Climate variability drives recent tree mortality in Europe

Tree mortality is an important process in forest ecosystems, frequently hypothesized to be highly climate sensitive. Yet, tree death remains one of the least understood processes of forest dynamics. Recently, changes in tree mortality have been observed in forests around the globe, which could profoundly affect ecosystem functioning and services provisioning to society. We describe continental‐scale patterns of recent tree mortality from the only consistent pan‐European forest monitoring network, identifying recent mortality hotspots in southern and northern Europe. Analyzing 925,462 annual observations of 235,895 trees between 2000 and 2012, we determine the influence of climate variability and tree age on interannual variation in tree mortality using Cox proportional hazard models. Warm summers as well as high seasonal variability in precipitation increased the likelihood of tree death. However, our data also suggest that reduced cold‐induced mortality could compensate increased mortality related to peak temperatures in a warming climate. Besides climate variability, age was an important driver of tree mortality, with individual mortality probability decreasing with age over the first century of a trees life. A considerable portion of the observed variation in tree mortality could be explained by satellite‐derived net primary productivity, suggesting that widely available remote sensing products can be used as an early warning indicator of widespread tree mortality. Our findings advance the understanding of patterns of large‐scale tree mortality by demonstrating the influence of seasonal and diurnal climate variation, and highlight the potential of state‐of‐the‐art remote sensing to anticipate an increased likelihood of tree mortality in space and time.     

多菌灵处理对克隆植物大米草(Spartina anglica)表型可塑性的影响

对外来植物大米草(Spartina anglica)衰退种群进行高、中、低3个浓度(即50%多菌灵可湿性粉剂的300倍、600倍和1200倍稀释液)多菌灵灌根处理,测定大米草在杀菌剂处理条件下的形态可塑性、克隆生长特性及生物量积累与分配格局.结果表明:与对照相比,各浓度多菌灵处理对大米草的株高、叶数、叶片厚度、叶片面积和根长均没有显著影响(P〉0.05);中浓度处理后,大米草种群的根状茎节数和分枝强度均显著高于对照和其它处理,而根状茎总长和间隔子长度均显著高于对照和低浓度处理(p<0.05),与高浓度处理差异不显著;高浓度处理的大米草地下生物量和根生物量分配显著高于对照和其它处理,而地上生物量分配却显著低于对照和其它处理(P相似文献   

Disease progress of Jatropha dieback caused by Fusarium sp. in Samaru,Zaria

A survey was conducted from June 2012 to May 2013 in the Institute for Agricultural Research Jatropha plantation along Shika road to determine the progress of incidence and severity of Jatropha dieback caused by Fusarium sp. over a year. The disease incidence did not significantly differ among the months under review while disease severity was highest in August and lowest in March 2013.     

Factors affecting vegetation dieback of an oligohaline marsh in coastal Louisiana: Field manipulation of salinity and submergence

Vegetation dieback is an important component of wetland loss in low salinity marshes of coastal Louisiana. A field experiment was conducted to determine the factors responsible for vegetation dieback within oligohaline marshes of Louisiana. Sections of marsh, dominated by Sagittaria lancifolia L., were transplanted into one of four locations depending on the treatment: (1) increased submergence—sods were lowered 15 cm below the donor marsh surface, (2) increased salinity—sods were transplanted into a higher salinity marsh and adjacent dieback pond, (3) increased salinity and submergence—sods were transplanted into a higher salinity marsh and adjacent dieback pond at 15 cm below the marsh surface, and (4) control—sods were exhumed and replaced at the ambient elevation of the donor marsh. Plant biomass and edaphic characteristics were measured after 5 mo. An increase in submergence caused decreased plant growth of the S. lancifolia-dominated marsh community. An increase in salinities to 4–5 g/kg were not detrimental to plant growth. Although saltwater intrusion alone did not cause decreased growth of the S. lancifolia-dominnled plant community, the combination of saltwater intrusion and increased plant submergence caused the greatest decrease in plant growth due to increased toxic sulfides and a likely reduction in the uptake of NH₄-N by the wetland vegetation. This illustrates that the dieback of oligohaline marsh vegetation can be alleviated by decreasing plant submergence even at salinities as high as 4.6 g/kg.     

