Besides competition, positive interactions also play an important role in shaping the social structure of mixed‐species bird flocks. This study aimed to illuminate the interspecific interactions of ...competition and facilitation in mixed‐species bird flocks. We recorded the foraging behavior and microhabitat use of flocking species in montane coniferous forests of Taiwan under different social contexts. Foraging niche breadth and niche‐overlap with other flocking species were compared between individuals inside and outside of mixed flocks. For the three microhabitat variables (foraging locations, vertical strata and horizontal strata), relationships between niche‐overlaps of heterospecific pairs of these flocking species and their corresponding interspecific associations were determined using a simple linear regression. While in mixed flocks, two understory species, Taiwan fulvetta Fulvetta formosana and yellowish‐bellied bush warbler Horornis acanthizoides, shifted their foraging from shrubs upwards into coniferous trees. Meanwhile, flamecrests Regulus goodfellowi moved downwards vertically within the canopy, and black‐throated tits Aegithalos concinnus spread out horizontally along branches. In addition, flamecrests applied many more sally‐hovers inside of mixed flocks than outside of flocks. All four species are insectivores which might find it more difficult to obtain sufficient food during the colder winters when food resources become scarcer. Therefore, they may be using the increased vigilance afforded by the flock to expand their foraging niches and thus to increase their foraging opportunities inside mixed flocks. Furthermore, niche‐overlaps of heterospecific pairs of the 11 common flocking species were positively correlated with their corresponding interspecific associations on all three microhabitat variables. These results indicate that a greater foraging niche‐overlap between two flocking species would result in higher coexistence of the two species in mixed flocks. Consequently, facilitative interactions occurred in these mixed‐species flocks in addition to competitive interactions.
1. Mixed conifer-hardwood forests can be more productive than pure forests and they are increasingly considered as ecosystems that could provide adaptation strategies in the face of global change. ...However, the combined effects of tree-to-tree competition, rising atmospheric CO₂ concentrations and climate on such mixtures remain poorly characterized and understood. 2. To fill this research gap, we reconstructed 34-year series (1980-2013) of growth (basal area increment, BAI) and intrinsic water-use efficiency (iWUE) of Scots pine (Pinus sylvestris L.)-European beech (Fagus sylvatica L.) mixed stands at two climatically contrasting sites located in the southwestern Pyrenees. We also gathered data on tree-to-tree competition and climate variables in order to test the hypotheses that (1) radial growth will be greater when exposed to inter- than to intraspecific competition, that is, when species complementarity occurs and (2) enhanced iWUE could be linked to improved stem radial growth. 3. Growth of both species was reduced when intraspecific competition increased. Species complementarity was linked to improved growth of Scots pine at the continental site, while competition overrode any complementarity advantage at the drought-prone Mediterranean site. Beech growth did not show any significant response to pine admixture likely due to shade tolerance and the highly competitive nature of this species. Increasing interspecific competition drove recent iWUE changes, which increased in Scots pine but decreased in European beech. The iWUE enhancement did not involve any growth improvement in Scots pine. However, the positive BAI-iWUE relationship found for beech suggests an enhanced beech growth in drought-prone sites due to improved water use. 4. Synthesis. Complementarity may enhance growth in mixed forests. However, water scarcity can constrict light-related complementarity for shade intolerant species (Scots pine) in drought-prone sites. Basal area increment-intrinsic water-use efficiency relationships were negative for Scots pine and positive for European beech. These contrasting behaviours have got implications for coping with the expected increasing drought events in Scots pine-European beech mixtures located near the ecological limit of the two species. Complementarity effects between tree species should be considered to avoid overestimating the degree of future carbon uptake by mixed conifer-broadleaf forests.
