Fire History in California’s Southern Sierra Nevada Blue Oak Woodlands

California has, in recent years, become a hotspot of interannual climatic variability, recording devastating climate-related disturbances with severe effects on tree resources. Understanding the patterns of tree cover change associated with these events is vital for developing strategies to sustain critical habitats of endemic and threatened vegetation communities. We assessed patterns of tree cover change, especially the effects of the 2012–2016 drought within the distribution range of blue oak (Quercus douglasii), an endemic tree species to California with a narrow geographic extent. We utilized multiple, annual land-cover and land-surface change products from the U.S. Geological Survey (USGS) Land Change Monitoring, Assessment and Projection (LCMAP) project along with climate and wildfire datasets to monitor changes in tree cover state and condition and examine their relationships with interannual climate variability between 1985 and 2016. Here, we refer to a change in tree cover class without a land-cover change to another class as “conditional change.” The unusual drought of 2012–2016, accompanied by anomalously high temperatures and vapor pressure deficit, was associated with exceptional spikes in the amount of both fire and non-fire induced tree cover loss and tree cover conditional change, especially in 2015 and 2016. Approximately 1,266 km2 of tree cover loss and 617 km2 of tree cover conditional change were recorded during that drought. Tree cover loss through medium to high severity fires was especially large in exceptionally dry and hot years. Our study demonstrates the usefulness of the LCMAP products for monitoring the effects of climatic extremes and disturbance events on both thematic and conditional land-cover change over a multi-decadal period. Our results signify that blue oak woodlands may be vulnerable to extreme climate events and changing wildfire regimes. Here, we present early evidence that frequent droughts associated with climate warming may continue to affect tree cover in this region, while drought interaction with wildfires and the resulting feedbacks may have substantial influence as well. Consequently, efforts to conserve the blue oak woodlands, and potentially other vegetation communities in the Western United States, may benefit from consideration of climate risks as well as the potential for climate-fire and vegetation feedbacks.

Download Full-text

Fire History of a Lower Elevation Jeffrey Pine-Mixed Conifer Forest in the Eastern Sierra Nevada, California, USA

Fire Ecology ◽

10.4996/fireecology.0503004 ◽

2009 ◽

Vol 5 (3) ◽

pp. 4-19 ◽

Cited By ~ 10

Author(s):

Nicole M. Vaillant ◽

Scott L. Stephens

Keyword(s):

Sierra Nevada ◽

Fire History ◽

Conifer Forest ◽

Mixed Conifer ◽

Jeffrey Pine ◽

Mixed Conifer Forest ◽

Lower Elevation ◽

History Of ◽

Eastern Sierra Nevada

Download Full-text

Coarse Woody Debris in Oak Woodlands of California

Western Journal of Applied Forestry ◽

10.1093/wjaf/17.3.139 ◽

2002 ◽

Vol 17 (3) ◽

pp. 139-146 ◽

Cited By ~ 8

Author(s):

William D. Tietje ◽

Karen L. Waddell ◽

Justin K. Vreeland ◽

Charles L. Bolsinger

Keyword(s):

Land Use ◽

Coarse Woody Debris ◽

Forest Inventory ◽

Woody Debris ◽

Forest Products ◽

Oak Woodlands ◽

Blue Oak ◽

Live Oak ◽

Umbellularia Californica ◽

Quercus Spp

Abstract An extensive forest inventory was conducted to estimate the amount and distribution of coarse woody debris (CWD) on 5.6 million ac of woodlands in California that are outside of national forests and reserved areas. Woodlands consist primarily of oak (Quercus spp.) types and are defined as forestland incapable of producing commercial quantities of traditional forest products because of adverse site and tree morphophysiology. Approximately 671 million ft3 of CWD were estimated to occur over the study area. Almost 3 million ac of woodland (52% of the sampled area) were estimated to have no CWD. The large-end diameter of CWD was <12 in. on 67% of all logs sampled. Blue oak (Q. douglasii) CWD occurred over the largest area and gray pine (Pinus sabiniana) produced the most volume (164.1 million ft3) of CWD. An average of 115 ft3/ac, 1.2 tons/ac, 21 logs/ac, and 56.8 linear ft/ac were estimated for CWD across all woodland types. The coast live oak (Q. agrifolia) type produced the largest per-acre measure of CWD volume (164.1 ft3/ac). The California laurel (Umbellularia californica) type produced the highest log density (48 logs/ac) and the most linear feet per acre of CWD (131.8 ft/ac). CWD was most abundant in the central coast and least abundant in the northeastern portion of the state. Results of this study suggest that CWD is not common across much of California's woodlands. More detailed research is needed to evaluate the amount and distribution of CWD, affects of land-use, and the implications for wildlife. West. J. Appl. For. 17(3):139–146.

