Geoscience Reference
In-Depth Information
IMPACTS OF FOREST DEFOLIATION BY PINE-WILT
DISEASE ON BIOGEOCHEMICAL CYCLING AND
STREAMWATER CHEMISTRY IN A HEADWATER
CATCHMENT IN CENTRAL JAPAN
NOBUHITO OHTE
∗,†
, NAOKO TOKUCHI
§
and SATORU HOBARA
‡
∗
Graduate School of Agriculture, Kyoto University
Kyoto 606-8502, Japan
†
nobu@bluemoon.kais.kyoto-u.ac.jp
§
Field Science Education and Research Center, Kyoto University
Kyoto 606-8502, Japan
‡
Faculty of Environmental Systems, Rakuno Gakuen University
Ebetsu 069-8501, Japan
In order to evaluate the impact of the forest disturbance by pine-wilt disease
(PWD), changes in nutrient status in soils and streamwater chemistry have
been investigated in a small headwater catchment in central Japan, focusing
on the nitrogen dynamics and hydrological processes. Decreased N uptake by
roots and increased N supply from litter fall caused by the 1992-1994 PWD
caused a threefold increase in NO
3
and Ca
2+
,andMg
2+
concentrations of
stream and groundwater. Seasonal peaks in stream NO
3
concentration during
the rainy season occurred during 1992-1996. The mechanism of this seasonal
pattern can emphasize the importance of hydrological seasonality with high
precipitation, groundwater level in summer of Japan under Asian monsoon
climate. The N loss through the streamwater was much smaller than N con-
tribution of PWD litter inputs throughout the observation period. This large
discrepancy suggested substantial nitrogen immobilization in soils.
1. Introduction
Several forest declines have been reported in Japan since the 1960s. A major
disaster for the Japanese forestry industry has been the decline of Japanese
pine forests due to pine-wilt disease (PWD), which over the past three
decades has spread extensively in western Japan.
The mechanisms of forest decline due to PWD have been studied
continuously since the 1970s.
1
PWD is caused by pinewood nematode
(
Bursaphelenchus xylophilus (Steiner et Buhrer) Nickle
2
), and its vector
is a sawyer beetle (
Monochamus alternatus
3
). Recently, this forest declines
have also become a major concern for Japanese citizens utilizing water
resources from forested catchments, since there is a possibility that severe
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