Pine Mistletoe Research Articles

Viscum album subsp. austriacum (Santalaceae R. Br.) in Volyn Polissia and Zhytomyr Polissia (Ukraine): current distribution, ecology and prediction of future spread

Background. One of the subspecies of the European mistletoe, the so called pine mistletoe (Viscum album subsp. austriacum (Wiesb.) Vollm.) is a hemiparasitic, evergreen, epiphytic phanerophyte that parazitizes predominantely on the Scots pine (Pinus sylvestris L.) in Ukraine. The pine trees infested with V. album subsp. austriacum lack moisture for transpiration and photosynthesis, which reduces their primary productivity, viability and health. The purpose of this study was: 1) to determine the current distribution of V. album subsp. austriacum in Volyn and Zhytomyr Polissia regions using GIS-technology; 2) study the main taxation parameters of pine stands infested with V. album subsp. austriacum; 3) predict the possible further spread of V. album subsp. austriacum in the studied Region. Materials and Methods. The grid mapping method based on GIS technology, with a grid size of 10×10 km and 20×20 km, was used to create the map of the species distribution. The spatial distribution of soil moisture in the forest soils of Drevlyanskyi Nature Reserve was determined using satellite images and data on soil moisture from the Earth Engine Data Catalog. The taxation parameters of the mistletoe-infested pine stand (i.e., participation of the Scots pine in the stand composition, area distribution of pine stands by age, relative completeness, stand quality class, trophotope, and hygrotope) were obtained from standard taxation descriptions. Results and Discussion. The study found that V. album subsp. austriacum is more widespread in Volyn Polissia than in Zhytomyr Polissya – 87 and 20 localities respectively. It was shown that the forest plantations colonized by V. album subsp. austriacum in Drevlyansky Nature Reserve are located in areas with the lowest moisture content, with a moisture reserve of 16–70 mm in the 0–100 cm soil layer, which corresponds to dry and fresh hygrotopes. Conclusions. V. album subsp. austriacum is more widely distributed in such nature reserves of the region as Shatskyi National Nature Park and Drevlianskyi Nature Reserve, and less so in Rivne, Cheremskyi, Polissia Nature Reserves and Pripyat-Stokhid National Nature Park. In the region under study, V. album subsp. austriacum mostly affects pure pine forests aged 80‒140 years, of medium completeness (0.5‒0.7), and relatively high and high stand quality classes – Ic–II, in fresh hygrotopes – 67.3 % of the area and in fairly infertile pine site type (trophotope B) – 51.5 %. Based on the distribution of forest site types in the region and their susceptibility to V. album subsp. austriacum, the possibility of its further intensive spread in the study region can be predicted.

The effects of pine mistletoe (Viscum album subsp. austriacum) on the growth of Scots pine and Crimean pine in Turkey

AbstractIn this study, the effect of pine mistletoe (Viscum album subsp. austriacum) on basal area increment of Crimean pine and Scots pine was investigated. Dendrochronological data were collected from 223 (71 uninfected and 152 infected) Crimean pines and 195 (77 uninfected and 118 infected) Scots pines located in Kastamonu province of Turkey in 2014. Infected sample trees were classified as light, moderate or severe infection levels. Growth trends and basal area increment loses were compared between uninfected and infected trees for the periods of the last 10, 20 and 30 years. In addition, infection status of forest stands was investigated using temporary sample plots; 27 plots in Crimean pine stands and 26 plots in Scots pine. Results demonstrated that basal area increments were negatively affected by pine mistletoe for both species. Mean basal area increment losses of infected trees for the last decade were determined as 24% for Scots pine and 26% for Crimean pine. Basal area increment losses varied by infection levels (light, moderate and severe) as follows: 25%, 20% and 28% for Scots pines and 20%, 32% and 9% for Crimean pines. Scots pine stands were more severely infected by pine mistletoe than Crimean pine stands. There were negative correlations between number of infected trees and stand density for both species, while positive correlation was detected between the number of infected trees and mean diameter for Scots pine. The results of this study indicate that the pine mistletoe infection has negative effect on radial growth of Scots pine and Crimean pine trees. The results can be an important contribution to the forest management and protection activities in mistletoe‐infected stands.

