A method for quantifying vertical forest structure

Vertical forest structure is an attribute of forests that is of interest to many disciplines and is consistently discussed in the context of ecosystem management. The vertical stratification of tree crowns is a forest attribute that influences both tree growth and understory community structure. Therefore, it should be considered when making management decisions that affect the structure of stands. However, current methods of quantifying vertical structure are either arbitrarily-defined and do not represent natural stratification patterns of stands or forests, or are too time consuming for landscape analyses. The program, TSTRAT, was developed to place trees into vertical strata in a structural classification of forest vegetation developed for the Inland Northwest (USA). The primary classification criteria were cover types and classes of stand development described by structural criteria. The TSTRAT algorithm defines strata on the basis of an assumption related to a competition cut-off point among tree crowns in a given area. The predicted strata assignments of trees closely approximated vertical strata that were visually identified, in addition to those identified through cluster analysis. TSTRAT assigns each tree to a stratum, produces various descriptive statistics by vertical stratum, and quantifies overstory tree species diversity and inequality of tree heights. Because TSTRAT simulates the natural vertical arrangement of tree crowns, it is potentially useful in identifying strata that are biologically-related to processes that determine natural vertical stratification patterns. (C) 1998 Elsevier Science B.V.