Deep rooting is an advantageous plant strategy because it expands a tree’s available water sources to reliable pools at depth. This trait is predicted to be more common in drylands with seasonal precipitation regimes, allowing trees to maintain positive water status throughout dry periods and droughts. Seasonally dry tropical forests of the Yucatán Peninsula in Mexico represent these ecosystems and are notably understudied. Here, deep roots emerge from the ceilings and walls of shallow caves, providing the opportunity to directly observe root distribution and structure. Despite their prevalence, it is unknown which species provide these roots and how they impact surface processes. This research evaluated relationships between above ground biomass and composition and root abundance and biodiversity along a depth-to-groundwater gradient. Paired above and below ground plots were established at random positions along transects over selected caves. In the surface plots, trees were identified and non-destructive measurements were made to estimate biomass. In the cave plots, diameter and length of all visible roots were measured to estimate root abundance and root basal area to allow comparisons with above ground biomass and basal area. Samples of all roots were collected and species diversity was assessed via morphological differences and genetic approaches.
Results/Conclusions
Above and below ground vegetation surveys were conducted at five caves in the state of Quintana Roo, along the Caribbean coast. Masses of intertwined roots sharing cave ceiling conduits were commonly observed, suggesting that access to deep water is limited by the karst bedrock and that there may be competition for access to both below ground space and resources. Incorporation of roots into speleothems provide evidence that trees have historically extended deep roots into caves, contributing to the growth and structure of the cave itself. Strangler fig (Ficus cotinifolia), locally known as Alamo, is a dominant species below ground. Where Ficus is observed above ground, it is dominant below ground. Although we cannot directly estimate below ground biomass, our observations of abundance and root basal area suggest relatively low root biomass in the dry caves. Significant proliferation of fine roots in pools and flooded systems, however, suggests potentially high root biomass. Our results in this seasonally dry tropical forest align with our expectation that above ground productivity is linked to availability of deep water resources.