Riparian Vegetation and Stream Condition in a Tropical Agriculture–secondary Forest Mosaic

Abstract

Changes in land cover from forest to agriculture often alter riparian vegetation, which modifies the physical conditions of streams. To understand the impacts of different categories of land cover on riparian and stream habitats, we sampled riparian vegetation and stream conditions in three adjacent watersheds in southeastern Puerto Rico. Land cover categories (pasture, mixed, and forest) were determined using aerial photographs. Vegetation structure and composition and characteristics of streams were assessed for 35 riparian sites. Sites were located along first‐order streams, at 400–600 m elevation in the wet‐forest life zone. Understory vegetation in the forest sites was mainly shrubs, herbs, and ferns, whereas the mixed and pasture sites were dominated by grasses, vines, and bare soil. Syzygium jambos and Spathodea campanulata, nonnatives, and Guarea guidonia, a native, were the most common tree species in the riparian areas. Surrounding land cover explained >60% of the variation among stream sites. There was a positive relationship between tree cover and percentage of dissolved oxygen, and a negative relationship between tree cover and percentage of substrata covered by sediments from eroded soil. The amount of woody debris in the streams tended to increase with forest cover. Overall, land cover is a landscape feature that effectively characterized riparian understory cover, tree species composition, and stream condition. Corresponding Editor: W. L. Silver.

Input of litter in deforested and forested areas of a tropical headstream

“…Graça, 2001). Given that riparian vegetation is the main source of leaves, and therefore the main energy source (Graça, 2001;Graça and Canhoto, 2006), changes in its composition affect structure and process within streams (Heartsill-Scalley and Aide, 2003). This alteration was clearly shown by the low contribution of leaf litter in the deforested area.…”

“…This alteration was clearly shown by the low contribution of leaf litter in the deforested area. In a way to maximise conservation, to establish connectivity and to increase the minimum riparian forest width, priority should be given to the stream ecosystem (Heartsill-Scalley and Aide, 2003).…”

“…In Brazil, as well as in many other countries, the degradation of riparian vegetation results from the disordered expansion of agricultural borders (Rodrigues and Gandolfi, 2001;Heartsill-Scalley and Aide, 2003), contributing to the formation of immense open areas, characterised by grassy and herbaceous vegetation.…”

“…Those changes in land cover can also modify the physical conditions of streams (Heartsill-Scalley and Aide, 2003), with a forest landscape certainly contributing with more biomass to the stream than herbaceous vegetation (Afonso et al, 2000;Heartsill-Scalley and Aide, 2003). However, it is important to determine the actual contribution of the litter input for different conditions of riparian vegetation .…”

Effects of land use on fish assemblages in Patagonian low order streams

“…Conversion of native forest into pastures as a consequence of land use for agriculture has produced a wide-scale degradation of aquatic ecosystems in several countries (Heartsill-Scalley and Aide, 2003;Gerhard et al, 2004;Lorion and Kennedy, 2009). This land use practice affects freshwater systems by increasing the runoff of silt, fertilizers, and pesticides, whereas removal of large volumes of water for irrigation often reduces habitat availability, and increases salinity.…”