Degree Of Defoliation Research Articles

Herbivory can reduce perennial grass seedling survival, but temperature and cumulative precipitation are more important predictors in the first growing season

Successful establishment of desired species during restoration is challenging in drylands. Much research has focused on the importance of the critical life stages such as germination and emergence, but factors influencing survival through the seedling stages of perennial grasses may be equally important. We asked whether seedling defoliation by insects and/or mammals could cause restoration failure. We quantified the degree of defoliation on seedlings of common perennial grass species at 46 restoration sites throughout Oregon, Idaho, and Nevada, and calculated survival probabilities during the first growing season after planting. At each site, we excluded small mammals and insects for 6 weeks and compared defoliation and survival probabilities with seedlings in controls without exclusions. Seedlings were classified as either: large perennial grasses (LPG), primarily from the Triticeae tribe, or Bluegrasses (Poa spp.). Defoliation of LPG reduced seedling survival, but the effect was small compared to the influence of meteorological variables, such as precipitation and temperature. Based on bite patterns, most defoliation resulted from insects. Only a small percentage of vegetation was removed (36% of individuals were defoliated, mean = 13.2% vegetation removal). Defoliation of bluegrasses was less common than that of LPG seedlings, with only 16% experiencing defoliation, primarily from insects (mean = 4.3% vegetation removal). Some defoliation did occur within the exclusion treatments, but the effect of defoliation on seedling survival did not appear to interact with treatment. Based on the results of this study, seedling herbivory is unlikely to be a major factor in restoration failure in the Northern Great Basin.

Effects of needle cast diseases on the growth of a 33-year-old Douglas-fir provenance plantation in northwestern Bulgaria

Abstract In this study, the effects of defoliation caused by fungal pathogens on the tree vitality and growth of a 33-year old Douglas-fir (Pseudotsuga menziesii) provenance plantation in northwestern Bulgaria was presented. The results of the conducted surveys in 2011 and 2020 showed that there were significant differences between the individual provenances of Douglas-fir concerning their susceptibility to the needle cast diseases, caused by the fungal pathogens Rhabdocline pseudotsugae and Phaeucryptopus gaeumannii. The extent of damage, expressed as the amount of Douglas-fir needles cast, varied among provenance groups in individual years. A serious degree of defoliation was assessed among all continental provenances. In 2011, all examined trees from the group of continental provenances had severe symptoms of the needle cast disease. In 71.5% of them, the defoliation of the crowns was over 25% – moderately to severely affected. The average degree of defoliation varied from 18.3% (32 Wаrm Springs) to 89.3% (55 Alamogordo). In 2020, severe defoliation was found among all continental provenances. Both fungal pathogens were found as causes of the defoliation of 64.3% of the trees. The growth indicators: average height, average diameter at breast height, average height- and diameter increment for survived provenances in 2011 (at age 24) and 2020 (at age 33) were evaluated. The loss of needles and the reduced physiological function of the trees affected their vitality in the following years. Relationships between the average current annual height and diameter increment by provenance groups for 2003–2011 and 2011–2020 were calculated. It was found that with an increase in the degree of defoliation, the height and diameter increment of the provenances decreases.

Responses of Ethylene Emission, Abscission, and Fruit Quality to the Application of ACC as a Chemical Thinner in ‘Flatbeauti’ Peach