Current Problems of Forest Protection (25–27 October 2022, Katowice Poland)

Forestry is one of the sectors particularly affected by the threats posed by changing climatic conditions. This is reflected in the deterioration of the health status of stands due to the synergistic effect of numerous abiotic and biotic factors. Current forest health problems are due to dynamic, negative changes in the forest environment. While the amount of precipitation remains at a similar level, its distribution varies throughout the year and, in particular, the lack of soil moisture during the growing season leads to the weakening of trees, including the main forest-forming species in Poland such as Pinus sylvestris. The weakening of trees, in turn, leads to species of insect pests that were previously considered secondary becoming primary pests, such as Ips acuminatus. It is likely that weakening of trees also favours increased occurrence of parasitic plants such as Viscum album ssp. austriacum or Loranthus europaeus. Infestations of the hemiparasitic, xylem-secreting pine mistletoe are of great interest because they are spreading rapidly throughout Europe. Drought in forests is not only a long-term water shortage, but also a situation in which plant-fungal relationships are disrupted. Reduced water availability leads to a number of negative changes in the soil and the mycobiota that live there, affecting entire ecosystems. The effects of climate change and increased international trade are leading to the spread of pathogenic fungi and other harmful organisms whose range was previously restricted to the south of our continent. Unfavourable abiotic and biotic factors leading to weakening of oak stands in the western part of Poland have resulted in activation of new pests like Mediterranean oak borer. Intensification of transport and shortening of its duration, as well as climatic changes, favour the introduction of various organisms, including bark beetles (Scolytinae). In Poland, cyclic insect outbreaks are one of the most important problems in forest protection. Developing methods to monitor, prevent outbreaks and control the density of insect populations below harmful levels can be a challenge to consider. Finding an innovative system for applying insecticides to control spruce bark beetle could also be an interesting solution, where insects attracted to pheromones die after contact with the insecticide. Contact with the insecticide has a dual effect: either directly when the tree is treated, or when the bark beetle attempts to invade the tree. Opportunities for the use of biostimulants in forestry and is an attractive way to regenerate plants after negative stressors such as frost, drought or damage caused by improper use of pesticides, as well as the negative effects of diseases and pests. It acts indirectly by stimulating leaf, stem and root development and improving nutrient uptake. The effects of chemical treatments on fungal biodiversity in forests should be studied using powerful molecular tools such as NGS.

Prediction of pine mistletoe infection using remote sensing imaging: A comparison of the artificial neural network model and logistic regression model

AbstractIn this study, the prediction of pine mistletoe distribution in Scots pine ecosystems was explored using remote sensing variables to compare the multilayer perceptron (MLP) artificial neural network (ANN) and logistic regression (LR) model performances. For this purpose, 109 sample plots were distinguished in pure Scots pine forests (natural) in the Eastern Black Sea Region of Turkey. Distinguishing mistletoe‐infected stands (69) and uninfected stands (40) was performed with field observations. The variables acquired from Landsat 8 (Level 1) images were used as independent variables for independent‐sample t‐test, MLP ANN and LR models. Remote sensing variables indicated that mistletoe‐infected stands were in drier areas with a lower vegetation‐leaf area index. Based on the performance results of both models, the sensitivity (SEN), specificity (SPE), positive predictive value (PPV), negative predictive value (NPV) and accuracy of the MLP ANN model were superior to those of the LR model. The prediction percentages (SEN, SPE, PPV and NPV) of mistletoe‐infected stands were better than the prediction percentages of uninfected stands. The prediction accuracies of LR and MLP ANN models were 74.3% and 89.6%, respectively. However, all remote sensing variables were included in the prediction equation of the MLP ANN model, while the thermal infrared 1 (TIRS1) variable was included in the LR model. In the MLP ANN model, the TIRS1 variable also had the highest normalized importance (100%). The area under the curve (AUC) value for identifying the mistletoe‐infected stands of Scots pine forests used by the MLP ANN model (0.892 ± 0.034) was higher than in the LR model (0.838 ± 0.039), explaining the more accurate predictions obtained from the MLP ANN model. The MLP ANN model showed much better performance than the LR model. The results of this study are expected to make important contributions to the identification of potential mistletoe‐infected areas.

There Is No Carbon Transfer Between Scots Pine and Pine Mistletoe but the Assimilation Capacity of the Hemiparasite Is Constrained by Host Water Use Under Dry Conditions.

