is known about the effects of mixtures combining two coniferous tree species. We assessed the effects of mixed versus monospecific stands of Pinus sylvestris and P. pinaster on the understory richness and composition and its relationship with the soil status, based on research with six triplets in northern Spain. In ten square meter quadrats randomly located per plot, the cover of every understory vascular plant species was estimated visually and data were codified according to Raunkiaer’s life-forms. One soil pit of 50 cm depth was dug in each plot to determine the soil water (water holding capacity) and fertility (carbon and exchangeable cations stocks) status. A water-stress gradient associated with the overstory composition indicated that P. pinaster tolerates lower soil water content than P. sylvestris. Mixed stands are under greater water stress than monospecific P. sylvestris stands but maintain the same level of understory richness. Also, a soil fertility gradient defined by organic carbon and exchangeable magnesium stocks was identified. Hemicryptophytes, whose abundance is greater in mixed stands, were the only understory life-form positively correlated to soil fertility. We conclude that the mixture of both Pinus species should continue to be favored in the study area because it helps to maintain understory richness under greater water-stress conditions and improves soil fertility.

Canopy transpiration of a Larix sibirica and Pinus sylvestris forest in Central Siberia

Russian boreal forests represent the largest forested region on Earth and comprise one-fifth of the world's forest cover. The two most common genera in Siberia are Larix and Pinus, which together cover more than 80% of the region’s forested area. One observable ongoing effect of climate warming is that natural populations of Siberian larch are gradually being replaced by Scots pine. The present work focuses on comparing effects of environmental variables on sap flow density in two even-aged stands of Larix sibirica and Pinus sylvestris. While the two study stands were identical in age (49 years) with similar basal areas and leaf area index, they exhibited very different transpiration rates and response mechanisms to environmental signals. Stand water use was higher for larch than it was for pine, even though transpiration for deciduous larch trees occurred over shorter time periods. The cumulative annual transpiration of the larch stand was 284 ± 4 mm measured over two consecutive growing seasons (2015–2016), while for pine this was 20% lower. Seasonal transpiration accounted for 50% and 40% of the reference evapotranspiration and 91% and 67% of growing season precipitation for larch and pine, respectively. Water stored in soil provided an important source of water for transpiration, observed as roughly 100 mm, which was then replenished from snowmelt the following spring. The greatest difference between two species related to how well they controlled transpiration, notably in the context of high vapor pressure deficit; under these conditions, pine maintained greater control over transpiration than larch. For all soil moisture levels measured, larch transpired more water than pine. Importantly, our results point to potential future effects of global warming, most notably an increasing decline of larch forests, changes in the ratio between latent and sensitive heat fluxes, and significant modifications in ecosystem water availability.

Is thinning an alternative when trees could die in response to drought? The case of planted Pinus nigra and P. Sylvestris stands in southern Spain

Previous research has provided insights into the potential response of growth and water use efficiency to thinning in Mediterranean forests, but little is known about the potential benefits of silviculture for plantations under severe drought stress. We selected two stands of Pinus sylvestris L. and P. nigra Arnold., and used dendrochronology and carbon isotopes (δ13C) to understand the growth and functional responses of high-density planted pine forests to thinning in drought-prone areas. Resistance, recovery, and resilience indices were calculated for each species using BAI data. We expected heavy thinning to produce stands that were more resilient to drought, particularly for the more drought-tolerant P. nigra. Differences in the basal area increments (BAI) and intrinsic water-use efficiency (iWUE) were found between the unthinned stand and the thinned stands, for both species. After thinning, BAI decreased as iWUE increased but this relationship was only marginally significant in P. sylvestris. Thinning increased growth resistance, recovery, and resilience following the severe drought of 2012. Our findings suggest that water shortage, linked to recurrent droughts, together with high tree competition, negatively affected tree growth and increased iWUE, which explains the dieback of some of these pine plantations. We evidence the vulnerability of densely planted Mediterranean pines to the forecasted warmer and drier conditions. These results show that a heavy thinning treatment (60% of basal area removed) provides a promising silvicultural framework for the adaptation of these drought-sensitive Mediterranean mountain pine forests to the potential risks of climate change.