Harvesting and comparative thinning alternatives in Gmelina arborea plantations

Harvesting of Gmelina arborea presents some unique considerations due to the environments in which it is grown and to the growing characteristics of the species. On low, wet sites, soil compaction is an important consideration when planning for harvests. Gmelina root systems tend to be superficial and special care is needed when thinning to minimize root damage. Clear felling for pulpwood is done primarily with chainsaws, moving the wood to roadside with forwarders, wheel tractors and trailers or small highlead cable systems. Pulpwood needs to be manually bunched for ease of collection by forwarders. Gmelina is an increasingly important species for solid wood products, both lumber and veneer, and plantation management for sawtimber requires thinnings to improve residual tree form and to increase sawlog diameters. Precommercial thinning along with early commercial thinning can significantly increase sawlog productivity when compared with the use of commercial thinnings only. Tree-length logging will become a common method for wood extraction in final harvests where both sawlogs and pulpwood are produced. Skidders mounted with logging arches are effective for wood extraction after felling trees with chainsaws. Comparative yield calculations are presented for veneer log production with two thinning systems. Palabras Clave: Aserrío, Cable de arrastre, Fuste entero, Precomercial, Transportador Resumen. La cosecha de Gmelina arborea implica tener consideraciones especiales, debido al ambiente en donde se planta y a las características de crecimiento de la especie. La compactación del suelo es una consideración importante al planear la cosecha en sitios bajos y húmedos. Hay que tener un cuidado especial durante las entresacas con el fin de minimizar daños a las raíces, las cuales tienden a crecer en forma superficial. La tala rasa para la producción de madera para pulpa se hace principalmente con motosierras, trasladando la madera al camino con portatrozas, tractores y remolques, o por pequeños sistemas con cable de arrastre. Se deberá arrumar la madera para pulpa para facilitar su extracción por los tractores portatrozas. La gmelina es una especie que cada día se hace más importante para la producción de madera sólida, al igual que para madera aserrada, como para enchapes. Se requieren entresacas con el propósito de mejorar la forma de los árboles residuales y aumentar sus diámetros. El empleo de las entresacas precomerciales junto con entresacas comerciales tempranas pueden mejorar la productividad de madera de aserrío en forma significativa, en comparación con el empleo de entresacas comerciales, únicamente. La extracción de fustes enteros será un método común para la cosecha final, donde se produce madera para pulpa y aserrío. Los tractores articulados con arcos de arrastre montados son efectivos para la extracción después de la tala con motosierra. Se presentan cálculos de los rendimientos comparativos para madera para enchapes utilizando dos regímenes de entresacas.     

Biomass harvesting in Eucalyptus plantations in Western Australia

Australia is at an early stage of exploring the use of forest biomass to generate energy. This study evaluated the biomass yield and the productivity rates of equipment for harvesting biomass in a poor-quality eucalypt plantation. The operation consisted of a tracked feller-buncher, grapple skidder and mobile chipper. Time study methods were used to measure the harvesting operation. A multiple regression model was constructed to predict skidding productivity. Biomass production was 63.9 t ha^?1 based on the recorded load weight of eight trucks. Delays were documented and analysed. The average delay for all equipment was about 30% of working time. The study results will help guide biomass harvesting managers to estimate productivity and cost of similar operation sites.     

A mathematical model for generating land-use allocation alternatives for agroforestry systems

Agroforestry has been considered a viable land-use system particularly in the tropical regions. In developing or designing agroforestry systems, various concerns have to be addressed namely: (1) economic; (2) biological and physical; and (3) silvicultural and ecological considerations. This paper addresses these concerns from an interdisciplinary perspective. A land-use allocation model which ensures the simultaneous consideration of these concerns is proposed.     

Farming carbon: an economic analysis of agroforestry for carbon sequestration and dryland salinity reduction in Western Australia

The widespread removal of native trees from the agricultural zone and replacement with annual crops and pastures is a major cause of dryland salinity in Australia. It has been recognised that a large proportion of the landscape needs to be replanted to trees to prevent further salinisation. However, for much of the agricultural zone, agroforestry is not an option due to lack of species that can viably generate the products currently demanded by the market. The emerging carbon market may provide a new agroforestry option for landholders, through carbon sequestration. This analysis assesses the viability of growing trees for the purpose of selling carbon credits, from a landholder’s perspective. Benefits of trees in preventing the onset of dryland salinity are accounted for. Two regions in Western Australia; a low rainfall (330 mm/year) region and a medium rainfall (550 mm/year) region, are analysed. At the expected carbon price of A$15/tCO₂-e, growing trees for carbon is not a viable alternative for landholders in the low rainfall region, due to low sequestration rates. In the medium rainfall region, growing trees for carbon and timber is a viable alternative; however the opportunity costs of land mean the carbon price would still need to be higher than expected for growers to choose this alternative. Accounting for the salinity prevention benefits makes growing trees a more attractive investment for landholders in both regions. However in both regions, even after accounting for salinity benefits, the price of carbon would need to be A$25–A$46/tCO₂-e higher than expected to make growing trees a worthwhile investment.     

