Defoliation Classes Research Articles

Influence of Tree Attributes on Silver Fir (Abies alba Mill.) Transitioning to Higher Defoliation Classes Determined by Logistic Regression

The age, size and morphology of trees, including crown dimensions, can influence crown defoliation. In Croatia, the selection management of silver fir (Abies alba Mill.) forests involves pure or mixed stands, either of which can be affected by various disturbances, resulting in unbalanced stand structures. The aim of this study was to estimate the probability of trees transitioning from one defoliation class to the next, examine the influence of tree attributes on that process and analyze the changes in survival over time. The study was conducted over a 18-year period (1990–2007) on two sites with contrasting stand structures: a uniform stand with a dominant share of silver fir (Site A) and an uneven-aged mixed beech–fir stand (Site B). Logistic regression was used to model tree transitions between defoliation classes. Uniform stand structure increased the likelihood of silver fir trees transitioning to a higher defoliation class, with limited dependence on the tree crown position. In contrast, suppressed and central trees in uneven-aged stands were more likely to transition to a higher defoliation due to greater competition between them. Diameter at breast height (DBH) was found to be a significant predictor of tree transition to higher defoliation classes, with a linear trend of increasing probability with increasing DBH. Crown position and crown length were also found to be significant predictors of changing defoliation class, with observed differences between sites occurring due to differences in stand structure. To ensure a balanced stand structure and enhance tree vitality, careful consideration of easily measurable tree elements such as DBH, crown length, and tree crown position is imperative when selecting trees for felling.

Mineral nutrients improve phosphonate effectiveness against cork oak root disease

Phosphonate fungicides are the most efficient chemicals for the control of oomycete root diseases which are causing significant economic and ecological losses in Mediterranean climate-type forests and natural ecosystems worldwide. However, a more environmental-friendly disease management demanded by society requires the optimization of chemicals application. Thereby, the main goal of this study was to develop a new resistant inducer (RI) formulation based on potassium phosphonate (PP) combined with mineral nutrients efficient against the root rot caused by Phytophthora cinnamomi and Pythium spiculum on cork oak that improve potassium phosphonate effectiveness. The potential phytotoxicity of five RI formulations composed of PP at five concentrations (25, 40, 50, 100 and 200 g/l) and each including 2.15 g/l ZnCl2 (Zn) and 0.25 g/l CaCl2 (Ca), were tested on 1-year old Quercus suber seedlings. Two weeks after treatments, only seedlings treated with the RIs containing the two highest doses of PP (100 and 200 g/l) showed symptoms of toxicity. RI with 40 g/l of H3PO3 (RI40), as well as its compounds individually and in combination two by two (PP (40 g/l), Ca, Zn, PP + Ca, PP + Zn, Ca + Zn), were tested against root disease development induced by P. cinnamomi and Py. spiculum on cork oak seedlings. For both oomycetes, seedlings submitted to every treatment with PP exhibited a significantly lower severity of root symptoms than plants artificially inoculated and treated with water. Furthermore, plants treated with RI40 did not differ to the plants growing in uninfested soil, improving PP alone effect. These results were validated by a field experiment where 60 mature cork oaks in three different defoliation classes (asymptomatic, slight, and moderate defoliation) were trunk injected with RI40 or water (controls). Three years after treatments, root disease development was significantly lower in cork oaks with slight and moderate initial defoliation level and treated with RI40 in comparison with water-treated controls. No effect was detected over both pathogens’ dynamics in soil. Results strongly support that PP effectiveness in controlling Q. suber root disease caused by P. cinnamomi and Py. spiculum is improved by its combination with Zn and Ca, allowing to reduce the PP application rates according to current society demands and the European Plant Health Legislation.

