[MCN] Streamflows change when old-growth converted to doug-fir plantation

Lance Olsen lance at wildrockies.org
Tue Nov 15 17:03:51 EST 2016

Ecohydrology: Early View, Online Version of Record before inclusion in an issue
First published: 14 November 2016

Summer streamflow deficits from regenerating Douglas-fir forest in 
the Pacific Northwest, USA
Timothy D. Perry, Julia A. Jones

Abstract [bold added]

Analysis of 60-year records of daily streamflow from eight 
paired-basin experiments in the Pacific Northwest of the United 
States (Oregon) revealed that the conversion of old-growth forest to 
Douglas-fir plantations had a major effect on summer streamflow. 
Average daily streamflow in summer (July through September) in basins 
with 34- to 43-year-old plantations of Douglas-fir was 50% lower than 
streamflow from reference basins with 150- to 500-year-old forests 
dominated by Douglas-fir, western hemlock, and other conifers. Study 
plantations are comparable in terms of age class, treatments, and 
growth rates to managed forests in the region. Young Douglas-fir 
trees, which have higher sapwood area, higher sapflow per unit of 
sapwood area, higher concentration of leaf area in the upper canopy, 
and less ability to limit transpiration, appear to have higher rates 
of evapotranspiration than old trees of conifer species, especially 
during dry summers. Reduced summer streamflow in headwater basins 
with forest plantations may limit aquatic habitat and exacerbate 
stream warming, and it may also alter water yield and timing in much 
larger basins. Legacies of past forest management or extensive 
natural disturbances may be confounded with effects of climate change 
on streamflow in large river basins. Continued research is needed 
using long-term paired-basin studies and process studies to determine 
the effects of forest management on streamflow deficits in a variety 
of forest types and forest management systems.

"The global average lake summer surface water warming rate found here 
implies a 20% increase in algal blooms and a 5% increase in toxic 
blooms over the next century [Brookes and Carey, 2011; Rigosi et al., 
2015], as well as a 4% increase in methane emissions from lakes 
during the next decade. Increased evaporation associated with warming 
can lead to declines in lake water level, with implications for water 
security [Vorosmarty, 2000; Hanrahan et al., 2010], substantial 
economic consequences [Gronewold and Stow, 2014], and in some cases, 
complete ecosystem loss (e.g., [Smol and Douglas, 2007]). Already, 
changes in thermal structure and mixing have decreased productivity 
of some lakes, which threaten human communities that depend on 
fisheries as a nutritional and economic resource [O'Reilly et al., 
2003]. Lakes with high rates of surface temperature change may appear 
more likely to experience major ecosystem changes [Smol et al., 2005; 
Smol and Douglas, 2007], but we caution that even lakes with low 
rates of change may be under ecosystem stress if the initial water 
temperatures are already near physiological maxima [Tewksbury et al., 
2008]. The widespread warming reported here suggests that large 
changes in Earth's freshwater resources and their processes are not 
only imminent but already under way."

Catherine M. O'Reilly, Sapna Sharma, Derek K. Gray, Stephanie E. 
Hampton et al. Rapid and highly variable warming of lake surface 
waters around the globe. Geophysical Research Letters, December 28, 
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