The Paramos, alpine tropical ecosystems found in the mountaintops along the Northern Andes, provide critical environmental services; one of them is water regulation, which is crucial for local water supply in major South American cities. Its water regulation ability is due to their soils and vegetation’s traits. One of the most abundant genera in the paramos is Hypericum. Previous studies have shown that species in this genus tends to be distributed in response to soil moisture, but since those studies have not considered its physiology and ecological interactions is impossible to understand if their distribution respond to physiological limitations or ecological interactions. Here we evaluated the distribution pattern of three Hypericum; H. goyanesii, H. juniperinum, and H. Mexicanum to understand how drought vulnerability influences their distribution and to understand ecological and spatial relationships between water and vegetation. To do so, we established 10 plots (10 x 10 m each) in Matarredonda, a paramo in the oriental range of the Colombian Andes along a moisture gradient that was detected using a spatial analysis of variables that affect soil water content: slope, aspect, and water accumulation. On each plot we took soil moisture and temperature measurements within a 6x6m internal subplot every 1m. Same measurements were taken under each Hypericum found on the plot. Using aerial photographs, we estimated the vegetation cover on each plot and around each Hypericum species in the plot. We evaluate three physiological traits related to plant water relations: plant water potential, vulnerability curves, and vulnerability index.
Results/Conclusions
At the larger scale, we found significant differences in soil moisture between plots, as expected from the model, and no evidence that the type of vegetation cover is affecting soil moisture. At the Hypericum local scale, we found that H. mexicanum distribution was associated with bare soil cover, higher soil temperatures, and lower soil moisture. The other two species, H. goyanesii and H. juniperinum tend to be located in wetter sites. At the physiological scale, we found that H. goyanesii and H. juniperinum are very vulnerable to drought and were found on wetter sites suggesting that the presence Hypericum species was dictated by the soil water content and by its vulnerability to drought. Paramos have rarely been exposed to drought and our results suggest that some species are wetter specialist and could be too vulnerable to drought to resist longer drought episodes expected in a climate change scenario.