Improve Tree Growth Research Articles

Forest management positively reshapes the phyllosphere bacterial community and improves community stability

Research has shown that forest management can improve the post-drought growth and resilience of Qinghai spruce in the eastern Qilian Mountains, located on the northeastern Tibetan Plateau. However, the impact of such management on the tree-associated phyllosphere microbiome is not yet fully understood. This study provides new evidence of positive forest management effects on the phyllosphere microbiome after extreme drought, from the perspectives of community diversity, structure, network inference, keystone species, and assembly processes. In managed Qinghai spruce forest, the α-diversity of the phyllosphere bacterial communities increased, whereas the β-diversity decreased. In addition, the phyllosphere bacterial community became more stable and resistant, yet less complex, following forest management. Keystone species inferred from a bacterial network also changed under forest management. Furthermore, forest management mediated changes in community assembly processes, intensifying the influence of determinacy, while diminishing that of stochasticity. These findings support the hypothesis that management can re-assemble the phyllosphere bacterial community, enhance community stability, and ultimately improve tree growth. Overall, the study highlights the importance of forest management on the phyllosphere microbiome and furnishes new insights into forest conservation from the perspective of managing microbial processes and effects.

Genomic selection for growth characteristics in Korean red pine (Pinus densiflora Seibold & Zucc.).

Traditionally, selective breeding has been used to improve tree growth. However, traditional selection methods are time-consuming and limit annual genetic gain. Genomic selection (GS) offers an alternative to progeny testing by estimating the genotype-based breeding values of individuals based on genomic information using molecular markers. In the present study, we introduced GS to an open-pollinated breeding population of Korean red pine (Pinus densiflora), which is in high demand in South Korea, to shorten the breeding cycle. We compared the prediction accuracies of GS for growth characteristics (diameter at breast height [DBH], height, straightness, and volume) in Korean red pines under various conditions (marker set, model, and training set) and evaluated the selection efficiency of GS compared to traditional selection methods. Training the GS model to include individuals from various environments using genomic best linear unbiased prediction (GBLUP) and markers with a minor allele frequency larger than 0.05 was effective. The optimized model had an accuracy of 0.164-0.498 and a predictive ability of 0.018-0.441. The predictive ability of GBLUP against that of additive best linear unbiased prediction (ABLUP) was 0.86-5.10, and against the square root of heritability was 0.19-0.76, indicating that GS for Korean red pine was as efficient as in previous studies on forest trees. Moreover, the response to GS was higher than that to traditional selection regarding the annual genetic gain. Therefore, we conclude that the trained GS model is more effective than the traditional breeding methods for Korean red pines. We anticipate that the next generation of trees selected by GS will lay the foundation for the accelerated breeding of Korean red pine.

Nutrient Management Impacts on HLB-affected ‘Valencia’ Citrus Tree Growth, Fruit Yield, and Postharvest Fruit Quality

Since the first occurrence of Huanglongbing (HLB) in the Florida commercial citrus industry in 2004, fruit yield and yield components of HLB-affected citrus have declined in endemically affected citrus tree groves. Optimal fertilization is thus critical for improving tree performance because nutrients are vital for tree growth and development, and play a significant role in tree disease resistance against various biotic and abiotic stresses. The objective of the current study was to determine whether leaf nutrient concentration, tree growth, yield, and postharvest quality of HLB-affected citrus trees were improved by the split application of nutrients. The four micronutrient application rates were used as fixed factors and the three nitrogen (N) rates were used as random factors for leaf nutrient analyses, tree growth, fruit yield, and postharvest analyses. Significant leaf manganese (Mn) and zinc (Zn) concentrations were detected when trees received foliar and soil-applied micronutrients regardless of the N rates. There was a strong regression analysis of leaf Mn and Zn nutrient concentration and nutrient rates with R2: 0.61 and 0.59, respectively. As a result, a significant leaf area index associated with foliar and soil-applied micronutrient rates had a positive correlation with leaf area index and soil pH with R2: 0.58 and 0.63 during the spring and summer seasons, respectively. Trees that received a moderate (224 kg·ha−1) N rate showed the least fruit decay percentage and total soluble solids (TSS) of 8% more than the lowest (168 kg·ha−1) and highest (280 kg·ha−1) N rates, even though fruit yield variations were barely detected as these micronutrients promoted vegetative growth. Moreover, the TSS to titratable acidity (TA) ratio of foliar and soil-applied micronutrient-treated trees showed 2% and 7% greater values than the foliar-only treated and control trees, respectively. Although micronutrients exacerbated stem-end rind breakdown (SERB), these nutrients significantly improved fruit storage when the fruits were stored for extended periods (8–11 weeks). Thus, moderate N rate, foliar (1×), and soil-applied (1×) micronutrient treatments improved tree growth, fruit postharvest, and fruit storage characteristics.

