The invasion of woody shrubs into grasslands has led to heterogeneous landscapes and the formation of “islands of fertility”. Islands of fertility are formed around plants through the accumulation of nutrients and organic matter surrounded by bare soil. Such accumulation leads to changes in water infiltration and holding capacity that mediate plant responses to water availability. Studies about islands of fertility have been mainly associated with positive feedbacks sustaining shrub encroachment. Our objective was to study physical characteristics of accumulation dunes surrounding grass patches and examine how changes in precipitation would impact material accumulation and water infiltration rates. In order to address this objective, we used a rainfall manipulation experiment at the Jornada LTER consisting of 2 randomly chosen quadrats for each of the 40 experimental plots (80 quadrats total), 10 random bare patches, and 36 random grass patches of varying sizes outside the experimental plots. On 40 experimental plots we measured dune height, dune length, dune width, grass height, grass length, and grass width. We hypothesized that drought would result in smaller grass plants, dune sizes and lower infiltration rates.
Results/Conclusions
Our results showed that precipitation affected accumulation dune characteristics. There is a significant positive effect of precipitation on mean dune height (P = 4.02e-05), mean dune width (P = 2.13e-06), mean dune length (P = 1.67e-05) and mean dune area (P = 8.35e-05). Precipitation also affected mean grass height (P = 9.55e-07), mean grass width (P = 2.77e-06), mean grass length (P = 3.16e-05), and mean grass area (P = 9.88e-05). Water infiltration rate was lower on bare patches (mean = 133 seconds) than on grass dunes (mean = 77 seconds) and total dune area had a positive effect on infiltration rates. These results highlight the importance of novel feedbacks supported by oasis of water retention caused by accumulation dunes around grass plants. Projected increases of extreme drought may disrupt such feedback causing widespread grass cover loss.