Accounting for large-scale factors in the study of understory vegetation using a conditional logistic model
Artikel i vetenskaplig tidskrift, 2007

Local-scale and large-scale factors can affect the presence of a species of understory vegetation in the forest. Local-scale factors may be the influence of surrounding trees, while climate and latitude are typically considered large-scale factors. A model for the presence of a species needs to take into account both scales. A conditional logistic model is proposed for those studies where only the local-scale factors are of interest and that avoids estimating the large-scale parameters. Conditioning is carried out by the number of quadrats in the plot where the vegetation is found. As the latter is a sufficient statistic for the large-scale factors, a model free from these parameters is obtained. Data gathered in the permanent sample plots of the 1985-1986 National Forest Inventory of Finland is used for illustration, where the local-scale factor of interest is the influence of the trees, quantified by an index based on the size and location of the trees. The model fitted to Vaccinium vitis-idaea showed a significant and positive influence of Scots pine on the presence of this species, while for Calamagrostis arundinacea, a decrease in the odds ratio was observed due to the influence of Norway spruce.

STAND

forestry

logistic

FOREST

FINLAND

local scale

influence potential

sufficient statistics

odds ratio

regression

ecology

nuisance parameters

Författare

S. Kuhlmann-Berenzon

Swedish Institute for Infectious Disease Control

Chalmers University of Technology

Urban Hjorth

Chalmers, Matematiska vetenskaper

Göteborgs universitet

Environmental and Ecological Statistics

1352-8505 (ISSN) 1573-3009 (eISSN)

Vol. 14 149-159

Ämneskategorier

Matematik

DOI

10.1007/s10651-007-0009-0