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Introduction
The Calakmul region, located southeast of Campeche, is considered the second largest forest mass in the Americas (Ellis et al., 2017; Martínez & Galindo-Leal, 2022). The region's location is of great importance as a link between the forest areas of Campeche and Quintana Roo. Together with El Petén, the region represents one of the three largest forest extensions in Mesoamerica and includes five types of vegetation communities: evergreen tropical forest, tropical dry forests, palm groves and savannas (Martínez & Galindo-Leal, 2022). Within rainforests, the 'selva de ramón' rainforest stands out, recognized as the characteristic plant association of the vegetation conserved in the community of Nuevo Becal, where the present study was carried out.
The successional and structural characteristics of vegetation in the region have been of interest to address aspects of conservation, management and use (Jiménez Osornio et al., 2010). Notably, the resilience of woody species to regenerate after being cut is remarkable (Clarke et al., 2013). This adaptation guarantees the persistence of species, which grow from intact root systems that favor the rapid development of individuals, shorten the successional process and favor forest harvesting (Chazdon, 2014; Haas-Ek et al., 2019). In this regard, forest management that enables the vegetative propagation of species in the region's forests will become an ally in stopping land use changes (Báez Vargas et al., 2017; Jiménez et al., 2010).
Currently, in the Calakmul region, the Peninsular Silvicultural Method is implemented, which involves the use of thin trees (diameter at breast height [DBH] < 20 cm) with the objective of commercializing individuals of hardwood species used in the construction industry. These materials are called 'polewood' (Mendoza-Briseño et al., 2021) and are generally obtained in areas of secondary vegetation with 20 to 30-years fallow. In the ejidos of the region, polewood is classified according to its DBH, which can have dimensions of 5 to 20 cm. Another locally appreciated material are 'xiles' which include sticks with a DBH between 3 to 5 cm and are used for the construction of fences and roofs.
To generate alternatives for the sustainable use of forests in the Yucatán Peninsula, it was considered important to evaluate the potential supply of timber products in secondary vegetation. Therefore, this study aimed to assess the quantity (number of individuals) and quality of tree species suitable for xiles and polewood, in both secondary and mature vegetation, in the ejido of Nuevo Becal, Calakmul, Campeche.
Materials and Methods
Study area
The ejido Nuevo Becal is located in the municipality of Calakmul in Campeche, between the coordinates 18.6920 N, -89.2511 W and 21.0161 N, -89.8772 W (Briceño-Méndez et al., 2017). Average annual precipitation ranges from 1 100 to 1 200 mm, with an average temperature of 24.6°C, and the climate is warm subhumid with summer rains (Martínez & Galindo-Leal, 2002). This ejido is the largest in the municipality, covering 53 000 hectares, and was founded by Yucatec Mayans in the 1970s. It was later populated by migrants from various states of Mexico (Reyna-Hurtado, 2009).
About 50 % of the ejido's surface area is under forest management and the other 50 % is distributed among urban zones, agricultural and livestock use areas and secondary vegetation. The economy is based on the commercialization of cedar (Cedrela odorata L.) roundwood, mahogany (Swietenia macrophylla King), squared timber, charcoal, chicle tree (Manilkara zapota [L.] P. Royen.) latex extraction and, on a smaller scale, cedar and mahogany seeds, allspice (Pimenta dioica [L.] Merr.) and xate palm (Chamaedorea sp.). They also engage in subsistence agriculture and subsistence hunting (Briceño et al., 2017).
Vegetation sampling
The structural attributes of the tree vegetation (composition, density, diameter at breast height and total height of individuals) were evaluated in sampling units (SU) of 500 m2 (20 x 25 m) in areas with secondary vegetation of 20 to 30-years fallow and in mature vegetation (>60 years fallow). The first condition (20 to 30 years) is found in 50 % of the ejidos dedicated to agricultural activities and the second (mature vegetation) is located in the portion destined for forest management, where it was verified that there was no sign of previous harvesting. This selection was supported by the land use and vegetation chart, series VI, of the Instituto Nacional de Estadística y Geografía (INEGI, 2017). The area of interest of this chart was gridded and numbered to subsequently and randomly defined the location of the 18 SU: nine in secondary vegetation and nine in mature vegetation. Each SU was divided into five rectangles (subunits) of 5 x 20 m (100 m2). The subunits in turn include a 5 x 5 m (25 m2) square and within these squares two 1 m2 sub-squares were drawn (Figure 1).
