A simple and cost-effective method for cable root detection and extension measurement in estuary wetland forests

This work presents the development of a low-cost method to measure the length cable roots of black mangrove (Avicennia germinans) trees to define the boundaries of central part of the anchoring root system (CPRS) without the need to fully expose root systems. The method was tested to locate and measure the length shallow woody root systems. An ultrasonic Doppler fetal monitor (UD) and a stock of steel rods (SR) were used to probe root locations without removing sediments from the surface, measure their length and estimate root-soil plate dimensions. The method was validated by comparing measurements with root lengths taken through direct measurement of excavated cable roots and from root-soil plate radii (exposed root-soil material when a tree tips over) of five up-rooted trees with stem diameters (D130) ranging between 10 and 50 cm. The mean CPRS radius estimated with the use of the Doppler was directly correlated with tree stem diameter and was not significantly different from the root-soil plate mean radius measured from up-rooted trees or from CPRS approximated by digging trenches. Our method proved to be effective and reliable in following cable roots for large amounts of trees of both black and white mangrove trees. In a period of 40 days of work, three people were capable of measuring 648 roots belonging to 81 trees, out of which 37% were found grafted to other tree roots. This simple method can be helpful in following shallow root systems with minimal impact and help map root connection networks of grafted trees

Driving forces of Antarctic krill abundance

Antarctic krill, crucial to the Southern Ocean ecosystem and a vital fisheries resource, is endangered by climate change. Identifying drivers of krill biomass is therefore essential for determining catch limits and designating protection zones. We present a modeling approach to pinpointing effects of sea surface temperature, ice cover, chlorophyll levels, climate indices, and intraspecific competition. Our study reveals that larval recruitment is driven by both competition among age classes and chlorophyll levels. In addition, while milder ice and temperature in spring and summer favor reproduction and early larval survival, both larvae and juveniles strongly benefit from heavier ice and colder temperatures in winter. We conclude that omitting top-down control of resources by krill is only acceptable for retrospective or single-year prognostic models that use field chlorophyll data but that incorporating intraspecific competition is essential for longer-term forecasts. Our findings can guide future krill modeling strategies, reinforcing the sustainability of this keystone species

Small‐scale heterogeneity shapes grassland diversity in low‐to‐intermediate resource environments

Questions Soil resource heterogeneity influences the outcome of plant–plant interactions and, consequently, species co-existence and diversity patterns. The magnitude and direction of heterogeneity effects vary widely, and the processes underlying such variations are not fully understood. In this study, we explored how and under what resource conditions small-scale heterogeneity modulates grassland plant diversity. Location Oderhänge Mallnow, Potsdam, Brandenburg, Germany. Methods We expanded the individual-based plant community model (IBC-grass) to incorporate dynamic below-ground resource maps, simulating spatial heterogeneity of resource availability. Empirical centimeter-scale data of soil C/N ratio were integrated into the model, accounting for both configurational and compositional heterogeneity. We then analyzed the interplay between small-scale heterogeneity and resource availability on the interaction and co-existence of plant species and overall diversity. Results Our results showed significant differences between the low- and high-resource scenarios, with both configurational and compositional heterogeneity having a positive effect on species richness and Simpson's diversity, but only under low-resource conditions. As compositional heterogeneity in the fine-scale C/N ratio increased, we observed a positive shift in Simpson's diversity and species richness, with the highest effects at the highest level of variability tested. We observed little to no effect in nutrient-rich scenarios, and a shift to negative effects at the intermediate resource level. The study demonstrates that site-specific resource levels underpin how fine-scale heterogeneity influences plant diversity and species co-existence, and partly explains the divergent effects recorded in different empirical studies. Conclusions This study provides mechanistic insights into the complex relationship between resource heterogeneity and diversity patterns. It highlights the context-dependent effects of small-scale heterogeneity, which can be positive under low-resource, neutral under high-resource, and negative under intermediate-resource conditions. These findings provide a foundation for future investigations into small-scale heterogeneity–diversity relationships, contributing to a deeper understanding of the processes that promote species co-existence in plant communities

Resilience trinity: safeguarding ecosystem functioning and services across three different time horizons and decision contexts

