Healthy Stands Research Articles

Outbreak of Drepanopeziza fungus in aspen forests and variation in stand susceptibility: leaf functional traits, compensatory growth and phenology.

In the spring of 2015, a severe outbreak of the necrotrophic pathogen Drepanopeziza (also known as Marssonina) spread across large portions of aspen (Populus tremuloides Michx.) forests in the western United States. Among adjacent stands, some were diseased and others were not. Drepanopeziza infection in diseased aspen stands stimulated compensatory growth of second-flush leaves at the top of the canopy. These patterns of infection provided an opportunity to characterize associations of pathogen infection and leaf functional traits. Eight pairs of adjacent healthy and diseased aspen stands were identified across a forest landscape in northern Utah. Average leaf surface area, specific leaf area (SLA), photosynthesis, starch concentration and defense chemistry expression (phenolic glycosides and condensed tannins) were measured on original, first-flush leaves in the lower portion of the tree canopy of healthy and diseased stands and compensatory, second-flush leaves produced in the canopy top of diseased stands. Only first-flush leaves of diseased stands showed high levels of Drepanopeziza infection. Leaf area of second-flush leaves of diseased stands was threefold larger than all other leaf types in healthy or diseased stands. Lower canopy leaves of healthy stands had the highest SLA. Photosynthesis was lowest in infected first-flush leaves, highest in second-flush leaves of diseased stands and intermediate in leaves of healthy stands. Foliar starch concentrations were lower in leaves of diseased stands than leaves from healthy stands. Condensed tannins were greater in second-flush leaves than first-flush leaves in both healthy and diseased stands. Phenolic glycoside concentrations were lowest in infected leaves of diseased stands. Diseased stands leafed out a week earlier in the spring than healthy stands, which may have exposed their emerging leaves to rainy conditions that promote Drepanopeziza infection. Compensatory leaf regrowth of diseased stands appears to offset some of the functional loss (i.e., photosynthetic capacity) of infected leaves.

Modelling of the spread of Dothistroma septosporum in Europe

SummaryDothistroma needle blight (DNB), a disease affecting several pine species, is currently generating great concern in Europe. Caused by Dothistroma pini and Dothistroma septosporum, DNB affects pine needles and causes premature defoliation, which results in growth reduction and, in extreme cases, mortality. The disease has increased in importance in Europe over the last 20 years, with an increase in the number of observations of DNB in regions with large areas of Pinus sylvestris in northern Europe. This article presents a cell‐based spatiotemporal model for predicting the likelihood and intensity of the future spread of D. septosporum in Europe. Here, “spread” includes both invasion of new regions and infection of healthy stands within already‐colonized regions. Predicted spread depends on the availability of host species, climatic suitability of different regions to D. septosporum and dispersal of sexual and asexual spores from infected trees to surrounding forests via water splash, mist and wind. Long‐distance spread through transport of infected seedlings is also included in the model. Simulations of spread until 2007 and 2015 were used to validate the model. These simulations produced similar patterns of spread to those observed in Europe. Simulations for 2030 suggested that additional and new outbreaks are likely to occur in Scotland, southern Norway, southern and central Sweden, northern parts of Germany and Poland, Estonia, Latvia and south‐west Finland. Preventing the delivery of infected seedlings would be an effective method for reducing the spread of D. septosporum in the Nordic countries, Scotland and Ireland, the Baltic countries, and parts of Germany, Poland and Belarus. In these states, prevention of transport of infected seedlings can reduce the probability of additional spread by 15%–40%.

Development of a method for monitoring of insect induced forest defoliation – limitation of MODIS data in Fennoscandian forest landscapes