Humic Acid Improves the Resilience to Salinity Stress of Drip-Irrigated Mexican Lime Trees in Saline Clay Soils

Organic fertilization improves soil fertility and ameliorates the deleterious effects of accumulated salts in soil for sustainable agricultural production. This research was carried out on thirteen-year-old Mexican lime trees to study the effect of humic acid (HA), applied as soil (10, 20 or 30 mL·tree−1) and foliar (0.1 or 0.2%) applications, on soil fertility, tree growth, productivity and fruit quality. The experiment was conducted during the 2020 and 2021 seasons in a randomized complete block design of twelve treatments with three replicates with two trees each. Soil and foliar applications of HA were performed once and twice a month in Marsh, May and July, respectively. HA enhanced the soil’s N, P, K, Ca, Mg, Fe, Mn, Zn, Cu and B availability and microbial activity, in addition to improved tree growth, canopy size, leaf chlorophyll and nutrient contents with reduced proline levels. The total yield and number of fruit per tree were increased with increased HA levels. Fruit weight, juice and soluble solids were also increased. The best results were achieved with the combined soil (30 mL·tree−1) and foliar (0.2%) applications of HA, which indicated a great potential to alleviate the effects of salinity stress on Mexican lime growth and productivity.

Agroforestry systems with Khaya ivorensis provide improved tree growth and economic benefits to rural producers

Agroforestry systems with Khaya ivorensis provide improved tree growth and economic benefits to rural producers

Climate-mediated lodgepole pine tree growth response to thinning and fertilization in interior British Columbia

In the interior British Columbia, forest managers use thinning to reduce inter-tree competition and soil fertilization to enhance the soil nutrient status for improved tree growth. In recent decades, thinning has been promoted as a tool to increase tree resilience to drought. However, fertilization may modulate tree response to drought by altering biomass allocation from below- to above-ground depending on soil moisture availability. Here, we analyzed two long-term thinning and fertilization trials set up in fire-origin lodgepole pine (Pinus contorta Douglas ex Loudon) stands in two biogeoclimatic subzones in interior British Columbia that differ in soil productivity. Both trials featured untreated control, fertilized-only, thinned-only, and the combination of thinning and fertilization treatments. Drought Index (i.e., Standardized Precipitation Evapotranspiration Index, SPEI) was estimated for each site and used as a covariate in a linear mixed effects model to assess the impacts of thinning and fertilization on tree growth sensitivity to drought. Tree growth was increased by fertilization at the very dry-cold site, and more so in the thinned plot than the unthinned plot. The opposite effect of thinning on tree growth was found at the dry-cold relatively fertilized site. Tree growth was less sensitive to drought in the thinned-only plots at both sites. Our results, however, showed increased tree growth sensitivity to drought under the thinning and fertilization combination treatment at the less dry and relatively more productive site. The results suggest that the combination of thinning and fertilization can increase tree growth on very dry-cold and dry-cold sites and may be a suitable strategy to mitigate drought stress on tree productivity.

Do Distance-Dependent Competition Indices Contribute to Improve Diameter and Total Height Tree Growth Prediction in Juvenile Cork Oak Plantations?

