Differential growth and recovery rates following defoliation in related deciduous and evergreen trees |
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Authors: | Steven C Krause Kenneth F Raffa |
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Institution: | (1) Department of Entomology, University of Wisconsin, Madison, WI 53706, USA, US |
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Abstract: | Deciduous larches, Larix spp., and evergreen pines, Pinus spp., are sympatric Pinaceae conifers. Adjacent monocultures of 10-year-old Larix decidua Mill. and Pinus resinosa Ait. were subjected to single-season artificial defoliation by clipping from 0% to 99% of each needle. Survival, above-ground
productivity, and architecture were measured for 36 months. P. resinosa and L. decidua exhibited differential relationships with defoliation intensity and recovery time. Two months after treatment, defoliation
reduced larch height growth but had no effect on radial growth. By contrast, P. resinosa stem radial growth was reduced immediately, but height growth was not decreased until the following year. Pine leader growth
and above-ground biomass following 66% defoliation never recovered to control values or 33% defoliated pines. Conversely,
defoliated larch quickly recovered from an initial growth loss to eliminate all treatment effects on biomass. The plasticity
in architectural response found in larch, but not pine, might partially account for defoliation tolerance. Both P. resinosa and L. decidua exhibited non-linear responses to defoliation. These patterns may be caused partially by the uneven distribution of nutrients
within needles, rather than a simple function of leaf area lost to defoliators. Concentrations of 13 nutrients in P. resinosa were highest either in the mid- (Ca, Mg, S, Zn, B, Mn, Fe, Al and Na) or basal- (N, P, K, and Cu) section. The relatively
low nutrient content in needle tips may contribute to similar biomass productivity between trees defoliated 33% and controls.
Removal of needle mid-sections significantly reduced whole-plant productivity. In contrast, L. decidua nutrients are concentrated in the distal sections. Nutrient concentrations were generally highest in larch. Our results agree
with an emergent prediction of the carbon/nutrient balance theory that defoliation more severely reduces growth of evergreen
than deciduous species. These results are discussed within the physiological, ecological and evolutionary context of allocation
theory, with implications for natural resource management and plant-insect interaction theory.
Received: 6 April 1995 / Accepted: 29 August 1995 |
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Keywords: | Herbivory Plant-insect interactions Leaf lifespan Pinus Larix |
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