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1. Defoliated trees die below a critical threshold of stored carbon

   https://doi.org/10.1111/1365-2435.13891  

   Barker Plotkin, Audrey ; Blumstein, Meghan ; Laflower, Danelle ; Pasquarella, Valerie J. ; Chandler, Jennifer L. ; Elkinton, Joseph S. ; Thompson, Jonathan R. ( August 2021 , Functional Ecology)

   Carbon starvation posits that defoliation‐ and drought‐induced mortality results from drawing down stored non‐structural carbohydrates (NSCs), but evidence is mixed, and few studies evaluate mortality directly. We tested the relationships among defoliation severity, NSC drawdown and tree mortality by measuring NSCs in mature oak trees defoliated by an invasive insect,Lymantria dispar, across a natural gradient of defoliation severity.

   We collected stem and root samples from mature oaks (Quercus rubraandQ.alba) in interior forests (n = 34) and forest edges (n = 47) in central Massachusetts, USA. Total NSC (TNC; sugar + starch) stores were analysed with respect to tree size, species and defoliation severity, which ranged between 5% and 100%.

   TNC stores declined significantly with increasingly severe defoliation. Forest edge trees had higher TNC stores that were less sensitive to defoliation than interior forest trees, although this may be a result of differing defoliation history. Furthermore, we observed a mortality threshold of 1.5% dry weight TNC.

   Our study draws a direct link between insect defoliation and TNC reserves and defines a TNC threshold below which mortality is highly likely. These findings advance understanding and improve model parametrization of tree response to insect outbreaks, an increasing threat with globalization and climate change.

   A freePlain Language Summarycan be found within the Supporting Information of this article.

    

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2. The meaning(s) of place: Identifying the structure of sense of place across a social–ecological landscape

   https://doi.org/10.1002/pan3.10112  

   Rajala, Kiandra ; Sorice, Michael G. ; Thomas, Valerie A. ; Ellis, ed., Erle C. ( June 2020 , People and Nature)

   Sense of place holds promise to understand how people perceive and respond to social and ecological change; however, using this concept to explore vulnerability and adaptation first depends on identifying the multiple ways people define their relationship with a place.

   We introduce the meaning‐dependence framework to account for the broad array of person–place connections within social–ecological landscapes.

   We applied this framework to private landowners in the Southern Great Plains of the United States, a working landscape experiencing ecological transformation from grasslands to degraded woodlands.

   Using a mail survey, we explored the structure of sense of place based on the relationship between place meanings and place attachment. We employed complementary analytical methods: correlation analysis, ordinary least squares regression, and machine learning through a regression tree and random forest.

   Place meanings explained a large amount of variation in place attachment and were characterized by intercorrelations and interactions. Across analyses, experiential meanings reflecting personal psychological connections to one's land were the predominant drivers of landowners' place attachment.Way of lifeemerged as a central meaning for understanding sense of place on private lands.

   The meaning‐dependence framework builds on existing research to account for the multiple ways meanings inform human connections to a place. This framework is broadly applicable to any setting and can capture diverse configurations of person–place relationships and increase the utility of sense of place in social–ecological research.

   A freePlain Language Summarycan be found within the Supporting Information of this article.

    

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3. Potential Impacts of Insect-Induced Harvests in the Mixed Forests of New England

   https://doi.org/10.3390/f11050498  

   MacLean, Meghan Graham ; Holt, Jonathan ; Borsuk, Mark ; Markowski-Lindsay, Marla ; Butler, Brett J. ; Kittredge, David B. ; Duveneck, Matthew J. ; Laflower, Danelle ; Orwig, David A. ; Foster, David R. ; et al ( May 2020 , Forests)

   Forest insects and pathogens have significant impacts on U.S. forests, annually affecting an area nearly three times that of wildfires and timber harvesting combined. However, coupled with these direct effects of forest insects and pathogens are the indirect impacts through influencing forest management practices, such as harvesting. In an earlier study, we surveyed private woodland owners in the northeastern U.S. and 84% of respondents indicated they intended to harvest in at least one of the presented insect invasion scenarios. This harvest response to insects represents a potentially significant shift in the timing, extent, and species selection of harvesting. Here we used the results from the landowner survey, regional forest inventory data, and characteristics of the emerald ash borer (Species: Agrilus planipennis Fairmaire, 1888) invasion to examine the potential for a rapidly spreading invasive insect to alter harvest regimes and affect regional forest conditions. Our analysis suggests that 25% of the woodland parcels in the Connecticut River Watershed in New England may intend to harvest in response to emerald ash borer. If the emerald ash borer continues to spread at its current rate within the region, and therefore the associated management response occurs in the next decade, this could result in an increase in harvest frequencies, from 2.6% year−1 (historically) to 3.7% year−1 through to approximately 2030. If harvest intensities remain at levels found in remeasured Forest Inventory and Analysis plots, this insect-initiated harvesting would result in the removal of 12%–13% of the total aboveground biomass. Eighty-one percent of the removed biomass would be from species other than ash, creating a forest disturbance that is over twice the magnitude than that created by emerald ash borer alone, with the most valuable co-occurring species most vulnerable to biomass loss. 

