Susceptibility of Coulter pine (Pinus coulteri) to western dwarf mistletoe (Arceuthobium campylopodum) in southern California

The susceptibility of Coulter pine (Pinus coulteri) to western dwarf mistletoe (Arceuthobium campylopodum) was evaluated in southern California. Eight stands infested with western dwarf mistletoe and dominated by Coulter and Jeffrey pines (Pinus jeffreyi) were sampled. Infection of Coulter pine was evaluated using circular plots established around large, severely infected Jeffrey pines and with rectangular transects. A total of 25 plots and 10 transects were sampled. In each plot and transect, live trees > 5 cm in diameter at breast height (1.4 m above the ground) were assigned a dwarf mistletoe rating (6‐class system). Nearly 600 Jeffrey pines and more than 400 Coulter pines were evaluated. Infection of Jeffrey and Coulter pines in the plots and transects averaged 96% and 97%, respectively. These data indicate that Coulter pine should be classified as a principal host of WDM and not as a secondary host as previously reported.     

Transformation of western hemlock (Tsuga heterophylla) tree crowns by dwarf mistletoe (Arceuthobium tsugense,Viscaceae)

Dwarf mistletoes (Arceuthobium species) are arboreal, hemiparasitic plants of conifers that can change the structure and function of the tree crown. Hemlock dwarf mistletoe (Arceuthobium tsugense subsp. tsugense) principally parasitizes western hemlock (Tsuga heterophylla) and effects 10.8% of all western hemlock trees in Oregon, USA. In this study, we climbed 16 western hemlock trees (age 97–321 years, height 33–54.7 m) across a gradient of infection (0%–100% of branches infected) and measured occurrence of all dwarf mistletoe infections, dwarf mistletoe caused deformities, foliage, branch and crown metrics, and sapwood area. We then modelled over 25 different response variables using linear and generalized linear models with three metrics of severity as explanatory variables: total infection incidence, proportion of all live branches infected, and proportion of all live, infected branches with 33 per cent or more foliage distal to infection. A strong effect of dwarf mistletoe intensification was the reduction of branch foliage and an increase in the proportional amount of foliage distal to infections, with severely infected trees having the majority of foliage distal to infections. Increasing severity led to an apparent crown compaction as crown volumes decreased and became increasingly comprised of deformities. Sapwood area was unrelated to infection severity. Branch length and diameters were unrelated to increasing infection severity despite severely infected branches supporting 1–70 infections. The most severely infected tree had 3,615 individual plants in the crown. Our results suggested that shifts in crown structure and branch deformation, foliage amount, and foliage distal to infection, reflected a likely reduction of capacity for tree growth that coincided with a hypothesized increase in resource demand by dwarf mistletoe plants as infection severity intensified.     

The effect of competition on individual tree basal area growth in mature stands of Pinus cooperi Blanco in Durango (Mexico)

In this paper, we evaluated how well-selected distance-dependent and distance-independent competition indices explain individual tree basal area growth of trees, growing in mature and even-aged stands of Pinus cooperi Blanco. A total of 18 competition measures were analyzed of which six do not need tree location (distance-independent) and 12 that utilize tree location (distance-dependent). The competition situation of a stand and/or an individual tree was studied using 11 different competitor selection methods. The mean square error reduction relative to no-competition was used to judge the performance of each competition index. It was found that the best distance-independent competition indices performed as well as the best distance-dependent competition indices. It was concluded that the BALMOD-index would be a good competition index to be incorporated into further individual tree basal area growth models for the study area.

Evidence of resistance to hemlock dwarf mistletoe (Arceuthobium tsugense) in western hemlock (Tsuga heterophylla) clones

Records from western hemlock (Tsuga heterophylla) trees naturally exposed to infection by hemlock dwarf mistletoe (Arceuthobium tsugense) and controlled inoculations of grafted branch scions from a selection of these trees indicated a repeatability of the levels of resistance to the disease in the clonal material. Evidence pointed to a resistance mechanism operating within, rather than outside, the host branch.     

