查看更多>>摘要：? 2022 Elsevier B.V.Induced defences in conifers are an effective strategy that allows individuals to increase resistance against pests and pathogens by optimizing associated costs. Studies exploring inducibility of defences in conifers have usually been conducted in young individuals (i.e., seedlings and saplings) whereby effects were addressed within weeks or months after induction, limiting knowledge and generalization of long-term patterns in mature individuals growing under natural conditions. In addition, few studies have explored how plasticity and genetic differentiation among populations may affect the inducibility of defences in mature trees. We took advantage of two long-term Pinus pinaster common gardens to explore the interactive and independent contribution of genetic differentiation (i.e., variation among populations) and the environment (i.e., plasticity between sites) as drivers of variation in short-term, long-term and systemic inducibility of chemical defences (resin flow, non-volatile resin, phenolics) in response to simulated herbivore damage associated with jasmonate signalling. We provide evidence that the external application of methyl jasmonate increased the production of resin based defences in mature P. pinaster trees for at least two years after its application. We found that inducibility of defences did not differ among populations, but was rather contingent on local environmental conditions. Systemic effects of methyl jasmonate were also observed and suggest that induced responses likely involve complex within-individual reallocation of chemical defences. Our results contribute to better understanding of the ecological and evolutionary relevance of induced defence strategies in conifers and have important implications for integrating forest management practices aiming to improve forest health and resistance to pests and pathogens.
查看更多>>摘要：? 2022 Elsevier B.V.The Atlantic Forest of the southern Brazilian highlands is a biocultural mosaic of Araucaria Forest and grasslands. Despite adverse impacts on biodiversity, extensive areas are being afforested with non-native pine (Pinus spp.), triggering forest succession on areas that were previously native grasslands. The long-term effects of afforestation with these non-native trees for biodiversity conservation are still unknown. Here, we assess this issue by comparing the fruit-feeding butterfly assemblages in young (20 year) and old (70 year) pine plots with nearby native Araucaria Forest. Abundance and richness of butterflies were positively correlated with temperature and mean humidity only in the native forest. Abiotic conditions differed between vegetation types: there was more sunlight, and was warmer and drier in the pine afforestation plots than in the Araucaria Forest. Butterfly species composition was similar between young and old pine plots, but distinct from the native Araucaria Forest. Butterfly species abundances in native forests were more evenly distributed than in afforestation sites. In these pine sites, assemblages were dominated by small, grass-feeding satyrines, whereas old pine sites had more liana-feeding biblidines, and the Araucaria Forest had more large-sized bamboo-feeding species. Our results indicate that even after 70 years of succession a non-native pine afforestation cannot support a butterfly assemblage as that found in the neighboring preserved forest. Moreover, threatened grassland specialist species have been locally extinct after only 20 years of pine afforestation. The evidence gathered here points against the use of silviculture with non-native trees in these biocultural mosaic landscapes.
查看更多>>摘要：? 2022Tree growth is a physio-ecological phenomena of high interest among researchers across disciplines. Observing changes in tree characteristics has conventionally required either repeated measurements of the characteristics of living trees, retrospective measurements of destructively sampled trees, or modelling. The use of close-range sensing techniques such as terrestrial laser scanning (TLS) has enabled non-destructive approaches to reconstruct the three-dimensional (3D) structure of trees and tree communities in space and time. This study aims at improving the understanding of tree allometry in general and interactions between tree growth and its neighbourhood in particular by using two-date point clouds. We investigated how variation in the increments in basal area at the breast height (Δg1.3), basal area at height corresponding to 60% of tree height (Δg06h), and volume of the stem section below 50% of tree height (Δv05h) can be explained with TLS point cloud-based attributes characterizing the spatiotemporal structure of a tree crown and crown neighbourhood, entailing the competitive status of a tree. The analyses were based on 218 trees on 16 sample plots whose 3D characteristics were obtained at the beginning (2014, T1) and at the end of the monitoring period (2019, T2) from multi-scan TLS point clouds using automatic point cloud processing methods. The results of this study showed that, within certain tree communities, strong relationships (|r| > 0.8) were observed between increments in the stem dimensions and the attributes characterizing crown structure and competition. Most often, attributes characterizing the competitive status of a tree, and the crown structure at T1, were the most important attributes to explain variation in the increments of stem dimensions. Linear mixed-effect modelling showed that single attributes could explain up to 35–60% of the observed variation in Δg1.3, Δg06h and Δv05h, depending on the tree species. This tree-level evidence of the allometric relationship between stem growth and crown dynamics can further be used to justify landscape-level analyses based on airborne remote sensing technologies to monitor stem growth through the structure and development of crown structure. This study contributes to the existing knowledge by showing that laser-based close-range sensing is a feasible technology to provide 3D characterization of stem and crown structure, enabling one to quantify structural changes and the competitive status of trees for improved understanding of the underlying growth processes.
