Degree Of Defoliation Research Articles

Synergistic effects of past historical logging and drought on the decline of Pyrenean silver fir forests

The causal factors and effects of forest declines are not well understood in temperate conifer forests. Most studies have focused on climatic and environmental stressors and have obviated the potential role of historical forest management as a predisposing factor of decline. Here, we assess if the recent silver fir ( Abies alba) decline observed in the Spanish Pyrenees was predisposed by historical logging and incited by warming-induced drought stress. We analysed a dataset of environmental, structural, and historical variables at the tree and stand level including 32 sites with contrasting degrees of defoliation distributed over 5600 km 2. We followed a dendroecological approach to reconstruct historical logging and to infer the effects of warming-induced drought stress on growth. The silver fir decline was more severe and widespread in western low-elevation mixed forests dominated by trees of small size and slow growth. These sites were subject to higher water deficits than eastern sites, where late-summer rainfall as the key climatic variable controlling silver fir growth was higher. Declining sites showed more frequent growth releases induced by historical logging than non-declining sites. Historical logging and warming-induced drought acted as long-term predisposing and short-term inciting factors of silver fir decline in the Pyrenees, respectively. We suggest that biomass increases caused by past intense logging affected the vulnerability of silver fir against late-summer water deficit. Future research in declining temperate conifer forests should consider the interacting role of predisposing historical management and inducing climatic stressors such as droughts.

An agro-economic appraisal of the response of okra to leaf defoliation: Growth and marketable yeild

The leaves, shoots, immature pods and dry seeds of okra are used extensively in vegetable food preparations in the tropics. The fruit is rich in minerals and vitamins, which are essential for body functions. The soft and succulent nature of the leaves make them vulnerable to attack and subsequent damage by a range of leaf eating insects, animal pests and man. Such damage results in remarkable yield loss and reduced market value. Identification of the critical stages of attack and extent of loss taking place at each stage of development of the plant could aid in planning strategies for prevention and/or control. Thus, two field experiments were conducted to determine the effect of leaf removal on the growth and marketable yield of okra. The treatments on leaf defoliation at different stages of development consisted of removal of leaves at 4 weeks after sowing (WAS) as early vegetative stage, 6WAS (at floral budding stage) and 8 WAS (at early fruiting stage). The treatments on the degrees of defoliation included the control (no leaf removal), removal of a quarter (D25), half (D50), three quarter (D75) or total removal (D100) of every fully expanded leaf. Different proportions of every leaf were removed with sharpened scissors. Each treatment was replicated four times. The experiment was 3 x 5 factorial with randomized complete block design. Current market price was used to value the yields. The removal of up to a quarter of each leaf did not affect the fruit yield significantly but the yield was significantly reduced by 39, 79 and 86% when ½, ¾ of each leaf and complete leaf were defoliated, respectively. In money terms, the losses were N26,390($175.93), N52,780($351.87), and N57,876($385.84) per hectare, respectively for these various defoliation levels. Removal of okra leaves during the early fruiting stage led to 82% marketable yield reduction. Complete leaf defoliation was detrimental to fruit yield. The results suggested that okra could tolerate 25% defoliation as might occur from leaf eating insects, human predators or foliage pathogenic infections but beyond this level, it would be detrimental. A programme of control of leaf predators in okra management should therefore commence prior to or at the early fruiting phase in order to realize yields of good value. Further research on commercial uses of okra and the economics of pest control on okra fields is recommended. Key words : Agro-economic, Defoliation, Fruiting, Yield, Commercial

Detection and Prognosis Defoliators Tortrix viridana and Pristiphora abietina in the Northwestern Transylvania Forests

Forest pest detection and prognosis are important works in forest protection activities, and because of these it can be known the health of forests at any time of year. In the sylviculture point of view, there are the primary meaning forestry pests and pests distinguish secondary, the first that stands against a culture and under certain conditions of vegetation, climate and mass medium can replicate. Establishing forecasts to reflect the real situation of forest sampling of surfaces requires control data referring to quantity, quality and rate of injuries. Thus, for each stand or for groups of stands with similar conditions (in terms of stationary and stand composition and age) and the same degree of defoliation, it will be taken 32 samples of litter and soil. Each sample will represent the collected material on a surface of 25 x 25 cm. The data presented in this paper, on the forecast Tortrix viridana, 2010 shows that infestations will be very weak and weak, except for two bodies Forest Forest Departments in Oradea and Satu Mare, where defoliation will be strong and very strong.