Download Full-text

Variation in fire scar phenology from mixed conifer trees in the Sierra Nevada

Canadian Journal of Forest Research ◽

10.1139/cjfr-2017-0297 ◽

2018 ◽

Vol 48 (1) ◽

pp. 101-104 ◽

Cited By ~ 2

Author(s):

Scott L. Stephens ◽

Liam Maier ◽

Lilah Gonen ◽

Jennifer D. York ◽

Brandon M. Collins ◽

...

Keyword(s):

Sierra Nevada ◽

Fire History ◽

Fire Regimes ◽

Fire Season ◽

Mixed Conifer ◽

Outer Bark ◽

Individual Tree ◽

Fire Scar ◽

The Individual ◽

In Fire

Fire scar based studies have provided robust reconstructions of past fire regimes. The season in which a fire occurs can have considerable impacts to ecosystems but inference on seasonality from fire scars is relatively uncertain. This study examined patterns in the phenology of cambium formation and wounding responses in the five common mixed conifer tree species of the Sierra Nevada. The outer bark was shaved on 35 trees and individual locations within the shaved portions were wounded systematically by applying direct heat using a handheld torch. Most of the trees had not commenced annual ring development by the first burning treatment in late May. By the second treatment, scars were identified mostly within the early or middle earlywood, although variation was high compared with other treatment periods. By late October, all scars were recorded at the ring boundary. Although intra-ring scar positions generally followed a logical temporal pattern, there was high tree to tree variation such as Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) burned on 26 June induced scars in the early, mid, and late earlywood depending on the individual tree. This high variation makes it somewhat challenging to precisely assign past fire season to published fire history studies.

Download Full-text

Socioecological transitions trigger fire regime shifts and modulate fire–climate interactions in the Sierra Nevada, USA, 1600–2015 CE

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1609775113 ◽

2016 ◽

Vol 113 (48) ◽

pp. 13684-13689 ◽

Cited By ~ 61

Author(s):

Alan H. Taylor ◽

Valerie Trouet ◽

Carl N. Skinner ◽

Scott Stephens

Keyword(s):

Climate Change ◽

Native American ◽

Sierra Nevada ◽

Fire History ◽

Climate Models ◽

Fire Regime ◽

Fire Suppression ◽

Gold Rush ◽

Climatic Effects ◽

Fire Activity

Large wildfires in California cause significant socioecological impacts, and half of the federal funds for fire suppression are spent each year in California. Future fire activity is projected to increase with climate change, but predictions are uncertain because humans can modulate or even override climatic effects on fire activity. Here we test the hypothesis that changes in socioecological systems from the Native American to the current period drove shifts in fire activity and modulated fire–climate relationships in the Sierra Nevada. We developed a 415-y record (1600–2015 CE) of fire activity by merging a tree-ring–based record of Sierra Nevada fire history with a 20th-century record based on annual area burned. Large shifts in the fire record corresponded with socioecological change, and not climate change, and socioecological conditions amplified and buffered fire response to climate. Fire activity was highest and fire–climate relationships were strongest after Native American depopulation—following mission establishment (ca. 1775 CE)—reduced the self-limiting effect of Native American burns on fire spread. With the Gold Rush and Euro-American settlement (ca. 1865 CE), fire activity declined, and the strong multidecadal relationship between temperature and fire decayed and then disappeared after implementation of fire suppression (ca. 1904 CE). The amplification and buffering of fire–climate relationships by humans underscores the need for parameterizing thresholds of human- vs. climate-driven fire activity to improve the skill and value of fire–climate models for addressing the increasing fire risk in California.

