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Tree infection by Hypsipyla grandella in Swietenia macrophylla and Cedrela odorata (Meliaceae) in Mexico's southern Yucatan Peninsula
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Forest Ecology and Management 255 (2008) 324–327 www.elsevier.com/locate/foreco
Tree infection by Hypsipyla grandella in Swietenia macrophylla and Cedrela odorata (Meliaceae) in Mexico’s southern Yucatan Peninsula Diego R. Pe´rez-Salicrup a,*, Ricardo Esquivel b a
Centro de Investigaciones en Ecosistemas, Universidad Nacional Auto´noma de Me´xico, Antigua Carretera a Pa´tzcuaro 8701, Morelia, Michoaca´n, Mexico b Universidad Marista de Me´rida, Perife´rico Norte Tablaje Catastral 13941, Me´rida, Yucata´n, Mexico
Abstract In small-scale plantations (0.5–2 ha) of Swietenia macrophylla King (big-leaf mahogany) and Cedrela odorata L. (Spanish cedar) in the southern Yucatan Peninsula, we evaluated whether the proportion of Hypsipyla grandella (mahogany shoot borer) was affected by the species used in the plantation (S. macrophylla, C. odorata or both) or by the density and height of individuals planted. We found that the proportion of infected individuals did not differ between the species used in plantations, either planted as monocultures or in mixed plantations. The proportion of infected S. macrophylla and C. odorata individuals in plantations differed among locations and was affected by the mean height of planted individuals, but was not affected by the density of individuals planted. # 2007 Elsevier B.V. All rights reserved. Keywords: Big-leaf mahogany; Mahogany shoot borer; Mixed plantations; Spanish cedar
1. Introduction Swietenia macrophylla King (big-leaf mahogany) and Cedrela odorata L. (Spanish cedar) are two species in the Meliaceae family which are vulnerable to infection by Hypsipyla grandella Zeller (shoot borer or driller worm; Bauer and Francis, 1998; Arteaga and Izaguirre, 2004). H. grandella larvae attack the apical meristem of S. macrophylla and C. odorata individuals, causing increased branching and slowing down tree growth. Furthermore, as secondary branches become dominant, the bole of infected individuals becomes deformed. For these reasons, H. grandella has been identified as the most important factor limiting the successful establishment of plantations of these two species in Mexico and other countries in the Neotropics (Bauer and Francis, 1998; SEMARNAT, 2005). Swietenia macrophylla and C. odorata account for only 0.5% of volume and 1.5% of value of timber produced in Mexico (SEMARNAT, 2005). However, in the southern Yucatan Peninsula many communities dedicated to timber production depend largely on the income produced from these two species (Flachsenberg and Galletti, 1998; Galletti, 1998). To alleviate timber exploitation pressure on natural forests and to insure
* Corresponding author. Tel.: +52 55 56232708; fax: +52 55 56232719. E-mail address: [email protected] (D.R. Pe´rez-Salicrup). 0378-1127/$ – see front matter # 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.foreco.2007.09.054
harvestable timber volumes in the future, the Mexican government has promoted agroforestry systems in which S. macrophylla and C. odorata are planted in areas formerly used for shifting agriculture (SEMARNAT, 2005). In the region around the Calakmul Biosphere Reserve in the southern Yucatan Peninsula, farmers of several communities (locally called ejidos) have voluntarily established plantations of S. macrophylla and C. odorata (Acopa and Boege, 1998). These plantations usually cover small areas, ranging from 0.5 to 5 ha, and because seedlings of these light demanding species are planted in open areas, it has been suggested that conditions for their growth are ideal (Ramos and Grace, 1990; Snook, 1998). However, management practices in these plantations vary widely among farmers, who receive little or no advice on how to maximize seedling survival and growth in their plantations. First, farmers might plant monocultures with one of these species, or they might incorporate both species in a single plantation (henceforth called mixed plantations). Second, some farmers plant additional fruit species in addition to S. macrophylla or C. odorata. Finally, the distance between planted seedlings also varies. As distance between individuals increases, density of planted individuals decreases and more trees of different species naturally establish between planted individuals, turning the plantation into an unintended polyculture. Because the success of the timber production and conservation goals of these plantations depends largely on
D.R. Pe´rez-Salicrup, R. Esquivel / Forest Ecology and Management 255 (2008) 324–327
