Forest Harvesting Impacts on the Structure and Composition of Coniferous Forests in Mexico

Article Forest Harvesting Impacts on the Structure and Composition of Coniferous Forests in Mexico

Giovanni Estrada Valdés 1, Angel Rolando Endara Agramont 1,*, Santiago Vazquez-Lozada 1 and Fredericksen S. Todd 2

1 Col. Centro, Instituto de Ciencias Agropecuarias y Rurales, Campus el Cerrillo Piedras Blancas, Instituto Literario No. 100, Universidad Autónoma del Estado de México (UAEMex), Toluca CP 50000, Mexico; [email protected] (G.E.V.); [email protected] (S.V.-L.) 2 School of Arts and Sciences, Ferrum College, Ferrum, VA 24088, USA; [email protected] * Correspondence: [email protected]

Abstract: The effect of forest harvesting on the composition and structure of a temperate coniferous forest in Mexico was evaluated after three harvesting periods from 2007–2015. In this forest, we identiﬁed seven families and eight tree species. The dominant species is Pinus pseudostrobus Lindl. which is also the most important commercial species. Harvesting was oriented towards increasing the abundance of the dominant pine species, resulting in a decrease in forest diversity and favoring a transition to a monospeciﬁc forest. The tree canopy structure following harvesting showed a gradual recovery in the number of individuals in each diameter class, but the diameter increment may not necessarily guarantee a sustainable harvest because cutting cycles appear to be too short. The size of harvesting gaps and overall forest cover determine the presence and/or abundance of

regeneration (small seedlings, seedlings, saplings, large saplings, and young trees). The establishment of Pinus pseudostrobus and Ilex discolor Hemsl. differed according to their ecological groups.

Citation: Estrada Valdés, G.; Endara Agramont, A.R.; Vazquez-Lozada, S.; Keywords: canopy gaps; forest structure; ecological groups; Pinus pseudostrobus Todd, F.S. Forest Harvesting Impacts on the Structure and Composition of Coniferous Forests in Mexico. Forests 2021, 12, 1068. https://doi.org/ 1. Introduction 10.3390/f12081068 Sustainable forest management involves decisions and activities about harvesting forest resources according to best management practices integrated with forest conservation Academic Editor: Timothy A. Martin and economic development and social needs, both direct (wood products) and indirect (carbon fixation, aesthetics, and soil protection) [1–4]. Received: 11 May 2021 Sustainable forest management is important in temperate and tropical forests [5,6] to Accepted: 6 August 2021 conserve biodiversity and maintain forest composition and structure as well as ecosystem Published: 10 August 2021 function [7]. Forest harvesting can degrade forest structure [8,9], cause soil erosion [10] and negatively alter forest composition [11,12]. It may also, however, be fundamental Publisher’s Note: MDPI stays neutral for the conservation of forest ecosystems [13,14] by increasing tree growth rates and the with regard to jurisdictional claims in recruitment of regeneration through gap dynamics [9,15]. published maps and institutional affil- iations. The forest ecosystem structure is described by tree distribution by age and size [16–18]. The vertical forest structure describes the distribution of forest biomass stratified by tree height and is often defined by functional ecological groups [19], while horizontal stratification is determined by the number of individuals by diameter class and spatial arrangement [20]. Copyright: © 2021 by the authors. Forest composition is determined by environmental factors including geographic Licensee MDPI, Basel, Switzerland. position, climate, soils, topography and forest dynamics [21,22], as well as the ecological This article is an open access article traits of tree species [23]. The goal of forest management is to manage forests for forest distributed under the terms and conditions of the Creative Commons products while optimizing forest species composition [1,18,24]. Attribution (CC BY) license (https:// In Mexico, forest ecosystems occupy a large land area (65 million ha) [25], approxi- creativecommons.org/licenses/by/ mately half of which are temperate forests [26]. These forests are characterized by pines [27], 4.0/).