Figure 1 The design of the sampling units for the measurement of structural attributes of tree vegetation.
In the SUs, all trees with DBH ≥ 10 cm were recorded. In the subunits (100 m2), individuals with DBH ≥ 3 cm and DBH < 10 cm were recorded, which correspond to the minimum harvestable diameters recognized by the producers. In the 25 m2 squares only the density of individuals with DBH < 3 cm was counted and in the 1 m2 sub squares, tree individuals with total height < 1.3 m (repopulated) were recorded. The DBH was used to calculate the basal area (ba, cm2) with the formula ba = 0.7854 * DBH2; where 0.7854 = value of π/4. The basimetric area (BA, m2∙ha-1) is the sum of ba refered to 1 ha with the formula BA = ∑(ba/s); where s is the area of the plot (m2).
Woody individuals were identified by a parataxonomist expert in the local flora; in addition, cross-references were made with floristic lists from other authors in the region. (Martínez & Galindo-Leal, 2002; Ochoa-Gaona et al., 2018). The nomenclature of the species was consulted and standardized based on the websites of the Missouri Botanical Garden (https://www.tropicos.org/home), New York Botanical Garden (www.theplantlist.org) y Royal Botanic Garden Edinburgh (https://www.rbge.org.uk/).
Importance Value Index
The importance value index (IVI) of the species was calculated by the sum of frequency, density and relative BA for both conditions (secondary and mature) (Curtis, 1959). IVI was also calculated for each of the size classes using this same procedure.
Foresters survey
To identify the species used and the types of products obtained, a semi-structured survey was made to 26 local foresters. From this, the local classification of product types based on DBH was obtained: xiles (3 cm ≤ DBH < 5 cm), polewood-I (5 cm ≤ DBH < 10 cm), polewood-II (10 cm ≤ DBH < 20 cm), poles-beams (DBH ≥ 20 cm in DBH) and firewood. The latter is obtained from poorly grown trees and from branches and trunks of trees harvested for other products.
Harvesting forest products
The forest products harvested were classified as xiles, polewood, poles, beams and firewood. Each of these were quantified exclusively in the secondary vegetation plots, where the materials were collected at ground level. The tips and branches were removed from these materials until the products had the correct dimensions. All the material that could not be included in the classified forest products was recovered as firewood. The forest products were only obtained in six of the nine SU, due to logistical problems and because the owners of the properties did not provide consent for harvesting.
Estimated forest products
Based on the information obtained from the vegetation sampling, the products (xiles, polewood, poles and beams) were classified according to size classes and species. The individuals were evaluated based on the attributes of composition (useful species), density, basal area and height.
Statistical Analysis
In order to compare the structural attributes of richness, density, DBH and timber volume between the two vegetation conditions (by size class and product types), and because in some cases the data were not homoscedastic according to Levene's and Bartlett's tests, a permutation procedure (9 999) with Welch's two-sample t-test was employed using the 'MKinfer' package (Kohl, 2024) on the R platform (v. 4.3.1) (R Core Team, 2023). The probability of differences between means, noted in the tables, refers to the probability generated by the permutation.
Results
Floristic composition of woody vegetation
A total of 108 species grouped in 92 genera of 37 families were recorded. In secondary vegetation 100 species in 83 genera and 35 families were found and in mature vegetation 70 species, 64 genera and 31 families. Species richness in size classes (SC) I to III is higher in secondary vegetation than in mature vegetation. According to Table 1, SC III has the highest number of species (30.6 ± 6); trees in this category have the appropriate dimensions for xiles and polewood.
