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1. The importance of secondary growth to plant responses to snow in the arctic

   https://doi.org/10.1111/1365-2435.13323  

   Addis, Claire E. ; Bret‐Harte, Marion S. ; Cooke, ed., Julia ( April 2019 , Functional Ecology)

   In arctic environments, drifting snow around large shrub patches during winter may enhance growth by insulating the soil and facilitating overwinter nutrient turnover, leading to increased summer plant growth and potentially widespread increases in shrub cover.

   To determine whether snow enhances growth of arctic plants, we examined the effect of 6 years of added snow on plant biomass allocation and growth of nine common vascular plant species collected in 2010 and 2011 on either side of snowfences established in 2005 across a gradient of shrub biomass and productivity near Toolik Lake, Alaska.

   The deciduous shrubSalix pulchraresponded most positively to added snow showing an 88% increase in total ramet biomass,because increased secondary growth allowed plants to support more branches and leaves. Some graminoid species also showed growth increases, especially where they were more abundant and larger than nearby shrub species.

   Species sharing the same growth strategy (deciduous shrubs, evergreen shrubs and graminoids) responded differently to increased snow, with some showing increased growth, others showing decreased growth, and some showing no effects. We found that relative biomass per ramet in combination with growth strategy is a better predictor of species’ growth responses to added snow than growth strategy alone.

   Our research shows that a primary mechanism for enhanced growth of shrubs in response to deeper snow is increased secondary growth. Improved growth may be an important way in which arctic plants spread, since they are often long‐lived and clonal, and this may help explain the increase in shrub cover observed across northern latitudes. As shrub patches continue to expand and increase surrounding snow depths during winter, secondary growth of fast‐growing deciduous shrub species may play an important role in defining future landscape community composition and ecosystem processes.

   Aplain language summaryis available for this article.

    

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2. Reciprocal transplants reveal asymmetric local adaptation of Himalayan Rhododendron approaching elevational range limit

   https://doi.org/10.1002/ecs2.4563  

   Mainali, Kumar ; Adhikari, Subodh ; Shrestha, Sushila ; Singer, Michael C. ; White, Joseph ; Parmesan, Camille ( July 2023 , Ecosphere)

   As plant species expand their upper limits of distribution under current warming, some retain both traditional climate space and biotic environment while others encounter novel conditions. The latter is the case forRhododendron campanulatum, a woody shrub that grows both above and below treeline at our study site in the Eastern Himalayas where a very conspicuous, stable treeline was defined by a nearly contiguous canopy of tallAbies spectabilistrees, many of which are over a century old. Prior work showed that treeline had remained static in this region whileR. campanulatumexpanded its elevational range limit. We tested local adaptation ofR. campanulatumby performing reciprocal transplants between the species' current elevational range limit (4023 m above sea level [asl]) and just above treeline (3876 m asl). Contrary to expectation, the coldest temperatures of late winter and early mid‐spring were experienced by plants at the lower elevation:R. campanulatumat species' limit (upper site) were covered by snow for a longer period (40 more days) and escaped the coldest temperatures suffered by conspecifics at treeline (lower site). The harsher spring conditions at treeline likely explain why leaves were smaller at treeline (15.3 cm²) than at species limit (21.3 cm²). Contrary to results from equivalent studies in other regions, survival was reduced more by downslope than by upslope movement, again potentially due to extreme cold temperatures observed at treeline in spring. Upslope transplantation had no effect on mortality, but mortality of species limit saplings transplanted downslope was three times higher than that of residents at both sites. A general expectation is that locals should survive better than foreign transplants, but survival of locals and immigrants at our species limit site was identical. However, those species limit saplings that survived the transplant to treeline grew faster than both locals at treeline and the transplants at species limit. Overall, we found asymmetric adaptation: Compared with treeline saplings, those at species limit (147 m above treeline) were more tolerant of extremes in the growing season but less tolerant of extremes in winter and early mid‐spring, displaying local adaptation in a more complex manner than simply home advantage, and complicating predictions about impacts of future regional climate change.

    

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3. Minimal mortality and rapid recovery of the dominant shrub Larrea tridentata following an extreme cold event in the northern Chihuahuan Desert

   https://doi.org/10.1111/jvs.12777  

   Ladwig, Laura M. ; Collins, Scott L. ; Krofcheck, Dan J. ; Pockman, William T. ; Paruelo, ed., José ( July 2019 , Journal of Vegetation Science)

   Woody encroachment into grasslands is a worldwide phenomenon partially influenced by climate change, including extreme weather events.Larrea tridentatais a common shrub throughout the warm deserts of North America that has encroached into grasslands over the past 150 years. Physiological measurements suggest that the northern distribution ofL. tridentatais limited by cold temperatures; thus extreme winter events may slow or reverse shrub expansion. We tested this limitation by measuring the response of individualL. tridentatashrubs to an extreme winter cold (−31°C) event to assess shrub mortality and rate of recovery of surviving shrubs.