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In Mexico, forest ecosystems occupy a large land area (65 million ha) [25], approxi- mately half of which are temperate forests [26]. These forests are characterized by pines [27], firs, oaks and other broadleaved species [28], the composition of which is determined by climate and soil type [29–31]. These forests are part of the trans-Mexican volcanic system [32,33]. Forests 2021, 12, 1068 These forests have long been subjected to a variety of human disturbances,2 of 12 such as logging and fire, causing changes to forest structure and species composition [5,25,34–37]. In addition, forest harvesting under the concept of common property land management (agrarianfirs, oaks and centers) other broadleavedhas been typical, species with [28], thethe composition main management of which is objective determined of byproviding cli- tim- bermate and and firewood soil type [29 for–31 local]. These communities. forests are part Land of the use trans-Mexican practices and volcanic natural system resource [32,33]. manage- mentThese have forestsbeen regulated have long beenby these subjected agrarian to a variety centers of under human their disturbances, rules and such traditions as [38], logging and fire, causing changes to forest structure and species composition [5,25,34–37]. butIn addition, this has forestalso led harvesting to a reduction under the of specie concepts of of economic common property importance land management[7,39,40]. Community forest(agrarian management centers) has aims been typical,to achieve with forest the main sustainability, management ensuring objective ofthe providing well-being of the ruraltimber population, and firewood alongside for local communities. the conservation Land useof forest practices systems and natural [41]. resource man- agementIn the have State been of regulated Mexico, by one these of agrarianthe most centers widely under used their species rules and is Pinus traditions pseudostrobus [38], due tobut the this quality has also of led its to wood a reduction and ofresin; species howeve of economicr, the importancespecies has [7 ,experienced39,40]. Community a reduction in forest management aims to achieve forest sustainability, ensuring the well-being of the its range as a result of climate change [42]. Likewise, the demand for raw materials is re- rural population, alongside the conservation of forest systems [41]. ducingIn thethe State state’s of Mexico,oak forests one of [43]. the mostParticularly widely used, in Nevado species is dePinus Toluca, pseudostrobus the roledue of local com- munitiesto the quality has ofa direct its wood influence and resin; on however, the conservation the species of has their experienced forests [44]. a reduction in its rangeThe asobjective a result of this climate study change was [ 42to]. evaluate Likewise, the the effect demand of timber for raw harvesting materials is on the tree canopyreducing structure the state’s and oak composition forests [43]. Particularly, of temperate in Nevadoforests dein Central Toluca, the Mexico, role of as local well as their capacitycommunities for recovery, has a direct under influence the oncurrent the conservation management of their system forests with [44]. agrarian centers. The objective of this study was to evaluate the effect of timber harvesting on the tree canopy structure and composition of temperate forests in Central Mexico, as well as their 2.capacity Materials for recovery, and Methods under the current management system with agrarian centers. 2.1. Study Site 2. Materials and Methods 2.1. StudyThe SiteNevado de Toluca (4690 masl) is located in the State of Mexico with multiple humanThe settlements Nevado de Tolucaaround (4690 it, characterized masl) is located by in a thetemperature State of Mexico of 14 with°C and multiple an average an- nualhuman rainfall settlements of 1212 around mm [45]. it, characterized Andisols are by th ae temperature predominant of 14soil◦C type, and ancovering average 90% of this areaannual [46]. rainfall Stands of 1212include mm conifer [45]. Andisols forest arespecies the predominant such as Pinus soil spp. type, and covering Abies 90%religiosa of (Kunth) Schltdl.this area & [46 Cham.]. Stands and include deciduou conifers forest forest species species suchincluding as Pinus Alnusspp. jorullensis and Abies religiosaKunth and Quer- cus(Kunth) laurina Schltdl. Humb. & Cham. & Bonpl and. deciduous[35]. The foreststudy species area was including in theAlnus Ejido jorullensis Palo SecoKunth Municipio of and Quercus laurina Humb. & Bonpl. [35]. The study area was in the Ejido Palo Seco Coatepec Harinas in the state of Mexico covering an area of 578 ha, of which 436 ha is Municipio of Coatepec Harinas in the state of Mexico covering an area of 578 ha, of which subjected436 ha is subjected to forest to harvesting forest harvesting (Figure (Figure 1). 1).

Figure 1. Study area—Ejido Palo Seco, Coatepec Harinas in the state of Mexico and map of harvested Figure 1. Study area—Ejido Palo Seco, Coatepec Harinas in the state of Mexico and map of har- areas in 2007, 2010 and 2015. vested areas in 2007, 2010 and 2015.