Competition indices may improve tree growth modelling in high-density stands, found often in new cork oak plantations. Distance-dependent competition indices have hardly been considered for juvenile cork oak plantations since existing models were developed for low-density mature stands. This study aims at inspecting the potential of including distance-dependent competition indices into diameter at breast height (d) and total height (h) growth models for Quercus suber L., comparing several distance-dependent and distance-independent competition indices. Annual d and h growth were modelled with linear and non-linear growth functions, formulated as difference equations. Base models were initially fitted considering parameter estimates depending only on site index (S) and/or stand density (N). They were refitted, testing the significance of adding each competition index to the model parameters. Selected models included the best-performing distance-dependent or -independent competition indices as additional predictors. Best base d and h growth models showed a modelling efficiency (ef) of ef = 0.9833 and ef = 0.9900, respectively. Adding a distance-dependent competition index slightly improved growth models, to an ef = 0.9851 for d and ef = 0.9902 for h. Best distance-dependent competition indices slightly overperformed distance-independent ones in diameter growth models. Neither S nor N were included on best fitted models. If inter-tree competition is present in juvenile undebarked cork oak plantations, it does not yet strongly impact individual tree growth, which may diminish the importance of using, at this stage, more complex spatially explicit competition indices on predicting individual tree growth.

Evaluation of winter cover crop methods for management of flatheaded appletree borer (Coleoptera: Buprestidae).

Winter cover crops grown at the base of red maples (Acer rubrum L.) can reduce flatheaded appletree borer (Chrysobothris femorata Olivier; Coleoptera: Buprestidae; FAB) damage by both physically blocking preferred oviposition sites and altering the environment around them. However, cover crop competition negatively affects tree growth. To investigate long-term cover crop effects, trees grown with cover crop for 2 yr were transitioned to a standard herbicide practice. After 4 yr, trees in the initial 2 yr cover crop plots were 1 yr behind in growth compared to trees grown in bare rows for all 4 yr. Most growth reduction occurred in the first year following transplant. Additional borer losses of 1-2% per year were observed in production years 3 and 4. A second experiment answered 2 questions: Can killing the cover crop once it reaches maximal height protect trees from borers while also reducing competition and thereby increase tree growth? and Do herbicide applications increase borer attacks? In this experiment, red maples were grown with (i) a standard herbicide program, (ii) a mulch mat, (iii) a cover crop that was killed early, or (iv) a cover crop allowed to senesce naturally. Evaluations after 2 yr indicated early kill of the cover crop was not enough to improve tree growth. Further, trees in the early kill cover crop treatment had the most FAB attacks. Cover crops allowed to senesce naturally reduced FAB attacks in both studies; however, more work is needed to minimize disparities in tree growth during the initial year post-transplant and determine the causal relationship between herbicide use and borer attacks.

Response of forest productivity to changes in growth and fire regime due to climate change

Climate change is having complex impacts on the boreal forest, modulating both tree growth limiting factors and fire regime. However, these aspects are usually projected independently when estimating climate change effect on the boreal forest. Using a combination of three different methods, our goal is to assess the combined impact of changes in growth and fire regime due to climate change on the timber supply at the transitions from closed to open boreal coniferous forests in Québec, Canada. To identify the areas that are likely to be the most sensitive to climate change, we projected climate-induced impacts on growth and fire activity at three different time periods: 2011–2040 RCP 8.5 for low growth change and minimum fire activity, 2071–2100 RCP 4.5 for moderate growth change and medium fire activity, and 2071–2100 RCP 8.5 for high growth change and maximum fire activity. Our study shows the importance of incorporating fire in strategic forest management planning especially in a context of climate change. Under the most extreme scenarios, the negative impact of fire activity on productive area and total volume mostly offsets the positive effects of climate change via improved tree growth.