Peach (Prunus persica (L.) Batsch) trees are prone to heavy cropping, but crop load management options are limited. 1-aminocyclopropane-1-carboxylic acid (ACC) has been suggested to reduce crop load and improve fruit quality in peaches, but many questions remain concerning the role of endogenous ethylene in the abscission response and other side effects. Here, the use of ACC as a chemical thinner in peach trees was studied at different rates (350, 500, and 750 mg L−1) and timings [at full bloom (FB) and after petal fall (AP) when the fruit was approximately 15–20 mm in diameter] by comparing the results to those of an untreated control and a hand-thinning treatment as a reference. The abscission response and ethylene emission were related to the ACC concentration. ACC-induced ethylene production, as well as some degree of defoliation, was time-dependent, with the highest ethylene emission peaks and the lowest defoliation degree occurring when ACC was applied at FB. On the other hand, the intra-annual differences in the abscission response between the FBs and APs varied depending on the season. AP-treated fruits produced more endogenous ethylene than did untreated fruits up to harvest, which could have influenced fruit color. Finally, our results indicate that ACC in the range of 500 and 350 mg L−1 can be used in ‘Flatbeauti’ peaches at FB and AP, respectively, to induce adequate levels of fruit crop load without or with minor undesired effects.

Макроэлементный состав листьев березы повислой (Betula pendula Roth) в градиенте аэротехногенного загрязнения АО «Карабашмедь»

The dependence of the macroelements content in the Silver birch (Betula pendula Roth) leaves on the vital state of the stand in the gradient of aerotechnogenic emissions by the Karabash Copper Smelting Plant was established. The content of macro- and microelements (nitrogen, phosphorus, potassium, magnesium, calcium, sulfur was studied, and NPK was calculated as the total content of nitrogen, phosphorus and potassium) in the leaves of a birch tree at different distances from the Karabashmed plant. The study showed that when air was polluted with sulfur dioxide, the total content of macronutrients in the leaves decreased. Severe damage to birch leaves by sulfur dioxide in the affected area of Karabashmed is indicated by an increased concentration of sulfur in the leaves — one and a half times more than on another sample area, as well as deterioration of the vital condition of the stand (the degree of defoliation and dechromation is 1,5–2 times higher, deterioration of the sanitary condition is 1,5 times more when in the others sites). With an increase in foliage dechromation, the potassium content decreases, the sulfur content increases; with a defoliation increase, the content of nitrogen, phosphorus and sodium decreases. The content of calcium and magnesium is not related either to defoliation, dechromation or the category of the tree condition.

Endophytic Strains of <i>Bacillus thuringiensis</i> for the Development of Means to Control the Number of the Colorado Potato Beetle in Potato Crops

Currently, the search for B. thuringiensis strains to be used as biological control agents is based on their toxicity to insects in laboratory tests. At the same time, a number of strains of these bacteria are able to exist in symbiotic relationships with host plants, including being endophytes. The ability of B. thuringiensis strains to penetrate into the internal tissues of plants was evaluated by counting colony-forming units (CFU) of microorganisms 7 days after inoculation of sterile potato plants in test tubes; insecticidal activity was tested on larvae of the 3rd age obtained from overwintered adults of the Colorado beetle collected from fields in the Chishminsky and Iglinsky districts of Bashkortostan. It was shown that the strain of B. thuringiensis B-5351, which inhabits the surface (50.01 ± 8.10 CFU × 105/g) and internal tissues (38.92 ± 9.62 CFU × 105/g) of plant shoots, but has less insecticidal activity than the strain B. thuringiensis B-5689, which exhibits high insecticidal activity and colonizes mainly plant roots (25.37 ± 3.82 CFU × 105/g), reduced colonization of potato crops by the Colorado potato beetle, and also increased the yield of tubers in a 2-year experiment (2020–2021). Under the influence of B. thuringiensis B-5351, a decrease in the number of larvae of early age was observed, in contrast to B. thuringiensis B-5689, which caused longer metamorphosis processes. Apparently, the effect of B. thuringiensis B-5351 was the death of insects. It is important that processing B. thuringiensis B-5351 contributed to a significant decrease in the number of late-instar larvae on crops treated with this strain, as well as the degree of defoliation of plants by the pest, which was not observed with the action of B. thuringiensis B-5689. On plots treated with B. thuringiensis B-5351, the yield of commercial tubers and the total yield increased. A method is proposed for studying the endophytic potential of strains in relation to the terrestrial part of plants to search for biocontrol agents as a basis for creating algorithms for constructing microbiomes in agrocenoses.

