Threshold Response to Extreme Drought Shifts Inter-Tree Growth Dominance in Pinus sylvestris

Many studies quantify short-term drought impact on tree growth relative to pre-drought growth averages. However, fewer studies examine the extent to which droughts of differing severity differentially impact tree growth or shape stand dynamics. Focusing on three droughts in high and low density stands of Pinus sylvestris in Scotland, we calculated pre-drought growth averages using climatically standardized antecedent growth years to assess tree level drought and post-drought growth performance as percentage growth change (PGC). We then used mixed-effects models to understand how droughts of differing severity impact tree growth and calculated indices of growth dominance (Gd), size inequality (Si), and size asymmetry (Sa) to detect changes in stand structure. Mixed-effects model results indicate that the magnitude and duration of the growth reduction during and following the more extreme drought was significantly larger compared to less severe droughts, for which we found limited evidence of drought impact. While no changes in Si or Sa were noted following any drought, we found evidence of a difference in Gd after the most extreme drought in both stand densities indicative of a threshold response, with smaller trees contributing proportionally more to stand growth relative to their size. Under less severe droughts, inter-tree variability may have partially buffered against stand-level growth change, however, a small increase in drought severity was associated with a significant reduction in average tree growth, an increase in the number of trees growing at >2SD below pre-drought levels and a shift in Gd toward smaller trees, indicating that a drought severity threshold in P. sylvestris may have been exceeded.

Delay of growth release after a windthrow event and climate response in a light-demanding species (European larch Larix decidua Mill.)

Key message Larch trees respond to stand opening with an approximately 4-year delay of growth, and low precipitation in July limits radial growth after a windthrow event. Abstract Precise cross-dating of disturbance events is crucial to understanding the functioning of forest stands, and may help explain ongoing ecological processes in a forest. Tree rings are very often used to reconstruct the history of disturbances and to study the response of trees to climatic factors. This study analyzed how quickly European larch can benefit from an abrupt change after catastrophic windthrow events and the extent of trees’ sensitivity to climate. The study is based on cores from 83 larch trees collected in a post-disturbance 100 ha plot established after a catastrophic windstorm in 2004 in the Slovakian High Tatras. Growth release was calculated from the percentage of growth change (PGC) measured in tree rings. The time lag between the disturbance event and release was related to tree diameter at breast height, tree age, and tree’s previous growth. The time lag between the year of the event and the year of growth reaction was 4.6 years on average (median 4 years) in a multi-aged group of trees. The climate analyses employed residual chronology. The new environmental conditions in the post-disturbance area have altered the trees’ growth reaction to climate; in particular, they show sensitivity to water deficit in July.

Past and Future of Temperate Forests State under Climate Change Effects in the Romanian Southern Carpathians

Research Highlights: Carpathian forests hold high ecological and economic value while generating conservation concerns, with some of these forests being among the few remaining temperate virgin forests in Europe. Carpathian forests partially lost their original integrity due to their management. Climate change has also gradually contributed to forest changes due to its modification of the environmental conditions. Background and Objectives: Understanding trees’ responses to past climates and forms of management is critical in foreseeing the responses of forests to future conditions. This study aims (1) to determine the sensitivity of Carpathian forests to past climates using dendrochronological records and (2) to describe the effects that climate change and management will have on the attributes of Carpathian forests, with a particular focus on the different response of pure and mixed forests. Materials and Methods: To this end, we first analysed the past climate-induced growth change in a dendrochronological reference series generated for virgin forests in the Romanian Curvature Carpathians and then used the obtained information to calibrate spatially explicit forest Landis-II models for the same region. The model was used to project forest change under four climate change scenarios, from mild to extreme. Results: The dendrochronological analysis revealed a climate-driven increase in forest growth over time. Landis-II model simulations also indicate that the amount of aboveground forest biomass will tend to increase with climate change. Conclusions: There are differences in the response of pure and mixed forests. Therefore, suitable forest management is required when forests change with the climate.

Powering Life in the Water: Phytoplankton in the San Francisco Estuary

Phytoplankton are probably the most important aquatic organisms that you have NEVER seen! Phytoplankton are nearly invisible and use sunlight, carbon dioxide, and nutrients in water to produce sugars that power the estuary food web. The amount of phytoplankton growth is important because phytoplankton are the food for aquatic animals like zooplankton and fish. Scientists working in the San Francisco Estuary are concerned because phytoplankton growth is low, and some animals are starved for food. Measuring phytoplankton growth is hard because growth is low and the conditions in the water that control growth change quickly. As a result, scientists created a mathematical equation, called a model, that brings together the number of phytoplankton available to grow, the amount of sunlight, and the muddiness of the water to estimate phytoplankton growth each day. This way, scientists can determine where and when food is available to power life in the San Francisco Estuary.