Pine mistletoe is a hemiparasitic shrub that can produce its own photosynthates. There is a lack of knowledge about the interaction of mistletoe and host under varying environmental condition that might influence carbon gain and allocation. In a 13C-pulse labeling experiment with mature Pinus sylvestris (pine) infected by mistletoes grown in naturally dry or irrigated conditions, (1) mistletoe clusters were shielded from 13CO2 added, and (2) mistletoes or host needles were removed to manipulate the local assimilate and water availability. No 13C signal was found in shielded mistletoes, indicating no carbon transfer from the host to the mistletoe. When the pine needles were removed from girdled branches, no 13C signal was found in the host tissues, implying no carbon transfer from mistletoe to the host. However, mistletoes on needle-removed pine trees accumulated more labeled assimilates and had higher non-structural carbohydrate (NSC) concentrations only under naturally dry conditions but not in irrigated plots. Our results suggest that mistletoes show full carbon autonomy, as they neither receive carbon from nor provide carbon resource to the host trees. Moreover, the high assimilation capacity of mistletoes seems to be constrained by the host water use under dry conditions, suggesting that drought stress is not only negatively impacting trees but also mistletoes. Therefore, we conclude that the hemiparasites live on their own in terms of carbon gain which, however, depends on the water provided by the host tree.

Effects of land use and topographic variables on distribution of pine mistletoe (Viscum álbum subsp. austriacum (Wiesb.) Vollm.) in northeastern Turkey

Background: This study evaluated the distribution of pine mistletoe in Scots pine ecosystems in relation to topographic variables and land uses. A total of 109 sample plots were selected from pure Scots pine forests in the Eastern Black Sea Region of Turkey. The 6-class dwarf mistletoe rating was used for infection severity. Pearson correlation analysis results showed significant relationships between mistletoe infection severity and topographic variables in 30 m buffer and land use in 500 m buffer. Results: Of the sample plots, 69 (63%) were mistletoe infected, and 40 (37%) were uninfected. The t-test results showed that there was a significant difference between mean topographic variables and land use in mistletoe infected and uninfected sample plots. The results of the binary logistic regression analysis showed that altitude, productive forest, slope, and road distance were the most significant predictors of the distribution of pine mistletoe as topographic variables and land uses. Conclusion: The common direction of mistletoe infected areas, in addition to Scots pine ecosystems, was low altitudes, sheltered valleys, more humid areas and different land use (agriculture, road and stream).

Leaf area – sapwood area relationship in Scots pine (Pinus sylvestris L.) under mistletoe (Viscum album ssp. austriacum) infection

Leaf area is linearly correlated with sapwood area in trees. The linearity of this relationship can be affected by some biotic and abiotic factors. Mistletoes are hemi parasitic plants that take up water and mineral nutrients from their hosts and affect host physiological responses. There is no conclusive evidence to show the effect of pine mistletoe (Viscum album ssp. austriacum) on leaf area and sapwood area relationship in Scots pine trees (Pinus sylvestris L.) at tree level. The aim of this study is to determine and quantify the effect of pine mistletoe on the structural variation of leaf area and sapwood area relationship at tree level in Scots pine. A total of 18 mistletoe infected and 12 uninfected Scots pine trees were destructively sampled. All needles and mistletoes were completely removed from sampled trees to determine needle and mistletoe characteristics, biomass and leaf area. Sapwood areas at breast height (BH) and at crown base height (CBH) were determined from wood discs taken from BH (1.3m) and CBH. Sapwood area was delineated by benzidine staining method. Pearson correlation, t-test and regression analyses were conducted to determine the relationship between sapwood area and needle-mistletoe leaf area relationships. The results indicated that both the relationships between sapwood area and leaf area in uninfected, and sapwood area and total leaf area (needle plus mistletoe leaf only) in infected trees were linear. However, the slope of regression equation for mistletoe infected trees was considerably lower when compared to the uninfected trees. As for the variation of the sapwood area along the stem below live crown, there was a slight difference between sapwood area at BH and CBH. The study showed also that mistletoe infection led to a significant reduction in needle size (length, width, area and weight) in Scots pine trees. Significant relationships were found between the sapwood area and leaf area in this study. The results of this study may help fill the gap in the knowledge concerning the impacts of pine mistletoe on the dynamics of Scots pine trees.

