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Author: Sophia Lemmo
Publisher:
ISBN:
Category : Trees
Languages : en
Pages : 0
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Book Description
The 2012-2016 California drought was the most severe in the state’s recorded history, contributing to the death of millions of trees. While the effects of this drought on forests are relatively well studied in the central and southern Sierra Nevada, less is known about its effects on the heavily timbered and diverse forests of northern California. Through sampling 54 0.25 ha plots in northern California, this study compared tree mortality and regeneration patterns before, during, and after California’s most recent record-setting drought. This study evaluated 1) the influence of habitat and competitive covariates on mortality and regeneration trends using ridge regression analysis; and 2) tree death and seedling/sapling establishment dates using dendrochronology and Superposed Epoch Analysis to explore the influence of climate on forest demographics. Montane drought-induced tree mortality occurred primarily in trees smaller than 40 cm diameter at breast height (DBH), with no coastal drought-related mortality in trees with DBH greater than 80 cm. The highest rates of overstory mortality across all sites were observed in Abies grandis (51%), Pinus lambertiana (43%), and Pinus monticola (37%). Picea breweriana (6%) and Picea sitchensis (9%) had the lowest average mortality rates. In montane environments, years with high rates of mortality were positively associated with climatic water deficit (CWD; drier than expected conditions) in the 1-2 years preceding and during tree death dates. Pre-drought montane mortality was greater at wet sites than dry sites, and recent montane mortality (~2013-2020) was positively related with canopy openness. In coastal environments, recent tree mortality was positively associated with maximum temperature and topographic position. Regeneration was dominated by advanced regeneration (median age of 32 years) of shade-tolerant species. In montane environments, regeneration dates were significantly associated with lower-than-average CWD the year proceeding. In coastal environments, regeneration was greater at dry sites than wet sites, and was positively associated with stand density and maximum temperature. These data demonstrate that these forests are not actively perpetuating as diversely into the future, especially in montane environments where more mortality is found in white pine species (Pinus lambertiana and P. monticola) and where the regeneration is weighted towards advanced regeneration of shade-tolerant fir species. This work indicates a need to implement targeted management aimed at generating disturbances to foster balanced and responsive regeneration. This management should preferentially retain medium to larger trees, as these size classes seem to be the least vulnerable to mortality. Such management would be promising for supporting the resilience and diversity of northern California landscapes.
Author: Sophia Lemmo
Publisher:
ISBN:
Category : Trees
Languages : en
Pages : 0
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Book Description
The 2012-2016 California drought was the most severe in the state’s recorded history, contributing to the death of millions of trees. While the effects of this drought on forests are relatively well studied in the central and southern Sierra Nevada, less is known about its effects on the heavily timbered and diverse forests of northern California. Through sampling 54 0.25 ha plots in northern California, this study compared tree mortality and regeneration patterns before, during, and after California’s most recent record-setting drought. This study evaluated 1) the influence of habitat and competitive covariates on mortality and regeneration trends using ridge regression analysis; and 2) tree death and seedling/sapling establishment dates using dendrochronology and Superposed Epoch Analysis to explore the influence of climate on forest demographics. Montane drought-induced tree mortality occurred primarily in trees smaller than 40 cm diameter at breast height (DBH), with no coastal drought-related mortality in trees with DBH greater than 80 cm. The highest rates of overstory mortality across all sites were observed in Abies grandis (51%), Pinus lambertiana (43%), and Pinus monticola (37%). Picea breweriana (6%) and Picea sitchensis (9%) had the lowest average mortality rates. In montane environments, years with high rates of mortality were positively associated with climatic water deficit (CWD; drier than expected conditions) in the 1-2 years preceding and during tree death dates. Pre-drought montane mortality was greater at wet sites than dry sites, and recent montane mortality (~2013-2020) was positively related with canopy openness. In coastal environments, recent tree mortality was positively associated with maximum temperature and topographic position. Regeneration was dominated by advanced regeneration (median age of 32 years) of shade-tolerant species. In montane environments, regeneration dates were significantly associated with lower-than-average CWD the year proceeding. In coastal environments, regeneration was greater at dry sites than wet sites, and was positively associated with stand density and maximum temperature. These data demonstrate that these forests are not actively perpetuating as diversely into the future, especially in montane environments where more mortality is found in white pine species (Pinus lambertiana and P. monticola) and where the regeneration is weighted towards advanced regeneration of shade-tolerant fir species. This work indicates a need to implement targeted management aimed at generating disturbances to foster balanced and responsive regeneration. This management should preferentially retain medium to larger trees, as these size classes seem to be the least vulnerable to mortality. Such management would be promising for supporting the resilience and diversity of northern California landscapes.