   Sevilleta National Wildlife Refuge, Socorro County, New Mexico, USA.

   Canopy dieback and recovery following an extreme cold event were measured for 869 permanently marked individualL. tridentatashrubs in grass–shrub ecotone and shrubland sites. Individual shrubs were monitored for amount of canopy dieback, rate of recovery, and seed set for three growing seasons after the freeze event.

   Shrubs rapidly suffered a nearly complete loss of canopy leaf area across all sites. Although canopy loss was high, mortality was low and 99% of shrubs resprouted during the first growing season after the freeze event. Regrowth rates were similar within ecotone and shrubland sites, even when damage by frost was larger in the latter. After three years of recovery,L. tridentatacanopies had regrown on average 23–83% of the original pre‐freeze canopy sizes across the sites.

   We conclude that isolated extreme cold events may temporarily decrease shrubland biomass but they do not slow or reverse shrub expansion. These events are less likely to occur in the future as regional temperatures increase under climate change.

    

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4. Tolerance of Immature Black Soldier Flies (Diptera: Stratiomyidae) to Cold Temperatures Above and Below Freezing Point

   https://doi.org/10.1093/jee/toz186  

   Villazana, Joshua ; Alyokhin, Andrei ; Lohmeyer, ed., Kimberly ( July 2019 , Journal of Economic Entomology)

   Black soldier flies, Hermetia illucens (L.), consume decaying organic materials at the larval stage and can be used for recycling a variety of biogenic wastes into value-added products. Black soldier flies are normally found in subtropical and warm temperate regions. Cold temperatures may prevent their establishment in colder areas, thus alleviating a concern of their becoming an invasive species. Potentially, cold temperatures can also be used to manipulate the rate of black soldier fly development, which may be needed for timing certain life stages for mass-production needs. In the present study, immature black soldier flies were highly susceptible to freezing. Their survivorship decreased as time spent at −12°C increased from 10 to 60 min. Only ca. 2% of eggs, <1% of larvae, and no pupae survived after 60 min of exposure. Chilling at 4°C also had a significant negative effect that became more pronounced as duration of exposure increased from 24 to 72 h. Only ca. 2% of eggs and second instars and ca. 23% of pupae survived after 72 h. In the same time, >80% of third instars and >90% of fifth instars were still alive following 72 h of exposure. Chilling fifth instars resulted in smaller adults but freezing them for 48 h resulted in bigger adults. Based on these results, black soldier fly is unlikely to establish in areas with long periods of subfreezing winter temperatures. Low temperatures may be used to manipulate development of the late instars, but at a cost of higher mortality.

    

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5. Long-term reliability of the Figaro TGS 2600 solid-state methane sensor under low-Arctic conditions at Toolik Lake, Alaska

   https://doi.org/10.5194/amt-13-2681-2020  

   Eugster, Werner ; Laundre, James ; Eugster, Jon ; Kling, George W. ( January 2020 , Atmospheric Measurement Techniques)

   null (Ed.)

   Abstract. The TGS 2600 was the first low-cost solid-state sensor that shows a response to ambient levels of CH4 (e.g., range ≈1.8–2.7 µmol mol−1). Here we present an empirical function to correct the TGS 2600 signal for temperature and (absolute) humidity effects and address the long-term reliability of two identical sensors deployed from 2012 to 2018. We assess the performance of the sensors at 30 min resolution and aggregated to weekly medians. Over the entire period the agreement between TGS-derived and reference CH4 mole fractions measured by a high-precision Los Gatos Research instrument was R2=0.42, with better results during summer (R2=0.65 in summer 2012). Using absolute instead of relative humidity for the correction of the TGS 2600 sensor signals reduced the typical deviation from the reference to less than ±0.1 µmol mol−1 over the full range of temperatures from −41 to 27 ∘C. At weekly resolution the two sensors showed a downward drift of signal voltages indicating that after 10–13 years a TGS 2600 may have reached its end of life. While the true trend in CH4 mole fractions measured by the high-quality reference instrument was 10.1 nmolmol-1yr-1 (2012–2018), part of the downward trend in sensor signal (ca. 40 %–60 %) may be due to the increase in CH4 mole fraction because the sensor voltage decreases with increasing CH4 mole fraction. Weekly median diel cycles tend to agree surprisingly well between the TGS 2600 and reference measurements during the snow-free season, but in winter the agreement is lower. We suggest developing separate functions for deducing CH4 mole fractions from TGS 2600 measurements under cold and warm conditions. We conclude that the TGS 2600 sensor can provide data of research-grade quality if it is adequately calibrated and placed in a suitable environment where cross-sensitivities to gases other than CH4 are of no concern. 

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