In this study, we automate tree species classification and mapping using field-based training data, high spatial resolution airborne hyperspectral imagery, and a convolutional neural network ...classifier (CNN). We tested our methods by identifying seven dominant trees species as well as dead standing trees in a mixed-conifer forest in the Southern Sierra Nevada Mountains, CA (USA) using training, validation, and testing datasets composed of spatially-explicit transects and plots sampled across a single strip of imaging spectroscopy. We also used a three-band ‘Red-Green-Blue’ pseudo true-color subset of the hyperspectral imagery strip to test the classification accuracy of a CNN model without the additional non-visible spectral data provided in the hyperspectral imagery. Our classifier is pixel-based rather than object based, although we use three-dimensional structural information from airborne Light Detection and Ranging (LiDAR) to identify trees (points > 5 m above the ground) and the classifier was applied to image pixels that were thus identified as tree crowns. By training a CNN classifier using field data and hyperspectral imagery, we were able to accurately identify tree species and predict their distribution, as well as the distribution of tree mortality, across the landscape. Using a window size of 15 pixels and eight hidden convolutional layers, a CNN model classified the correct species of 713 individual trees from hyperspectral imagery with an average F-score of 0.87 and F-scores ranging from 0.67–0.95 depending on species. The CNN classification model performance increased from a combined F-score of 0.64 for the Red-Green-Blue model to a combined F-score of 0.87 for the hyperspectral model. The hyperspectral CNN model captures the species composition changes across ~700 meters (1935 to 2630 m) of elevation from a lower-elevation mixed oak conifer forest to a higher-elevation fir-dominated coniferous forest. High resolution tree species maps can support forest ecosystem monitoring and management, and identifying dead trees aids landscape assessment of forest mortality resulting from drought, insects and pathogens. We publicly provide our code to apply deep learning classifiers to tree species identification from geospatial imagery and field training data.
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.
Bidirectional reflectance distribution function (BRDF) is a distribution of directional reflectance for varying viewing and solar geometry. BRDF of a target is important in processing optical image ...data from satellites, because the observed radiance has great dependency on the direction (or angle) of reflection. It is desirable that the BRDF of any targets is characterized for rigorous BRDF correction of satellite data, since the sun-sensor-target geometry of satellites often varies in a very limited range, limiting the full characterization of target BRDF. This study provides BRDF data set for typical coniferous forests in Korea, by using a multispectral camera onboard a unmanned aerial vehicle (UAV). By operating the UAV in a goniometer-like way, reflectance data for all possible viewing zenith and azimuth angles were obtained. The BRDF data collected from the 3 campaigns in different days were visualized in a polar-coordinate, together with the standard deviation calculated for each zenith/azimuth bin made in 1˚ interval. The data sets demonstrated reflectance distribution over the wide range of angles with sound data quality, suggesting commonly known BRDF characteristics for forests such as strong back-scattering and hot spot area in the viewing zenith angle near the solar zenith angle. This data set is expected to be utilized for the BRDF correction of various satellites including Agro-forest satellite of Korea which is to be launched in 2025 that has similar spectral bands with the ones used in this study.
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.
Key message
There was an inconsistent positive correlation between tree ring width and NDVI in the Tianshan Mountains, and this correlation gradually weakened from west to east and decreased with ...increasing elevation.
Tree ring width and the normalized difference vegetation index (NDVI) are two effective indicators used to monitor changes in forest dynamics. Most studies focus on the relationship between tree ring width and regional NDVI in the mountainous areas of arid regions, failing to reflect the relationship between forest radial growth and forest canopy activities. In this paper, four study areas were selected ranging from west to east on the northern slope of the Tianshan Mountains in China. Tree cores of
Picea schrenkiana
were collected at three elevations in each study area, and NDVI values were extracted for the forest cover at each location. Emphasis was placed on the relationship between the tree ring width and NDVI values of montane evergreen coniferous forests in an arid region in the period 2000–2012. There was an inconsistent positive correlation between tree ring width and NDVI in the Tianshan Mountains, and the relationship became increasingly weak from west to east and decreased with increasing elevation. The varied forest growth and its response to climatic factors as a result of the different environmental conditions present in arid mountain regions may be the underlying reason for the inconsistency between the tree ring width and NDVI of forests. Drought stress may be the major driving factor of the positive correlation between the tree ring width and NDVI of montane evergreen coniferous forests in arid regions. This result may be useful for integrating tree ring width and NDVI to study the ecology of montane evergreen coniferous forests in arid regions.
