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Stone Pine (Pinus pinea L.) is currently the pine species with the highest commercial value with edible seeds. In this respect, this study introduces a new methodology for extracting Stone Pine trees from Digital Surface Models (DSMs) generated through an Unmanned Aerial Vehicle (UAV) mission. We developed a novel enhanced probability map of local maxima that facilitates the computation of the orientation symmetry by means of new probabilistic local minima information. Four test sites are used to evaluate our automated framework within one of the most important Stone Pine forest areas in Antalya, Turkey. A Hand-held Mobile Laser Scanner (HMLS) was utilized to collect the reference point cloud dataset. Our findings confirm that the proposed methodology, which uses a single DSM as an input, secures overall pixel-based and object-based F 1 -scores of 88.3% and 97.7%, respectively. The overall median Euclidean distance revealed between the automatically extracted stem locations and the manually extracted ones is computed to be 36 cm (less than 4 pixels), demonstrating the effectiveness and robustness of the proposed methodology. Finally, the comparison with the state-of-the-art reveals that the outcomes of the proposed methodology outperform the results of six previous studies in this context.

Key message The effects of MJ on pine trees are species-specific and trigger a resistant phenotype to the PWN. A more dynamic response of hormones and gene expression in Pinus pinea explains the high resistance to Bursaphelenchus xylophilus of this species. Knowledge on hormonal and genetic mechanisms of pine trees in response to the pinewood nematode (PWN; Bursaphelenchus xylophilus ) is limited. To describe tree defence strategies against B. xylophilus , this study used the plant stress hormone methyl jasmonate (MJ) on four pine species with different susceptibility ( Pinus pinaster  <  P. radiata ≈ P. sylvestris  <  P. pinea ). Three-year-old trees were sprayed with MJ at 0, 25, and 50 mM, and 2 months later challenged with the PWN. Multiple samples were taken to assess nematode content, oxidative stress, secondary metabolites, phytohormone levels, and stress-related gene expression. Nematode infestation in trees correlated negatively with the water content of needles and phenolics of stems, and positively with the concentration of indole-3-carboxylic acid in stems. MJ spray reduced in a dose-dependent manner the nematode content in P. pinaster and P. sylvestris . The effects of MJ were species-specific, although a more pronounced impact was observed in the susceptible P. pinaster species, leading to a decrease of chlorophyll and water loss and to the upregulation of the gene involved in the biosynthesis of terpenoids ( AFS ). After MJ spray, increased levels of JA-Ile were observed in P. pinea only. Hormone profiling, predisposition to activate antioxidant response, and gene expression in P. pinea trees provide evidence of why this species is highly resistant to B. xylophilus . On the contrary, the lack of effective hormonal changes in P. pinaster explained the lack of defence responses to B. xylophilus of this susceptible species. This study is a first approach to explore biochemical, molecular, and hormonal interactions between Pinus species and the PWN, and presents unprecedented insights into alterations induced by exogenous MJ in regulating defence mechanisms in pine trees.

Subalpine forests in the northern Rocky Mountains have been resilient to stand-replacing fires that historically burned at 100- to 300-year intervals. Fire intervals are projected to decline drastically as climate warms, and forests that reburn before recovering from previous fire may lose their ability to rebound. We studied recent fires in Greater Yellowstone (Wyoming, United States) and asked whether short-interval (< 30 years) stand-replacing fires can erode lodgepole pine (Pinus contorta var. latifolia) forest resilience via increased burn severity, reduced early postfire tree regeneration, reduced carbon stocks, and slower carbon recovery. During 2016, fires reburned young lodgepole pine forests that regenerated after wildfires in 1988 and 2000. During 2017, we sampled 0.25-ha plots in stand-replacing reburns (n = 18) and nearby young forests that did not reburn (n = 9). We also simulated stand development with and without reburns to assess carbon recovery trajectories. Nearly all prefire biomass was combusted (“crown fire plus”) in some reburns in which prefire trees were dense and small (≤4-cm basal diameter). Postfire tree seedling density was reduced sixfold relative to the previous (long-interval) fire, and high-density stands (>40,000 stems ha−1) were converted to sparse stands (< 1,000 stems ha−1). In reburns, coarse wood biomass and aboveground carbon stocks were reduced by 65 and 62%, respectively, relative to areas that did not reburn. Increased carbon loss plus sparse tree regeneration delayed simulated carbon recovery by > 150 years. Forests did not transition to nonforest, but extreme burn severity and reduced tree recovery fore-shadow an erosion of forest resilience.

