Document: JAM-3-63-40

Fertility and light control canopy dynamics in a fast-growing tropical forest.

FOWNES, J.H.* ¹, M.G.RYAN ², C.GIARDINA ¹, R.S.SENOCK ³ and D.BINKLEY ⁴

University of Hawaii, Honolulu, Hawaii ¹
USDA Forest Service, Ft. Collins CO 80526 USA ²
University of Hawaii, Hilo Hawaii ³
Colorado State University, Ft. Collins, CO 80523 USA ⁴

Abstract:
To better understand the controls of carbon balance and forest growth and decline, we studied the controls of leaf area dynamics of an Eucalyptus saligna plantation. Two spacings (1 by 1 m and 3 by 3 m) times three fertilization regimes (establishment only, continuous high, and late-rotation high) were replicated three times on the windward side of the island of Hawaii. Monthly optical estimates of leaf area index (LAI) were corrected using factors derived from harvest and allometric analysis, and leaf litterfall was collected monthly over five years. LAI was increased by fertilization and closer spacing. Average leaf lifespan was greater in the low fertility treatment (1 yr) compared to the continuous high (0.8 yr) treatment, suggesting that increased leaf lifespan increased nutrient use efficiency. Seasonal variation in LAI (minima were 60 percent of maxima) was strongly associated with incident light three months earlier, but not with air temperature or rainfall. Leaf production (increment in canopy mass plus leaf litterfall) was correlated with incident light of the current month and two months earlier, but not air temperature or rainfall. If primary productivity is maximized when high light and high LAI occur simultaneously, our results indicate that variation in weather can be amplified by the lags in the leaf area response, leading to high year to year variation in carbon gain.

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This abstract is being presented at: 10:30 AM in session:
Poster Session #1: Light Relations.