查看更多>>摘要：? 2022 Elsevier B.V.The effects of abiotic and biotic factors on plant stoichiometry have been widely reported at the global scale. However, stand age has not always been considered and its effect on stoichiometry showed large uncertainties at the global scale. In this study, we examined the role of stand age in leaf N:P, and observed the general pattern of leaf N:P for global planted forests across age gradients through the compilation and analysis of published data from individual studies. We found that stand age, together with life form and climatic variables, strongly affected leaf N:P. This result indicates that stand age is an indispensable underlying mechanism on stoichiometry. Leaf N:P increased with stand age for all planted forests pooled together, revealing the existence of the general pattern in leaf stoichiometry for planted forests across age gradients. Leaf N:P exhibited no trend in evergreen trees, but an increasing trend was obtained in deciduous trees along age sequences. Meanwhile, leaf N:P rose with stand age for planted forests in humid subtropical regions, but it did not vary in dry temperate regions. Our results reveal that the effects of age on tree stoichiometry cannot be neglected. These age-related patterns of stoichiometry indicated that global planted forests changed from N limitation to P limitation with increasing stand age, particularly for deciduous planted forests and in planted forests in humid regions. The study highlights the importance of considering stand age when exploring nutrient patterns in planted forests, which contributes to improving the plant stoichiometry theory and offers guidance for the nutrient management of planted forests at regional and global scales.
查看更多>>摘要：? 2022The distinction of changes in herb layer communities related to the dynamics of the forest stand and / or the regimes of forest management from that managed by random or non-random, global environmental disturbance, would allow for more precise recognition, and counteracting the effects of contemporary threats. In this work, we integrated databases of long-term vegetation records from tree research periods and archival forest inventory datasets to examine the changes in forest herb layer communities over time intervals of up to five decades across the major mountain forest habitat in the Polish Eastern Carpathians (managed semi-natural fertile mountain beech forests). Over the past half – century, these forests have been gradually aging. In this work, based on long-term datasets, we found clear differences in herb layer composition and diversity between beech forest developmental stages. Herb layer characteristics were compared between three forest stages, classified as broadly defined Growing (G), Optimum (O), and Terminal (T) stage. Stands in the Growing stage had the largest stocking, as well as the smallest volume, tree DBH and high, and age. Stands in the Optimum stage had the largest volume and tree height. Stands in the Terminal stage had the smallest stocking and the largest tree DBH and age. Although in the Optimum stage, the lowest beta diversity was recorded, this stage provided the best habitat conditions for species important from a beech forest's conservation status point of view (e.g. diagnostic for beech forests, ancient forest species). Moreover, in this stage the highest alpha diversity was recorded. We found that in gradually aging Carpathian forests the changes in the structure of stands play a significant role in controlling herb vegetation composition and diversity. The cause was the dominance of single developmental stages during temporally synchronous forest development in the studied region of the Carpathians over the past half – century (i.e. G in the 1970s, O in the 2000s and T in 2010s). Our results have important implications for forest management and biodiversity conservation. In particular, forest managers should ensure the creation and maintenance of forest landscapes with a more even share of development stages (mosaic of different age-classes). Additionally, this age differentiation of stands should be planned not on a local scale but on a regional scale.