Is the field water use of Eucalyptus largiflorens F. Muell. affected by short-term flooding?

Abstract Transpiration of and water sources for Eucalyptus largiflorens F. Muell trees at three sites on a semi-arid floodplain of the lower River Murray in southern Australia were investigated during the course of a flood. Two of the sites were flooded for 32 days while the third was not flooded. At both flooded sites transpiration was not suppressed during the period when the sites were flooded, indicating that anoxia did not occur. Available literature suggests that E. largiflorens has very low O² consumption, and that lateral roots can absorb O² from soil water at very low partial pressures. The oxygen stored in the unsaturated region of the soil appeared sufficient, in this case, to meet the requirements of the trees. Transpiration at the flooded sites did not increase in comparison with that at the non-flooded site in the period following flooding. We suggest that this was possibly due to the above-average rainfall experienced in the months preceding the flood and/or physiological adaptations to the highly saline conditions that prevented the trees taking full advantage of the additional water. The sources of water used by the trees were investigated using the naturally occurring stable isotopes of water and measurements of soil water suction. These showed that prior to the flood shallow rain-derived soil water was being used at all three sites. Ten days after flooding ceased trees at both flooded sites were using shallow flood-derived soil water while at the non-flooded sites they were using groundwater. Results from the flooded sites 7 and 22 weeks after flooding ceased showed that as the flood- and rain-derived water became limited the trees supplemented their supplies with groundwater from the capillary fringe. The non-flooded trees used various combinations of rain-derived soil water and groundwater during this period.     

Historical and event‐based bioclimatic suitability predicts regional forest vulnerability to compound effects of severe drought and bark beetle infestation

Vulnerability to climate change, and particularly to climate extreme events, is expected to vary across species ranges. Thus, we need tools to standardize the variability in regional climatic legacy and extreme climate across populations and species. Extreme climate events (e.g., droughts) can erode populations close to the limits of species' climatic tolerance. Populations in climatic‐core locations may also become vulnerable because they have developed a greater demand for resources (i.e., water) that cannot be enough satisfied during the periods of scarcity. These mechanisms can become exacerbated in tree populations when combined with antagonistic biotic interactions, such as insect infestation. We used climatic suitability indices derived from Species Distribution Models (SDMs) to standardize the climatic conditions experienced across Pinus edulis populations in southwestern North America, during a historical period (1972–2000) and during an extreme event (2001–2007), when the compound effect of hot drought and bark beetle infestation caused widespread die‐off and mortality. Pinus edulis climatic suitability diminished dramatically during the die‐off period, with remarkable variation between years. P. edulis die‐off occurred mainly not just in sites that experienced lower climatic suitability during the drought but also where climatic suitability was higher during the historical period. The combined effect of historically high climatic suitability and a marked decrease in the climatic suitability during the drought best explained the range‐wide mortality. Lagged effects of climatic suitability loss in previous years and co‐occurrence of Juniperus monosperma also explained P. edulis die‐off in particular years. Overall, the study shows that past climatic legacy, likely determining acclimation, together with competitive interactions plays a major role in responses to extreme drought. It also provides a new approach to standardize the magnitude of climatic variability across populations using SDMs, improving our capacity to predict population's or species' vulnerability to climatic change.     

Genetic Variability of Hymenoscyphus pseudoalbidus on Ash Leaf Rachises in Leaf Litter of Forest Stands in Poland