Accuracy of Defoliation Estimates from Aerial and Ground Surveys in a Boreal Forest during an Outbreak of the Hemlock Looper, Lambdina fiscellaria (Guenée)

Annual estimates of defoliation are important tools for managing forest insect defoliators such as the hemlock looper, which feeds on conifer needles of all age classes. We tested the accuracy of defoliation classes obtained from aerial surveys by comparing them with ground-based estimates during a recent outbreak of this insect. We used an approach derived from the Fettes method to estimate defoliation on the current-year shoots as well as on the shoots of the four previous years. Defoliation on the current-year shoots provided accurate estimates of the overall defoliation and the strength of the relationship gradually decreasing for one-year-old to four-year-old foliage. The aerial survey provided accurate estimates of light and moderate defoliation during the first year of the outbreak, but accuracy was lower for both ends of the defoliation gradient and was much less reliable after the second year of the outbreak. All levels of defoliation were then observed in stands where defoliation had not been detected by an aerial survey. Cumulative defoliation on all age classes of foliage brings a new challenge to crews assigned to aerial survey programs. Ground-level defoliation estimates on the current-year shoots can help appraise the risk of tree mortality in the following year.

Defoliation-Induced Growth Reduction of Pinus sylvestris L. after a Prolonged Outbreak of Diprion pini L.—A Case Study from Eastern Finland

The frequency and intensity of insect outbreaks have increased in boreal forests, along with associated impacts on the growth and economic losses of host trees. In Finland, the common pine sawfly (Diprion pini L.) is a serious pest, causing declines in health and growth responses of Scots pine (Pinus sylvestris L.). We focused on investigating the species’ defoliating impact on tree radial and volume growth and estimated the economic value of the declined growth. Managed P. sylvestris forests in our study area in eastern Finland have suffered from extended defoliation by D. pini for 15 years since 1999 at varying intensity levels. We classified 184 trees into four defoliation classes and compared annual growth, expressed as growth indices between the classes. We modelled tree volume, estimated economic loss, and compared those to a reference period preceding the initial outbreak. We found significant differences in growth indices between the defoliation classes. Growth losses of 4.2%, 20.8%, and 40.4% were obtained for the mild, moderate, and high defoliation classes, with related economic impacts of 51 €, 272 €, and 734 € per ha for 11 years, respectively. Growth was slightly enhanced in the lowest defoliation class. We suggest that growth-related economic loss caused by D. pini may be significant and depend on defoliation intensity and outbreak duration.

Silver Fir Decline in Pure and Mixed Stands at Western Edge of Spread in Croatian Dinarides Depends on Some Stand Structure and Climate Factors

Silver fir is one of the most threatened conifer species in Croatia, especially at the western edge of its spread in Croatian Dinarides, where the decline in fir trees has resulted in significant ecological and economic issues. The aim of this study was to determine, over an 18-year monitoring period, the relationships of silver fir crown defoliation with climatic factors and structural attributes. We further analyzed the tree retention time in a given defoliation class and transition dynamics between defoliation classes, as well as the survival/mortality of trees. Data on silver fir defoliation were analyzed in two different forest types: in pure silver fir and in mixed silver fir and common beech stands. The climatic factors, primarily vegetation period air temperature, potential evapotranspiration, and dry season water deficit, were correlated with crown defoliation. Regarding the structural attributes, in the mixed stand with predominantly smaller trees, crown defoliation increased with reduced diameter at breast height, crown diameter, social class, and crown illumination. In the pure fir stand, crown defoliation increased with reduced crown diameter, greater crown asymmetry, greater crown illumination, and on trees with a stork’s nest crown. The retention time in defoliation classes differed for research sites. Transition dynamics were different only for trees in the highest defoliation class (dead trees). At the end of the study period, silver fir mortality was higher in the pure fir stand. Increased silver fir defoliation and mortality can be expected in the future, particularly in overmature stands under prolonged drought stress. Permanent forest monitoring could ensure the high-quality data needed for adaptive management of fir stands that could positively influence the structure of these stands and, thus, improve their health status.