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Experimental Design Experimental Design We compared forest stands at three sites that were similar in site and stand charac- teristicsWe comparedand where forest tree harvesting stands at three was sites carri thated out were during similar three in site different and stand years: character- 2007, istics2010 and 2015. where The tree three harvesting harvest was areas carried serve outas a duringspace for three time different chronosequences years: 2007, to 2010ex- andamine 2015. the Theeffects three of harvesting harvest areas on serveforest asstructure a space and for timecomposition. chronosequences to examine the effectsAt all ofsites, harvesting harvesting on forestwas carried structure out andby selecting composition. individual trees in all categories (>7.5At cm all DBH) sites, and harvesting using directional was carried felling out by with selecting a chainsaw. individual The extraction trees in all rates categories were (>7.5similar: cm 2007 DBH) (2736.3 and using m3 in directional 27.02 ha), 2010 felling (2539.9 with am chainsaw.3 in 53.3 ha) The and extraction 2015 (2662.7 rates m were3 in 3 3 3 similar:30.39 ha). 2007 The (2736.3 focus of m harvestingin 27.02 ha), was 2010 Pinus (2539.9 pseudostrobus m in 53.3, the ha) most and important 2015 (2662.7 commer- m in 30.39cial species ha). The in focusthese offorests. harvesting was Pinus pseudostrobus, the most important commercial species in these forests. 2.2. Sampling Plots 2.2. Sampling Plots The sampling of the forest composition and tree canopy structure was conducted The sampling of the forest composition and tree canopy structure was conducted in a in a 1 ha plot at each harvested site based on the methodology of Valdez [47] and Lam- 1 ha plot at each harvested site based on the methodology of Valdez [47] and Lamprecht [48] (Figureprecht 2[48]). The (Figure location 2). The of the location plot was of the selected plot was using selected a random using walk a random to select walk the mooringto select pointthe mooring for the plot.point Thefor the average plot. The altitude average and altitude slope of and the plotsslope wereof the 2970 plots masl were and 2970 3◦ , respectively.masl and 3°, respectively.

FigureFigure 2.2. SamplingSampling designdesign with with a a 1 1 ha ha plot plot with with 25 25 subplots subplots sampled sampled during during each each harvest harvest year. year. Tree Tree measurements for height and DBH. Sampling plots were distributed based on tree size clas- measurements for height and DBH. Sampling plots were distributed based on tree size classes. ses. 2.3. Species Composition and Diversity 2.3. SpeciesAn importance Composition value and index Diversity (IVI) was calculated based on the values of relative abundance,An dominance, importance and value frequency index for(IVI) each was species calculated [48]. based on the values of relative abundance,Species dominance, diversity was and estimated frequency using for each Simpson, species Margalef [48]. and Shannon–Wiener in- dicesSpecies [17,49]. diversity The Sorensen was indexestimated of similarity using Simp wasson, also Margalef used to compare and Shannon–Wiener forest communities in- indices different [17,49]. years The followingSorensen harvesting.index of similarity was also used to compare forest communities in different years following harvesting.

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2.4. Tree Canopy Structure Vertical structure was determined using counts of trees of the dominant species for each harvesting year, and a one-way analysis of variance was carried out to test for differences among harvesting years. Horizontal structure was evaluated based on the spatial distribution of trees and the abundance of individuals by diameter class.

3. Results 3.1. Species Composition and Diversity The sampling plot contained eight species of commercial tree species in seven families: Aquifoliaceae (Ilex discolor), Betulaceae (Alnus jorullensis Kunth), Clethraceae (Clethra mexicana), Cupressaceae (Cupressus lindleyi Klotzsch ex Endl.), Fagaceae (Quercus laurina Bonpl.), Pinaceae (Abies religiosa Flora. and Pinus pseudostrobus) and Salicaceae (Salix sp.). Trees of the Pinaceae species were the most dominant. P. pseudostrobus was the most dominant species and had the highest IVI in each harvest sampling year, with different codominant species in each of the three years: A. religiosa (2015), A. jorullensis (2010) and Salix sp. (2007). In each sampling year, Q. laurina only occurred in the understory (Table1).

Table 1. Importance value index calculations for commercial tree species Palo Seco, Coatepec Harinas, Estado de México for three harvesting periods. Relative abundance (Ar), relative dominance (Dr), relative frequency (Fr), importance value index (IVI).

