Papers by Christopher Dolanc
Application of Historical Geospatial Data and Field- Based Work to Monitor Rates of Erosion Along the Bluffs of Shades Beach in Erie Pennsylvania
Abstracts with programs, 2022
Application of Remote Sensing and Field Survey for Quantifying Bluff Erosion Rates in Western Erie County, Pennsylvania
Geological Society of America Abstracts with Programs
ISSUE Widespread shifts in the demographic structure of subalpine forests in the
Aim Many climate-linked vegetation models predict major contraction of subalpine forests within t... more Aim Many climate-linked vegetation models predict major contraction of subalpine forests within the next 100 years, which would require a relatively rapid replacement of high-elevation species by lower-elevation species over large portions of subalpine forest. We tested this prediction by comparing empirical data from a historic data set with data collected from re-sampled sites from 2007–09. Location Central Sierra Nevada, CA, USA, 2300–3400 m elevation. Methods We re-sampled 139 undisturbed historical vegetation plots across 5500 km 2 originally sampled from 1929–34 in the subalpine zone of the Sierra Nevada, and compared historical with current forest structure and composition. We compared historic and modern climatic conditions using two high-elevation climate stations nearby. Results Subalpine forests experienced a net increase in tree stem density of 30.4%, including a 63.3% increase in small trees. Six of eight tree species showed statistically significant increases in small ...
Forest Science, 2016
Landsat imagery was analyzed to understand changes in subalpine forest stands since the mid-1980s... more Landsat imagery was analyzed to understand changes in subalpine forest stands since the mid-1980s in the Sierra Nevada region of California. At locations where long-term plot measurements have shown that stands are becoming denser in the number of small tree stems (compared with the early 1930s), the 30-year analysis of normalized difference vegetation index (NDVI) indicated that no consistent increases in canopy leaf cover have occurred at these same locations since the mid-1980s. Interannual variations in stand NDVI closely followed snow accumulation amounts recorded at nearby stations. In contrast, at Sierra whitebark pine stand locations where it has been observed that widespread tree mortality has occurred, decreasing NDVI trends over the past 5-10 years were consistent with rapid loss of forest canopy cover. The matching of patterns and trends in the NDVI with measured stand attributes can better inform regionwide assessments of forest growth trends using Landsat image analysis. The management implications of these results will depend on the recruitment rates of subalpine trees across forest ecotones in decades to come.
PloS one, 2016
Quantifying historical fire regimes provides important information for managing contemporary fore... more Quantifying historical fire regimes provides important information for managing contemporary forests. Historical fire frequency and severity can be estimated using several methods; each method has strengths and weaknesses and presents challenges for interpretation and verification. Recent efforts to quantify the timing of historical high-severity fire events in forests of western North America have assumed that the "stand age" variable from the US Forest Service Forest Inventory and Analysis (FIA) program reflects the timing of historical high-severity (i.e. stand-replacing) fire in ponderosa pine and mixed-conifer forests. To test this assumption, we re-analyze the dataset used in a previous analysis, and compare information from fire history records with information from co-located FIA plots. We demonstrate that 1) the FIA stand age variable does not reflect the large range of individual tree ages in the FIA plots: older trees comprised more than 10% of pre-stand age bas...
Recent, Climate-driven Changes in Demography and Radial Growth of Subalpine Conifers of the Central Sierra Nevada
Stream Discharge and Sediment Load Variation During Three Dry Years at Kings River Experimental Watershed in the Southern Sierra Nevada in California
The Kings River Experimental Watershed (KREW) is now in its third year of data collection on eigh... more The Kings River Experimental Watershed (KREW) is now in its third year of data collection on eight small watersheds from 1600-2400 m in the Sierra Nevada. We are collecting meteorology, stream discharge, sediment load, water chemistry, stream microclimate, shallow soil water chemistry, vegetation, macro-invertebrate and air quality data. This paper examines connections between meteorology, stream discharge and sediment yield in
This paper was prepared as the result of work sponsored by the California Energy Commission. It d... more This paper was prepared as the result of work sponsored by the California Energy Commission. It does not necessarily represent the views of the Energy Commission, its employees or the State of California. The Energy Commission, the State of California, its employees, contractors and subcontractors make no warrant, express or implied, and assume no legal liability for the information in this paper; nor does any party represent that the uses of this information will not infringe upon privately owned rights. This paper has not been approved or disapproved by the California Energy Commission nor has the California Energy Commission passed upon the accuracy or adequacy of the information in this paper.