Life condition assessment of scotch pine in the area of location of municipal solid waste landfill “Zhiroshkino”

The bioindication method is used to assess the general vital condition of coniferous phytocoenoses growing at different distances (0.25, 0.75, 1.4, 2.4 km) from municipal solid waste landfill Zhiroshkino (Moscow region, Domodedovo district). The object of study is ordinary pine ( Pinus sylvestris L. ), as the most sensitive to the action of pollutants and often used in Russia phytoindicator. The state of generative organs (number of old and new cones, increase of shoots), defoliation and depigmentation class were selected as diagnostic indicators; the category of vital condition was determined and the stand state index was calculated. It was found out that closed objects of production and consumption waste disposal have a negative impact on the stand of an ordinary pine tree. Thus, trees growing at a distance of 250 m from the landfill within its sanitary-protective zone, according to the stand status index are characterized as strongly weakened. At the distance from the waste landfill the tendency of increasing the number of healthy trees in the structure of phytocoenosis was recorded, and their vital condition was assessed as weakened by the growing stock. The index of stand condition, classes of defoliation and depigmentation, the number of generative organs have reached the control values (Kuzminsky Forest Park, the prevailing category of weakened trees) at the distance of 2.4 km from the disposal site. However, the values of these indicators are much lower than the background ones (Prioksko-Terrasny Reserve, the prevailing category healthy trees) for all studied coniferous phytocoenoses. The conclusion is made about the possibility of bioindication method using morphological features of ordinary pine as an express method of assessment of negative impact of waste disposal objects on the environment.

Evaluating annual spruce budworm defoliation using change detection of vegetation indices calculated from satellite hyperspectral imagery

During spruce budworm (SBW; Choristoneura fumiferana (Clem.)) outbreaks, defoliation causes severe tree damage and mortality to spruce-balsam fir (Picea spp.-Abies balsamea (L.) Mill.) forests. Annual defoliation thematic maps provide vital information for forest protection planning against outbreaks, but such data are challenging to accurately collect over large areas during a short (2–3 week) period when damaged foliage peaks. Current operational methods for estimating annual defoliation are aerial surveys, through visual observations by professionals from small aircraft, defining broad defoliation classes which are subjective and spatially can be inaccurate. Remote sensing studies estimating annual defoliation are limited due to lack of ground verification data and difficulty of capturing spectral changes specific to the short detection period. Only one study has used satellite hyperspectral imagery to detect annual SBW defoliation, classifying just two classes of defoliation and using inaccurate aerial survey results for training and validation. In this paper, we introduce a new method to estimate annual SBW defoliation in three classes (light ≤ 30%, moderate 30–70%, and severe ≥ 70%), using change detection of vegetation indices (VIs) derived from satellite (EO-1 Hyperion) hyperspectral imagery acquired before and after annual defoliation. Random Forest and Support Vector Machine classifiers were used to classify defoliation, and intensive field measurements of branch-level defoliation per plot were used for accuracy assessment. Field plots, with spatially correlated defoliation within stands, were used to derive an additional 624 plots to obtain sufficient and independent datasets for training and validating the detection results. The top four VIs for detecting annual defoliation, based on Random Forest Total Variable Importance Score and Spearman's rank correlations, were Plant Senescence Reflectance Index, Normalized Difference Water Index, Moisture Stress Index, and Enhanced Vegetation Index. The spectral regions of VIs used to classify defoliation included visible, near-infrared, red-edge, and shortwave infrared. Accuracies of the light, moderate, and severe defoliation classes using our method ranged from 55–85%, 40–76%, and 40–80%, respectively, which were significantly higher than the 32% accuracy of aerial survey defoliation data for the plots.

Silver birch health condition in the parks of Kharkiv National Agrarian University named after V.V. Dokuchaev

