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UCSB Biogeography Lab Publications Abstracts
SPATIAL AND TEMPORAL DYNAMICS OF A BLUE OAK WOODLAND
HARVEY, LARRY EDWARD. 1989.
PhD Dissertation, Department of Geography, University of California, Santa Barbara. 184 pp.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.