Susceptibility of red fir and white fir to fir dwarf mistletoe (Arceuthobium abietinum) in California

Fir dwarf mistletoe (Arceuthobium abietinum, Viscaceae) is a damaging parasite of true firs (Abies spp.) in California. In the Sierra Nevada Mountains, fir dwarf mistletoe consists of two special forms (formae speciales, f. sp.) which are morphologically similar, but exhibit a high degree of host specificity: A. abietinum f. sp. concoloris whose principal host is Sierra white fir (Abies lowiana) and A. abietinum f. sp. magnificae which only parasitizes red fir (Abies magnifica). Although field observations and cross‐inoculation studies have consistently supported the extreme host specialization demonstrated by these special forms of fir dwarf mistletoe, little quantitative data from mixed red fir/white fir stands infested with fir dwarf mistletoe have been available. Therefore, I sampled 20 mixed conifer stands dominated by red and white fir and infested with f. sp. concoloris (8 stands) or f. sp. magnificae (12 stands) from near Mount Shasta to the southern Sierra Nevada Mountains near Sherman Pass. Infection of red and white fir was evaluated using temporary circular plots (0.012 ha) established around large, severely infected trees and with rectangular transects placed within fir dwarf mistletoe‐infested stands. In each plot and transect, live trees >5 cm in diameter at breast height were assigned a dwarf mistletoe rating (6‐class system). A total of 55 plots and 51 transects were established in the 20 stands, and over 1,900 red firs and 1,700 white firs were sampled. Ninety‐nine per cent of the red firs and 98% of the white firs were infected in stands infested with f. sp. magnificae or f. sp. concoloris, respectively. In contrast, no infection of red fir was observed in stands infested with f. sp. concoloris and no infected white firs were observed in stands infested with f. sp. magnificae. These data provide further support that the special forms of fir dwarf mistletoe are extremely host specific in California.     

Incidence,severity, and aggregation patterns of two sympatric dwarf mistletoe species (Arceuthobium spp.) in Central Mexico

Dwarf mistletoes are widely studied because of their significant impact on host populations; however, few studies have focused on sympatric species. The understanding of their coexistence is important because it can provide useful knowledge for future management plans. We investigated the incidence, severity, and aggregation patterns of Arceuthobium vaginatum and A. globosum coexisting in Central Mexico. We estimated the correlation between both species incidences (N = 75 plots), the incidence–severity correlation (N = 47 plots) for each species, and the effect of biotic (host and non-host species abundance) and abiotic (altitude and slope) factors on the mistletoe incidence. In addition, we compared the hierarchical aggregation among and within plots of the two mistletoe species with a χ ² test. There is a clear dominance of A. vaginatum in the area, and both species incidences are negatively correlated with each other (r _s = ? 0.54, P < 0.05) and host abundance (r = ? 0.26, P < 0.05). The remaining factors were non-significant. Both species have a linear relationship between incidence and severity, i.e., they show a uniform increase in severity with incidence, which could help diagnose the degree of tree infection from incidence measurements. The species are aggregated within plots, but only A. globosum shows an aggregation among plots (χ ² = 82.25, P < 0.001); aggregation has not been shown previously for two sympatric dwarf mistletoe species. Our results can improve the scientific basis for forest management planning to control dwarf mistletoe and maintain biodiversity.     

The influence of prescribed crown fire on lodgepole pine dwarf mistletoe (Arceuthobium americanum) populations 33 years post‐fire

Dwarf mistletoes (Arceuthobium spp.) are a group of obligate, hemiparasitic plants that infect numerous species in the Pinaceae in North America. Wildland fire is considered to be the primary natural agent influencing the population and distribution of dwarf mistletoes across landscapes. Based on this understanding, prescribed fire has been suggested as a potential method for dwarf mistletoe sanitation and control; however, experimental work has primarily focused on prescribed surface fire. In this study, we report long‐term impacts of three experimental crown fires on dwarf mistletoe severity in infested lodgepole pine stands in Colorado 33 years post‐fire. The three fires achieved tree mortality rates ranging from 20% to 100%. Our results suggested a significant negative relationship between the amount of fire‐caused tree mortality and future dwarf mistletoe severity. These findings supported the presumed natural role of fire in altering dwarf mistletoe populations, which perhaps exhibits a linear relationship between fire‐caused host tree mortality and future dwarf mistletoe severity.     