LAI estimation through remotely sensed NDVI following hail defoliation in maize (Zea mays L.) using Sentinel-2 and UAV imagery

Extreme events such as hailstorms are a cause for concern in agriculture, leading to both economic and food supply losses. Traditional damage estimation techniques have recently been called into question since damages have rarely been quantified at the large-field scale. Damage-estimation methods used by field inspectors are complex and sometimes subjective and hardly account for damage spatial variability. In this work, a normalized difference vegetation index (NDVI)-based parametric method was applied using both unmanned aerial vehicles (UAV) and Sentinel-2 sensors to estimate the leaf area index (LAI) of maize (Zea mays L.) resulting from simulated hail damage. These methods were then compared to the LAI values generated from the Sentinel-2 Biophysical Processor. A two-year experiment (2020–2021) was conducted during the maize cropping season, with hail events simulated during a range of maize developmental stages (the 8th-leaf, flowering, milky and dough stages) using a 0–40% defoliation gradient of damage intensities performed with the aid of specifically designed prototype machines. The results showed that both sensors were able to accurately estimate LAI in a nonstandard damaged canopy while requiring only the calibration of the extinction coefficient k(vartheta ) in the case of parametric estimations. In this case, the calibration was performed using 2020 data, providing k(vartheta ) values of 0.59 for Sentinel-2 and 0.37 for the UAV sensor. The validation was performed on 2021 data, and showed that the UAV sensor had the best accuracy (R2 of 0.86, root-mean-square error (RMSE) of 0.71). The k(vartheta ) value proved to be sensor-specific, accounting for the NDVI retrieval differences likely caused by the different spatial operational scales of the two sensors. NDVI proved effective in parametrically estimating maize LAI under damaged canopy conditions at different defoliation degrees. The parametric method matched the Sentinel-2 biophysical process-generated LAI well, leading to less underestimations and more accurate LAI retrieval.

Impact of Progressive Pruning on Leaf Miner (<i>Coelaenomenodera lameensis</i>) Incidence and the Yield of Oil Palm (<i>Elaeis guineensis</i>) <br/>—A Case Study of Benso Oil Palm Plantation Plc, Adum Banso Estate, Ghana

The oil palm leaf miner, Coelaenomenodera lameensis, is currently the most destructive pest of oil palm in Ghana and other African oil palm growing countries, causing significant losses in fresh fruit bunch yield. Progressive pruning is an oil palm pruning method in which pruning is done at the same time as fresh fruit bunch harvesting. This study evaluated the impact of progressive pruning on leaf miner population in oil palm and how these two factors (leaf miner and progressive pruning) affect the yield of oil palm at the Benso Oil Palm Plantation Public listed company (BOPP. Plc). Five distinct blocks in the plantation were selected for observations on fronds at various ranks (33, 25, or 17) based on the degree of defoliation by counting the number of pests on leaflets at different phases of insect development. Fronds from selected plots were sampled in a Complete Randomized Design (CRD). The size of plots used for the study ranged between 19 to 45 hectares. A minimum of 78 fronds were evenly cut from each block for pest count depending on the block size. Secondary data on annual yields of fresh fruit bunches before and after the introduction of progressive pruning were also obtained from BOPP. Plc records from 2011-2020. The results from the analyzed data on leaf miner index before and after the introduction of progressive pruning showed that progressive pruning has, to a high extent (64% to 36%), reduced leaf miner populations in the plantation. Paired t-test on fresh fruit bunch yield has also revealed a significant (p , however, revealed a lower rate of yield loss (3.05 to 2.7 tonnes) to leaf miner infestation after the introduction of progressive pruning. The study recommends progressive pruning as a key cultural practice for improving crop yields in leaf miner prone plantations.