Components of the water balance for tree species under evaluation for agroforestry to control salinity in the wheatbelt of Western Australia

The soil water balance technique was used to study evaporation from two fodder tree species, tenEucalyptus species and annual pasture over a three year period after planting in the Western Australian wheatbelt. Evaporation is the total water loss by the processes of transpiration, evaporation from the soil surface and evaporation of water intercepted by plant canopies.Evaporation from both fodder trees and from seven of theEucalyptus species was greater than from pasture for one or more of the study years. The maximum difference in evaporation between trees and pasture was 82, 84 and 70 mm in the first, second and third study years, respectively. Higher evaporation from trees was associated with greater depletions in soil water than occurred beneath pasture. Upward movement of water from wet soil beneath the root zone was found under trees, with a maximum flux of 30 mm observed over a one year period beneathE. camaldulensis.The water use efficiency of fodder trees was significantly higher than for mostEucalyptus species, due to greater yields from fodder trees. Biomass production was found to be a good indicator of the water use of eucalypts over the first two years of growth, but the relationship between productivity and water use was found to differ for species with tree and mallee forms. In the third year of study, obvious differences in the relation between water use and yield were observed for some species of eucalypts with high evaporation.     

Identifying key factors affecting coffee leaf rust incidence in agroforestry plantations in Peru

Coffee leaf rust (CLR), caused by Hemileia vastarix, is one of the most serious diseases of coffee plantations and cause great losses in coffee production. We aimed to examine coffee varieties, shade, age of coffee plants, coffee plant density and soil properties in relation to CLR infection. To do this, we established a total of 75 plots in three agroforestry coffee plantations in the central Peruvian Amazon. We gathered data there in 2011 (dry season) on the presence/absence of CLR; coffee variety; age and density of coffee plants, and also took hemispherical photographs to determine canopy openness. In 2014 (wet season), we again gathered data on the same variables. In 2012, we collected soil samples from a subset of the plots. At all plantations, coffee variety had a significant effect on CLR incidence, with the Catimor variety infected less frequently than Caturra. Coffee plant age had a significant positive effect on CLR incidence. Increasing coffee density also increased CLR incidence for some of the studied plantations/seasons. Comparing those plots from which data were collected in the dry and wet seasons, we found that CLR presence was significantly higher in the wet season. The effect of shade on CLR incidence was not clear. Catimor and Caturra varieties showed opposite trends of CLR incidence in response to shade quantity in most cases (Caturra variety CLR incidence was decreasing with shading increase and Catimor CLR incidence decreasing with decreasing shading). Finally, the soil properties did not affect CLR incidence.     

Evaluating a simple radiation/dry matter conversion model using data from Eucalyptus globulus plantations in Western Australia

A simple model that describes growth in terms of physical and physiological processes is needed to predict growth rates and hence the productivity of trees at particular sites. The linear relationship expected between absorbed photosynthetically active radiation (phi(pa), MJ m(-2)) and dry mass production (G(t)); i.e., G(t) = epsilonphi(pa), where epsilon is the radiation utilization coefficient, was fitted to three years' data from five Western Australian Eucalyptus globulus Labill. plantations for which monthly growth measurements, leaf area indices, weather data and soil water measurements were available. Reductions in growth efficiency relative to absorbed photosynthetically active radiation were associated with high vapor pressure deficits (D, kPa) so the relationship between monthly aboveground biomass increments and D was used to calculate utilizable phi(pa). Plotting cumulative aboveground growth against utilizable phi(pa) gave strong linear relationships with slope epsilon. Values of epsilon ranged from 0.93 to 2.23 g dry mass MJ(-1) phi(pa). The variation could not be explained either in terms of soil water content in the root zones, because all plantations appeared to have access to groundwater, or in terms of soil chemistry. A value of epsilon approximately 2.2 is considered near the maximum likely to be applicable to Eucalyptus plantations. An interesting peripheral finding was a strong relationship between allometric ratios and soil phosphorus; this, if confirmed elsewhere, will be of considerable value in converting biomass increments to wood production. There was also a strong negative relationship between the average ratio of leaf/total aboveground biomass and soil nitrogen content.     