Two hundred and thirty cultures of Hymenoscyphus pseudoalbidus were obtained from ascospores created in apothecia on the previous years' ash leaf rachises in the stand floor. Fruiting bodies of the pathogen were collected in four regions of Poland differing by geographical location, the altitude above sea level and climatic conditions. Isolates were identified based on the sequences of ribosomal DNA (ITS1‐5.8S‐ITS2) and the calmodulin gene. Only the presence of H. pseudoalbidus was identified in the decaying ash stands in Poland; morphologically similar, saprotrophic species of H. albidus was absent. Intrapopulation and interpopulation genetic variability of isolates was determined based on 84 RAMS markers obtained using four primers. Genetic variability of the fungus populations, measured by the Dice coefficient of genetic similarity and the Shannon coefficient of genetic diversity, decreased along with a decrease in the location of isolate collection area above sea level. A significant dependency was shown between intrapopulation genetic variability of isolates and altitude of regions above sea level. The Mantel test excluded existence of dependence between geographical and genetic distance among populations (r = ?0.038, P = 0.55). A significant correlation was found between the genetic distances of individuals within populations and locations above sea level. Based on PCA and geographical location of populations, it was shown that populations create four distinct groups. amova showed that a majority of total genetic variability (65.80%) constitutes intrapopulation variability. Variability between populations was high (28.7%), and individual regions had a smallest influence (5.5%) on the level of total variability.     

Non‐lethal foraging by bell miners on a herbivorous insect: Potential implications for forest health

Tree health is often negatively linked with the localized abundance of parasitic invertebrates. One group, the sap‐sucking psyllid insects (Homoptera: Psyllidae) are well known for their negative impact upon vegetation, an impact that often culminates in the defoliation and even death of hosts. In Australia, psyllid‐infested forest in poor health is also frequently occupied by a native honeyeater, the bell miner (Manorina melanophrys; Meliphagidae), so much so that the phenomenon has been dubbed ‘bell miner‐associated dieback’ (BMAD). Bell miners are thought to be the causative agent behind BMAD, in part because the species may selectively forage only upon the outer covering (lerp) exuded by psyllid nymphs, leaving the insect underneath to continue parasitizing hosts. As bell miners also aggressively exclude all other avian psyllid predators from occupied areas, these behavioural traits may favour increases in psyllid populations. We examined bell miner foraging behaviour to determine if non‐lethal foraging upon psyllid nymphs occurred more often than in a congener, the noisy miner (M. melanocephala; Meliphagidae). This was indeed the case, with bell miners significantly more likely to remove only the lerp covering during feeding, leaving the insect intact underneath. This arose from bell miners using their tongue to pry off the lerp cases, whereas noisy miners used their mandibles to snap at both the lerp and insect underneath. Furthermore, psyllids left behind following a bell miner foraging event were significantly more likely to be viable and regrow a lerp covering than those exposed by noisy miners. Together, this behaviour supports the theory that non‐lethal foraging behaviour of bell miners may contribute to high psyllid abundance, consistent with the mechanisms by which BMAD is thought to develop.     

Evaluation of a visual assessment method for tree condition of eucalypt floodplain forests

Summary For decades the floodplain forests of the River Murray have endured the effects of prolonged water stress. This has resulted in significant crown dieback and loss of condition. The Living Murray (TLM) initiative aims to restore the ecological health of six Icon Sites along the River. The two eucalypts River Red Gum (Eucalyptus camaldulensis) and Black Box (Eucalyptus largiflorens) that dominate the forests at five of the six Icon Sites are undergoing widespread decline. To enable effective management and restoration of these forests, we developed a standardised tree condition assessment method. Named the TLM tree condition assessment method, it utilises visual assessment of a range of tree crown variables (extent and density of the foliage in the crown, epicormic growth, new tip growth, reproductive activity, leaf die‐off, mistletoe infestation) and measurements of bark condition, diameter at breast height and dominance class. This article describes the TLM tree condition assessment method and assesses it for consistency between multiple observer teams after limited training. The level of observer agreement between six teams each comprised of two observers was assessed for seven of the ten variables. Intra‐class correlation was used to compare scores of 30 River Red Gum trees assessed on Gunbower Island on the River Murray. The level of agreement for all variables was statistically significant with six of seven variables having correlation coefficients over R = 0.5. The TLM tree condition assessment method was found to provide accurate estimates of a range of tree variables that can be used to determine tree condition. The TLM tree condition assessment method provides a valuable monitoring tool that can be used to assess management interventions, such as management flooding and silvicultural thinning.