查看更多>>摘要：? 2022 The AuthorsLarge, severe wildfires continue to burn in frequent-fire adapted forests but the mechanisms that contribute to them and their predictability are important questions. Using a combination of ground based and remotely sensed data we analyzed the behavior and patterns of the 2020 Creek Fire where drought and bark beetles had previously created substantial levels of tree mortality in the southern Sierra Nevada. We found that dead biomass and live tree densities were the most important variables predicting fire severity; high severity fire encompassed 41% of the area and the largest high severity patch (19,592 ha) comprised 13% of total area burned. Areas with the highest amounts of dead biomass and live tree densities were also positively related to high severity fire patch size indicating that larger, more homogenous conditions of this forest characteristic resulted in adverse, landscape-scale fire effects. The first two days of the Creek Fire were abnormally hot and dry but weather during the days of the greatest fire growth was largely within the normal range of variation for that time of year with one day with lower windspeeds. From September 5 to 8th the fire burned almost 50% of its entire area and fire intensity patterns inferred from remotely sensed brightness-temperature data were typical except on September 6th when heat increased towards the interior of the fire. Not only was the greatest heat concentrated away from the fire perimeter, but a significant amount of heat was still being generated within the fire perimeter from the previous day. This is a classic pattern for a mass fire and the high amount of dead biomass created from the drought and bark beetles along with high live tree densities were critical factors in developing mass fire behavior. Operational fire behavior models were not able to predict this behavior largely because they do not include post-frontal combustion and fire-atmosphere interactions. An important question regarding this mass fire is if the tree mortality event that preceded it could have been avoided or reduced or was it within the natural range of variation for these forests? We found that the mortality episode was outside of historical analogs and was exacerbated by past management decisions. The Creek Fire shows us how vulnerable of our current frequent-fire forest conditions are to suffering high tree mortality and offering fuel conditions capable of generating mass fires from which future forest recovery is questionable because of type conversion and probable reoccurring high severity fire.
查看更多>>摘要：? 2022 Elsevier B.V.Long-term studies are key to understanding the dynamics of managed forests, especially as related to timber supplies. We evaluated 20 years of recovery of pre-harvest structure, biomass, and timber stocks of a Subtropical Atlantic Forest in Argentina subjected to either conventional selective logging (CL = ～15 m3 ha?1) or reduced-impact logging (RIL = ～11 m3 ha?1); we also monitored the dynamics of interspersed plots of unlogged forest (Control). All trees ≥10 cm DBH were measured before and at variable intervals for 20 years post-logging; the results are presented for all stems and for only those of species that provide commercial timber. After logging, basal areas and volume of all stems increased two-times faster after CL than after RIL, whereas biomass increments were similar between logged treatments. In contrast, commercial timber tree stocking did not recover regardless of the harvesting system applied. Mortality rates were high in both CL and RIL plots but also in unlogged Control plots (1.6–3.6 % year?1). The failure of timber stocks to recover was apparently due to high tree mortality rates coupled with the proliferation of understory bamboos. Alternative silvicultural methods are clearly needed to avoid degrading the remaining species-rich Subtropical Atlantic Forest.
查看更多>>摘要：? 2022 Elsevier B.V.Crown size is strongly correlated with tree growth. Crown width (CW) is affected by tree size, site quality and competition, but most CW models do not quantify the effects of stand structure, intra and inter-specific competition, especially in mixed-species forest. In this study, we quantified these effects by developing nonlinear mixed effects CW model for natural spruce-fir-broadleaf mixed forest in northeast China. Data from a total of 10,086 individual trees in the 192 plots were used for the purpose. Plot-level random effect parameters accounting for stand heterogeneity and randomness were included in the CW model. The results showed the optimal model could explain 63% of the variation of CW with no substantial residual heterogeneity. Gini coefficient by tree size (GC) was tested as a predictor denoting tree size inequality or stand structural diversity in the model. Among all predictor variables, diameter at breast height (DBH), GC, the cumulative basal area of trees larger than the subject tree (BAL) including intra-specific (BALintra) and inter-specific (BALinter) competition, and height to DBH ratio (HDR) contributed most significantly to the model. Tree CW increased with the increasing GC, but decreased with the increasing HDR, BALintra and BALinter. The effect of intra-specific competition on CW was greater than that of inter-specific competition. Our study highlighted the importance of tree size inequality in tree CW modelling for mixed forest.