Impact of eastern dwarf mistletoe (Arceuthobium pusillum) infection on the needles of red spruce (Picea rubens) and white spruce (Picea glauca): oxygen exchange, morphology and composition

Eastern dwarf mistletoe (Arceuthobium pusillum Peck) is a hemiparasitic angiosperm that infects white spruce (Picea glauca (Moench) Voss) and red spruce (P. rubens Sarg.) in northeastern North America. The effects of mistletoe infection differ substantially between white and red spruce, with white spruce suffering greater infection-induced mortality. In the present study, we sought to determine the role that species-specific differences in needle-scale responses to parasitism may play in the observed differences in the effect of infection on host tree health. Based on the measurements made, the most apparent effect of parasitism was a reduction in needle size distal to infections. The magnitude of this reduction was greater in white spruce than in red spruce. Eastern dwarf mistletoe was a sink for host photosynthate in red spruce and white spruce; however, there were no adjustments in needle photosynthetic capacities in either host to accommodate the added sink demands of the parasite. Needle total nonstructural carbohydrate concentrations (TNC) were also unaltered by infection. Red spruce needles had higher TNC concentrations despite having lower overall photosynthetic capacities, suggesting that red spruce may be more sink limited and therefore better able to satisfy the added sink demands of parasitic infection. However, if carbon availability limits the growth of the mistletoe, one may expect that the extent of the parasitic infection would be greater in red spruce. Yet in the field, the extent of infection is generally greater in white spruce. Taken together, these results suggest that dwarf mistletoe may not substantially perturb the carbon balance of either host spruce species and that species-specific differences in needle-scale responses to the parasite cannot explain the contrasting effects of infection on white spruce and red spruce.     

Effects of precommercial thinning on growth parameters in Pinus nigra Arn. subsp. pallasiana(Lamb.) Holmboe stand

We investigated the effects of precommercial thinning(PCT) applied at different levels on the growth parameters of natural Anatolian black pine stand. The experimental site was located in the province of Isparta in southern Turkey. PCT was set up using a randomized complete block design with three replicates and three treatments(control, 2–2.5 m × 2–2.5 m and 3–3.5 m ×3–3.5 m spacing). The experimental plots were established in March 2014. At the end of the growing seasons for three years(2014–2016), growth parameters such as diameter, height and crown radius were measured. PCT was found to be significantly effective on diameter, height,individual tree basal area, and crown radius increment at the end of the third year(p 0.05). While diameter,individual tree basal area and crown radius increment increased with increasing PCT intensity, height increment was higher in control than PCT. Although the PCT treatments applied with 3–3.5 m spacing affected individual tree development positively, we need long-term results on wood quality and yield. According to the short-term results, it is thought that it is better to lower the standcloseness gradually, so, it may be advisable to apply PCT by 2–2.5 × 2–2.5 m spacing.     

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

In 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.     

Spread of European mistletoe (Viscum album) in California,U.S.A.

Viscum album was introduced in about 1900 into an area north of San Francisco, California. By 1984, the gross area covered by the parasite had spread to about 114 sq. km. The average distance of spread from the point of introduction was 5.8 km. Viscum occurs on at least 22 hosts in California, the most common are Acer saccharinum, Malus sylvestris, Robinia pseudoacacia, Alnus rubra, Populus fremontii, and Salix lasiandra.     

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

In 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 album ssp. austriacum) rating, Tomicus sp. 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.     

Fertility variation in endemic populations of Ehrami black pine(Pinus nigra Arnold. subsp. pallasiana var. pyramidata)

Fertility variation and effective number of parents were estimated in the 100 individuals from each of three plantation populations(P1, P2 and P3) of the endangered Pinus nigra. subsp. pallasiana var. pyramidata established in the Isparta–Golcuk district in southern Turkey in 1990. Potential relations between cone yield and growth characters(height, diameter at breast height,diameter at base and crown diameter) were also investigated. Large differences were found among populations and within populations for cone production and growth characters. Mean cone production was eight(ranging from6.5 in P2 to 9.1 in P1) for the three populations. The 10 most productive individuals for cones produced 32% of the total cones in P1, 39% in P2 and 34% in P3; 21, 16 and 6individuals, respectively did not produce any cones in the populations. According to the correlation analyses, the relation between cone yield and growth characters changed for the populations, while height, diameter at breast height and crown diameter were positively significantly correlated(r = 0.182, 0.135 and 0.209; p B 0.05) with cone production for the three populations. Fertility variation was1.81 in total of three populations, ranging from 1.72 in P3 to 3.45 in P1). Effective number of parents was 142(55.2of number of parents censused; 29%, P1; 49.8%, P2;58.3%, P3).     

Distribution and vegetation of Pinus mugo subsp. mugo dieback patches in Maiella massif (Central Italy)

European Journal of Forest Research - Forest dieback in the last decade has been reported all over the world and not only causes a significant loss of forest yield but also affects successional...     

