Improve Tree Growth Research Articles

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.

Mineralisation and nitrification of biuret and urea nitrogen in two New Zealand forest soils

Context Biuret has potential to improve tree growth when applied at high rates as a slow-release nitrogen (N) fertiliser. However, there is little comparative research into the transformation of biuret and urea-N in forest soils. Aims This study comparatively investigated the mineralisation, nitrification and immobilisation of biuret and urea-N in two forest soils (a sandy loam soil and a silt loam soil) to further evaluate the suitability of biuret as a slow-release N source. Methods A 112-day long soil C and N mineralisation incubation study was conducted following application of 0, 4.08, 40.8 and 408 mg N kg−1 soil of biuret (referred to as control, B4, B41 and B408) and urea (referred to as control, U4, U41 and U408). CO2-C, microbial biomass C and N, NH4+-N and NO3−-N were measured at six times (on Days 2, 7, 14, 28, 56 and 112) to quantify net mineralisation and nitrification. Key results In both soils, biuret (especially in B408) was slowly mineralised with a steady increase in soil NH4+-N while urea was readily hydrolysed with a sharp increase and subsequently considerable decrease in soil NH4+-N. B408 had less nitrification than U408 in both soils, especially during the first 56 days. Conclusions Due to the lower mineralisation, nitrification and greater immobilisation, more biuret-N remained in the soils compared to urea-N. Biuret could be used as a potential slow-release N fertiliser in forest soils. Implications The research findings could have important implications for future biuret fertiliser development for plantation forests.

Phosphonate Treatment Effects on Phytophthora Root Rot Control, Phosphite Residues and Phytophthora cactorum Inoculum in Young Apple Orchards.

Phytophthora root rot, caused by Phytophthora cactorum, is an economically important disease on young apple trees. Limited information is available on the effect of different phosphonate application methods and dosages on disease control, fruit and root phosphite concentrations, and soil and root pathogen inoculum levels. Evaluation of phosphonate treatments in three apple orchard trials (two in the Grabouw and one in the Koue Bokkeveld region) showed that foliar sprays (ammonium or potassium phosphonate), trunk sprays and trunk paints, were equally effective at increasing trunk diameter in one trial and yield in a second trial over a 25-month period. Foliar ammonium and potassium phosphonate sprays (12 g of phosphorous acid/tree), and two different dosages of the ammonium phosphonate sprays (∼4.8 g or 12 g of phosphorous acid/tree) were all equally effective at improving tree growth. The addition of a bark penetrant (polyether-polymethylsiloxane-copolymer) to trunk sprays did not improve the activity of trunk sprays. The low dosage ammonium phosphonate foliar spray (∼4.8 g a.i./tree) was the only treatment that, in general, yielded significantly lower root phosphite concentrations than the other phosphonate treatments. Root phosphite concentrations were significantly positively correlated (P < 0.0001) with an increase in trunk diameter and negatively (P < 0.0001) with P. cactorum root DNA quantities. Phosphite fruit residues were <31 ppm for all treatments, with the trunk paint treatment (80 g of phosphorous acid/tree applied annually) yielding significantly lower residues than the higher dosage foliar sprays (∼12 g a.i./tree). Twenty-one months posttreatment, most of the phosphonate treatments in all of the trials similarly significantly reduced P. cactorum DNA quantities estimated directly from roots, but not from soil based on soil baiting DNA analysis. Pathogen quantities in fine feeder roots did not differ significantly from those in higher-order roots (<5 mm diameter). P. cactorum DNA quantities estimated using DNA quantification directly from roots were significantly correlated (P < 0.0001) with those obtained through root leaf baiting DNA analysis and, to a lesser extent, with soil leaf baiting DNA quantities (P = 0.025).

Climate Signals for Growth Variations of F. sylvatica, P. abies, and P. sylvestris in Southeast Germany over the Past 50 Years

Since recent drought events have already caused severe damage to trees and droughts in the near future are expected to occur even more frequently, this study investigated the response of forest ecosystems to changing climate conditions in the topographically complex region of Bavaria, southeast Germany. For this purpose, climate–growth relationships of important European deciduous and coniferous tree species were investigated over the past 50 years at three middle mountain ranges and corresponding basins. A response analysis between tree-ring width and climate variables was applied to detect modifications in tree responses comparing two 25-year periods at individual forest sites. Furthermore, tree responses to climatic extreme years and seasons were analyzed using a superposed epoch analysis. The results showed that Scots pine (Pinus sylvestris) proved to be the most vulnerable and least drought-resistant of all investigated tree species. Likewise, Norway spruce (Picea abies) and European beech (Fagus sylvatica) revealed a higher drought sensitivity over the past 25 years, even though an extended growing season partially improved tree growth at high-elevation sites. In conclusion, all studied tree species were affected by drought events, even at humid high-elevation sites. Correlations with daily climate variables confirmed that even short-term weather conditions could strongly influence trees’ radial growth. Tree responses to climate conditions have shifted significantly between past and present periods but vary considerably among sites and are generally stronger in humid regions than in already dry areas.

