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Accueil du site → Doctorat → Allemagne → 2008 → Production potential and ecosystems quality of secondary forests recovered from agriculture - tools for landuse decisions

Georg-August-University Göttingen (2008)

Production potential and ecosystems quality of secondary forests recovered from agriculture - tools for landuse decisions

Ruiz-Garvia, Carlos Alberto

Titre : Production potential and ecosystems quality of secondary forests recovered from agriculture - tools for landuse decisions

Produktionspotential und Ökosystemqualität von Sekundärwäldern mit vorheriger landwirtschaftlicher Nutzung - Methoden zur Landnutzungsentscheidungsfindung.

Auteur : Ruiz-Garvia, Carlos Alberto

Université de soutenance : Georg-August-University Göttingen

Grade : Doctor of Philosophy (PhD) 2008

Résumé
Secondary forests in large areas of Semiarid Americas play a vital role in the maintenance of land quality and are also important for the community. The total benefits of ecosystem services provided by forest fallows and the potential for forest production have not been evaluated, largely because forest productivity under secondary land cover has rarely been measured with an eye to marketable products. This study evaluates the productivity of forest fallows derived from agricultural activities (Henequen plantations ; Agave fourcroydes Lem) in a climatically vulnerable semiarid region in Northern Yucatan. We explored options for improved landuse management in secondary forest and measured nutrient budgets in soils and vegetation and use tree-ring analysis to predict tree productivity in fallow vegetation of different succession states. Floristic composition, species richness, and diversity of the seasonally was described. We sampled eighteen 1,000 m2 sites and recorded species and dbh of trees and shrubs of trees >1 cm dbh. Cross dating techniques were used to identify correlation between tree growth and climatic patterns. Furthermore, root-ingrowth trials were established to identify limiting factors in soils. To validate these results, we conducted a trial with Cordia dodecandra to identify limiting P and N on black and red soils at a nursery stage. Our results showed that secondary forests rapidly attain a forest structure similar to mature forests after 35 years. The results of the correspondence analysis indicated that species composition varies with stand age. In the sampling sites, data from 715 individuals (> 8cm dbh) and 708 individual (< 8cm and >1 cm dbh) were recorded, representing 63 woody species, 56 genera, and individuals Gymnopodium (Polygonaceae) and Bursera (Birseracea) were the most common species. Species richness among sites ranged from 43-63. These results indicate that these forests have low values of species richness and structure attributes in relation with other tropical dry forest of Mexico and the world. The soil analyses at different stand age reveal that the overall fertility may be lower in young secondary forest. Unlike the other indices of fertility, K levels were significantly higher in young forest which may indicate translocation functions of plants when K becomes limiting factor. Litter production increased consistently with age. Interaction between the forest age and soil type was a determining factor for OC and total N contents in these ecosystems. Red soils had less OC and N compared to the black ones. These differences between both soils were strongly marked by their mineralogical properties. The root-ingrowth experiment showed a significant effect of K addition, a moderate effect of P, especially in red soils, with no effect of N or Co interaction. The results from the second experiment (using Cordia dodecandra seedlings in a nursery) show the fertilizer application enhanced the seedling height after 6 months. Forest inventory and tree ring analysis show that these secondary forests have the potential to produce an average amount of timber of about 0,087 m3 /tree over 50 years or an average amount of firewood 2,6 m3 /ha/yr. Although these potential may be limited for industrial wood production, previous experiences in similar regions demonstrated that silvicultural strategies could be identified to stimulate the production of commercial timber species in this forest fallows, such as liberation thinning, enrichment plantings and refining. Mots Clés : Forest production ; ecosystem quality ; secondary forest ; tree ring analysis ; Yucatan

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