Hybrid height growth and survival model for juvenile Eucalyptus globoidea (Blakely) and E. bosistoana (F. Muell) in New Zealand

Juvenile plantation forest dynamics are complex but understanding and predicting early growth and survival enables effective management. Information provided by traditional growth and yield models is an essential input in decision-making processes for managing planted forests. They are generally fitted using permanent sample plot data, thus they are robust and simple. However, the introduction of explanatory factors affecting tree development (e.g. wetness index, morphometric protection index etc.) not only to improve the quality of predictions but also to add useful information underpinning forest management decisions (e.g. species choice, silvicultural practice etc.). In this study, three different hybrid growth and yield approaches for modelling height growth and survival were tested, culminating in models being developed for Eucalyptus globoidea and E. bosistoana by integrating climatic, edaphic and topographic factors. Permanent sample plot data (n = 84) were used to develop these models. The results showed that inclusion of topographic and climatic factors alongside potentially usable light sum (PULS) slightly improved both height and survival prediction of both species compared to time-based models (TA). The ranking and alignment of coefficient of determination for height models were PULS = 0.79 > 0.77 > TA = 0.75 and survival models were PULS = -0.47 > TA = -0.45, respectively. Both of the species were site-sensitive, especially to soil moisture and wind speed. This sensitivity also indicated the optimal requirements for height growth and survival for these species. All three modelling approaches can be applied for juvenile Eucalyptus plantations in any given site-specific case, based on available information and management demands. The models developed in this study can help forest managers make better decisions for new plantation establishment and management.

Automated summary

The dynamics of juvenile plantation forest are complex, but understanding early growth and survival is crucial for effective management. Traditional growth and yield models provide essential information for decision-making in managing planted forests. The integration of explanatory factors such as wetness index and morphometric protection index can improve predictions and support forest management decisions. In this study, hybrid growth and yield approaches were tested for Eucalyptus species, with topographic and climatic factors enhancing height growth and survival prediction. These models can assist forest managers in making informed decisions for plantation establishment and management.