Explore Research Products in the PAR
It may take a few hours for recently added research products to appear in PAR search results.


  • NSF Public Access
  • Search Results
  • Betting on rains that do not come: Monsoon failure and leaf area overshoot relate to increased tree mortality from drought
Title: Betting on rains that do not come: Monsoon failure and leaf area overshoot relate to increased tree mortality from drought
Structural overshoots, where biomass is overallocated to tree leaf area compared to sapwood area, could result in lethal stress during droughts. Climate change may alter climatic cues that drive leaf area production, such as temperature and precipitation, as well as seasonal dynamics that underlie summer rainfall due to the North American Monsoon (NAM). Combined, this could lead to temporal mismatches between leaf area‐driven water demand and availability, and increased drought‐induced mortality events.We used leaf area to sapwood area ratios to investigate the prevalence of overshoots and whether overshoots increase drought‐induced mortality. We measured populations of aspen spanning the northern transition zone of the NAM during and following severe droughts.We observed increased overshoots and drought‐induced mortality in southern latitude populations that rely more on summer monsoon rainfall. Changes in convective activity from low snowpack the preceding winter may be a climatic driver of heightened summer monsoon rainfall in the region and therefore may also trigger increased production of leaf area during wetter summers.Our results suggest that an overshoot of leaf area to sapwood area (AL:AS) ratios is associated with drought‐induced tree mortality and highlight that climate‐change driven alterations to the NAM could have major consequences for tree species' acclimation to environmental change. Read the freePlain Language Summaryfor this article on the Journal blog.  more » « less
Award ID(s):
2003205 2003017 2044937
PAR ID:
10635469
Author(s) / Creator(s):
; ; ;
Publisher / Repository:
British Ecological Society
Date Published:
Journal Name:
Functional Ecology
Volume:
39
Issue:
7
ISSN:
0269-8463
Page Range / eLocation ID:
1840 to 1852
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ; (, Functional Ecology)
    Abstract Climate change has increased the frequency and severity of drought and large wildfire events across western North America. Despite the increasing concurrence of drought and wildfire events and the importance of forests as a global carbon sink, the impacts of fire on tree drought and carbon acquisition traits are not well understood, particularly on multi‐year time‐scales.In 2022–2024, we leveraged a natural experiment at a large 2018 wildfire in southwestern Colorado, comparing leaf and xylem functional traits related to drought resistance and carbon acquisition in burned and unburned ponderosa pine, quaking aspen, subalpine fir, and Engelmann spruce trees.Relative to unburned trees of the same species, we found reduced xylem vulnerability to embolism (P50) in burned ponderosa pine and subalpine fir; decreased leaf heat tolerance (T50) in burned quaking aspen and ponderosa pine; and increased investment in leaf structural over photosynthetic components (leaf C:N isotopic ratio) in burned quaking aspen, subalpine fir, and Engelmann spruce.In contrast to previous studies, our results suggest that wildfire positively impacts functional traits related to drought resistance and water movement in surviving burned trees. However, generally negative impacts of wildfire were found with respect to leaf physiological and photosynthetic traits, suggesting divergent water and carbon responses to fire. Read the freePlain Language Summaryfor this article on the Journal blog. 
    more » « less
  2. ; ; ; (, New Phytologist)
    Summary Observational evidence indicates that tree leaf area may acclimate in response to changes in water availability to alleviate hydraulic stress. However, the underlying mechanisms driving leaf area changes and consequences of different leaf area allocation strategies remain unknown.Here, we use a trait‐based hydraulically enabled tree model with two endmember leaf area allocation strategies, aimed at either maximizing carbon gain or moderating hydraulic stress. We examined the impacts of these strategies on future plant stress and productivity.Allocating leaf area to maximize carbon gain increased productivity with high CO2, but systematically increased hydraulic stress. Following an allocation strategy to avoid increased future hydraulic stress missed out on 26% of the potential future net primary productivity in some geographies. Both endmember leaf area allocation strategies resulted in leaf area decreases under future climate scenarios, contrary to Earth system model (ESM) predictions.Leaf area acclimation to avoid increased hydraulic stress (and potentially the risk of accelerated mortality) was possible, but led to reduced carbon gain. Accounting for plant hydraulic effects on canopy acclimation in ESMs could limit or reverse current projections of future increases in leaf area, with consequences for the carbon and water cycles, and surface energy budgets. 