SINGLE DEFOLIATION HAD LITTLE INFLUENCE ON GROWTH AND DRY MATTER ATTRIBUTES OF SHEA (VITELLARIA PARADOXA C. F. GAERTN.) SEEDLINGS

ABSTRACT Seedlings of Vitellaria paradoxa are normally subjected to annual environmental hazards within the savanna environment that tends to constitute serious impediment to their growth. A field and nursery experiment was conducted in July 2009 to July 2010 to test seedling recovery when subjected to 3 defoliation times (22, 26 and 30 weeks after planting) and levels (0, 50 and 100%). Factorial combinations of this were laid out in randomized blocks and replicated three and four times respectively in the field and nursery experiments. Results of analysis of variance indicated container raised seedlings showed significant response only to defoliation time in which case leaf removal 30 weeks after planting resulted to seedlings with significantly lower values of leaf width and leaf area. Field grown seedlings did not respond significantly in any of the growth parameters to treatment but showed a tendency towards lower values when defoliated 30 weeks after planting. Generally, seedlings defoliated 30 weeks after planting showed a tendency towards reduced fresh/dry weight and dry matter attributes except dry matter partitioning to the root where the reverse was the case. Degree of defoliation did not significantly affect seedling growth and dry matter attributes although the most severe defoliation treatment (100%) tended to have the lowest values for most parameters. Generally, single defoliation, or one year disturbance in the field, only marginally affects seedling growth.

Health status of forest stands on permanent research plots in the Krkonoše Mts.

Damage to beech, mixed (beech with spruce to spruce with beech) and spruce stands in the Krkonoše Mts. is described on the basis of evaluation of transition matrices describing the probability of a change in the assessment of defoliation of particular trees in defoliation classes. The condition and development of health status were evaluated in the long run on PRP 1–32 in the Krkonoše Mts. by foliage and degrees of defoliation. Features describing the health status of the tree crown (damage by snow, frost, wood-decaying fungi, and insects) were also evaluated. Average defoliation, standard deviation of defoliation, estimation of minimum defoliation, and frequency of the tree number in defoliation classes were calculated for each plot, and each year. Three characteristic periods were distinguished according to different trend of foliage dynamics: period of the first symptoms of damage (1976–1980) – a decrease in foliage on average max. by 1% per year, period of great damage (1981–1988) – annual defoliation on average around 3–16%, period of damage abatement (1989–2009) – annual defoliation on average between 0% and 4%. The incomparably higher resistance of autochthonous stands to air pollution stress culminating in the eighties of the last century was demonstrated unambiguously.

Drought-induced growth decline of Aleppo and maritime pine forests in south-eastern Spain.

Climate warming may enhance the negative effects of droughts on radial growth in areas with severe water deficit, such as Mediterranean mountains under semi-arid conditions. The impacts of drought on growth decline of Mediterranean pines have not been evaluated considering species with different vulnerability and areas with contrasting climates. Dendrochronological methods were used to assess the responses of basal area increment to drought in Pinus pinaster and P. halepensis plantations. We compared growth trends of trees with different defoliation degree in two sites in south-eastern Spain (Sierra de los Filabres and Sierra de Baza) with contrasting climatic conditions. In the more xeric area (Filabres) both pine species showed a sharp growth reduction in response to extreme droughts such as those observed in 1994-1995, 1999 and 2005. The radial growth of both species was enhanced by May and June precipitation of the year of tree-ring formation. P. pinaster showed higher defoliation in the xeric area (Filabres) than in the more mesic area (Baza) but needle loss was not linked to an abrupt growth reduction. Contrastingly, divergent radial growth patterns between trees showing high and low defoliation degrees were found for P. halepensis in the more xeric area, where a negative relationship between recent basal area increment and defoliation was found. Pine plantations in Mediterranean mountains under semi-arid conditions are highly vulnerable to warming-induced droughts. Such marginal stands constitute valuable monitoring systems to assess the negative impacts of drought on tree growth, and to test if management strategies as thinning can mitigate the negative impacts of climate warming on similar drought-stressed forests.

