Typhoon impacts on stream water chemistry in a plantation and an adjacent natural forest in central Taiwan

We studied the hydro-chemical responses to a category 3 typhoon of two forested watersheds at Lienhuachi
Experimental Forest: a 24 year old China-fir plantation (WS4) and a natural hardwood forest (WS5).
One hundred and nineteen millimeters of precipitation fell in 26 h resulting in a peak stream flow of
80 l s1 ha1 in WS4 and 11 l s1 ha1 in WS5 despite a much lower base flow at WS4: 0.012 l s1 ha1
as compared to 0.38 l s1 ha1 at WS5. Stream water conductivity, an indicator of overall ionic strength,
decreased by approximately 50% in WS4 and 30% in WS5. The observation that the China-fir plantation
had a higher stream flow and ion fluctuation than the natural forest during typhoon Talim was the opposite
of that observed during non-storm periods. The output of suspended solids in stream water was two
orders of magnitudes higher in the plantation than in the natural forest during the storm period (8.8 vs.
0.06 kg ha1 net export of suspended solids). The plantation exhibited lower resistance than the natural
forest to the stream water chemistry impacts of a category 3 typhoon with a return interval of six years.
Among the 11 ions analyzed, nitrogen, phosphorus, and potassium were the only elements that had
higher concentrations in the natural forest than in the plantation, a pattern consistent with the aggradation
of biomass and the concomitantly high demand on the macro-essential elements in the plantation.
Conversion of a native broad leaf forest to a conifer plantation has persistent and large effects on hydrochemical
cycling, changes that are still evident after two decades of growth.