Split application of nutrients improve growth and yield of Huanglongbing‐affected citrus trees

AbstractCitrus production in Florida declined steadily because of Huanglongbing (i.e., HLB, citrus greening) caused by the bacteria Candidatus Liberibacter asiaticus. The objectives of the study were to determine whether leaf tissue nutrient concentration, tree growth, fruit yield, and juice content were improved with split applications of essential nutrients on selected rootstocks on Florida sandy soils. The treatments were arranged in a split‐split plot design where the nitrogen (N) was fertigated in 20 splits and the Ca + Mg nutrients were also split three times coinciding with the spring, summer, and late summer flush seasons on trees budded on two rootstocks of ‘Hamlin’ citrus trees [Citrus sinensis (L.) Osbeck]. A significant difference in leaf N, calcium (Ca), and magnesium (Mg) concentration were detected between rootstocks when trees received the highest N rate and remained within the optimum range of critical nutrition concentration even with the lowest N rate, suggesting a lower N requirement with split N applications. Yet, leaf Mg concentration remained in the minimum range implying a low soil Mg pool. For Ca, Mg, and Ca + Mg treatments, we recorded 1.41×, 1.23×, and 1.23× and 1.22×, 1.26×, and 1.30× greater tree canopy volumes (TCV) on Cleopatra and Swingle rootstocks, respectively, as compared with control trees. Significantly greater fruit yield was detected for trees budded on Cleopatra rootstocks that received either Ca or Ca + Mg treated trees with 59.7 and 63.0 kg tree–1 as compared with the control trees (36.9 kg tree–1), respectively. A magnitude of 1.14× more average fruit weight than control trees was noted for trees budded on Swingle rootstock in response to Mg nutrition. Therefore, the application of essential nutrients has a positive impact to ameliorate tree growth and nutrient deficiency associated with Candidatus Liberibacter asiaticus‐induced problems, thereby improving tree growth and yield.

Non-invasive sensing techniques to phenotype multiple apple tree architectures

Tree fruit architecture results from combination of the training system and pruning and thinning processes across multiple growth and development years. Further, the tree fruit architecture contributes to the light interception and improves tree growth, fruit quality, and fruit yield, in addition to easing the process of orchard management and harvest. Currently tree architectural traits are measured manually by researchers or growers, which is labor-intensive and time-consuming. In this study, the remote sensing techniques were evaluated to phenotype critical architectural traits with the final goal to assist tree fruit breeders, physiologists and growers in collecting architectural traits efficiently and in a standardized manner. For this, a consumer-grade red–green–blue (RGB) camera was used to collect apple tree side-images, while an unmanned aerial vehicle (UAV) integrated RGB camera was programmed to image tree canopy at 15 m above ground level to evaluate multiple tree fruit architectures. The sensing data were compared to ground reference data associated with tree orchard blocks within three training systems (Spindle, V-trellis, Bi-axis), two rootstocks (‘WA 38 trees grafted on G41 and M9-Nic29) and two pruning methods (referred as bending and click pruning). The data were processed to extract architectural features from ground-based 2D images and UAV-based 3D digital surface model. The traits extracted from sensing data included box-counting fractal dimension (DBs), middle branch angle, number of branches, trunk basal diameter, and tree row volume (TRV). The results from ground-based sensing data indicated that there was a significant (P < 0.0001) difference in DBs between Spindle and V-trellis training systems, and correlations between DBs with tree height (r = 0.79) and total fruit yield per unit area (r = 0.74) were significant (P < 0.05). Moreover, correlations between average or total TRV and ground reference data, such as tree height and total fruit yield per unit area, were significant (P < 0.05). With the reported findings, this study demonstrated the potential of sensing techniques for phenotyping tree fruit architectural traits.

