Vascular development in very young conifer seedlings: Theoretical hydraulic capacities and potential resistance to embolism

Miller, Megan L.; Johnson, Daniel M.

doi:10.3732/ajb.1700161

Cited by 24 publications

(21 citation statements)

References 65 publications

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“…Despite the importance of the delivery of water from roots to above-ground tissues, we know very little about hydraulic traits or drought tolerance strategies of young seedlings, and how these vary by species (Johnson et al, 2011). Seedlings <10 weeks old maximize water supply to growing tissues (consistent with the critical role of moisture for establishment), but at the cost of greater risk of hydraulic failure at the onset of drought (Miller & Johnson, 2017).…”

Section: Seed Germination Seedling Establishment and Seedling Surmentioning

confidence: 99%

Anticipating fire‐mediated impacts of climate change using a demographic framework

2018

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Climate change indirectly affects forest ecosystems through changes in the frequency, size, and/or severity of wildfires. In addition to its direct effects prior to fire, climate also influences immediate postfire recruitment, with consequences for future vegetation structure and fire activity. A major uncertainty, therefore, is if, when and where vegetation shifts will occur. With an emphasis on species traits, we use a demographic framework to examine how the interaction of changing climate and fire will affect postfire woody vegetation recruitment and the likelihood of vegetation shifts. Each demographic stage – adult mortality, propagule availability, seed germination, seedling establishment, and seedling survival – serves as a filter through which a species must pass for establishment and recovery to occur. We apply this framework to case studies in western North American forests, including boreal and southwestern U.S. Pinus ponderosa forests, to help understand the mechanisms behind recent postfire vegetation changes. The case studies highlight how changes in climate and fire properties will make it increasingly difficult for some species to pass through each demographic filter in the future. As climate warming continues, we expect increased dominance of species that resprout following fire, maintain canopy or soil seed banks, have long distance seed dispersal, produce drought‐tolerant seedlings, and/or reach reproductive maturity quickly. The persistence of postfire vegetation shifts will depend the on ratio of recovery time to disturbance interval(s). An advantage of the demographic‐filter framework is that it places emphasis on mechanisms, thus improving our ability to anticipate future vegetation shifts. As such, it highlights the clear need for more mechanistic studies of postfire recruitment to disentangle the relative effects of multiple drivers in postfire environments. A http://onlinelibrary.wiley.com/doi/10.1111/1365-2435.13132/suppinfo is available for this article.

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Section: Seed Germination Seedling Establishment and Seedling Surmentioning

confidence: 99%

Anticipating fire‐mediated impacts of climate change using a demographic framework

2018

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“…Martínez‐Vilalta et al ., ; Maherali et al ., ; Johnson et al ., ). Within‐plant variation in vulnerability has also been reported for conifers (Kavanagh et al ., ; Beikircher & Mayr, ; Willson et al ., ; Domec et al ., ; Delzon et al ., ; McCulloh et al ., ; Losso et al ., ; Miller & Johnson, ). It is likely that vulnerability segmentation is species‐specific and can show various patterns.…”

Section: Introductionmentioning

confidence: 99%

Insights from in vivo micro‐CT analysis: testing the hydraulic vulnerability segmentation in Acer pseudoplatanus and Fagus sylvatica seedlings

et al. 2018

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Summary The seedling stage is the most susceptible one during a tree′s life. Water relations may be crucial for seedlings due to their small roots, limited water buffers and the effects of drought on water transport. Despite obvious relevance, studies on seedling xylem hydraulics are scarce as respective methodical approaches are limited. Micro‐ CT scans of intact Acer pseudoplatanus and Fagus sylvatica seedlings dehydrated to different water potentials (Ψ) allowed the simultaneous observation of gas‐filled versus water‐filled conduits and the calculation of percentage loss of conductivity ( PLC ) in stems, roots and leaves (petioles or main veins). Additionally, anatomical analyses were performed and stem PLC measured with hydraulic techniques. In A. pseudoplatanus , petioles showed a higher Ψ at 50% PLC (Ψ 50 −1.13 MP a) than stems (−2.51 MP a) and roots (−1.78 MP a). The main leaf veins of F. sylvatica had similar Ψ 50 values (−2.26 MP a) to stems (−2.74 MP a) and roots (−2.75 MP a). In both species, no difference between root and stems was observed. Hydraulic measurements on stems closely matched the micro‐ CT based PLC calculations. Micro‐ CT analyses indicated a species‐specific hydraulic architecture. Vulnerability segmentation, enabling a disconnection of the hydraulic pathway upon drought, was observed in A. pseudoplatanus but not in the especially shade‐tolerant F. sylvatica . Hydraulic patterns could partly be related to xylem anatomical traits.