Author:
Publisher:
ISBN:
Category : Forest declines
Languages : en
Pages : 0
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Book Description
Climate change is projected to bring more frequent and prolonged droughts, causing widespread forest die-off. Identifying tree mortality over large spatial extents in response to the most recent California drought will help forest managers and conservationists understand where there may be a greater likelihood of future die-offs. In order to find more at-risk areas, this study evaluated how interacting site-specific topographic, climate, substrate, and stand characteristics mediated tree mortality in the Central Sierra Nevada during the 2012-2016 drought. The author used lidar and hyperspectral imagery provided by the National Ecological Observatory Network to identify individual dead trees using the Random Forest classification method and created a Random Forest Regression model to assess site-specific environmental variables that had a greater influence on tree mortality. The results show that the most influential variables were tree height, density, and elevation. Results also found higher mortality rates in pines and oaks, meaning further widespread die-off of these trees could reduce forest productivity, increase fire hazard risk, and drive a shift in community composition over the long-term. This study provides a finer resolution mapping of tree mortality over the research area than was reported by the USFS Aerial Detection Survey. Due to the confounding evidence regarding the relative influence of environmental factors on tree mortality during droughts, these results provide robust information to help maintain these changing forests in a climate-informed manner. Because this study is site-specific, more research is needed to assess how environmental factors mediate drought-induced mortality in other regions also projected to have more intense droughts as a result of climate change.
Author: Samuel W. Flake
Publisher:
ISBN:
Category : Electronic books
Languages : en
Pages : 218
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Book Description
Widespread dieoff of trees associated with severe drought is a recent global phenomenon of increasing conservation and management concern. Tree dieoff is likely to produce dramatic and widespread alterations to plant community composition and successional dynamics, with associated changes in nutrient cycling, hydrology, and wildlife habitat. In order to predict and manage the effects of future widespread drought, there is a need for greater understanding of both the causes of drought-associated tree mortality as well as the subsequent effects of mortality on tree regeneration and understory dynamics. In this study, we investigated the effects of climate, stand structure, and insect herbivores on tree mortality and canopy dieback of semi-arid pinyon-juniper woodlands, as well as the implications of woodland overstory mortality on the abundance of juvenile trees and the distribution of understory plants. In 2015 we resampled 102 plots in a permanent plot network established in 2005 spanning pinyon-juniper woodlands in eleven mountain ranges in central Nevada, encompassing strong gradients of topography, elevation, soil conditions, and aridity. Using individually-tagged trees, we measured tree survival and changes to canopy greenness. In order to assess the effects of neighborhood tree density on changes in tree canopy health, we recorded high-precision GPS locations for each tree and calculated the basal area of neighboring trees and the distance to the nearest neighbor. We measured tree regeneration in two size classes: seedlings (20 cm tall) and sapling (20cm tall). We also measured understory cover by species in 1-m2 quadrats. We noted the microhabitat of tree juveniles and quadrats in order to assess the importance of fine-scale microhabitat heterogeneity to understory dynamics. This study is the first to document widespread dieoff and canopy decline in Great Basin pinyon-juniper woodlands in response to recent severe drought. We found mortality was most strongly predicted by high growing-season vapor pressure deficit and low winter precipitation (Forest Drought Stress Index), while canopy decline was most closely associated with cumulative climatic water deficit. Trees in sites with deeper soils also experienced greater health declines. Stand structure had a smaller, but significant, effect on tree survival and canopy