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Abstract A two decade‐long megadrought, with likely anthropogenic causes, has impacted forest growth and mortality across the southwestern U.S. Given this event, and the future likelihood of similar climate challenges, it is important to understand how different water resources are used by semi‐arid forests in this region. Within the geographic domain of the North American Monsoon climate system, we studied seasonal water‐use in eight differentPinus ponderosamontane forests distributed across a climate gradient with varying contributions from winter and summer precipitation. We collected oxygen isotopes from precipitation, soil, and xylem water during two contrasting hydrologic years to determine how trees differentially use winter versus summer precipitation sources. Most trees switched from using snowmelt water as the primary source during the early‐summer hyper‐arid period, to monsoon rainwater during the late‐summer. However, during the low snowpack year, which represents the most common climate phenomenon during the megadrought, trees at all sites used less summer rain when compared to the higher snowpack year, demonstrating a drought‐induced antecedent influence of winter precipitation on the uptake of summer rain. A possible mechanism to explain the antecedent effect is an earlier snow disappearance during the low snowpack year weakening hydrologic connectivity within the soil profile, decreasing the soil infiltration of summer rains. However, in years with higher snowpack, the snow lasts longer, and this can improve the hydrologic connectivity within the soil profile. As a result, there is more infiltration of summer rains into the soils. This can enhance the maintenance of active shallow fine‐root biomass during the period when snowpack disappears, and monsoon rains have yet to arrive. These findings provide insight into how the seasonal interactions between major seasonal climate systems influence forest tree water use in the face of an extreme megadrought.
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Alternate Growth Forms Can Protect Climate-Threatened Trees from Freezing Stressors
Abstract Climate change creates a variety of novel stressors for species, such as a decline in snowpack. Loss of snow has many impacts, including the loss of thermal insulation of soils. Winter/spring freezing of soils has been tied to forest mass mortality in multiple locations around the world. Many species, however, can take alternative growth forms, such as tall tree forms and short shrub-like forms. Shrub-forms may provide a unique protection from the snow loss phenomenon by providing a similar thermal insulation as snowpack. That hypothesis is tested here using yellow-cedar, a species undergoing mass mortality due to snow loss. Temperature loggers were placed under both tree- and shrub-form cedars, including areas where the species was experimentally removed. The number of soil freezing days was high in open areas, areas of tree mortality, and where the shrub-form was removed, but was almost zero in areas where the shrub-form was left intact. This suggests that growth-form temperature moderation is possible and may provide an important resistance to the mortality mechanism. In other areas around the world where snow loss is resulting in soil freezing and mortality, growth forms should be investigated as a potential moderating mechanism for this particular climate change stress.
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- PAR ID:
- 10494112
- Publisher / Repository:
- Oxford Academic
- Date Published:
- Journal Name:
- Forest Science
- Volume:
- 68
- Issue:
- 5-6
- ISSN:
- 0015-749X
- Page Range / eLocation ID:
- 435 to 439
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1093/forsci/fxac038