马尾松毛虫危害程度对马尾松生长影响的研究

通过人工模拟危害程度和自然状况下马尾松毛虫危害等试验所获得的大量数据,利用微机进行统计和分析。结果表明:5～10年生马尾松针叶损失50%时,越冬代对当年高生长有显著的影响;5～20年生马尾松针叶损失50%,第二代对后一年的树高、胸径、材积有显著的影响;针叶损失70%以上时,越冬代对当年、第一代对当年、第二代对后一年的树高、胸径和材积均有极显著的影响;针叶损失100%时,第一代还对后一年的树高、胸径和材积有极显著的影响。其中以第一代马尾松毛虫危害最大,越冬代和第二代相近似。这为制定马尾松毛虫防治指标,开展综合治理工程提供了重要的科学依据。     

Effects of Eucalyptus obliqua (L'Herit) density on young stands of even-aged Pinus radiata (D. Don)

In a 10-year-old Pinus radiata plantation, increasing densities of Eucalyptus obliqua, a woody weed species, caused reductions in the canopy leaf area and total stem volume of P. radiata. As the density of E. obliqua increased stand volume (the sum of stem volumes of the two species) was constant, but the sum of projected leaf area of the two species decreased. Higher E. obliqua density also resulted in higher mean height to diameter ratio of P. radiata. With increasing E. obliqua density the size distribution of P. radiata became more positively skewed and the size hierarchy of P. radiata increased. The effects of E. obliqua density on P. radiata are more likely due to below-ground competition than competition for light above-ground. Understanding the effects of E. obliqua density on the characteristics of P. radiata can benefit weed control programs and subsequent management of plantations with naturally regenerated E. obliqua.     

Effects of season,needle age and elevated atmospheric CO(2) on photosynthesis in Scots pine (Pinus sylvestris)

Five-year-old Scots pine (Pinus sylvestris L.) seedlings were grown in open-top chambers at ambient and elevated (ambient + 400 &mgr;mol mol(-1)) CO(2) concentrations. Net photosynthesis (A), specific leaf area (SLA) and concentrations of nitrogen (N), carbon (C), soluble sugars, starch and chlorophyll were measured in current-year and 1-year-old needles during the second year of CO(2) enrichment. The elevated CO(2) treatment stimulated photosynthetic rates when measured at the growth CO(2) concentration, but decreased photosynthetic capacity compared with the ambient CO(2) treatment. Acclimation to elevated CO(2) involved decreases in carboxylation efficiency and RuBP regeneration capacity. Compared with the ambient CO(2) treatment, elevated CO(2) reduced light-saturated photosynthesis (when measured at 350 &mgr;mol mol(-1) in both treatments) by 18 and 23% (averaged over the growing season) in current-year and 1-year-old needles, respectively. We observed significant interactive effects of CO(2) treatment, needle age and time during the growing season on photosynthesis. Large seasonal variations in photosynthetic parameters were attributed to changes in needle chemistry, needle structure and feedbacks governed by whole-plant growth dynamics. Down-regulation of photosynthesis was probably a result of reduced N concentration on an area basis, although a downward shift in the relationship between photosynthetic parameters and N was also observed.     

北美短叶松引种试验效果浅析

将引种的北美短叶松与大兴安岭地区主要针叶树种进行比较分析表明，北美短叶松生长量远高于其它针叶树种，建议推广、引种。     

Impacts of inoculation with Herpotrichia pinetorum,Gremmenia infestans and Gremmeniella abietina on Pinus nigra subsp. pallasiana and Cedrus libani seedlings in the field

Herpotrichia pinetorum, Gremmenia infestans and Gremmeniella abietina were inoculated onto 2‐year‐old Anatolian black pine (Pinus nigra subsp. pallasiana) and Taurus cedar (Cedrus libani) seedlings planted in a high mountain forest (1800 m a.s.l) in south‐western Turkey, to determine the effects of these fungi during winter. In June, 8 months after inoculation, 39.9% of experimental plants were dead and 20.4% of the surviving plants failed to flush. Gremmeniella abietina and H. pinetorum caused the most fatalities. Prevention of new shoot formation on surviving plants, however, was mainly an effect of G. abietina infections, although many surviving plants inoculated with G. infestans or H. pinetorum also failed to flush. All three pathogens had the potential to severely damage young plants of P. nigra subsp. pallasiana and C. libani growing at high elevations near to forests with heavy inoculum loads. The implications of this finding for P. nigra afforestations at high altitudes in Turkey are discussed. This study is also the first to report that G. infestans can infect and cause disease on young C. libani plants.