Robust tree regeneration following high-severity wildfire is key to the resilience of subalpine and boreal forests, and 21st century climate could initiate abrupt change in forests if postfire temperature and soil moisture become less suitable for tree seedling establishment. Using two widespread conifer species, lodgepole pine (Pinus contorta var. latifolia) and Douglas-fir (Pseudotsuga menziesii var. glauca), we conducted complementary experiments to ask (1) How will projected early-to mid-21st-century warming and drying affect postfire tree seedling establishment and mortality? (2) How does early seedling growth differ between species and vary with warming and drying? With a four-year in situ seed-planting experiment and a one growing season controlled-environment experiment, we explored effects of climate on tree seedling establishment, growth, and survival and identified nonlinear responses to temperature and soil moisture. In our field experiment, warmer and drier conditions, consistent with mid-21ˢᵗ-century projections, led to a 92% and 76% reduction in establishment of lodgepole pine and Douglas-fir. Within three years, all seedlings that established under warmer conditions died, as might be expected at lower elevations and lower latitudes of species' ranges. Seedling establishment and mortality also varied with aspect; approximately 1.7 times more seedlings established on mesic vs. xeric aspects, and fewer seedlings died. In the controlled-environment experiment, soil temperatures were 2.0°–5.5°C cooler than the field experiment, and warming led to increased tree seedling establishment, as might be expected at upper treeline or higher latitudes. Lodgepole pine grew taller than Douglas-fir and produced more needles with warming. Douglas-fir grew longer roots relative to shoots, compared with lodgepole pine, particularly in dry soils. Differences in early growth between species may mediate climate change effects on competitive interactions, successional trajectories, and species distributions. This study demonstrates that climate following high-severity fire exerts strong control over postfire tree regeneration in subalpine conifer forests. Climate change experiments, such as those reported here, hold great potential for identifying mechanisms that could underpin fundamental ecological change in 21st-century ecosystems.

Environmental change is accelerating in the 21st century, but how multiple drivers may interact to alter forest resilience remains uncertain. In forests affected by large high-severity disturbances, tree regeneration is a resilience linchpin that shapes successional trajectories for decades. We modeled stands of two widespread western U.S. conifers, Douglas-fir (Pseudotsuga menziesii var. glauca), and lodgepole pine (Pinus contorta var. latifolia), in Yellowstone National Park (Wyoming, USA) to ask (1) What combinations of distance to seed source, fire return interval, and warming-drying conditions cause postfire tree-regeneration failure? (2) If postfire tree regeneration was successful, how does early tree density differ under future climate relative to historical climate? We conducted a stand-level (1 ha) factorial simulation experiment using the individual-based forest process model iLand to identify combinations of fire return interval (11–100 yr), distance to seed source (50–1,000 m), and climate (historical, mid-21st century, late-21st century) where trees failed to regenerate by 30-yr postfire. If regeneration was successful, we compared stand densities between climate periods. Simulated postfire regeneration were surprisingly resilient to changing climate and fire drivers. Douglas-fir regeneration failed more frequently (55%) than lodgepole pine (28% and 16% for non-serotinous and serotinous stands, respectively). Distance to seed source was an important driver of regeneration failure for Douglas-fir and non-serotinous lodgepole pine; regeneration never failed when stands were 50 m from a seed source and nearly always failed when stands were 1 km away. Regeneration of serotinous lodgepole pine only failed when fire return intervals were ≤20 yr and stands were far (1 km) from a seed source. Warming climate increased regeneration success for Douglas-fir but did not affect lodgepole pine. If regeneration was successful, postfire density varied with climate. Douglas-fir and serotinous lodgepole pine regeneration density both increased under 21st-century climate but in response to different climate variables (growing season length vs. cold limitation). Results suggest that, given a warmer future with larger and more frequent fires, a greater number of stands that fail to regenerate after fires combined with increasing density in stands where regeneration is successful could produce a more coarse-grained forest landscape.

