BREAKDOWN AND DETRITIVORE COLONIZATION OF LEAVES IN 3 NEW-ZEALAND STREAMS

Breakdown of leaves from three native riparian tree species, and their colonisation by shredding and collecting insect larvae, were investig ated in three streams on Banks Peninsula, New Zealand. Leaves were int roduced in baskets at the time of leaf fall. Breakdown rates of leaves were faster than previously recorded in New Zealand streams and were comparable to those of many northern hemisphere deciduous species. Shr edder and total detritivore densities and biomass in leaf baskets were also greater than previously found in New Zealand streams. Peaks of s hredder biomass on red beech and mahoe leaves were found when only abo ut 20% of leaf biomass remained. No shredder peak was recorded on fuch sia leaves, and no collector peaks occurred in any of the streams. Rel ative shredder and collector biomass (per g DW leaf) in leaf baskets d id not exceed or was smaller than in leaf litter accumulations of mixe d origin and conditioning throughout the streams during leaf breakdown although absolute shredder and collector biomass (per m(2) stream bot tom) was occasionally larger in baskets than in the rest of the stream . These findings support contentions that spatial and temporal relatio nships between detrital inputs and detritivore biomass and life histor ies are weak in New Zealand streams.