the growth of planted trees, it is important to evaluate whether individual practices implemented by local farmers affect the proportion of H. grandella infected individuals. In this article we evaluate whether the proportion of infected individuals of S. macrophylla and C. odorata in monocultures differs from the proportion of infected individuals when both Meliaceae species were planted in mixed plantations. We then tested the hypothesis that the proportion of infected individuals in a plantation was directly related to the density of planted individuals. Because the probability of infection might increase with age, and tree height and tree age are correlated, we also evaluated whether the proportion of infected individuals increased with mean tree height in a plantation. We expected that plantations with lower S. macrophylla and C. odorata densities should have lower proportions of infected individuals under the assumption that the presence of other naturally established tree species might diminish the incidence of H. grandella. Answers to these questions could inform local farmers as to whether they should plant single or mixed species plantations, and whether they should reduce the density of Meliaceae seedlings in plantations in order to reduce the potential for H. grandella infection. 2. Methods We evaluated the proportion of S. macrophylla and C. odorata individuals infected with H. grandella in 45 plantations located in the vicinity of Calakmul Biosphere Reserve in the southern Yucatan Peninsula in August 1999. Precipitation in the region ranges between 910 and 1353 mm year 1 (Pe´rezSalicrup, 2004). Plantations were located in eight ejidos where farmers allowed us to study at least four different plantations (Table 1). All plantations were 5 years old and ranged between 0.5 and 2 ha in size. Plantations varied in density of Meliaceae planted seedlings, and density of Meliaceae planted seedlings was negatively correlated with density of other species (Table 1). Plantations were established in sites formerly used for shifting agriculture, so that most were surrounded by agricultural fields or secondary forests. We classified plantations as monocultures or mixed plantations. In each plantation, we counted and measured the height of all individuals of S. macrophylla and C. odorata in
325
three contiguous rows chosen randomly. We considered H. grandella damaged individuals as those in which secondary branches had taken over vertical growth due to death of the apical meristem, although in many instances H. grandella larvae could not be found. We measured the length and width of the three selected rows in each plantation, and estimated Meliaceae seedling density. We evaluated whether the proportion of infected individuals of S. macrophylla and C. odorata in monocultures differed from the proportion of infected individuals in mixed plantations with a Mann–Whitney U-test. We used the same test to evaluate differences in the proportion of infected individuals in monocultures of S. macrophylla versus C. odorata. Plantations were located within different ejidos, and plantations differed slightly in age, and in the height of planted individuals. Because age and height of planted individuals are usually correlated but the latter can be more accurately measured than the former, location, density and mean height of individuals in a plantation were evaluated simultaneously. We used an ANCOVA to evaluate whether the proportion of infected Meliaceae saplings in plantations differed between locations (i.e., ejidos) considering sapling density and mean sapling height as covariates. We transformed sapling density to logarithmic scale to fulfill normality requirements of ANCOVA (Sokal and Rohlf, 1995). 3. Results and discussion Of the 45 studied plantations, 11 were planted with S. macrophylla, 18 with C. odorata, and 16 were mixed plantations. The proportion of infected individuals did not differ between S. macrophylla and C. odorata planted in monocultures (U = 132, P = 0.13). Neither did the proportion of infected individuals of S. macrophylla and of C. odorata differ between monocultures and mixed plantations (U = 97, P = 0.65, and U = 138.5, P = 0.85, respectively). Hence, it appears that the proportion of H. grandella infected individuals is not different for these two Meliaceae species, and that the proportion of infected individuals is not affected by planting monocultures or mixed plantations of these two species. This suggests that the choice of selecting one or the other species should be based on the availability of seedlings and other economic considerations such as projections of future timber values.
