Spatial and Temporal Dynamics of a Blue Oak Woodland

TitleSpatial and Temporal Dynamics of a Blue Oak Woodland
Publication TypeThesis
Year of Publication1989
AuthorsHarvey, LE
Academic DepartmentGeography
Number of Pages184
Date Published1989
UniversityUniversity of California
CitySanta Barbara

The purpose of this research was to analyze spatial and temporal patterns of regeneration and mortality of blue oak (Quercus douglasii H. & A.). Specific objectives were to: (1) describe the population age and size structure, (2) reconstruct variations in blue oak recruitment rates over the past century, (3) relate recruitment to land-use changes, climate variation and fire history, (4) describe the spatial relationship between blue oak life stages, and (5) describe the spatial dynamics of blue oaks. Blue oaks at four sites were described by their height, diameters at the base and breast height, and crown shape. Age structure was determined from growth-ring counts and the statistical relationship between size and age. Study sites included a blue oak savanna with many large trees and no seedlings, two woodland sites of mixed ages and sizes, and a forest with few large trees and numerous seedlings. Blue oak survivorship functions based on the log-logistic survivorship distribution were used to construct time series of expected survivorship. Recruitment indices derived by standardizing the ratio of observed versus expected survivorship were compared to historical records of livestock grazing and precipitation using linear regressions. Prior to the introduction of livestock recruitment at the forested site followed winter precipitation trends. Recent declines in recruitment were correlated with increased grating intensity at two of four sites. Fires did not significantly affect recruitment. A second-order neighborhood analysis of overall dispersion detected clustering and spatial randomness at two sites each. Spatial patterns of height- and age-based life stages were analyzed using the matrix comparison method. Seedlings were clustered, saplings were randomly dispersed, and adults were uniformly distributed. Spatial dynamics were inferred from maps of aged trees using the matrix comparison method, but trends were weak. Acorns germinated in clusters, but over time members of these clusters died in a nonrandom thinning process. The geographic structure evolves from a clustered pattern to a random pattern of juveniles and adults. An inhibitory parent-offspring spatial relationship is suggested for blue oaks at one site. This spatial pattern is indistinguishable from random after 40 years of age.