Introduction

In the state of Michoacán, the priority surface for reforestation consists of eroded areas and induced grasslands adding up to 641 971 ha, equivalent to 10.9 % of the surface of the state (^{Cofom, 2014}). Due to the existing need of reestablishing the capacity of the forest ecosystems to generate environmental services and productive activities based on a sustainable exploitation, the recovery of those areas that were covered by vegetation through active reforestation and through soil restoration is crucial (^{Conafor, 2007}).

Because of its ecological, geological, physiographic and topographic characteristics, Michoacán exhibits favorable conditions for the development of forest plantations with various species (^{Muñoz et al., 2012}); one of these, Brosimum alicastrum Sw., is an alternative for the restoration of dry tropical ecosystems that may also benefit the rural communities through its various uses.

Brosimum alicastrum, Moraceae (^{Trópicos, 2017}), breadnut, known in the region as ramón, is native to the tropical regions of the American continent; it grows in areas with warm, semi-warm, tropical and temperate climates, at altitudes ranging between 10 and 1 600 masl; it is a wild species associated to various types of vegetation (^{Pellicer, 2005}; ^{Batis et al., 1999}).

In the low deciduous rainforest, it is considered to have a high fodder potential, though at the same time it provides important environmental services, such as the conservation of the soil and the control of erosion, and counteracts the effects of strong winds; it is also used for the recovery of degraded lands (^{Peters and Pardo, 1982}; ^{Batis et al., 1999}; ^{Carranza-Montaño et al., 2003}; ^{CNIC, 2005}). It is used as a living hedge in agro-habitats, a wind-breaking barrier, shade and a shelter for wildlife. Furthermore, its wood is used for the manufacture of sheets, floor boards, parquet, packing crates, saddles and tool handles; due to its aesthetic characteristics of hardness and dimensional stability, it can be used in the manufacture of furniture (carpentry), agricultural utensils, timber dado linings, sports items (bowling ninepins), broomsticks and shoe trees (^{Zavala, 1999}; ^{MAE and FAO, 2014}; ^{CIBTS, 2016}).

In order to select the most adequate species for each site or geographical region, it is essential to contrast the agro-ecological requirements of the studied taxon with the environmental characteristics of the selected region (^{Martínez, 1999}; ^{Rueda et al., 2013}). Through the use of Geographic Information Systems it is possible to group the environmental factors and their interactions, and thus to define the regions where the conditions exist for achieving feasible results. Experience shows that this technique is useful for making decisions on ecological zoning plans, the monitoring of forest resources, and the diagnosis of the productive potential and of the areas in risk of deterioration.

Recent maps of the productive potential for forest species were generated using geographic information systems supported by such software as ArcGIS and IDRISI, having previously defined the environmental requirements of these species, including annual precipitation, mean annual temperature, altitude, slope, climate, soil type and land use (^{Rueda et al., 2006} and ²⁰⁰⁷; ^{Díaz, 2007}; ^{Muñoz et al., 2016a}, ^2016b); this process included the georeferenced analysis of these requirements, the most restrictive of which have often been related to altitude, soil type, land use, and climate, such as temperature and precipitation, for Pinus spp. and Eucalyptus spp. (^{Flores and Moreno, 1994}; ^{Flores et al., 1997}); the chemical phases of the soil, for Abies religiosa (Kunth) Schltdl. et Cham, and the minimum temperature and a soil without physical phases, for Turnera diffusa (^{Meza, 2003}).

The aim of the present study was to determine the potential area for the establishment of Brosimum alicastrum plantations for restorative purposes in the state of Michoacán, through the use of geographic information systems.

Materials and Methods

Description of the study area. The state of Michoacán is located in the western portion of the country, between the coordinates 20°23’43’’ - 18°09’ 47’’ N and 100°04’45’’ - 103°44’49’’ W, has a territory of 59 864 km², formed by 113 municipalities. The Comisión Forestal del Estado de Michoacán (Forestry Commission of the State of Michoacán) (Cofom) divides it into 10 forest regions (Figure 1): I Lerma-Chapala, II Bajío, III Cuitzeo, IV Oriente, V Tepalcatepec, VI Meseta Purépecha, VII Pátzcuaro-Zirahuen, VIII Tierra Caliente, IX Sierra Costa and X Infiernillo (Table 1) (^{Cofom, 2014}).

Figure 1 Location of the study area. 