Recently health condition of silver birch (Betula pendula Roth.) stands worsens in the forest and ornamental stands. It is important to know the probability of its improvement or deterioration in particular stands to take the necessary measures in time. 
 The aim of the research was to assess the trends in the health condition dynamics of silver birch stands depending on their age class and the initial health condition of the trees. The research was carried out in 2015-2019 in the Silver birch linear stands in two parks of Kharkiv National Agrarian University named after V.V. Dokuchaev (49º53' N, 36º27' E). Five sample plots of the 3th age class are located in Veterans Park and the other 4 sample plots of the 5rd age class – in Arboretum of this University.
 For each inspected tree diameter at breast height (DBH) was measured in 2015 and 2019. Crown defoliation and health condition class were visually assessed in July of each year. Health condition index (HCI) was calculated as mean weighted from trees number of each category of health condition, separately for all living and dead trees (HCI1–6) and for living trees only (HCI1–4). Tree mortality was expressed as a percentage of lost (dead) trees for research period out of the total trees in 2015.
 It was shown that the silver birch stands of the 3rd age class didn't change their health condition for 2015-2019 or improved it. The stands of the 5th age class worsened their health condition in three sample plots and improved it in one sample plot. Within each age class, the stands of lower diameter class had a worse health condition. Tree mortality was registered in two out of five sample plots in the stands of the 3rd age class and in three out of four sample plots in the stands of the 5th age class. In the stands of the 5th age class the trees from the stands of the smallest diameter class characterized by the highest mortality level (22.4%) and the worse health condition (HCI1-4 =2.8).
 In pooled sample of plots, the death probability for silver birch trees, which 4 years ago had the 1st class of health condition is 3.5%, those of the 2nd class have the death probability of 10.7%, the trees of the 3rd class – 36.9%, those of the 4th class – 84.6%. As for an initially weakened stand, its trees which 4 years ago had the 1st, the 2nd, the 3rd or the 4th health condition class, have the death probability of 5%, 18.5%, 33.3%, and 100% respectively.
 Thus, the weakened silver birch stand which contains trees of 1st - 3rd classes of health condition is able to restore condition to a healthy one, and the deterioration may be expected only for severely weakened trees (having 3rd class of health condition in 2015). The weakened silver birch stand which has the trees of 1st - 4th health condition classes is most likely to weaken even more severely over 4 years.

Fosetyl-aluminium injection controls root rot disease affecting Quercus suber in southern Spain

In Spain, natural and managed cork oak woodlands are severely affected by decline caused by the root rot oomycetes Phytophthora cinnamomi and Pythium spiculum. The need for environmental-friendly disease management makes the use of resistance inducers a suitable option. As the use of phosphite is prohibited in Spain, trunk injections of fosetyl-aluminium were tested in a seminatural cork oak woodland (dehesa). Sixty cork oaks in three different defoliation classes (asymptomatic, slight, and moderate defoliation) were selected for fosetyl- aluminium or control (water) trunk injections, and periodically checked for defoliation and presence of both pathogens in roots and rhizosphere soil. Three years after treatments, fosetyl-aluminium injection significantly decreased defoliation in treated cork oaks in comparison with water-injected controls, regardless of the initial defoliation class considered. Changes in inoculum density in the rhizosphere or presence of the two pathogens in roots were not significantly dependent on treatment. However, a trend to a lower presence of pathogens in roots of treated oaks was observed with increasing soil inoculum densities. Fosetyl-aluminium, a phosphonate fungicide registered in the European Union, was experimentally proved to protect cork oaks against root rot caused by P. cinnamomi and Py. spiculum, even exhibiting a therapeutic effect on preexisting infections. This effective measure can therefore be used to fight against this highly destructive disease in seminatural woodlands and in protected natural ecosystems.

Trunk injection of fosetyl‐aluminium controls the root disease caused by Phytophthora cinnamomi on Quercus ilex woodlands

In Spain, Quercus open woodlands are animal ranching systems of organic production seriously threatened by the exotic pathogen Phytophthora cinnamomi. The root disease it causes kills thousands of oaks annually. Effective disease management needs to integrate different techniques, and the use of a resistance inducer such as fosetyl‐Al can play a key role, because the use of potassium phosphite is prohibited in Spain. In a woodland where the pathogen recently arrived, 60 holm oaks in three different defoliation classes (asymptomatic, slight and moderate defoliation) were selected for trunk injection with pressurised capsules containing 4% of commercial fosetyl‐Al or water (controls). Holm oaks were checked periodically for defoliation and presence of the pathogen in roots and rhizosphere soil. Three years after treatments, defoliation was significantly lower in oaks treated with fosetyl‐Al, which even increased canopy cover, in comparison with control oaks, independent of the initial defoliation class considered. Chlamydospore density in rhizosphere soil, as well as the presence of the pathogen into the roots, was not significantly influenced by fosetyl‐Al treatments, although a trend to a lower presence of P. cinnamomi in roots was observed in treated oaks at every soil inoculum density detected. This study has shown that fosetyl‐Al, a phosphonate registered as a fungicide in the European Union, provides protection to holm oaks against P. cinnamomi, even exhibiting a therapeutic effect on pre‐existing infections. Consequently, this effective measure should be considered as part of the integrated approach to control this highly destructive pathogen in holm oak woodlands.

