Tree spatial patterns and stand development along the pine-grassland ecotone in the Colorado Front Range

摘要

Spatial patterns of tree age and size were studied in 16 stands in 2 distinct types of lower timberline habitats in the Colorado Front Range (intermontane basins near Estes Park and the ecotone with the Plains grasslands near Boulder) to determine if they are consistent with the episodic pattern of tree regeneration proposed for ponderosa pine (Pinus ponderosa) and expected changes in tree spatial patterns as cohort patches age. The proposed hypothesis indicated that internal patch structure shouldbecome less clumped as single cohort patches age due to self-thinning, with few trees attaining dominance in a small patch. Analytical methods included Ripley's K(t) (a univariate statistic of tree spatial distribution), Ripley's K12(t) (a bivariate statistic of spatial association), and Moran's I (a measure of spatial autocorrelation). Spatial patterns implied establishment of patches of pines followed by self-thinning. Continued stand development resulted in strong size hierarchies as manifested by stronger spatial autocorrelation of tree age than tree size. P. ponderosa exhibited a strong size class hierarchy developed within an even-aged patch.