Interspecific plant-plant interactions increase the soil microbial network stability, shift keystone microbial taxa, and enhance their functions in mixed stands

Mixed forests can improve biomass productivity and soil quality compared with monospecific stands. Soil microbial communities are important for the functions and services in forests. However, the mechanisms by which mixed stands improve tree growth and soil nutrient availability remain unclear. Here, we assessed the soil microbial communities and soil characteristics of Betula albosinensis and Picea asperata growing alone (B and P), monospecific stands of B. albosinensis (BB) and P. asperata (PP), and a mixed stand of B. albosinensis with P. asperata (BP). Results showed that soil characteristics, composition and network of bacterial and fungal community differed significantly between tree species and stand types. Compared with monospecific stands, the mixed stand had 1) 65.36%, 57.51%, and 17.42% higher in SOC, TN, and SAP concentration, respectively; 2) higher diversity of soil bacterial and fungal communities; 3) better microbial networks and higher abundance of keystone bacterial and fungal taxa associated with nutrient decomposition and utilization. The results indicated that increasing of soil bacterial and fungal diversity, network stability and specialized keystone bacterial and fungal taxa by interspecific plant-plant interactions in mixed forests improve soil nutrient availability. This study highlights the importance of sustaining soil microbial taxa and ecological function in the soil nutrient cycling processes for better forest management.

Tree Growth and Vegetation Diversity in Northern Idaho Forest Water Reclamation Facilities

Forest water reclamation can improve tree growth and renovate municipal wastewater. Although there are indications that long-term application may exceed forest assimilation capacity, there is limited information on the long-term effects of reclaimed water application on coniferous ecosystems. The purpose of our study was to assess the impacts of prolonged reclaimed water application on forest growth responses and vegetation diversity. We examined the effects of reclaimed water at five water reuse facilities established between 1978 and 2013 in a four-decade time series. We collected tree cores and stem measurements to determine current and retrospective increments. We assessed plant diversity with vegetation surveys. The greatest diameter response observed for reclaimed water amendment compared to controls was 166.1% for western redcedar, while Douglas-fir increased up to 116.4% and ponderosa pine increased up to 100.6%. The minimum response observed was 30.3%. Current annual increments showed that the basal area and volume were significantly greater at long-established facilities for reclaimed-water-amended plots. The understory vegetation diversity declined with application time, while overstory vegetation diversity increased with application time. We conclude that reclaimed water can be a valuable resource to improve forest productivity, but continued application without stocking control may have detrimental effects on forest growth and vegetation diversity.

D2BOF-COVIDNet: A Framework of Deep Bayesian Optimization and Fusion-Assisted Optimal Deep Features for COVID-19 Classification Using Chest X-ray and MRI Scans.

In 2019, a corona virus disease (COVID-19) was detected in China that affected millions of people around the world. On 11 March 2020, the WHO declared this disease a pandemic. Currently, more than 200 countries in the world have been affected by this disease. The manual diagnosis of this disease using chest X-ray (CXR) images and magnetic resonance imaging (MRI) is time consuming and always requires an expert person; therefore, researchers introduced several computerized techniques using computer vision methods. The recent computerized techniques face some challenges, such as low contrast CTX images, the manual initialization of hyperparameters, and redundant features that mislead the classification accuracy. In this paper, we proposed a novel framework for COVID-19 classification using deep Bayesian optimization and improved canonical correlation analysis (ICCA). In this proposed framework, we initially performed data augmentation for better training of the selected deep models. After that, two pre-trained deep models were employed (ResNet50 and InceptionV3) and trained using transfer learning. The hyperparameters of both models were initialized through Bayesian optimization. Both trained models were utilized for feature extractions and fused using an ICCA-based approach. The fused features were further optimized using an improved tree growth optimization algorithm that finally was classified using a neural network classifier. The experimental process was conducted on five publically available datasets and achieved an accuracy of 99.6, 98.5, 99.9, 99.5, and 100%. The comparison with recent methods and t-test-based analysis showed the significance of this proposed framework.

