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1. The influence of weevil herbivory on leaf litter chemistry in dioecious willows

   https://doi.org/10.1002/ece3.9626  

   Ramstack Hobbs, Joy M.; Garthwaite, Iris J.; Lancaster, Logan; Moffett‐Dobbs, Jordan A.; Johnson, Kelly; Criss, Nichole; McConathy, Victoria; James, C. Andrew; Gipe, Alex; Claeson, Shannon M.; et al (December 2022, Ecology and Evolution)

   Abstract Leaf litter inputs can influence the structure and function of both terrestrial and adjacent aquatic ecosystems. Dioecy and herbivory are two factors that together have received little attention, yet have the potential to affect the quantity, quality, and timing of riparian litterfall, litter chemistry, and litter decomposition processes. Here, we explore litter chemistry differences for the dioecious Sitka willow ( Salix sitchensis Sanson ex. Bong), which is establishing on primary successional habitats at Mount St. Helens (WA, USA) and is heavily infested with a stem‐boring weevil ( Cryptorhynchus lapathi ). Weevil‐attacked branches produced summer senesced litter that had significantly higher %N, lower C:N ratios, and lower condensed tannins than litter from branches that were unattacked by the weevil and senesced naturally in the autumn. Weevils more often attack female willows; however, these common litter chemicals did not significantly differ between males and females within the weevil‐attacked and ‐unattacked groups. High‐resolution mass spectrometry was used to isolate compounds in litter from 10 Sitka willow individuals with approximately 1500–1600 individual compounds isolated from each sample. There were differences between weevil‐attacked litter and green leaf samples, but at this level, there was no clustering of male and female samples. However, further exploration of the isolated compounds determined a suite of compounds present only in either males or females. These findings suggest some variation in more complex litter chemistry between the sexes, and that significant differences in weevil‐attacked litter chemistry, coupled with the shift in seasonality of litter inputs to streams, could significantly affect in‐stream ecological processes, such as decomposition and detritivore activity. 

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2. Spatial Habitat Structure Assembles Willow-Dependent Communities across the Primary Successional Watersheds of Mount St. Helens, USA

   https://doi.org/10.3390/f14020322  

   Minsavage-Davis, Charles D.; Garthwaite, Iris J.; Fisher, Marisa D.; Leigh, Addison; Ramstack Hobbs, Joy M.; Claeson, Shannon M.; Wimp, Gina M.; LeRoy, Carri J. (February 2023, Forests)

   The eruption of Mount St. Helens in 1980 resulted in a cataclysmic restructuring of its surrounding landscapes. The Pumice Plain is one of these landscapes, where tree species such as Sitka willow (Salix sitchensis) and their dependent communities have been established along newly-formed streams. Thus, the study of these dependent communities provides a unique and rare opportunity to investigate factors influencing metacommunity assembly during true primary succession. We analyzed the influence of landscape connectivity on metacommunity assembly through a novel application of circuit theory, alongside the effects of other factors such as stream locations, willow leaf chemistry, and leaf area. We found that landscape connectivity structures community composition on willows across the Pumice Plain, where the least connected willows favored active flyers such as the western tent caterpillar (Malacosoma fragilis) or the Pacific willow leaf beetle (Pyrrhalta decora carbo). We also found that multiple levels of spatial habitat structure linked via landscape connectivity can predict the presence of organisms lacking high rates of dispersal, such as the invasive stem-boring poplar weevil (Cryptorhynchus lapathi). This is critical for management as we show that the maintenance of a heterogeneous mixture of landscape connectivity and resource locations can facilitate metacommunity dynamics to promote ecosystem function and mitigate the influences of invasive species. 

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3. Culturable fungal endophyte communities of primary successional plants on Mount St. Helens, WA, USA

   https://doi.org/10.1186/s12862-022-01974-2  

   Wolfe, Emily R.; Dove, Robyn; Webster, Cassandra; Ballhorn, Daniel J. (December 2022, BMC Ecology and Evolution)

   Abstract Background While a considerable amount of research has explored plant community composition in primary successional systems, little is known about the microbial communities inhabiting these pioneer plant species. Fungal endophytes are ubiquitous within plants, and may play major roles in early successional ecosystems. Specifically, endophytes have been shown to affect successional processes, as well as alter host stress tolerance and litter decomposition dynamics—both of which are important components in harsh environments where soil organic matter is still scarce. Results To determine possible contributions of fungal endophytes to plant colonization patterns, we surveyed six of the most common woody species on the Pumice Plain of Mount St. Helens (WA, USA; Lawetlat'la in the Cowlitz language; created during the 1980 eruption)—a model primary successional ecosystem—and found low colonization rates (< 15%), low species richness, and low diversity. Furthermore, while endophyte community composition did differ among woody species, we found only marginal evidence of temporal changes in community composition over a single field season (July–September). Conclusions Our results indicate that even after a post-eruption period of 40 years, foliar endophyte communities still seem to be in the early stages of community development, and that the dominant pioneer riparian species Sitka alder ( Alnus viridis ssp. sinuata ) and Sitka willow ( Salix sitchensis ) may be serving as important microbial reservoirs for incoming plant colonizers. 