Management Years 2007 2010 2015 IVI Species Ar Dr Fr Ar Dr Fr Ar Dr Fr 2007 2010 2015 Pinus pseudostrobus 88.1 93.4 100 76 88.5 100 82 93.4 100 281.5 264.5 275.4 Abies religiosa 5.65 2.12 52 1.1 0.28 20 10 4.34 64 59.77 21.38 78.34 Alnus jorullensis 1.54 0.85 16 12 6.63 80 2.6 1.17 16 10.38 98.63 19.77 Salix sp. 4.45 1.24 52 1.1 0.15 8 4.1 0.93 16 57.69 9.25 21.03 Quercus laurina 0.17 0.06 4 0.9 0.08 4 0.7 0.15 8 4.23 4.98 8.85 Cupressus lindleyi - - - 8.1 4.32 8 - - - - 20.42 -

Species diversity estimated using the Simpson index (Table2) showed that the 2007 harvest area had the lowest diversity. The abundance of P. pseudostrobus was higher in the 2007 harvest area compared to the areas harvested in 2010 or 2015.

Table 2. Simpson index of diversity before forest harvesting: n = tree density; pi2 = square of propor- tional abundance; N = overall tree abundance; D = Simpson’s D; 1-D = Simpson diversity index.

Simpson Index before Forest Harvesting Year 2007 n pi2 N D 1-D A. jorullensis 9 0.000205 593 0.78572 0.2142849 A. religiosa 33 0.003008 P. pseudostrobus 524 0.78065 Q. laurina 1 0 Salix sp. 26 0.001852 Year 2010 A. jorullensis 59 0.015792 466 0.60867 0.3913332 A. religiosa 5 0.0000923 C. lindleyi 37 0.0061470 I. discolor 2 0.0000092 Forests 2021, 12, 1068 5 of 12

Forests 2021, 12, x FOR PEER REVIEW 5 of 12 Table 2. Cont.

Simpson Index before Forest Harvesting Salix sp. 26 0.001852 Year 2010 2 Yearn 2010 pi N D 1-D A. jorullensisP. pseudostrobus 59 3570.015792 0.5865153466 0.60867 0.3913332 Q. laurina 4 0.0000554 A. religiosa Salix sp.5 0.0000923 4 0.0000554 C. lindleyi 37 0.0061470 Year 2015 I. discolor A. jorullensis 2 0.00000927 0.000578 270 0.68804 0.3119648 P. pseudostrobus A. religiosa 357 0.586515328 0.010409 Q. laurina P. pseudostrobus 4 0.0000554222 0.675506 Q. laurina 2 0.0000275 Salix sp. Salix sp.4 0.0000554 11 0.0015145 Year 2015 A. jorullensis The Margalef7 index (0.000578DMg) showed 270 a relatively0.68804 low diversity0.3119648 of species, perhaps A. religiosabecause of human28 disturbance, 0.010409 with values of 0.602 in 2007, 0.97 in 2010 and 0.71 in 2015, P. pseudostrobuswith a dominance222 of P. pseudostrobus0.675506 in all harvest areas. Q. laurina Trends over the2 sampling0.0000275 years in the Shannon–Wiener index (H’) were as follows: 2007 (0.48), 2010 (0.82) and 2015 (0.65). These values coincided with the results from the Salix sp.Margalef and Simpson11 indices.0.0015145 Likewise, the Sorensen index had values for (1) 2007–2010 (0.83), (2) 2007–2015 (0.97) and (3) 2010–2015 (0.71). 3.2. Tree Canopy Structure 3.2. Tree Canopy Structure 3.2.1. Horizontal Structure 3.2.1. Horizontal Structure Based on the abundanceBased of on individuals the abundance by of diameter individuals class, by diameterthe horizontal class, thestructure horizontal structure increased in the firstincreased two diameter in the categories ﬁrst two diameter for 2007 categories compared for 2007to 2010 compared and 2015, to 2010 which and 2015, which resulted in a gradualresulted recovery in a of gradual P. pseudostrobus recovery of (FigureP. pseudostrobus 3). (Figure3).