Batting for rice: The effect of bat exclusion on rice in North-East India

Insectivorous bats are gaining increasing attention for their potential as biological agents of pest suppression. Studies around the world have demonstrated their tendency to track and hunt agricultural pests over time and space, and thus to have a positive impact on reducing plant damage and protecting yield of agricultural crops. We documented the effect of insectivorous bats on the health and yield of a rice crop in Assam, India. Using six sets of paired experimental and control plots (of which five were analysed), where bats were selectively excluded from the experimental plots, we collected two measures of plant damage and one measure of total yield to assess the impact of bats on the crop. In parallel, bat activity at the six sites was recorded over the rice growing season using passive acoustic recorders. Our results show that the exclusion of insectivorous bats causes an increase in the degree of defoliation suffered by rice plants. We also report non-significant differences in the degree of yellowing of rice and of the total yield between the experimental and control plots. Bat activity levels showed a mono- or bi-modal peak in activity over the growing season, which broadly tracked the maturity of rice, a pattern also seen in many insect pests. Our results strongly suggest that bats have suppressive impact on pest action in rice fields. The general trend in activity levels, as well as the significant difference in plant damage, would indicate that bats are hunting insect pests and that the non-significant difference in final yield was likely the result of methodological limitations. These findings suggest that bats add significant ecological and economic value to Indian rice ecosystems and hold great potential to be used in integrated pest management (IPM) strategies aimed at suppressing pests.

Phenology, growth, and yield of almond cultivars under organic and conventional management in southwestern Spain

Aim of study: To advance implementation of sustainable agriculture from organic production system on almond crop by means of the assessment of physiological and agronomical responses of commercial almond cultivars. Area of study: Irrigated almond in the Guadalquivir River Valley. Material and methods: Physiological and agronomic aspects of almond such as defoliation, phenology, tree growth, N and P leaf reserves, susceptibility to aphids and fruit yield were assessed on five almond cultivars under organic and conventional production management during four consecutive seasons from 2017 to 2021. Main results: A lower flower density, tree growth, and almond production, an earlier and more intense defoliation degree, and a higher susceptibility to aphids were observed in the organic plot compared to the conventional orchard. 'Lauranne' was the cultivar that showed the best productivity under organic and conventional management. 'Marcona' showed the higher flower density and medium vigor, although was the most susceptible cultivar to aphids and the less productive cultivar under both managements. Research highlights: Cultivation of irrigated almond still presents numerous difficulties, especially the control of pests and diseases due to the use of environmentally friendly pesticides which are less effective than chemicals. These pathogenic factors and others such as nutrition especially affect the yield of the crop, although the differences with the conventional system are reduced over time. Despite these difficulties, the high added value of organic almonds together with the increasing demands by consumers of healthy environmental practices and food safety are a stimulus to continue and develop research on sustainable agriculture.

Actions for Monitoring the Gonipterus Pest in Eucalyptus on the Cantabrian Coast

Forests are a natural resource of great importance for sustainable development. They represent the primary use of Spanish territory and cover 36% of its area. Eucalyptus shrublands are the most productive, particularly on the Cantabrian coast, occupying a total area of 406,566 ha. Since 1991, some of these shrublands have been affected by the eucalyptus snout beetle (Gonipterus platensis), a coleoptera (weevil) from the Curculionidae family that feeds on eucalyptus leaves and produces significant damage. The innovation project of the Supra-regional Operational Health Group on Gonipterus in Eucalyptus was developed (2019–2020) to establish a global approach to the serious problem it causes in Asturias and Galician Eucalyptus stands. A group of experts devised two action protocols to unify the methods and variables measured in the field: a protocol for measuring and estimating damage (degree of defoliation) and a parasitism protocol to establish actions to monitor the degree of parasitism (collection of oothecae, management of the sample, laboratory procedure). In the results, in addition to establishing the sampling protocol, an analysis of the data (from 2017 to spring 2020) provided by the different administrations of the Autonomous Communities studied has been carried out. The data analysis reveals an improvement in the impact of the damage on the Cantabrian coast (29.8% reduction in damage in Galicia and 14.7% in Asturias). In Galicia, the number of adult insects decreased from 2017 to 2019, increasing in the spring (from April to June) of 2020 above the mean values of previous years in that period. The number of larvae in the different larval stages showed similar development in all cases. The mean larvae (in their different stages) and mean oothecae showed a significant decline in the year 2018 compared to the spring of 2017, with an upturn in 2019 and again similar values to 2018 in the spring of 2020. In Asturias, similar mean values of the order of 0.5 insects per plot on dates (May–June) in spring were observed in 2019. While in 2020, a progressive increase could be seen in the mean number of insects throughout March, up to 1.9 insects per plot. Results of research on the biological treatment of parasitisation of oothecae with A.nitens were also collected to adjust the number of oothecae per bag deposited in the field and the number of Anaphes released per ha. Based on the field observations, the appropriate release time was determined to succeed in controlling the Gonipterus population.