The distribution of pine mistletoe (Viscum album ssp. austriacum) in Scots pine (Pinus sylvestris) forests: from stand to tree level

ABSTRACTThis paper reports and discusses the distribution of pine mistletoe in Scots pine forests at stand and tree level in relation to some site, stand, and tree characteristics. Population characteristics (age, number and biomass) and distribution of pine mistletoe in the canopy of Scots pine trees were also evaluated. A total of 1408 trees were measured in 114 representative sample plots in the Eastern Black Sea Region of Turkey. Of the measured trees, 648 (46%) were mistletoe infected and 760 (54%) were uninfected. The 6-class dwarf mistletoe rating system (DMRS) was used for infection severity rating. Correlation analysis results indicated significant relationships between mistletoe infection severity and stand and tree characteristics. The t-test results showed that there was a significant difference between mean stand and tree characteristics in mistletoe infected and uninfected stands. The results of the binary logistic regression analysis indicated that altitude and stand volume were the most significant predictor of the distribution of pine mistletoe at stand level. As for the population characteristics of pine mistletoe, the results indicated that the life span of pine mistletoe was about 24 years and that biomass distribution gradually increased from lower to upper part of the crowns.

The effect of mistletoe (Viscum album) on branch wood and needle anatomy of Scots pine (Pinus sylvestris)

ABSTRACTMistletoes are hemi-parasitic plants growing on many tree species. They grow on the tree branches or trunk of a tree and form root-like structures called haustoria that penetrate into the tree, taking up water and mineral nutrients. Mistletoe is capable of causing a variety of effects to its hosts, including changes in wood formation and leaf development. We investigate and discuss the effects of pine mistletoe (Viscum album ssp. austriacum, Santalaceae) on branch wood and needle anatomy of Scots pine (Pinus sylvestris, Pinaceae). Parasitized and nonparasitized branches of Scots pine were sampled from host tree crowns of trees growing on the same site. Branches were taken from mid-crown facing south. They were cut at 2 cm proximal and 2 cm distal to the mistletoe on each host branch and at the corresponding position in the case of uninfected branches from the same host. The wood anatomy at proximal and distal parts and the parts at the corresponding position in the non-parasitized section was compared. The anatomy of one-year-old needles from both parasitized and non-parasitized branches was also compared. Mistletoe had significant influences on wood and needle anatomy. The major changes were the decreases in the double wall thickness, lumen area, tangential lumen area and radial lumen area of the tracheids in the wood and a decrease in vascular area in the needles. These results help to understand how mistletoe acts on its host.

Quantifying the effect of pine mistletoe on the growth of Scots pine

SummaryMistletoe infection results in substantial growth losses in mistletoe‐infected forests. This study reports and evaluates the results of retrospective analyses of radial growth of Scots pine (Pinus sylvestris) in relation to the level of infection of pine mistletoe (Viscum album ssp. austriacum). A total of 43 Scots pine trees were destructively sampled from different sites. Of these trees, 14 were uninfected and 29 were infected. Infection classes were determined using six‐class dwarf mistletoe rating system (DMRS). All needle and mistletoe biomass were removed completely and weighed for each sampled tree. Subsamples from needles and all mistletoe biomass were taken to the laboratory for oven‐dried weight determinations. Five‐cm‐thick wood discs were cut from the stem at the breast height (1.3 m) to determine annual basal area increment for the last 25 years. In addition to DMRS, new infection classes were created using mistletoe‐to‐needle biomass (MB/NB) ratio. The results showed that the radial growth losses could be as much as 41% to 64% at different infection levels. The rate of growth loss in relation to DMRS and MB/NB ratio was similar, but with a larger variability in DMRS values. The results showed that both DMRS rating and MB/NB ratio seem to be important for quantifying growth loss on Scots pine trees infected with mistletoe. The results of this study can also be invaluable in modelling the effects of mistletoe on the growth of Scots pine trees.