Figure 3. Horizontal structure of Pinus pseudostrobus in three different harvest years based on diameter distribution. Figure 3. Horizontal structure of Pinus pseudostrobus in three different harvest years based on diameter distribution.Harvesting intensities relative to the original stand volume increased over the three years—2007 (17.63%), 2010 (29.17%) and 2015 (30.76%)—with a direct impact on horizontal Harvesting intensitiesstructure relative (Figure4 to). Thethe totalorig removalinal stand of somevolume deciduous increased species over ( C. the mexicana three, A. jorullensis) years—2007 (17.63%),in lower2010 diameter(29.17%) classes and 2015 favored (30.76%)—with the growth increments a direct of impact dominant on specieshori- but reduced zontal structure (Figurespecies 4). diversityThe total (Table removal3). The of smallersome deciduous diameter trees species (<25 DBH)(C. mexicana are used, byA. local people for handicrafts, construction and ﬁrewood. jorullensis) in lower diameter classes favored the growth increments of dominant species but reduced species diversity (Table 3). The smaller diameter trees (<25 DBH) are used by local people for handicrafts, construction and firewood.

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FigureFigure 4. 4.Horizontal Horizontal structure structure characterized characterized by by diameterdiameter distributiondistribution inin threethree yearsyears ofof harvestingharvesting (Ejido(Ejido de de Palo Palo Seco, Seco, Coatepec Coatepec Harinas). Harinas).

TableTable 3. 3.Harvesting Harvesting intensity intensity by by species species and and diameter diameter class. class.

P. pseudostrobusP. pseudostrobus Salix sp.Salix sp. C. mexicanaC. mexicana A. jorullensisA. jorullensis A. A. religiosa religiosa C.C. lindleyi lindleyi DiametricDiametric Category 2007 2010 2015 2010 2015 2015 2015 2015 2010 2007 2010 2015 2010 2015 2015 2015 2015 2010 Category(cm) Harvesting Per Category (%) (cm)10 2.68 69.23 9.09 33.33 Harvesting 14.29 Per Category100.00 (%) 100.00 6.67 11.11 15 11.58 54.35 12.50 50.00 75.00 100.00 33.33 0.00 0.00 10 2.68 69.23 9.09 33.33 14.29 100.00 100.00 6.67 11.11 1520 11.5826.67 54.35 51.09 12.50 19.05 50.00 0.00 75.00 0.00 100.00100.00 33.3395.24 0.000.00 0.000.00 2025 26.6712.20 51.09 18.87 19.05 12.90 0.00 - 0.00100.00 100.00- 95.2433.33 0.00- 0.000.00 2530 12.2024.44 18.87 25.64 12.90 33.33 - - 100.000.00 -- 33.330.00 -0.00 0.000.00 3035 24.4431.25 25.64 7.69 33.33 36.00 - - 0.0033.33 -- 0.00- 0.000.00 0.000.00 35 31.25 7.69 36.00 - 33.33 - - 0.00 0.00 4040 33.3333.33 24.39 24.39 50.00 50.00 - - 100.00100.00 -- -- 0.000.00 0.000.00 4545 20.0020.00 10.34 10.34 30.00 30.00 - - 100.00100.00 -- 0.000.00 -- - - 5050 28.5728.57 30.77 30.77 42.31 42.31 ------0.000.00 - - 5555 42.8642.86 17.65 17.65 47.83 47.83 ------0.000.00 - - 60 45.45 41.18 42.86 ------6560 18.7545.45 33.33 41.18 14.29 42.86 ------100.00- 0.00- - - 65 18.75 33.33 14.29 - - - 100.00 0.00 -

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70 31.25 87.50 42.86 - 100.00 - - - - 75 0.00 0.00 37.50 - - - - - 0.00 80 33.33 75.00 0.00 ------Forests 2021, 12, 1068 7 of 12 85 0.00 0.00 ------90 100.00 100.00 ------95 0.00 0.00 - - - Table 3. -Cont. - - - 100 0.00 0.00 100.00P. pseudostrobus - - Salix sp. - C. mexicana A.- jorullensis A. religiosa- C. lindleyi- Diametric 2007 2010 2015 2010 2015 2015 2015 2015 2010 Category 3.2.2. Vertical Structure (cm) Harvesting Per Category (%) 70Harvest 31.25 years 87.50 (Figure 42.86 5) differed - 100.00 significantly - in the lower - canopy - (p < 0.05); - data 75 0.00 0.00 37.50 - - - - - 0.00 from80 2007 33.33 and 2015 75.00 revealed 0.00 a dominance - - of P. pseudostrobus - - (p < 0.05), -and 2010 showed - a codominance85 0.00 (p 0.00 > 0.05) - among - P. pseudostrobus -, A. jorullensis - and C. -lindleyi, with - the 90 100.00 100.00 ------201595 data 0.00reflecting 0.00 reforestation - - efforts. - The abundance - of -small trees -of A. religiosa - (an intermediate100 0.00 shade-tolerant 0.00 100.00 species) - in - 2015 decreased - as -the number - of canopy - gaps increased. 3.2.2. Vertical Structure The intermediate strataHarvest also years showed (Figure5) differedsignificant signiﬁcantly differences in the lower among canopy ( pspecies< 0.05); data (p from< 0.05) in the three-harvest 2007year, and with 2015 revealed a dominance a dominance of of P.P. pseudostrobus pseudostrobus(p < 0.05), in and 2010, 2010 showed2015 and a codom- a codominance with A. religiosainance (p > in 0.05) 2007. among TheP. pseudostrobus canopy ,stA.ratum jorullensis wasand dominatedC. lindleyi, with by the 2015P. pseudo- data reﬂecting reforestation efforts. The abundance of small trees of A. religiosa (an intermediate strobus (p < 0.05). shade-tolerant species) in 2015 decreased as the number of canopy gaps increased.