Table 1 Number of plantations and plantation characteristics in eight ejidos in the southern Yucatan Peninsula, Mexico Ejido
Number of plantations
Types of plantations (S, C, M)a
Density of individuals (ind/10 m2)
Mean proportion of infected individuals
Range of proportion of infected individuals
Veinte de Noviembre Diaz Ordaz La Lucha Narciso Mendoza Nueva Vida Valentin Gomez Farias Nuevo Campanario Heriberto Jara
5 11 5 4 5 7 4 4
S, M S, C, M S, C, M S, C, M C, M S, C, M C C, M
3.4–28.4 0.5–17.6 3.3–17.2 1.5–3.7 6.7–14.8 1.1–12.0 5.5–8.6 2.9–9.3
0.10 0.28 0.43 0.47 0.52 0.70 0.71 0.74
0.00–0.28 0.00–0.65 0.00–0.86 0.00–1.00 0.27–0.71 0.22–0.95 0.53–0.90 0.58–0.95
a
S: Swietenia macrophylla; C: Cedrela odorata; M: mixed plantation.
326
D.R. Pe´rez-Salicrup, R. Esquivel / Forest Ecology and Management 255 (2008) 324–327
The proportion of infected individuals in plantations differed among locations, and was affected by the mean height of planted individuals but not by their density (F location = 3.52, Plocation = 0.006; F height = 10.48, Pheight = 0.003; F logdensity = 0.02, Plogdensity = 0.88; Fig. 1). Despite the fact that location of plantations influenced the proportion of H. grandella infected individuals, there are no obvious differences in the studied ejidos in terms of rainfall, altitude or land use which might suggest why infections rates differed. Plantations in ejidos Veinte de Noviembre and Diaz Ordaz had means of infection of 10% and 28%, respectively, while the other ejidos had means of infection ranging from 43% to 78% (Table 1). As is the case for many other insect species, H. grandella populations might experience oscillations driven by stochastic or unpredictable processes, so it might be that variation in the proportion of infected individuals across locations varies in response to population densities of H. grandella. Plantations with taller S. macrophylla or C. odorata individuals had a higher probability of infection (Fig. 1). Because age and tree size are correlated (Martı´nez-Ramos and Alvarez-Buylla, 1998), taller individuals might be older, which allows for more time of exposure to H. grandella infection. Alternatively, H. grandella might have a preference to infect taller individuals, so a plantation with taller plants might be more susceptible to infection. Contrary to our expectations, density of S. macrophylla and C. odorata did not affect the proportion of infected individuals. Densities of plantations in this study ranged from 0.5 to
28.4 individuals/10 m2, which represents a very wide range of variation, so lack of an effect of density presumably was not caused by lack of variation within the range of observed densities. Other studies in different parts of the world have found contrasting results regarding the proportion of H. grandella infected individuals in plantations of S. macrophylla and C. odorata mixed with other tree species. In a study conducted in Brazil, plantations of S. macrophylla mixed with Eucalyptus urophylla reduced infection by H. grandella from 71% to 25%, though growth of S. macrophylla increased when planted in monocultures (Guimara˜es et al., 2004). In a different study in the southern Yucatan Peninsula, most S. macrophylla and C. odorata individuals were affected by H. grandella, despite being planted under different canopy structures (Arteaga and Izaguirre, 2004). It is possible that a reduction of H. grandella infection rates reported by Guimara˜es et al. (2004) was not caused by a reduction in density of S. macrophylla, but rather by an effect of E. urophylla on H. grandella. While their study is not conclusive in this respect, it opens the possibility that a reduction of the proportion of H. grandella infected individuals in a plantation of S. macrophylla or C. odorata might depend on the tree species that is mixed with them. However, it