From Fire to Flood: Historic Human Destruction of Sonoran Desert Riverine Oases. Henry F. Dobyns. Socorro: Ballena Press Anthropological Papers No. 20. 222 pp., $11.95.

In the 20th century, a policy of fire suppression provided the opportunity for regeneration of vegetation in excess of historical levels of density, with disproportionately high amounts of shade tolerant, more flammable trees across mixed conifer forests of the western US. Historical data on levels of density and cover of vegetation is fragmentary. Gaps in historical data make the task of ecological restoration challenging. One alternative is to use a proxy condition to guide restoration. The Sierra San Pedro Mártir (SSPM), Baja California, Mexico, is a Jeffrey pine mixed conifer forest similar to forests of southern California (SoCal) and elsewhere that has not experienced programmatic levels of fire suppression The hypothesis tested is that if Jeffrey pine mixed conifer forests in southern California and the SSPM, Baja California, Mexico, are a continuation of the California Floristic Province, then locations with similar fire histories should have similar species composition and stand structure. Chapter 1 results indicate that historical species associations are still intact after a century of fire suppression, but levels of shade-tolerant more flammable species are higher, not only because of the time since the last fire of record, but also because of long fire intervals that have elapsed between the most recent fire and the previous fire of record. Chapter 2 results indicate that time-since-fire is a strong predictor of stand structure and composition. Sites with similar fire histories and species composition had similar stand structure except where long intervals between fires left more dense residual stands after a fire event, or where levels of precipitation in the driest sites were found to result in lower levels of recruitment in the understory, but statistically similar levels of canopy trees. Chapter 3 results for downed woody debris indicate that accumulation of rotten woody debris is strongly related to time-since-fire, while sound woody debris is deposited as a continuous rain of material from the canopy. As sound wood decays, it adds to the accumulation of rotten wood that is largely consumed by the next fire event. Results were found to be statistically similar in both SoCal and the SSPM.

Conifer populations in the Peninsular Range of southern California and Baja California form isolated biogeographic "sky-islands" on mountains with orographic enhanced precipitation. Fire suppression management altered burning patterns in southern California since ca. 1900. Significant changes in tree composition, density, and diameters are documented over a 75-year period in mixed conifer forest at Cuyamaca Mt. by replicating ground-based measurements sampled in 1932 for the Weislander Vegetation Type Map survey. Average conifer density more than doubled, from 271 trees ha-1 ± 82 (standard error) to 716 ha-1 ± 79. Repeat aerial photographs for 1928 and 1995 show significant increase in canopy cover from 47% ± 2 to 89% ± 1. Changes comprise mostly ingrowth of shade-tolerant Calocedrus decurrens in the smallest stem diameter class (10 cm to 29.9 cm dbh). The 1932 density of overstory conifer trees (> 60 cm dbh) and 1928 canopy cover were similar to modern mixed conifer forest in the Sierra San Pedro Mártir, ~200 km S in Baja California, Mexico, where fire-suppression had not been practiced.

The winter of 2001-2002 was the driest in southern California since instrumental records began in 1850. Whole-stand die-off of a serotinous pine (Pinus coulteri) occurred over much of the northern Peninsular and eastern Transverse Ranges, before an outbreak of wildfires in 2003 extensively burned drought-killed stands. I investigated four regeneration condition classes: (1) live unburned stands (control group) and those (2) fire-killed (i.e., drought surviving but burned), (3) posthumously burned (i.e., burned after death by drought), and (4) stands with mixed mortality by drought and fire. Posthumously burned stands had an average tree to seedling ratio of 13:1, and the systematic census failed to detect any Coulter pine seedlings among two-thirds of plots. Crown-fire in drought-killed posthumously burned stands is sufficiently intense to destroy the canopy seedbank of serotinous cones. In contrast, an isolated population of Cuyamaca Cypress (Cupresses arizonica var. stephensonii) successfully reproduced in King Creek and at a nearby plantation site. A significant decline in seedling and tree size was measured with distance from King Creek, suggesting that soil moisture is a likely factor limiting growth.

ABSTRACT OF THE THESIS

Glacial Chronology of a High Altitude Moraine Series,

Tamarack Bench/Francis Canyon, Sierra Nevada, California

by

Daryl Lee Kohut

Master of Science, Graduate Program in Geological Sciences

University of California, Riverside, August 2011

Dr. Richard Minnich, Chairperson

Alpine glaciers in the Sierra Nevada are sensitive to regional climate fluctuations and preserve a high resolution record of climate change in the form of glacial deposits (surficial and lacustrine). Fluctuations of alpine glaciers signify shifts in precipitation and temperature. Developing a regional chronology of changes will enable correlation to regional and global climate records, assist in understanding the mechanisms behind these shifts, and help predict possible future changes. A chronology of a high altitude moraine series on the Tamarack Bench /Francis Canyon, eastern Sierra Nevada showing a complex late Pleistocene retreat during MIS 2 was developed through mapping and dating of 3 glacial deposits: TBm2 (18.8 ka), FLm2 (16.6 ka), and FCm3 (12.6 ka) using terrestrial cosmogenic nuclide 10Be. Currently no standard practice exists for interpretation of cosmogenic nuclide ages creating problems with correlation. Here I present a method of interpretation through application to our data and critical evaluation of current regional studies. Attempts at resolving the timing of the regional Recess Peak advance in the Sierra Nevada using only TCNs will be unsuccessful until accuracy improves.

