Browsing by Subject "INCREMENT"

Sort by: Order: Results:

Now showing items 1-2 of 2
  • Tian, Xianglin; Sun, Shuaichao; Mola-Yudego, Blas; Cao, Tianjian (2020)
    Key message We propose a methodology to develop a preliminary version of a growth model when tree-level growth data are unavailable. This modelling approach predicts individual tree growth using only one-time observations from temporary plots. A virtual dataset was generated by linking the whole stand and diameter distribution models. The individual tree model was parameterized using Bayesian calibration and a likelihood of diameter distributions. Context A key component of tree-level growth and yield prediction is the diameter increment model that requires at least two different points in time with individual tree measurements. In some cases, however, sufficient inventory data from remeasured permanent or semitemporary plots are unavailable or difficult to access. Aims The purpose of this study was to propose a three-stage approach for modelling individual tree diameter growth based on temporary plots. Methods The first stage is to predict stand dynamics at 5-year intervals based on stand-level resource inventory data. The second stage is to simulate diameter distribution at 5-year intervals using a Weibull function based on tree-level research inventory data. The final stage is to improve the reliability of individual tree diameter estimates by updating parameters with Bayesian calibration based on a likelihood of diameter distributions. Results The virtual-data-based diameter increment model provided logical patterns and reliable performances in both tree- and stand-level predictions. Although it underestimated the growth of suppressed trees compared with tree cores and remeasurements, this bias was negligible when aggregating tree-level simulations into stand-level growth predictions. Conclusion Our virtual-data-based modelling approach only requires one-time observations from temporary plots, but provide reliable predictions of stand- and tree-level growth when validated with tree cores and whole-stand models. This preliminary model can be updated in a Bayesian framework when growth data from tree cores or remeasurements were obtained.
  • Luoma, Ville; Yrttimaa, Tuomas; Kankare, Ville; Saarinen, Ninni; Pyorala, Jiri; Kukko, Antero; Kaartinen, Harri; Hyyppa, Juha; Holopainen, Markus; Vastaranta, Mikko (2021)
    Tree growth is a multidimensional process that is affected by several factors. There is a continuous demand for improved information on tree growth and the ecological traits controlling it. This study aims at providing new approaches to improve ecological understanding of tree growth by the means of terrestrial laser scanning (TLS). Changes in tree stem form and stem volume allocation were investigated during a five-year monitoring period. In total, a selection of attributes from 736 trees from 37 sample plots representing different forest structures were extracted from taper curves derived from two-date TLS point clouds. The results of this study showed the capability of point cloud-based methods in detecting changes in the stem form and volume allocation. In addition, the results showed a significant difference between different forest structures in how relative stem volume and logwood volume increased during the monitoring period. Along with contributing to providing more accurate information for monitoring purposes in general, the findings of this study showed the ability and many possibilities of point cloud-based method to characterize changes in living organisms in particular, which further promote the feasibility of using point clouds as an observation method also in ecological studies.