Field Evaluation of Chemotherapy on HLB-Affected Citrus Trees With Emphasis on Fruit Yield and Quality.

Huanglongbing (HLB) is one of the most devastating diseases of citrus, which is associated with Candidatus Liberibacter asiaticus (Las) in the United States. To date, no effective antimicrobial compound is commercially available to control the disease. In this study, we investigated the effects of different antimicrobial chemicals with suitable surfactants on HLB-affected matured citrus trees with emphasis on the fruit yield and quality. Each treatment was applied three times in a 2-week interval during the spring flush period, one time in summer and three times during the autumn flushing period. We extensively examined different parameters such as pathogenic index, disease index, tree canopy, fruit yield, quality, and nutritional status. The results showed that among the treatments, penicillin (PEN) with surfactant was most effective in suppressing Las titer in infected citrus trees, followed by Fosetyl-Al (ALI), Carvacrol (CARV), and Validamycin (VA). Fruit quality analysis revealed that PEN treatment increased the soluble solids content (SSC), whereas Oxytetracycline (OXY) treatment significantly reduced titratable acidity (TA) level and increased the SSC/TA ratio compared to the control. Nutrient analysis showed increased N and Zn levels in ALI and PEN treatments, and OXY treatment increased leaf P, K, S, and Mg levels compared to untreated control. Furthermore, B, Ca, Cu, Fe, and Mn in leaves were reduced in all chemical treatments than that of the untreated control. These findings revealed that some of the chemical treatments were able to suppress Las pathogen, enhance nutritional status in leaves, and improve tree growth and fruit quality of HLB-affected trees.

Effect of tree mixture on Collembola diversity and community structure in temperate broadleaf and coniferous forests

Springtails (Collembola) are the most abundant arthropods in terrestrial ecosystems and, are considered as key indicators of organic matter turnover and soil functioning. Mixture of tree species are often regarded as a mean to improve tree growth, soil fertility and biodiversity.We compared α-diversity, taxonomic β-diversity and functional diversity of Collembola of mixed forest stands to pure stands in two forest sites, a mountain and a lowland site composed of a coniferous and a deciduous species for effect on. We choose sessile oak (Quercus petraea) and Scot pine (Pinus sylvestris) in lowland, and beech (Fagus sylvatica) and silver fir (Abies alba) in mountain stands.In total 41 species Collembola were identified. We showed that richness and abundance in mixed stands were in between those found in the pure stands, with a more pronounced response of the soil fauna in lowland compared to mountain. In the lowland, Shannon diversity index followed the same pattern, and we found species richness from 6.3 to 11.7 mean species, and 4400 to 9000 ind.m−2, dominated by epedaphic group. In the mountain, we found species richness from 7 to 9 mean species, and 6600 to 103,000 ind.m−2, dominated by euedaphic group.Among the 12 soil and litter characteristics, many differs between sites and/or stand type. The best predictors of the model explaining differences in mean Collembola were litter chemical composition including the lignin to N ratio and C to N ratio. Soil characteristics, such as humus index, organic layer thickness or pH, was also a good predictors for some life-forms and one or the other site.In addition, mixture modified Collembola community structure with some species found only in the pure stands. Jaccard similarity index showed that mixture, even composed of different tree species, homogenized Collembola community structure.We conclude that mixture of tree species in temperate forests can locally increase Collembola diversity, but this management should not be generalized to maximize the β-diversity.

Leaf gas exchange and foliar macronutrients vary in Quercus bicolor but not Quercus phellos between a designed soil pavement system and open lawn

Structural soils are a type of designed soil intended to improve tree growth in the built environment by increasing the rooting volume available to trees underneath pavement. While urban trees can experience multiple environmental stressors, tree water relations and leaf nutrients are not well studied in structural soil systems. We examined leaf level gas exchange, foliar nutrient concentrations, and crown condition to evaluate the potential effects of water and nutrient related stressors in this setting. Located in Brooklyn, NY, USA, the study site included Quercus bicolor and Q. phellos planted in both sidewalk pits underlain with structural soil and in open lawn areas. Tree size measurements indicate that around 16–20 years post-installation, lawn trees have started to become larger than those in the sidewalk, though the size differences are comparatively small. Leaf level net photosynthetic assimilation and stomatal conductance of Q. bicolor were significantly lower in sidewalk trees compared to lawn trees in 2016. Yet no differences in gas exchange were observed for Q. phellos which suggests the two species likely have different water use strategies. Out of 27 elements measured in leaf tissue, Ca, K, Ba, and Sr were significantly lower in Q. bicolor sidewalk trees. Both species appeared to have elevated foliar concentrations of Na. For Q. phellos, sidewalk trees had significantly lower crown vitality (fine twig dieback) scores, though no differences were observed for Q. bicolor. These findings suggest Q. bicolor may be more sensitive to water and nutrient stress in the structural soil system compared to Q. phellos.