Download Full-text

The Ancient Blue Oak Woodlands of California: Longevity and Hydroclimatic History

Earth Interactions ◽

10.1175/2013ei000518.1 ◽

2013 ◽

Vol 17 (12) ◽

pp. 1-23 ◽

Cited By ~ 21

Author(s):

D. W. Stahle ◽

R. D. Griffin ◽

D. M. Meko ◽

M. D. Therrell ◽

J. R. Edmondson ◽

...

Keyword(s):

Environmental History ◽

San Francisco ◽

Sierra Nevada ◽

Ring Width ◽

Storm Track ◽

Late Nineteenth Century ◽

Old Growth ◽

Blue Oak ◽

Oak Trees ◽

Coast Ranges

Abstract Ancient blue oak trees are still widespread across the foothills of the Coast Ranges, Cascades, and Sierra Nevada in California. The most extensive tracts of intact old-growth blue oak woodland appear to survive on rugged and remote terrain in the southern Coast Ranges and on the foothills west and southwest of Mt. Lassen. In the authors' sampling of old-growth stands, most blue oak appear to have recruited to the canopy in the middle to late nineteenth century. The oldest living blue oak tree sampled was over 459 years old, and several dead blue oak logs had over 500 annual rings. Precipitation sensitive tree-ring chronologies up to 700 years long have been developed from old blue oak trees and logs. Annual ring-width chronologies of blue oak are strongly correlated with cool season precipitation totals, streamflow in the major rivers of California, and the estuarine water quality of San Francisco Bay. A new network of 36 blue oak chronologies records spatial anomalies in growth that arise from latitudinal changes in the mean storm track and location of landfalling atmospheric rivers. These long, climate-sensitive blue oak chronologies have been used to reconstruct hydroclimatic history in California and will help to better understand and manage water resources. The environmental history embedded in blue oak growth chronologies may help justify efforts to conserve these authentic old-growth native woodlands.

Download Full-text

Vegetation, fire, climate and human disturbance history in the southwestern Mediterranean area during the late Holocene

Quaternary Research ◽

10.1016/j.yqres.2012.11.008 ◽

2013 ◽

Vol 79 (2) ◽

pp. 110-122 ◽

Cited By ~ 38

Author(s):

Gonzalo Jiménez-Moreno ◽

Antonio García-Alix ◽

María Dolores Hernández-Corbalán ◽

R. Scott Anderson ◽

Antonio Delgado-Huertas

Keyword(s):

Sierra Nevada ◽

Human Disturbance ◽

Fire History ◽

Mediterranean Area ◽

Fuel Load ◽

Lake Levels ◽

Susceptibility Data ◽

Lake Sediment Core ◽

Oscillation Modes ◽

Humid Period

AbstractDetailed pollen, charcoal, isotope and magnetic susceptibility data from an alpine lake sediment core from Sierra Nevada, southern Spain record changes in vegetation, fire history and lake sedimentation since ca. 4100 cal yr BP. The proxies studied record an arid period from ca. 3800 to 3100 cal yr BP characterized by more xerophytic vegetation and lower lake levels. A humid period is recorded between ca. 3100 and 1850 cal yr BP, which occurred in two steps: (1) an increase in evergreen Quercus between 3100 and 2500 cal yr BP, indicating milder conditions than previously and (2) an increase in deciduous Quercus and higher lake levels, between ca. 2500 and 1850 cal yr BP, indicating a further increase in humidity and reduction in seasonal contrast. Humid maxima occurred during the Roman Humid Period, previously identified in other studies in the Mediterranean region. Intensified fire activity at this time could be related to an increase in fuel load and/or in human disturbance. An arid period subsequently occurred between 1850 and 650 cal yr BP, though a decrease in Quercus and an increase in xerophytes. The alternation of persistent North Atlantic Oscillation modes probably played an important role in controlling these humid–arid cycles.

Download Full-text