We investigated if coarse-resolution satellite data from the MODIS sensor can be used for regional monitoring of insect disturbances in Fennoscandia. A damage detection method based on z-scores of seasonal maximums of the 2-band Enhanced Vegetation Index (EVI2) was developed. Time-series smoothing was applied and Receiver Operating Characteristics graphs were used for optimisation. The method was developed in fragmented and heavily managed forests in eastern Finland dominated by Scots pine ( L.) (pinaceae) and with defoliation of European pine sawfly ( Geoffr.) (Hymenoptera: Diprionidae) and common pine sawfly ( L.) (Hymenoptera: Diprionidae). The method was also applied to subalpine mountain birch ( N.I. Orlova) forests in northern Sweden, infested by autumnal moth (Borkhausen) and winter moth ( L.). In Finland, detection accuracies were fairly low with 50% of the damaged stands detected, and a misclassification of healthy stands of 22%. In areas with long outbreak histories the method resulted in extensive misclassification. In northern Sweden accuracies were higher, with 75% of the damage detected and a misclassification of healthy samples of 19%. Our results indicate that MODIS data may fail to detect damage in fragmented forests, particularly when the damage history is long. Therefore, regional studies based on these data may underestimate defoliation. However, the method yielded accurate results in homogeneous forest ecosystems and when long-enough periods without damage could be identified. Furthermore, the method is likely to be useful for insect disturbance detection using future medium-resolution data, e.g. from Sentinel‑2.Pinus sylvestrisNeodiprion sertiferDiprion piniBetula pubescensssp. Czerepanovii Epirrita autumnata Operophtera brumata

State, ecological-coenotic characteristics, and prospects of the silver birch (Betula pendula Roth, Betulaceae, Dicotyledones) forest cultures in steppe afforestation

In the summer of 2010, thermal damages to birch in cultures reached 4.2–4.8 points according to the authors’ five-point scale. In 2011, the stands of birch trees were weakened to variable degrees, but some healthy stands remained. High-density forest massifs and birch forest belts are more drought-resistant. The grass cover is weakly developed therein. Thinned birch cultures become overgrown with herbs and die out after droughts. The root exudates of shrubs depress the intensity of photosynthesis of steppe plants by 10–25%. In vegetation experiments, various species of shrubs stimulate or slow down the growth of shoots and roots and the intensity of photosynthesis of the birch by 10–30%, on average. It is recommended to cultivate birch trees in forest belts using shrubby borders with high allelopathic activity for biological defense of the soil from overgrowth with weedy and steppe plants.

Competition from native hydrophytes reduces establishment and growth of invasive dense-flowered cordgrass (Spartina densiflora)

Experimental studies to determine the nature of ecological interactions between invasive and native species are necessary for conserving and restoring native species in impacted habitats. Theory predicts that species boundaries along environmental gradients are determined by physical factors in stressful environments and by competitive ability in benign environments, but little is known about the mechanisms by which hydrophytes exclude halophytes and the life history stage at which these mechanisms are able to operate. The ongoing invasion of the South American Spartina densiflora in European marshes is causing concern about potential impacts to native plants along the marsh salinity gradient, offering an opportunity to evaluate the mechanisms by which native hydrophytes may limit, or even prevent, the expansion of invasive halophytes. Our study compared S. densiflora seedling establishment with and without competition with Phragmites australis and Typha domingensis, two hydrophytes differing in clonal architecture. We hypothesized that seedlings of the stress tolerant S. densiflora would be out-competed by stands of P. australis and T. domingensis. Growth, survivorship, biomass patterns and foliar nutrient content were recorded in a common garden experiment to determine the effect of mature P. australis and T. domingensis on the growth and colonization of S. densiflora under fresh water conditions where invasion events are likely to occur. Mature P. australis stands prevented establishment of S. densiflora seedlings and T. domingensis reduced S. densiflora establishment by 38%. Seedlings grown with P. australis produced fewer than five short shoots and all plants died after ca. 2 yrs. Our results showed that direct competition, most likely for subterranean resources, was responsible for decreased growth rate and survivorship of S. densiflora. The presence of healthy stands of P. australis, and to some extent T. domingensis, along river channels and in brackish marshes may prevent the invasion of S. densiflora by stopping the establishment of its seedlings.

