Growth and structural dynamics of uneven-aged ponderosa pine stands in eastern Montana.

摘要

The growth and structural attributes of uneven-aged ponderosa pine forests of eastern Montana were investigated for the purpose of addressing critical knowledge gaps in uneven-aged silviculture. Fourteen stem-mapped plots, stratified by site quality and stocking level, were established in uneven-aged ponderosa pine stands in eastern Montana to examine spatial attributes, size/density relationships, and growth efficiency trends.; Clustering was the most prominent spatial attribute of the investigated stands. Within tree clusters, age was more strongly autocorrelated than DBH and may be directly attributable to the establishment of regeneration patches, which self-thin over time leading to a random distribution of mid- to large-sized individuals. Randomly spacing large diameter trees and allowing smaller diameter trees to cluster should be spatial guidelines for uneven-aged silvicultural selection treatments in eastern Montana ponderosa pine stands. Uneven-aged size/density relationships are not a robust phenomenon due to: self-thinning relationships being dependent on the scale of investigation, apparent lack of self-thinning on low quality sites, and the insensitivity of mean tree size to stand structural differences. Stand density index (SDI) was found to apportion greater relative density to small trees than larger ones, thus SDI may over-predict site occupancy of balanced diameter distributions and under-predict site occupancy of irregular or flat distributions. Individual tree growth efficiencies have significant trends through uneven-aged structures, as tree size increases, growth efficiency decreases. Growth efficiencies also decreased under increasing competition, an effect more pronounced in smaller diameter trees. Site quality appeared to not affect these trends. Growth models predicted that both the structure and spatial arrangement of trees has a significant effect on site occupancy and growth.; The growth and structure of any uneven-aged stand are heavily influenced by the unique spatial arrangement and sizes of its trees, and its stand development history. Couched in these quantifiable traits is the opportunity for scientific, sustainable management of uneven-aged ponderosa pine in eastern Montana.