Changes in stream chemistry associated with insect defoliation in a Pennsylvania hemlock-hardwoods forest

Absence of effects on nutrient budgets after insect defoliation

“…The absence of significant increments in the mean annual values of nutrient concentrations after insect defoliation, observed in this study, are somehow different to the results obtained in earlier studies that reported an increase in cation concentrations after insect defoliation (Webb et al, 1995;Eshelman et al, 1998;Tokuchi et al, 2004;Lewis and Likens, 2007) as a consequence of increased nitrification. In our case, the comparison with a post-thinning period could affect the results, particularly for K, but the modifications in nutrient concentrations observed after thinning were small and restricted to the f irst post-thinning year (Fernández et al, in press).…”

“…Most of this N is immobilized by soil microorganisms (Lovett et al, , 2006 or incorporated into soil organic matter Lovett et al, 2002). Although increases in nitrate leaching have been frequently reported after insect defoliation (Swank et al, 1981;Webb et al, 1995;Eshelman et al, 1998;Reynolds et al, 2000;Tokuchi et al, 2004;Hubber, 2005;Lewis and Likens, 2007) this did not happen in our case, probably because it was rapidly taken up by regrowing plants Frost and Hunter, 2004) which expanded very fast at the same time that eucalypts decline. On the other hand, it is possible that if the trees do not die from the defoliation and their roots to be capable of taking up available N in the soil even though their foliage has largely been removed .…”

“…Swank et al, 1981;Webb et al, 1995;Eshelman et al, 1998;Lewis and Likens, 2007) and as authors know, being inexistent in eucalypt plantations.…”

Direct and indirect effects of alien insect herbivores on ecological processes and interactions in forests of eastern North America

“…Effects of alien insects on biogeochemical cycles also have been detected at the level of the watershed (Swank et al 1981;Ellison et al 2005;Lewis and Likens 2007). Grady et al (2007) found that 66 watersheds in western Virginia had reduced concentrations of dissolved silica from 1988 to 2003.…”

Soil and stream water acidification in a forested catchment in central Japan

“…Defoliation and dieback of Japanese red pine due to pine wilt disease caused by the nematode Bursaphelenchus xylophilus should have decreased nitrogen retention. Defoliation stimulates nitrogen mineralization and nitrification in surface soils (Lewis and Likens 2007) and enhances stream water NO 3 -concentration for several years after a lag of several months to years following defoliation (Webb et al 1995;Eshleman et al 1998;Tokuchi et al 2004;Lewis and Likens 2007). At the study site, however, it seems unlikely that the defoliation was a major factor in the increase in NO 3 -discharge since 1996/ 1997 because red pine stands occupied only 15% of the catchment area.…”