Below-ground hydraulic constraints during drought-induced decline in Scots pine

Below-crown hydraulic resistance, a proxy for below-ground hydraulic resistance, increased during drought in Scots pine, but larger increases were not associated to drought-induced defoliation. Accounting for variable below-ground hydraulic conductance in response to drought may be needed for accurate predictions of forest water fluxes and drought responses in xeric forests. Hydraulic deterioration is an important trigger of drought-induced tree mortality. However, the role of below-ground hydraulic constraints remains largely unknown. We investigated the association between drought-induced defoliation and seasonal dynamics of below-crown hydraulic resistance (a proxy for below-ground hydraulic resistance), associated to variations in water supply and demand in a field population of Scots pine (Pinus sylvestris L.) Below-crown hydraulic resistance (rbc) of defoliated and non-defoliated pines was obtained from the relationship between maximum leaf-specific sap flow rates and maximum stem pressure difference estimated from xylem radius variations. The percent contribution of rbc to whole-tree hydraulic resistance (%rbc) was calculated by comparing stem water potential variations with the water potential difference between the leaves and the soil. rbc and %rbc increased with drought in both defoliated and non-defoliated pines. However, non-defoliated trees showed larger increases in rbc between spring and summer. The difference between defoliation classes is unexplained by differences in root embolism, and it is possibly related to seasonal changes in other properties of the roots and the soil-root interface. Our results highlight the importance of increasing below-ground hydraulic constraints during summer drought but do not clearly link drought-induced defoliation with severe below-ground hydraulic impairment in Scots pine.

Tree canopy defoliation impacts avifauna

Tree canopies, critical elements of many ecosystems, are damaged by a variety of processes. We investigate how defoliation of manna gum (Eucalyptus viminalis), a species often over-browsed by koalas (Phascolarctos cinereus), influences winter use of trees by birds at Cape Otway, Victoria, Australia. We conducted bird surveys at 55 trees (‘sites’) that were classified into four defoliation classes. Canopy cover declined and the number of dead limbs increased with more defoliation, but tree size, proximity to trees in other defoliation classes, and sub-canopy vegetation (cover and structure) did not vary between defoliation classes. Species richness of birds was lower and assemblages changed, at highly defoliated sites. Fewer microhabitats (especially those in the canopy) were used by birds in defoliated sites. This suggests that defoliated canopies provide fewer resources to birds than those that are intact. Current management of high-density koala populations focusses on koala welfare. Our study highlights the need to consider the impacts of the defoliation caused by this species to other woodland fauna.

Does butt rot affect the crown condition of Norway spruce trees?

Due to the effect of butt rot, Norway spruce crown defoliation has increased, and the proportion of healthy trees has decreased; butt rot acts as a predisposing factor for the decline of spruce. The exact contribution of butt rot in influencing the health and vitality of Norway spruce is still unclear. Previous studies have mostly evaluated the effect of butt rot on the radial increment in Norway spruce, as an indicator of the productivity and vitality of the tree. To our knowledge, no study has evaluated the influence of butt rot on the crown condition of Norway spruce; previous studies mainly determined the incidence and frequency of butt rot based on external signs (crown parameters). In this paper, we performed a comparison of the average crown defoliation among decayed and non-decayed Norway spruce trees within three single Norway spruce stands. We addressed the following questions: did the average Norway spruce crown defoliation differ among decayed and non-decayed trees? Did butt rot predispose, initiate, or contribute to the Norway spruce decline process? Results revealed that the average crown defoliation was higher among decayed trees in all three assessed stands. Among the decayed Norway spruce trees, the proportion of trees with defoliation class 0 (crown defoliation from 0 to 10%) was considerably low and that of trees with defoliation class 2 (crown defoliation from 26 to 60%) was much greater compared to that in non-decayed trees. The study was able to verify the assumption that as per Manion’s tree decline concept, butt rot acts as a predisposing factor for the decline of Norway spruce because of a non-lethal effect. This study provides meaningful knowledge about the influence of butt rot on the crown condition of Norway spruce and contributes to a better understanding of the impact of disease on spruce vitality.

