|Title||Chinantec shifting cultivation : InTERAcTIVE landuse : a case-study in the Chinantla, Mexico, on secondary vegetation, soils and crop performance under indigenous shifting cultivation|
|Author(s)||Wal, H. van der|
|Source||Agricultural University. Promotor(en): R.A.A. Oldeman. - S.l. : s.n. - ISBN 9789058081315 - 162|
|Department(s)||Biological Farming Systems|
|Publication type||Dissertation, internally prepared|
|Keyword(s)||zwerflandbouw - vegetatietypen - bosbouw - agroforestry - landgebruik - vegetatie - herbegroeiing - vegetatiebeheer - secundaire bossen - mexico - shifting cultivation - vegetation types - forestry - agroforestry - land use - vegetation - revegetation - vegetation management - secondary forests - mexico - cum laude|
|Categories||Agriculture in North America|
The development of secondary vegetation, soils and crop performance was studied in local variants of shifting cultivation in two villages in the Chinantla, Mexico. In Chapter 1, the institutional, social and political context of the research are presented and the reader is advertised that the scope of the study is limited to the interaction between ecological-productive aspects and the landuse pattern as practiced by the farmers.
In Chapter 2 a conceptual framework is presented. Indigenous shifting cultivation is defined as a general form of landuse, characterized by the continuous recontextualization of a many-sided relation between man and nature, the continuous recreation of knowledge and the making and use of dynamic fields according to a landuse pattern. A great specificity of indigenous shifting cultivation in response to local environmental and socio-economical factors is observed.
The ecology of secondary vegetation is reviewed, paying attention to mountain areas such as the Chinantla. The development of forest eco-units is not a simple, unilinear process, but, on the contrary, a process that can take one of many possible courses, influenced by environmental factors and the use-history of the land. Soils develop as an integral part of eco-units, as has been observed by comparing the soil in hurricane tracts and eco-units of different ages. The development of secondary vegetation and soils, as related to the landuse pattern for shifting cultivation, leads to variation in the ecological conditions within the mosaic of fields. Consequently, the performance of crops may vary within the mosaic of fields.
In the Chinantla region a large variation in climate occurs due to a wide altitudinal range (Chapter 3). As a consequence, several vegetation types occur. Soils in the area have developed from limestone or sandstone/metamorphic rocks. Chapter 4 describes the variants of shifting cultivation and the landuse pattern in the Chinantec communities Santa Cruz Tepetotutla and Santiago Tlatepusco. Three variants of shifting cultivation were distinguished: shifting cultivation in the area of 'selva alta perennifolia de montaña' (the most widely practised), shifting cultivation in the limestone area, and shifting cultivation in the Quercus -forests. In all variants maize is the principal crop.
In Chapter 5 the development of secondary vegetation as related to the use-history of fields is studied, concentrating on secondary vegetation in the area of 'selva alta perennifolia de montaña'. Secondary regrowths were sampled in 28 fields. Ages of regrowths varied from 5 to 50 years, and orders of regrowths (first-order regrowths develop after cutting primary or old secondary vegetation; second-order regrowths after cutting a first-order regrowth) varied from 1 to 4. On each field, data on the trees and shrubs with a diameter at breast-height of more than 2 cm were recorded in four transects, each of 100 m 2surface area, which were all laid out on steep slopes.
A total of 5691 trees and shrubs, belonging to 229 species, were found on the sampled area. Thirty-seven species comprised 90% of all sampled individuals. Cluster and ordination analysis showed variation of the species composition of secondary vegetation with age, altitude, geographic location, lithology and order of regrowth. Analysis of farmers' information on the relation between order of regrowth and species composition confirmed the results of sampling.
Structural parameters, species composition, tree development and eco-unit development varied between orders of regrowth. Basal area, number of trees and crown area index were high in first- and second-order regrowths, but fell sharply in subsequent regrowths. First-order regrowths were dominated by one or two species. In several second-order regrowths, Hedyosmum mexicanum was the single dominant. In other second-order and in later-order regrowths polydominance was observed. Analysis of height-diameter relations in frequent species also indicated a relation between the order of regrowth and the development of the trees of a certain species, demonstrating the flexibility of trees in responding to a changing environment. Whereas first- and second-order regrowths were composed of few eco-units, third- and fourth-order regrowths showed fragmentation of eco-units from early phases of development onwards. The results indicate that the number of consecutive eco-units per time unit diminishes with increasing order of regrowth.
Changes in soils during one cropping season were studied by comparing soil parameters in samples obtained after slashing the vegetation (May), after burning (June) and at harvest (October-November). No significant differences in bases, pH, nitrogen and carbon were found between May- and June-samples on limestone-derived soils. Between burning and harvest, pH and the sum of exchangeable bases increased slightly. In the area of 'selva alta perennifolia de montaña' pH and exchangeable bases increased significantly between May and June. During the cropping season (June to October-November), the sum of exchangeable bases declined slightly. No relation of these changes with the use-history of fields was found, possibly due to the small number of sampled fields and burns being partial and heterogenous in the year of sampling (1993).
Sampling of soils in a chronosequence of fields in the area of 'selva alta perennifolia de montaña' gave strong indications of an increase of pH and exchangeable bases in the course of several decades, from the cutting of primary or old secondary vegetation onwards. The strongest increase was observed in the quantity of exchangeable calcium. Correlations between use-history parameters and carbon, nitrogen and phosphorus were not significant. A mechanism of soil change based on a combination of physical and biological processes is proposed, wherein an initial increase in pH through the addition of bases triggers of an increased biological activity resulting in a more hospitable soil.
The performance of maize crops in a chronosequence of fields was studied in 1994 by determining several parameters referring to the crops (Chapter 7). Crop performance varied strongly between fields, both in the limestone area and in the area of 'selva alta perennifolia de montaña'. In the limestone area, yield per square meter sloping surface diminished with increasing number of burns; there was no relation between yield and any of the measured soil parameters. In the area of 'selva alta perennifolia de montaña', yields were not significantly correlated with any of the parameters applied to characterize the use-history of fields. However, yields per square meter sloping surface were correlated with several soil parameters: CEC-BaCl 2 , exchangeable calcium, total phosphorus and the C/N-ratio. At values smaller than 3.9 also pH-KCl was positively correlated with yields. In fertilization experiments, the combined application of nitrogen and phosphorus improved yield on a field where without fertilization a low yield was obtained; fertilization had no effect where high yields were obtained without fertilization.
The development of secondary vegetation, soils and crop performance in indigenous shifting cultivation in two villages in the Chinantla, Mexico, illustrates the interactive and iterative character of this form of agriculture. This character should be taken as the point of departure for its redesign in such a way that the production of a variety of goods is combined with the production of a variety of services in a complex mosaic of eco-units.