Tj. Fahey et Jw. Hughes, FINE-ROOT DYNAMICS IN A NORTHERN HARDWOOD FOREST ECOSYSTEM, HUBBARD BROOK EXPERIMENTAL FOREST, NH, Journal of Ecology, 82(3), 1994, pp. 533-548
1 Patterns of fine root biomass, morphology, growth and longevity were
examined in the northern hardwood zone of Hubbard Brook Experimental
Forest to aid understanding of the role of roots in ecosystem function
. 2 Fine root biomass in the mature hardwood forest was 471 g m(-2) fo
r < 2 mm roots in June 1987 and was concentrated in the surface soil,
with 43% in the forest floor horizons. After clearcutting, fine root b
iomass accumulated rapidly in the regrowing forest, reaching 71% of th
at in the mature forest after only four years of recovery. 3 Fine root
diameter distributions and specific root length (SRL; length/mass) di
ffered among species. SRL was higher in the forest floor than mineral
soil horizons, and decreased with increasing root diameter. 4 Fine roo
t production in the mature forest, measured with in-growth cores, aver
aged 254 gm(-2) year(-1), but this method probably underestimated prod
uction. Rapid disappearance of fine roots was observed for roots growi
ng through in situ screens, and these ephemeral roots are difficult to
quantify. 5 The initiation of fine root growth in the forest floor wa
s coincident with leaf expansion in the forest canopy; root growth in
the mineral soil began 1-2 weeks later. Root growth was most rapid in
early summer (mid-June to early July), and the lifespan of these early
season roots averaged about 8-10 months across three years of study.
This estimate of longevity was consistent with that obtained from the
ratio of fine root biomass to production, after correcting the product
ion value for the observed root disappearance from in situ screens (ab
out 50% of fine roots disappeared from screens within an annual cycle)
. These longevity estimates also appeared to be consistent with an ana
lysis of the soil C budget based upon soil and fine root respiration a
nd total root allocation. Fine root production was apparently nearly t
wice as high as leaf production in this ecosystem. 6 These fine root p
roduction and turnover estimates are not consistent with results from
previous studies of fine root decomposition, and we suggest that fine
root decay has been underestimated because existing methods inhibit th
e saprotrophic activity of rhizosphere organisms.