The distribution of the climates in the state is strongly related to the altimetric contrasts of the relief; it includes the following types: A (w), warm subhumid; A (C) (m),semi-warm humid; A (C) (w), semi-warm subhumid, C (m), temperate humid; C (w), temperate subhumid; C (E) (m), semi-cold humid; and BS1 (h), dry and semi-dry, very warm and warm. The mean monthly temperatures vary from 13 to 29 °C; the highest temperatures occur in the regions of the Coast and Tierra Caliente, particularly in the areas with the lowest altitude, where the mean annual values reach extremes closer to 30 °C; the lower temperatures range between 27 and 48 °C, and the minimum extreme temperatures, between -7 and 18 °C. The precipitation ranges between 600 and 1 600 mm per year (^{Inegi, 1985}; ^{Anguiano et al., 2007}).

17 soil units are present: Acrisol, Andosol, Cambisol, Castañozem, Phaeozem, Fluvisol, Gleysol, Histosol, Lithosol, Luvisol, Planosol, Ranker, Regosol, Rendzina, Solonchak, Vertisol, and Xerosol; the volcanic soils (andosols) are located in the Transversal Neovolcanic Axis in the Southern Sierra Madre. In the lower parts of the region of the Balsas Depression are vertisols, gleysols, rendzinas, fluvisols, lithosols and regosols (^{Cofom, 2014}; ^{Inafed, 2016}).

Natural distribution and environmental requirements. An extensive bibliographical revision was carried out for the obtainment of the natural distribution and the environmental requirements of B. alicastrum (^{Rzedowski, 1981}; ^{Chavelas and Dewall, 1988}; ^{Vega 1989}; ^{Von Carlowitz et al., 1991}; ^{Batis et al., 1999}; ^{Vega et al., 2003}; ^{CNIC, 2005}; ^{Pellicer, 2005}; ^{SIRE, 2005}). General information regarding the conditions of the dry tropic of the state was obtained and systematized, and the requirements for B. alicastrum were subsequently determined.

The environmental requirements for the estimation of the potential areas were: altitude, total annual precipitation, mean annual temperature, slope, soil type and land use (Table 2).

Development of maps of the potential areas. The potential areas were delimited by using the IDRISI 32 ver. 4.0 software (^{Eastman et al., 2009}), which works with Geographic Information Systems (GIS), and the cartographic and climatic digital information generated by INIFAP. The maps were developed using the RECLASS command, which discarded those areas in the region that did not meet the specific characteristics for the species of interest. For this purpose, a stratification system of the potential areas was designed based on the following categories and levels of aptitude: Not apt = 0, comprises those areas that do not exhibit favorable conditions for the development and growth of the studied species and areas; Apt = 1, comprises those areas that ensure the adaptation of the species, as they exhibit conditions that are favorable to its development. These coverages individually contain the interval of each variable associated to distribution. The images thus obtained were superimposed using the OVERLAY command (which is accessed by clicking on the Analysis/DataQuery/Overlay menu). In this manner the potential areas for the taxon were obtained. The surface of these areas was estimated using the AREA command. The images in the RASTER format were converted to a vector with the REFORMAT command. Each image was exported to a shapefile format in order to work in SIG ArcView version 3.2 (^{Zeiler, 1999}), which was used to generate images at the scales of 1: 100 000 and 1:250 000.

In-field verification. The generated maps were verified by means of a survey of the verification sites, both with and without forest vegetation; this was done with the purpose of corroborating whether or not the developed maps coincided with the reality of the terrain. This activity included the following actions: first, a questionnaire was developed to collect the information regarded as relevant for the assessment and characterization of each verification site. Then, based on the generated maps by forest regions, the sites were located and georeferenced with GPS; this made it possible to compare the environmental demands of the studied species with the actual existence of the area or of the location marked as potential. Furthermore, the location of the sampling sites in the plantations established in previous years was verified in order to determine whether they are within or outside the potential areas determined in this study. Furthermore, samples of the soil were collected from certain verification sites and sent for physicochemical analysis to a soil laboratory BELTEC, S. de R.L. in Uruapan, Michoacán, in order to compare the results with the characteristics of the soil cited in the literature as soil requirements of B. alicastrum.

Results and Discussion

Two maps showing the potential areas for B. alicastrum were generated. Non-mechanized plantations (15 to 30 % slope) are those in which the furrows where the trees will be planted are dug manually, and the mechanized plantations (0 to 15 % slope) are those in which the furrows are made using machinery; mechanization accelerates the planting process but requires the investment of capital.

Maps of the potential areas. In the IV Oriente region, the municipalities that comprise potential areas with a 0-15 % slope are Tuzantla and Tiquicheo, with a total of 7 470 ha, while the potential areas in sites with 15-30 % slopes in Tiquicheo cover a surface of 778 ha (Figure 2).