Viscotoxin 1-PS from Scots pine mistletoe– Ecophysiological Hints

Viscotoxin 1-PS from Scots pine mistletoe– Ecophysiological Hints

Parasitic plants and forests: a climate change perspective

Infection of trees by parasitic plants can be costly, since parasites usually decrease tree growth and fruit production or increase tree mortality. In Switzerland, for example, damage from Viscus album ssp. austriacum (pine mistletoe) infection has been estimated to cause the cutting or death of 10% of Pinus sylvestris (Scots pine) in the Rhone Valley (Dobbertin et al. 2005). However, at the ecosystem scale, parasitic plants also play important roles in providing structural diversity in forest stands and food sources for birds (Watson 2001), as well as increasing local nutrient cycling by concentrating nitrogen in their leaves at much higher levels than the host tree (Escher et al. 2004, Reblin et al. 2006). In this issue, Bell and Adams (2011) review the effects of plant parasites on woody species. They emphasize physiological research, but also scale up to examine implications for ecosystem functioning, and scale down to point out recent advances in plant–parasite interactions from molecular biology, an approach that Tree Physiology strongly advocates. While the effects of infection on host carbon and water fluxes have received a fair amount of study, scaling these effects to the ecosystem level has not, as Bell and Adams (2011) note. Importantly, our lack of understanding of how parasitic plants impact forest functioning impedes our ability to predict how these symbioses will affect forests in the future as the climate changes. Data from dendrochronology show that the growth of infected trees is more sensitive to climate, especially moisture stress, than that of uninfected trees (Stanton 2007). Since rising temperatures and changing precipitation patterns are expected to increase drought frequency and severity in many regions (IPCC 2007), and plant parasites increase host tree water stress and drought-associated mortality (Dobbertin 1999, Dobbertin and Rigling 2006), infection is likely to exacerbate climate-related drought stress in forests. Warmer, drier conditions are also expected to cause more frequent fires. While fire can control parasitic plant infestations by killing infected branches or individuals, low-intensity surface fires can jump into the canopy more easily in infested than healthy stands, thus becoming severely damaging crown fires (Hoffman et al. 2007). In contrast to the potential for parasitic plant infection to intensify climate change stress, rising CO2 might benefit infected trees. Host trees with greater carbon resource uptake also support greater growth rates in parasitic plants (Bickford et al. 2005). Thus, while higher host photosynthetic rates under elevated CO2 may stimulate parasitic plant growth, the extra tree carbon uptake could also help compensate for the extra carbon sinks of holoparasitic plants, which rely on their host for not only water and nutrients, but also carbon. Predicting how climate change will alter tree–parasitic plant relationships is difficult, since climate change can be expected to affect both the host and the parasite species individually, leading to changes in the strength or even presence of the symbiosis. We might expect parasite ranges to move with their host species as the climate changes, and there is evidence that warming has already extended the altitudinal range of some tree parasitic plant species (Dobbertin et al. 2005). However, over a much longer time scale, there are many factors that can disrupt the match between host and parasite range and migration. Using fossil pollen data and population genetics, Tsai and Manos (2010) found that since the last glaciation, Fagus grandifolia (American beech) density was a more important predictor of the spread of an obligate, hostspecific parasite, Epifagus virginana, than was the range expansion of the tree itself. Thus, as trees migrate in response to changes in climate, parasitic species may not be able to follow. The dependence of many parasitic plants on birds for pollination and seed dispersal adds another layer of intricacy to predicting how the entire species assemblage involved in the host tree–parasitic plant relationship will respond to climate change. Bell and Adams (2011) provide a comprehensive overview of our current knowledge of the effects of parasitic plants on tree physiology and the few studies of larger-scale forest implications, but more research on the role Commentary

Mistletoe-induced crown degradation in Scots pine in a xeric environment

Increasing Scots pine (Pinus sylvestris L.) mortality has been recently observed in the dry inner valleys of the European Alps. Besides drought, infection with pine mistletoe (Viscum album ssp. austriacum) seems to play an important role in the mortality dynamics of Scots pines, but how mistletoes promote pine decline remains unclear. To verify whether pine mistletoe infection weakens the host via crown degradation, as observed for dwarf mistletoes, we studied the negative effects of pine mistletoe infestation on the photosynthetic tissues and branch growth of pairs of infested and non-infested branches. Pine mistletoe infection leads to crown degradation in its host by reducing the length, the radial increment, the ramification, the needle length and the number of needle years of the infested branches. This massive loss in photosynthetic tissue results in a reduction in primary production and a subsequent decrease in carbohydrate availability. The significant reduction in needle length due to mistletoe infection is an indication for a lower water and nutrient availability in infested branches. Thus, mistletoe infection might lead to a decrease in the availability of water and carbohydrates, the two most important growth factors, which are already shortened due to the chronic drought situation in the area. Therefore, pine mistletoe increases the risk of drought-induced mortality of its host when growing in a xeric environment.

Using Viscum album extracts (ISCADOR) for successful management of neoplasms of the skin in horses and cats in consideration of aspects relevant to human medicine