Evaluation of citrus grove floor management strategies for water use efficiency and conservation

Perennial crops require water year-round, straining water resources, particularly in arid and semi-arid regions throught the world. Of those regions, the Lower Rio Grande Valley of Texas, USA, depends on flood irrigation to meet water demands of crops. Approximately 60–70% of citrus producers use flood irrigation to irrigate their groves, which is less efficient than other irrigation methods such as micro-jet or drip irrigation. Flood irrigation is to reduce cost, equipment, and energy required, and no land needs to be taken out of production to be used for holding ponds. Therefore, conservation practices that are adapted for flood irrigation are necessary in these areas where infrastructure is less conducive to other practices. Water use efficiency and potential water savings in different grove-floor management strategies, citrus tree growth, soil moisture, and irrigation volume were measured over the course of 3 years (from establishment to first harvest) in four different grove floor management strategies. These strategies, flat-bed no plastic mesh groundcover (traditional), flat-bed with plastic mesh groundcover, raised bed no groundcover, and raised bed with groundcover showed varying impacts on young citrus tree growth, soil moisture, and water savings over this study period. By the end of the study, 2.2% water savings (44,403 L over 4 years) were found in the flat bed with groundcover treatment compared to traditional grove floor management. This treatment also resulted in higher water use efficiency and greater initial growth of young citrus. Overall, the use of ground cover showed much potential for conserving water compared to traditional, uncovered flat bed management methods. These grove floor management practices can improve tree growth and establishment in young citrus trees in addition to improving water use efficiency. However, it is yet to see how these benefits will translate to more mature trees.

Does natural root grafting make trees better competitors?

Natural root grafts (anastomoses) are morphological unions formed between roots of different trees. Common root systems allow translocation of water, nutrients and photosynthesis products between grafted trees, affecting their growth and their physiology. As carbohydrates are redistributed among grafted trees, the formation of a common root system could reduce the negative effect of intraspecific competition for light or soil resources within stands. The aim of this study was to investigate the role of root grafting on intraspecific competition and growth of balsam fir Abies balsamea. We studied inter‐tree relationships in three natural balsam fir stands of the boreal forest of Quebec (Canada) that contained an average 36% of grafted trees. At each stand, ring width and basal area of trees were measured using dendrochronology techniques. We used mixed linear models to test the effect of root grafting and intraspecific competition on annual basal area increment of trees. Trees before grafting had higher growth rates than trees once grafted. Thus, root grafting did not improve tree growth. Growth of grafted trees was more negatively affected by intraspecific competition than growth of non‐grafted trees. Thus, grafted trees cannot be considered as better competitors than non‐grafted trees. Under high intraspecific competition, growth of larger grafted trees was less affected than that of smaller trees suggesting that they were able to divert resources at their advantage within a union. Our study demonstrated that grafted trees acted on each other's growth and provides support for the idea that grafted trees respond to competition for resources more as a community rather than as individual trees.

Increasing water-use efficiency mediates effects of atmospheric carbon, sulfur, and nitrogen on growth variability of central European conifers

Climate controls forest biomass production through direct effects on cambial activity and indirectly through interactions with CO2, air pollution, and nutrient availability. The atmospheric concentration of CO2, sulfur and nitrogen deposition can also exert a significant indirect control on wood formation since these factors influence the stomatal regulation of transpiration and carbon uptake, that is, intrinsic water use efficiency (iWUE). Here we provide 120-year long tree-ring time series of iWUE, stem growth, climatic and combined sulfur and nitrogen (SN) deposition trends for two common tree species, Pinus sylvestris (PISY) and Picea abies (PCAB), at their lower and upper distribution margins in Central Europe. The main goals were to explain iWUE trends using theoretical scenarios including climatic and SN deposition data, and to assess the contribution of climate and iWUE to the observed growth trends. Our results showed that after a notable increase in iWUE between the 1950s and 1980s, this positive trend subsequently slowed down. The substantial rise of iWUE since the 1950s resulted from a combination of an accelerated increase in atmospheric CO2 concentrations (Ca) and a stable level of leaf intercellular CO2 (Ci). The offset of observed iWUE values above the trajectory of a constant Ci/Ca scenario was explained by trends in SN deposition (all sites) together with the variation of drought conditions (low-elevation sites only). Increasing iWUE over the 20th and 21st centuries improved tree growth at low-elevation drought-sensitive sites. In contrast, at high-elevation PCAB sites, growth was mainly stimulated by recent warming. We propose that SN pollution should be considered in order to explain the steep increase in iWUE of conifers in the 20th century throughout Central Europe and other regions with a significant SN deposition history.