Refining the standardized growth change method for pointer year detection: bias-adjustment and definition of the recovery period

<p>Detecting pointer years in tree-ring data is a central aspect of extreme-event ecology. Pointer years usually represent extraordinary secondary tree growth, which can often be interpreted as response to extraordinary environmental conditions such as late-frosts or droughts. Identifying pointer-years in larger tree-ring networks and relating those to specific climatic conditions may allow for a deeper understanding of how trees perform under extreme climate and consequently, under anticipated climate change (Meyer et al., 2020; Rehschuh et al., 2017).  </p><p>Recently, Buras et al. (2020) demonstrated how frequently used pointer-year detection methods are suboptimal for such large-scale analyses due to an either too low or sometimes too high sensitivity in detecting extraordinary growth. In their study, Buras et al. (2020) proposed a novel approach for detecting pointer years – the standardized growth change (SGC) method. Despite a higher success rate with regards to identifying artificially introduced pointer years in simulated tree-ring data, Buras et al. (2020) concluded that the SGC method could be further refined to capture pointer years following a gradual growth decline. Moreover, they discussed the possibility to incorporate growth changes at higher lags, thereby allowing the duration of the recovery period following a pointer year to be estimated.</p><p>Under this framework, we here present a refined version of the SGC-method – the bias-adjusted standardized growth change method (BSGC). The methodological adjustment to the SGC approach incorporates conflated probabilities of time-step specific growth changes with probabilities of time-step independent growth changes. Application of BSGC to simulated and measured tree-ring data indicated a successful bias adjustment which now allows for the identification of pointer years following years of successive growth decline. Moreover, the length of simulated recovery periods was well reproduced and revealed plausible results for existing tree-ring data. Based on these validations, BSGC can be considered a further refinement of pointer-year detection, allowing for a more precise detection and consequently better understanding of the radial growth response of trees to extreme events.</p><p> </p><p>Buras, A., Rammig, A., Zang, C.S., 2020. A novel approach for the identification of pointer years. Dendrochronologia 125746. https://doi.org/10.1016/j.dendro.2020.125746</p><p>Meyer, B.F., Buras, A., Rammig, A., Zang, C.S., 2020. Higher susceptibility of beech to drought in comparison to oak. Dendrochronologia 64, 125780. https://doi.org/10.1016/j.dendro.2020.125780</p><p>Rehschuh, R., Mette, T., Menzel, A., Buras, A., 2017. Soil properties affect the drought susceptibility of Norway spruce. Dendrochronologia 45, 81–89. https://doi.org/10.1016/j.dendro.2017.07.003</p><p> </p>

McClusky’s Theory of Margin and its implications on adult learners in higher education institutions

This paper draws on McClusky’s Theory of Margin which contains elements of life transitions. Adulthood period is one of growth, change and integration of balance between energy needed to engage in learning. There is an increasing participation of adult learners in higher education institutions. This paper finds out whether learners complete degree programmes on time, or otherwise by examining responsibilities, resources required for learning, challenges faced and margin available to learners. This qualitative case study used Accra Learning Centre and adopted homogenous, random and sequential purposive sampling procedures. Fifteen participants participated in the in-depth interview conducted. Thematic, narrative and interpretivist approaches were adapted in analysing data collected. It emerged that adult learners have limitless potentials to learn, yet poor time management, work commitments and financial challenges made it difficult to complete programmes on time. Engagement in multiplicities of responsibilities consumed adult learners’ time and energy to learn. The findings made are discussed and recommendations are made.

A Supporting Tool for Requirements Prioritization Process in Agile Software Development

Requirements engineering is a crucial phase of software engineering, and requirements prioritization is an essential stage of requirements engineering particularly in agile software development. Requirements prioritization goals at eliciting which requirements of software need to be covered in a particular release. The key point is which requirement will be selected in the next iteration and which one will be delayed to other iterations for minimizing risk during development and meeting stakeholders’ needs. There are many existing techniques for requirement prioritization, but most of these techniques do not cover continuous growth, change of requirements, and requirements dependencies. The prioritization techniques need to be more continuous, scalable, implemented easily and integrated with software development life cycle. This paper introduces a supporting tool for a proposed framework to prioritize requirements in agile software development. This framework tries to find solutions for the challenges facing this prioritization process such as how to make this prioritization continuous and scalable and how to deal with rapidly requirement changes and its dependencies. The proposed framework is validated in a real case study using its supporting tool, and the results are promising

Growth change in Polish women: Reduction of the secular trends?

The aim of the study was to analyse changes in the average height of adult Polish women born in 1931–2001 in the aspect of dynamically changing economic and socio-economic conditions of the living environment. An ethnically homogeneous group of 6,028 adult women from large Polish cities, born in 1931–2001, living between 1931 and 2020, were examined using the same research methods and research equipment. All women were divided into eight birth cohorts. The Kruskal-Wallis test and multiple regression analyses were used. Root Mean Square Standardized Effect (RMSSE), critical value of the test, and test power were calculated. The average height of women born during 70 years of the study increased by 9.63 cm, from 158.22 cm (SD = 5.57 cm) to 167.85 cm (SD = 6.91 cm) (H = 1084.84, p<0.001). The intensity of the intergenerational trend in subsequent cohorts of years of birth varied strongly between decades, averaging 1.34 cm/decade. The body height in women increased significantly up to the height of those born between 1970 and 1979 and then the trend weakened noticeably, although it remained positive. The observed secular trend confirms positive changes in the standard of living of Polish women between 1931 and 2020. Improving living conditions allow people to fully achieve their genetically determined growth potential.