Mixing increases drought exposure through a faster growth in beech, but not in oak

Promoting mixed forests is often seen as a management option to increase the resilience of forests to droughts. However, mixing can also improve tree growth, and if faster-growing trees use more water, they may be exposed to higher risks of drought. Across Belgium, we tested whether increased tree growth in mixed sessile oak/common beech stands results in increased drought exposure of these forests in severe dry summers. We sampled wood cores from 222 trees in mixed and corresponding pure stands at eight different sites and measured ring widths and stable carbon isotope composition (δ13C) in the wood formed during 2001 (wet summer as a reference year) and 2003 (severe dry summer). Pre-drought growth (PG), an index of tree growth in normal climatic conditions, was calculated as the mean ring width in the five years preceding the drought, and drought exposure was assessed as the difference in δ13C between the dry and the reference year. Growth of individual beech trees was faster in mixtures and both mixing and pre-drought tree growth were positively related to beech drought exposure. These two effects were not independent: the increased drought exposure in mixed stands was an effect of the faster growth. Analysis of δ13C values suggests that in reference conditions, beech trees in mixtures had a less conservative water use than trees in pure stands, but that they shifted to a functioning similar to that in pure stands under drought. By contrast, growth and drought exposure of oak trees did not differ between pure and mixed stands. Our results emphasize the different strategies of these two species regarding their response to mixing and drought. Beech maximizes its growth as a result of greater resource capture in mixed stands, but this increases the risk of suffering from severe droughts. Oak, on the other hand, exhibits lower variability in growth and in drought exposure across pure and mixed stands. We should stress that if mixing is used as a management strategy to mitigate the negative effects of climate change on temperate forests, forest managers should be aware that the performance benefits of mixed forests in non-drought years could in fact hinder the drought resistance of these forests in severe drought years.

Ten Years of Provenance Trials and Application of Multivariate Random Forests Predicted the Most Preferable Seed Source for Silviculture of Abies sachalinensis in Hokkaido, Japan

Research highlights: Using 10-year tree height data obtained after planting from the range-wide provenance trials of Abies sachalinensis, we constructed multivariate random forests (MRF), a machine learning algorithm, with climatic variables. The constructed MRF enabled prediction of the optimum seed source to achieve good performance in terms of height growth at every planting site on a fine scale. Background and objectives: Because forest tree species are adapted to the local environment, local seeds are empirically considered as the best sources for planting. However, in some cases, local seed sources show lower performance in height growth than that showed by non-local seed sources. Tree improvement programs aim to identify seed sources for obtaining high-quality timber products by performing provenance trials. Materials and methods: Range-wide provenance trials for one of the most important silvicultural species, Abies sachalinensis, were established in 1980 at nine transplanting experimental sites. We constructed an MRF to estimate the responses of tree height at 10 years after planting at eight climatic variables at 1 km × 1 km resolution. The model was applied for prediction of tree height throughout Hokkaido Island. Results: Our model showed that four environmental variables were major factors affecting height growth—winter solar radiation, warmth index, maximum snow depth, and spring solar radiation. A tree height prediction map revealed that local seeds showed the best performance except in the southernmost region and several parts of northern regions. Moreover, the map of optimum seed provenance suggested that deployment of distant seed sources can outperform local sources in the southernmost and northern regions. Conclusions: We predicted that local seeds showed optimum growth, whereas non-local seeds had the potential to outperform local seeds in some regions. Several deployment options were proposed to improve tree growth.

