Results 1 - 10 of 1621
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[en] Aim of study: To evaluate the impact of Cistus ladanifer L. (rockrose) tannins on ruminal degradability and fermentation characteristics and the use of polyethylene glycol (PEG), as feed additive, to mitigate the anti-nutritional effects of rockrose tannins. Material and methods: Aerial parts of rockrose plants were harvested in March, freeze dried and divided in 4 subsamples which were treated with 0, 25, 50 and 75 g of PEG/kg of dry matter (DM). The mixtures were analysed for chemical composition including total phenolics, total tannins and condensed tannins. In situ rumen organic matter (OM) and N rumen degradability was evaluated using three rumen-cannulated rams and ruminal fermentation pattern (volatile fatty acids (VFA), gas production) was evaluated in vitro using a Rumen Simulation Technique (RUSITEC) apparatus. Main results: In situ experiment indicated that the effective degradability of the OM and N increased linearly (p<0.05) with PEG inclusion due to an increase of the degradation rate (p<0.05). RUSITEC data indicated that substrate disappearance and gas and VFA production increased linearly (p<0.05) with PEG inclusion. Research highlights: Inclusion of PEG to C. ladanifer feed was effective to prevent the anti-nutritive effects of tannins. Thus, the use of PEG as feed additive can promote a better utilization of this shrub by ruminants.
[en] Aim of study: In this study we applied 3D point clouds generated by images obtained from an Unmanned Aerial Vehicle (UAV) to evaluate the uniformity of young forest stands. Area of study: Two commercial forest stands were selected, with two plots each. The forest species studied were Eucalyptus spp. and Pinus taeda L. and the trees had an age of 1.5 years. Material and methods: The individual trees were detected based on watershed segmentation and local maxima, using the spectral values stored in the point cloud. After the tree detection, the heights were calculated using two approaches, in the first one using the Digital Surface Model (DSM) and a Digital Terrain Model, and in the second using only the DSM. We used the UAV-derived heights to estimate an uniformity index. Main results: The trees were detected with a maximum 6% of error. However, the height was underestimated in all cases, in an average of 1 and 0.7 m for Pinus and Eucalyptus stands. We proposed to use the models built herein to estimate tree height, but the regression models did not explain the variably within the data satisfactorily. Therefore, the uniformity index calculated using the direct UAV-height values presented results close to the field inventory, reaching better results when using the second height approach (error ranging 2.8-7.8%). Research highlights: The uniformity index using the UAV-derived height from the proposed methods was close to the values obtained in field. We noted the potential for using UAV imagery in forest monitoring.
[en] Aim of the study: To analyse the effectiveness of thinning on tree growth, forest structure and microclimatic variables along seven years after cuttings in a secondary Nothofagus antarctica forest in Southern Patagonia. Area of study: Five hectares of homogeneous stand of secondary forests (54º15’46” SL, 66º59’41” WL) in Tierra del Fuego, Argentina. Material and methods: One control and two thinning levels were established, and forest structure, growth, crown dynamic and microclimate variables in long-term permanent plots were evaluated. Main comparisons were made using multiple ANOVAs. Main results: Intensive thinning in secondary forests allowed to increase tree individual growth rates by doubling the radiation levels at the understory level that enhances the silvopastoral management. These forests showed a desirable resilience to the forest interventions and natural disturbances (e.g. heavy defoliator attack), with a rapid reaction in the canopy cover growth. Research highlights: Monitoring of thinning for silvopastoral management must include easy and cheap measuring variables, e.g. diameter growth as a proxy for timber production objectives and hemispherical photos (crown cover and radiation) as a proxy for pasture production. Long-term monitoring allowed to identify reliable indicators that assist new sustainable management alternatives.
[en] Aim: Several national forest inventories use a complex plot design based on multiple concentric subplots where smaller diameter trees are inventoried when lying in the smaller-radius subplots and ignored otherwise. Data from these plots are truncated with threshold (truncation) diameters varying according to the distance from the plot centre. In this paper we designed a maximum likelihood method to fit the Weibull diameter distribution to data from concentric plots. Material and methods: Our method (M1) was based on multiple truncated probability density functions to build the likelihood. In addition, we used an alternative method (M2) presented recently. We used methods M1 and M2 as well as two other reference methods to estimate the Weibull parameters in 40000 simulated plots. The spatial tree pattern of the simulated plots was generated using four models of spatial point patterns. Two error indices were used to assess the relative performance of M1 and M2 in estimating relevant stand-level variables. In addition, we estimated the Quadratic Mean plot Diameter (QMD) using Expansion Factors (EFs). Main results: Methods M1 and M2 produced comparable estimation errors in random and cluster tree spatial patterns. Method M2 produced biased parameter estimates in plots with inhomogeneous Poisson patterns. Estimation of QMD using EFs produced biased results in plots within inhomogeneous intensity Poisson patterns. Research highlights:We designed a new method to fit the Weibull distribution to forest inventory data from concentric plots that achieves high accuracy and precision in parameter estimates regardless of the within-plot spatial tree pattern.