| The leaves and wood from vegetation surrounding headwater streams constitute a
major food source for aquatic invertebrates, providing they are retained upon the streambed
and not transported downstream. This study investigated the response of aquatic
invertebrates to artificially increased detritus retention, in an effort to reproduce the
naturally occurring build up of dead organic matter associated with streams in old-growth
forest. The background detrital standing stock in streams in Kielder Forest
(Northumberland, UK) was low, approximately 32 gm-2. Two streams flowing through dense
conifer plantation and one in open broadleaved woodland were manipulated by the addition
of logs over a 10 m stream reach. After several months, log addition significantly enhanced
detrital standing stocks in both conifer and broadleaved streams. Total invertebrate
abundance, taxon richness and the numbers of certain numerically dominant families were
significantly higher in experimental than reference reaches in both conifer and broadleaved
streams. This response was most marked for detritivores, whilst non-detritivore groups
often showed no response to the manipulation. Whilst in the short term the responses to
enhanced retention may reflect a redistribution of the local fauna, it is argued that over
a longer time-scale, a genuine increase in invertebrate density and diversity could occur.
Allowing old-growth forest to develop in planted valley bottoms may be a viable management
option for conservation. If established alongside streams, it would ensure continuous
input of woody material and the fauna may benefit from the resulting increase in detritus
retention.
Keywords: forestry, detritivores, old-growth conifers, river management, woody debris |