would be necessary to screen tree species to evaluate which ones might have such an effect. Because planting densities did not affect the proportion of infected Meliaceae individuals in this study, we recommend that local farmers in the southern Yucatan Peninsula engaged in agroforestry plantations using S. macrophylla or C. odorata should try to maximize the density of their plantations in order to obtain higher future harvest volumes, as reducing density will not result in lower proportion of H. grandella infected individuals. Of course, densities of S. macrophylla and C. odorata in plantations should reflect spacing requirements that minimize competition between individuals. We also recommend that local authorities involved in promoting plantations of S. macrophylla and C. odorata in the southern Yucatan Peninsula offer more information to engaged farmers to help them receive the maximum profit possible from their plantations. Acknowledgements
Fig. 1. Proportion of S. macrophylla and C. odorata individuals infected with H. grandella as a function of mean height in plantations in eight ejidos in the southern Yucatan Peninsula. Dashed lines represent ejidos with significantly less proportion of infected individuals (Diaz Ordaz and Veinte de Noviembre), continous lines represent the remaining ejidos. Symbols represent individual plantations in different ejidos (open circle: Diaz Ordaz; open diamond: Heriberto Jara; open square: La Lucha; open triangle: Narciso Mendoza; closed circle: Nueva Vida; closed diamond: Nuevo Campanario; closed square: Valentin Gomez Farias; closed triangles: Veinte de Noviembre).
This work was undertaken through the auspices of the Southern Yucata´n Peninsular Region (SYPR) project with core sponsorship from NASA’s LCLUC (Land-Cover and Land-Use Change) program (NAG 56406) and the Center for Integrated Studies on Global Change, Carnegie Mellon University (CISCMU; NSF-SBR 95-21914). Additional funding from LTER GRU supported Ricardo Esquivel. SYPR is a collaborative project of El Colegio de la Frontera Sur (ECOSUR), Harvard Forest – Harvard University, the George Perkins Marsh Institute – Clark University, and CIS-CMU. We thank Vı´ctor Chi Noh, Karen Vitkay and Autumn Bryant for their support. Ricardo Esquivel was supported through a program at Harvard Forest. We are grateful for comments by two anonymous reviewers which improved the clarity of this manuscript.
D.R. Pe´rez-Salicrup, R. Esquivel / Forest Ecology and Management 255 (2008) 324–327
References Acopa, D., Boege, E., 1998. The Maya forest in Campeche, Mexico: experiences in forest management at Calakmul. In: Primack, R.B., Bray, D., Galletti, H.A., Ponciano, I. (Eds.), Timber, Tourists and Temples: Conservation and Development in the Maya Forest of Belize, Guatemala, and Mexico. Island Press, Washington DC, USA, pp. 81–97. Arteaga, M.B., Izaguirre, R.C., 2004. Comportamiento de especies tropicales bajo tres sistemas de plantacio´n. Foresta Veracruzana (a Mexican Journal) 6, 45–51. Bauer, G.P., Francis, J.K., 1998. Swietenia macrophylla King, Honduras Mahogany, Caoba. U.S. Department of Agriculture, Forest Service, Southern Forest Experiment Station, New Orleans, LA, USA, p. 7. Flachsenberg, H., Galletti, H., 1998. Forest management in Quintana Roo, Mexico. In: Primack, R.B., Bray, D., Galletti, H.A., Ponciano, I. (Eds.), Timber, Tourists and Temples: Conservation and Development in the Maya Forest of Belize, Guatemala, and Mexico. Island Press, Washington DC, USA, pp. 47–60. Galletti, H.A., 1998. The Maya forest of Quintana Roo: thirteen years of conservation and community development. In: Primack, R.B., Bray, D., Galletti, H.A., Ponciano, I. (Eds.), Timber, Tourists and Temples: Conservation and Development in the Maya Forest of Belize, Guatemala, and Mexico. Island Press, Washington DC, USA, pp. 33–46.