Long-term effects of prescribed fire on large tree growth in mixed conifer forests at Lassen Volcanic National Park, California

Prescribed fire in dry coniferous forests of the western U.S. is used to reduce fire hazards. How large, old trees respond to these treatments is an important management consideration. Growth is a key indicator of residual tree condition, which can be predictive of mortality and response to future disturbance. Using a combination of long-term plot records and dendrochronological samples, we analyzed the effects of prescribed fire treatments from the early 1990 s on forest structure and individual tree growth in mixed-conifer forests of Lassen Volcanic National Park in northern California. Prescribed fire reduced stand live tree basal area and stem density at our sites up to 10 years following fire. Within two prescribed fire burn units and two adjacent unburned stands, we analyzed tree cores from 136 large (mean stem diameter > 70 cm) yellow pine (Pinus jeffreyi and P. ponderosa) and 136 large (mean stem diameter > 50 cm) white fir (Abies concolor). After accounting for annual precipitation, basal area increment for individual trees initially declined up to < 3 years post-fire for white fir and > 10 years post-fire for yellow pine, presumably in response to tree injuries. Growth improved for both species at a site that was burned twice, particularly for white fir. Recent average basal area increment was positively related to crown ratio and negatively associated with an index of local competition. Our findings suggest that forest management, such as prescribed fire and mechanical thinning, may be beneficial in terms of maintaining or improving tree growth among large residual trees. However, managers may want to balance the benefits of these treatments against inadvertent injury and mortality of large trees.

How mounds are made matters: seismic line restoration techniques affect peat physical and chemical properties throughout the peat profile

Seismic lines are prominent linear disturbances across boreal Canada with large-scale consequences to wildlife and ecosystem function. Although seismic line restoration has been observed to improve tree growth and survival, application in peatlands has been shown to alter ecosystem functions such as hydrology and carbon storage. The most common active restoration method is called mechanical mounding, where the classic technique inverts the peat profile. New mounding methods that maintain the peat profile may provide benefits by preserving existing vegetation and reducing disturbance. To determine the effects of different mounding methods on soil quality, we collected and analyzed peat cores from two different sites for various soil properties (C/N ratios, δ13C, δ15N, and Fourier transform infrared (FTIR) spectroscopy humification indices). Vegetation surveys were also conducted. The two sites are both a collection of seismic lines crossing poor fens in Alberta. One site was treated with the classic method, while the other was treated with two new mounding methods. Classic mechanical mounding significantly increased the degree of decomposition, indicative of lower substrate quality. Mechanical mounding also greatly reduced moss cover and introduced large amounts of bare ground cover. The two newer mounding methods did not result in these changes and were largely comparable to natural peat properties and vegetation communities. Preserving the peat profile in new mounding methods may support faster return of ecosystem function.

Genomic Comparisons of Two Armillaria Species with Different Ecological Behaviors and Their Associated Soil Microbial Communities.

Armillaria species show considerable variation in ecological roles and virulence, from mycorrhizae and saprophytes to important root pathogens of trees and horticultural crops. We studied two Armillaria species that can be found in coniferous forests of northwestern USA and southwestern Canada. Armillaria altimontana not only is considered as a weak, opportunistic pathogen of coniferous trees, but it also appears to exhibit in situ biological control against A. solidipes, formerly North American A. ostoyae, which is considered a virulent pathogen of coniferous trees. Here, we describe their genome assemblies and present a functional annotation of the predicted genes and proteins for the two Armillaria species that exhibit contrasting ecological roles. In addition, the soil microbial communities were examined in association with the two Armillaria species within a 45-year-old plantation of western white pine (Pinus monticola) in northern Idaho, USA, where A. altimontana was associated with improved tree growth and survival, while A. solidipes was associated with reduced growth and survival. The results from this study reveal a high similarity between the genomes of the beneficial/non-pathogenic A. altimontana and pathogenic A. solidipes; however, many relatively small differences in gene content were identified that could contribute to differences in ecological lifestyles and interactions with woody hosts and soil microbial communities.