Aspen mortality in the Colorado and southern Wyoming Rocky Mountains: Extent, severity, and causal factors

Aspen mortality and overstory dieback have occurred at unusually high levels throughout Colorado and western North America over the past fifteen years. Findings from southwestern Colorado indicated dieback and mortality was clearly related to climate stress, coupled with disease and insect attack. To determine whether similar amounts and causes of mortality were occurring in other mountainous regions of Colorado and southern Wyoming, we determined the health status of aspen on five national forests during 2009–2010. We established 500 random characterization plots in aspen-dominated stands on four of the five national forests and 97 detailed measurement plots, with half in ‘damaged’ and half in ‘healthy’ aspen stands (as defined by USDA Forest Service aerial detection surveys). Overstory aspen was healthy overall, in spite of nearly ubiquitous presence of disease among plots (99%) and high incidence of insect damage (50–75%); in detailed plots standing adult dead aspen percentages ranged from 20% to 33% among the five national forests. Adult aspen in damaged stands occurred at lower densities, and had thinner crowns (41% dead crown, compared to 16% in healthy stands). Damaged stands also had more standing dead adult trees (37%) than in healthy stands (16%). The proportion of live sapling stems and density of saplings did not differ between healthy and damaged stands. Incidence of select mortality agents, including wood-boring insects (Agrilus liragus and Saperda calcarata) (40% in damaged, 18% in healthy), aspen bark beetles (Procryphalus mucronatus and Trypophloeus populi) (31% in damaged, 12% in healthy) and Cytospora canker (caused by fungi in the genus Cytospora) (40% in damaged, 18% in healthy) was considerably greater among damaged stands. Aspen bark beetles were more common on south-facing sites than east or west-facing sites (27%, 17%, and 15%, respectively); Cytospora canker was less common on sites above 2800m (23%) than on lower-elevation sites (28–34%). Prevalence of wood borers, aspen bark beetles and Cytospora canker were all significantly and negatively correlated with latitude among at least two of three aspen size classes. Attempts to model various measures of health of adult aspen (i.e. crown dieback and stem mortality) using site and climatic variables were largely unsuccessful. Since no differences were detected in density of regeneration between damaged or healthy stands, we conclude that most stands will persist upon the landscape for the foreseeable future. Further, we note that although observed densities of regeneration in damaged stands are not as great as levels observed following complete stand removal, suckering does occur, and stems are measurably healthier than regeneration in healthy stands.

Disease, fuels and potential fire behavior: Impacts of Sudden Oak Death in two coastal California forest types

In the Douglas-fir (Pseudotsuga menziesii Mirb. Franco) and redwood (Sequoia sempervirens (D. Don) Endl.) forests of the central California coast, Sudden Oak Death (SOD) has led to landscape-scale mortality of tanoak (Notholithocarpus densiflorus (Hook. and Arn.) Manos, Cannon and S.H. Oh). As tanoak mortality progresses, fuel loads and potential fire behavior in these forests are changing. We documented increases in fuel loads over time in long-term monitoring plots in infested forests at Point Reyes National Seashore. Throughout the study, we observed a significant positive relationship between dead tanoak basal area and surface fuels. We used the fire behavior modeling program BehavePlus to compare potential fire behavior between diseased and healthy stands. Model outputs indicated the potential for longer flame lengths, higher rates of spread and more intense surface fire in diseased stands. The potential for increased fire intensity in diseased redwood and Douglas-fir forests may create additional challenges for fire and natural resources managers and may affect the ecology of these forests into the future.

Western hemlock growth response to increasing intensity of Swiss needle cast on Douglas-fir: changes in the dynamics of mixed-species stands