FigureFigure 5. 5. Vertical structure structure following following harvesting inharvesti three differentng in years; three (a) Abies different religiosa, years; (b) Salix sp.,(a) (c) AbiesPinus religiosa pseudostrobus, (b), Salix Alnus jorullensis Cupressus lindleyi sp.,(d) (c) stump, Pinus (e) pseudostrobus, (f) , (d) stump, .(e) Strata-Un: Alnus lower jorullensis canopy; Mi:, (f) intermediate Cupressus canopy, lindleyi Up: canopy. Strata-Un: stratum; lower mean height and DBH by species, year and stratum; median height by year and stratum. canopy; Mi: intermediate canopy, Up: canopy stratum; mean height and DBH by species, year and stratum; median height by year and stratum.

3.3. Forest Regeneration Canopy gaps created by harvesting allowed for the growth of shade-intolerant species, while shade-tolerant species are favored by a closed canopy [50]. The establishment patterns of the species in this forest are listed in Table 4. The most abundant species (other than P. pseudostrobus) were Ilex discolor, Abies religiosa, Salix sp. and Alnus jorullensis (Table 5). For Clethra mexicana, its absence is attributable to its establishment being restricted to riverine areas and ravines with slopes greater than 45°.

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The intermediate strata also showed signiﬁcant differences among species (p < 0.05) in the three-harvest year, with a dominance of P. pseudostrobus in 2010, 2015 and a codominance with A. religiosa in 2007. The canopy stratum was dominated by P. pseudostrobus (p < 0.05).

3.3. Forest Regeneration Canopy gaps created by harvesting allowed for the growth of shade-intolerant species, while shade-tolerant species are favored by a closed canopy [50]. The establishment patterns of the species in this forest are listed in Table4. The most abundant species (other than P. pseudostrobus) were Ilex discolor, Abies religiosa, Salix sp. and Alnus jorullensis (Table5 ). For Clethra mexicana, its absence is attributable to its establishment being restricted to riverine areas and ravines with slopes greater than 45◦.

Table 4. Ecological groups following descriptions by Fredericksen et al. [51].

Ecological Group Description Species Shade-intolerant, regenerate in Long-lived Aile (Alnus jorullensis) disturbed areas and are long-lived shade-intolerant Cedro blanco (Cupressus lindleyi) and occupy the canopy. Oyamel (Abies religiosa) Cucharillo (Clethra mexicana) Partially tolerant of shade, but Capulincillo (Ilex discolor) Partial shade-tolerant depend on gap formation for Encino (Quercus laurina) growth and occupy the canopy. Pino (Pinus pseudostrobus) Guajote (Salix sp.)

Table 5. Natural regeneration of tree species (Ejido Palo Seco, Coatepec Harinas, México) in a harvested forest.

Small Large Species Seedlings Saplings Small Trees Seedlings Saplings Relative Abundance (%) P. pseudostrobus 94.96 78.95 72.41 38.64 47.19 I. discolor 4.32 21.05 3.45 13.64 5.62 A. religiosa 0.72 - 13.79 4.55 15.73 Salix sp. - - 10.34 18.18 15.73 Q. laurina - - - 13.64 6.74 A. jorullensis - - - 11.36 6.74 C. mexicana - - - - 2.25

The type of forest regeneration in harvested forests depends on the canopy gap size and the ecological group [9,50] and tends to promote pioneer species [52,53]. Justiniano and Fredericksen [54] highlighted the need to understand the phenology of tree species in order to manage timber cutting with periods of seed dispersal to promote regeneration.

