Birds, charcoal and cattle: Bird community responses to human activities in an oak forest landscape shaped by charcoal extraction
Introduction
Oak forests are important elements of both temperate and tropical ecosystems (Abrams, 2003, Valencia, 2004). Mexico is one of the centers of diversification for the genus Quercus (over 160 species), with oak forests covering ∼5.5% of the landscape (Rzedowski, 1978, Valencia, 2004). These ecosystems present a high floristic and physiognomic diversity, and have great ecological importance (Flores and Gerez, 1994), especially for birds, being one of the five richest habitats for avian species throughout the Neotropics, and having the largest number of endemic bird species for any given habitat in Mexico (Flores and Gerez, 1994, Stotz et al., 1996).
In addition to their ecological value, oak forests are regarded worldwide as an ecosystem with high economic importance, being used intensely for the production of wood and timber (Abrams, 2003, Valencia, 2004, McShea et al., 2007, Arriaga Cabrera et al., 2009). In developing countries like Mexico, about 80% of the wood extracted from oaks is used to obtain energy as charcoal and/or firewood (Rzedowski, 1978, Aguilar et al., 2012). As a result, in recent decades charcoal production has been one of the main causes of deforestation of large stands of oaks in this country (Rzedowski, 1978, Works and Hadley, 2004, Challenger et al., 2009). Oak forests managed for charcoal production tend to form landscapes with complex and diverse habitat mosaics. Usually they include forest fragments of different ages, which are generated by the rotation of wood cutting among forest patches (Kubo et al., 2005, García Burgos, 2007). In addition to wood extraction, other productive activities, such as cattle grazing, tend to be carried out within these charcoal producing landscapes. While this is a common practice, there is little information on the effects of these human activities on biodiversity oak forests of western Mexico.
In this study, we used bird communities as a model to understand effects of oak forest management on biodiversity. We compared avian communities among four management units related to the production of charcoal. We define a management unit as a forest patch that shows uniformity in land use (Zonneveld, 1989). The four management units we studied include: (a) three successional stages that occur after most of the trees have been removed for charcoal production where also cattle-grazing is conducted, and (b) ungrazed mature oak forest patches. We used this study system to determine how avian species richness, bird densities, and the structure and composition of bird communities changed in relation to habitat management for charcoal extraction and cattle grazing. We hypothesized that species richness should increase in relation to habitat structural complexity and as a response to the absence of cattle in the system. On the other hand, because disturbed/simpler habitats tend to present high quantities of a low number of food resources, bird density should be higher in the management units that are structurally simpler and used for cattle grazing activities (Winker et al., 1990, Petit et al., 1999, Dunn, 2004). We also hypothesized that the responses of resident and migratory bird species should differ in each of the management units. Resident bird species should present larger differences in their communities among management units than Neotropical migrants because they have to confront the existing habitat conditions throughout the year, while migrants can act as habitat generalists because they use different environments in different seasons (Hutto, 1989, Lynch, 1989, Levey, 1994, Smith et al., 2001).
Section snippets
Study area and study sites
Our study was conducted in the Cuitzeo watershed, located in the central-northeast region of the state of Michoacán in west central Mexico (19°30′–20°05′N; 100°35′–101°30′W). The Cuitzeo watershed comprises an area of 4026 km2 including 28 municipalities from the states of Michoacán and Guanajuato (Leal-Nares et al., 2010). The altitudinal range varies between 1830 and 3420 masl. This watershed presents high ecological diversity, including several temperate types of forests that include oak,
Results
We recorded a total of 82 bird species and 1778 individuals in our surveys (Appendix A). When we compared the ACE-1 estimator for cumulative species richness for the study area, our data represented 97% of the total species predicted for summer and 98% for winter (using SPADE; Chao and Shen, 2006, MacGregor-Fors and Schondube, 2012). This indicates that our sampling effort provided a good representation of the avian communities in the management units. We recorded a total of 40 resident
Discussion
Summer and winter bird communities in a landscape shaped by charcoal extraction responded differently to the successional process and to the presence of cattle. In summer, the ungrazed late successional unit had the highest bird species richness of all the management units. During winter, although the ungrazed late successional unit continued to present the higher species richness, it did not differ from the middle successional unit which also presented high species richness. We found
Acknowledgments
Research funds were granted to J.E.S. by the Universidad Nacional Autónoma de México. We are grateful for field assistance by Adrian Ceja Madrigal, Lorena Morales Pérez, Luis Manuel Maya Elizarrarás, Baldemar Maya, and Luz Elena López Ferreyra. We thank Rafael Aguilar for his valuable commentars and information shared about the study sites. We thank Katherine Renton for reviewing an early version of the manuscript. E. Friedewold reviewed our manuscript, and corrected grammatical and style
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