François Houllier

Linking growth modelling to timber quality assessment for Norway spruce

Abstract The aim of this paper is to propose a consistent framework for analyzing the influence of silviculture, site quality and, to some extent, genetics on the wood production of Norway spruce from both a quantitative and a qualitative point of view. Tree and stand volume, stem taper, wood basic density, proportion of juvenile wood as well as knottiness are considered as the result of growth processes. Two complementary applications are presented. (1) An average-tree growth model which is built of several interrelated processes: site quality has an effect on height growth and hence on all other tree and stand characteristics; crown development is driven by height growth and controlled by stand density; stand basal area increment is predicted from empirical rules; tree basal area increment is then distributed along the stem. (2) A model that aims at assessing timber quality of a standing tree from usual inventory measurements such as tree age, height and diameter at breast height: growth equations are used to reconstruct the past growth of a tree and to predict its current internal structure, namely ring distribution. Both models are linked to allometric equations that estimate the characteristics of branchiness, to densitometric models that predict wood basic density from ring distribution and to a software that simulates the grading of any board located in a stem whose morphology is known in detail. The aim of these models is not to make precise quantitative predictions but to show how different pieces of knowledge of silviculturists, forest biometricians and wood scientists may be brought together in simulation software in order to help forest managers and wood industrialists to make decisions. This framework could be extended to other fast-growing coniferous species.

A model simulating above- and below-ground tree architecture with agroforestry applications

Modelling plant growth and architecture requires two consecutive and complementary approaches. The first is a qualitative botanical analysis, in which the development sequence of a tree is studied by the identification of various levels of organisation and of homogeneous subunits. All of these — architectural unit, axis, growth unit — follow particular growth processes which can be described by using the second approach, the quantitative analysis. Modelling of the functioning of meristems based upon stochastic processes has been carried out since 1980, in combination with a large amount of experimental work on temperate and tropical plants. Calculations involved in tree simulations from field data are based upon the probabilistic Monte Carlo method for the topological part and on analytical geometry for the morphological part. Computer graphics methods are then used to visualise the computed plant. Several sectors in agroforestry are concerned with application of such plant architecture modelling: tree growth and yield, radiative transfers, timber quality and mechanics, simulation of competition, interaction between plant morphology and physiology.

Ecological meaning and predictive ability of social status, vigour and competition indices in a tropical rain forest (India)

Abstract The aim of this paper is to assess and compare the ecological meaning and predictive ability of several competition indices, which belong to several types – tree vigour indices, tree social status indices, local density indices and spatial competition indices – and come from different disciplines – ecology, silviculture, growth and yield modeling. We consider the case of an upper canopy and light-demanding dipterocarp species, Vateria indica L., which is frequent and endemic in the low to medium elevation moist evergreen forests of the Western Ghats in South India. Multivariate analyses showed that most indices are closely correlated with each other, as well as with tree size itself because they share common information on tree social status. Some indices bore additional information on local stand density that is independent from tree social status. The index that most accurately predicted diameter at breast height (dbh) increment is a modified version of the Dawkins code. This index can be assessed in the field without any complicated measurements but it requires preliminary training and regular cross-checking in order to ensure reproducibility across time and among observers. These results are consistent with those obtained on other light sensitive evergreen species in French Guiana. There is a need to generalize such studies to other species and forests and to better assess the meaning and predictive ability of competition indices in relation to the ecological behavior of the species.