[Aztlan] Questions about vegetation on Mesoamerican ruins

[Carlos Rincón Mautner]

Dear Listeros

Vegetation growing on ruins is basically similar to that growing in areas surrounding a site. The vegetation found along a site's edges, however far from the site, are the likely seed sources for the colonization of abandoned sites. The majority of the vegetation initially got there as seeds from the surrounding forest or vegetation association, less so by vegetative reproduction such as stolons. If you are referring to vegetation that grows once the site has been abandoned, bats and birds quickly bring in the seeds in their droppings, other seeds may be wind-dispersed. Colonizing species tend to be more aggressive... that is they can take hold under less than ideal environmental conditions (i.e. low humidity and poor soil conditions, even non-existent soil conditions). Once abandoned, the buildings on a site are no longer being swept or maintained, so seeds in the droppings sprout and take root in any nook and cranny. In humid and subhumid areas, ficus "strangler" trees tend to be among the first colonizers. 

Overall we have a relatively poor understanding of plant succession on ruins. We have a much better understanding of the successional sequence for abandoned agricultural fields, especially where slash-burn agriculture has been practiced, and better still for certain biomes like the tropical rainforest where a tree falls and the canopy is opened, and fast growing species outcompete slower growing species for the light. Some trees like ramon or palms found on sites may be preserved, and those act as seeds sources as well. 

The bulk of forest successional work has focused on less disturbed environments and on biomes rich in biodiversity like tropical rainforests and even seasonal forests. Both of these have been studied to a greater extent than xerophytic scrub forests for example. You might look at the work done by Carlos Vázquez-Yañez of INIREB for tropical rainforests and that of other botanists working with the Instituto de Biología, Instituto de Ecología at UNAM, or some of the basic tropical ecology work done in Costa Rica by Dan Janzen and others, but do not expect much mention of vegetation on ruins in that literature, since the focus is on "natural" associations where evidence of human presence is believed to not have been so strong. Of course, this topic of human-modified forests has been the subject of much debate over the last 15 years or so. 

Structures breaking down act as sediment and humidity traps and this generally means that they will be colonized by plants first and stand out given a milieu with greater moisture and soil than surrounding areas. Generally those plants tend to thrive and remain. They may be taller, although I have walked among Classic and post-Classic ruins along limestone ridges in the Mixteca and noticed that the oak forests that cover them which are several hundreds of years old tend to be thinner and just as tall suggesting younger, and/or perhaps more stressed, than old growth oak forest away from the ruins. Palmetto also tends to grow on disturbed areas, but no necessarily on the ruins.

Root growth tends to be a function species, its habit, substrate and of how much humidity is available to the plant. Some of the more extensive root systems I have seen were among Ficus trees and columnar cacti in the more arid zones of the Tehuacan Valley. 

Soils from sites are increasingly being studied, but I do not find that the vegetation associated with those soils has been the specific focus of any of these studies which seem aimed at identifying evidence of antropic activity. 

I hope this is helpful. 

All the best,

Carlos

----------------------------------------> Date: Tue, 2 Oct 2007 19:14:36 -0500> From: jules at cafecancun.com> To: aztlan at lists.famsi.org> Subject: [Aztlan] Questions about vegetation on Mesoamerican ruins>> Over the years I have tried to find answers to the following questions> without much success. I tried Internet searching again today and found> myself dealing with a bewildering variety of irrelevant hits no matter> how I formed the search pattern. I'd very much appreciate some thoughts> about these points based on sound scientific research rather than> speculation. Many thanks for your consideration, folks.>> What is the tallest structure entirely covered in vegetation growing on> it (as opposed to around it forming a canopy)?>> How did the vegetation get there?>> What kind of vegetation is typically found?>> How deep are the roots?>> The depth of the soil?>> Is it true that seashells have been found in the soil on top of> Mesoamerican monuments? If so, how did they get there? What kind? Age?>> --> JULES SIEGEL Apdo. 1764, 77501-Cancun, Q. Roo, Mexico> http://www.cafecancun.com/bookarts>> Newsroom-l, news and issues for journalists> http://www.newsroom-l.net/>> _______________________________________________> Aztlan mailing list> Aztlan at lists.famsi.org> http://www.famsi.org/mailman/listinfo/aztlan

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