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1. Habitat‐specific effects of bark on wood decomposition: Influences of fragmentation, nitrogen concentration and microbial community composition

   https://doi.org/10.1111/1365-2435.13547  

   Jones, Jennifer M. ; Heath, Katy D. ; Ferrer, Astrid ; Dalling, James W. ; Timothy Paine, ed., C. E. ( March 2020 , Functional Ecology)

   Identifying the drivers of decomposition is critical for understanding carbon cycling dynamics in forest ecosystems. Woody biomass is an important pool of carbon, composed of bark and underlying wood which vary in structure, nutrient concentrations and exposure to the environment. We hypothesized that higher nutrient concentrations in bark would speed the decomposition of underlying wood, and that this effect would be greater in streams, where nutrients are less available to decomposers than on land.

   Replicate branches of three tree species, with and without bark, were placed in streams and on land in a lowland tropical forest in Panama. After 3 and 11 months of decomposition, we measured mass loss and nitrogen (N) concentrations and sequenced the fungal and bacterial communities of both wood and bark tissues.

   While bark decomposed faster than the underlying wood and had higher N concentrations, bark presence slowed wood mass loss. Nitrogen concentration could account for interspecific variation in wood mass loss, but not bark mass loss. In contrast, bark mass loss, but not wood mass loss, was faster in streams than on land, suggesting fragmentation is more important for bark mass loss in streams. Differences in fungal and bacterial community composition between bark and wood substrates were significant but small.

   Our results indicate that bark can slow wood decomposition instead of promoting it, and that at least for branch wood, the primary drivers of decomposition differ between bark and wood. Differences in the factors driving decomposition rate between bark and wood suggest that the contribution of bark to the decomposition of woody biomass may depend on habitat.

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

    

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2. Fine root dynamics across pantropical rainforest ecosystems

   https://doi.org/10.1111/gcb.15677  

   Huaraca Huasco, Walter ; Riutta, Terhi ; Girardin, Cécile A. J. ; Hancco Pacha, Fernando ; Puma Vilca, Beisit L. ; Moore, Sam ; Rifai, Sami W. ; del Aguila‐Pasquel, Jhon ; Araujo Murakami, Alejandro ; Freitag, Renata ; et al ( May 2021 , Global Change Biology)

   Fine roots constitute a significant component of the net primary productivity (NPP) of forest ecosystems but are much less studied than aboveground NPP. Comparisons across sites and regions are also hampered by inconsistent methodologies, especially in tropical areas. Here, we present a novel dataset of fine root biomass, productivity, residence time, and allocation in tropical old‐growth rainforest sites worldwide, measured using consistent methods, and examine how these variables are related to consistently determined soil and climatic characteristics. Our pantropical dataset spans intensive monitoring plots in lowland (wet, semi‐deciduous, and deciduous) and montane tropical forests in South America, Africa, and Southeast Asia (n = 47). Large spatial variation in fine root dynamics was observed across montane and lowland forest types. In lowland forests, we found a strong positive linear relationship between fine root productivity and sand content, this relationship was even stronger when we considered the fractional allocation of total NPP to fine roots, demonstrating that understanding allocation adds explanatory power to understanding fine root productivity and total NPP. Fine root residence time was a function of multiple factors: soil sand content, soil pH, and maximum water deficit, with longest residence times in acidic, sandy, and water‐stressed soils. In tropical montane forests, on the other hand, a different set of relationships prevailed, highlighting the very different nature of montane and lowland forest biomes. Root productivity was a strong positive linear function of mean annual temperature, root residence time was a strong positive function of soil nitrogen content in montane forests, and lastly decreasing soil P content increased allocation of productivity to fine roots. In contrast to the lowlands, environmental conditions were a better predictor for fine root productivity than for fractional allocation of total NPP to fine roots, suggesting that root productivity is a particularly strong driver of NPP allocation in tropical mountain regions.

    

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3. Weak but consistent abundance–occupancy relationships across taxa, space and time

   https://doi.org/10.1111/geb.13472  

   Ten Caten, Cleber ; Holian, Lauren ; Dallas, Tad ( March 2022 , Global Ecology and Biogeography)

   Abundance–occupancy relationships posit that more locally abundant species occupy more sites than less abundant species. Although widely supported, the occurrence and detection of abundance–occupancy relationships is sensitive to sampling and detection processes. Data from large‐scale standardized sampling efforts are key to address abundance–occupancy relationships. We aimed to use such a dataset to evaluate the occurrence of abundance–occupancy relationships across different spatial grains and over time for aquatic and terrestrial taxa.

   USA.

   2014–2019.

   Birds, mammals, beetles, ticks, fishes, macroinvertebrates and zooplankton.

   Species abundance and occupancy data were obtained from the National Ecological Observatory Network (NEON). Species mean abundance and occupancy (fraction of sampled locations that were occupied) were estimated for three different spatial grains (i.e., plot, site and domain) for all years sampled. Linear models were used to explore the consistency of interspecific abundance–occupancy relationships. The slope coefficients of these models were related to temporal and spatial variables and to species richness while controlling for taxa in a linear mixed‐effects model (LMM) framework.