Tree species composition and management influence short-term resilience to defoliation by Lymantria dispar L. in oak forests

The frequency and intensity of natural disturbances such as infestations by forest insect pests are expected to increase under a scenario of climate change. Thus, tools for monitoring the impact of these disturbance events at large spatial scales are required, together with appropriate management practices for enhancing the ability of forest ecosystems to overcome affectations by insect pests. Here, we used the Enhanced Vegetation Index (EVI) combined with ‘ground truth’ measurements to assess the effects of tree species diversity and forest management on the resistance, recovery and short-term (two years) resilience in mixed oak forests after a severe Lymantria dispar L. defoliation episode. Our results showed that, although neither diversity nor management influenced forest resistance to defoliation, both factors interacted and influenced EVI recovery after the disturbance event. This interaction revealed the complex role tree diversity plays in increasing (in managed forests) or decreasing (in unmanaged forests) resilience to defoliation, thereby suggesting that tree species composition may be more relevant than tree species diversity per se. Indeed, in the field we observed a variety of species-specific degrees of defoliation (e.g. higher in Quercus ilex L.), as well as the preference of L. dispar adults for ovipositing in unmanaged areas and on particular trees (Arbutus unedo L.) that were barely defoliated. In addition, we also found significant and positive effects of tree size (dbh) on avoiding defoliation damage. We thus make three management recommendations for increasing the resilience of oak forests to L. dispar defoliation: i) the application of continuous-cover silviculture (30% thinning intensity in basal areas), ii) the retention of larger trees, and iii) the maintenance of a preferential combination of tree species in mixed stands (e.g. Q. suber and Q. pubescens).

Impact of an Extremely Dry Period on Tree Defoliation and Tree Mortality in Serbia.

This paper presents research results on forest decline in Serbia. The results were obtained through monitoring defoliation of 34 tree species at 130 sample plots during the period from 2004 to 2018. This research aimed to determine whether the occurrence of defoliation and tree mortality were caused by drought. Defoliation was assessed in 5% steps according to the International Co-operative Programme on Assessment and Monitoring of Air Pollution Effects on Forests (ICP Forests) methodology. All the trees recorded as dead were singled out, and annual mortality rates were calculated. To determine changes in air temperature and precipitation regimes during the study period, we processed and analysed climatic data related to air temperature and precipitation throughout the year and in the growing season at 28 main weather stations in Serbia. Tree mortality patterns were established by classifying trees into three groups. The first group of trees exhibited a gradual increase in defoliation during the last few years of monitoring, with dying as the final outcome. The second group was characterised by sudden death of trees. The third group of trees reached a higher degree of defoliation immediately after the first monitoring year, and the trees died after several years. Tree mortality rates were compared between years using the Standardised Precipitation Evaporation Index (SPI) and the Standardised Precipitation Evapotranspiration Index (SPEI), the most common methods used to monitor drought. The most intensive forest decline was recorded during the period from 2013 to 2016, when the largest percentage of the total number of all trees died. According to the annual mortality rates calculated for the three observation periods (2004–2008, 2009–2013, and 2014–2018) the highest forest decline rate was recorded in the period from 2014 to 2018, with no statistically significant difference between broadleaved and coniferous tree species. As the sample of coniferous species was small, the number of sample plots should be increased in order to achieve better systematic forest condition monitoring in Serbia. The analysis of the relationship between defoliation and climatic parameters proved the correlation between them. It was noted that the forest decline in Serbia was preceded by an extremely dry period with high temperatures from 2011 to 2013, supporting the hypothesis that it was caused by drought. We therefore conclude that these unfavourable climatic conditions had serious and long-term consequences on forest ecosystems in Serbia.

