Herbivory by rodents, lagomorphs and insects may locally constrain woo
dy plant seedling establishment and stand development. Recruitment may
therefore depend either upon plant tolerance of herbivory, or low her
bivore abundance, during seedling establishment. We tested potential h
erbivory tolerance by quantifying growth, biomass allocation, and surv
ival of defoliated Prosopis glandulosa seedlings under optimal abiotic
conditions in the absence of competition. Realized tolerance was asse
ssed by clipping seedlings of known age grown in the field with and wi
thout herbaceous competition. At 18-d (= 'young') or 33-d (= 'old') of
age, seedlings in the growth chamber were clipped just above the firs
t (cotyledonary) node, above the fourth node, or were retained as non-
clipped controls. Potential tolerance to defoliation was high and neit
her cohort showed evidence of meristematic limitations to regeneration
. Clipping markedly reduced biomass production relative to controls, e
specially belowground, but survival of seedlings defoliated 5 times wa
s still greater than or equal to 75%. Contrary to expectations, surviv
al of seedlings defoliated above the cotyledonary node 10 times was gr
eater (P < 0.10) for 'young' (75%) than 'old' (38LTo) seedlings. Under
field conditions, survival of defoliated 11-month-old P. glandulosa s
eedlings was less than or equal to 59% after one defoliation and only
less than or equal to 13% after six defoliations. Results indicate P.
glandulosa is potentially tolerant of repeated shoot removal early in
its life cycle. Seedling tolerance to defoliation under field conditio
ns therefore appears dependent upon abiotic stresses or resource limit
ations rather than a lack of intrinsic adaptations for shoot replaceme
nt or a depletion of the seedlings' bud bank. Curtailment of root grow
th, a consequence of top removal observed in the growth chamber experi
ment, may reduce the capacity of P. glandulosa seedlings to acquire so
il resources needed for meristem activation and shoot growth under fie
ld conditions. The importance of resource availability to post-defolia
tion regeneration was implicated in the field experiment, where surviv
al, shoot elongation, and aboveground productivity of clipped seedling
s was greatest in plots without herbaceous interference. In light of t
he marked increases in P. glandulosa abundance in grasslands in recent
history, our results suggest that (1) utilization of Prosopis seedlin
gs by herbivores may be infrequent or sporadic, (2) periodic episodes
of seed production and germination may satiate herbivore populations,
and/or (3) Prosopis seedling establishment occurs during periods of lo
w herbivore density.