The forest production in Mexico is not self-sufficient, given the demand for forest products, although approximately 6.2 million hectares of temperate and tropical forests are allocated to silvicultural activities (^{Torres-Rojo et al., 2016}); in these forests, conifers have the most intense management (^{Semarnat, 2016}). This situation demands the implementation of both technical and administrative alternatives aiming toward the achievement of an efficient industrial transformation (^{Flores et al., 2007}) and an increase in the productivity of forests and plantations; toward the improvement of the commercialization channels, of an integral and sustainable management of resources, and toward compliance with the legislation currently in force (^{Flores et al., 2018}). As for the administrative part, the regionalization of wooded areas based on particular (e.g. ecological) characteristics could be a key element that supports the management of tree masses without limiting the technical and economic efforts of the operational areas at a local or state level or within the forest management units (Umafor).

The genus Abies is the second timber pine species in the country (^{Semarnat, 2016}), and Abies religiosa (Kunth) Schltdl. & Cham. is the species with the greatest economic importance, since it is the most exploited in conifer forests, contributing 2.8 % of the annual timber production (^{Semarnat, 2016}). It reports valuable dividends to the industrial sector, because it is used to produce paper pulp, packing crates, poles, beams, andirons, piles, firewood and charcoal (^{Arriola et al., 2015}). In terms of silviculture, efforts have been made to determine the productivity of this species in forest masses (^{Vásquez-Bautista et al., 2016}); however, sustainable production and conservation schemes still need to be implemented.

Within this context, the purpose of the present study was to determine the timber production of A. religiosa in the germplasm movement zones (GMZ) of Mexico; these are sufficiently homogeneous ecological areas where the species dwells, and whose operational management extends beyond the conventional scopes: local, state or forest management units (Umafor).

The GMZs were described as having an adequate regionalization level for use in the nationwide management of the species.

The data of the timber (m³) harvested in 2017, compiled by the Secretaría de Medio Ambiente y Recursos Naturales (Department of the Environment and Natural Resources, (Semarnat) (Table 1) ―which are used in the preparation of the Statistical Yearbook of Forest Production, and therefore constitute a good indicator of its contribution to the national Gross Domestic Product (GDP)― were utilized to estimate the output of each GMZ.

The GMZs proposed by the Comisión Nacional Forestal (National Forest Commission) (^{Conafor, 2016}) were utilized as forest management regions because they are forest resources management areas (^{Flores, 2018}). Activities related to the establishment of germplasm producing units and to the management of forest germplasm are carried out in them (^{Secretaría de Economía, 2016}). Within these areas, the distribution of the species was determined based on the geographic data of the plots of the National Inventory of Forests and Soil (NIFS, 2004-2007), and was represented using the QGIS software (http://qgis.osgeo.org) (^{QGIS Development Team, 2015}). This software has been developed for the analysis and projection of geographic data. The output of timber in each GMZ was estimated based on the relative importance of the sacred fir per GMZ and on the state outputs, according to the following proposed formula:

Where:

Vol. GMZ = Volume of timber (m³) of the germplasm movement zone

IR _i (Relative Importance) = Number of plots of the NFIS with the presence of Abies religiosa within the i ^th GMZ / Total number of plots with the presence of Abies religiosa of the NIFS

PE _j = Timber output (m³) of the j ^th state

The analysis determined that GMZ X.3 had the largest timber production, amounting to 67.94 %, while X.1, X.2, XII.1 and XII.3 contributed 32.06 % (Table 2, Figure 1). Nevertheless, zones III.1, III.2, XII.4 and XII.5 did not contribute to the timber production (0.00 %), due to the low density of A. religiosa individuals (the NIFS records 5 to 91 individuals in the zones) of natural forests (^{Ruelas and Dávalos, 1999}). The results indicate that the largest volume comes from forests located in the central part of the country: zone X.3 (Hidalgo, Michoacán, Morelos, Puebla, Tlaxcala, Veracruz). Therefore, sustainable management activities must be maintained and increased, and the sustainable management activities must be augmented in order to perpetuate the species in question and exploit it for other purposes; i.e. ecosystemic services (^{Cepeda et al., 2016}).

Figure 1 Timber production of Abies religiosa (Kunth) Schltdl. & Cham. in the GMZs. 

On the other hand, although many efforts have been made to characterize some of the forest states in the country, for example, based on forest products and their production system (^{Carrillo et al., 2017}), this has not been done at a regional level, which would allow planning an optimal integral exploitation of the species of interest. The decision-making process in the management of A. religiosa forests may be circumscribed to the GMZs, as these areas are subjected to sufficiently homogeneous ecological conditions, with stands that have uniform genetic or phenotypic characteristics (^{Flores et al., 2014}); also, the timber supply and transformation activities can be optimized within them without being limited to local or state operational areas or to forest management units (Umafor). This condition facilitates a more effective management of tree populations through the implementation of sustainable conservation and management policies intended to bring greater economic, social and industrial benefits.

Sustainable management of A. religiosa in the GMZs requires taking into account the environmental changes that will affect the populations of this species, in order to establish actions that may ensure their permanence and recovery, such as assisted migration into zones with a higher altitude and environmental suitability (^{Sáenz-Romero et al., 2012}).

A. religiosa is a conifer that contributes significantly to the production chain of the forestry sector; the management of A. religiosa forests based on the sustainable conservation of homogeneous ecological zones (GMZs) must be therefore considered. This will favor the exploitation of the species at the level of regions where the stands can maintain uniform characteristics.

The analyzed areas differ as to their timber output: GMZ X.3 provides 67.94 % of the national production, while zones X.1, X.2, XII.1 and XII.3 contribute 32.06 %.

Forest management efforts ―such as the establishment of germplasm producing units, protection of areas for the preservation of genetic resources, and forest germplasm management― must be increased in zone X.3, in order to ensure the continuity and sustainability of the species.

It is also necessary to delve into the results presented herein, in order to estimate the timber volumes (m³ ha^-1) that can be produced in each GMZ, by developing statistical models for forest management.