Exploring stand and tree variability in mixed Nothofagus second-growth forests through multivariate analyses

Abstract

Second-growth forests of Nothofagus obliqua (roble), N. alpina (raulí) and N. dombeyi (coihue), known locally as RO-RA-CO forest type, are among the most important natural mixed forest types of Chile. Several studies have identified a wide range of factors that could influence both stand and tree variability found in these forests. To better characterize potential tree-and stand-level factors that are associated with RO-RA-CO variability, and that are available in typical forest inventories, several unsupervised multivariate statistical methods were evaluated: 1) non-metric multidimensional scaling (NMDS); 2) principal coordinates analysis (PCoA); and 3) principal component analysis (PCA). The data used in this study originated from a sample of 158 plots consisting of two plot networks that covered the full geographic area of the RO-RA-CO forest type in Chile. We found that site productivity and growth zones did not explain the differences within the sampled population. However, stand development stages, tree-to-tree competition, and tree-size attributes were critical variables with a high percentage of variance explained using PCA, ranging from 61 % to 67 %. In addition, for the PCoA analysis, the variable stand density is important, with ~78 % variance explained.

Stand-Level Components of a Growth and Yield Model for Nothofagus Mixed Forests from Southern Chile

“…The similarity on growth behaviors of N. alpina and N. dombeyi [31] and the reliability of stand-level projections presented in this study justified the grouping of these species into a single cohort. In addition, there is evidence of low differentiation among these species, as reported in a multivariate analysis that used the same dataset from the current study [26] and from other authors indicating that stands dominated by either N. alpina or N. obliqua do not greatly differ in the total basal area or canopy height [30]. While it could be useful to have individual stand models for each of the Nothofagus species for further granularity, the present limitations of the dataset (which has not adequately represented each species) is likely to affect the accuracy of the final fitted models.…”

“…Dominant height (HD) is the average total height of the thickest 100 trees per hectare. Site index (SI) is the stand dominant height at 20 years (see [26] for further details). Additionally, for each of the cohorts, basal area for Nothofagus and companion species (BAN and BAC, respectively, m 2 ha −1 ), and number of trees of Nothofagus and companion species (NHAN and NHAC, respectively, trees ha −1 ) were calculated.…”

“…Finally, the proportion of basal area and number of trees of Nothofagus (PBAN, PNHAN) and companion species (PBAC, PNHAC) were also obtained. To study the effect of geographic location in growth and productivity, all plots were assigned to their growth zone (ZONE) (further details on zoning are presented in [26]).…”

“…To predict basal area for the two cohorts, BAN and BAC, this study fitted two independent models. All three Nothofagus species were combined into the same cohort based on reported low levels of differentiation between the species [26]. Given the limitation of the data, the TP1 and TP2 plots were used as training data, whereas only PP plots were used as validation data.…”

Prediction Comparison of Stand Parameters and Two Ecosystem Services through New Growth and Yield Model System for Mixed Nothofagus Forests in Southern Chile

“…In addition, dom-inant age at breast height (AGE, years) and dominant height (HD, m) were obtained with the average of the thickest 100 trees per hectare. Site index (SI) was estimated using dominant height-site models previously reported by Moreno et al [16]. All plots were assigned a growth zone (ZONE 1, 2, 3, and 4), according to Moreno et al [16] (see Figure 1).…”