Sensitivity analysis of RapidEye spectral bands and derived vegetation indices for insect defoliation detection in pure Scots pine stands

This study investigated the statistical relationship between defoliation in pine forests infested by nun moths (Lymantria monacha) and the spectral bands of the RapidEye sensor, including the derived normalized difference vegetation index (NDVI) and the normalized difference red-edge index (NDRE). The strength of the relationship between the spectral variables and the ground reference samples of percent remaining foliage (PRF) was assessed over three test years by the Spearman’s ρ correlation coefficient, revealing the following ranking order (from high to low ρ): NDRE, NDVI, red, NIR, green, blue, and red-edge. A special focus was directed at the vegetation indices. In both discriminant analyses and decision tree classification, the NDRE yielded higher classification accuracy in the defoliation classes containing none to moderate levels of defoliation, whereas the NDVI yielded higher classification accuracy in the defoliation classes representing severe or complete defoliation. We concluded that the NDRE and the NDVI respond very similarly to changes in the amount of foliage, but exhibit particular strengths at different defoliation levels. Combining the NDRE and the NDVI in one discriminant function, the average gain of overall accuracy amounted to 7.8 percentage points compared to the NDRE only, and 7.4 percentage points compared to the NDVI only. Using both vegetation indices in a machine-learning-based decision tree classifier, the overall accuracy further improved and reached 81% for the test year 2012, 71% for 2013, and 79% for the test year 2014.

HEALTH CONDITIONS OF THE UKRAINIAN CARPATHIANS FORESTS IN 2016 AND THEIR DYNAMICS ACCORDING TO FOREST MONITORING

ICP-Forest monitoring program provides European forests health estimation from the late 1980 s. Forty two percent of estimated trees had damages and their main cause was insects. Therefore, our colleagues have been providing Ukrainian Carpathians forests monitoring since 1989 according to the ICP-Forest methods. The results of 13 objects estimation in 2016 and the analysis of regional forests health from 1991 to 2016 are an object of the paper. Our investigation has obtained the following results. Firstly, tree crown defoliation in 2016 fluctuated from 7.1 % – for Silver fir to 12.3 % – for hornbeam. Tree crown damages in 2016 fluctuated from 9.4 % – for Silver fir to 21.4 % – for Pedunculate oak. Dry branches for coniferous species and defoliators (insects) for deciduous species were main types of crown damages this year. The proportion of trees without damages was 40.3 % in 2016. The dynamics of the forests health indicators from 1991 to 2016 was estimated on the example of main species. Their damage (defoliation) class dynamics was similar to the sinewave during last 26 years, but it substantially differs for some species. Norway spruce defoliation class fluctuated from 0.3 to 1.8 and its dynamics approximation had higher assurance (0.72) than other species. Common beech defoliation class fluctuated from 0.4 to 1.2 and its dynamics approximation was the best (0.77). Average forest damages dynamics also was similar to the sinewave during last 26 years in the Ukrainian Carpathians, but its correlation with defoliation dynamics was strong only for Norway spruce (r=0,747), but not for Common beech (r=0.411) and for Pedunculate oak (r=0.466). Norway spruce entomological damages fluctuated from 6 to 22 (mean – 13.6 %) and were maximal within main species. Its dynamics approximation was the best (0.600). Common beech entomological damages fluctuated from 4 to 12 % (mean – 7.2 %) and its dynamics approximation was one of the worst (0.311). Thus we have made certain conclusions. Average health conditions of Ukrainian Carpathians forests were good in 2016 as damages were small. The best health conditions were in regional common beech forests and their intensive improving occurred during last 6 years after their intensive deterioration from 2000 to 2011. Common regional beech forests also had the smallest entomological damages within main forest species, it was insignificant. Health conditions of Ukrainian Carpathians forests were also good during last 26 years (1991-2016). Maximal defoliation and entomological damages were in Norway spruce regional forests and in regional Pedunculate oak forests, but even they were small.

