Figure 5
Conceptual figure of ecosystem response to synergistic effects of invasion and extreme drought coupled with the forecasted increasing dryness.
Grey dash lines indicate forecasted decreasing trend in precipitation. Dark blue lines represent ecosystem transpiration, reflecting the variability of yearly water use. Lighter blue and orange dashed lines indicate the critical cavitation threshold for trees and shrubs, respectively. Red arrows represent an extreme drought event that can shift the system near critical limits of functioning. Resilience to extreme drought (green arrows) is higher in uninvaded systems and lower in systems invaded by water spending shrub species. Shrubs will enhance the amplitude and variability of ecosystem transpiration and gain competitive advantage over trees. If shrub invasion and extreme drought decrease water availability below the critical hydraulic thresholds for tree functioning, the resilience of the key-stone tree species will decrease and eventually lead to tree death. A critical transition point can turn open savannah-type of ecosystems into alternative states of degraded shrublands. Photographs by M C Caldeira.