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4. Woodland wildfire enables fungal colonization of encroaching Douglas‐fir

   https://doi.org/10.1111/1365-2435.14382  

   Smith, Gabriel Reuben ; Peay, Kabir G. ( June 2023 , Functional Ecology)

   Self‐reinforcing differences in fire frequency help closed‐canopy forests, which resist fire, and open woodlands, which naturally burn often, to co‐occur stably at landscape scales. Forest tree seedlings, which could otherwise encroach and overgrow woodlands, are killed by regular fire, yet fire has other effects that may also influence these feedbacks. In particular, many forest trees require symbiotic ectomycorrhizal fungi in order to establish. By restructuring soil fungal communities, fire might affect the availability of symbionts or the potential for symbiont sharing between encroaching trees and woodland vegetation.

   To investigate this possibility, we performed a soil bioassay experiment using inoculum from burned and unburned oak woodlands and Douglas‐fir forests. We examined how fire, ecosystem type, and neighboring heterospecific seedlings affect fungal root community assembly of Douglas‐firs and oaks. We asked whether heterospecific seedlings facilitated fungal colonization of seedling roots in non‐native soil, and if so, whether fire influenced this interaction.

   External fungal colonization of oak roots was more influenced by fire and ecosystem type than by the presence of a Douglas‐fir, and oaks increased the likelihood that Douglas‐fir roots would be colonized by fungi in oak woodland soil. Yet, fire increased colonization of Douglas‐fir in oak soil, diminishing the otherwise crucial role played by oak facilitation. Fire also strengthened the positive effect of Douglas‐firs on oak root‐associated fungal diversity in Douglas‐fir forest soil.

   Prior work shows that fire supports woodland ecosystems by stemming recruitment of encroaching seedlings. Here, we find evidence that it may contrastingly reduce fungal limitation of invasive seedling growth and establishment, otherwise relieved only by facilitation. Future work can investigate how these opposing effects might contribute to the net impact of changes in fire regime on landcover stability.

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5. Dynamic energy landscapes of predators and the implications for modifying prey risk

   https://doi.org/10.1111/1365-2435.14478  

   Papastamatiou, Yannis P. ; Binder, Benjamin M. ; Boswell, Kevin M. ; Malone, Margaret A. ; Heithaus, Michael R. ; Huveneers, Charlie ; Mourier, Johann ; Harborne, Alastair R. ( December 2023 , Functional Ecology)

   Landscapes of fear describe a spatial representation of an animal's perceived risk of predation and the associated foraging costs, while energy landscapes describe the spatial representation of their energetic cost of moving and foraging. Fear landscapes are often dynamic and change based on predator presence and behaviour, and variation in abiotic conditions that modify risk. Energy landscapes are also dynamic and can change across diel, seasonal, and climatic timescales based on variability in temperature, snowfall, wind/current speeds, etc.

   Recently, it was suggested that fear and energy landscapes should be integrated. In this paradigm, the interaction between landscapes relates to prey being forced to use areas of the energy landscape they would avoid if risk were not a factor. However, dynamic energy landscapes experienced by predators must also be considered since they can affect their ability to forage, irrespective of variation in prey behaviour. We propose an additional component to the fear and dynamic energy landscape paradigm that integrates landscapes of both prey and predators, where predator foraging behaviour is modulated by changes in their energyscape.

   Specifically, we integrate the predator's energy landscape into foraging theory that predicts prey patch‐leaving decisions under the threat of predation. We predict that as a predator's energetic cost of foraging increases in a habitat, then the prey's foraging cost of predation and patch quitting harvest rate, will decrease. Prey may also decrease their vigilance in response to increased energetic foraging costs for predators, which will lower giving‐up densities of prey.

   We then provide examples in terrestrial, aerial, and marine ecosystems where we might expect to see these effects. These include birds and sharks which use updrafts that vary based on wind and current speeds, tidal state, or temperature, and terrestrial predators (e.g. wolves) whose landscapes vary seasonally with snow depth or ice cover which may influence their foraging success and even diet selection.

   A predator perspective is critical to considering the combination of these landscapes and their ecological consequences. Dynamic predator energy landscapes could add an additional spatiotemporal component to risk effects, which may cascade through food webs.

   Read the freePlain Language Summaryfor this article on the Journal blog.

    

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