LIFE-SPAN AND DYNAMICS OF LEAVES OF HERBACEOUS PERENNIALS IN HIGH-ELEVATION ENVIRONMENTS - NEWS FROM THE ELEPHANTS LEG

1. Leaf life spans, determined as half-lives, of 16 herbaceous perenni al plant species from the aseasonal, tropical Andes at altitudes betwe en 4000 and 4600 m were on average 193 +/- 19 days and thus two to thr ee times greater than those of herbaceous perennials from the seasonal northern hemisphere. The duration of lamina expansion was positively correlated with life span. Growth was continuous all year round, but r ates of leaf initiation in the high-elevation tropics were lower than in the temperate zone. 2. Significant positive inter-relationships wer e found between leaf life span and mass based foliar nitrogen concentr ation of Andean taxa. The correlation between life span and leaf mass per area (LMA) was marginally significant, while life span and area-ba sed foliar N content were unrelated. 3, Leaf traits of 46 Andean herba ceous perennials (forbs and graminoids), spanning an altitudinal range of 1500 m, indicated that the 16 taxa utilized for growth and leaf li fe span determinations were representative. For graminoids no altitudi nal changes in LMA or foliar N were observed across species. However, in forbs LMA and area-based foliar N increased significantly with alti tude. No differences in leaf traits were observed between herbaceous r osette and cushion growth forms. 4, The Andean data set was used in co njunction with data from the temperate, sub-arctic and arctic zones to evaluate the significance of leaf life spans in herbaceous plants fro m a biogeographical perspective. Leaf life span declined significantly with increasing seasonality, expressed as latitude and duration of th e annual growth period. Because temperature regimes are similar along this gradient during the respective growth periods (Diemer 1996), obse rved differences should be the result of variation in the day length a nd/or duration of the growing season. 5. Data on leaf life spans and l eaf traits of herbaceous plants from contrasting latitudes were used t o evaluate the validity of general inter-relationships proposed by Rei ch (1993). The high correlation between LMA and life span observed in both data sets indicates that this relationship holds for various grow th forms. On the other hand, the apportionment of mass-based foliar N concentration in relation to life span appears to differ between herba ceous and woody growth forms.