Field reactions of plum cultivars to the shot-hole disease in southern Italy

The reactions to shot-hole disease ( Stigmina carpophila) of nine plum cultivars and seed-propagated myrobalan trees were evaluated during three years in three commercial orchards located at Nova Siri, Matera, Italy. In July 2006, May 2007, June 2007 and June 2008, shot-hole severity and twig defoliation were assessed. Pathogen pressure was higher in 2007 and 2008 than in 2006. In the three years of study, cultivar Golden Plumza was the most susceptible to the shot-hole measured by leaf severity, however it showed variable defoliation percentages in different years. The seed-propagated myrobalan trees were the most resistant, although they showed a slight degree of defoliation in 2007 and 2008. Intermediate reactions to the disease occurred in cultivars Angeleno, Autumn Giant, Fortune, Green Sun, October Sun, Santa Rosa, Sorriso di Primavera and T.C. Sun. A significant correlation between shot-hole leaf severity and twig defoliation was detected. To our knowledge, this is the first report on screening for resistance of plum cultivars to shot-hole disease.

Spectral mixture analysis to monitor defoliation in mixed-aged Eucalyptus globulus Labill plantations in southern Australia using Landsat5-TM and EO-1Hyperion data

Defoliation is a key parameter of forest health and is associated with reduced productivity and tree mortality. Assessing the health of forests requires regular observations over large areas. Satellite remote sensing provides a cost-effective alternative to traditional ground-based assessment of forest health, but assessing defoliation can be difficult due to mixed pixels where vegetation cover is low or fragmented. In this study we apply a novel spectral unmixing technique, referred to as weighted Multiple Endmember Spectral Mixture Analysis (wMESMA), to Landsat 5-TM and EO-1 Hyperion data acquired over a Eucalyptus globulus (Labill.) plantation in southern Australia. This technique combines an iterative mixture analysis cycle allowing endmembers to vary on a per pixel basis (MESMA) and a weighting algorithm that prioritizes wavebands based on their robustness against endmember variability. Spectral mixture analysis provides an estimate of the physically interpretable canopy cover, which is not necessarily correlated with defoliation in mixed-aged plantations due to natural variation in canopy cover as stands age. There is considerable variability in the degree of defoliation as well as in stand age among sites and in this study we found that results were significantly improved by the inclusion of an age correction algorithm for both the multi-spectral (R2no age correction=0.55 vs R2age correction=0.73 for Landsat) and hyperspectral (R2no age correction=0.12 vs R2age correction=0.50 for Hyperion) image data. The improved accuracy obtained from Landsat compared to the Hyperion data illustrates the potential of applying SMA techniques for analysis of multi-spectral datasets such as MODIS and SPOT-VEGETATION.

Evaluation of <i>Themeda triandra</i> as an indicator for monitoring the effects of grazing and fire in the Bontebok National Park

Up until 2004, the burning regime applied in the Bontebok National Park was aimed at maintaining grazing conditions suitable for bontebok (Damaliscus pygargus pygargus). It was, however, not suitable for maintaining plant species diversity, an increasingly urgent conservation priority for the park. Accordingly, the burning regime was changed in 2004 to increase the interval between fires. A possible unintended outcome of the new burning regime is the spread of grazing lawns which is likely to be deleterious for maintaining the diversity of rare plants. Red grass, Themeda triandra, a species often locally abundant in areas preferred by bontebok, is potentially a good indicator of the anticipated change because, although it persists with moderate grazing, it is sensitive to localised intense grazing and will decrease on grazing lawns. To gauge the potential of this indicator, the canopy spread cover, degree of defoliation and inflorescence production of T. triandrawas determined at 13 permanently marked sites in November 2005. The results are compared with a survey conducted 20 years previously (October–November 1984 and October–November 1985) using similar methodology. The results suggest that T. triandra remained abundant over the previous 20 years’ application of the prior burning regime. In 1984–1985, defoliation of T. triandra was high within 1 year after a fire but declined quickly thereafter. In 2005, the tendency for the defoliation level to decline with increasing time after a fire was still apparent, but it was much less marked than in the previous survey period. A likely cause of this was the fact that Cape mountain zebra (Equus zebra zebra) and red hartebeest (Alcelaphus buselaphus caama) were present in 2005 but absent in 1984–1985 and these taller-grass grazers would have contributed to the use of the older veld. Provided it is interpreted together with other monitoring programmes, the use of T. triandra cover and defoliation intensity appears promising as an efficient indicator of some of the potentially deleterious outcomes of the interactions between herbivory and the new burning regime.Conservation implications: The conservation objectives of maintaining (1) large mammal herbivory as an ecological process and (2) plant species diversity may be difficult to reconcile with each other in the highly fragmented renosterveld and lowland fynbos ecosystems. This paper explores a rapid approach to monitoring impacts of bontebok and other grazing ungulates.