The economics of agroforestry with pine and pasture in the 500 to 700 mm annual rainfall zone of Western Australia

This study mainly compares the economics of one form of agroforestry (involving the simultaneous use of land for pine sawlog, sheep, wool and hay production) with conventional agriculture (sheep and wool production) in the 500 and 700 mm annual rainfall zone of Western Australia. The region is marked by environmental problems, particularly soil and water salinity, owing to past extensive clearly of indigenous deep-rooted vegetation for agriculture. Agroforestry can be a way to control and ameliorate the problems.The major conclusion is that pine agroforestry can be more profitable in the long term than conventional agriculture. It would be a profitable way to control and ameliorate the environmental problems in the region. It would also generate other benefits. A number of measures can be adopted to reduce or avert any problems arising from agroforestry's annual net returns (which fluctuate and are negative for most years before log sales) and annual labour requirements (which vary over time and are generally higher than those for agriculture for about the first half of the agroforestry rotation). These measures include using a low tree density and converting only part of a farm to agroforestry so that the activity is practised in combination with conventional agriculture.The study concerns a region with a Mediterranean climate so that the principles and findings of the study could be of particular relevance to other similar regions of the world.     

Sustainable management of native and exotic plantations in Australia

The emphasis of plantation management changes as the resource and the market develop. This is especially the case when a plantation program is developing a new timber resource, is not the case with many of the Pinus radiata (D. Don) plantings in the southern hemisphere. Australia establishes and manages plantations of both exotic conifer and native hardwood (Eucalyptus spp.) plantations, and these vary in their stage of development. The tenure and objectives in establishment have varied, but some key aspects of the resources may be analyzed. Optimization of production per unit area was not a prime objective during the developmental stages of many exotic pine plantations. Currently, with increased commercial emphasis, this has changed to a greater focus on increased value through Site Specific Management and tree improvement through which gains of at least 20 percent are expected during the first stages. With a key objective of sustainability, questions regarding impacts of soils, water, and biological changes need consideration and are being addressed. The eucalypt plantation resource in Australia is smaller in extent than is the pine resource, but of increasing importance, especially as the plantations are perceived to be more environmentally and ecologically acceptable than exotic conifers. In the past, questions of productivity, especially in relation to impacts of natural pests and diseases, have been raised. Sustainability of all plantations is a critical aspect, however, for specific issues there are different emphases with different species. For example, the relatively, high removal of calcium in smooth barked Eucalyptus plantations is seen as important in long term forest management. This revised version was published online in June 2006 with corrections to the Cover Date.     

Growth of widely spaced trees. A case study from young agroforestry plantations in France

Pessimistic forecasts often suggest that widely spaced trees enjoying free growth (no competition with other trees) will fail to provide high quality timber. This challenges the temperate agroforestry practice of planting widely spaced trees to produce high quality timber. We analyse tree growth data from recent temperate agroforestry plantations aged three to eight years, featuring low tree plantation densities (50 to 400 stems ha−1), the association of trees with intercrops (silvoarable systems) or animals (silvopastoral systems), and the use of plastic shelter tubes to protect trees (1.2 to 2.5 m high) and avoid damage by cattle or sheep in pastures or facilitate maintenance in silvoarable systems. The plantations are located in climates ranging from Mediterranean, dry central temperate plains, cold and wet central uplands to mild oceanic areas. Some plantations included a forestry control (high density of plantation, no tree shelter, no intercropping nor grazing). Trees were evaluated for height and diameter growth and stem form (straightness and absence of knots). Trees in most agroforestry plots grew satisfactorily, often faster than in forestry control plots. In some experimental plots, average annual height increments as high as 1 m and diameter increments as high as 1.5 cm were observed. Few agroforestry plantations were unsuccessful, and the reasons for the failures are discussed: animal damage in silvopastoral plots, but also a wrong choice of tree species unsuitable for local soil and climate characteristics. From these early results we can formulate some guidelines for designing future agroforestry plantations in temperate climates, concerning tree density, use of tree shelters and care required for widely spaced trees. This revised version was published online in June 2006 with corrections to the Cover Date.     