Key messageExogenous MJ does not alter the resin duct structure of pines in the cortex, but increases the number, density and mean size of resin ducts in the secondary xylem, particularly in Pinus sylvestris and P. radiata.Methyl jasmonate (MJ) is an organic compound capable of modulating defence responses in plants. Exogenous application of MJ has been shown to modify the structure of the resin canal system in conifers by inducing the formation of dense concentric bands of traumatic resin ducts in the xylem. Because inducibility of resin ducts has been little explored across pine species, 3-year-old Pinus pinaster, P. pinea, P. sylvestris and P. radiata trees were sprayed with 0, 25 and 50 mM solutions of MJ, and plant growth, external symptoms and histology were assessed 60 days after treatment. Exogenous application of MJ diminished primary or secondary growth in all species (61 and 25%, respectively) and caused needle damage in P. sylvestris. Exogenous MJ did not alter the resin duct structure of Pinus spp. in the cortex. In the secondary xylem, however, the effect of MJ differed considerably between species: ducts, duct density and area covered by ducts increased in P. sylvestris and P. radiata, but not in P. pinaster and P. pinea. In MJ 50 mM-treated trees, resin duct abundance peaked at the first half of the ring in P. sylvestris and at one-third distance from the previous ring in P. radiata. In MJ treated P. radiata trees, large traumatic axial resin ducts, 120–160 µm in diameter, were aligned in the secondary xylem. The study helps to elucidate macroevolutionary aspects of inducibility of resin-based defences in the genus Pinus, where varying responses to MJ could reveal different defence strategies among species.

Pinus pineaL. (Stone pine) is an important tree species in the Mediterranean basin, particularly in coastal regions characterized by a subtropical Mediterranean climate with dry summers. It is widely cultivated for its pine nuts and aesthetic appearance. The recent decrease in pine nut production in the Aegean Region has prompted us to investigate whether the growth of stone pine trees is affected by climate change. We collected 60 cores from 30 trees at two sites representing lower and higher elevations. Using standard dendrochronological analysis, two site chronologies were constructed for the lower and higher altitudes. Linear and non-linear analyses were performed to determine the climate-growth relationship of sampled trees. Furthermore, we calculated growth resilience to drought, including resistance and recovery components. We also examined the climatic trends in the study area to enhance our understanding of the climate-growth relationship. The air temperature time series analyzed in this study has shown a recent shift towards higher average temperatures, observed around the late 1980s and early 1990s. We observed a positive correlation between residual chronologies and total precipitation from December to July. Adequate precipitation in early autumn is essential for latewood formation. The positive correlation between tree-ring growth and winter temperatures indicates that milder winters extend the vegetation period and affects the radial growth of pines. Moreover, moving correlation analysis revealed a notable shift, with the limiting effect of drought significantly increasing and the limiting impact of winter cold diminishing in the early 1990s. Generalized additive mixed model (GAMM) analysis described thresholds for additional increment based on the non-linear relationship with precipitation and weakly non-linear relationship with temperature. Stone pine trees showed relatively low resistance, high recovery, and a general low resilience to drought.

Stone pine (Pinus pinea) produces a highly demanded dried fruit, the pine nuts; Tuber borchii produces a well-known commercialized truffle. Thus, the co-culture of P. pinea and T. borchii may represents an interesting productive option. This work evaluated the effect of T. borchii inoculation on stone pine tree growth, survival, health, entry into cone production, and mycorrhization level during the first 3 years after establishment along a 2000 km gradient in Chile. We tested two treatments (inoculation and non-inoculation) in a multi-environment trial (MET) involving seven sites along Chile. Plantations were repeatedly measured during 3 years after establishment. In all environments, inoculation enhanced tree height, root collar diameter (RCD) and crown diameter (6.9, 10 and 8.3% higher for inoculated than for non-inoculated plants). Vigor was also favored (14.1% more vigorous trees). Stone pine performance was enhanced in all sites, but mainly in those with extreme environmental conditions. T. borchii mycorrhizae were abundant (over 60% of mycorrhized root apexes) 3 years after establishment. The truffle-host plant combination was not previously evaluated in Chile. The results showed high root colonization levels and the persistence of mycorrhization 3 years after establishment, and an enhanced effect of mycorrhization on tree growth and vigor under different soil and climate conditions, confirming the high plasticity of both species.