Which factors explain lepidopteran larvae variance in seasonal guilds on some oaks?

Differences between the oak lepidopteran communities were studied in Slovakia in 1993 and 1994. Sampling was undertaken between April and October on 3 oak species. Biological traits of larvae were examined in order to explain differences in seasonal guilds among oaks. Cluster analysis shows similarities between communities in the flush feeder guild where the results were influenced mainly by temporal variability; in the late spring guild mainly by site; factors influencing summer feeder and autumn feeder similarities remain unclear. Detrended Correspondence Analysis (DCA) was used to investigate the main gradients explaining variability in communities. Results indicated that the host specificity along axis 1 (A1) and larval ballooning along axis 2 (A2) were important in the flush feeder guild; larval feeding strategy along A1 and the degree of defoliation by <I>Lymantria dispar</I> along A2 were important in late spring feeders; the year of study along A1 and host specificity along A2 were important in the summer feeder guild; and adaptation to lower quality of food along A1 and host specificity along A2 for the autumn feeder guild. The results are discussed.

Mapping insect defoliation in Scots pine with MODIS time-series data

Insect damage is a general problem that disturbs the growth of forests, causing economic losses and affecting carbon sequestration. Coarse-resolution data from satellites are potentially useful for national and regional mapping of forest damage, but the accuracy of these methods has not been fully examined. In this study, a method was tested for the mapping of defoliation in Scots pine [ Pinus silvestris] forests in southeast Norway caused by the pine sawfly [ Neodiprion sertifer], with the use of multi-temporal MODIS 16-day composite vegetation index data and the TIMESAT processing method. The damage mapping method used differences in summer mean values and angles of the seasonal profiles, indicating decreasing foliage density, to identify pixels that represent areas containing forest damage. In addition to 16-day NDVI the Wide Dynamic Range Vegetation Index (WDRVI) was tested. Damage areas were identified by classifying data into pixels representing damaged versus undamaged forest areas using a boolean combination of thresholded parameters. Classification results were evaluated against the change in LAI estimated from airplane LIDAR measurements, as an indicator of defoliation. The damage classifications detected 71% to 82% of the pixels with damage, and had kappa coefficients varying between 0.48 and 0.63, indicating some overestimation. This was due e.g. to failure to include clear-cut areas in the evaluation data. Damage classification with WDRVI only resulted in slight improvement compared to the NDVI. Only weak relationships were found between the LIDAR-estimated defoliation and the change parameters obtained from MODIS. Consequently, mapping of the degree of defoliation from MODIS was abandoned. In conclusion, the damage detection method based on MODIS data was found to be useful for locating insect damage, but not for estimating its intensity. Control of the detected damage areas using high-resolution remote sensing data, aerial survey, or fieldwork is recommended for accurate delineation in operational applications.

Late leaf development in pedunculate oak (Quercus robur): An antiherbivore defence?

Two phenological forms of the pedunculate oak co-occur in the same habitats throughout the species range: the early trees (Quercus robur var. praecox) develop leaves up to 5 weeks before the late ones (Quercus robur var. tardiflora). This study tests the idea that late leaf flushing serves as an antiherbivore defence, i.e. late trees, which develop leaves asynchronously with eclosion of folivorous caterpillars, avoid the costs of defoliation, which could offset the costs of a later onset of the growing season. Effects of folivorous caterpillars foraging on oaks were observed in 1998–2006 in remnants of primeval temperate lowland forest preserved in the Białowieża National Park (eastern Poland). Observations covered trough and outbreak years of the major defoliator, the winter moth [Operophtera brumata L. (Geometridae)]. In seven out of nine seasons, including all peak caterpillar years, the amount of frass produced by folivorous caterpillars on late trees (n=8–18) was significantly (up to 7.1 times) lower than on the early ones (n=12–32). Assessment of the degree of defoliation in 2002–2006 showed that the late oaks were visibly defoliated only during a caterpillar peak (2003), while the early trees were affected in all years and in 2003 almost completely lost their leaves. The results confirm the effect of late budburst on lowering herbivore damage, and give support to the idea that late leaf flushing acts as an antiherbivore defence.