Table 1 Number of tree species, genera and families in four size classes of secondary (SV) and mature (MV) vegetation in Calakmul, Campeche.
| SC | Species | Genera | Families | ||||
|---|---|---|---|---|---|---|---|
| SV | MV | P value | SV | MV | SV | MV | |
| I | 17.9 ± 5 a | 11.6 ± 1 b | 0.002 | 48 | 59 | 25 | 29 |
| II | 20.2 ± 4 a | 13.3 ± 3 b | 0.001 | 59 | 32 | 30 | 21 |
| III | 30.6 ± 6 a | 17.0 ± 4 b | 2E-04 | 72 | 47 | 31 | 23 |
| IV | 16.7 ± 5 a | 14.3 ± 3 a | 0.23 | 50 | 41 | 27 | 23 |
| Total | 100 | 70 | 81 | 66 | 33 | 31 | |
The ‘total’ value considers species, genera or families that were not repeated in the size classes. Size class (SC) based on diameter at breast height (DBH): I) 1.3 in height, II) DBH < 3 cm, III) 3 cm ≤ DBH < 10 cm, IV) DBH ≥ 10 cm. Mean values (± standard deviation) with different letter indicate significant difference between SV and MV according to the probability generated with permutations of Welch's t-test.
In secondary vegetation, the families with the highest species richness were Fabaceae (13 species), Rubiaceae (7), Sapotaceae and Sapindaceae (6), Polygonaceae (5) and Euphorbiaceae (5); and in mature vegetation, they were Rubiaceae (7), Fabaceae (6), Sapotaceae (5), Meliaceae and Sapindaceae (4). We found 29 families and 60 tree species inhabiting both conditions. The families with the highest number of shared species were Fabaceae, Rubiaceae, Sapotaceae and Sapindaceae.
Density
Table 2 indicates that, for each of the four SC, the average density was significantly higher (P < 0.05) in secondary vegetation than in mature vegetation. In particular, for SC II and III, the values were three times higher than those recorded in mature vegetation. The density of individuals per hectare was higher in SC I and lower in SC IV.
Table 2 Density recorded according size class in secondary vegetation (SV) and mature vegetation (MV) in Calakmul, Campeche.
| SC | Sampling area (m2) | SV | MV | P value | Density (individuals∙ha-1) | |
|---|---|---|---|---|---|---|
| SV | MV | |||||
| I | 10 | 158.22 ± 72.35 b | 88.67 ± 29.93 a | 0.018 | 158 220 | 88 670 |
| II | 125 | 106.66 ± 34.06 b | 39.33 ± 16.10 a | 0.0001 | 8 532 | 3 146 |
| III | 500 | 171.11 ± 43.80 b | 58.66 ± 12.84 a | 2.2E-16 | 3 422 | 1 173 |
| IV | 500 | 48.77 ± 8.12 b | 35.77 ± 8.74 a | 0.005 | 975 | 715 |
| 171 149 | 93 704 | |||||
Size class (SC) based on diameter at breast height (DBH): I) 1.3 in height, II) DBH < 3 cm, III) 3 cm ≤ DBH < 10 cm, IV) DBH ≥ 10 cm. Mean values (± standard deviation) with different letter indicate significant difference between SV and MV according to the probability generated with permutations of Welch's t-test.
Basimetric Area
Mature vegetation has greater BA than secondary vegetation; however, in two SC (II and III), the BA of secondary vegetation is greater than in mature vegetation (P < 0.0001; Table 3). In contrast, in SC IV, the BA accumulated by mature vegetation (89 % of the total) was higher than that recorded in areas with secondary vegetation (P = 0.006).
Table 3 Basimetric area recorded according to size class in secondary vegetation (SV) and mature vegetation (VM) in Calakmul, Campeche.
| SC | Area | Basimetric area (m2∙ha-1) | P value | |
|---|---|---|---|---|
| (m2) | SV | MV | ||
| I | 10 | 0.0 ± 0.0 a | 0.0 ± 0.0 a | 0.0000 |
| II | 125 | 1.87 ± 0.5 b | 0.67 ± 0.2 a | 0.0001 |
| III | 500 | 8.80 ± 1.9 b | 3.40 ± 0.6 a | 2.2E-16 |
| IV | 500 | 21.96 ± 5.3 a | 32.18 ± 8.6 b | 0.0060 |
| Total | 32.7 | 36.2 | ||
Size class (SC) based on diameter at breast height (DBH): I) 1.3 in height, II) DBH < 3 cm, III) 3 cm ≤ DBH < 10 cm, IV) DBH ≥ 10 cm. Mean values (± standard deviation) with different letter indicate significant difference between SV and MV according to the probability generated with permutations of Welch's t-test.
