, Volume 28, Issue 3, pp 776-792

Does harvesting sustain plant diversity in central Mexican wetlands?

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Abstract

In Central México, wetland plants are harvested for weaving, fodder, and fertilizer. To test whether harvesting alters plant diversity, we compared the effects of harvesting all vegetation once, follow-up harvesting of Typha domingensis Pers. one or three more times, and a non-harvested control, using two sites differing in water depth in an annually burned wetland near Morelia, México. After one year, harvesting treatments increased species richness at both the plot (14-m2) and wetland scales, increased the Shannon diversity index at the plot and subplot (1-m2) scales, and changed plant community composition (measured by Bray-Curtis distance) relative to control plots. Response among harvesting treatments was similar, and increased Typha harvesting did not have additive effects on Typha or on community composition. Grasses and short forbs (< 0.5-m tall) significantly increased in importance value in harvested plots, as did five individual forb species that were capable of vegetative spread. Uncommon species were significantly more likely to be found only in harvested plots than only in control plots, and new species (not initially present at the site) tended to recruit in harvested plots. Most new species were perennials that could likely tolerate additional harvesting. All harvesting treatments reduced Typha height, density, and rhizome starch reserves after five months, and responses were significantly affected by site, water depth, flowering ramet density, and pre-treatment values. Typha recovered in all harvested plots after one year, even when harvested four times, although flowering-ramet density declined in the wetter site. Community composition was more highly correlated with water depth and litter cover than with harvesting in an NMS ordination including both sites. Within sites, harvesting, light availability, leaf area index, and litter cover correlated similarly with variation in community composition. Given that our treatments reflect a subset of actual local management practices, harvesting could provide a sustainable and economically attractive management strategy for biodiversity conservation in this system, while the cessation of harvesting could lead to species loss.