Composted Solid Digestate and Vineyard Winter Prunings Partially Replace Peat in Growing Substrates for Micropropagated Highbush Blueberry in the Nursery

The “soilless” cultivation of blueberry (Vaccinium corymbosum L.) in containers with peat as substrate allows overcoming the problem of unsuitable soils, thus enhancing the spread of this crop in new areas. Since the use of peat presents several critical environmental and economic sustainability issues, the evaluation of alternative solutions is required. The effectiveness of compost produced with solid digestate and residues from the vine-wine chain to replace part of the peat was therefore tested. Micropropagated plants of cultivar Duke grown in three substrates consisting of a mixture of commercial peat with three compost fractions (10, 20, 40%) were compared with plants grown in 100% unfertilized or fertilized peat (0.3 g of Osmocote per pot). Plant height did not significantly differ between the five theses at the end of the trial, whereas the total number of nodes per plant was higher than in the control theses, due to a greater development of secondary shoots. The nutritional status of the plants, monitored with Dualex, during the growing season, was generally not significantly different in the innovative substrates compared to peat alone. In mid-summer the plants grown in substrates with compost showed the best nitrogen balance index (NBI values). Plants cultivated with medium-high percentages of compost (20–40%) showed a lower degree of defoliation at the end of the trial, dependent on a slower decline of vegetative activity. The final destructive measures of fresh and dry weight of biomass and of its partitioning between roots and shoots highlight that the use of compost did not negatively affect the production of biomass, but rather, in the theses with the highest percentages of compost (20–40%), root development was stimulated.

Еxperience of maidenhair tree cultivation (Ginkgo biloba L.) in the dendrological park “Berezynka” of Mukachevo state forestry

An inventory of the only in Ukraine ginkgo biloba stand, created by planting forest crops in the arboretum «Berezynka». The distribution of tree trunks by thickness and statistical characteristics by diameter are given, the degree of defoliation and sanitary condition of ginkgo biloba stand are determined. The obtained results can be used to model the forest mesuration structure and merchantable volume structure of future ginkgo biloba stands during its plantation cultivation. The results of the study indicate the high resistance of the species to environmental factors in the region, which makes it possible to recommend this relict species for implementation in forestry practice.

Monitoring and Management of the Pine Processionary Moth in the North-Western Italian Alps

The pine processionary moth (PPM), Thaumetopoea pityocampa (Denis and Schiffermüller, 1775) (Lepidoptera, Notodontidae), is considered one of the main insect defoliators of conifers in Southern Europe and North Africa. The species is oligophagous on pines and cedars in Mediterranean countries. This 6-year investigation (2014–2019), carried out in Aosta Valley (NW Italy), on Pinus sylvestris L. aimed to: (i) Monitor the PPM population with pheromone-baited funnel traps; (ii) assess the infestation index (0–5 classes) according to the degree of defoliation; and (iii) apply control strategies, namely Bacillus thuringiensis var. kurstaki (Btk) and mating disruption (MD). In total, 9618 ha were visually monitored and assigned an infestation index. The percentage of woodland stands that were strongly defoliated by PPM (infestation index ≥ 3) increased progressively between 2015 and 2016, affecting from 8% to 19% of the total area monitored; this area decreased to 16% and 13% in 2017 and 2018, respectively, followed by an abrupt decline to 4% in 2019. Both Btk applications and mating disruption significantly reduced the infestation. Where Btk was applied, the rate of larval mortality ranged from 79.47% to 98.43%; conversely, in the control plots, the larval mortality was, on average, 1.56%. The mean number of PPM males captured in traps was significantly lower in the plots where MD was performed, ranging from 8.36 ± 2.37 to 13.47 ± 4.68. The mean number of males captured in the control plots was, on average, 119.16 ± 12.68. The total number of nests recorded per tree was significantly lower in MD plots, ranging from 0.41 ± 0.05 to 0.94 ± 0.14. In the control plots, there were, on average, 4.37 ± 0.76 nests per tree. As already documented for several defoliating forestry insect pests, both Btk and mating disruption proved effective in controlling PPM infestations, and thus, microbial insecticides should be strongly encouraged and adopted by forest managers.