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Guimara˜es, N.A.B., Felfili, J.M., da Silva, F.G., Mazzei, L., Fagg, C.W., Nogueira, P.E., 2004. Evaluation of mahogany homogenous stands, Swietenia macrophylla King, compared with mixed stands with Eucalyptus ´ rvore (a Brazilian Journal) urophylla S.T. Blake, 40 months after planting. A 28, 777–784. Martı´nez-Ramos, M., Alvarez-Buylla, E.R., 1998. How old are tropical rain forest trees? Trends Plant Sci. 3, 400–405. Pe´rez-Salicrup, D.R., 2004. Forest types and their implications. In: Turner, II, B.L., Geoghegan, J., Foster, D.R. (Eds.), Integrated Land-Change Science and Tropical Deforestation in the Southern Yucata´n: Final Frontiers. Oxford University Press, Oxford, UK, pp. 63–80. Ramos, J., Grace, J., 1990. The effects of shade on the gas exchange of seedlings of four tropical trees from Mexico. Funct. Ecol. 4, 667–677. SEMARNAT, 2005. Anuario estadı´stico de la produccio´n forestal 2003. Secretarı´a del Medio Ambiente y Recursos Naturales, Me´xico City, DF, Mexico. p. 152. Snook, L.K., 1998. Sustaining harvests of mahogany (Swietenia macrophylla King) from Mexico’s Yucata´n forests: past, present, and future. In: Primack, R.B., Bray, D., Galletti, H.A., Ponciano, I. (Eds.), Timber, Tourists and Temples: Conservation and Development in the Maya Forest of Belize, Guatemala, and Mexico. Island Press, Washington DC, USA, pp. 61–80. Sokal, R.R., Rohlf, F.J., 1995. Biometry, 3rd ed. W.H. Freeman and Company, San Francisco, CA, USA, 885 pp.
Forest Ecology and Management 255 (2008) 324–327 www.elsevier.com/locate/foreco
Tree infection by Hypsipyla grandella in Swietenia macrophylla and Cedrela odorata (Meliaceae) in Mexico’s southern Yucatan Peninsula Diego R. Pe´rez-Salicrup a,*, Ricardo Esquivel b a
Centro de Investigaciones en Ecosistemas, Universidad Nacional Auto´noma de Me´xico, Antigua Carretera a Pa´tzcuaro 8701, Morelia, Michoaca´n, Mexico b Universidad Marista de Me´rida, Perife´rico Norte Tablaje Catastral 13941, Me´rida, Yucata´n, Mexico
Abstract In small-scale plantations (0.5–2 ha) of Swietenia macrophylla King (big-leaf mahogany) and Cedrela odorata L. (Spanish cedar) in the southern Yucatan Peninsula, we evaluated whether the proportion of Hypsipyla grandella (mahogany shoot borer) was affected by the species used in the plantation (S. macrophylla, C. odorata or both) or by the density and height of individuals planted. We found that the proportion of infected individuals did not differ between the species used in plantations, either planted as monocultures or in mixed plantations. The proportion of infected S. macrophylla and C. odorata individuals in plantations differed among locations and was affected by the mean height of planted individuals, but was not affected by the density of individuals planted. # 2007 Elsevier B.V. All rights reserved. Keywords: Big-leaf mahogany; Mahogany shoot borer; Mixed plantations; Spanish cedar
1. Introduction Swietenia macrophylla King (big-leaf mahogany) and Cedrela odorata L. (Spanish cedar) are two species in the Meliaceae family which are vulnerable to infection by Hypsipyla grandella Zeller (shoot borer or driller worm; Bauer and Francis, 1998; Arteaga and Izaguirre, 2004). H. grandella larvae attack the apical meristem of S. macrophylla and C. odorata individuals, causing increased branching and slowing down tree growth. Furthermore, as secondary branches become dominant, the bole of infected individuals becomes deformed. For these reasons, H. grandella has been identified as the most important factor limiting the successful establishment of plantations of these two species in Mexico and other countries in the Neotropics (Bauer and Francis, 1998; SEMARNAT, 2005). Swietenia macrophylla and C. odorata account for only 0.5% of volume and 1.5% of value of timber produced in Mexico (SEMARNAT, 2005). However, in the southern Yucatan Peninsula many communities dedicated to timber production depend largely on the income produced from these two species (Flachsenberg and Galletti, 1998; Galletti, 1998). To alleviate timber exploitation pressure on natural forests and to insure
