An inaugural workshop was held under the project at CATIE, Costa Rica, from 5-9th July, 1999 to define the needs and scope for the manual and training materials on yield regulation. The papers submitted to the workshop were published as:
Proceedings of a workshop on Humid and semi-humid tropical forest yield regulation with minimal data
Wright, HL & Alder,D [Editors] (2000) OFI Occasional Papers 52
The published edition can be obtained from the Oxford Forestry Institute. Abstracts are listed below, and full articles can be downloaded as Word 97 files.
Howard L Wright
This paper highlights the importance of yield regulation in the management of tropical forests. It emphasises that one of the most important aspects of yield regulation is the determination of the Annual Allowable Cut (AAC) or prescribed yield. It sets out to describe a selection of the classical methods for the estimation of the AAC developed primarily for the even and uneven-aged forests of Europe from the beginning of the last century. In all but the simplest of systems some estimate of the rate of growth of the forest is needed.
Yield regulation is a central concept in sustainable forest management. Yield usually implies standing volume commercial timber, but can include non-timber products. Allowable cut is the harvest corresponding to sustainable yield. Felling damage must be allowed for in calculating this. Mean annual increment (MAI) is often confused with current or periodic increment, whilst different volume equations, diameter limits, and the gross or net increment can further confuse the issue. MAI is not sustainable yield as the forest is not normal and an allowance must be made for felling damage. Yield regulation is not sufficiently defined by the classical concepts of felling cycle and minimum felling diameter. Felling cycle does not have a definite optimum in mixed forest, whilst diameter limit alone is too simple a criterion for management. Tropical forests are spatially and structurally diverse, and practically, MAI and annual allowable cut can only be estimated by simulation or stand projection. This should be done stand by stand, with a further calculation to then determine felling series by cutting parts or aggregates of stands. A strategy is discussed for simplifying these steps and applying it where only static inventory data is available, using tabulated data and simplified modelling tools.
Roderick J. Zagt, Peter van der Hout, Marc Parren
Tropenbos develops methods for sustainable forest management in its programmes in Guyana and Cameroon. In both countries, growth and yield models are currently not available to guide management decisions, but they are developed as part of the research projects. In Guyana, a population model is available for Greenheart, the major commercial species. In this contribution this model is used to show that yield prediction based on limited data in the form of size class distribution data has limited reliability. Minor variations in dynamic characteristics may lead to substantial differences in expected yield. It is concluded that even in conditions of limited data availability some knowledge about population dynamics is required, but that this requirement can be reduced by classifying species in functional groups.
David Thomas and Thorsten Jolitz
The SUBIR Project is an integrated conservation and development project run by CARE Ecuador with major financing from USAID. The geographical focus is primarily the province of Esmeraldas, north-western Ecuador, working with communities, in the buffer zone of the Cotacachi-Cayapas reserve. The project is made up of five components: social, legal, biodiversity monitoring, improved land use and commercialization. The aim of the project is biodiversity conservation through protecting the reserve and improving livelihoods in the buffer zone.
The province of Esmeraldas is estimated to have up to 300,000 hectares of natural forest designated for production. It has been, and is, the most important source of timber from natural forest in the country, supplying around 70% of national demand. The forest is owned by communities and privately. In theory the state also owns production forest though in practice all has been colonised.
Ernest G. Foli
The policy for natural forest exploitation within the forest estates of Ghana is that of sustainable management. In this connection, yield regulation is recognised as an essential component of sustainable management of the forest resources. Several approaches to yield control have therefore been tried in the past, often as a temporary measure until more information on forest dynamics can be obtained to improve the system. Some of these past methods, as well as the current yield regulation protocols are reviewed against the backdrop of the limitations that have rendered them impractical as tools for controlling over-exploitation of the forest resources. The development of a pan-tropical yield regulation system that uses the kind of minimal data that is often available from PSP programmes may enhance the effectiveness of these controls.
Yield regulation in a commercial context.
Responsible forest managers need to know if the rate of resource extraction from a given area of forest is sustainable. Sustainability is poorly defined, but does imply a systematic approach to optimising resource utilisation over the long term. If forest managers are to harvest sustainably they need a systematic process by which concepts of yield regulation are included within strategic planning and daily operations.
