Variations in hydrological connectivity of Australian semiarid landscapes indicate abrupt changes in rainfall-use efficiency of vegetation

[1] Dryland vegetation frequently shows self‐organized spatial patterns as mosaic‐like structures of sources (bare areas) and sinks (vegetation patches) of water runoff and sediments with variable interconnection. Good examples are banded landscapes displayed by Mulga in semiarid Australia, where the spatial organization of vegetation optimizes the redistribution and use of water (and other scarce resources) at the landscape scale. Disturbances can disrupt the spatial distribution of vegetation causing a substantial loss of water by increasing landscape hydrological connectivity and consequently, affecting ecosystem function (e.g., decreasing the rainfall‐use efficiency of the landscape). We analyze (i) connectivity trends obtained from coupled analysis of remotely sensed vegetation patterns and terrain elevations in several Mulga landscapes subjected to different levels of disturbance, and (ii) the rainfall‐use efficiency of these landscapes, exploring the relationship between rainfall and remotely sensed Normalized Difference Vegetation Index. Our analyses indicate that small reductions in the fractional cover of vegetation near a particular threshold can cause abrupt changes in ecosystem function, driven by large nonlinear increases in the length of the connected flowpaths. In addition, simulations with simple vegetation‐thinning algorithms show that these nonlinear changes are especially sensitive to the type of disturbance, suggesting that the amount of alterations that an ecosystem can absorb and still remain functional largely depends on disturbance type. In fact, selective thinning of the vegetation patches from their edges can cause a higher impact on the landscape hydrological connectivity than spatially random disturbances. These results highlight surface connectivity patterns as practical indicators for monitoring landscape health

Heterogeneidad espacial y gestión de medios semiáridos

La heterogeneidad espacial de los factores ambientales y de la vegetación constituye una de las principales características de las zonas áridas y semiáridas. Durante décadas, los científicos han descrito esta heterogeneidad y discutido sus causas. Sin embargo, esta característica intrínseca de los sistemas áridos y semiáridos apenas ha sido considerada en la gestión y restauración de estos ambientes. En el presente artículo se revisan algunos conceptos básicos sobre la relación heterogeneidad-funcionamiento del ecosistema en zonas semiáridas, se presentan algunos de los principales marcos conceptuales desarrollados sobre esta relación y se discuten contextos prácticos. Un ejemplo de estos últimos son los relacionados con la evaluación del funcionamiento del paisaje o el desarrollo ecotecnológico, en los que la incorporación de la heterogeneidad espacial permitiría mejorar la gestión de estos ecosistemas.Esta revisión ha sido elaborada en el marco del proyecto financiado por el Plan Nacional de IDI-FEDER, FANCB (REN2001-0424-C02-02/GLO)

Capture of overland flow by a tree belt on a pastured hillslope in south-eastern Australia

We describe a rainfall simulator experiment designed to measure the capture, by a fenced tree belt, of excess water generated as Hortonian flow from a pasture slope. Three rainfall events (48, 49, and 75 mm/h for 13, 30, and 30 min, respectively) were applied, of which 15%, 29%, and 44%, respectively, ran off and drained onto the tree belt. The tree belt captured 100%, 32–68%, and 0–28% of the runoff from the 3 events, respectively. These captured runoff volumes represented 31–39%, 22–45%, and 0–29% increases in water supply to the trees, in addition to incident rainfall. Infiltration rates within the tree belt were up to 46% higher than in the pasture zone. This higher infiltration was mainly attributed to better soil surface conditions in the absence of stock and a 50-mm layer of tree litter. Overland flows within the tree belt formed tree litter into microterraces, which spread and slowed flows and allowed greater time for infiltration