Subalpine forests that historically burned every 100–300 yr are expected to burn more frequently as climate warms, perhaps before trees reach reproductive maturity or produce a serotinous seedbank. Tree regeneration after short-interval (<30-yr) high-severity fire will increasingly rely on seed dispersal from unburned trees, but how dispersal varies with age and structure of surrounding forest is poorly understood. We studied wind dispersal of three conifers (Picea engelmannii, Abies lasiocarpa, and Pinus contorta var. latifolia, which can be serotinous and nonserotinous) after a stand-replacing fire that burned young (≤30 yr) and older (>100 yr) P. contorta forest in Grand Teton National Park (Wyoming, USA). We asked how propagule pressure varied with time since last fire, how seed delivery into burned forest varied with age and structure of live forest edges, what variables explained seed delivery into burned forest, and how spatial patterns of delivery across the burned area could vary with alternate patterns of surrounding live forest age. Seeds were collected in traps along 100-m transects (n = 18) extending from live forest edges of varying age (18, 30, and >100 yr) into areas of recent (2-yr) high-severity fire, and along transects in live forests to measure propagule pressure. Propagule pressure was low in 18-yr-old stands (~8 seeds/m²) and similarly greater in 30- and 100-yr-old stands (~32 seeds/m²). Mean dispersal distance was lowest from 18-yr-old edges and greatest from >100-yr-old edges. Seed delivery into burned forest declined with increasing distance and increased with height of trees at live forest edges, and was consistently higher for P. contorta than for other conifers. Empirical dispersal kernels revealed that seed delivery from 18-yr-old edges was very low (≤2.4 seeds/m²) and concentrated within 10 m of the live edge, whereas seed delivery from >100-yr-old edges was >4.9 seeds/m² out to 80 m. When extrapolated throughout the burned landscape, estimated seed delivery was low (<49,400 seeds/ha) in >70% of areas that burned in short-interval fire (<30 yr). As fire frequency increases, immaturity risk will be compounded in short-interval fires because seed dispersal from surrounding young trees is limited.

The influence of the local environmental conditions on invasive small spruce bark beetle Ips amitinus (Eichhoff) (Coleoptera: Curculionidae: Scolytinae) populations and on the vitality of Siberian stone pine (Pinus sibirica Du Tour) trees has been investigated. The field measurements were carried out in the Siberian stone pine forests near settlements (semi-artificial high-productive stands) of Tomsk region damaged by I. amitinus outbreaks. On eleven plots, the population characteristics and reproductive success of the bark beetle, Siberian stone pine vitality, attributes of the stand (e.g, age, height, and diameter), presence of rot and canker diseases, phytosociological characteristics (as a proxy of soil moisture and fertility), and dendrochronological features (as a proxy of weather impact) were measured. By principal component analysis for mixed data and by linear regression with or without mixed effects, we have analyzed the structure of relationships between the measured features. It was found that I. amitinus populations and Siberian stone pine vitality during the bark beetle outbreak were influenced by several parallel processes. The long-term decrease in the resistance of Siberian stone pine stands is provoked by aging and low soil fertility. This decrease leads both to more frequent small spruce bark beetles attacks and to higher attack density (nuptial chambers per dm–2). Another cause of an increase in attack density is high variance of Siberian stone pine height along with short-term stresses triggered by a deficit of precipitation early in the growing season. In such a situation, the number of suitable microstations of I. amitinus, i.e., stressed trees with a well-lit crown, increased. The abundance of the trees attacked by the small spruce bark beetle (m3 ha–1) is positively related to the total volume of Siberian stone pine per hectare. The review of the literature about natural Siberian stone pine forests in the taiga zone allow us to propose a low likelihood of I. amitinus outbreaks under these conditions. Such forests in the taiga have a lot of differences from P. sibirica semi-artificial forests near settlements, and these differences are unfavorable for the small spruce bark beetle. In the native south- and middle-taiga forests, the risk of bark beetle outbreaks is high with the correspondence of several criteria. First, the Siberian stone pine stands must be old-grown with a high variance of age. This is possible only if the stand is undisturbed. Second, the soil must be moderately dry. The possible exception is forests under acute stress, like defoliation or fire. I. amitinus may impact the undisturbed Siberian stone pine stands as a consequence of migration from such stressed forests.