A spatially explicit census reveals population structure and recruitment patterns for a narrowly endemic pine, <Emphasis Type="Italic">Pinus torreyana</Emphasis> |
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Authors: | Janet Franklin Elizabeth V Santos |
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Institution: | (1) Department of Biology, San Diego State University, San Diego, CA 92182-4614, USA;(2) School of Geographical Sciences and Urban Planning and School of Life Sciences, Arizona State University, P.O. Box 875302, Tempe, AZ 85287-5302, USA |
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Abstract: | We conducted a census of the rare pine, Pinus torreyana ssp. torreyana, to determine (a) its population size and whether it is stable, growing, or declining; (b) the spatial variation in population
structure; (c) the spatial patterning of trees in different life stages; and (d) the environmental factors that are related
to seedling recruitment. Trees were classified into four stage classes: adult (>160 cm tall with cones); sub-adult (>160 cm
without cones); saplings (30–160 cm); and seedlings (<30 cm). Stem diameter was measured for adults and sub-adults, and height
for saplings and seedlings. Stands were defined by spatial clustering of the tree map. Univariate and bivariate point pattern
analyses were used to explore spatial patterns for adult and juvenile trees and identify potential stand development processes
such as density dependence, dispersal limitations, and patchy recruitment. Logistic regression was used to analyze seedling
establishment and survival in relation to environmental variables derived from digital maps. Earlier studies reported little
or no recruitment. We mapped 5,394 individuals, and tree size had “reverse J-shaped” distribution suggestive of a recruiting
population. However, population structure was variable among stands. The predominant spatial pattern detected for adult and
juvenile trees was clustering at lag distances <10 m. Bivariate pattern analysis did not suggest repulsion between adult and
juvenile size classes. Seedlings tended to be found close to adults and on certain soil types. This suggests that the clustered
patterns resulting from patchy recruitment of juveniles persist over time. |
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