Effects of parent material, stand type and oak species on defoliation of coppice-originated oak (Quercus spp.) forests in Northern Turkish Thrace

Cases of significant defoliation in oak (Quercus spp.) forests have been reported in Turkey and throughout the world. Oak trees are important in Turkish forests and forestry and cover vast pieces of land in Thrace. In this study, in a quest to determine the general health condition of pure oak forests in Northern Turkish Thrace, the defoliation rate of tree crowns was evaluated for 8,769 trees in 336 sample plots corresponding to different geological parent materials, regions, oak species and stand types. The defoliation rates were designated and assessed based on the criteria of the European Union Forest Health Monitoring Program (UNECE-ICP Forests). The defoliation rate was, to a significant extent, affected by stand type, the geological parent material, and oak species. In general, 47 % of trees exhibited defoliation. The highest ratio of defoliation was found in Kirklareli Region, where water deficit was the highest, and the parent material was schist-calcschist. Medium diameter forests (MDF, mean dbh: 8-20 cm, ratio of defoliated trees = 65 %) among stand types, and sessile oaks (ratio of defoliated trees = 53 %) among oak species, had the highest defoliation rates. Achieved results demonstrated that the defoliation classes in observed oak stands have a significant relation with variables concerning stand types, oak species and geological parent materials.

The role of defoliation and root rot pathogen infection in driving the mode of drought-related physiological decline in Scots pine (Pinus sylvestris L.).

Drought-related tree die-off episodes have been observed in all vegetated continents. Despite much research effort, however, the multiple interactions between carbon starvation, hydraulic failure and biotic agents in driving tree mortality under field conditions are still not well understood. We analysed the seasonal variability of non-structural carbohydrates (NSCs) in four organs (leaves, branches, trunk and roots), the vulnerability to embolism in roots and branches, native embolism (percentage loss of hydraulic conductivity (PLC)) in branches and the presence of root rot pathogens in defoliated and non-defoliated individuals in a declining Scots pine (Pinus sylvestris L.) population in the NE Iberian Peninsula in 2012, which included a particularly dry and warm summer. No differences were observed between defoliated and non-defoliated pines in hydraulic parameters, except for a higher vulnerability to embolism at pressures below -2 MPa in roots of defoliated pines. No differences were found between defoliation classes in branch PLC. Total NSC (TNSC, soluble sugars plus starch) values decreased during drought, particularly in leaves. Defoliation reduced TNSC levels across tree organs, especially just before (June) and during (August) drought. Root rot infection by the fungal pathogen Onnia P. Karst spp. was detected but it did not appear to be associated to tree defoliation. However, Onnia infection was associated with reduced leaf-specific hydraulic conductivity and sapwood depth, and thus contributed to hydraulic impairment, especially in defoliated pines. Infection was also associated with virtually depleted root starch reserves during and after drought in defoliated pines. Moreover, defoliated and infected trees tended to show lower basal area increment. Overall, our results show the intertwined nature of physiological mechanisms leading to drought-induced mortality and the inherent difficulty of isolating their contribution under field conditions.