Proceedings of the National Academy of Sciences, 2015
Significance Declines in the number of large trees in temperate and tropical forests have attract... more Significance Declines in the number of large trees in temperate and tropical forests have attracted attention, given their disproportionate importance to forest structure, function, and carbon storage. Yet, factors responsible for these declines are unclear. By comparing historic (1930s) and contemporary (2000s) surveys of California forests, we document that across 120,000 km 2 , large trees have declined by up to 50%, corresponding to a 19% decline in average basal area and associated biomass, despite large increases in small tree density. Contemporary forests also exhibit increased dominance by oaks over pines. Both large tree declines and increased oak dominance were associated with increases in climatic water deficit, suggesting that water stress may be contributing to changes in forest structure and function across large areas.
Forest Ecology and Management, 2003
Common logging practices in tropical rainforest are often not sustainable and can degrade the for... more Common logging practices in tropical rainforest are often not sustainable and can degrade the forest. The Palcazú Forest Management system (strip clear-cutting) has been proposed as one sustainable alternative. However, low growth rates of commercial tree species during early regeneration indicate that strip-cutting may not be sustainable. To test whether a silvicultural treatment enhances the growth, survival, recruitment or richness of regenerating trees, we carried out an experimental thinning in 1996 within two strips cleared in 1989 at Jenaro Herrera, Peru, then censussed and remeasured trees on thinned and control plots in 2000. In addition, for strip 2, we compared tree regeneration on two felling treatments, clearcutting and deferment-cutting. Thinning significantly enhanced annual growth increment (AGI) for stems of all regeneration categories (recruits, stump sprouts, and advance regeneration) of commercial species in strip 1, and for all categories of recruits and stump sprouts in strip 2. In most cases, mean increment in the thinned treatment was approximately twice that of the control. Recruitment, survival and richness, however, demonstrated little response to thinning. Although growth tended to be higher in clear-cut portions, significant differences in increment for felling treatment were detected for only two of seven categories on strip 2, and there was no effect of felling treatment on survival, recruitment or richness. Thinning is likely to raise the value of the second harvest on the strips by enhancing the growth rates of regenerating trees, so thinning should be included in the strip clear-cutting system. This system should not, however, be considered sustainable unless growth rates are sufficient to ensure the value of successive harvests.
Applied Vegetation Science, 2013
Questions: Has tree density changed consistently across vegetation types? Do changes in component... more Questions: Has tree density changed consistently across vegetation types? Do changes in component species correspond with changes across vegetation types? Do patterns of changes suggest potential drivers of change? Location: Northern two-thirds of the Sierra Nevada, CA, USA, ca. 45 000 km 2. Methods: Using two data sets that cover the span of elevations and land jurisdictions in the study area, we classified 4321 historical plots and 1000 modern plots into nine broad groups of vegetation types that are widely used by land managers and researchers in the region. We compared tree density and composition between historical and modern plots across and within these nine types. Results: In the modern data set, tree density was significantly higher in eight of nine vegetation types. Total density was significantly higher in modern plots for all west slope types, especially for montane hardwood, where modern forests are 128% denser, and mixed conifer forests, which are 69% denser. Relative density of component species was also very different between data sets in these forests, and suggests a shift in dominance toward shade-tolerant conifers and evergreen oaks. Fire suppression is likely a driving factor in these types but density was also significantly higher in high-elevation types such as sub-alpine forest (+20%), where neither fire suppression nor logging have had major impacts on structure. East slope forest types (eastside P. jeffreyi forest and piñon-juniper woodland) were very similar in both modern and historical data sets, with no significant differences in density or composition. Conclusion: West slope forest types, especially montane hardwood and mixed conifer forest, appear the most altered types of the mountain range. These types are more productive but have also been subject to greater disturbance than high-elevation and east slope forest types. Climate change may also be driving changes across the study area. Species such as Quercus chrysolepis and Calocedrus decurrens, which have each increased markedly in abundance, appear well positioned to dominate in the near future, especially under continued fire suppression and a warmer climate.