Background: Mistletoe extracts (Viscum album extracts, VAE) such as ISCADOR, have been used successfully in human oncology for many years. In veterinary medicine, there have been reports of successful treatment, but scientific data on efficacy are lacking. Two studies were therefore conducted to assess whether VAE can serve as an adjunct to standard treatment in horses and cats. Methods: As part of a placebo-controlled double-blind study (study 1), 53 horses with equine sarcoid (a solitary or multifocal skin tumor) were treated with VAE pini (pine mistletoe) in progressively increasing doses (n=32) or with a sodium chloride solution (n=21). Three times a week for 15 weeks. All horses were observed over a period of 12 months for tumor recurrence and cure. In an observational study (study 2), 44 cats with fibrosarcoma, a very common skin tumor with a high rate of recurrence, were treated postoperatively with 0.1% (0.5ml per dose) oral VAE quercus (oak mistletoe) twice daily, and disease free survival was measured. Results: In study 1, treatment with ISCADOR led to significantly better results than placebo. Improvement was seen in 41% of the cases (placebo 14%), and cure was achieved in 28% of the cases (placebo 14%). In study 2, disease-free survival time in cats treated postoperatively with VAE quercus was 438 days compared with 365 to 475 days for conventional chemotherapies and 120 to 261 days for surgery alone, as seen in literature. Aggressive surgery combined with radiation and chemotherapy led to markedly superior results (661 to 986 days). Conclusion: The study 1 was able to demonstrate, for the first time, the efficacy of VAE compared to placebo control. This study also showed that the effect of VAE apparently extends considerably beyond the treatment period; unexpectedly, only very few recurrences were observed between the end of treatment and the 12th month of observation. The results of the study 2 show that oral administration of mistletoe preparations also yields satisfactory prophylactic effects. The discussion surrounding oral treatment and the question whether it can replace injection treatment must therefore be continued, even in human medicine.

Pine mistletoe (Viscum albumssp.austriacum) contributes to Scots pine (Pinus sylvestris) mortality in the Rhone valley of Switzerland

SummaryIn recent years unusual high mortality of Scots pine (Pinus sylvestris) has been observed in the Swiss Rhone Valley. The exact causes, however, are not known. At a 2‐ha monitoring plot, tree mortality and crown condition have been monitored since 1996. Between 1996 and 2004, 59% of the Scots pines died, most of them following the drought periods 1996–1998 and 2003–2004, while only 15% of the deciduous trees died. Crown transparency, needle discolouration, dead branch percentage, mistletoe (Viscum albumssp.austriacum) rating,Tomicussp. shoot feeding, male flowering effect, tree stem diameter, crown shading and social tree class assessed in 1998 were used in a logistic regression model to predict tree mortality. Crown transparency, mistletoe rating and percentage of dead branches were found significant in the model and the probability of tree mortality increased with increasing rankings of these parameters. Needle discolouration could be used to substitute ‘dead branch percentage’ as predictor. While crown transparency increased with mistletoe rating, for trees in the same transparency class, trees with medium and heavy mistletoe infection were two to four times more likely to die than trees with no or only low mistletoe infection. For the surviving trees we found that trees with mistletoes showed a significantly higher increase in transparency in the year following a drought than trees without, while in a drought year the opposite was true. At the beginning of the observations no significant differences in transparency had been found between the trees with and without mistletoe. However, by the end of the observation period trees with mistletoe had significantly higher crown transparency. We conclude that mistletoe infection can be considered as both a predisposing factor for tree death, by increasing needle loss following drought and a contributing factor by increasing water stress during drought.

The upward shift in altitude of pine mistletoe (Viscum album ssp. austriacum) in Switzerland—the result of climate warming?

Pine mistletoe (Viscum album ssp. austriacum) is common in natural Scots pine (Pinus sylvestris L.) forests in the alpine Rhone Valley, Switzerland. This semi-parasite, which is regarded as an indicator species for temperature, increases the drought stress on trees and may contribute to the observed pine decline in the region. We recorded mistletoes on representative plots of the Swiss National Forest Inventory ranging from 450 to 1,550 m a.s.l. We found mistletoe on 37% of the trees and on 56% of all plots. Trees infested with mistletoe had a significantly higher mortality rate than non-infested trees. We compared the current mistletoe occurrence with records from a survey in 1910. The current upper limit, 1,250 m, is roughly 200 m above the limit of 1,000-1,100 m found in the earlier survey 100 years ago. Applying a spatial model to meteorological data we obtained monthly mean temperatures for all sites. In a logistic regression mean winter temperature, pine proportion and geographic exposition significantly explained mistletoe occurrence. Using mean monthly January and July temperatures for 1961-1990, we calculated Skre's plant respiration equivalent (RE) and regressed it against elevation to obtain the RE value at the current mistletoe elevation limit. We used this RE value and temperature from 1870-1899 in the regression and found the past elevation limit to be at 1,060 m, agreeing with the 1910 survey. For the predicted temperature rise by 2030, the limit for mistletoe would increase above 1,600 m altitude.