Long-term standardized forest phenology in Sweden: a climate change indicator

Because climate change alters patterns of vegetative growth, long-term phenological measurements and observations can provide important data for analyzing its impact. Phenological assessments are usually made as records of calendar dates when specific phase changes occur. Such assessments have benefits and are used in Citizen Science monitoring. However, these kinds of data often have low statistical precision when describing gradual changes. Frequent monitoring of the phenological traits of forest trees and berries as they undergo gradual change is needed to acquire good temporal resolution of transitions relative to other factors, such as susceptibility to frosts, insects, and fungi, and the use of berries as a food resource. Intensive weekly monitoring of the growth of apical and branch buds and the elongation of shoots and leaves on four tree species, and the abundance of flowers and berries of bilberry and lingonberry, has been performed in Sweden since 2006. Here, we present quantitative methods for interpolating such data, which detail the gradual changes between assessments in order to describe average rates of development and amount of interannual variation. Our analysis has shown the active growth period of trees to differ with latitude. We also observed a change in the timing of the maximum numbers of ripening berries and their successive decline. Data from tree phenology assessments can be used to recommend best forestry practice and to model tree growth, while berry data can be used to estimate when food resources for animals are most available

Optimizing height measurement for the long-term forest experiments in Sweden

Information on tree height is useful for volume estimation and site productivity assessment and as such, remains one of the most important variables often measured in forest inventories. Measuring a sufficient number of sample trees requires considerable sampling effort and cost. In this study, we developed height functions for optimizing tree height measurement in the Swedish long-term forest experiments (LTFEs). Two large datasets from the LTFE databases: fitting data (from thinning, fertilisation and mixed species experiments) and validation data (tree species and spacing experiments) collected over several decades were used. The fitting and validation data comprise 133,788 and 68,440 observations, respectively, each covering a large range of growth and environmental conditions across Sweden. A multilevel nonlinear mixed-effects modelling approach was used to build the generalised height functions for Scots pine, Norway spruce, birch (Silver and Downy birch united), other conifers and other broadleaves, considering variations in heights and other stand characteristics at sample plot-level and revision-level. The response calibration of the functions was first carried out with all measured heights of the validation data, and second, using heights of one to six sample trees obtained from different tree selection strategies (diameter extremes, largest diameters, and smallest diameters). The mixed-effects height functions explained most of the height variations in the fitting dataset (pseudo R2: 0.938 - 0.970; RMSE: 0.957 - 1.363 m) without any residual trends. The validation showed that the functions accounted for 95 - 98 % of the height variation in the validation dataset, with RMSE ranging between 0.770 and 1.040 m, confirming the functions' high accuracy. We recommend the measurement of four sample tree heights based on diameter ex-tremes as the ideal threshold for response calibration. These functions and the suggested sampling technique would reduce sampling effort and inventory cost of height measurements for subsequent inventories of the LTFEs

Arealförluster av näringsämnen efter ristäkt och markberedning på sydsvenska hyggen

Arealförlusterna av 13 olika näringsämnen bestämdes i ett föryngringsförsök på hyggen i södra Sverige. De markbehandlingar som studerades var ristäkt (ca 80 % av grenar och toppar avlägsnades), och mekanisk markberedning (högläggning). I studien ingick totalt tio hyggen varav fem var belägna i Småland och fem i Halland. Studien pågick under 3 år, och hyggenas ålder var 0-4 år vid försökets start. Arealförlusten bestämdes med hjälp av kemiska analyser av markvatten som provtogs med hjälp av undertryckslysimetrar. Avrinningen simulerades med hjälp av SOIL modellen. Ristäkt minskade arealförlusten av kalium både i Småland och Halland, och det fanns en tendens till minskad arealförlust av kväve efter ristäkt. Även arealförlusten av aluminium, klor och kol (TOC) påverkades av ristäkt men effekten var olika på de studerade lokalerna. Markberedning medförde inga signifikant förhöjda arealförluster av kväve, medan vi för flera av de andra studerade ämnena uppmätte förhöjda arealförluster. Detta gäller H, Cl, Na, Al och TOC på hyggena i Halland och Mg och Mn på hyggena i Småland. För de flesta av ämnena var arealförlusterna betydligt större på hyggena i Halland jämfört med Småland. Tidsförloppet i arealförlusterna efter hyggesupptagningen varierade såväl mellan ämnena och lokalerna. Dessutom var mellanårsvariationen stor. Den generella slutsats som kan dras från studien är att effekten av slutavverkning var tydlig för flera av de studerade ämnena, men att effekten av ristäkt och markberedning var liten jämfört med hyggeseffekten

Lake salinization drives consistent losses of zooplankton abundance and diversity across coordinated mesocosm experiments

Human-induced salinization increasingly threatens inland waters; yet we know little about the multifaceted response of lake communities to salt contamination. By conducting a coordinated mesocosm experiment of lake salinization across 16 sites in North America and Europe, we quantified the response of zooplankton abundance and (taxonomic and functional) community structure to a broad gradient of environmentally relevant chloride concentrations, ranging from 4 to ca. 1400 mg Cl- L-1. We found that crustaceans were distinctly more sensitive to elevated chloride than rotifers; yet, rotifers did not show compensatory abundance increases in response to crustacean declines. For crustaceans, our among-site comparisons indicate: (1) highly consistent decreases in abundance and taxon richness with salinity; (2) widespread chloride sensitivity across major taxonomic groups (Cladocera, Cyclopoida, and Calanoida); and (3) weaker loss of functional than taxonomic diversity. Overall, our study demonstrates that aggregate properties of zooplankton communities can be adversely affected at chloride concentrations relevant to anthropogenic salinization in lakes.Peer reviewe