Forecasting Forest Vulnerability to Drought in Pyrenean Silver Fir Forests Showing Dieback

Forest dieback is manifested as widespread loss of tree vigour, growth decline and high mortality rates. Forest dieback is becoming increasingly frequent and extended, particularly in drought-prone regions. This is the case of the south-western Spanish Pyrenees, where keystone species such as Silver fir reach their xeric and southern distribution limits. While dieback of this species has been widely documented in this area, we still lack methodologies to forecast the vulnerability of these forests in response to increasing drought stress so as to anticipate their potential dieback in the future. Here we study multiple features of Silver fir forest and trees to evaluate whether previous growth rates and their growth trends are valid predictors of forest dieback. Further, we validate our methodology revisiting two Silver fir sites sampled two decades ago. The defoliation degree was strongly related with radial growth, and growth trends differed between moderately to highly defoliated trees and non-defoliated trees. Forests showing dieback, i.e. those in which 25% of the sampled trees showing defoliation > 50%, were located at low elevation and received less rainfall in summer than forests showing no dieback. Trees showing high defoliation presented lower growth rates than non-defoliated trees. Moreover, we ratified that defoliation has increased considerably over the last two decades in one of the two revisited sites, but we were unable to accurately forecast growth trends in both sites, particularly in the site not showing dieback. The retrospective assessment of growth rates and trends offers valuable information on the vulnerability of Silver fir trees to drought. However, we are still far from being able to forecast the vulnerability of Silver fir forest to increasing drought. A systematic monitoring of growth across a wide tree-ring network of sites might provide valuable information to advance in this direction.

Zdravstveno stanje drvenastih i žbunastih vrsta Topčiderskog parka

The research deals with the health condition of tree and shrub species of the natural resource known as Topčider Park assessed on the basis of the conducted visual assessment and determination of the degree of defoliation and discolouration. During the growing season 2018-2019, the health condition of plant species belonging to 50 different genera was determined. The following species were found to be healthy, without any visible damage: Cedrus atlantica, Corylus avelana, C. colurna, Juglans nigra, Maclura aurantiaca, Mahonia aquifolium, Prunus cerasifera, P. spinosa, Quercus rubra and Sambucus nigra. Trees with visible injuries included: Acer negundo, A. pseudoplatanus, Aesculus hippocastanum, Cryptomeria japonica, Fagus moesiaca, Gleditsia triacanthos, Morus alba, Platanus acerifolia, Populus alba. P. nigra, and P. tremula. Dying trees and dead trees were not recorded in Topčider Park. The plant species most threatened by the attack of pathogenic fungi and fungus-like organisms were the species of maple, horse chestnut, lime, poplar, and plane. The species of insects and mites here present did not significantly affect the health status of the investigated plant species.