Geoadditive Bayesian models for forestry defoliation data: a case study

AbstractWe analyze forestry defoliation data from the Emission Impact and Forest Nutrition (IWE) survey, which was carried out in Baden‐Württemberg, Germany in the year 1988. The survey contains information on individual trees such as the degree of defoliation, age, species and measurements on nutrients in the needles, as well as information on tree locations such as soil and geographical characteristics. Our goal is to find suitable predictors for tree defoliation from the above information, and to find a set of models which can explain the underlying biological and environmental processes. To model the spatial correlation in the data and possible nonlinear effects of the covariates we use a geoadditive hierarchical Bayesian model. Posterior inference and model comparison are computationally assessed via Markov Chain Monte Carlo (MCMC) techniques and deviance information criterion (DIC) respectively. Copyright © 2008 John Wiley & Sons, Ltd.

Reaction of South African soybean cultivars to rust caused by Phakopsora pachyrhizi

Soybean rust was recorded in South Africa in February 2001 in the Vryheid area of KwaZulu-Natal, from where it spread throughout production areas east of the escarpment. Management of the disease is presently, based on fungicide spray programs. Commercial soybean cultivars were evaluated for rust resistance at Cedara during 2003/04 and 2004/05. Field trials consisted of 26 entries in fungicide sprayed and unsprayed plots, replicated three times. Weekly (2003/04) or two weekly (2004/05) disease assessments were expressed as affected leaf area based on visual assessments of rust severity and the degree of defoliation. Physiological stage at first detection of disease differed significantly between cultivars with the greatest delay in LS678 during both seasons. There were significant differences in Area Under the Disease Progress Curve (AUDPC) between cultivars and AUDPC was significantly, negatively related to growth stage at first detection. Yield loss was poorly related to AUDPC values but was significantly related to days to maturity, with lower losses in shorter season varieties than in longer season varieties. This, in turn, was related to premature defoliation which was 16 to 21 days earlier in the longer maturity group, in unsprayed plots. Reductions in yield losses were, however, not sufficient to be of economic value and none of the cultivars showed significant rust tolerance.

Selection of feeding areas by cattle in a spatially heterogeneous environment: selection between two tropical grasses

A herd of 28–33 Japanese Black cows (Bos taurus) were allowed to graze on an experimental plot comprising monoculture swards of centipedegrass (Eremochloa ophiuroides) and bahiagrass (Paspalum notatum) (0.39 and 0.61 ha, respectively) for 3–5 days each month (from 0850 to 1600 hours) between May (late spring) and October (mid-autumn). On a monthly basis, the animals showed an increasing trend to select centipedegrass in preference to bahiagrass as the relative crude protein (CP) concentration of the former increased relative to the latter. On a daily basis, the animals showed a decreased selectivity for centipedegrass with the progression of grazing days, as centipedegrass sward lost both quantity and quality faster than bahiagrass sward under higher degrees of defoliation. Animals maintained similar bite rates on the two swards by modifying feeding station behavior as soon as they switched between the swards, i.e., they increased the number of bites per feeding station and decreased the number of feeding stations selected per unit grazing time soon after switching to centipedegrass, with the reverse process occurring soon after the switch to bahiagrass. The results show CP concentration to be a partial forage factor influencing animals’ choice between tropical grasses growing as patches. The results also demonstrate that animals have an ability to adapt their foraging behavior flexibly and rapidly to varying types of vegetation.