4. Discussion 4.1. Species Composition In this study, indices of species diversity and similarity in composition show a decrease in diversity with forest harvesting, which coincides with the resuts reported by Endara et al. [35], who afﬁrm that the extraction of individuals of pine trees results in a considerable reduction in their population density. This conﬁrms that harvesting in temperate forests can reduce broadleaved species diversity in genera such as Quercus, Alnus, Clethra and Salix. The results show that in 2015, compared to 2007 and 2010, trees in smaller diameter categories (10 and 15 cm) had a lower density due to selective extraction because pine species in these forests are shade-intolerant and disturbance-adapted [27] and occupy early successional stages that are eventually replaced by Quercus species [55,56]. Forests 2021, 12, 1068 9 of 12

Jiménez et al. [57] noted that management needs to be based on the biological requirements of species, the spatial distribution of trees and their growth and size. The removal of less valuable species (Alnus jorullensis, Clethra mexicana, Cupressus lindleyi, Ilex discolor, Quercus laurina and Salix sp.) favors the development of high-value species such as Pinus pseudostrobus. The Margalef index (Dmg) showed a low diversity of species with a dominance of P. pseudostrobus. Furthermore, according to the IVI, the P. pseudostrobus forests had different codominant tree species in each year: A. religiosa (2015), A. jorullensis (2010) and Salix sp. (2007). The economic value of P. pseudostrobus is attributed to its rapid growth, straight stem and high wood quality [58–60].

4.2. Tree Canopy Structure Forest regeneration is associated with the creation of canopy gaps and the degree of shade tolerance among species. In the forests of this study, Alnus jorullensis and Salix sp. are indicators of disturbance because of their response to forest harvesting, corresponding to ecological groups of species that are shade-intolerant and regenerate in areas disturbed by tree harvesting [51,61]. The removal of understory species may have increased the growth of P. pseudostrobus (Figure5) and less abundant species, such as A. jorullensis, which is used for ﬁrewood and fences [62], as well as Salix sp., which is used for handicrafts [63]. Forest harvesting modiﬁes the site conditions for the establishment of many commercial tree species [64], but selective harvesting tends to decrease tree species diversity [39]. Mostacedo et al. [65] note that establishing minimum cutting diameters allows for species to reach the age for seed production before harvesting, which may improve regeneration. The recommended time for the economic recovery of forests following harvesting is determined by cutting cycles and in Mexico is 10 years; in [66–68], this is noted to be shorter compared to other countries such as Bolivia (20 years) [69,70] and Costa Rica (15 years) [71]. It is notable in this study that, according to the forest structure following harvesting in 2007 and 2015, the cutting cycle is too short to allow for sustainable harvests. From a study in Bolivia, Dauber et al. [72] found that a cutting cycle of 20–35 years could allow for the recovery of timber stocks in tropical forests, which may be neces- sary for forests in Mexico, depending on forest type, to improve the sustainability of forest harvesting.

5. Conclusions The abundance and size-class distribution of Pinus pseudostrobus allows for the selective harvesting of this species across different diameter classes. The tree canopy structure following harvesting displays a trend of gradual recovery, but lengthening the cutting cycle with appropriate minimum diameters can help to increase chances for sustainability. The size of canopy gaps and degree of forest cover determine the growth and abundance of species and the dominance of different ecological groups. Harvesting forests decreased species diversity, stimulating the growth of P. pseudostrobus, which displaces species of the same ecological group, particularly broadleaf species, due to competition.

Author Contributions: G.E.V., field work, writing and data analysis; A.R.E.A., conceptualization and methodology; S.V.-L., mapping and field work; F.S.T., formal analysis. All authors have read and agreed to the published version of the manuscript. Funding: This article was funding by CONAFOR-UAEM project 3668/2014E. Data Availability Statement: The datasets in this study are available within this article. Acknowledgments: We thank the personnel of Ejido Palo Seco, Juan Alvarado and José Luis Hernández, for permission to work, as well as the high mountain forests team of ICAR for the field work. Conflicts of Interest: The authors declare no conflict of interest. Forests 2021, 12, 1068 10 of 12

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