Species-specific responses to targeted fertilizer application on reconstructed soils in a reclaimed upland area

Forested reclamation of oil sand mines in northern Alberta often use peat salvaged from lowland organic soils as a coversoil during soil reconstruction of man-made landforms. Previous studies suggest that planted tree seedlings may be limited in part by low phosphorus (P) and potassium (K) availability in peat. Fertilization is commonly used to treat nutrient limitations on reclamation sites; however, broad spectrum applications can induce strong competition from colonizing vegetation. This study explores the ability of a targeted application of individual macronutrients to (1) reduce nutrient deficiencies in peat coversoils and improve tree growth, while (2) minimizing the colonizing competition. Liquid fertilizer was applied to 6-yr-old aspen, pine, and spruce trees in the field using five nutrient combinations: control (no fertilizer), NPK, PK, P, and K. Tree growth, foliar nutrient concentrations, vegetation cover, and environmental parameters were monitored over two growing seasons. Aspen responded the strongest to fertilization, particularly in the P treatment, whereas pine and spruce marginally responded to NPK. Competing vegetation increased in the NPK but did not respond to the P and K treatments, indicating targeted fertilization can reduce colonizing competition. Additional analyses of the soil conditions of the site suggest that other factors were potentially more limiting to the trees during the study. Targeted fertilization of forest reclamation sites at a later stand age can be an option to improve efficacy and cost savings; however, response will also depend on other site (e.g., soil pH, precipitation, and soil water content) and management (e.g., fertilizer application rate) factors.

SHORT-TERM IMPACT OF AMMONIUM NITRATE AND WOOD ASH APPLICATION ON GROUND VEGETATION DIVERSITY AND SPECIES COMPOSITION IN DRAINED FORESTS

Fertilization is a way of improving tree growth and thus profitability of forestry, however this practice may cause negative side effects, such as loss of biodiversity. Ground vegetation represents a major part of plant biodiversity in forest and it is sensitive to environmental changes. The aim of the study was to characterize a short-term impact of ammonium nitrate and wood ash application on floristic composition and species diversity in conifer and deciduous forests on drained mineral and peat soils. The study was conducted in 6 stands representing Myrtillosa, Myrtillosa turf.mel., Vacciniosa mel. and Vacciniosa turf. mel. forest types. The projective cover of each species was estimated visually, separately for moss, herb and shrub layer. Shannon diversity index was calculated and compared between the plots, where fertilizers were added, and control plots. Results show that species composition corresponds to the respective forest types regardless of the application of fertilizers. In Myrtillosa mel. stands, Myrtillosa turf. mel. birch stand and Vacciniosa mel. stand nitrophilous species were more frequently observed and had a slightly larger projective cover in treatment plots, which could be explained by the impact of fertilization. Species diversity in the moss layer might have lowered as a result of fertilization, whereas no consistent patterns were observed for the herb layer. A repeated survey will show, if changes in ground vegetation persist longer.

Long-term logging residue loadings affect tree growth but not soil nutrients in Pinus contorta Doug. ex Loud. forests

The 19-year monitoring study revealed continuously positive and dynamic responses of tree growth to logging residue loadings. However, the lack of changes in soil nutrients suggested that increased growth might result from enhanced nutrient cycling with no net accumulation in the soil. Understanding how logging residue loadings affect soil nutrients and forest growth is critical for designing management strategies for sustaining long-term productivity in forest ecosystems. We aimed to examine the relationships among logging residue loadings, soil nutrients, and tree growth over a long-term field experiment in lodgepole pine (Pinus contorta Doug. ex Loud.) forests. We established a field experiment in 1996 to examine the responses of lodgepole pine growth and soil nutrients to four residue loading treatments in the central interior of British Columbia, Canada. The four treatments were removal of all residues on the forest floor (N, 0 mg ha−1), residues loading similar to whole-tree harvesting (W, 35–45 mg ha−1), residues loading similar to stem-only harvesting (S, 60–70 mg ha−1), and residues loading similar to that found in disease- or insect-killed forests (D, 100–120 mg ha−1). Logging residue loadings had significantly positive and dynamic effects on diameter and height growths. The logging residue loadings did not significantly change soil nutrients in mineral soil pools in the long run, and there was no difference in tree growth between the treatments S and W over the study period. Logging residue loadings significantly improved tree growth. The lack of response of soil nutrients leads to the hypothesis that nutrient fluxes from logging residues might play a more important role in tree growth in lodgepole pine forests. Our results can have important implications for bio-energy production and designing of nature-based practices for sustainable forest productivity.