* Corresponding author. Tel.: +52 55 56232708; fax: +52 55 56232719. E-mail address: [email protected] (D.R. Pe´rez-Salicrup). 0378-1127/$ – see front matter # 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.foreco.2007.09.054
harvestable timber volumes in the future, the Mexican government has promoted agroforestry systems in which S. macrophylla and C. odorata are planted in areas formerly used for shifting agriculture (SEMARNAT, 2005). In the region around the Calakmul Biosphere Reserve in the southern Yucatan Peninsula, farmers of several communities (locally called ejidos) have voluntarily established plantations of S. macrophylla and C. odorata (Acopa and Boege, 1998). These plantations usually cover small areas, ranging from 0.5 to 5 ha, and because seedlings of these light demanding species are planted in open areas, it has been suggested that conditions for their growth are ideal (Ramos and Grace, 1990; Snook, 1998). However, management practices in these plantations vary widely among farmers, who receive little or no advice on how to maximize seedling survival and growth in their plantations. First, farmers might plant monocultures with one of these species, or they might incorporate both species in a single plantation (henceforth called mixed plantations). Second, some farmers plant additional fruit species in addition to S. macrophylla or C. odorata. Finally, the distance between planted seedlings also varies. As distance between individuals increases, density of planted individuals decreases and more trees of different species naturally establish between planted individuals, turning the plantation into an unintended polyculture. Because the success of the timber production and conservation goals of these plantations depends largely on
D.R. Pe´rez-Salicrup, R. Esquivel / Forest Ecology and Management 255 (2008) 324–327
the growth of planted trees, it is important to evaluate whether individual practices implemented by local farmers affect the proportion of H. grandella infected individuals. In this article we evaluate whether the proportion of infected individuals of S. macrophylla and C. odorata in monocultures differs from the proportion of infected individuals when both Meliaceae species were planted in mixed plantations. We then tested the hypothesis that the proportion of infected individuals in a plantation was directly related to the density of planted individuals. Because the probability of infection might increase with age, and tree height and tree age are correlated, we also evaluated whether the proportion of infected individuals increased with mean tree height in a plantation. We expected that plantations with lower S. macrophylla and C. odorata densities should have lower proportions of infected individuals under the assumption that the presence of other naturally established tree species might diminish the incidence of H. grandella. Answers to these questions could inform local farmers as to whether they should plant single or mixed species plantations, and whether they should reduce the density of Meliaceae seedlings in plantations in order to reduce the potential for H. grandella infection. 