1. Introduction
During the process of executing the SEAP model formulation consultancy for forest management of secondary forests and its subsequent extrapolation with consortium technicians, the need to establish minimum cutting diameters per species (priority) was established as the main criterion for selecting trees identified as usable in the forest census.
Not having national studies on the determination of DMC, the consultant undertook the task of establishing DMC from the empirical knowledge of local farmers, as well as local loggers (coyotes), who have knowledge based on the experience of use of trees, in agricultural and / or construction activities.
This document aims to present the results of the interviews carried out with local farmers and loggers, which originated a table of DMC and priority species to be considered in the management plans of the Guazapa and Tenancingo region.
2. Objectives
2.1. General objective
Strengthen the planning context of the secondary forest forest management plan, starting from the minimum cutting diameters, priority species to be managed and silvicultural management through the analysis of diameter classes.
2.2. Specific objectives
Present the results of the collection of information, carried out in the two initial management plans and 18 management plans carried out through the technicians, which it integrates in the DMC table by priority species.
Reinforce the technical criteria of forest management, through the analysis of tables of diameter classes.
Consolidate the forest management process of secondary forests in the Guazapa and Tenancingo region, through the generation of tools that allow an adequate silvicultural decision-making process.
3. Justification
Currently, there is no technical information to establish DMC, in Salvadoran secondary forests, this work aims to be a first approach, strengthening the management processes and forest management of secondary forests, being considered as the first technical framework, which will allow the national forest service, extrapolate the experience to other regions of the country.
4. Methods for determining the DMC
Silvicultural treatments are a series of operations with their own specifications that have been developed gradually.
These treatments seek to improve the productive conditions of the mass of future harvest and to increase in general, the epidometric and dimometric growth. The purpose of the treatments is to manipulate the natural dynamics of the ecosystem, in such a way as to increase the productivity of usable biomass.
The effectiveness of the management, which is provided to a given forest, has as the main parameter of comparison the increment of the dimension. Starting from the previous selection of the trees to be extracted (usable), using “minimum cutting diameters”, which consists of the empirical or scientific estimation of the diameter (circumference), that a tree species reaches its maturity balance, to be used (forest products and by-products).
4.1. Diameter distribution
The simplest method to define the DMC is through an analysis of the diameter distribution of the species of interest. There is no point in setting a DMC, for example 60 centimeters if the diameter distribution shows that very few individuals reach this diameter. Figure No. 1 illustrates this situation, for the species of: Aspidosperma megalocarpon; Swetenia humilis; Pseudobombas ellipticum, larger than 60 cm, no Aspidosperma spp trees were found.
IN THIS DIAMETRIC CLASS. This indicates that the DMC for this species is less than 60 cm dbh, given the few individuals in the 50-59 cm class, most likely less than 50 cm. The other consideration is that the DMC has to be less than the diameter of most individuals found to be rotten.
These aspects can be known by monitoring records during harvesting by species and diameter. The other factor that must be considered is that the lower the DMC, the greater the percentage of waste from the sawmill, especially with rustic equipment, and this problem makes it difficult to take advantage of smaller diameters. The costs per cubic meter of extracted wood, too, increase with smaller diameters. The weak point in using only an abundance histogram is that the fact that a species reaches large diameters does not indicate the diameter where the increase is maximized.
Figure No. 1
"Diameter distribution of three commercial species"
4.1.1. Growth studies
Although inventory and census data do not provide information on growth rates, growth results are important from an economic point of view, and can be one way to justify the DMC. Therefore, other sources of information should be examined, if available. If the management objective is to produce lumber, the calculation of the DMC should be determined when the mean annual increment is maximized, taking mortality into account. Alder (1992) described a simple method using a spreadsheet to calculate maximized DMC, for which growth data of at least 20 individuals per species and per diameter class must be available.
4.1.2. Phenological studies
The maximum point of volumetric increase is not the only consideration in setting the DMC. It is also beneficial to know at what diameter a species is capable of producing fruits and even more important at what diameter it produces a sufficient quantity of seeds. This becomes more important when the species is a durable heliophyte, such as mahogany and cedar, since there is no “bank! Of brizales typically found like with the sciófitas.
Mahogany appears to distribute most of its carbohydrates to growth function up to 80 centimeters dbh, at which point the proportion of carbohydrates for reproduction increases, reaching a maximum of 110 centimeters in diameter.
4.1.3. Analysis of the abundance of fustales
The abundance analysis by commercial species suggests which silvicultural treatment would be suitable to maintain sustainable production. Figure No. 2 indicates that it would be difficult to submit to a polycyclic system for cedar in a secondary forest, where a certain amount of trees larger than the minimum diameter of cut (DMC) are used, with the hope that the smallest individuals would reach the DMC in the next uses. Although there are almost no small cedars.
Figure No. 2
"Diameter distribution of the abundance of cedar and conacaste
5. Bibliography
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Finegan, B. The management potential of lowland neotropical secondary moist forests. CATIE-COSUDE, 1992.
Finegan, B; Quiros, D. Sustainable management of a natural tropical forest in Costa Rica, CATIE-COSUDE, 1994.
Guariguata, M. Ecological considerations on natural regeneration applied to forest management, CATIE, 1998.
Hutchinson, I. Starting points and diagnostic sampling for the silviculture of natural forests of the humid tropics. CATIE-COSUDE, 1993.
Louman, B; Quiros, D; Nilsson, M. Silviculture of Humid Broadleaf Forests, with an emphasis on Central America. CATIE, 2001.
Melgar, M. Model training manual for formulating forest management plans for small forest producers, IICA / CATIE / CRS / UCA consortium, El Salvador, 2001.
Melgar, M. Manual de Viveros Forestales, National Central School of Agriculture, ENCA, 1995.
Melgar, M. Report on the incidence of forest fires in the protected areas of southern Petèn, PROSELVA, 1998.
Perreira, L. Forest Management Compendium, INAB-PROCAFOR Project, 1998.
Reuter, F, Forest Management Manual, Broadleaf Forest Projects, Honduras, 1991.
SEGEPLAN-PROSELVA, Progress report of the southern Peten forest management belt, Peten, Guatemala, 2001.
Scott, A. Guide for interpreting the results of a forest inventory, CATIE-CONAP, 1997
