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Euan G. Mason 《New Forests》2013,44(6):951-959
Forest managers often estimate gains from site preparation treatments during plantation establishment using the reduction in time required to grow a given yield compared with a control (when treatments are employed compared to when they are not employed). Two types of responses to treatments have been identified; temporary changes that offer a time gain that becomes constant after site changes cease to affect growth (type I) and persistent changes that result in a continuously increasing time gain throughout a crop rotation (type II). An alternative to this statistical approach is to use a hybrid physiological/mensurational model of forest production that explicitly represents growth processes underlying observed responses. We compared a regional hybrid growth and yield model with a purely mensurational one for representing observed responses in two site preparation experiments in the Central North Island region of New Zealand. Simulations were initiated with crop measurements following the first 5 years of growth in the two experiments, along with reasonable estimates of impacts of site preparation on sites and growth processes. These estimates of site changes were made prior to the simulation and were not varied after simulation results were known. The hybrid model successfully predicted a type I response following weed control and a type II response following soil cultivation, while the mensurational model failed to represent the type II response. Growth in basal area without soil cultivation was underestimated by 3 m3 ha?1, leading to an overestimate of gain. A hybrid modelling approach is therefore an alternative to a purely statistical time gain analysis that can provide useful estimates of gain so long as changes to sites and growth processes made by site preparation are well understood. 相似文献
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Productivities of monoclonal plots and clonal mixtures of 10 radiata pine (Pinus radiata D. Don.) clones were compared in a trial established in 1993 at Dalethorpe, Canterbury, New Zealand. Ten monoclonal and one mixture of the 10 clones were planted in a complete randomised block design with three replications using 40-tree plots (un-thinned, pruned to 2.5 m, stocking of 1250 stems per hectare). The study was conducted to determine if mode of deployment (monoclonal versus clonal mixture) affected overall productivity and how or if each clone was affected by mode of deployment. 相似文献
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Allometric equations predict tree seedling biomass from non-destructively measured variables such as stem diameter (D), height (H) and seedling silhouette area (A), measured by digital imaging. This study investigates whether one general allometric equation can predict biomass of radiata
pine (Pinus radiata D.Don) seedlings grown under three levels of photosynthetic photon flux density (PPFD). It also identifies which commonly
used variables (A, D
2
H or D
2) were the best for predicting seedling biomass under these conditions. Radiata pine seedlings were grown with constant daytime
(12 h d−1) PPFD = 500, 250 or 125 μmol m−2 s−1 for 11 weeks. Seedlings were randomly selected every 10 d for measurement. Analysis of covariance tested whether the relationship
between seedling biomass and A, D
2
H or D
2 varied for each PPFD level. PPFD levels influenced the relationship between biomass and A, D
2
H or D
2. As a result, “full” allometric models which varied with PPFD levels were more accurate and precise at predicting biomass
than “reduced” models which did not vary with PPFD level, although a “reduced” model using D
2 also performed well. 相似文献
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Daniel Bloom Paul A. Butcher Andrew P. Colefax Euan J. Provost Brian R. Cullis Brendan P. Kelaher 《Fisheries Management and Ecology》2019,26(4):311-318
The issues surrounding illegal, unregulated and unreported fishing, and that of abandoned, lost and discarded fishing gears, leading to ghost fishing, are intensifying. Estuarine crab trapping is likely subject to high levels of illegal and potential ghost fishing, because it also has good economic incentives regarding potential catch, low gear acquisition costs and accessible fishing grounds. To improve the efficiency and effectiveness of fisheries monitoring, control and surveillance operations, the efficacy of small consumer‐grade drones for sighting traps in an estuary in NSW, Australia, was tested. Twelve sets of two flights were undertaken at 20 and 30 m altitude over a 600‐m stretch of estuary for 5 days to quantify the detectability of submerged mesh traps of three different mesh colours. The drone was able to detect the majority of traps efficiently, with depth in relation to water clarity being the main factor affecting detection. In shallow water, detection rates were high for all mesh colours, but in the slightly deeper placements, orange traps were more readily detected. This study demonstrates that drones could be an efficient and reliable tool for rapidly assessing areas for illegal and derelict traps and can be supplemented into land or vessel‐based fisheries operations. 相似文献
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Advances in modelling and decision support systems for vegetation management in young forest plantations 总被引：1，自引：0，他引：1
The two most common forest vegetation management objectivesare to (1) minimize resource competition, and (2) to developmethods for managing specific weed species. This paper reviewsrelevant models and decision support systems for assisting inachieving these objectives. The aim of reducing resource competitionis to increase crop-tree growth and survival. Several modellingapproaches have been applied to this problem and these generallyestimate crop survival and growth benefits following some formof generalized weed control. Linkages with models of older treecrops are needed for comparing vegetation management strategiesin the context of complete silvicultural regimes. More refinedindividual tree models use competition indices to estimate thequantity of weed vegetation within the growing space aroundeach tree. The indices reflect resource use by the weeds andare sensitive to changes in weed growth over time and to theapplication of specific vegetation management treatments. Hybridand process-based models have the potential to provide moregeneralized models of inter-specific competition, but theirusefulness for forest practitioners has yet to be proven. Someforest vegetation management problems require a more detailedunderstanding of the biology and ecology of a specific species.In this case, different modelling approaches that consider overallweed population dynamics, distribution or spread may be appropriate. 相似文献
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Euan G. Mason Emma Holmström Urban Nilsson 《Scandinavian Journal of Forest Research》2018,33(2):147-154
Precision and bias of a model designed to predict site index of Scots pine (P. sylvestris L.) from site variables in Sweden were tested using data from 1985 inventory plots. The model was biased and relatively imprecise (standard error = 3.7 m). A new model was constructed using a fitting subset of data, employing sums of mean monthly estimates of photosynthetically active radiation modified by local monthly climatic conditions as a primary independent variable. The best model used day-time temperature modifiers to calculate potential radiation-use efficiency. Modifiers for vapour pressure deficit and soil water did not improve the model. Elevation, distance to the sea, and phytometer indicators of nutritional fertility added small but significant improvements to the predictions. The final model had a standard error of 2.06 m for predictions of site index that ranged from 18 to 30 m at age 100. When applied to a validation subset of plots the model displayed a standard error of 2.09 m and very similar residual patterns to those observed during fitting. The new model represents a significant improvement over the older model, and further improvements may be feasible when historical climatic estimates and a higher resolution digital elevation model become available. 相似文献
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