2. Methods We evaluated the proportion of S. macrophylla and C. odorata individuals infected with H. grandella in 45 plantations located in the vicinity of Calakmul Biosphere Reserve in the southern Yucatan Peninsula in August 1999. Precipitation in the region ranges between 910 and 1353 mm year 1 (Pe´rezSalicrup, 2004). Plantations were located in eight ejidos where farmers allowed us to study at least four different plantations (Table 1). All plantations were 5 years old and ranged between 0.5 and 2 ha in size. Plantations varied in density of Meliaceae planted seedlings, and density of Meliaceae planted seedlings was negatively correlated with density of other species (Table 1). Plantations were established in sites formerly used for shifting agriculture, so that most were surrounded by agricultural fields or secondary forests. We classified plantations as monocultures or mixed plantations. In each plantation, we counted and measured the height of all individuals of S. macrophylla and C. odorata in
325
three contiguous rows chosen randomly. We considered H. grandella damaged individuals as those in which secondary branches had taken over vertical growth due to death of the apical meristem, although in many instances H. grandella larvae could not be found. We measured the length and width of the three selected rows in each plantation, and estimated Meliaceae seedling density. We evaluated whether the proportion of infected individuals of S. macrophylla and C. odorata in monocultures differed from the proportion of infected individuals in mixed plantations with a Mann–Whitney U-test. We used the same test to evaluate differences in the proportion of infected individuals in monocultures of S. macrophylla versus C. odorata. Plantations were located within different ejidos, and plantations differed slightly in age, and in the height of planted individuals. Because age and height of planted individuals are usually correlated but the latter can be more accurately measured than the former, location, density and mean height of individuals in a plantation were evaluated simultaneously. We used an ANCOVA to evaluate whether the proportion of infected Meliaceae saplings in plantations differed between locations (i.e., ejidos) considering sapling density and mean sapling height as covariates. We transformed sapling density to logarithmic scale to fulfill normality requirements of ANCOVA (Sokal and Rohlf, 1995). 3. Results and discussion Of the 45 studied plantations, 11 were planted with S. macrophylla, 18 with C. odorata, and 16 were mixed plantations. The proportion of infected individuals did not differ between S. macrophylla and C. odorata planted in monocultures (U = 132, P = 0.13). Neither did the proportion of infected individuals of S. macrophylla and of C. odorata differ between monocultures and mixed plantations (U = 97, P = 0.65, and U = 138.5, P = 0.85, respectively). Hence, it appears that the proportion of H. grandella infected individuals is not different for these two Meliaceae species, and that the proportion of infected individuals is not affected by planting monocultures or mixed plantations of these two species. This suggests that the choice of selecting one or the other species should be based on the availability of seedlings and other economic considerations such as projections of future timber values.
Table 1 Number of plantations and plantation characteristics in eight ejidos in the southern Yucatan Peninsula, Mexico Ejido
Number of plantations
Types of plantations (S, C, M)a
Density of individuals (ind/10 m2)
Mean proportion of infected individuals
Range of proportion of infected individuals
Veinte de Noviembre Diaz Ordaz La Lucha Narciso Mendoza Nueva Vida Valentin Gomez Farias Nuevo Campanario Heriberto Jara
5 11 5 4 5 7 4 4
S, M S, C, M S, C, M S, C, M C, M S, C, M C C, M
3.4–28.4 0.5–17.6 3.3–17.2 1.5–3.7 6.7–14.8 1.1–12.0 5.5–8.6 2.9–9.3
0.10 0.28 0.43 0.47 0.52 0.70 0.71 0.74
0.00–0.28 0.00–0.65 0.00–0.86 0.00–1.00 0.27–0.71 0.22–0.95 0.53–0.90 0.58–0.95
a
S: Swietenia macrophylla; C: Cedrela odorata; M: mixed plantation.