   We found evidence for positive abundance–occupancy relationships across the three spatial grains and over time for all taxa we studied. However, our linear models had low explanatory power, suggesting that relationships, although general, were weak. Abundance–occupancy relationships were slightly stronger at the smallest spatial grain than at the largest spatial grain, but showed no detectable change over time for any taxa. Finally, species richness was not associated with the strength of these relationships.

   Together, our results suggest that positive interspecific abundance–occupancy relationships are fairly general but are not capable of explaining substantial variation in spatial patterns of abundance, and that other factors, such as species traits and niche, are also likely to influence these relationships.

    

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4. A trait‐based approach to assessing resistance and resilience to wildfire in two iconic North American conifers

   https://doi.org/10.1111/1365-2745.13480  

   Rodman, Kyle C. ; Veblen, Thomas T. ; Andrus, Robert A. ; Enright, Neal J. ; Fontaine, Joseph B. ; Gonzalez, Angela D. ; Redmond, Miranda D. ; Wion, Andreas P. ; Battipaglia, ed., Giovanna ( August 2020 , Journal of Ecology)

   Ongoing changes in fire regimes have the potential to drive widespread shifts in Earth's vegetation. Plant traits and vital rates provide insight into vulnerability to fire‐driven vegetation shifts because they can be indicators of the ability of individuals to survive fire (resistance) and populations to persist (resilience) following fire.

   In 15 study sites spanning climatic gradients in the southern Rocky Mountains, USA, we quantified variation in key traits and vital rates of two co‐occurring, widely distributed conifers (Pinus ponderosaDouglas ex. P. Lawson & C. Lawson andPseudotsuga menziesii(Mirb.) Franco). We used mixed‐effects models to explain inter‐ and intraspecific variation in tree growth, survival, bark thickness and seed cone production, as a function of species, tree life stage (i.e. diameter, height and age), average climate, local competition and site conditions.

   Pinus ponderosawas predicted to survive low‐severity fire at a 23% earlier age thanP. menziesii.Pinus ponderosahad thicker bark and more rapid juvenile height growth, traits conferring greater fire resistance. In contrast,P. menziesiiwas predicted to produce seed cones at a 28% earlier age thanP. ponderosa. For both species, larger individuals were more likely to survive fire and to produce cones. ForP. ponderosa, cone production increased where average actual evapotranspiration (AET) was higher and local competition was lower. More frequent cone production on productive sites with higher AET is an important and underappreciated mechanism that may help to explain greater resilience to fire in these areas.

   Synthesis. Our analyses indicated that many plant traits and vital rates related to fire differed betweenPinus ponderosaandPseudotsuga menziesii, with trade‐offs between investment in traits that promote individual defence to fire and those that promote recolonization of disturbed sites. Future changes in fire regimes will act as a filter throughout North American forests, with our findings helping to infer which individuals and populations of two iconic species are most vulnerable to future change and offering a framework for future inquiry in other forests facing an uncertain future.

    

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5. Precipitation, Not Land Use, Primarily Determines the Composition of Both Plant and Phyllosphere Fungal Communities

   https://doi.org/10.3389/ffunb.2022.805225  

   Dea, Hannah I. ; Urban, Abigail ; Kazarina, Anna ; Houseman, Gregory R. ; Thomas, Samantha G. ; Loecke, Terry ; Greer, Mitchell J. ; Platt, Thomas G. ; Lee, Sonny ; Jumpponen, Ari ( July 2022 , Frontiers in Fungal Biology)

   Plant communities and fungi inhabiting their phyllospheres change along precipitation gradients and often respond to changes in land use. Many studies have focused on the changes in foliar fungal communities on specific plant species, however, few have addressed the association between whole plant communities and their phyllosphere fungi. We sampled plant communities and associated phyllosphere fungal communities in native prairie remnants and post-agricultural sites across the steep precipitation gradient in the central plains in Kansas, USA. Plant community cover data and MiSeq ITS2 metabarcode data of the phyllosphere fungal communities indicated that both plant and fungal community composition respond strongly to mean annual precipitation (MAP), but less so to land use (native prairie remnants vs. post-agricultural sites). However, plant and fungal diversity were greater in the native remnant prairies than in post-agricultural sites. Overall, both plant and fungal diversity increased with MAP and the communities in the arid and mesic parts of the gradient were distinct. Analyses of the linkages between plant and fungal communities (Mantel and Procrustes tests) identified strong correlations between the composition of the two. However, despite the strong correlations, regression models with plant richness, diversity, or composition (ordination axis scores) and land use as explanatory variables for fungal diversity and evenness did not improve the models compared to those with precipitation and land use (ΔAIC < 2), even though the explanatory power of some plant variables was greater than that of MAP as measured by R². Indicator taxon analyses suggest that grass species are the primary taxa that differ in the plant communities. Similar analyses of the phyllosphere fungi indicated that many plant pathogens are disproportionately abundant either in the arid or mesic environments. Although decoupling the drivers of fungal communities and their composition – whether abiotic or host-dependent – remains a challenge, our study highlights the distinct community responses to precipitation and the tight tracking of the plant communities by their associated fungal symbionts.

    

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