Tree growth responses to extreme drought after mechanical thinning and prescribed fire in a Sierra Nevada mixed-conifer forest, USA

An estimated 128 M trees died during the 2012–2016 California drought, largely in the southern Sierra Nevada Range. Prescribed burning and mechanical thinning are widely used to reduce fuels and restore ecosystem properties, but it is unclear if these treatments improve tree growth and vigor during extreme drought. This study examined tree growth responses after thinning, prescribed burning, and extreme drought at the Teakettle Experimental Forest, a historically frequent fire mixed-conifer forest in the southern Sierra Nevada of California, USA. Mechanical thinning (no thin, understory thin, and overstory thin) and prescribed burning (unburned, fall burning) were implemented in 2000–2001. Using annual growth data from increment cores, over 10,000 mapped and measured trees, and lidar-derived metrics of solar radiation and topographic wetness, we had two primary questions. First, what were the growth responses to thinning and prescribed burning treatments, and did these responses persist during the 2012–2016 drought? Second, what tree-level attributes and environmental conditions influenced growth responses to treatments and drought?Thinning increased residual tree growth and that response persisted through extreme drought 10–15 years after treatments. Growth responses were higher in overstory versus understory thinning, with differences between thinning types more pronounced during drought. Species-specific growth responses were strongest with overstory thinning, with sugar pine (Pinus lambertiana) and incense-cedar (Calocedrus decurrens) having higher growth responses compared to white fir (Abies concolor) and Jeffery pine (Pinus jeffreyi). For individual trees, factors associated with higher growth responses were declining pretreatment growth trend, smaller tree size, and post-treatment low neighborhood basal area. Growth responses were initially not influenced by topography, but topographic wetness became important during extreme drought. Mechanical thinning resulted in durable increases in residual tree growth rates during extreme drought over a decade after thinning occurred, indicating treatment longevity in mitigating drought stress. In contrast, tree growth did not improve after prescribed burning, likely due to fire effects that reduced surface fuels, but had little effect on reducing tree density. Thinning treatments promoted durable growth responses, but focusing on stand-level metrics may ignore important tree-level attributes such as localized competition and topography associated with higher water availability. Mechanical thinning was effective at improving growth in trees that had been experiencing declining growth trends, but was less effective in improving growth responses in large old trees of higher ecological importance.

Morphological Variation in Absorptive Roots in Downy Birch (Betula pubescens) and Norway Spruce (Picea abies) Forests Growing on Drained Peat Soils

Peatland drainage based on ditch systems is a widely used forestry management practice in the boreal and hemiboreal forests to improve tree growth. This study investigated the morphological variation in absorptive roots (first- and second-order roots) across the distance gradient from the ditch with four sampling plots (5, 15, 40, and 80 m) in six drained peatland forests dominated by Downy birch and Norway spruce. The dominating tree species had a significant effect on the variation in absorptive root morphological traits. The absorptive roots of birch were thinner with a higher specific root area and length (SRA and SRL), higher branching intensity (BI), and lower root tissue density (RTD) than spruce. The distance from the ditch affected the absorptive root morphological traits (especially SRA and RTD), but this effect was not dependent on tree species and was directionally consistent between birch and spruce. With increased distance from the ditch (from plot 5 to plot 80), the mean SRA increased by about 10% in birch and 5% in spruce; by contrast, the mean RTD decreased by about 10% in both tree species, indicating a potential shift in nutrient foraging. However, soil physical and chemical properties were not dependent on the distance from the ditch. We found a species-specific response in absorptive root morphological traits to soil properties such as peat depth, pH, and temperature. Our results should be considered when evaluating the importance of morphological changes in absorptive roots when trees acclimate to a changing climate.