Modelling silvicultural and economic alternatives for Scots pine (Pinus sylvestris L.) plantations in north-western Spain

Two silvicultural alternatives for Scots pine (Pinus sylvestrisL.) plantations in north-western Spain were simulated and compared.One corresponded to the current management practice appliedin the region and the other was an intensive silvicultural regime.Both alternatives were described by a specific combination ofplantation density, precommercial treatments, thinning patternand rotation age. Stand development of each silvicultural alternativewas generated using a regional growth and yield model implementedin a simulator called GesMO, for three site qualities that representedpoorest, intermediate and best sites found in the region. Differenttimber grades associated with each alternative were predicted,and estimates of costs and selling prices were used to predicta cash flow pattern for each of the simulated alternatives.The alternatives were ranked using the criterion of net presentvalue of an infinite series of rotations. Sensitivity analysis,in terms of basic prices, discount rate and rotation length,was also carried out. In addition, the effects of risk of fireon net revenues were evaluated. For the present regional marketconditions the results showed that the currently applied alternativeis not the best one if the main aim is profit maximization.For very poor quality sites the proposed schedules are uneconomicalfor all silvicultural alternatives.     

Species-site matching in mixed species plantations of native trees in tropical Australia

Mixed species plantations using native trees are increasingly being considered for sustainable timber production. Successful application of mixed species forestry systems requires knowledge of the potential spatial interaction between species in order to minimise the chance of dominance and suppression and to maximise wood production. Here, we examined species performances across 52 experimental plots of tree mixtures established on cleared rainforest land to analyse relationships between the growth of component species and climate and soil conditions. We derived site index (SI) equations for ten priority species to evaluate performance and site preferences. Variation in SI of focus species demonstrated that there are strong species-specific responses to climate and soil variables. The best predictor of tree growth for rainforest species Elaeocarpus grandis and Flindersia brayleyana was soil type, as trees grew significantly better on well-draining than on poorly drained soil profiles. Both E. grandis and Eucalyptus pellita showed strong growth response to variation in mean rain days per month. Our study generates understanding of the relative performance of species in mixed species plantations in the Wet Tropics of Australia and improves our ability to predict species growth compatibilities at potential planting sites within the region. Given appropriate species selections and plantation design, mixed plantations of high-value native timber species are capable of sustaining relatively high productivity at a range of sites up to age 10 years, and may offer a feasible approach for large-scale reforestation.     

Caribbean pine in an agroforestry system on the Atherton Tableland in north east Australia

A trial demonstrating an establishment and maintenance technique forPinus caribaea var hondurensis in an agroforestry land use system on the Atherton Tableland, north east Australia, is described. The establishment of the tree component involves mechanical cultivation and the application of herbicides which in combination are technically feasible and acceptable to a landholder who wishes to integrate pine trees and pasture grasses. The cost of establishment and maintenance of the pines up to age 39 months was calculated at $A809 ha^?1 (1986 values). This includes the cost of thinning. The sale of some thinnings for Christmas trees realised a net profit of $A564 from 300 trees ($A188 ha^?1). At age 38 months the stand had a stocking of 254 trees ha^?1, a mean height of 6 m and a mean diameter at breast height of 12.1 cm. The growth compares favourably with other plantation grownPinus caribaea var hondurensis on the Atherton Tableland.     

Faunal use of bluegum ( Eucalyptus globulus ) plantations in southwestern Australia

We examined the faunal use of Eucalyptus globulus plantations in southern Western Australia, and compared use of remnant vegetation, agricultural land and plantations in different positions relative to large tracts of remnant vegetation. In general, faunal use of plantations is less than in comparison with adjacent remnant vegetation, but more than in open pasture. For all faunal groups there were almost twice as many species recorded in the native vegetation than in any site in the plantations or on agricultural land and they were in greater abundance. Faunal use of plantation edges and interiors did not show consistent patterns. Generally, edges next to remnants were most frequently used, but individual species showed a wide range of patterns of use across the various habitat types studied. More species of bird identified as being “at risk” were found in plantation edges than in interiors. Adjacency to remnant vegetation increased plantation use by some species, but the overall differences between isolated plantations and those adjacent to remnant vegetation were relatively small. We conclude that plantations provide some value in terms of habitat for some species, including some of conservation concern, but that this value is limited by the lack of habitat complexity in the intensively-managed plantations. This revised version was published online in June 2006 with corrections to the Cover Date.     

Planning methods for agroforestry

One of the major issues facing the world is the interrelated problem of deforestation and concurrent degradation of agricultural lands in tropical and subtropical nations. Agroforestry is one technique to help alleviate this problem. Implementation of newly developed agroforestry techniques in various places all over the world, has made it clear that:

Problem solving cannot be limited to the individual farmstead or plot level from a social and ecological point of view.

Existing landscapes present both constraints and opportunities for further land development.

More appropriate agroforestry techniques can be applied by classifying landscape units and existing land-use systems.

Planning is necessary because agroforestry requires a holistic perspective to be sustained during the long time necessary for implementation.

