Maarten Nieuwenhuis

Retrieval of forest structural parameters using LiDAR remote sensing

In this paper, a literature overview is presented on the use of laser rangefinder techniques for the retrieval of forest inventory parameters and structural characteristics. The existing techniques are ordered with respect to their scale of application (i.e. spaceborne, airborne, and terrestrial laser scanning) and a discussion is provided on the efficiency, precision, and accuracy with which the retrieval of structural parameters at the respective scales has been attained. The paper further elaborates on the potential of LiDAR (Light Detection and Ranging) data to be fused with other types of remote sensing data and it concludes with recommendations for future research and potential gains in the application of LiDAR for the characterization of forests.

Biomass expansion factors for Sitka spruce ( Picea sitchensis (Bong.) Carr.) in Ireland

The assessment of a forest resource in national inventories provides a firm basis for the calculation of biomass and carbon (C) stocks of forests. Biomass expansion factors (BEFs) and conversion factors provide a robust and simple method of converting from forest tree stem volume to total forest biomass. These factors should be constructed on the basis of nationally specific data in order to take account of regional differences in growth rates, management practices, etc. The objective of this study is to improve the accuracy of biomass estimation by calculating a range of age-dependant BEFs from representative data that more accurately describe the allometry of present forests. The results from this study show that the allocation of biomass to compartments in forest stands and throughout a rotation varies considerably, and that the use of BEFs for the calculation of C stocks in forests of sub-timber dimensions is highly impractical.

A comparative analysis of kNN and decision tree methods for the Irish National Forest Inventory

Two non-parametric estimation techniques were tested in two study areas in Ireland. For each area, plot level estimates of standing volume per hectare and basal area per hectare were computed from the National Forest Inventory field data and combined with SPOT 4 XS satellite imagery and a digital elevation model to form a set of observations. These observations were then used to predict variables across the satellite image using k-Nearest Neighbour (kNN) estimation and a Random Forest algorithm. Comparisons between the two techniques were assessed based on the estimation errors primarily using the Root Mean Square Error (RMSE) and relative mean deviation (bias). In both study areas it was found that the RMSE was lower for kNN than for RF. Overall, the RMSEs and mean deviations were lower in Study Area 1 when compared to Study Area 2, largely due to a difference in the number of available NFI reference plots.

Site index of Sitka spruce (Picea sitchensis) in relation to different measures of site quality in Ireland

To examine the relationships between Sitka spruce (Picea sitchensis (Bong.) Carr.) site index and site quality variables, we sampled 201 Sitka spruce stands covering the entire range of sites supporting the growth of the species in Ireland. Site index varied significantly with climate and climate surrogate variables, some site quality variables, soil physical and chemical properties, edatopes (combinations of soil nutrient and moisture regimes), rotation types, provenance, and fertilizer regimes. We developed a series of models to predict site index using climate, site, soil physical and chemical properties, edaphic variables, and management factors as predictor variables. Soil nutrient regime (SNR) exhibited the strongest relationship of all variables examined in the study, explaining 51% of the variation in site index, with site index increasing with increasing SNR. We found that edaphic variables of soil moisture regime and SNR produced the best prediction of site index. The species showed the best dev...

Health and Safety Issues and Perceptions of Forest Harvesting Contractors in Ireland

Abstract The aim of this study was to examine the extent and severity of accidents and long-term health problems, and to evaluate perceptions of health and safety issues among forest harvesting contractors and sub-contractors in Ireland. A postal questionnaire was distributed to 450 forest harvesting (sub)contractors with the co-operation of the Irish Forestry Contractors Association (IFCA) and Coillte Teoranta (the State Forestry Company, referred to as Coillte). The questionnaire was completed and returned by 61 respondents. The majority of these were chainsaw, harvester and forwarder operators. The occurrence of an accident (requiring medical attention) in the last three years was reported by two respondents, while long-term health problems were reported by 23 (40%) of the respondents. Results showed that long-term health problems were not significantly correlated to age or training level. The two work elements in forest harvesting operations that were found to be most hazardous were operating a chainsaw and machine maintenance. When asked about the perceived dangers in the industry and the obstacles to improvements, 59% of the respondents identified harvesting work as dangerous, while 62% described financial pressure as the main barrier to improvements in safety, followed by the pressure of work (39%) and a lack of adequate training (36%). Suggestions on ways to improve the overall health and safety situation within forest harvesting included improved training and safety education (45%) and reduced work pressure (36%).

Assessment of tree response to drought: validation of a methodology to identify and test proxies for monitoring past environmental changes in trees

A thinning experiment stand at Avoca, Ballinvalley, on the east coast of the Republic of Ireland was used to test a developed methodology aimed at monitoring drought stress, based on the analysis of growth rings obtained by coring. The stand incorporated six plots representing three thinning regimes (light, moderate and heavy) and was planted in the spring of 1943 on a brown earth soil. Radial growth (early- and latewood) was measured for the purpose of this study. A multidisciplinary approach was used to assess historic tree response to climate: specifically, the application of statistical tools such as principal component and canonical correlation analysis to dendrochronology, stable isotopes, ring density proxy, blue reflectance and forest biometrics. Results showed that radial growth was a good proxy for monitoring changes to moisture deficit, while maximum density and blue reflectance were appropriate for assessing changes in accumulated temperature for the growing season. Rainfall also influenced radial growth changes but not significantly, and was a major factor in stable carbon and oxygen discrimination, mostly in the latewood formation phase. Stable oxygen isotope analysis was more accurate than radial growth analysis in drought detection, as it helped detect drought signals in both early- and latewood while radial growth analysis only detected the drought signal in earlywood. Many studies have shown that tree rings provide vital information for marking past climatic events. This work provides a methodology to better identify and understand how commonly measured tree proxies relate to environmental parameters, and can best be used to characterize and pinpoint drought events (variously described using parameters such as like moisture deficit, accumulated temperature, rainfall and potential evaporation).

