Geology topics

Research about Kings Canyon National Park, Sequoia National Park

Source-linked reports with geographic coverage including Kings Canyon National Park, Sequoia National Park.

6 recordsLinked to original sources

USGS2025

The effectiveness of wildfire at meeting restoration goals across a fire severity gradient in the Sierra Nevada

As a consequence of both warming temperatures and over a century of fire suppression, wildfires in the historically frequent-fire forests of the western US have increased both in size and intensity, resulting in large patches of high severity fire that are well outside the historic range of variation. Postfire fuels research has often focused on such high severity patches because of the risk of both type conversion and repeated high severity fire. Yet a substantial portion of any given wildfire will likely still have burned at low to moderate severity. These areas generally retain live mature trees and surface fuels, suggesting that wildfire effects may be in keeping with some forest restoration goals. To better understand the range of postfire fuels conditions across severity classes and how well those conditions align with restoration targets, we sampled three wildfires in mixed conifer forests and giant sequoia groves of the southern Sierra Nevada. These wildfires appear to have met short-term restoration goals for surface fuel reduction, with burned areas having 79.5 % less fuels than unburned areas. Fine woody debris and litter and duff declined with severity, while coarse woody debris was more variable. Small tree density targets were roughly met after low and moderate severity fire, but large tree densities tended to be lower than restoration targets, possibly due to high levels of recent tree mortality. For long-term management, restoration plans set targets for the proportions of the landscape that should be in different fuel load categories, reflecting patterns shaped by many frequent and patchy fires. Observed post-wildfire surface fuels outside of groves were overwhelmingly in the lowest fuels category across severity classes, which is in keeping with short-term goals to reduce surface fuels but is not necessarily contributing to the heterogeneity desired at landscape scales. Surface fuels within giant sequoia groves were higher than those outside groves and therefore more closely matched long-term management targets for variation in fuel loads. However, for a highly valued species that has recently seen substantial losses to high severity fire, managers may find that these higher fuel loads are not desirable even in a landscape context. In summary, low and moderate severity wildfire appear to have beneficial effects in terms of meeting several management goals, however, the large amount of standing postfire fuels, the relative dearth of large trees, and the potential lack of postfire fuel heterogeneity may still pose potential management concerns.

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USGS2024

Effects of recent wildfires on giant sequoia groves were anomalous at millennial timescales: a response to Hanson et al.

Background The giant sequoia ( Sequoiadendron giganteum [Lindley] Buchholz) of California’s Sierra Nevada recently suffered historically unprecedented wildfires that killed an estimated 13–19% of seed-bearing sequoias across their native range. Hanson et al. recently sought to characterize post-fire reproduction in two severely burned sequoia groves, but their two papers (1) inaccurately portrayed sequoia fire ecology, (2) had methodological flaws, and (3) without supporting evidence, questioned efforts to prevent large, stand-replacing wildfires and to plant sequoia seedlings in areas of low post-fire regeneration. Results Our analyses and literature review contradict many of Hanson et al.’s claims and implications. First, evidence indicates that preceding the recent wildfires, large, contiguous areas (>10 to >100 ha) of fire severe enough to kill most sequoias had been absent for at least a millennium, and probably much longer. The ancient sequoia fire regime was instead overwhelmingly dominated by surface fires in which most forest area burned at low or moderate severity interspersed with small forest gaps (hundredths of a hectare to a few hectares) created by local patches of higher-severity fire, within which most mature sequoias survived and most successful reproduction occurred. Prescribed fires have typically mimicked ancient fires and induced adequate sequoia regeneration. In contrast, in some extensive areas where recent wildfires killed most (or all) mature sequoias, regeneration has been well below historical levels, threatening a net loss of sequoia grove area. Methodologically, Hanson et al. reported sixfold greater post-fire sequoia seedling densities than others who sampled the same area; our assessments suggest their higher densities may have largely resulted from plot-placement bias. Finally, Hanson et al.’s comparisons of median seedling densities were inappropriate. Conclusions Hanson et al. questioned efforts to prevent large, high-severity wildfires in sequoia groves but did not acknowledge (1) that past fires sustained sequoia reproduction without the deaths of large fractions of mature sequoias, (2) the anomalous effects of recent wildfires, and (3) the acute conservation threat of losing large fractions of seed-bearing sequoias. Hanson et al.’s further implication, made without supporting evidence, that decisions to plant sequoia seedlings may be unwarranted ignores research showing that recent post-wildfire regeneration has often been well below historical levels.

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USGS2021

Forest resistance to extended drought enhanced by prescribed fire in low elevation forests of the Sierra Nevada

Prescribed fire reduces fire hazards by removing dead and live fuels (small trees and shrubs). Reductions in forest density following prescribed fire treatments (often in concert with mechanical treatments) may also lessen competition so that residual trees might be more likely to survive when confronted with additional stressors, such as drought. The current evidence for these effects is mixed and additional study is needed. Previous work found increased tree survivorship in low elevation forests with a recent history of fire during the early years of an intense drought (2012 to 2014) in national parks in the southern Sierra Nevada. We extend these observations through additional years of intense drought and continuing elevated tree mortality through 2017 at Sequoia and Kings Canyon National Parks. Relative to unburned sites, we found that burned sites had lower stem density and had lower proportions of recently dead trees (for stems ≤47.5 cm dbh) that presumably died during the drought. Differences in recent tree mortality among burned and unburned sites held for both fir (white fir and red fir) and pine (sugar pine and ponderosa pine) species. Unlike earlier results, models of individual tree mortality probability supported an interaction between plot burn status and tree size, suggesting the effect of prescribed fire was limited to small trees. We consider differences with other recent results and discuss potential management implications including trade-offs between large tree mortality following prescribed fire and increased drought resistance.