Ensuring ecosystem resilience is an intuitive approach to safeguard the functioning of ecosystems and hence the future provisioning of ecosystem services (ES). However, resilience is a multi‐faceted concept that is difficult to operationalize. Focusing on resilience mechanisms, such as diversity, network architectures or adaptive capacity, has recently been suggested as means to operationalize resilience. Still, the focus on mechanisms is not specific enough. We suggest a conceptual framework, resilience trinity, to facilitate management based on resilience mechanisms in three distinctive decision contexts and time‐horizons: 1) reactive, when there is an imminent threat to ES resilience and a high pressure to act, 2) adjustive, when the threat is known in general but there is still time to adapt management and 3) provident, when time horizons are very long and the nature of the threats is uncertain, leading to a low willingness to act. Resilience has different interpretations and implications at these different time horizons, which also prevail in different disciplines. Social ecology, ecology and engineering are often implicitly focussing on provident, adjustive or reactive resilience, respectively, but these different notions of resilience and their corresponding social, ecological and economic tradeoffs need to be reconciled. Otherwise, we keep risking unintended consequences of reactive actions, or shying away from provident action because of uncertainties that cannot be reduced. The suggested trinity of time horizons and their decision contexts could help ensuring that longer‐term management actions are not missed while urgent threats to ES are given priority

The impact of salps (Salpa thompsoni) on the Antarctic krill population (Euphausia superba): an individual-based modelling study

Krill (Euphausia superba) and salps (Salpa thompsoni) are key macrozooplankton grazers in the Southern Ocean ecosystem. However, due to differing habitat requirements, both species previously exhibited little spatial overlap. With ongoing climate change-induced seawater temperature increase and regional sea ice loss, salps can now extend their spatial distribution into historically krill-dominated areas and increase rapidly due to asexual reproduction when environmental conditions are favorable. Understanding the potential effects on krill is crucial, since krill is a species of exceptional trophic significance in the Southern Ocean food web. Negative impacts on krill could trigger cascading effects on its predators and prey. To address this question, we combined two individual-based models on salps and krill, which describe the whole life cycle of salp individuals and the dynamic energy budget of individual krill. The resulting new model PEKRIS (PErformance of KRIll vs. Salps) simulates a krill population for 100 years under varying chlorophyll-a concentrations in the presence or absence of salps. All of the investigated krill population properties (abundance, mean length, and yearly egg production) were significantly impacted by the presence of salps. On the other hand, salp density was not impacted if krill were present. The medians of krill population properties deviated during variable maximum chlorophyll-a density per year when salps were introduced by − 99.9% (− 234 individuals per 1000 m3) for krill density, − 100% (− 22,062 eggs per 1000 m3) for krill eggs and − 0.9% (− 0.3 mm) for mean length of krill. If both species compete for the same food resource in a closed space, salps seem to inhibit krill populations. Further simulation studies should investigate whether this effect prevails if different phytoplankton sizes and consumption preferences of krill are implemented. Furthermore, direct predation of the two species or consumption of krill fecal pellets by salps could change the impact size of the food competition

Blooms of a key grazer in the Southern Ocean – An individual-based model of Salpa thompsoni

The Southern Ocean near the Western Antarctic Peninsula (WAP) is strongly affected by climate change resulting in warmer air temperature, accompanied with reduced sea ice coverage, increased sea water temperature and potential changes in the abundances of two key grazer species Salpa thompsoni (salp) and Euphausia superba (Antarctic krill). While salp abundance is hypothesized to increase, krill abundance is hypothesized to decline with dramatic consequences for the entire food web of the Southern Ocean. A better understanding of the biotic interaction between krill and salps and their population dynamics is thus crucial. However, the life cycle of salps is complicated and barely understood. Therefore, we have developed an individual-based model describing the whole life cycle to better understand the population dynamics of salps and the conditions for blooms. The model has been used to explore if and under what conditions the empirical pattern of large variability in observed salp abundances at the WAP, generated by the long-term data of the US Antarctic Marine Living Resources Program (AMLR) can emerge from a small seeding population. The model reproduced this empirical pattern if daily growth rates of oozoids were higher than previously reported for the WAP (mean growth rate for oozoids ~ 1 mm d−1) and if growth rates of blastozooids were lower (mean growth rate ~ 0.2 mm d−1). The model suggests that a prerequisite for local salp blooms requires a small founding population in early spring. With climate change it has been suggested that more frequent and earlier transport of salps into the WAP or winter survival will occur. Hence, the risk of salp blooms in the WAP is likely to substantially increase. These findings highlight the importance for an improved quantitative understanding of how primary production and the southward advection of salps will be impacted by climate change