… Citation Dolanc, Christopher R.; …, 2007
Description: The Kings River Experimental Watershed (KREW) is a watershed-level study on headwate... more Description: The Kings River Experimental Watershed (KREW) is a watershed-level study on headwater streams in the Sierra Nevada, California. Eight perennial streams, from 1500 m (4920 ft) to 2490 m (8170 ft) elevation, have been instrumented and collecting data since 2002. ...
Widespread shifts in the demographic structure of subalpine forests in the Sierra Nevada, California, 1934 to 2007
Global Ecology and Biogeography, 2012
ABSTRACT Aim Many climate‐linked vegetation models predict major contraction of subalpine forests... more ABSTRACT Aim Many climate‐linked vegetation models predict major contraction of subalpine forests within the next 100 years, which would require a relatively rapid replacement of high‐elevation species by lower‐elevation species over large portions of subalpine forest. We tested this prediction by comparing empirical data from a historic data set with data collected from re‐sampled sites from 2007–09.Location Central Sierra Nevada, CA, USA, 2300–3400 m elevation.Methods We re‐sampled 139 undisturbed historical vegetation plots across 5500 km2 originally sampled from 1929–34 in the subalpine zone of the Sierra Nevada, and compared historical with current forest structure and composition. We compared historic and modern climatic conditions using two high‐elevation climate stations nearby.Results Subalpine forests experienced a net increase in tree stem density of 30.4%, including a 63.3% increase in small trees. Six of eight tree species showed statistically significant increases in small tree density, including species with distributions at both the upper and lower boundaries of subalpine. Increases in small tree density were partly offset by a 20% decrease in large trees. These shifts were significant throughout the landscape of our study area. Modern stand composition was indistinguishable from historical composition. Daily minimum temperature (+ 1.2°C) and precipitation (+ 15–48%) both increased during the same period.Main conclusions Warming temperatures plus steady to increasing precipitation have led to less stressful conditions for recruitment and survival of small trees, and are probably contributing to increased mortality of large trees. Tree abundance and composition in the subalpine has not changed in the direction predicted by vegetation models linked to future climate scenarios. Our results underline the fundamental role that moisture balance plays in structuring mediterranean‐zone montane forests. Future shifts in vegetation composition and structure from these regions are likely to depend on interactions between water balance and disturbance factors like fire, insects and disease.
Ecosphere, 2015
Fire in high-elevation forest ecosystems can have severe impacts on forest structure, function an... more Fire in high-elevation forest ecosystems can have severe impacts on forest structure, function and biodiversity. Using a 105-year data set, we found increasing elevation extent of fires in the Sierra Nevada, and pose five hypotheses to explain this pattern. Beyond the recognized pattern of increasing fire frequency in the Sierra Nevada since the late 20th century, we find that the upper elevation extent of those fires has also been increasing. Factors such as fire season climate and fuel build up are recognized potential drivers of changes in fire regimes. Patterns of warming climate and increasing stand density are consistent with both the direction and magnitude of increasing elevation of wildfire. Reduction in high elevation wildfire suppression and increasing ignition frequencies may also contribute to the observed pattern. Historical biases in fire reporting are recognized, but not likely to explain the observed patterns. The four plausible mechanistic hypotheses (changes in fire management, climate, fuels, ignitions) are not mutually exclusive, and likely have synergistic interactions that may explain the observed changes. Irrespective of mechanism, the observed pattern of increasing occurrence of fire in these subalpine forests may have significant impacts on their resilience to changing climatic conditions.