Variation in shoot mortality within crowns of severely defoliated Betula maximowicziana trees in Hokkaido, northern Japan

AbstractTo clarify mortality patterns of current‐year shoots within the crown of Betula maximowicziana Regel after severe insect herbivory in central Hokkaido, northern Japan, we investigated the degree of defoliation, pattern of shoot development, shoot mortality, and leaf tissue‐water relations. One hundred current‐year long shoots growing in a B. maximowicziana plantation were observed for defoliation and mortality in June 2002. An outbreak of herbivorous insects (Caligula japonica and Lymantria dispar praeterea) occurred in the stand in mid‐to‐late June, and the monitored shoots were defoliated to various degrees. Within 1 month of defoliation, some of the severely defoliated shoots had produced new leaves on short shoots that had emerged from axillary buds. Stepwise logistic regression revealed that the probability that current‐year long shoots would put out axillary short shoots with leaves is closely related to the degree of defoliation. To evaluate the water relations of the leaves, we determined pressure–volume curves for the leaves that survived the herbivorous insect outbreak and the new leaves that emerged after defoliation. The water potential at turgor loss (Ψl,tlp) and the osmotic potential at full turgidity (Ψπ,sat) were higher for the new leaves than for the surviving leaves, indicating a lower ability to maintain leaf cell turgor against leaf dehydration in the new leaves. Of the 100 shoots, 13 died after the emergence of new leaves. Stepwise logistic regression revealed that the probability that the long shoots would die generally increased with the emergence of new leaves, with increasing shoot height. This result suggests that the combined effect of the vulnerability of newly emerged leaves and low water availability, associated with higher shoot positions within the crown, caused shoot mortality. Based on our results, some possible mechanisms for mortality in severely defoliated B. maximowicziana are discussed.

Are myrmecophytes always better protected against herbivores than other plants?

The present field study compared the degree of defoliation of three Guianian melastome, two myrmecophytes (i.e. plants sheltering ants in hollow structures) and Clidemia sp., a nonmyrmecophytic plant serving as a control. Maieta guianensis Aubl. hosted mostly Pheidole minutula Mayr whatever the area, whereas Tococa guianensis Aubl. hosted mostly Azteca bequaerti Wheeler along streams and Crematogaster laevis Mayr or Azteca sp. 1 in the understory where it never blossomed. Only Tococa, when sheltering A. bequaerti in what can be considered as a truly mutualistic relationship, showed significantly less defoliation than control plants. In the other associations, the difference was not significant, but P. minutula is mutualistic with Maieta because it furnishes some protection (exclusion experiments) plus nutrients (previous studies). When devoid of ants, Tococa showed significantly greater defoliation than control plants; therefore, it was deduced that Tococa probably lacks certain antidefoliator metabolites that control plants possess (both Tococa and control plants are protected by ground‐nesting, plant‐foraging ants, which is termed ‘general myrmecological protection’). Consequently, plant‐ants other than A. bequaerti probably also protect Tococa slightly, thus compensating for this deficiency and permitting it to live in the understory until treefall gaps provide the conditions necessary for seed production. © 2006 The Linnean Society of London, Biological Journal of the Linnean Society, 2006, 89, 91–98.

Yellow sticky boards: a possible way of monitoring little spruce sawfly (Pristiphora abietina) (Hymenoptera: Tenthredinidae)

Several methods of Pristiphora abietina adults catching were compared (Malaise trap, white and yellow sticky boards, sweeping). The yellow sticky boards are handy in the field, and under the high population density appear to be a reliable method of detecting sawfly populations: 1. There was a statistically significant coincidence between the samples of Malaise traps and yellow sticky boards. 2. There was a highly significant linear correlation between the number of caught adults on five sticky boards and the degree of defoliation in seven localities. 3. We did not observe any statistically significant differences between the samples on yellow sticky boards taken in different intervals. To estimate the abundance of adults, it is sufficient to install yellow sticky boards before swarming and check them after the swarming. 4. No statistically significant differences were found between the catch means per board in line with different number of boards, it means with different distance, in both male and females.

Temporal development of crown condition of beech and oak as a response variable for integrated evaluations

