Abstract
ABSTRAT The first step for constructing models of tree growth and yield is site quality assessment. To estimate this attribute, several methodologies are available in which site index (SI) is a standard one. However, this approach, that uses height at a reference age of trees, can be simplified if age is replaced by another reference variable easier to measure. In this case, the diametric site index (DSI) represents the mean height of dominant trees at a reference mean diameter at breast height. The aim of this work was to develop DSI in pure and mixed Nothofagus alpina and N. obliqua forests, and compare these models with the classical proposals based on height-age variables, within the temperate forest of northwestern Patagonia from Argentina, South America. Data originated from temporary plots and stem analyses were used. Tree age and diameter at breast height were obtained from each plot and used for establishing DSI family functions, following the guide-curve methodology. Site classes were proportionally represented among DSI curves of 17.0, 21.5, 26.0, 30.5 and 35.0 m of dominant tree height. Reference diameter instead of reference age can be cautiously used in order to fit site index models.
Highlights
Forest stand productivity is largely defined as site quality which expresses the growth potential of the species, and it is influenced mainly by forest soils (SKOVSGAARD and VANCLAY, 2008; AVERY and BURKHART, 2015)
Different methodologies exist to determine site quality according to employed biometric variables, and one of the most used methods for regular stands are based on indirect parameters using the average dominant height of the stand (BINOTI et al, 2012)
Dominant height growth is considered one of the best indicators, it is possible to relate it with the productivity of each site (MONSERUD, 1984), and in addition be correlated with growth in volume (DONOSO, 1981) with scarce influence of tree density within a wide range of conditions (DANIEL et al, 1982; AVERY and BURKHART, 2015)
Summary
Forest stand productivity is largely defined as site quality which expresses the growth potential of the species, and it is influenced mainly by forest soils (SKOVSGAARD and VANCLAY, 2008; AVERY and BURKHART, 2015). It is not possible to make reliable decisions without silvicultural references, as site quality and other stand conditions and variables which directly influences tree growth (DANIEL et al, 1982). Dominant height (hdom) growth is considered one of the best indicators, it is possible to relate it with the productivity of each site (MONSERUD, 1984), and in addition be correlated with growth in volume (DONOSO, 1981) with scarce influence of tree density within a wide range of conditions (DANIEL et al, 1982; AVERY and BURKHART, 2015)
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