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4. Canopy development influences early successional stream ecosystem function but not biotic assemblages

   https://doi.org/10.1007/s00027-023-00972-w  

   LeRoy, Carri J.; Claeson, Shannon M.; Garthwaite, Iris J.; Thompson, Madeline A.; Thompson, Lauren J.; Kamakawiwo’ole, Brandy K.; Froedin-Morgensen, Angie M.; McConathy, Victoria; Ramstack Hobbs, Joy M.; Stancheva, Rosalina; et al (July 2023, Aquatic Sciences)

   Abstract Determining how streams develop naturally, particularly the ecological role of newly developed riparian canopy cover, is essential to understanding the factors that structure new stream communities and provides valuable information for restoring highly disturbed ecosystems. However, attempts to understand primary succession in riverine ecosystems have been hindered by a lack of data owing to the infrequent formation of new rivers on the landscape. In the present study, we used five streams formed following the 1980 eruption of Mount St. Helens (WA, USA) to examine the influence of canopy cover development on algal and benthic macroinvertebrate assemblages, biomass, and organic matter processing. Newly established closed canopy reaches had less available light, but no significant differences in algal biomass or macroinvertebrate assemblages compared to open canopy reaches. Instead, algal and macroinvertebrate communities were structured mainly by hydrologic differences among watersheds. In contrast, organic matter processing rates were sensitive to canopy cover development, and rates were faster under closed canopies, especially in late summer or after terrestrial preconditioning. After 40 years of stream and riparian primary successional development, canopy cover strongly influences ecosystem function, but aquatic organism assembly was more influenced by physio-chemical and hydrologic variation. Our findings provide insight into the development of in-stream assemblages and ecosystem functions, which is also relevant to efforts to address major disturbances to stream channels, such as volcanic eruptions, floods, forest fires, and clear-cut logging. 

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5. Effects of elevated nutrient supply on litter decomposition are robust to impacts of mammalian herbivores across diverse grasslands

   https://doi.org/10.1007/s00442-025-05791-4  

   Keller, Adrienne B; Borer, Elizabeth T; Buyarski, Christopher R; Cleland, Elsa E; Gill, Allison; MacDougall, Andrew S; Moore, Joslin L; Morgan, John W; McCulley, Rebecca L; Risch, Anita C; et al (October 2025, Oecologia)

   Abstract Litter decomposition is one of the largest carbon (C) fluxes in terrestrial ecosystems and links aboveground biomass to soil C pools. In grasslands, decomposition drivers have received substantial attention but the role of grassland herbivores in influencing decay rates is often ignored despite their potentially large effects on standing biomass and nutrient cycling. Recent work has demonstrated that nutrient addition increases early-stage decay and suppresses late-stage decay. Mammalian herbivores can mediate the effects of nutrient supply on biomass, suggesting herbivores may alter the effects of nutrients on decomposition, though this is largely unknown. We examined how herbivory mediates the effects of nutrient supply on long-term decomposition across 19 grassland sites of the Nutrient Network distributed experiment. At each site, a full-factorial experiment of combined nitrogen (N), phosphorus (P), and micronutrient (K) enrichment (‘control’ or ‘ + NPK’) and mammalian herbivore (> ~ 50 g) exclusion (‘unfenced’ or ‘fenced’) was carried out in a randomized block design. We hypothesized that nutrient effects on litter decomposition would be strongest where herbivores caused the greatest reductions in aboveground plant biomass (i.e., at sites with more intense herbivory). After accounting for wide variation in decomposition rates across sites, we found that, within sites, elevated nutrients increased early-stage decay and suppressed late-stage decay. In contrast, neither herbivore exclusion (i.e., fencing) nor site level changes in aboveground biomass due to herbivory altered the nutrient effects on decomposition rates. Across grasslands, our results indicate that elevated nutrient supply modifies litter decomposition rates independent of herbivore impacts. 

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