health, with trees in dense 4-m neighborhoods and those with close neighbors experiencing increased mortality risk and canopy dieback. As predicted, the regeneration of pinyon pine was strongly influenced by changes to the overstory trees. Both seedlings and saplings were positively associated with plot-level dead tree basal area and with fine-scale mortality-associated microhabitats, suggesting that drought mortality may create canopy gaps with increased recruitment. In contrast to microhabitat results, pinyon seedlings were much more abundant in stands with lower levels of canopy dieback and in stands with more live basal area, suggesting that new recruitment may be limited by reduced seed availability. The dynamics of tree regeneration in woodlands will likely depend upon seed availability, resource levels, timescale, and the abundance and spatial arrangement of larger juveniles (advance regeneration) present before the drought. We found little evidence of response to tree mortality for most understory plant functional types. However, Poa secunda and Bromus tectorum were both more abundant than expected in mortality-associated microhabitats. At a plot scale, Bromus tectorum abundance was positively associated with canopy dieback, and has increased in dominance since 2005 in arid sites with high levels of dieback. While some native species may respond positively to resources released by tree mortality, there is a risk of invasion and increasing dominance of cheatgrass under future droughts, underlining the importance of understanding overstory-understory interactions in arid woodlands. This study highlights the need for further research into the effects of within-stand structural heterogeneity on woodland responses to drought. Pinyon-juniper woodlands have a complex, patchy distribution of trees which likely affects the ways in which competition may predispose trees to drought mortality. Overstory mortality creates heterogeneous microhabitats which alter the distribution of juvenile trees as well as understory species, thus spatially structuring the response of these species to drought. Aridity and severe drought are likely to increase in coming decades, and understanding the complex interactions that drive woodland tree mortality and the subsequent understory response is critical to the effective management of resilient woodlands.
Author: Bruce Krumland
Publisher:
ISBN:
Category :
Languages : en
Pages : 7
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Author: Chance C. Callahan
Publisher:
ISBN:
Category : Conifers
Languages : en
Pages : 48
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Book Description
Drought-induced tree mortality can drastically alter forest composition, structure, carbon dynamics, and ecosystem function. Increasingly, forest policy and management focuses on how to improve forest resistance and resilience to drought stress. This study used tree ring data at Teakettle Experimental Forest (TEF), a historically frequent fire mixed-conifer forest in the California Sierra Nevada, to quantify how prescribed fire and mechanical thinning conducted in 2001-2002 influenced stand and tree-level growth responses to the extreme California drought of 2012-2016. Overstory thinning and understory thinning significantly enhanced growth responses to treatments alone and treatments during the drought at the stand-level. In each year of the drought, distinct tree species were the only significant predictors of drought resistance at the stand-level. As drought persisted, shade-intolerant pine species yielded greater drought resistance values than shade-tolerant white fir and incense cedar. No prescribed burn effects were found, likely due low fire intensity. At the tree-level, tree diameter (DBH), tree height (HT), crown ratio (CRNR), topographic position index (TPI), and change in growing space over time (competition) were the most important predictors of growth responses to treatments and drought resistance. Mechanical thinning, in both understory and overstory thinning can enhance mixed-conifer forests ability to resist drought by reducing competition and increasing resource availability. This study suggests forest managers have flexibility in prescribing various thinning intensities to promote drought resistance. Prescribed burn effects were not found in this study, but further research is needed to understand long-term burn effects for promoting drought resistance in Sierra Nevada mixed-conifer forests.