The evaluation uses the longest available time series for beech and oak defoliation in Germany. The data from Hesse, starting from 1984, show a typical pattern: for the first 12 years, a continuous increase in defoliation was observed ranging from an average value of 14% in 1984 to a peak value of 30%. This was followed by a subsequent decrease in the loss of foliage accompanied by a high variability, until the last monitoring in 2003, where an average value of 25% defoliation was observed. For both tree species, the years of trend reversal were identical. The same pattern was observed in the German federal states: Rhineland-Palatinate, North Rhine-Westphalia, and Bavaria. The year of trend reversal was identical in Hesse and Rhineland-Palatinate. In North Rhine-Westphalia, it occurred 1 year earlier and in Bavaria 3 years earlier. Whereas defoliation trends were clearly demonstrated, tree mortality did not appear on a large scale. The sample trees were grouped into four discrete clusters according to their annual defoliation values from 1984 to 2003. In 1996, the clusters represent 15, 25, 35, and 50% defoliation values. Regarding beech in Hesse, there was no overlap in the defoliation curves observed among the different clusters. These four clusters having different degrees of defoliation over the whole time span of 20 years were used for a further detailed statistical analysis. For discrete variables like crown spacing and—in the case of beech—fruit bearing, mosaic plots were applied in order to visualize relations of low dimensional contingency tables, with defoliation trends being used as the response variable. The data show for beech a very clear relation between defoliation and age, relative crown spacing, stand composition, and fruit bearing. Regarding oak, besides age and relative crown spacing, the years with significant appearance of biotic stress factors—leaf eating insects—show a clear relation to trends of defoliation. The statistical model used in this study—logistic regression—allows applying a multinomial response variable and a number of continuous or categorical explanatory variables. With this approach, an iterative optimized selection of effect variables was used to test the relevance of different variables on the defoliation pattern of the same four clusters mentioned above. For this, the variables were grouped in an iterative process with five steps, starting with a few basic variables of tree and site information, and ending with a total of more than 20 variables in the fifth step. The process selects first the variables which are of significance on the defoliation, and calculates the possible errors in the grouping of the different trees to the four clusters. In this analysis of beech, the basic tree and stand variables: age, relative crown spacing, stand composition and fruit bearing proved to be the most relevant group of parameters, with the other variables explaining the variation of defoliation only to a minor extent. More complex model levels do not change any basic selected variables; however, Cation Exchange Capacity (CEC), C/N-ratio, Al- and Ca-proportion of CEC are additionally selected and give a hint of the relevance of soil conditions. Regarding beech, the errors of the statistical model are lower compared to oak.

Inventory of the degree of tree defoliation in small areas

The employment of small-area surveys for evaluating forest health is becoming increasingly important because in recent years, new ecological methods of management and conservation have been introduced in commercial forests and in the partial protection zones of national parks. In Poland, in relatively small areas, including forest sections, nature reserves or their fragments, close-to-nature management and near-natural management have been introduced and, in protected areas, typical partial protection is giving way to passive protection. Radical changes in the ways of management and conservation have developed a need for monitoring possible changes in the condition of trees, mainly through the application of precise, small-area methods for assessing their health. The aim of this paper is to present a small-area survey for assessing the degree of tree defoliation and its preliminary verification, in particular the evaluation of the degree of defoliation to fir ( Abies alba Mill.), beech ( Fagus sylvatica L.), pine ( Pinus sylvestris L.), larch ( Larix decidua Mill. subsp. polonica [Racib.] Domin) and oaks ( Quercus robur L. and Q. petraea [Matt.] Liebl.) on Chełmowa Góra Hill in the Świętokrzyski National Park (Poland). Part of the area of Chełmowa Góra comprises a strict nature reserve, set up in 1921, which is one of the oldest strict nature reserves in Poland. The area of Chełmowa Góra is slightly more than 183 ha. The degree of tree damage, determined on the basis of the degree of defoliation, was shown in sub-blocks P 3 of the system of information on natural environment (SINUS). To estimate the spatial distribution of the degree of tree defoliation, survey sampling – based on the scheme of simple random sampling with replacement (SRSWR) – was used. In 1999, Chełmowa Góra's beech and larch were in the best condition, and the worst were young-generation fir, pine and oak. During preliminary verification of the applied method, the mean total errors of the evaluation of proportions of trees in the distinguished defoliation classes, calculated as α = 0.05, reached almost 31% in particular sub-blocks P 3 of the SINUS system; however, in most cases they did not exceed 20%. The average values of mean total errors, calculated for particular tree species in all sub-blocks P 3, were generally lower than 20%. The applied method of inventory enables the assessment of the degree of defoliation and spatial differentiation of tree health in small areas, which in turn, allows the detailed planning of protection and silvicultural measures. The proper assessment of the extent of tree defoliation and its spatial distribution is of fundamental importance for employing the ecological methods of management and rational protection of forest ecosystems, and should be included in the monitoring of both economically used and protected forests.