Riparian deforestation, stream narrowing, and loss of stream ecosystem services

Abstract

A study of 16 streams in eastern North America shows that riparian deforestation causes channel narrowing, which reduces the total amount of stream habitat and ecosystem per unit channel length and compromises in-stream processing of pollutants. Wide forest reaches had more macroinvertebrates, total ecosystem processing of organic matter, and nitrogen uptake per unit channel length than contiguous narrow deforested reaches. Stream narrowing nullified any potential advantages of deforestation regarding abundance of fish, quality of dissolved organic matter, and pesticide degradation. These findings show that forested stream channels have a wider and more natural configuration, which significantly affects the total in-stream amount and activity of the ecosystem, including the processing of pollutants. The results reinforce both current policy of the United States that endorses riparian forest buffers as best management practice and federal and state programs that subsidize riparian reforestation for stream restoration and water quality. Not only do forest buffers prevent nonpoint source pollutants from entering small streams, they also enhance the in-stream processing of both nonpoint and point source pollutants, thereby reducing their impact on downstream rivers and estuaries.

Is smaller necessarily better? Effects of small-scale forest harvesting on stream ecosystems

“…Large-scale forest management and deforestation are known to deeply affect stream habitats including channel morphology, substrate composition, water temperature and chemistry (e.g., Sweeney et al, 2004;Zhang et al, 2009). Our results indicate that small-scale riparian forest harvesting could produce somewhat similar effects on stream ecosystems.…”

“…Here, the decrease in bankfull width to bankfull depth ratios in harvested stream reaches may be the first evidence of channel incision and narrowing (Montgomery, 1997). Over time, this may result in substrate homogenization and decreased wet channel width (Sweeney et al, 2004;Zhang et al, 2009). Loss of large woody debris and pool area also frequently occurs after riparian forest harvesting (Mellina and Hinch, 2009).…”

“…In addition, forest canopy regulates water temperature and solar radiation while terrestrial arthropods that fall into streams are a crucial food source for salmonids (Wipfli, 1997). There is now consistent evidence that large-scale forest harvesting profoundly alters several key components of stream ecosystems such as channel morphology, hydrology, temperature, water chemistry, biodiversity, productivity, paths of energy flow and rates of material processing (e.g., England and Rosemond, 2003;Sweeney et al, 2004;Moore et al, 2005;Kreutzweiser et al, 2008;Zhang et al, 2009;Ely and Wallace, 2010). Overall, evidence indicates that impacts on streambed morphology or hydrology can be reduced by maintaining riparian forest strips along streams (Broadmeadow and Nisbet, 2004).…”

Spatially cascading effect of perturbations in experimental meta-ecosystems

“…For instance, slow-growing woody plants of riparian forests exposed to recurrent fires are progressively replaced by alien annuals of higher growth rates in Mediterranean areas [39,42]. Such high perturbation regimes will both deforest and re-structure the autotrophic riparian community towards a lower biomass system, and decline macro-invertebrate densities in streams by reducing leaf litter inputs [43]. Here we show that, more generally, a habitat-or ecosystem-specific response to any kind of perturbation can strongly impact neighbouring ecosystems through the disruption of detritus flows.…”

A Comparison of the Temperature Regime of Short Stream Segments under Forested and Non‐Forested Riparian Zones at Eleven Sites Across North America

“…Nevertheless, where urbanization, agriculture, or livestock grazing occurs, riparian forests are often cleared and are then succeeded by meadow or other herbaceous communities with a more open canopy. This alteration in riparian community can lead to major changes in stream ecosystem structure and function, including narrower and more embedded channels (because of encroachment by herbaceous plants), impaired ability to breakdown organic pollutants, changes in macroinvertebrate abundance, and higher water temperatures (Sweeney et al, 2004;Lecerf et al, 2012;Studinski et al, 2012). Recent studies have documented increases in stream temperature over large geographic areas in many parts of the world (Nelson and Palmer, 2007;Kaushal et al, 2010;Hester and Doyle, 2011) that have been attributed to climate change, human alterations of stream channels and hydrology, or a combination of these factors.…”