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“…). Alternatively, variations in species traits between Douglas‐fir and ponderosa pine seedlings (Miller and Johnson ), or abiotic differences among sites, may account for these patterns. For example, water deficit from 1992 to 2015 was significantly higher at seedling sites dominated by ponderosa pine (mean [SD] = 556 [69] mm) vs. Douglas‐fir (495 [75] mm; df = 45, t = 2.9, P = 0.01; Fig.…”

Section: Discussionmentioning

confidence: 99%

“…Further, wetter sites tend to have higher post-fire regeneration densities for Douglas-fir (Tepley et al 2017), indicating that overall, increased moisture availability promotes Douglas-fir regeneration and survival (Davis et al 2019a). Alternatively, variations in species traits between Douglas-fir and ponderosa pine seedlings (Miller and Johnson 2017), or abiotic differences among sites, may account for these patterns. For example, water deficit from 1992 to 2015 was significantly higher at seedling sites dominated by ponderosa pine (mean [SD] = 556 [69] mm) vs. mm; df = 45, t = 2.9, P = 0.01; Fig.…”

Section: Climate and Post-fire Conifer Regenerationmentioning

confidence: 99%

Impacts of growing‐season climate on tree growth and post‐fire regeneration in ponderosa pine and Douglas‐fir forests

et al. 2019

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We studied the impacts of climate variability on low‐elevation forests in the U.S. northern Rocky Mountains by quantifying how post‐fire tree regeneration and radial growth varied with growing‐season climate. We reconstructed post‐fire regeneration and radial growth rates of Pinus ponderosa and Pseudotsuga menziesii at 33 sites that burned between 1992 and 2007, by aging seedlings at the root–shoot boundary. We also measured radial growth in adult trees from 12 additional sites that burned between 1900 and 1990. To quantify the relationship between climate and regeneration, we characterized seasonal climate before, during, and after recruitment pulses using superposed epoch analysis. To quantify growth sensitivity to climate, we performed moving regression analysis for each species and for juvenile and adult life stages. Climatic conditions favoring regeneration and tree growth differed between species. Water deficit and temperature were significantly lower than average during recruitment pulses of ponderosa pine, suggesting that germination‐year climate limits regeneration. Growing degree days were significantly higher than average during years with Douglas‐fir recruitment pulses, but water deficit was significantly lower one year following pulses, suggesting moisture sensitivity in two‐year‐old seedlings. Growth was also sensitive to water deficit, but effects varied between life stages, species, and through time, with juvenile ponderosa pine growth more sensitive to climate than adult growth and juvenile Douglas‐fir growth. Increasing water deficit corresponded with reduced adult growth of both species. Increases in maximum temperature and water deficit corresponded with increases in juvenile growth of both species in the early 20th century but strong reductions in growth for juvenile ponderosa pine in recent decades. Changing sensitivity of growth to climate suggests that increased temperature and water deficit may be pushing these species toward the edge of their climatic tolerances. Our study demonstrates increased vulnerability of dry mixed‐conifer forests to post‐fire regeneration failures and decreased growth as temperatures and drought increase. Shifts toward unfavorable conditions for regeneration and juvenile growth may alter the composition and resilience of low‐elevation forests to future climate and fire activity.

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Vascular development in very young conifer seedlings: Theoretical hydraulic capacities and potential resistance to embolism

Abstract: Theoretical measurements suggest that hydraulic transport capacities and vulnerability to embolism varied for each species over the first 10 wk of growth; thus, the timing of germination and onset of limited soil moisture is critical for growth and survival of seedlings.

Cited by 24 publications

References 65 publications

Anticipating fire‐mediated impacts of climate change using a demographic framework

Anticipating fire‐mediated impacts of climate change using a demographic framework

Insights from in vivo micro‐CT analysis: testing the hydraulic vulnerability segmentation in Acer pseudoplatanus and Fagus sylvatica seedlings

Impacts of growing‐season climate on tree growth and post‐fire regeneration in ponderosa pine and Douglas‐fir forests

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