Slope and Vegetation Effects on the Nitrogen Cycle in a Selective-Cut Japan LTER Forest

This study addresses the influence of catchment topography and vegetation types on nitrogen cycling in surface water and soil within a selective-cut forest ecosystem of the Nakagawa Experimental Forest in Hokkaido using spatial and statistical analyses. The Nakagawa Experimental Forest, located in the northernmost island of Japan, is a part of Japan LTER core-site (North Hokkaido Experimental Forests) and is where Hokkaido University conducts research expansively.  Hokkaido University and Oregon State University, which is the home of the H. J. Andrews Experimental Forest, have been collaborating to improve understanding in forest ecosystems.  This study adds and expands the collaboration efforts that two universities have been building for the last 20 years.

Soil and stream water were collected to analyze nitrogen amounts in catchments of Nakagawa.  This study focused on net nitrogen mineralization and nitrification within soil as the net production of ammonium (NH­₄⁺) and nitrate (NO₃^-) in relation to slope and vegetation in two catchments with different forest management history over the last 40 years. Concentrations of NH­₄⁺, NO₃^-, and dissolved organic nitrogen in surface water were also analyzed to examine the difference of the nitrogen cycle in the catchments. Overall, NO₃^- contents in the control catchment were high in soils of Sasa dwarf bamboo (Sasa senanensis), dominant understory vegetation, compared to soils of coniferous and broad-leaved trees.