Importance Value Index (IVI)
According to Table 4, in secondary vegetation, 15 out of 100 species had IVI >1 %, which together comprise 50 % of the total index. For mature vegetation, taking into account the above limit, 15 out of 70 species account for 67 % of the total IVI. Only six species were present in both conditions: Eugenia ibarrae Lundell, Bursera simaruba (L.) Sarg., Myrciaria floribunda (H. West ex Willd.) O. Berg, Dendropanax arboreus (L.) Decne. & Plancha, Mosannona depressa (Baill.) Chatrou and Pouteria campechiana (Kunth) Baehni.
Table 4 Tree species with importance value index (IVI) >1 % in secondary vegetation (SV) and mature vegetation (VM) in Calakmul, Campeche.
| Species | IVI SV (%) | IVI MV (%) |
|---|---|---|
| Eugenia ibarrae Lundell | 7 | 2 |
| Bursera simaruba (L.) Sarg. | 5 | 5 |
| Lonchocarpus xuul Lundell | 4 | - |
| Lysiloma latisiliquum (L.) Benth. | 4 | - |
| Piscidia piscipula (L.) Sarg. | 4 | - |
| Myrciaria floribunda (H. West ex Willd.) | 4 | 6 |
| Coccoloba cozumelensis Hemsl. | 3 | - |
| Croton arboreus Millsp. | 3 | - |
| Nectandra salicifolia (Kunth) Nees | 3 | - |
| Dendropanax arboreus (L.) Decne. & Planch. | 3 | 6 |
| Caesalpinia yucatanensis (Britton & Rose) Greenm. | 2 | - |
| Coccoloba spicata Lundell | 2 | - |
| Thouinia paucidentata Radlk. | 2 | - |
| Mosannona depressa (Baill.) Chatrou | 2 | 3 |
| Pouteria campechiana (Kunth) Baehni | 2 | 3 |
| Pouteria reticulata (Englés) Eyma | - | 11 |
| Brosimum alicastrum Sw. | - | 7 |
| Cryosophila argentea Bartlett | - | 5 |
| Drypetes lateriflora (Sw.) Krug & Urb. | - | 4 |
| Manilkara zapota (L.) P. Royen | - | 4 |
| Pseudolmedia spuria (Sw.) Griseb. | - | 4 |
| Trichilia minutiflora Standl. | - | 3 |
| Protium copal (Schltdl. & Cham.) Engl. | - | 2 |
| Talisia floresii Standl. | - | 2 |
| Sum IVI species | 50 | 67 |
Valuable species
Table 5 indicates that the species most used for polewood, firewood and charcoal (mentioned by the interviewed producers) and which, in turn, are better represented (IVI > 1 %) in both types of vegetation, total 12. Of these, 11 are found in secondary vegetation and only six in mature vegetation; the presence of Pouteria reticulata (Englés) Eyma stands out with IVI = 11 %.
Table 5 Importance value index (IVI) of the species preferred by farmers for use in xiles, polewood, firewood and charcoal in secondary vegetation (SV) and mature vegetation (MV) in Calakmul, Campeche.
| Species | IVI SV (%) | IVI MV (%) |
|---|---|---|
| Eugenia ibarrae Lundell | 7.0 | 2.0 |
| Lonchocarpus xuul Lundell | 4.0 | 0.3 |
| Piscidia piscipula (L.) Sarg. | 4.0 | 0.2 |
| Lysiloma latisiliquum (L.) Benth. | 4.0 | 0.0 |
| Nectandra salicifolia (Kunth) Nees | 3.0 | 2.0 |
| Croton arboreus Millsp. | 3.0 | 0.3 |
| Pouteria reticulata (Englés) Eyma | 2.0 | 11.0 |
| Pouteria campechiana (Kunth) Baehni | 2.0 | 3.0 |
| Mosannona depressa (Baill.) Chatrou | 2.0 | 3.0 |
| Metopium brownei (Jacq.) Urb. | 2.0 | 0.4 |
| Lonchocarpus castilloi Standl. | 2.0 | 0.3 |
| Caesalpinia mollis (Kunth) Spreng. | 0.1 | 1.0 |
| Sum IVI species | 35.1 | 23.5 |
Estimated and actual existence of forest products
According to Table 6, the stock of polewood was estimated at 4 479 pieces∙ha-1 for secondary vegetation and 1 927 pieces∙ha-1 for mature vegetation. The density of useful pieces for xiles, polewood I and II was higher in secondary vegetation; however, for poles and beams (DBH ≥ 20 cm), the highest number of pieces was recorded in mature vegetation, exceeding secondary vegetation by more than double. Total volumetric stocks of forest products were higher in mature vegetation, but that of small dimension products such as xiles and polewood (I and II) were higher in secondary vegetation.