    more » « less
  3. ; ; ; ; ; (, Functional Ecology)
    Abstract Understanding how local climate patterns select for thermal and drought tolerance traits is needed to predict differential responses to climate change across complex ecosystems. Here, we used high‐throughput methods to measure traits that confer heat and drought tolerance across a tropical climatic variability gradient and examined how forest type and leaf habit mediate these traits.We estimated thermotolerance thresholds (Tcrit, T50, T95), drought tolerance traits (water potential at turgor loss point [𝝭TLP] and osmotic potential [𝞹osm]), and morphological traits (wood density and leaf mass per area [LMA]) for 92 woody plant species across six sites along a tropical dry‐to‐wet gradient in Área de Conservación Guanacaste, Costa Rica.Among evergreen species, T95 weakly declined with elevation, LMA was positively associated with T50 and T95, and greater drought tolerance values were found at lower elevations and with greater wood density. Among deciduous species, no significant associations were found between tolerance traits and elevation or wood density, though LMA was positively associated with T50.T95 was higher on average among seasonal dry and ecotonal forest species compared with wet forest species. Additionally, evergreen species from dry and ecotonal forests exhibited greater drought tolerance than those from wet forests, whereas drought tolerance indices did not differ among deciduous species across forest types. These results point to multiple adaptive pathways for evergreen species and provide evidence that evergreen trees face greater drought‐induced selection pressure.Surprisingly, thermal tolerance traits were largely decoupled with drought tolerance traits, suggesting that coordination among traits that confer tolerance to environmental stressors is not generalizable in tropical forests. Read the freePlain Language Summaryfor this article on the Journal blog. 
    more » « less
  4. ; ; ; ; ; ; (, Plant Biology)
    Abstract Drought events may increase the likelihood that the plant water transport system becomes interrupted by embolism. Yet our knowledge about the temporal frequency of xylem embolism in the field is frequently lacking, as it requires detailed, long‐term measurements.We measured xylem embolism resistance and midday xylem water potentials during the consecutive summers of 2019 and 2020 to estimate maximum levels of embolism in leaf and stem xylem of ten temperate angiosperm tree species. We also studied vessel and pit membrane characteristics based on light and electron microscopy to corroborate potential differences in embolism resistance between leaves and stems.Apart fromA.pseudoplatanusandQ.petraea, eight species experienced minimum xylem water potentials that were close to or below those required to initiate embolism. Water potentials corresponding to ca. 12% loss of hydraulic conductivity (PLC) could occur in six species, while considerable levels of embolism around 50% PLC were limited toB.pendulaandC.avellana. There was a general agreement in embolism resistance between stems and leaves, with leaves being equally or more resistant than stems. Also, xylem embolism resistance was significantly correlated to intervessel pit membrane thickness (TPM) for stems, but not to vessel diameter and total intervessel pit membrane surface area of a vessel.Our data indicate that low amounts of embolism occur in most species during moderate summer drought, and that considerable levels of embolism are uncommon. Moreover, our experimental andTPMdata show that leaf xylem is generally no more vulnerable than stem xylem. 
    more » « less
  5. ; ; (, New Phytologist)
    Summary Human‐caused climate change is predicted to bring more frequent droughts and higher temperatures in the western United States, which threaten ecologically important trembling aspen forests.We used ring‐specific vulnerability curves of aspen branches along two climate gradients to determine whether damages to pit membranes accumulate as the xylem ages.We found that rings older than 3 yr have a significant decline in hydraulic conductivity, especially at average summer water potentials for the species. These differences were not due to differences in the diameter of the vessels, but a difference in how much xylem was active between rings older than 3 yr and 1 yr, suggesting the presence of accumulated damage to pit membranes impairing water transport.Vulnerability to embolism differs across ring age and between wetter and drier populations, underscoring that damages due to drought may accumulate to lethal levels if the xylem does not acclimate to climate change in newer growth. 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Text Encoded Conversion
  • XML
  • Save / Share this Record
  • Send to Email