SUMMARY
Spruces (Picea spp.) are coniferous trees widespread in boreal and mountainous forests of the northern hemisphere, with large economic significance and enormous contributions to global carbon ...sequestration. Spruces harbor very large genomes with high repetitiveness, hampering their comparative analysis. Here, we present and compare the genomes of four different North American spruces: the genome assemblies for Engelmann spruce (Picea engelmannii) and Sitka spruce (Picea sitchensis) together with improved and more contiguous genome assemblies for white spruce (Picea glauca) and for a naturally occurring introgress of these three species known as interior spruce (P. engelmannii × glauca × sitchensis). The genomes were structurally similar, and a large part of scaffolds could be anchored to a genetic map. The composition of the interior spruce genome indicated asymmetric contributions from the three ancestral genomes. Phylogenetic analysis of the nuclear and organelle genomes revealed a topology indicative of ancient reticulation. Different patterns of expansion of gene families among genomes were observed and related with presumed diversifying ecological adaptations. We identified rapidly evolving genes that harbored high rates of non‐synonymous polymorphisms relative to synonymous ones, indicative of positive selection and its hitchhiking effects. These gene sets were mostly distinct between the genomes of ecologically contrasted species, and signatures of convergent balancing selection were detected. Stress and stimulus response was identified as the most frequent function assigned to expanding gene families and rapidly evolving genes. These two aspects of genomic evolution were complementary in their contribution to divergent evolution of presumed adaptive nature. These more contiguous spruce giga‐genome sequences should strengthen our understanding of conifer genome structure and evolution, as their comparison offers clues into the genetic basis of adaptation and ecology of conifers at the genomic level. They will also provide tools to better monitor natural genetic diversity and improve the management of conifer forests. The genomes of four closely related North American spruces indicate that their high similarity at the morphological level is paralleled by the high conservation of their physical genome structure. Yet, the evidence of divergent evolution is apparent in their rapidly evolving genomes, supported by differential expansion of key gene families and large sets of genes under positive selection, largely in relation to stimulus and environmental stress response.
Significance Statement
The genomes of four closely related North American spruces indicate that their high similarity at the morphological level is paralleled by the high conservation of their physical genome structure. Yet, the evidence of divergent evolution is apparent in their rapidly evolving genomes, supported by differential expansion of key gene families and large sets of genes under positive selection, largely in relation to stimulus and environmental stress response.
Interactions between wind and trees control energy exchanges between the atmosphere and forest canopies. This energy exchange can lead to the widespread damage of trees, and wind is a key disturbance ...agent in many of the world's forests. However, most research on this topic has focused on conifer plantations, where risk management is economically important, rather than broadleaf forests, which dominate the forest carbon cycle. This study brings together tree motion time-series data to systematically evaluate the factors influencing tree responses to wind loading, including data from both broadleaf and coniferous trees in forests and open environments.
Summary
Pinus sylvestris (Scots pine) is the most widespread coniferous tree in the boreal forests of Eurasia, with major economic and ecological importance. However, its large and repetitive genome ...presents a challenge for conducting genome‐wide analyses such as association studies, genetic mapping and genomic selection. We present a new 50K single‐nucleotide polymorphism (SNP) genotyping array for Scots pine research, breeding and other applications. To select the SNP set, we first genotyped 480 Scots pine samples on a 407 540 SNP screening array and identified 47 712 high‐quality SNPs for the final array (called ‘PiSy50k’). Here, we provide details of the design and testing, as well as allele frequency estimates from the discovery panel, functional annotation, tissue‐specific expression patterns and expression level information for the SNPs or corresponding genes, when available. We validated the performance of the PiSy50k array using samples from Finland and Scotland. Overall, 39 678 (83.2%) SNPs showed low error rates (mean = 0.9%). Relatedness estimates based on array genotypes were consistent with the expected pedigrees, and the level of Mendelian error was negligible. In addition, array genotypes successfully discriminate between Scots pine populations of Finnish and Scottish origins. The PiSy50k SNP array will be a valuable tool for a wide variety of future genetic studies and forestry applications.
Significance Statement
In the genomic era, the gigantic size of conifer genomes still hampers advances in a wide range of fields of applied and fundamental sciences. To facilitate Scots pine genetic research and modern breeding methods, we developed a 50K SNP genotyping array and provide information that links the array markers to genetic diversity and gene expression levels across tissues.
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