Mechanisms by Which Pre-Commercial Thinning Increases Black Spruce Growth in Different Climates and Soil Types

In the province of Québec (Canada), pre-commercial thinning (PCT) is a common silvicultural practice applied to young black spruce (Picea mariana (Mill.) BSP) stands. PCT removes some of the competing vegetation and smaller black spruce stems, in order to improve growth rates and reduce forest rotation intervals. It is uncertain whether this positive response in black spruce growth is primarily due to lower competition for resources or to other mechanisms, which may vary according to climate or edaphic conditions. We sampled soils and black spruce needles in PCT-treated and non-treated control plots occurring in two climate regimes, as well as on two contrasting soil parent materials within one of these two climate regimes (i.e., three “site types”). We performed our sampling approximately 20 years after treatment. Paired treatment plots (i.e., PCT vs. control) were replicated at four independent sites in each of the three site types, for a total of 24 plots. Over two consecutive years, we measured stand structural characteristics, indices of soil N fertility, soil microbial activity, indices of soil moisture availability, canopy openness, and foliar characteristics in each plot. In each site type, PCT decreased total basal area but increased radial growth of individual trees. Across all plots, soil N mineralization rates measured in 2016 were positively related to foliar N concentrations of one-year-old needles collected in 2017. Annual precipitation, drainage class, potential evapotranspiration, and climate moisture index all indicated that plots occurring in the drier climate and on glacial till deposits were more prone to summer moisture deficits. Accordingly, PCT increased forest floor moisture only in this site type, which may benefit tree growth. In the wetter climate and on poorly drained soils, however, we found evidence that PCT reduces soil N fertility, presumably by increasing the spread of ericaceous shrubs in the understory. In the dry fertile site type, the range in canopy openness was substantially higher (12–37%) and correlated negatively with tree diameter, suggesting that greater light availability did not improve tree growth. Taken collectively, our data suggest that PCT increases black spruce growth across a broad range of site conditions found in Québec, presumably by lowering intraspecific competition for resources. However, on drier sites, PCT may also benefit trees by increasing soil moisture availability, whereas wetter climates may mitigate the beneficial effect of PCT due to a loss of soil N fertility.

A Review of Non-Chemical Weed Control Practices in Christmas Tree Production

Weeds interfere with Christmas tree growth at any time and at any stage of production. Growers mostly rely on mechanical mowing and applications of herbicides for weed control in their fields. However, herbicides can be phytotoxic to non-target plants, can cause environment-related issues, and their repeated application can even cause herbicide-resistant weeds. The main objective of this manuscript is to provide a review of non-chemical weed control strategies in Christmas tree production and identify areas where current practices could potentially be improved or in which further research is required. Preventing the introduction of weed seeds requires controlling weeds along farm roads, maintaining clean equipment, and eliminating new weeds before they start seeding. Mowing helps to reduce the number of seeds produced by the weeds and can significantly reduce competition with trees. Shropshire sheep are well suited for grazing Christmas tree plantations as they prefer grazing on grasses and weeds rather than on coniferous trees. Weeds can also be controlled around Christmas trees by mulching. Organic mulch can improve soil moisture, maintain soil temperatures, enhance root establishment and transplant survival, and improve plant establishment and overall growth. Incorporating cover crops into Christmas tree plantations may improve tree growth, quality, and soil fertility and can supplement conventional nitrogen fertilizers. However, if cover crops are not properly managed, they can be highly competitive with the trees. Flaming can cause suppression of many annual weed species but is less effective on larger weeds and needs to be applied with caution. Several insects have been used as biological agents to control selective weed species. However, further research is required to focus on several potential biological agents, different types and depths of mulches, on cover crops types and their competition with different species of Christmas trees and their effects on seedling survival and growth.

Irrigation of Young Cork Oaks under Field Conditions—Testing the Best Water Volume

This study is the beginning of the first long-term study on cork oak irrigation under field conditions, with a structural-functional approach. Cork oaks are currently facing disturbances affecting cork quality and quantity, jeopardizing the future of the economic sector. There is a need for new production techniques that maximize cork oak growth and vitality. In this study, irrigation was implemented in a new intensive cork oak plantations to test the best irrigation volume. The long-term goal is to improve tree growth with minimum water requirements. A 6 ha intensive plantation was installed in Coruche, Portugal. The experimental plot consisted of a subsurface drip fertigation system, buried 40 cm deep; with five independent irrigation treatments. It was tested four irrigation volumes during the dry period—21 weeks in the summer of 2016—ranging from 1.88 mm to 5.62 mm a week. Information on meteorological conditions, soil moisture profile and leaf stomatal conductance were gathered periodically and dendrometric measurements were performed before and after the treatments. Cork oaks’ structural and functional parameters were associated with irrigation volume Response to irrigation showed an inflection point in treatment 2, corresponding to a water supply of 3.12 mm per week: below the inflection point, stomatal conductance was reduced by 15% and relative diameter growth at the base was reduced by 10%. Stomatal conductance also showed a positive relationship with soil moisture below the irrigation tubes and with plants’ stem diameter. In conclusion, irrigation supply during the period of water stress improved function and structure of cork oaks seedlings under field conditions. These results suggest that irrigation can be a viable alternative to improve cork oak growth in afforestation and reforestation.

