Stand-scale tree mortality factors differ by site and species following drought in southwestern mixed conifer forests

Continued increases in global temperatures and incidences of drought have been implicated in elevated tree mortality in many regions, prompting interest in better understanding tree mortality processes. A recent extreme drought in the southwestern U.S. (1996–2003) contributed to elevated tree mortality throughout the region. We used this event to investigate the relationship of short- and long-term tree growth characteristics to recent (1996–2008) tree mortality in the mixed-conifer forests in northern Arizona. We compared radial growth characteristics over a 50-year period between paired live and recently dead white fir (Abies concolor (Gordon & Glend.) Lindl. ex Hildebr.), limber pine (Pinus flexilis E. James), trembling aspen (Populus tremuloides Michx.), and Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco). We found that (i) dead trees of all species typically had lower mean growth rates than live trees, (ii) dead trees of most species had a greater coefficient of variation in growth over long time periods (>20 years) than live trees, (iii) dead aspen and dead Douglas-fir trees had larger negative growth trends than live trees for some time periods, (iv) dead trees of most species had larger numbers of abrupt growth declines than live trees, and (v) a combination of short- and long-term growth characteristics distinguished live and dead trees, with greater importance of short-term growth for aspen, long-term growth for limber pine, and a mix of short- and long-term growth for white fir and Douglas-fir. These results strongly suggest that recent tree mortality in southwestern mixed-conifer forests is caused by a mixture of short- and long-term processes.

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Recent bark beetle outbreaks influence wildfire severity in mixed‐conifer forests of the Sierra Nevada, California, USA

Ecological Applications ◽

10.1002/eap.2287 ◽

2021 ◽

Author(s):

Rebecca B. Wayman ◽

Hugh D. Safford

Keyword(s):

Sierra Nevada ◽

Bark Beetle ◽

Conifer Forests ◽

Mixed Conifer ◽

Mixed Conifer Forests

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Pyric tree spatial patterning interactions in historical and contemporary mixed conifer forests, California, USA

Ecology and Evolution ◽

10.1002/ece3.7084 ◽

2020 ◽

Author(s):

Justin P. Ziegler ◽

Chad M. Hoffman ◽

Brandon M. Collins ◽

Eric E. Knapp ◽

William (Ruddy) Mell

Keyword(s):

Spatial Patterning ◽

Conifer Forests ◽

Mixed Conifer ◽

Mixed Conifer Forests

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Characterizing the light environment in Sierra Nevada mixed-conifer forests using a spatially explicit light model

Canadian Journal of Forest Research ◽

10.1139/x04-013 ◽

2004 ◽

Vol 34 (6) ◽

pp. 1332-1342 ◽

Cited By ~ 26

Author(s):

Rolf Gersonde ◽

John J Battles ◽

Kevin L O'Hara

Keyword(s):

Leaf Area ◽

Sierra Nevada ◽

Forest Type ◽

Individual Species ◽

Spatially Explicit ◽

Conifer Forests ◽

Prediction Equations ◽

Mixed Conifer ◽

Sapwood Area ◽

Mixed Conifer Forests

The spatially explicit light model tRAYci was calibrated to conditions in multi-aged Sierra Nevada mixed-conifer forests. To reflect conditions that are important to growth and regeneration of this forest type, we sampled a variety of managed mature stands with multiple canopy layers and cohorts. Calibration of the light model included determining leaf area density for individual species with the use of leaf area sapwood area prediction equations. Prediction equations differed between species and could be improved using site index. The light model predicted point measurements from hemispherical photographs well over a range of 27%63% light. Simplifying the crown representation in the tRAYci model to average values for species and canopy strata resulted in little reduction in model performance and makes the model more useful to applications with lower sampling intensity. Vertical light profiles in managed mixed-conifer stands could be divided into homogeneous, sigmiodal, and continuous gradients, depending on stand structure and foliage distribution. Concentration of leaf area in the upper canopy concentrates light resources on dominant trees in continuous canopies. Irregular canopies of multiaged stands, however, provide more light resources to mid-size trees and could support growth of shade-intolerant species. Knowledge of the vertical distribution of light intensity in connection with stand structural information can guide regulation of irregular stand structures to meet forest management objectives.

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