Modeling dominant height growth using permanent plot data for Pinus brutia stands in the Eastern Mediterranean region

Aim of the study: At current, forest management in the Eastern Mediterranean region is largely based on experience rather than on management plans. To support the development of such plans, this study develops and compares site index equations for pure even-aged Pinus brutia stands in Syria using base-age invariant techniques that realistically describe dominant height growth.Materials and methods: Data on top height and stand age were obtained in 2008 and 2016 from 80 permanent plots capturing the whole range of variation in site conditions, stand age and stand density. Both the Algebraic Difference Approach (ADA) and the Generalized Algebraic Difference Approach (GADA) were used to fit eight generalized algebraic difference equations in order to identify the one which describes the data best. For this, 61 permanent plots were used for model calibration and 19 plots for validation.Main results: According to both biological plausibility and model accuracy, the so-called Sloboda equation based on the GADA approach showed the best performance.Research highlights: The study provides a solid classification and comparison of Pinus brutia stands growing in the Eastern Mediterranean region and can thus be used to support sustainable forest management planning.Keywords: site index; Generalized Algebraic Difference Approach (GADA); Sloboda equation

Making predictions in a changing world: The benefits of individual-based ecology

Ecologists urgently need a better ability to predict how environmental change affects biodiversity. We examine individual-based ecology (IBE), a research paradigm that promises better a predictive ability by using individual-based models (IBMs) to represent ecological dynamics as arising from how individuals interact with their environment and with each other. A key advantage of IBMs is that the basis for predictions-fitness maximization by individual organisms-is more general and reliable than the empirical relationships that other models depend on. Case studies illustrate the usefulness and predictive success of long-term IBE programs. The pioneering programs had three phases: conceptualization, implementation, and diversification. Continued validation of models runs throughout these phases. The breakthroughs that make IBE more productive include standards for describing and validating IBMs, improved and standardized theory for individual traits and behavior, software tools, and generalized instead of system-specific IBMs. We provide guidelines for pursuing IBE and a vision for future IBE research

Change in drivers of mangrove crown displacement along a salinity stress gradient

1. Crown displacement in trees is an adaptive response driven by neighbours that optimizes space use and reduces competition. But it can also be the result of wind force. Although morphological responses to neighbours have been well studied, the interplay between neighbours and wind in driving crown shape, and the implications for plant interactions remain poorly understood. However, it is crucial to predict such changes in vegetation structure and function under the scope of global change. We test the hypothesis that aboveground interactions are reduced with increasing soil stress and that wind becomes the main driver of crown shape in mangrove forests. 2. We investigated the effect of neighbours and wind intensity and direction on crown displacement of mangrove canopy and below canopy trees along a salinity gradient, and assessed crown asymmetry for three mangrove tree species, as well as the contribution of crown displacement on reducing crown‐projected area overlap and thus neighbourhood competition. 3. Results show that crown displacement of canopy trees is strongly influenced by winds at all salinities. At low salinities, competition for space accounted for 48% of crown displacement away from neighbours, compared to 49% found for the synthetized effects of wind and neighbours. While trees below the canopy displace their crowns away from their neighbours, no response to wind could be detected. This can be due to the wind protection conferred by a dense canopy stand related to bigger crowns that effectively reduce wind drag. At higher salinities, there was a reduction in canopy overlap due to crown displacement, which suggests reduced aboveground plant interactions with increasing soil stress. 4. While neighbourhood avoidance is a fundamental strategy for optimal light foraging, this study shows that wind strength and directionality are main drivers of crown shape with increasing stress and highlights their potential influence in plant interactions and forest structure, pointing to an increased susceptibility of trees to disturbances that should be further studied