The mountain tree line correlates with the limit of carbon gain in photosynthesis, a temperature dependent process linked to atmospheric lapse rates. Studies of tree lines often do not focus on specific mechanisms that limit their distributions, including lateral snow transport (LST) and snow drifting, as well as wildfires. At Mount San Gorgonio (elevation 3505 m) in the eastern San Bernardino Mountains, 130 km east of Los Angeles, the subalpine forest tree-line (Pinus flexilis, P. contorta) has been stable over the 20th century. Above 3000 m blowing snow and snow drifting associated with the jet stream, combined with topographic wind enhancement, including forests denuded by fires, can significantly affect timberline dynamics. The reduction of surface roughness due to tree removal accelerates LST and lowers the timberline on leeward slopes subject to increased snow deposition. This paper evaluates LST at three ridgeline timberline sites in the San Gorgonio Wilderness that were burned in 1863, 1869 and 1951. Post-fire tree growth response is measured by using 200 m long sampling quadrats that traversed from windward to leeward slopes. Metrics include tree cover, height and diameter data. The results indicate that the LST is enhanced by fire which increases wind speeds, windward slope snow ablation, and leeward slope snow deposition, slowing tree establishment and growth. In the krummholz zone near San Gorgonio summit, recurrent damage from wind, snow and ice produce shear injury to windward slope tree canopies downwind (northeastward), result in continuous LST. On leeward slopes, late summer or perennial snow cover, maintains bare zones (tree lines) due to tree mortality, the snow decrease the growing season and increase the probability of tree death. At global scales, the tree line is predicted to ascend mountain slopes with planetary warming because the upper elevation boundary of woody vegetation is assumed to represent temperature limitations to positive net photosynthesis. An essential issue in the growth of plant canopy is the separation of intrinsic productivity from physical dieback over ecological time scales: What is carbon gain in canopy versus the rate of canopy removal due to wind-driven disturbances and snow burial over the life of the tree that reduces photosynthetic capacities? Without mass loss from LST, a hypothetical increase in forest canopy would permit tree colonization to higher elevations than the modern empirical limit. These findings are applicable to other mountain ranges at temperate latitudes subject to jet stream induced LST, and must be accounted for in the observation and prediction of tree lines in response to global climate change.

Soil temperature plays an important role in physical, biological and microbiological processes occurring in the soil. It can be used as indicative of regional climate change. A long-term soil temperature database was collected at 75 locations in the Mojave Desert region by the Pallmann method from 1982-2000. This long-term database of soil temperature is invaluable and was used to analyze the spatiotemporal change pattern of soil temperature, and to examine the relationship between regional climate change and soil temperature over an extended period of time.

The main conclusions of this research are: 1) the accuracy and consistency of the Pallmann method was good in comparison with two other temperature measurement methods: thermistor sensor and diffusion-cell method. The Pallmann method is an ideal method for studying the spatial variation in soil temperature and long-term climate changes. 2) Elevation is the dominated factor governing the spatial variation of soil temperature in the Mojave Desert region and can be used to estimate the spatial distribution of soil temperature. In the Mojave Desert region, hyperthermic soil is the most extensive one, which accounts for around 55% of the whole region. Thermic soil accounts for 38.7%. Frigid and mesic soils only occur at high elevation mountains. 3) Seasonal soil temperatures vary greatly in the Mojave Desert region and decrease linearly with elevation. The differences of the summer and winter soil temperature are around 20 °C under the same elevation. The effect of elevation on soil temperature is more pronounced in summer season than in winter season. 4) Soil and air temperature are highly correlated in the Mojave Desert region. Both of the soil and air temperature were found to be highly correlated with elevation and their spatiotemporal variations are highly positively correlated. 5) The Mojave Desert is experiencing a warming trend. Based on continued measurements across the region, the air and soil temperatures have risen at the rates of 0.79 and 0.63°C per 10 year from 1982 to 2000. The anomalies of annual precipitation were inversely correlated with those of soil temperature. The soil temperature of the Mojave Desert would be cooler than normal under El Niño conditions. 6) The climatic variables of air temperature, precipitation and evaporation had significant correlation with soil temperature. The spatial-temporal variation of soil temperature can be predicted based on the linear regression equation with air temperature and precipitation as independent variables.

The Western Riverside County Multiple Species Habitat Conservation Plan has been presented to the public as a complete draft having been reviewed and modified as a result of comments from resource agencies, the Scientific Review Panel (SRP), local stakeholder groups, cities, and numerous other individuals at key intervals in the planning process. The goal is to develop a land-use plan that preserves open space for individual species of concern, protects existing natural communities that sustain the biodiversity of the planning region, and creates constraints for planned growth and development of the region that respect the rights of property owners. It seeks to use the “Best Available Science” as an approach to the planning process. This document is a review of the "science" in the final draft of the Western Riverside County Multiple Species Habitat Conservation Plan, by the Science Review Panel assembled by the Center for Conservation Biology at the University of California, Riverside.