Baseline assessment of the hydrological network and land use in riparian buffers of Pampean streams of Uruguay.

The integrated assessment of stream networks and terrestrial land use contributes a critical foundation for understanding and mitigating potential impacts on stream ecology. Riparian zone delineation and management is a key component for regulating water quality, particularly in agricultural watersheds. We present a national assessment of riparian zone land uses according to stream order for the entire hydrological network in the Uruguayan landscape in Southeastern South America. We classified over 82,500 km of streams and rivers in Uruguay into seven Strahler order classes and delineated riparian buffers of 100 and 500 m, depending on stream order, covering a total of 13% of the terrestrial land area in Uruguay. Natural vegetation cover in riparian zones averaged 77% among basins, whereby natural grassland dominated first and second order stream buffers at 58% and 49%, respectively. This highlighted the importance of grasslands in headwater regions of the country. Riparian forests formed corridors along larger streams, representing a mere 9% of buffers in first order streams but reaching 46% of buffers of 6th order streams. Among the six major basins of Uruguay, we found differences in the relative importance of riparian forests and crop cover in headwater stream riparian zones, as well as differences in relative crop cover within riparian zones. Results show that streams in subtropical grassland landscapes originate in open grassland environments, which has major implications for thermal regimes, carbon inputs, and stream biodiversity. Riparian buffer management should consider geographic differences among different basins and ecoregions within Uruguay.

How livestock and flooding mediate the ecological integrity of working forests in Amazon River floodplains.

The contribution of working forests to tropical conservation and development depends upon the maintenance of ecological integrity under ongoing land use. Assessment of ecological integrity requires an understanding of the structure, composition, and function and major drivers that govern their variability. Working forests in tropical river floodplains provide many goods and services, yet the data on the ecological processes that sustain these services is scant. In flooded forests of riverside Amazonian communities, we established 46 0.1-ha plots varying in flood duration, use by cattle and water buffalo, and time since agricultural abandonment (30-90 yr). We monitored three aspects of ecological integrity (stand structure, species composition, and dynamics of trees and seedlings) to evaluate the impacts of different trajectories of livestock activity (alleviation, stasis, and intensification) over nine years. Negative effects of livestock intensification were solely evident in the forest understory, and plots alleviated from past heavy disturbance increased in seedling density but had higher abundance of thorny species than plots maintaining low activity. Stand structure, dynamics, and tree species composition were strongly influenced by the natural pulse of seasonal floods, such that the defining characteristics of integrity were dependent upon flood duration (3-200 d). Forests with prolonged floods ≥ 140 d had not only lower species richness but also lower rates of recruitment and species turnover relative to forests with short floods <70 d. Overall, the combined effects of livestock intensification and prolonged flooding hindered forest regeneration, but overall forest integrity was largely related to the hydrological regime and age. Given this disjunction between factors mediating canopy and understory integrity, we present a subset of metrics for regeneration and recruitment to distinguish forest condition by livestock trajectory. Although our study design includes confounded factors that preclude a definitive assessment of the major drivers of ecological change, we provide much-needed data on the regrowth of a critical but poorly studied ecosystem. In addition to its emphasis on the dynamics of tropical wetland forests undergoing anthropogenic and environmental change, our case study is an important example for how to assess of ecological integrity in working forests of tropical ecosystems.