Assessing tree effect on total soil carbon in agroforestry parklands systems along a rainfall gradient in Burkina Faso (West Africa)

Trees contribution in improving soil carbon is well established, but few works addressed how this was affected by a climatic gradient. This research investigated effects of Vitellaria paradoxa C. F Gaertn and Parkia biglobosa (Jacq.) Benth on total soil carbon in parklands along a rainfall gradient for recommendations of tree species which better improve soil carbon under specific climatic conditions for parklands adaptation to climate change. Total soil carbon at topsoil and subsoil layers measured using spectrophotometry infrared method, was higher when rainfall increased and were respectively (1.598 ± 0.040; 1.033 ± 0.022; 0.834 ± 0.014; 0.857 ± 0.016%). It was higher at topsoil (0.529 ± 0.015%) and subsoil (0.282 ± 0.019%) under V. paradoxa when rainfall decreased while it was higher under P. biglobosa and V. paradoxa when rainfall increased slightly. Its improvement was higher under V. paradoxa and P. biglobosa when rainfall respectively decreased and increased. A decrease trend of total soil carbon under both tree species from trunk to outside the canopy whatever rainfall levels and soil layers was observed. Tree species choice could play an important role in improving total soil carbon and crop productivity according to rainfall level for parklands adaptation to climate change.

Analysis of Taper Functions for Larix olgensis Using Mixed Models and TLS

Terrestrial laser scanning (TLS) plays a significant role in forest resource investigation, forest parameter inversion and tree 3D model reconstruction. TLS can accurately, quickly and nondestructively obtain 3D structural information of standing trees. TLS data, rather than felled wood data, were used to construct a mixed model of the taper function based on the tree effect, and the TLS data extraction and model prediction effects were evaluated to derive the stem diameter and volume. TLS was applied to a total of 580 trees in the nine larch (Larix olgensis) forest plots, and another 30 were applied to a stem analysis in Mengjiagang. First, the diameter accuracies at different heights of the stem analysis were analyzed from the TLS data. Then, the stem analysis data and TLS data were used to establish the stem taper function and select the optimal basic model to determine a mixed model based on the tree effect. Six basic models were fitted, and the taper equation was comprehensively evaluated by various statistical metrics. Finally, the optimal mixed model of the plot was used to derive stem diameters and trunk volumes. The stem diameter accuracy obtained by TLS was >98%. The taper function fitting results of these data were approximately the same, and the optimal basic model was Kozak (2002)-II. For the tree effect, a6 and a9 were used as the mixed parameters, the mixed model showed the best fit, and the accuracy of the optimal mixed model reached 99.72%.The mixed model accuracy for predicting the tree diameter was between 74.22% and 97.68%, with a volume estimation accuracy of 96.38%. Relative height 70 (RH70) was the optimum height for extraction, and the fitting accuracy of the mixed model was higher than that of the basic model.

Assessment of continuous distribution of wood properties from a low number of samples: Application to the variability of modulus of elasticity between trees and within a tree

The aim of this study was to propose an alternative non-deterministic and non-parametric technique for describing continuous variation in modulus of elasticity (E) within and between stems. The material studied consisted of hybrid Eucalyptus (Eucalyptus urophylla×Eucalyptus grandis) stems felled at the age of 59 months. Samples for measuring E were taken along a diameter slab at 1.30 m above ground. The results showed that the proposed reconstruction technique is consistent compared to results from other studies on Eucalyptus. E increases from pith to bark, following a polynomial distribution. Local and tree-averaged E increased with cambial age, following a sigmoidal profile that can be described with five characteristic parameters (E at pith, E at inflection point, E after inflection point, cambial age when latency period ends, and cambial age at inflection point). The tree contributes little to the total variation. The most important changes in E value were found with increasing radial position, with this effect eight-fold more important than the tree effect.

Vertical trends in maximum branch diameter in two mixed-species spacing trials in the central Oregon Cascades

The influence of spacing and competitor species on vertical trends in maximum branch diameter, the thickest branch per whorl, was assessed in two central Oregon spacing studies. One study involved a mix of Pinus contorta Dougl. ex Loud. and Pinus ponderosa Dougl. ex Laws., the other a mix of Abies grandis (Dougl. ex D. Don) Lindl. and P. ponderosa. Impacts of autocorrelation became statistically insignificant after introduction of a single random tree effect. Although tree variables such as diameter, height, and crown length were able to account for most stand conditions, models with explicit treatment variables representing spacing and species composition were superior. All profiles of maximum branch diameter were curvilinear and widened with increasing spacing and tree relative height. For trees in mixtures, maximum branch diameter profiles of dominant and subordinate species were wider and thinner, respectively, than the same species in pure stands at the same spacing. However, as spacing increased, profiles of the subordinate species in mixtures had a greater response than those in adjacent pure plots and in the dominant species in the mixture. In contrast, the dominant species had a larger spacing response in the pure plots than in mixed plots.