Table 6 Density and timber volume of xiles, polewood and poles in secondary vegetation (SV) and mature vegetation (MV) in Calakmul, Campeche.
| Product | DBH (cm) | Density (pieces∙ha-1) | Volume (m3∙ha-1) | ||||
|---|---|---|---|---|---|---|---|
| VS | VM | Valor P | VS | VM | Valor P | ||
| Xiles | 3 ≤ DBH < 5 | 1 762 ± 613.4 b | 493 ± 160.0 a | 0.0001 | 8 ± 2.9 b | 2 ± 0.8 a | 2.2E-16 |
| Polewood I | 5 ≤ DBH < 10 | 1 727 ± 375.3 b | 715 ± 169.3 a | 2.2E-16 | 33 ± 5.7 b | 14 ± 2.4 a | 2.2E-16 |
| Polewood II | 10 ≤ DBH < 20 | 833 ± 178 b | 384 ± 145.0 a | 0.0001 | 92 ± 19.8 b | 48 ± 16.7 a | 0.0003 |
| Poles - beams | DBH ≥ 20 | 157 ± 87.4 a | 335 ± 104.7 b | 0.0004 | 86 ± 55.7 a | 286 ± 104.9 b | 2.2E-16 |
| Total | 4 479 | 1 927 | 219 | 350 | |||
DBH = 1.3 m Diameter at breast height. Mean values (± standard deviation) with different letters indicate significant difference between SV and MV according to the probability generated with permutations of Welch's t-test.
According to Table 7, when comparing the estimated products (materials) with those that were evaluated in the plots with secondary vegetation, only 32.9 % were harvested. The quantity harvested of xiles (48 %) and poles (52.3 %) was higher than the materials recovered from polewood I (20.4 %) and polewood II (16.8 %). Except for poles, the amount harvested of the other products was lower than estimated.
Table 7 Estimated and harvested forest products in the secondary vegetation of Calakmul, Campeche.
| Product | Diameter at breast height (cm) | Density (pieces∙ha-1) | Volume (m3∙ha-1) | ||||
|---|---|---|---|---|---|---|---|
| Estimated | Harvested | P value | Estimated | Harvested | P value | ||
| Firewood | 190.92 | ||||||
| Xiles | 3 ≤ DBH < 5 | 1 696 ± 681.3 b | 810 ± 662.6 a | 0.05 | 8.14 ± 3.5 b | 1.93 ± 1.4 a | 0.0031 |
| Polewood I | 5 ≤ DBH < 10 | 1 620 ± 343.6 b | 363 ± 273.0 a | 2.2E-16 | 33.57 ± 8.5 b | 4.5 ± 4.0 a | 0.0025 |
| Polewood II | 10 ≤ DBH < 20 | 800 ± 125.0 b | 140 ± 103.0 a | 2.2E-16 | 94.35 ± 17.9 b | 5.72 ± 4.23 a | 0.0013 |
| Poles | DBH ≥ 20 | 210 ± 48.5 a | 110 ± 93.0 a | 0.069 | 121 ± 22.7 b | 6.98 ± 4.8 a | 0.0018 |
| Total | 4 326 | 1 423 | 257.06 | 19.13 | |||
| Recovered % * | 32.9 % | 7.44 % | |||||
*Materials harvested compared to those estimated. Mean values (± standard deviation) with different letter indicate significant difference between estimated and harvested materials according to the probability generated with permutations of Welch's t-test.
The volume harvested for xiles (23.7 %) and polewood I (13.4 %) was low, while for the larger products (polewood II and poles) it was even lower (6 %). Taking these products together, the volume harvested reached only 7.44 %; however, if the firewood recovered from tips and branches is included, the volume reaches 81.7 % (Table 7).