查看更多>>摘要：? 2022 Elsevier B.V.In this study, we aimed to use tree-ring based fire reconstruction to understand the spatiotemporal patterns of past fires in different climate types of western Anatolia. We collected fire scarred wood samples from living trees as wedges and remnant woods from ten sites along a transect that represents a continental to Mediterranean climate gradient. We determined fire years and assigned seasonality of fires based on the intraring position of the fire scars. We calculated fire statistics and analysed fire-climate relationships. Breakpoints in our Anatolian regional fire chronology were estimated to determine the regime shifts. A decrease in fire frequency was recorded at most of the sites after the end of the 19th and the beginning of the 20th century. We observed two critical fire regime shift periods. The period between 1853 and 1934 is characterized by highly frequent (a total of 82 fires) and simultaneous fires occurring in multiple sites and this period overlapped with the longest and most severe drought period of the past 550 years. The fire frequency decline after 1934 coincided with the period of the first forest protection law in 1937. Dry, as well as prior wet conditions were main drivers of fires in the black pine forests in western Anatolia. We observed a decrease in fire frequency in the late 19th and early 20th centuries due to fire suppression activities. Continued fire suppression activities may cause fuel accumulation and pose a risk for more intense fires and thus a paradox for forests in the future. Based on future climate projections, we will face prolonged fire seasons as a consequence of increasing drought frequency, which may shift the fire regime from surface to crown fires with the accumulation of combustible material in the understory in black pine forests.
查看更多>>摘要：? 2022 Elsevier B.V.Disease combined with drought poses an important threat to plant survival, often compromising success in the restoration of riparian forests. Thus, understanding how biotic and abiotic stressors may affect plant survival and growth performance can greatly increase the success of ecosystem management strategies. The purpose of this study was to understand how two plant species, often used together in restoration of riparian ecosystems but with different ecological preferences, would respond to infection by each of two Phytophthora species in Mediterranean-climate regions, in the absence or presence of a simulated drought. Saplings of the drought resistant species Frangula californica, and of the riparian species Alnus rhombifolia were each inoculated in a greenhouse experiment with one of two Phytophthora species and exposed to two watering regimes. Saplings were allocated to six treatments, combining three levels of pathogen inoculation (no inoculation, inoculation with Phytophthora cactorum and inoculation with Phytophthora crassamura), and two watering regimes (well-watered and drought). The response of A. rhombifolia and F. californica saplings was assessed through the observation of health metrics and morphological parameters. Results showed that both P. cactorum and P. crassamura are important pathogens of A. rhombifolia and F. californica. As expected, drought conditions were the main cause of decline and mortality in A. rhombifolia saplings, while water availability was a facilitator of P. cactorum infection in F. californica saplings. We observed two seemingly contrasting results in A. rhombifolia saplings: infection by Phytophthora spp. decreased survival in well-watered plants, while the opposite was recorded for saplings under drought conditions whose survival increased in Phytophthora-inoculated treatments. Saplings of F. californica were able to cope with drought conditions, even when infected by Phytophthora species and water availability increased root infection and decreased sapling survival. We conclude that the continued use of F. californica and A. rhombifolia in sites infested by Phytophthora species can be beneficial in restoration, if appropriate management actions are adopted. Such actions include avoiding the planting of F. californica saplings in areas subjected to water accumulation, and ensuring that A. rhombifolia is planted in areas where drought stress is minimal and where Phytophthora species are possibly absent. We also emphasize the importance of ensuring that plant stock used in revegetation projects is not infected by Phytophthora species, and that biotic and abiotic risks are assessed prior to restoration actions.
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