Drought‐induced defoliation and long periods of near‐zero gas exchange play a key role in accentuating metabolic decline of Scots pine

Drought-induced defoliation has recently been associated with the depletion of carbon reserves and increased mortality risk in Scots pine (Pinus sylvestris). We hypothesize that defoliated individuals are more sensitive to drought, implying that potentially higher gas exchange (per unit of leaf area) during wet periods may not compensate for their reduced photosynthetic area. We measured sap flow, needle water potentials and whole-tree hydraulic conductance to analyse the drought responses of co-occurring defoliated and nondefoliated Scots pines in northeast Spain during typical (2010) and extreme (2011) drought conditions. Defoliated Scots pines showed higher sap flow per unit leaf area during spring, but were more sensitive to summer drought, relative to nondefoliated pines. This pattern was associated with a steeper decline in soil-to-leaf hydraulic conductance with drought and an enhanced sensitivity of canopy conductance to soil water availability. Near-homeostasis in midday water potentials was observed across years and defoliation classes, with minimum values of -2.5MPa. Enhanced sensitivity to drought and prolonged periods of near-zero gas exchange were consistent with low levels of carbohydrate reserves in defoliated trees. Our results support the critical links between defoliation, water and carbon availability, and their key roles in determining tree survival and recovery under drought.

Estimating crown defoliation of Scots pine (Pinus sylvestris L.) trees using small format digital aerial images

This study focuses on the possibilities of using small format digital aerial images for the estimation of tree crown condition. The test area was located in the eastern part of Lithuania where Scots pine (Pinus sylvestris L.) trees prevail and was photographed using a Canon EOS-1DsMark II digital camera installed on-board a SkyArrow ultra-light aircraft. The camera lenses were adopted to capture images corresponding to conventional color-infrared photography. In addition, the test area was photographed using a large format digital frame aerial camera (Vexcel UltraCam D) installed on board a Rockwell Turbo Commander 690A high performance commuter aircraft. The ground sampling density of the images taken was around 9-10 cm. Crown defoliation was assessed in the field for more than 500 Scots pine trees located in 46 sample plots representing stands of trees that were either 65 years old or 170 years old. Spearman’s correlations coefficients were used to check for relationships between tree crown defoliation and image characteristics. The defoliation was also predicted using the non-parametric k-Nearest Neighbor method applied on data available from aerial images alone. The results were validated using the “Leave One Out” technique by comparing the obtained data with data from the field assessed defoliation rates. The prediction root mean square errors were calculated using data from the small format aerial images as being 11.5% for the younger trees, whereas those calculated using conventional aerial images were between 9.5 and 9.9%. The differences in predicted root mean square errors disappeared in the older stands and both methods produced errors of between 8.1 and 8.5%. Defoliation class was correctly predicted for approximately 84-88% of the older tree crowns and correctly for 75-85% of the younger tree crowns. These results showed that small format aerial images had the potential to predict defoliation in tree crowns and were comparable with results obtained using conventional aerial images. Their main advantage is that small format images are much cheaper to obtain than conventional images when the areas targeted are thousands of hectares in size.

Genotypic Differences and Prior Defoliation Affect Re-Growth and Phytochemistry after Coppicing in Populus tremuloides

Although considerable research has explored how tree growth and defense can be influenced by genotype, the biotic environment, and their interaction, little is known about how genotypic differences, prior defoliation, and their interactive effects persist in trees that re-grow after damage that severs their primary stem. To address these issues, we established a common garden consisting of twelve genotypes of potted aspen (Populus tremuloides) trees, and subjected half of the trees to defoliation in two successive years. At the beginning of the third year, all trees were severed at the soil surface (coppiced) and allowed to regenerate for five months. Afterwards, we counted the number of root and stump sprouts produced and measured the basal diameter (d) and height (h) of the tallest ramet in each pot. We collected leaves one and two years after the second defoliation and assessed levels of phenolic glycosides, condensed tannins, and nitrogen. In terms of re-growth, we found that the total number of sprouts produced varied by 3.6-fold among genotypes, and that prior defoliation decreased total sprout production by 24%. The size (d(2)h) of ramets, however, did not differ significantly among genotypes or defoliation classes. In terms of phytochemistry, we observed genotypic differences in concentrations of all phytochemicals assessed both one and two years after the second defoliation. Two years after defoliation, we observed effects of prior defoliation in a genotype-by-defoliation interaction for condensed tannins. Results from this study demonstrate that genotypic differences and impacts of prior defoliation persist to influence growth and defense traits in trees even after complete removal of above-ground stems, and thus likely influence productivity and plant-herbivore interactions in forests affected by natural disturbances or actively managed through coppicing.