Áreas potenciales = Potential areas; Pendiente = Slope; Simbología = Symbology; Región oriente = Eastern region; Cuerpo de agua = Waterbody; Cabecera municipal = Municipality

Figure 2 A. Potential areas (0-15 % slope), B. Potential areas (15-30 % slope) for restorative forest plantations of Brosimum alicastrum Sw., in the IV Oriente region of the state of Michoacán.  

The presence of a small surface area with potential (8 248 ha) located in both slopes is mainly due to the fact that most of the municipalities that conform it have a temperate-cold climate, and only the municipalities of Tuzantla and Tiquicheo have a tropical climate with Vertisol soil and a mean annual precipitation of 700 to 1 000 mm, as well as an altitude gradient below 1 000 m.

In Region V Tepalcatepec, the potential areas with a 0-15 % slope correspond to the Aguililla, Buenavista, Tepalcatepec and Parácuaro municipalities, with a total of 19 053 ha; the 15-30 % slopes correspond to Aguililla, Buenavista, Tepalcatepec and Parácuaro, with 829 ha (Figure 3).

Áreas potenciales = Potential areas; Pendiente = Slope; Simbología = Symbology; Región oriente = Eastern region; Cuerpo de agua = Waterbody; Cabecera municipal = Municipality

Figure 3 A. Potential areas (0-15 % slope), B. Potential areas (15-30 % slope) for restorative forest plantations of Brosimum alicastrum Sw., in the region V Tepalcatepec in the state of Michoacán. 

In Region VIII Tierra Caliente, the municipalities with potential areas with a 0-15 % slope are San Lucas, Huetamo, Turicato, Madero, Nocupétaro and Carácuaro, with a total of 12 979 ha; those with a 15-30 % slope are located in San Lucas, Huetamo, Turicato, Madero and Nocupétaro, with a total of 3 572 ha (Figure 4).

Áreas potenciales = Potential areas; Pendiente = Slope; Simbología = Symbology;Región oriente = Eastern region;Cuerpo de agua = Waterbody; Cabecera municipal = Municipality

Figure 4 A. Potential areas (0-15% slope), B. Potential areas (15-30% slope) for restorative forest plantations of Brosimum alicastrum Sw., in region VIII Tierra Caliente in the state Michoacán. 

In Region IX Coast, the municipalities with potential areas for the two slope intervals, 0-15 % and 15-30 %, are Aquila, Coahuayana, Chinicuila and Coalcomán, with 18 773 ha and 8 883 ha, respectively (Figure 5).

Áreas potenciales = Potential areas; Pendiente = Slope; Simbología = Symbology; Región oriente = Eastern region; Cuerpo de agua = Waterbody; Cabecera municipal = Municipality

Figure 5 A. Potential areas (0-15 % slope), B. Potential areas (15-30 % slope) for restorative forest plantations of Brosimum alicastrum Sw., in region IX Coast in the state of Michoacán. 

This larger surface with a potential to establish restorative plantations of B. alicastrum coincides with the ecological areas where the species is naturally distributed (medium sub perennial rainforest); furthermore, in 1979 ^Cotecoca registered this as the vegetation type with the best distribution along the Pacific Coast (3 757 850 ha). B. alicastrum is a dominant arboreal species in the medium sub perennial rainforest (^{Vega et al., 2003}).

In Region X Infiernillo, the municipalities exhibiting potential areas with a 0-15 % slope are Nuevo Urecho, Ario de Rosales, Gabriel Zamora and La Huacana, with a total of 13 412 ha, while those with a 15-30 % slope occur in Nuevo Urecho, Gabriel Zamora and La Huacana, and cover a total of 648 ha (Figure 6).

Áreas potenciales = Potential areas; Pendiente = Slope; Simbología = Symbology; Región oriente = Eastern region; Cuerpo de agua = Waterbody; Cabecera municipal = Municipality

Figure 6 A. Potential areas (0-15 % slope), B. Potential areas (15-30 % slope) for restorative forest plantations of Brosimum alicastrum Sw., in region X Infiernillo in the state of Michoacán. 

The potential areas for the establishment of restorative forest plantations of B. alicastrum using machinery for 0-15% slopes by forest region are located in: IV Oriente (7 470 ha), V Tepaltepec (19 053 ha), VIII Tierra Caliente (12 979 ha), IX Sierra Costa (18 773 ha) and X Infiernillo (13 412 ha). The potential surface area in the state is 71 687 ha (Figure 7).

