Abstract
Forestry systems in Mexico are examples of traditional management of land and biodiversity that integrates the use, conservation and restoration of forest elements. Current in situ management practices of Agave maximiliana in western Mexico include the tolerance of many forest elements, reintroduction of young Agave plants and germination of seeds. More intense forms of management include monocultures, which are agroindustrialized systems developed in more recent times and characterized by the establishment of high densities of A. maximiliana plants in deforested areas and abandoned agricultural lands. We compared monocultures, forestry systems and wild populations (i.e., non/slightly-exploited forests) in order to evaluate whether these practices have had an effect on intraspecific morphological and genetic variation and divergence. We also tested whether divergence has a positive relationship with environmental and geographic distance. We analyzed 16 phenotypic traits in 17 populations of A. maximiliana, and 14 populations were further examined by amplifying 9 SSR loci. We employed multivariate methods and analyses of variance in phenotypic and genetic traits to test whether clusters and the percentage of variation contained in the managed and wild categories can be identified. Tests of isolation by environment (IBE) and distance (IBD) were performed to detect the magnitude of divergence explained by climatic and geographic variables. We found that forestry systems are effective as reservoirs of morphological and genetic diversity, since they maintain levels similar to those of wild populations. Moreover, the monocultures showed similar levels, reflecting their recent emergence. While the species showed high morphological diversity (IMD = 0.638, SE ± 0.07), it had low to intermediate genetic diversity (A = 2.37, HE = 0.418). Similar morphological and genetic divergences were found among populations, but these were not correlated with each other in population pairs. Non-significant morphological differentiation was found among categories. Only IBE was significant in the genetic structure (β = 0.32, p = 0.007), while neither IBE nor IBD was detected in the morphological differentiation. We discuss the implications of these results in the context of the weaknesses and strengths of A. maximiliana in the face of the socio-ecological changes predicted for the study area in the short term.
Highlights
Agaves have considerable cultural, economic and ecological importance in North America (Gentry, 1982)
We explored the case of Agave maximiliana Baker growing in pine-oak forest in western Mexico
No significant differences were found in mean Index of Morphological Diversity (IMD) among categories or populations (H = 16, p = 0.453), suggesting that the plants were morphologically diverse regardless of management condition or the population to which they belong
Summary
Economic and ecological importance in North America (Gentry, 1982). While AFS represent alternatives to the current problems relating to the management and conservation of biodiversity (Torres-García et al, 2019), Agave monocultures have had an impact on traditional ecological knowledge and agrobiodiversity, while depending heavily on the use of toxic agrochemicals (Bowen and Gerritsen, 2007). These agroindustrial management forms are characterized by the establishment of high densities of a single species for one simple purpose in deforested areas and/or abandoned agricultural lands (Torres-García et al, 2019). Weber Azul, used in the spirits industry for the production of tequila, have spread rapidly in western Mexico, from the end of the 20th century up to the present day (Leclert et al, 2010)
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