The transition from riparian to upland forest plant communities on headwater streams in the southern Sierra Nevada, California, United States
The Journal of the Torrey Botanical Society
PloS one, 2016
Quantifying historical fire regimes provides important information for managing contemporary fore... more Quantifying historical fire regimes provides important information for managing contemporary forests. Historical fire frequency and severity can be estimated using several methods; each method has strengths and weaknesses and presents challenges for interpretation and verification. Recent efforts to quantify the timing of historical high-severity fire events in forests of western North America have assumed that the "stand age" variable from the US Forest Service Forest Inventory and Analysis (FIA) program reflects the timing of historical high-severity (i.e. stand-replacing) fire in ponderosa pine and mixed-conifer forests. To test this assumption, we re-analyze the dataset used in a previous analysis, and compare information from fire history records with information from co-located FIA plots. We demonstrate that 1) the FIA stand age variable does not reflect the large range of individual tree ages in the FIA plots: older trees comprised more than 10% of pre-stand age bas...
PLoS ONE, 2013
Montane forests of western China provide an opportunity to establish baseline studies for climate... more Montane forests of western China provide an opportunity to establish baseline studies for climate change. The region is being impacted by climate change, air pollution, and significant human impacts from tourism. We analyzed forest stand structure and climate-growth relationships from Jiuzhaigou National Nature Reserve in northwestern Sichuan province, along the eastern edge of the Tibetan plateau. We conducted a survey to characterize forest stand diversity and structure in plots occurring between 2050 and 3350 m in elevation. We also evaluated seedling and sapling recruitment and tree-ring data from four conifer species to assess: 1) whether the forest appears in transition toward increased hardwood composition; 2) if conifers appear stressed by recent climate change relative to hardwoods; and 3) how growth of four dominant species responds to recent climate. Our study is complicated by clear evidence of 20 th century timber extraction. Focusing on regions lacking evidence of logging, we found a diverse suite of conifers (Pinus, Abies, Juniperus, Picea, and Larix) strongly dominate the forest overstory. We found population size structures for most conifer tree species to be consistent with self-replacement and not providing evidence of shifting composition toward hardwoods. Climate-growth analyses indicate increased growth with cool temperatures in summer and fall. Warmer temperatures during the growing season could negatively impact conifer growth, indicating possible seasonal climate water deficit as a constraint on growth. In contrast, however, we found little relationship to seasonal precipitation. Projected warming does not yet have a discernible signal on trends in tree growth rates, but slower growth with warmer growing season climates suggests reduced potential future forest growth.
The Kings River Experimental Watershed (KREW) is now in its third year of data collection on eigh... more The Kings River Experimental Watershed (KREW) is now in its third year of data collection on eight small perennial watersheds. We are collecting meteorology, stream discharge, sediment load, water chemistry, shallow soil water chemistry, vegetation, macro-invertebrate, stream microclimate, and air quality data. This paper primarily examines discharge and sediment data from six watersheds between 1600 m and 2400 m in elevation in the Sierra Nevada, California. The discharge discussion focuses on water year (Wy) 2004, which was relatively dry. The sediment discussion examines bulk mass data from Wy2001 through Wy2004, and presents some detailed analysis of the sediment load beginning with the Wy2003 dataset. Sediment loads in kilograms per hectare were low with the exception of Wy2003. Meteorology data from two stations at the top of the watersheds and two stations at the bottom is presented. Between 2007 and 2009, six of these eight watersheds are planned be harvested, undergo prescr...
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Papers by Christopher Dolanc