Current water quality guidelines across North America and Europe do not protect lakes from salinization

Human-induced salinization caused by the use of road deicing salts, agricultural practices, mining operations, and climate change is a major threat to the biodiversity and functioning of freshwater ecosystems. Yet, it is unclear if freshwater ecosystems are protected from salinization by current water quality guidelines. Leveraging an experimental network of land-based and in-lake mesocosms across North America and Europe, we tested how salinization-indicated as elevated chloride (C-) concentration-will affect lake food webs and if two of the lowest Cl- thresholds found globally are sufficient to protect these food webs. Our results indicated that salinization will cause substantial zooplankton mortality at the lowest Cl- thresholds established in Canada (120 mg Cl-/L) and the United States (230 mg Cl-/L) and throughout Europe where Cl- thresholds are generally higher. For instance, at 73% of our study sites, Cl- concentrations that caused a >= 50% reduction in cladoceran abundance were at or below Cl thresholds in Canada, in the United States, and throughout Europe. Similar trends occurred for copepod and rotifer zooplankton. The loss of zooplankton triggered a cascading effect causing an increase in phytoplankton biomass at 47% of study sites. Such changes in lake food webs could alter nutrient cycling and water clarity and trigger declines in fish production. Current Cl- thresholds across North America and Europe clearly do not adequately protect lake food webs. Water quality guidelines should be developed where they do not exist, and there is an urgent need to reassess existing guidelines to protect lake ecosystems from human-induced salinization.Peer reviewe

Widespread variation in salt tolerance within freshwater zooplankton species reduces the predictability of community-level salt tolerance

The salinization of freshwaters is a global threat to aquatic biodiversity. We quantified variation in chloride (Cl-) tolerance of 19 freshwater zooplankton species in four countries to answer three questions: (1) How much variation in Cl- tolerance is present among populations? (2) What factors predict intraspecific variation in Cl- tolerance? (3) Must we account for intraspecific variation to accurately predict community Cl- tolerance? We conducted field mesocosm experiments at 16 sites and compiled acute LC(50)s from published laboratory studies. We found high variation in LC(50)s for Cl- tolerance in multiple species, which, in the experiment, was only explained by zooplankton community composition. Variation in species-LC50 was high enough that at 45% of lakes, community response was not predictable based on species tolerances measured at other sites. This suggests that water quality guidelines should be based on multiple populations and communities to account for large intraspecific variation in Cl- tolerance.Peer reviewe

Interactions between near-ground temperature and radiation, silvicultural treatments and frost damage to Norway spruce seedlings

Several different silvicultural treatments were studied in two experiments. In the first, mechanical scarification, slash removal, vegetation control, clear-cut age and seedling types were investigated with respect to frost injury to Norway spruce (Picea abies (L.) Karst.) seedlings. Frost damage was also related to near-ground minimum temperature. In the other experiment, the effects of Scots pine (Pinus sylvestris (L.)) shelterwood density gradients, ranging from dense, uncut forest to complete clear-cuttings, were analysed. Near-ground temperature and radiation were monitored close to planted Norway spruce cuttings with a mobile data acquisition system. Growth, frost damage and chlorophyll fluorescence were monitored and analysed in relation to microclimate. Budburst date was estimated and the nocturnal near-ground temperature during the period when the seedlings were most susceptible to frost was analysed in both experiments. The shelterwood moderated near-ground radiation fluxes and diurnal temperature varia-tions, while the daily mean temperature was unaffected. Near-ground minimum tempera-tures were lower, and vertical temperature inversions were more pronounced in clear-cuttings than in shelterwoods, during clear and calm nights. The effects were most pro-nounced during a dry period. Budburst was delayed in the shelterwood. Later budburst was shown to reduce the risk of exposure to frosts during the most frost-susceptible period, when cuttings of two clones, differing in budburst date, were compared. Mechanical scarification reduced frost damage to seedlings in the first growing season, but neither herbicide treatment, nor mowing affected the frequency of frost injury. The frequency of frost injury was higher amongst containerised seedlings than amongst bare-rooted seedlings, especially in the first growing season. Neither clear-cut age nor slash removal affected the frequency of frost damage. Frost injury to the cuttings was reduced by the shelterwoods, since 80% were damaged by frost in clear-cuts and low-density shelterwoods, 27% in moderately dense shelterwoods, and only 5% in dense shelter-woods. Of the climatic variables tested, the accumulated net and global radiation the day after a severe frost event were the most strongly correlated with the degree of frost injury among cuttings, and the variation in their Fv/Fm ratios, in the graduated shelterwoods. Frost injuries were rarely lethal, but reduced growth and increased the proportion of seed-lings with multiple leaders and spike knots, especially amongst seedlings that were re-peatedly injured over several years. Height growth was lower in the clear-cut area than in moderately dense shelterwoods during years with severe frost dam

Marknära ozon i Asa : Årsrapport 2019

Månadsmedelvärde av marknära ozonhalt och summa AOT40 i Asa år 2019. Data för uppföljning av Miljökvalitetsmålet Frisk luft