Feature Selection Based on a Novel Improved Tree Growth Algorithm

Feature selection plays a significant role in the field of data mining and machine learning to reduce the data dimension, speed up the model building process and improve algorithm performance. Tree growth algorithm (TGA) is a recent proposed population-based metaheuristic, which shows great power of search ability in solving optimization of continuous problems. However, TGA cannot be directly applied to feature selection problems. Also, we find that its efficiency still leave room for improvement. To tackle this problem, in this study, a novel improved TGA (iTGA) is proposed, which can resolve the feature selection problem efficiently. The main contribution includes, (1) a binary TGA is proposed to tackle the feature selection problems, (2) a linearly increasing parameter tuning mechanism is proposed to tune the parameter in TGA, (3) the evolutionary population dynamics (EPD) strategy is applied to improve the exploration and exploitation capabilities of TGA, (4) the efficiency of iTGA is evaluated on fifteen UCI benchmark datasets, the comprehensive results indicate that iTGA can resolve feature selection problems efficiently. Furthermore, the results of comparative experiments also verify the superiority of iTGA compared with other state-of-the-art methods.

Eighteen-year growth responses to thinning and fertilization of a height-repressed lodgepole pine stand in interior British Columbia

Challenges to the mid-term timber supply in interior British Columbia resulting from losses to insect outbreaks and wild-fires have prompted interest in silvicultural interventions to hasten growth of regenerating forests, including high-density(overstocked), height-repressed stands of lodgepole pine (Pinus contorta Dougl. ex Loud. var. latifolia Engelm.). A trialwas established in a dense (4000 to 30 000 trees ha-1) 36-year-old wildfire-origin pine stand in the Cariboo-Chilcotinregion of interior BC to assess the efficacy of thinning, fertilization and a combination of the two treatments for improv-ing tree growth and stand development. Height and diameter of the 36 crop trees in each plot was greater in fertilizedplots then control plots for six years following fertilization, while the height and diameter responses to thinning and thin-ning + fertilization were sustained throughout the 18-year measurement period. Cumulative basal area and volumegrowth of crop trees and all stand trees over the 18-year period was significantly greater in thinned and thinned + fertil-ized treatments than control plots. Projections based on the TASS growth and yield model suggested that total stand vol-umes in thinned plots would surpass that of the control at age 74 and would surpass that of the fertilized treatment at 89years. Unthinned stands (i.e., control and fertilized treatments), did not accumulate significant merchantable volume; inthinned stands (i.e., thinned and thinned + fertilized treatments), the minimum harvest criteria of 80 m3 ha-1 for pine-leading stands in this region was reached at age 102 years. Repeated fertilization would be needed to further hasten standdevelopment. The potential long-term benefits of these silvicultural interventions for timber supply must be weighedagainst treatment costs and risks of mortality related to wildfire, insects and disease. These results highlight the value oflong-term research trials for informing silviculture decisions.

Variation in radial growth and wood density of Cyclocarya paliurus across its natural distribution

As a multiple function tree species, Cyclocarya paliurus is planted and managed for timber production and medicinal use. However, it remains unclear to what extent geographical gradients in growth and wood quality are shaped by the environment. We used data of 197 trees from 22 natural populations to assess geographic variation patterns in radial growth and wood density, and their correlations with environmental factors. Significant differences in mean annual DBH and wood basic density were observed among the 22 populations (p < 0.05). Based on mean annual DBH and wood basic density, the 22 populations were classified into three groups by hierarchical cluster analysis. Within its natural distribution, soil nutrients are more closely associated with DBH growth than are temperature and precipitation. However, correlations between wood density versus altitude and annual precipitation were found (p < 0.01). Trend surface analysis revealed that mean annual DBH growth and wood density displayed an increasing trend from north-west to south-east across its natural distribution. Our study provides valuable insights into the geographical patterns in growth and wood quality of C. paliurus, and an opportunity to improve tree growth and wood quality through phenotypic selection and selecting suitable sites for planting.