Westernhemlock(Tsugaheterophylla(Raf.)Sarg.)isamajorcommercialtreespeciesinwesternOregonandWashingtonandisoftenassociatedwithcoastDouglas-fir(Pseudotsugamenziesii(Mirb.)Francovarmenziesii)andother species in coniferous forests of the Coast Ranges and Cascade Mountains. Growth of Douglas-fir in many coastal forestshasbeennegativelyaffectedbySwissneedlecast (SNC),afoliardiseasecausedbytheascomycetePhaeocryptopusgaeumannii(T.Rohde)Petr.andcharacterizedbyprematurefoliagelossonseverelyinfectedDouglas-fir trees.TheeffectofSNConstanddynamicsinmixedDouglas-fir-westernhemlockstandswastestedbyconstructingadiameterincrementmodelforwesternhemlockthatquantifieditsgrowthresponsetovaryingSNCseverityin Douglas-fir. Diameter increment of western hemlock in any given growth period increased with increasing initial SNC severity as measured by Douglas-fir foliage retention (FR), here defined as the number of annual needle cohorts held by the tree. Furthermore, a decline in Douglas-fir FR during the growth period was associated with an additional increase in diameter increment of western hemlock trees. Assuming no change in FR over the growthperiod,westernhemlocktreesinstandswithseverelyimpactedDouglas-fir(initialFR ≤1.5years)averaged 79 per cent greater diameter growth than that in relatively healthy stands (initial Douglas-fir FR ≥3.5 years). The implied annual diameter growth response of a western hemlock with initial diameter at breast height of 10, 20, 30 or 40 cm was 0.29, 0.52, 0.65 and 0.68 cm year 21 , respectively. Compensatory growth by western hemlock inmixed-speciesstandsaltersstanddynamicsbyallowingthisspeciestosurpassthegrowthofDouglas-firexperiencing severe SNC.

Historical and present distribution of Zostera marina in the high north (Troms County, northern Norway) – a decline over the last century

Abstract Eelgrass meadows (Zostera marina) have been mapped in Troms (Norway), in the temperate northeast Atlantic, north of the polar circle, from 2008 to 2011. In this region, there is little knowledge of the distribution of the eelgrass meadows. Northern Norway has an extensive coastline with many pressures and stakeholders. Old records (back to 1900) have been revisited and new locations surveyed based on a combination of spatial modeling, using digital information on depth, slope, and wave exposure and stakeholder recommendations. The results showed that 42% of the previously mapped locations had disappeared. However, we found Z. marina meadows at seven locations where they had not previously been recorded. Most meadows (66%) were smaller than 10,000 m2. The largest meadow covered an area of 325,000 m2, and was located in Balsfjorden. The results clearly show that Z. marina is able to form actively growing stands even at ∼70°N. Three of the meadows were first registered over 100 years ago, indicating long-lived stands in stable conditions. This study cannot explain the causes for the observed decline, and only discusses possible relations. The eelgrass meadows are genetically isolated but yet diverse. Management at fjord range level is required to maintain healthy and stable stands of eelgrass meadows in this region.

Root-Inhabiting Bark Beetles (Coleoptera: Curculionidae) and their Fungal Associates Breeding in Dying Loblolly Pine in Alabama

