Flow analysis of models of the Hubbard Brook [forest] ecosystem [USA]

Several models of energy and nutrient flow on the Hubbard Brook Ecosystem, New Hampshire, USA, were analyzed for the pattern of flow through the models, cycling index CI, path length PL, and straight-though path length PL"s. CI represents the proportion of flow that cycles through components of the system. PL is the average number of components that a unit of flow passes through on its way from inflow to outflow. PL"s is that portion of PL attributable to flow passing straight through the system without cycling at all. The energy model had low values for PL, PL"s, and CI, compared to nutrient models. Flow measures for nutrients varied greatly. The order of the elements in terms of CI and K > Na > N > Ca > P > Mg > S. This could be explained by the mobility and biological role of each element, although Na is somewhat anomalous. PL was very large for K (24.3) but small for S (5.2). PL"s was near 4 for all elements but Na (2.6) and S (2.5). This was a reflection of different flow patterns for Na, which flows primarily between available nutrients and belowground biomass, and S, which flows primarily between available nutrients, and below- and aboveground biomass. Sulfur returns to available nutrients via stemflow and throughflow, bypassing the forest floor. The remaining elements cycle between above- and belowground biomass, forest floor, and available nutrients. Three different models of Ca flow were compared. When all three models were analyzed using the same nutrient flux data, flow measures become very close, despite structural differences in the models. For these models, flow values were more important than the architecture of the models in determining cycling and flow characteristics.