Genetic variation in tolerance to defoliation in Cirsium arvense

SummaryThe perennial weed, Cirsium arvense (creeping, Canada or Californian thistle), is notorious for its ability to tolerate defoliation by mowing, herbivores or herbicides. The tolerance of 36 genotypes of C. arvense was examined by establishing pairs of clonal replicates that were assigned to a clipped or unclipped treatment. Three clippings were applied from spring to early summer to simulate repeated mowing. The average final percentage reduction caused by the repeated clipping was 18%, 72%, 32% and 50% for shoot biomass, root biomass, number of shoots and shoot height respectively. While nearly all genotypes were negatively affected by clipping, some overcompensated, and achieved greater shoot biomass, number of shoots, or increased height than their unclipped counterparts. No genotype was able to overcompensate, or fully tolerate, the lost root biomass due to repeated clipping. Genetic variation for tolerance to defoliation was detected for the number of shoots, maximum shoot height and for relative height growth rate. For relative growth rate, significant genetic variation was not detected until after the third clipping event, indicating that genotypes were equally tolerant to a moderate degree of defoliation, but upon more severe defoliation, genetic differences were evident. Since repeated defoliation is a recommended control technique, selection for more tolerant genotypes is possible and should be considered for the management of this weed.

The current state of environmental pollution with sulfur dioxide (SO2) in Poland based on sulfur concentration in Scots pine needles

The current air pollution by SO2 due to anthropogenic pressure in Poland was assessed based on sulfur concentrations in pine needles (Pinus sylvestris L.). On 308 monitoring sample plots located in pine stands distributed across Poland, measurements were conducted in mineral soil layers (0–10 cm, 10–40 cm, 40–100 cm) and in the soil organic layer (+5–0 cm). Samples of Scots pine foliage (current-year needles) were then collected, and the sulfur concentration in these needles was determined. Based on these data, a map of the spatial variability of sulfur concentrations in pine needles was drawn. The mean sulfur concentration in the pine needles was 854.8 mg kg−1 in dry mass. Higher SO2 emissions were noted in regions influenced by industry, such as the Upper Silesia and regions under strong urban pressure. Sulfur concentrations in Scots pine needles were related to the stands' degrees of defoliation. A comparison of the current sulfur concentrations in pine needles from biomonitoring in 2015–2016 with those from previous biomonitoring (in 1983–1985, by Dmuchowski and Bytnerowicz (1995) showed that air quality has improved and SO2 emissions have decreased.

Effects of girdling and defoliation on the growth of female cones and branches and nutrient content in different tissues and organs of Pinus koraiensis.

To explore the nutrient source and supply-demand relationship of the female cone deve-lopment and new shoot growth of Pinus koraiensis, reproductive mother branches were experimentally girdled, defoliated, and under the combination of both treatments. The effects of different treatments on the female cones development, branch growth and the content of carbohydrate (NSC), nitrogen (N) and phosphorus (P) in different tissues and organs were measured. The results showed that girdling significantly affected female cone development, new shoot growth, and the contents of NSC, N and P in different tissues and organs, while defoliation treatment had limited effect. The NSC content in the mother branch xylem and phloem after girdling were significantly lower than that of the control (CK, ungirdling+0% defoliation), and decreased significantly with the increases of the degree of defoliation. The NSC content in mother branch xylem and phloem of girdling+100% defoliation was 59.0% and 64.8% lower than that of CK, respectively. The deficiency of NSC resulted in the death of mother branches and new shoots and the abortion of female cone. Under girdling treatment, the contents of N and P in xylem and phloem of mother branches of 0%, 50% and 100% defoliation treatment were significantly higher than that of CK. The contents of N and P in xylem of mother branches were 17.3%, 18.2% and 24.3% and 17.9%, 7.1% and 3.6% higher than those of CK, respectively. The contents of N and P in phloem of mother branches was 39.3%, 35.2% and 48.9% and 31.0%, 28.2% and 14.8% higher than those of CK, respectively. The female cone development and new shoot growth of P. koraiensis consumed a large amount of NSC, N and P. The carbohydrates and mineral nutrients manufactured or stored in the mother branches could not meet the needs of female cone development and new shoot growth, and thus they need to be imported from other tissues.