Vegetative Propagation of Eucalyptus nitens Using Stem Cuttings

SYNOPSIS Eucalyptus nitens (Deane & Maiden) Maiden is an economically important Eucalyptus species with a broad natural range in Australia and has been identified as a priority fuelwood plantation species in Lesotho. Unlike most eucalypts, E. nitens is a shy seed bearer. This study was aimed at propagating Eucalyptus nitens using stem cuttings. These were taken seasonally from an 11-year-old E. nitens stand and three-year-old stock plants. Cuttings were prepared in a factorial combination of four types of media (viz. peat, sand, vermiculite and a 1:1:1 mixture of the three) and two hormone dipping treatments (viz. no dipping and dipping in Seradix No. 3 rooting powder containing 0,8% IBA). In the last experiment, 0,2% IBA was used. Rooting performance was evaluated under glasshouse conditions using a warm bench propagation unit. Adventitious root formation on cuttings of E. nitens was not effectively influenced by the application of IBA. Rooting of cuttings obtained from 11-year-old E. nitens decreased fr...

Trade in medicinal tree and shrub products in three urban centres in Kenya

As pressures on agricultural and rural land increase, forest products are becoming a main source of non-farm income for many rural and urban households in sub-Saharan Africa. The trading of wild harvested medicinal tree and shrub material, mostly sourced from natural forest stands, bush, and savannah woodland, is poorly documented, particularly in Kenya. This study (a) profiles the socio-economic characteristics of traders and key species traded and (b) identifies the supply chain and quantities of material stocked and traded and assesses the economic value of the trade. Trading in medicinal tree and shrub products constitutes an important source of income for households and is often the only income generator, as 60% of the traders stated that they had no additional income-generating activities. There is a wide range in the quantities of material stocked and sold. There are significant differences regarding quantities and pricing of material between traders by location and gender. The material that supplies the markets is almost exclusively sourced through collection from the wild with little or no indication of sustainable supply from cultivated sources. And as the total volume of material collected from the wild and traded is largely unknown and potentially much greater than previously thought, this raises serious concerns for the sustainability of natural resources. Further species-specific research on the trade of medicinals is required to evaluate the extent of threat to natural populations, to analyse the value chains for sustainable production and marketing, and to assess the economic and ecological benefits from cultivating medicinal tree and shrub species on smallholder farms.

The Effect of Calibration on the Accuracy of Harvester Measurements

Abstract Almost all timber in Ireland is harvested using mechanical harvesting heads. All new harvesters come equipped with computerized measurement systems. The objective of the research reported in this article was to assess the impact of calibration on the accuracy of harvester head measurement systems in Irish forestry conditions. The research was carried out on a site in Co. Cork. The harvester was a Timberjack 1270D with a 762C harvester head and the Timbermatic 300 control and measurement system. The harvester measurement system was assessed on its accuracy in measuring the length and volume of individual stems and logs in 9 check runs of 7 or 8 stems. The harvester head measurements were compared to values obtained by caliper-and-tape measurements. The main point that can be taken from this research is that regular calibration will greatly improve the accuracy of the harvester measurement system. After calibration, length measurement by the harvester measurement system of individual logs was very accurate, while volume measurement was unsatisfactory for the pulp log assortment. The differences between the harvester measurements and the caliper-and-tape measurements fluctuated greatly, varying from positive to negative differences within a check run, even after calibration. These fluctuations could indicate an inherent problem associated with the design of the calibration procedure, as the positive and negative differences cancel each other out and the calibration, based on mean values, appears to indicate accurate measurements. More work needs to be done on reducing to impact of the roughness and branchiness of smaller dimension logs on the accuracy of diameter and length measurements in Irish conditions.

An Evaluation and Comparison of Mechanised and Manual Tree Planting on Afforestation and Reforestation Sites in Ireland

Abstract Recent labour shortages and rapid increases in labour costs in Irish forestry have directed attention to mechanised, containerised tree planting systems as an alternative to the traditional manual planting of bare-rooted stock. The objective of this study was to compare mechanised planting with manual operations, on both reforestation and afforestation sites, using Sitka spruce (Picea sitchensis (Bong.) Carr.) plants in three container types (i.e. hard container, root trainer, fen container). The Bräcke tree planting machine was selected for the study, as it is capable of handling a wide range of site conditions and a variety of plant types and sizes. A qualitative analysis of the collected data showed that, in general, manual planting scored significantly higher than mechanised planting for plant position and planting quality. However, the quality of planting resulting from mechanised operations was well within acceptable operational requirements. On the reforestation site, plant growth after one growing season was investigated. No overall significant differences in height growth and root collar diameter increment were found in the first growing season between mechanised and manual planting operations. Plants grown in ‘fen containers’ had the highest relative increase in height growth and root collar diameter, irrespective of planting method. The results showed that the Bräcke planting machine was capable of planting a range of containerised plants to an acceptable standard on both reforestation and afforestation sites. Further research to optimise the combination of machine, plant size and container type should result in improvements in both the quality and productivity of the planting operations.