Root feeding bark beetles in the genus Hylastes Hylastes breeding in loblolly pine across 3 crown (Coleoptera: Curculionidae: Scolytinae) commoncondition classes (healthy, dying, dead). Addition ly carry ophiostomatoid fungi (Ophistomatales: ally, the relationship between ophiostomatoid Ophistomataceae)and collectively contribute to species, their Hylastes species vectors, and tree root disorders of Pinus species around the world condition were investigated. (Jacobs & Wingfield 2001). One of the most damLoblolly pine stands across central Alabama aging root disorders is black-stain root disease have experienced high mortality rates, character of conifers in the Western United States, caused ized by scattered stand mortality with a distinct by the fungal species Leptographium wageneri lack of above-ground pests (Brown & McDowell Kendrick and its primary beetle vector H. nig1968). During an investigation of one stand in rinus (Mannerheim) (Witcosky et al. 1986). ReMay 2008 in central Alabama, dying trees were cently, Hylastes salebrosus Eichhoff and H. tenuis found to be infested with root-inhabiting beetles Eichhoff have been associated with loblolly pine and their associated ophiostomatoid fungi. Six (Pinus taeda L.) decline (Eckhardt et al. 2007), trees were selected based on crown condition, in which is considered an emerging forest health iseluding 2 with green, healthy crowns (healthy), sue in the southeastern United States (Eckhardt 2 with severely chlorotic and thinning crowns et al. 2010). (dying), and 2 with red crowns (dead). Two pri Loblolly pine decline (LPD) is a tree disease mary lateral roots were randomly selected and complex that is characterized by symptoms that excavated to approximately 3 meters from the include thinning tree crowns, growth reductions root collar. Roots were removed from trees and (Eckhardt et al. 2007) and premature mortality in carefully dissected. All insects, including imma localized areas (Brown and McDowell 1968). Eviture stages, were collected from roots and adult dence suggests the complex is the result of interbeetles were identified to species. Root tissue was acting abiotic (Eckhardt & Menard 2008) and biobtained from each brood gallery for the isolation otic (Eckhardt et al. 2007) stress factors. Hylastes of ophiostomatoid fungal species using methods species vector a variety of root-infecting ophiostodescribed in Eckhardt et al. (2007). Following matoid fungi (Klebzig et al. 1991, 1995; Eckhardt surface sterilization, tissue was placed on CSMA et al. 2007; Zanzot et al. 2010) which are patho(malt extract agar containing 800 mg/L of cyclo genic to loblolly pine (Matusick & Eckhardt 2010; heximide and 200 mg/1 of streptomycin sulfate) Matusick et al. 2011). Hylastes beetles and their selective nutrient agar (Jacobs & Wingfield 2001). associated fungi are thought to collectively contribEach adult insect was also rolled on CSMA to re ute to LPD by causing root damage through fungal cover ophiostomatoid fungi from insect bodies infection and insect feeding (Eckhardt et al. 2007). (Zanzot et al. 2010). Isolated ophiostomatoid fun Root and lower stem feeding beetle species (Colegal species were identified using morphological optera: Curculionidae) includingH. salebrosus and characters and established keys. Unknown iso H. tenuis are found in increased numbers within lates were sequenced and confirmed as new spe LPD-affected stands, compared to healthy stands cies by M. Wingfield (Forestry and Agricultural (Eckhardt et al. 2007, Menard 2007). A recent Biotechnology Institute, Pretoria, South Africa), study has found Hylastes to be the most common A total of 157 adult beetles (Coleoptera: Cur bark beetle genus observed in loblolly pine stands culionidae) were collected from roots, most from in central Alabama (Thompson 2011), illustrating dying trees (Table 1). A majority of the beetles col their dominance in this ecosystem. Despite their lected were Hylastes species, including a total of dominance and potential for damage in loblolly 113 H. salebrosus (all from dying trees) and 34 pine, the breeding behavior of Hylastes species in H. tenuis (31 from dying and 3 from dead trees), the southeastern United States is not well underIn addition, H. salebrosus larvae and pupae were stood. In the current study, observational methcollected from dying trees. Other adult insect spe ods were used to investigate the potential for cies collected include the black turpentine beetle

Climate induced birch mortality in Trans-Baikal lake region, Siberia

The Trans-Baikal (or Zabailkal’e) region includes the forest-steppe ecotones south and east of Lake Baikal in Russia and has experienced drought for several years. The decline and mortality of birch (Betula pendula) stands within the forest-steppe ecotone Trans-Baikal region was studied based on a temporal series of satellite data, ground measurements, and tree ring analysis. During the first decade of the 21st century birch stands decline and mortality were observed on about 5% of the total area of stands within our 1250km2 study area. Birch forest decline and mortality occurs mainly at the margins of stands, within the forest-steppe ecotone on slopes with direct insolation. During the first decade of the 21st century summer (June–August) precipitation was about 25% below normal. Soil water content measurements were lowest within dead stands and highest within healthy stands and intermediate within damaged stands. Drought impact on stands was amplified by an increase in summer air temperatures (+0.9°C) in comparison with the previous decade. Tree ring data of “surviving” and “dead” tree groups showed a positive correlation with summer/annual precipitation and negative correlation with summer air temperatures. Temperature and precipitation extreme anomalies tend to occur in the region with a period of about 27years. The observed anomaly was the most severe since the beginning of meteorological observations in the year 1900. Data for the other sites showed a positive climate impact on the growth and expansion of Siberian forests. That is, the same species (B. pendula) showed considerable increase (1.4 times both in height and stem volume) during 20th–21st centuries as temperature increased but precipitation remained at adequate levels.

