ABSTRACT
Plant growth rates drive ecosystem productivity and are a central element of plant ecological strategies. For seedlings grown under controlled conditions, a large literature has firmly identified the functional traits that drive interspecific variation in growth rate. For adult plants, the corresponding knowledge is surprisingly poorly understood. Until recently it was widely assumed that the key trait drivers would be the same (e.g. specific leaf area, or SLA), but an increasing number of papers has demonstrated this not to be the case, or not generally so. New theory has provided a prospective basis for understanding these discrepancies. Here we quantified relationships between stem diameter growth rates and functional traits of adult woody plants for 41 species in an Australian tropical rainforest. From various cost-benefit considerations, core predictions included that: (i) photosynthetic rate would be positively related to growth rate; (ii) SLA would be unrelated to growth rate (unlike in seedlings where it is positively related to growth); (iii) wood density would be negatively related to growth rate; and (iv) leaf mass:sapwood mass ratio (LM:SM) in branches (analogous to a benefit:cost ratio) would be positively related to growth rate. All our predictions found support, particularly those for LM:SM and wood density; photosynthetic rate was more weakly related to stem diameter growth rates. Specific leaf area was convincingly correlated to growth rate, in fact negatively. Together, SLA, wood density and LM:SM accounted for 52 % of variation in growth rate among these 41 species, with each trait contributing roughly similar explanatory power. That low SLA species can achieve faster growth rates than high SLA species was an unexpected result but, as it turns out, not without precedent, and easily understood via cost-benefit theory that considers whole-plant allocation to different tissue types. Branch-scale leaf:sapwood ratio holds promise as an easily measurable variable that may help to understand growth rate variation. Using cost-benefit approaches teamed with combinations of leaf, wood and allometric variables may provide a path towards a more complete understanding of growth rates under field conditions.
ABSTRACT
A series of 300 patients were implanted for chronic cerebellar stimulation (CCS) from February 1974 to June 1980. The charge density was in the range of 0.7-1.6 microCi/cm2/phase. There is a very narrow range of stimulation in which CCS is effective. Increasing above the range, clinical benefits cease; at levels over 10 microCi/cm2/phase, damage to the underlying conducting elements occurs which renders the prosthesis ineffective. Periodic monitoring of the implanted equipment is mandatory for a successful clinical program. Scalp recordings and radiography have detected a 53% failure rate in the I-108 RF linked system. The failed receivers were replaced with more reliable I-110 receivers and later with a fully implantable pulse generator. No change has been detected in the electrode button-cortex interface when measuring the access resistance up to 5 years later.