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'flcathcring of Ixinelal soil mil rock provides sax nutrients
but relevant data on rates of noztht;xting per unit ama under
ficlc conditions are unavailable.
Wference a betnean inputs
and outputs of nutrients for a site .my be taken only as a rough
guide to wecthring rates because of the coaplexity of eaoh
system, the usu~lly lob; pmcision in wtjaaulls~~ent of system
cqononts a:!the existence of long-tern trends in sone
oompments.
None of the most relevant available input and
output dzta for a.fforested catchments, four quoted in Likens
et al., (1967) and one in Jmes (19?1), include estincltr;.? of dl
possible nutrient inputs and outputs.
Although prduction of coqloto nutrient balance sheets for
forests is difficult, car,sidemtiofi of av&luble data above as
EL whole leads to the conclusion that managed fomst systcns tend to
accumlnte nutrients and do not deplete the soil of nutrients
excessively as swestetl by hmie (1956) who under-rated the
importance of the various nutricnt inputs to the fomst.
Rennie prduced some cseful dnt~
on average nutrient uptakes
by trees nnd parts of tmes over 50 and. -100 ycar3 and we have
wed these on a ndified besis to outimte re~oval a? nutrients
in tree stens during forestry operatiorla (Table 6). Bede
used published data on yield,- nutriont caposition and dIY
weights of trees in European forests as a bcsis for his
calaulz-klons, the data coming fro^ 42 originG1 st~ies
includhg
trees in growtl-1 clcsses I - V on prcdoclinmtly acid s d y
soils and soao base-rich soils,
Data vmre grouped into p,ines
(two species), other conif~rs (the aPec$es) and hardwoods
(ei&t species).
Rennie did not explain fUZy why he
sepamted off pin8 data fror, oth:..r data, but he implied that
this was because loa nutrient denand mas expected for this
group