Effectiveness of different trapping protocols for outbreak management of the engraver pine beetle Ips acuminatus (Curculionidae, Scolytinae)

A population of Ips acuminatus was monitored from 2007 to 2009 by multi-funnel pheromone-baited traps in a Scots pine forest of the southeastern Alps of Europe. We compared the captures obtained with two different lures (Austrian and Spanish pheromones, commercially available) in five infested types of forest. Although captures showed a similar trend among sites, with no significant interaction between lures and sites, the Spanish pheromone was on average eight times more attractive than the Austrian one. The mean number of trapped insects was lower in healthy stands (control) and old clearcuts (more than 1 year old) than in sites suffering recent infestation (standing or felled infested trees and recent clearcuts). Total captures were significantly correlated with tree mortality recorded annually within a 500 m radius around the traps. This pattern may be a useful input for establishing the timing of application of the best monitoring program of I. acuminatus populations.

Effects of Widespread Drought‐Induced Aspen Mortality on Understory Plants

Forest die-off around the world is expected to increase in coming decades as temperature increases due to climate change. Forest die-off will likely affect understory plant communities, which have substantial influence on regional biological diversity, ecosystem function, and land-atmosphere interactions, but how die-off alters these plant communities is largely unknown. We examined changes in understory plant communities following a widespread, drought-induced die-off of trembling aspen (Populus tremuloides) in the western United States. We assessed shrub and herbaceous cover and volume in quadrats in 55 plots located across a wide range of levels of aspen mortality. We measured species richness and composition of herbaceous plant communities by recording species presence and absence in 12 sets of paired (1 healthy, 1 dying) aspen plots. Although understory composition in healthy and dying stands was heterogeneous across the landscape, shrub abundance, cover, and volume were higher and abundance of herbaceous species, cover, and volume were lower in dying aspen stands. Shrub cover and volume increased from 2009 to 2011 in dying stands, which suggests that shrub growth and expansion is ongoing. Species richness of herbs declined by 23% in dying stands. Composition of herbs differed significantly between dying and healthy stands. Richness of non-native species did not differ between stand types. The understory community in dying aspen stands was not similar to other shrub-dominated plant communities in the region and may constitute a novel community. Our results suggest that changes in understory plant communities as forests die off could be a significant indirect effect of climate change on biological diversity and forest communities.

Morphological and histo-anatomical traits reflect die-back in Phragmites australis (Cav.) Steud.

The decline of Phragmites australis (Cav.) Steud., a well-known phenomenon in Central and Western Europe, was detected recently also in the Mediterranean Basin. A range of parameters were quantified in healthy and affected stands as a screening for indicators of die-back. These were: stem dimension, density and pattern, starch storage, presence of occlusions in the vessel cells, abnormal lignification and calli in the root parenchyma. First, high stem density, occlusions, lignification and calli did not always coincide with die-back. Second, starch content appeared a reliable indicator. The higher starch amount detected in the healthy stands can be related to the greater ability to perform photosynthesis and accumulate reserves. Furthermore, the starch lack detected in the declining stands might result from the increased starch demand, due to the shoot regeneration connected to the clumped habit.

The endophytic fungal communities associated with the leaves and roots of the common reed (Phragmites australis) in Lake Trasimeno (Perugia, Italy) in declining and healthy stands

Abstract We surveyed the fungal endophytes in the leaves and roots of Phragmites australis plants along a gradient of reed decline at Lake Trasimeno (central Italy) in Oct. 2010. An integrated approach consisting of cultivation and molecular identification was used. Endophytes were recovered from 61.59 % of the samples, with a total of 1 541 isolates. On the basis of a molecular analysis of the rDNA Internal Transcribed Spacer (ITS) region, 25 operational taxonomic units (OTUs) were identified. Fusarium sp. (OTU 21) and Gibberella moniliformis (OTU 1) were the most frequently isolated fungi. Comparisons of the leaf and root samples demonstrated spatial heterogeneity in the endophyte assemblages among the plant parts and sites. In this study, we have shown that reed plants in different states of decline harbour different endophytic communities. This finding may help to understand the very complex scenario of reed die-back.