Author: Douglas D. McCreary
Publisher: UCANR Publications
ISBN: 9781601073815
Category : Blue oak
Languages : en
Pages : 76
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Author: Seth Richard Gorelik
Publisher:
ISBN: 9781392023969
Category : Droughts
Languages : en
Pages : 0
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Book Description
In the early 2000s, severe drought and beetle outbreaks brought on by climate change led to extensive pinon pine mortality in northern New Mexico. Mapping pinon mortality is critical for understanding and monitoring impacts to ecosystem services. I used Landsat imagery, finer-resolution reference data, and statistical modeling to predict absolute within-pixel percent tree mortality (PTM). I found that a balanced random forest model had the highest accuracy. I applied the model to a time series and assessed spatial and temporal patterns of the estimated tree mortality. Pixels within the study area experienced a mean of 42.3% tree mortality, a mean duration of 3 years, and a mean rate of mortality of 22% per year. From 1987 to 2009, cumulative tree mortality reached 67,190 ha, or 19.8% of the woodland area, the equivalent of 48.9 million pinons. These results demonstrate the capability of mapping drought-induced PTM using a Landsat time series.
Author: Michael J. Vernon
Publisher:
ISBN:
Category : Douglas fir
Languages : en
Pages : 33
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Book Description
Climate change is predicted to increase the frequency, duration, and severity of drought events across many bioregions. Forest managers have two active management techniques to promote resistance and resilience to drought: prescribed fire and mechanical thinning. Generally applied to reduce fuels and fire hazard, treated areas may also reduce competition for resources that may improve tree-growth during drought and reduce mortality. The recent severe and prolonged drought in California allowed me to investigate the effects of climate stress and fuel treatments on tree growth responses in a dry mixed-conifer forest ecosystem. To assess tree-growth responses to fuel treatments during severe drought I collected and analyzed tree core samples from 300 ponderosa pine (Pinus ponderosa) and Douglas-fir (Pseudotsuga menziesii) trees in the mixed-conifer forests of Whiskeytown National Recreation Area in northern California. Tree-ring data was used to investigate factors that influenced tree-growth during the study period (2008-2015). Growth was positively associated with crown ratio and negatively associated with local competition and climate water deficit (1-yr lag). Douglas-fir generally had higher annual growth than ponderosa pine, though factors affecting growth were the same for both species. Overall, trees in thinning treatments had higher drought resistance compared to untreated stands. Drought resistance was significantly higher in treated stands compared to untreated stands during both years of extreme drought (2014-2015) for ponderosa pine but only one year (2014) for Douglas-fir. This information can help land managers decide on forest management practices that may enhance forest resistance to future drought events.
Author: Charles E. Little
Publisher: Viking Adult
ISBN:
Category : Nature
Languages : en
Pages : 296
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Book Description
From the sugarbush of Vermont and the dogwoods of Maryland to the hollows in Appalachia and the mountainsides of the West, a whole range of human-caused maladies--acid rain, ultraviolet rays, and other eco-hazards--has been the cause of major forest decline. Little explores the phenomenon with scientists and government officials, and recounts their respondes to this threat to global ecological balance.
Author: Harold Mooney
Publisher: Univ of California Press
ISBN: 0520278801
Category : Nature
Languages : en
Pages : 1008
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Book Description
This long-anticipated reference and sourcebook for CaliforniaÕs remarkable ecological abundance provides an integrated assessment of each major ecosystem typeÑits distribution, structure, function, and management. A comprehensive synthesis of our knowledge about this biologically diverse state, Ecosystems of California covers the state from oceans to mountaintops using multiple lenses: past and present, flora and fauna, aquatic and terrestrial, natural and managed. Each chapter evaluates natural processes for a specific ecosystem, describes drivers of change, and discusses how that ecosystem may be altered in the future. This book also explores the drivers of CaliforniaÕs ecological patterns and the history of the stateÕs various ecosystems, outlining how the challenges of climate change and invasive species and opportunities for regulation and stewardship could potentially affect the stateÕs ecosystems. The text explicitly incorporates both human impacts and conservation and restoration efforts and shows how ecosystems support human well-being. Edited by two esteemed ecosystem ecologists and with overviews by leading experts on each ecosystem, this definitive work will be indispensable for natural resource management and conservation professionals as well as for undergraduate or graduate students of CaliforniaÕs environment and curious naturalists.