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USGS2021

Nonlinear shifts in infectious rust disease due to climate change

Range shifts of infectious plant disease are expected under climate change. As plant diseases move, emergent abiotic-biotic interactions are predicted to modify their distributions, leading to unexpected changes in disease risk. Evidence of these complex range shifts due to climate change, however, remains largely speculative. Here, we combine a long-term study of the infectious tree disease, white pine blister rust, with a six-year field assessment of drought-disease interactions in the southern Sierra Nevada. We find that climate change between 1996 and 2016 moved the climate optimum of the disease into higher elevations. The nonlinear climate change-disease relationship contributed to an estimated 5.5 (4.4–6.6) percentage points (p.p.) decline in disease prevalence in arid regions and an estimated 6.8 (5.8–7.9) p.p. increase in colder regions. Though climate change likely expanded the suitable area for blister rust by 777.9 (1.0–1392.9) km 2 into previously inhospitable regions, the combination of host-pathogen and drought-disease interactions contributed to a substantial decrease (32.79%) in mean disease prevalence between surveys. Specifically, declining alternate host abundance suppressed infection probabilities at high elevations, even as climatic conditions became more suitable. Further, drought-disease interactions varied in strength and direction across an aridity gradient—likely decreasing infection risk at low elevations while simultaneously increasing infection risk at high elevations. These results highlight the critical role of aridity in modifying host-pathogen-drought interactions. Variation in aridity across topographic gradients can strongly mediate plant disease range shifts in response to climate change.

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USGS2018

Patterns and correlates of giant sequoia foliage dieback during California’s 2012–2016 hotter drought

Hotter droughts – droughts in which unusually high temperatures exacerbate the effects of low precipitation – are expected to increase in frequency and severity in coming decades, challenging scientists and managers to identify which parts of forested landscapes may be most vulnerable. In 2014, in the middle of California’s historically unprecedented 2012–2016 hotter drought, we noticed apparently drought-induced foliage dieback in giant sequoias ( Sequoiadendron giganteum Lindl. [Buchholz]) in Sequoia and Kings Canyon national parks, California. Characteristics of the dieback were consistent with a controlled process of drought-induced senescence: younger (distal) shoots remained green while older (proximal) shoots were preferentially shed. As part of an ongoing interdisciplinary effort to understand and map sequoia vulnerability to hotter droughts, we reviewed historical records for evidence of previous foliage dieback events, surveyed dieback along trail corridors in eight sequoia groves, and analyzed tree-ring data from a high- and a low-foliage-dieback area. In sharp contrast to the greatly elevated mortality of other coniferous species found at low and middle elevations, we estimate that <1% of sequoias died during the drought. Foliage dieback was notably elevated in 2014 – the most severe single drought year in our 122-year record – but much lower in subsequent years. We found no historical records of similar foliage dieback during previous droughts. Dieback in 2014 was highly variable both within and among groves, ranging from virtually no dieback in some areas to nearly 50% in others. Dieback was highest (1) at low elevations, probably due to higher temperatures, reduced snowpack, and earlier snowmelt; (2) in areas of low adult sequoia densities, which likely reflect intrinsically more stressful sites; and (3) on steep slopes, probably reflecting reduced water availability. Average sequoia ring widths were narrower at the high-dieback than the low-dieback tree-ring site, but for reasons that remain unclear the sites did not differ in their proportional ring-width responses to past droughts. Collectively, our results suggest that giant sequoia vulnerability to hotter droughts may be spatially quite variable, and that at least some of that variability can be explained by metrics related to site water balance. Future research will focus on integrating our results with physiological and remote-sensing data, including tracking sequoias as they recover from the drought.

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USGS2017

Fire and the distribution and uncertainty of carbon sequestered as above-ground tree biomass in Yosemite and Sequoia & Kings Canyon National Parks

Fire is one of the principal agents changing forest carbon stocks and landscape level distributions of carbon, but few studies have addressed how accurate carbon accounting of fire-killed trees is or can be. We used a large number of forested plots (1646), detailed selection of species-specific and location-specific allometric equations, vegetation type maps with high levels of accuracy, and Monte Carlo simulation to model the amount and uncertainty of aboveground tree carbon present in tree species (hereafter, carbon) within Yosemite and Sequoia & Kings Canyon National Parks. We estimated aboveground carbon in trees within Yosemite National Park to be 25 Tg of carbon (C) (confidence interval (CI): 23–27 Tg C), and in Sequoia & Kings Canyon National Park to be 20 Tg C (CI: 18–21 Tg C). Low-severity and moderate-severity fire had little or no effect on the amount of carbon sequestered in trees at the landscape scale, and high-severity fire did not immediately consume much carbon. Although many of our data inputs were more accurate than those used in similar studies in other locations, the total uncertainty of carbon estimates was still greater than ±10%, mostly due to potential uncertainties in landscape-scale vegetation type mismatches and trees larger than the ranges of existing allometric equations. If carbon inventories are to be meaningfully used in policy, there is an urgent need for more accurate landscape classification methods, improvement in allometric equations for tree species, and better understanding of the uncertainties inherent in existing carbon accounting methods.

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