Forest product sales
According to Table 8, the sale of forest products from one hectare with secondary vegetation (20 to 30 years) could generate 251 530 MXN. Of this amount, 24.10 % (60 630 MXN) would come from materials used in construction (xiles, polewood and poles) and the remaining 75.90 % from the sale of firewood and charcoal inputs.
Table 8 Quantification and economic value (2022) of forest products harvested per hectare in secondary vegetation with 30-years fallow in Calakmul, Campeche. The price refers to the value of the products for the end user.
| Product | Unit | Unit price (MXN) | Total (MXN) |
|---|---|---|---|
| Firewood | 190.9 m3 | 1 000 | 190 900 |
| Xiles | 810 pieces | 8 | 6 480 |
| Polewood I | 363 pieces | 50 | 18 150 |
| Polewood II | 140 pieces | 100 | 14 000 |
| Poles - beams | 110 pieces | 200 | 22 000 |
| Total | 251 530 |
Use and exploitation of secondary woody vegetation
According to the survey conducted with local producers, secondary vegetation has the capacity to provide polewood, firewood, and charcoal with the potential for commercialization; 20 % mentioned that beams, poles, and guano (palm leaves) are also obtained during this successional stage.
The 26 respondents agreed that after 20-years fallow, secondary vegetation has trees of sufficient size to obtain xiles, polewood, poles and beams, as well as firewood and charcoal; 10 % of the respondents mentioned that after 10-years fallow it is possible to obtain these products, which can also be transformed into charcoal. In smaller quantities, there are species that reach diameters that can be used to obtain poles or beams (Table 9).
Table 9 Perspective of local producers in relation to forest products generated in secondary vegetation in Calakmul, Campeche. The price refers to the value of the products for the end user.
| Product | Unit | Estimated unit price (MXN) | Abundance perspective | Level of commercialization |
|---|---|---|---|---|
| Firewood | kg | 2 | Abundant | Local |
| charcoal | kg | 3 | Abundant | Regional |
| Polewood I | Piece | 50 | Abundant | National |
| Polewood II | Piece | 100 | Abundant | National |
| Beam | Piece | 400 | Scarce | National |
| Poles | Piece | 200 | Regular | Local |
Respondents agreed that the high cost of developing forest management programs and the technical and regulatory restrictions for harvesting secondary vegetation are the main factors limiting the commercialization of their forest products.
Discussion
The botanical families recognized in this study are common and representative of tropical ecosystems in Mexico (Pennington & Sarukhán, 2005) and coincide with research conducted in the evergreen tropical forest of the Yucatán Peninsula (Martínez & Galindo-Leal, 2002; Rodríguez-Sánchez et al., 2019; Tadeo Noble et al., 2019), as well as in the states of Tabasco (García Licona et al., 2014) and Chiapas (Levy Tacher et al., 2017; Martínez Ramos et al., 2017; Sánchez Gutiérrez et al., 2017).
Secondary vegetation included 54 % of the total species recorded in the Calakmul region; in contrast, mature vegetation only comprised 38 % of the regional floristic richness (Martínez & Galindo-Leal, 2002). In terms of diversity, the described pattern of species richness remains consistent: secondary vegetation is 60 % more diverse than mature vegetation. The greater richness and diversity of forest species in secondary vegetation compared to mature vegetation has been documented in several studies (Cortes-Sosa et al., 2021; Rodríguez-Sánchez et al., 2019; Román et al., 2014; Vleut et al., 2013), where it is argued that the advanced stages of succession contain fewer species compared to areas with younger vegetation. This is because in mature vegetation only some persistent and late species are maintained, compared to intermediate stages of plant succession that have the presence of pioneer, intermediate and some late species.
The composition of useful species for obtaining forest materials such as xiles, polewood, poles and beams is a determining attribute for the choice and use by farmers in the region. Thus, the low number of common species between both types of vegetation stands out: the mature vegetation only shares 29 species with the secondary vegetation, totaling 98 species (30 %). Of the 108 species documented in the vegetation samples, only six species with IVI > 1 % are shared in both conditions (secondary and mature vegetation). The species preferred by farmers for xiles and polewood reach high values of importance (> 1 %) in the secondary vegetation compared to mature condition. This difference is evident when comparing SC III and IV, where most of the species useful for xiles and polewood correspond to secondary vegetation.