Amount of boron in Norway spruce stands in eastern Finland

The aim of this study was to determine the amount of boron in three Norway spruce (Picea abies (L.) Karst) stands in eastern Finland, where boron deficiency is common. A further aim was to estimate the effects of logging-residue harvest on boron balance and the boron-to-nitrogen ratio on these sites. The data were obtained from a 30-year-old and a 62-year-old healthy spruce stand as well as from a 35-year-old spruce stand with boron deficiency and growth disorders. Altogether 2.1 and 2.4kgha−1 boron, respectively, were bound in trees+organic layer+0–10cm mineral soil layer in the two healthy stands, and 0.9kgha−1 in the boron deficient stand. For the amount of boron in the healthy stands the trees made up 43% and 49%, respectively, and in the boron deficient stand 38%. Stems contained 30% and 40%, respectively, of the boron in trees in the healthy stands and 37% in the boron-deficient stand. Only 11–13% of the tree boron was in the needles. The amount of nitrogen bound in the ecosystem studied was 2.1 and 2.5Mgha−1, respectively, in the two healthy stands and 3.0Mgha−1 in the boron deficient stand. In the ecosystem the trees contained 21–29% of the amount of nitrogen. Stems contained 14–24%, respectively, and needles 26–36%, respectively, of the nitrogen in the trees on the studied stands. In stem-only harvestings, relatively more boron than nitrogen would be removed from a site. In the boron-deficient stand, boron fertilisation for 3years nearly doubled the amount of boron in the ecosystem. Only 38% of the fertiliser boron (2kgha−1) was found in the ecosystem components studied.

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

Assessing the Responses of Native Small Mammals to an Incipient Invasion of Beech Bark Disease through Changes in Seed Production of American Beech (Fagus grandifolia)

Abstract Exotic tree diseases have direct impacts on their host and may have indirect effects on native fauna that rely on host tree species. This paper reports on relative preference for European beech [Fagus sylvatica (L.)] and sugar maple [Acer saccharum (Marsh.)] seed to small mammals, the direct impacts of beech bark disease (BBD) on seed production of American beech [F. grandifolia (Ehrh.)], and indirect impacts of this disease complex on native small mammal fauna in the Upper Peninsula of Michigan. We expected these indirect effects to result from altered seed production in American beech, both in the short and long term. If present, a preference for beech could suggest a mechanism for an indirect impact of BBD on native small mammals. Seed production of infected American beech declined throughout the 3 y of the study, while production of trees in healthy stands varied annually. We found that the abundance of Peromyscus spp. were related to seed crop in the previous autumn but that the presence of ...

The proposal of biotic hazard zones in selected spruce dominated regions in Slovakia

 Biotic agents driven spruce decline has been observed over several regions in Europe. We studied the spatial pattern of spruce stands mortality due to biotic agents in three spruce dominated regions in Slovakia – the Kysuce, Orava and Low Tatras regions. Regularly reported data on sanitary felling were used for the analysis. Geostatistical techniques and other spatial modelling tools were used to design the zones of biotic hazard for each region. Zone A stands for the totally disintegrated stands with extremely elevated activity of biotic agents. Zone B represents the buffer zone around the zone A. Its width depends on the spreading potential of biotic agents and related stand mortality observed during the last years. Zone C stands for the background areas, with more or less healthy stands. Zone-specific forest protection measures are proposed. Such a system allows for the priority rating of unnatural spruce stand conversion and optimal allocation of forest protection measures.

Forest structure without ground data: Adaptive Full-Blind Multiple Forward-Mode reflectance model inversion in a mountain pine beetle damaged forest

A new approach for using canopy reflectance models (CRMs) is presented that requires no field data or knowledge about the study area or imagery. Multiple Forward-Mode Adaptive Full-Blind (MFM-AFB) modelling provides forest biophysical structural information (BSI), and can also be used for classification and spectral mixture analysis at sub-pixel scales without user-specified model inputs, training data or endmember spectra, as these are instead automatically derived. In an example application using 2007 Landsat imagery of forest damaged by a mountain pine beetle (MPB) epidemic in British Columbia, Canada, overall BSI accuracy was within ±1000 stems ha–1 for stand density, ±0.5 m for crown radius and ±1 m tree height for healthy and MPB stands. MFM-AFB software is suitable for regional, multi-temporal and unknown imagery and areas. By not requiring user-specified a priori model inputs to infer BSI, the MFM-AFB approach may help enable mainstream use of diverse and advanced CRMs for image analysis.