For these reasons, a review of planning methods used in agroforestry and suggestions for their improvement seems timely. Selected existing methods, with an emphasis on those being used in Kenya, are analyzed in terms of goals, community needs, site assesment, options for action, implementation, management, and evaluation. Our review was conducted through literature survey and interviews with key informants in Nairobi, Kenya; Wageningen, the Netherlands; and Washington, D.C., U.S.A. Landscape planning might be an approach that can be used with agroforestry to provide a more comprehensive perspective. The role of landscape planning in agroforestry projects is discussed in detail, using a study from Kenya for illustration.     

Assessment of small mammal diversity in coffee agroforestry in the Western Ghats,India

Coffee agroforestry is a conservation strategy that has shown promise to support the diversity of bird, bat, and insect communities, but few studies have focused on non-volant mammals in coffee farms. We assessed mammal diversity within coffee agroforestry systems in Kodagu, India and investigated the impacts of the non-native shade tree species, Grevillea robusta, on mammal diversity. Twenty farms, with varying amounts of G. robusta planted within the coffee farm, were sampled throughout three rainfall zones during the 4-month study period. We captured six species of small mammals, with indirect methods yielding an additional five species, totaling 11 mammal species. Contrary to current ecological thought, we found that increased amounts of G. robusta did not have a negative impact on either abundance or richness of mammals. Small mammal abundances were higher at farms with greater amounts of herbaceous ground cover and larger, mature shade trees, while small mammal species richness was found to increase with an increase in tree species richness as well as greater amounts of herbaceous ground cover. Additionally, small mammal abundance was higher at coffee farms closer to forested areas. Based on these findings, we suggest the maintenance or cultivation of shade tree richness, mature shade trees, and herbaceous ground cover within coffee farms and preservation of forested areas within the landscape to enhance coffee agroforestry habitat for non-volant mammals. We hope that these habitat requirements will be incorporated into conservation strategies for the promotion of biodiversity within coffee agroforestry systems.     

Managing productivity and drought risk in Eucalyptus globulus plantations in south-western Australia

More than 2.5 million ha of Eucalyptus globulus are now planted across the globe including approximately 500 000 ha in southern Australia. In this region average annual rainfall has declined since 1960 and this trend is predicted to continue in the coming decades. E. globulus is a premium species for paper manufacture and grows well under moderate seasonal water stress. The traits that underpin this rapid early growth also make the species vulnerable to prolonged water stress. We established nitrogen rate and nitrogen-by-stocking experiments in five 2-year-old E. globulus plantations along a climatic gradient in south-western Australia. We measured volume growth, predawn leaf water potential and leaf area index over 7 years or until the plantations were 9 years old. These data were used to explore the relationship between growth and water stress, to understand the mechanistic basis for the relationship and to identify best-bet management strategies for E. globulus plantations in southern Australia.     

Avian assemblages in eucalypt forests,plantations and pastures in northern NSW,Australia

Eucalypt plantations are expanding rapidly in Australia, and their value for native fauna requires investigation. The relative conservation value of young eucalypt plantations was investigated through assessment of avifauna richness, abundance and composition using transect surveys incorporating point counts in five broad habitat types—dryland forests, riparian forests, dryland plantations, riparian plantations, and riparian pastures (strips of riparian vegetation surrounded by pastures). A total of 73 species were recorded during formal surveys. Species richness and abundance were comparable among all habitat types except dryland plantations, which supported fewer species and in lower numbers. The avifauna assemblage differed according to broad habitat types. Forest habitats (dryland and riparian) harboured more forest- and woodland-dependent species, and a greater abundance of nectarivores and insectivores. Riparian plantations supported a similar number of forest- and woodland-dependent species to forest habitats, but also retained some open-country species. Riparian pastures had the highest cumulative species richness, reflecting a diverse mix of forest- and woodland-dependent birds and open-country species. It was the preferred habitat type for granivores and vertebrate eaters. Dryland plantations were dominated by common species and omnivores, and supported fewer forest- and woodland-dependent birds, insectivores and frugivores compared with other habitat types. The presence of riparian strips increased avifauna diversity and abundance in plantations and pastures to a greater extent than predicted by the proportional area of riparian habitat. The importance of riparian habitats needs to be recognised and incorporated into management policies if biodiversity conservation is to be an objective of plantation establishment.     

Data recording for agroforestry experiments

Examples of typical data-sets from agroforestry trials are considered and difficulties with the recording of such data are discussed. Suggestions for efficient data recording for a number of agroforestry trials are made so that easy data-checking, efficient computer entry and accurate analysis can be produced without the need for excessive data manipulation at each stage. General recommendations for data-recording from agroforestry trials are given.