Figure 7 A. Potential areas for restorative forest plantations of Brosimum alicastrum Sw., with a 0-15 % slope, B. Potential areas with a 15-30 % slope in the state of Michoacán. 

The potential areas for the establishment of non-mechanized or manual plantations of B. alicastrum at a state level in sites with a 15-30 % slope cover a total surface of 14 721 ha (Figure 7) and are located in the following regions: IV Oriente (778 ha), V Tepalcatepec (829 ha), VIII Tierra Caliente (3 573 ha), IX Sierra Costa (8 893 ha) and X Infiernillo (648 ha).

The total productive potential corresponds to 86 408 ha, mainly distributed in regions V and IX (Tepalcatepec and Sierra Costa), with 47 548 ha. The lowest limit of the altitude interval was considered to be the sea level, and the highest limit, up to 800 masl, as in the Pacific Coast (^{Vega et al., 2003}).

These results are similar to the ones cited by ^{Rueda et al. (2006)} and ^{Rueda et al. (2007)}, who used the same variables to generate the maps of potential areas for forest plantations of 11 species of pine and six tropical species in the state of Jalisco. They also agree with those of Sáenz et al. (2000), authors who use similar edafoclimatic variables to determine the potential areas for plantations of A. religiosa, P. pseudostrobus Lindl., P. michoacana Martínez, P. montezumae Lamb., P. teocote Schiede ex Schltdl. & Cham., P. oocarpa Schiede ex Schltdl., P. ayacahuite Ehrenb. ex Schltdl., P. lawsonii Roezl ex Gordon and P. herrerae Martínez, in eastern Michoacán.

Likewise, they agree with the results registered by ^{Sáenz et al. (2011a} and ²⁰¹²) for commercial forest plantations and for silvopastoral systems in Michoacán; with those of the study by ^{Meza (2003)} for the location of potential areas for the establishment of Damiana (Turnera diffusa Willd.) plantations, and with the results obtained by ^{Sáenz et al. (2011b)} and ^{Muñoz et al. (2016a}; ^2016b), for determining potential areas of commercial forest plantations in the state of Michoacán.

As for the verification of the maps, the information obtained in field was confronted with the environmental requirements existing in the bibliography in order to establish the degree of reliability of the generated maps. The purpose was to corroborate whether or not an area defined as potential for the studied species corresponded to the climate and soil conditions cited by various authors (^{Batis et al., 1999}; ^{Chavelas and Dewall, 1988}; ^{Von Carlowitz et al., 1991}; ^{SIRE, 2005}; ^{Vega et al., 2003}; ^{Vega 1989}; ^{Rzedowski, 1981}; ^{CNIC, 2005}; ^{Pellicer, 2005}).

The sampling of the four sites located in the municipalities of San Lucas, Huetamo and Nuevo Urecho confirm that the edafoclimatic conditions registered in these correspond to the soil type, slope, altitude and type of vegetation documented in the literature for B. alicastrum. However, they were insufficient, as the verification took place in only two of the five forest regions of Michoacán that had potentials to establish restorative plantations of this species (Table 3).

The generation of maps of the potential areas together with the implementation of good reforestation practices with native species (^{Vanegas, 2016}) will make it possible to restore the capacity of forest ecosystems to generate environmental services and productive activities through sustainable exploitation. It is crucial to recover those areas that were wooded in the past in the various forest regions of Michoacán.

This will also allow the reforestation of the priority surface area in the state, consisting of eroded areas and induced grasslands that add up to 641 971 ha, equivalent to 10.9 % of the total surface, and the prioritization of those forest regions with the largest total surface area registered by the Comisión Forestal del Estado de Michoacán (Forestry Commission of the State of Michoacán) through the Inventario Forestal y de Suelos de Michoacán de Ocampo (State Forestry and Soil Inventory of Michoacán de Ocampo), where there are plans to reforest the Sierra Costa region, 185 396 ha (29 %); Oriente, with 106 836 ha (17 %), and Tierra Caliente, with 96 284 ha (15 %) (^{Cofom, 2014}).

Conclusions

The total surface with a potential for the reestablishment of B. aliastrum plantations with restoration purposes in the state of Michoacán is 86 408 ha; from these, 71 687 has correspond to 0-15 % slopes, and 14 721 ha, to 15-30 % slopes, distributed in the following regions: IV Oriente, V Tepalcatepec, VIII Tierra Caliente, IX Sierra Costa and X Infiernillo. Due to its ecological, geological, physiographic and topographic characteristics, the dry tropic of the entity exhibits favorable conditions for the development of the proposed plantations. The information generated is a guide for decision making in regard to the establishment of restorative forest plantations.