326
D.R. Pe´rez-Salicrup, R. Esquivel / Forest Ecology and Management 255 (2008) 324–327
The proportion of infected individuals in plantations differed among locations, and was affected by the mean height of planted individuals but not by their density (F location = 3.52, Plocation = 0.006; F height = 10.48, Pheight = 0.003; F logdensity = 0.02, Plogdensity = 0.88; Fig. 1). Despite the fact that location of plantations influenced the proportion of H. grandella infected individuals, there are no obvious differences in the studied ejidos in terms of rainfall, altitude or land use which might suggest why infections rates differed. Plantations in ejidos Veinte de Noviembre and Diaz Ordaz had means of infection of 10% and 28%, respectively, while the other ejidos had means of infection ranging from 43% to 78% (Table 1). As is the case for many other insect species, H. grandella populations might experience oscillations driven by stochastic or unpredictable processes, so it might be that variation in the proportion of infected individuals across locations varies in response to population densities of H. grandella. Plantations with taller S. macrophylla or C. odorata individuals had a higher probability of infection (Fig. 1). Because age and tree size are correlated (Martı´nez-Ramos and Alvarez-Buylla, 1998), taller individuals might be older, which allows for more time of exposure to H. grandella infection. Alternatively, H. grandella might have a preference to infect taller individuals, so a plantation with taller plants might be more susceptible to infection. Contrary to our expectations, density of S. macrophylla and C. odorata did not affect the proportion of infected individuals. Densities of plantations in this study ranged from 0.5 to
28.4 individuals/10 m2, which represents a very wide range of variation, so lack of an effect of density presumably was not caused by lack of variation within the range of observed densities. Other studies in different parts of the world have found contrasting results regarding the proportion of H. grandella infected individuals in plantations of S. macrophylla and C. odorata mixed with other tree species. In a study conducted in Brazil, plantations of S. macrophylla mixed with Eucalyptus urophylla reduced infection by H. grandella from 71% to 25%, though growth of S. macrophylla increased when planted in monocultures (Guimara˜es et al., 2004). In a different study in the southern Yucatan Peninsula, most S. macrophylla and C. odorata individuals were affected by H. grandella, despite being planted under different canopy structures (Arteaga and Izaguirre, 2004). It is possible that a reduction of H. grandella infection rates reported by Guimara˜es et al. (2004) was not caused by a reduction in density of S. macrophylla, but rather by an effect of E. urophylla on H. grandella. While their study is not conclusive in this respect, it opens the possibility that a reduction of the proportion of H. grandella infected individuals in a plantation of S. macrophylla or C. odorata might depend on the tree species that is mixed with them. However, it would be necessary to screen tree species to evaluate which ones might have such an effect. Because planting densities did not affect the proportion of infected Meliaceae individuals in this study, we recommend that local farmers in the southern Yucatan Peninsula engaged in agroforestry plantations using S. macrophylla or C. odorata should try to maximize the density of their plantations in order to obtain higher future harvest volumes, as reducing density will not result in lower proportion of H. grandella infected individuals. Of course, densities of S. macrophylla and C. odorata in plantations should reflect spacing requirements that minimize competition between individuals. We also recommend that local authorities involved in promoting plantations of S. macrophylla and C. odorata in the southern Yucatan Peninsula offer more information to engaged farmers to help them receive the maximum profit possible from their plantations. Acknowledgements
Fig. 1. Proportion of S. macrophylla and C. odorata individuals infected with H. grandella as a function of mean height in plantations in eight ejidos in the southern Yucatan Peninsula. Dashed lines represent ejidos with significantly less proportion of infected individuals (Diaz Ordaz and Veinte de Noviembre), continous lines represent the remaining ejidos. Symbols represent individual plantations in different ejidos (open circle: Diaz Ordaz; open diamond: Heriberto Jara; open square: La Lucha; open triangle: Narciso Mendoza; closed circle: Nueva Vida; closed diamond: Nuevo Campanario; closed square: Valentin Gomez Farias; closed triangles: Veinte de Noviembre).
This work was undertaken through the auspices of the Southern Yucata´n Peninsular Region (SYPR) project with core sponsorship from NASA’s LCLUC (Land-Cover and Land-Use Change) program (NAG 56406) and the Center for Integrated Studies on Global Change, Carnegie Mellon University (CISCMU; NSF-SBR 95-21914). Additional funding from LTER GRU supported Ricardo Esquivel. SYPR is a collaborative project of El Colegio de la Frontera Sur (ECOSUR), Harvard Forest – Harvard University, the George Perkins Marsh Institute – Clark University, and CIS-CMU. We thank Vı´ctor Chi Noh, Karen Vitkay and Autumn Bryant for their support. Ricardo Esquivel was supported through a program at Harvard Forest. We are grateful for comments by two anonymous reviewers which improved the clarity of this manuscript.
D.R. Pe´rez-Salicrup, R. Esquivel / Forest Ecology and Management 255 (2008) 324–327
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