Jw. Hughes et Tj. Fahey, LITTERFALL DYNAMICS AND ECOSYSTEM RECOVERY DURING FOREST DEVELOPMENT, Forest ecology and management, 63(2-3), 1994, pp. 181-198
A field study was conducted at the Hubbard Brook Experimental Forest (
USA) to quantify changes in the mass, chemistry and timing of litterfa
ll during stand development of the northern hardwood forest and to rel
ate changes to other ecologically meaningful forest dynamics. Leaf fal
l on three contiguous watersheds, harvested 1, 15 and 66 years ago, wa
s measured with litter traps from 1984 to 1988. Woodfall into the 15-y
ear-old stand was monitored on permanent plots. During the first 17 ye
ars of forest development, fallen leaves and wood of Prunus pensylvani
ca accounted for 32-59% and more than 97%, respectively, of total mass
litter inputs. In the older forest, Acer saccharum, Fagus grandifolia
, and Betula alleghaniensis contributed 53%, 25%, and 21%, respectivel
y, of the total leaf fall mass of the stand. Changes in the leaf mass
of each species during forest development were the result of an increa
sed number of leaves rather than increased mass per leaf. Leaves fell
first in the oldest stand and last in the youngest stand. The nitrogen
(N) content and non-structural carbohydrates of fallen leaves were hi
ghest in the youngest stand, but there was no overall trend in later s
tages of forest development. In 1985, leaves of all species in all sta
nds had significantly reduced N contents (only 23-80% of N in leaves f
alling in 1984). In the oldest stand, this difference resulted in leaf
fall N of 30.3 kg ha-1 (1984) and only 15.6 kg ha-1 (1985). Leaves of
different species varied considerably in organic fractions but, with
few exceptions, cellulose and lipin were significantly higher in 1985
than in 1984. The large difference between 1984 and 1985 in organic fr
actions and N suggests that leaf litter quality may vary greatly from
year to year and may partially account for unbalanced nitrogen budgets
. Large pulses of wood fell each year into the mid-aged stand (1151-12
83 kg ha-1 year-1). This woodfall, high in lignin (28-3 1 %) but low i
n nitrogen (0.1-0.2%), supplemented leaf fall and yielded total litter
fall lignin: nitrogen ratios of 18.9 (1984) and 30.8 (1985). The timin
g of this deposition coincides with a transition to accretion of fores
t floor biomass from a protracted decline following disturbance. Appar
ently, the combined effects of high litterfall and low substrate quali
ty lead to a sustained accumulation of the forest floor until a steady
state is reached, about 50 years after disturbance.