Before committing capital a commercial forestry enterprise needs an estimate of the available yield that may be expected over the short term, and for long term projections an estimate of the cutting cycle and expected resource availability at the end of the first cycle.
Ismail Harun, Abd. Rahman Kassim and S. Appanah
Growth plots to monitor the growth and diameter increment of trees were established as early as 1901 in Peninsular Malaysia however these plots were invalidated later due to non-conformity of measurements. The first endeavour to study growth and yield in Peninsular Malaysia was only started in 1974 when the first permanent sample plots (PSP) were established. The first PSPs in Peninsular Malaysia for this purpose were set up at Terengganu. The study was initially conducted to investigate the economic and silviculture implications of forest management under various cutting intensities and cutting regimes. For this purpose, about 150 ha of PSPs in hill forest were established. Other than that, many more such study areas were established in various parts of Peninsular Malaysia so as to cover the major different forest type of the country.
The concept of growth and yield modelling is indeed new in Malaysian forest management. For Peninsular Malaysia, except for several isolated studies, there is no growth and yield model available that has been used in the current management system. Several documented studies before are FORSTAM, Linear Regression, Individual Tree Distance, Log Production Models, GandY Functions, STANDPRO, DIPSIM, FORMIX and Single Tree Model. The only growth and yield model in Malaysia is DIPSIM (A Dipterocarp Forest Growth Simulation Model for Sabah) and STANPRO (Stand Projection Model for Sarawak). DIPSIM was developed in 1994, and purposely formed for Sabah's mixed dipterocarp. Currently DIPSIM is being modified before it can be used in Peninsular Malaysia. Problems encountered in growth and yield studies in Peninsular Malaysia can be divided into four aspects namely: nature of the forest, management operation, permanent sample plot management and data analysis and modelling aspects.
1. The intensity of the harvesting and silvicultural treatments are determined according to the species abundance. The harvesting intensity will not exceed 60% of the number of trees with diameter at the breast heigth (dbh) of 60 centimetres or bigger, per species. A smaller reference dbh will be established for those species which do not reach a dbh of 60 cm, in this case, a technical justification is needed.
Silva. J.N.M and van Eldik, T
Roundwood production in the Brazilian Amazon ranks third in the world, only surpassed by Malaysia and Indonesia. In 1996-1997, annual volume of logs produced was c. 28 million m3 corresponding to an annual logging area of 1.0-1.5 million ha (Nepstad et al. 1999). Pará and Mato Grosso States are the main timber producers, accounting for 78% of the total production.
For timber production to be sustained, i.e. employing sound forest management practices, the area of closed forests needed to be under timber production would be around 30-45 million ha, considering a 30 year cutting cycle. The area under forest management plans in 1997 was 1.8 million ha. If we add the area of national forests (meant for production) in the North region, which amounts to c. 15 million ha, we find out that it is necessary to establish a further 13 to 28 million ha of production forests. This emphasises the strong need for establishment of a permanent forest estate in the country.
Nsita, Steve Amooti
Uganda is a tropical country located between latitudes 1º 30' S and 4º N and longitudes 29º 30' East and 35º E. It covers an area of 24 million hectares, 17% of which is open water and permanent swamp. Altitude averages between 900 - 1500 m above sea level. Rains average 1000 - 1200 mm while average temperatures range between 20ºC - 28ºC.
Population is about 20 million people averaging at about 100 persons per km². The rate of growth is about 2.5% per year.
Uganda's Tropical High Forests (THFs) cover nearly 900,000 ha. About 700,000 ha of these are in Protected Areas (includes patches of grassland). Nearly 60% of the PAs are in Forest Reserves (FR) while the rest are in National Parks.
No less than anywhere else in the world, ensuring sustainable forest management in Indonesia is a highly pressing issue. The significance of the forest sector in the national economy and the increasing global market demands for eco-labelled forest products have led the Government of Indonesia to pay increased attention to the subject. One of the primary problems surfacing recently is the urgent need for appropriate methods, techniques, or tools necessary for accelerating the progress toward accomplishing sustainable management of natural forests.
Personal anecdotes are used to highlight some important considerations for yield regulation and to introduce some pertinent literature. A checklist of key issues and research needs is offered. Perhaps the most important consideration is to maintain a holistic systems view, and to involve clients and to ensure their needs are met.