According to the surveys, 12 species useful for xiles and polewood are also used to produce charcoal or, in some cases, for poles L. castilloi Standl., L. xuul Lundell, Caesalpinia mollis [Kunth] Spreng) and sawn wood (P. piscipula [L.] Sarg. and L. latisiliquum [L.] Benth.).
In vegetation sampling, the high representativeness of the species L. castilloi, P. piscipula, and L. latisiliquum in mature vegetation stands out, as they are highly valued for polewood, firewood, construction poles, furniture making, and the production of high-quality charcoal (Moreno-Casasola & Paradowska, 2009; Secretaría del Medio Ambiente y Recursos Naturales [SEMARNAT], 2018).
According to several studies (Hartter et al., 2008; Lebrija-Trejos et al., 2010; Román et al., 2014; Urquiza-Haas et al., 2007), in post-agricultural tropical forests, basimetric area increases over time since abandonment, while the density of stems with a diameter (at breast height) greater than 1 or 2 cm decreases with fallow age. In the present study, tree density in secondary vegetation is double that reported for mature vegetation, which can partly be explained by self-thinning that occurs during the succession stage. It is important to note that the dimensions of the trees in mature vegetation allow obtaining mainly sawn timber (Tadeo Noble et al., 2019), while secondary vegetation is better suited for the commercial use of xiles and polewood.
In sampling for secondary and mature vegetation, the BA was similar to that reported by Urquiza-Haas et al. (2007), Hartter et al. (2008), Román et al. (2014), Dzib Castillo et al. (2014) and Zamora Crecencio et al. (2018) with values between 17 and 38 m2∙ha-1 and an average value of 28 m2∙ha-1 for vegetation 30 to 50-years fallow. Further analysis shows that the BA of classes II and III in secondary vegetation was three times higher than in mature vegetation. Forest products of economic interest (xiles and polewood) correspond to these classes and their quantity and quality is higher in secondary vegetation.
In Nuevo Becal and other forest ejidos that have forest management programs, commercial harvesting of polewood is carried out on mature vegetation (Báez Vargas et al., 2017). However, ejidos and communities that do not have these management plans benefit economically from the commercialization of polewood from secondary vegetation, which is an important signal to generate forest management strategies that allow the optimization of these harvests (Mendoza Fuente et al., 2020). It is evident that the extraction of firewood, xiles, polewood and poles is profitable considering the evaluation of the present study for a 20 to 30-year fallow (251 530 MXN∙ha-1); however, the amount could be higher if forest management aimed at generating higher quality products (more profitable, e.g. larger dimensions of the most appreciated species) in a shorter time was applied.
In 2018, forest harvesting in the forests of the state of Campeche generated an income of 8.4 million USD, distributed in the sale of poles, piles and beams (SEMARNAT, 2018). According to the data collected in the present study, timber forest products obtained from secondary vegetation could generate income of up to 13 973 USD∙ha-1. In this sense, the management of secondary vegetation in its initial stages (<5 years) could be a convenient strategy considering the predominance of woody species regrowth and the information regarding species preference for various uses. All of the above would be possible from selective thinning and training pruning, without detriment to biodiversity levels (Báez Vargas et al., 2017). Additionally, due to the increasing demand for polewood, the exploitation of secondary vegetation for this purpose is highly recommended (Mendoza-Briseño et al., 2021).
Conclusions
Products useful for exploitation, such as xiles and polewood, are present in greater quantity and quality in secondary vegetation compared to mature vegetation. The forest use of secondary vegetation is a viable option for the economic development of foresters in Campeche and the Yucatán Peninsula, based on sustainable practices. The demand for forest materials for the construction of tourist and residential infrastructure opens up a new possibility to meet the requirements for xiles and polewood from secondary vegetation. This increases the utility of secondary vegetation and creates an opportunity for sustainable commercial exploitation. However, it is necessary to recognize the lack of secondary vegetation management strategies focused on the production of a greater quantity and quality of forest products (xiles and polewood). The effect of sustainable harvesting of secondary vegetation could reduce pressure on Calakmul's forests and thus contribute to regional conservation strategies.
