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Titolo:
LANDSCAPE SCALE EVALUATION OF UNDERSTORY LIGHT AND CANOPY STRUCTURE -METHODS AND APPLICATION IN A NEOTROPICAL LOWLAND RAIN-FOREST
Autore:
CLARK DB; CLARK DA; RICH PM; WEISS S; OBERBAUER SF;
Indirizzi:
SELVA BIOL STN,INTERLINK 341,POB 02-5635 MIAMI FL 33152 UNIV MISSOURI,DEPT BIOL ST LOUIS MO 63121 UNIV KANSAS LAWRENCE KS 66054 STANFORD UNIV,CTR CONSERVAT BIOL STANFORD CA 94305 FLORIDA INT UNIV,DEPT BIOL SCI MIAMI FL 33199 FAIRCHILD TROP GARDEN MIAMI FL 33156
Titolo Testata:
Canadian journal of forest research
fascicolo: 5, volume: 26, anno: 1996,
pagine: 747 - 757
SICI:
0045-5067(1996)26:5<747:LSEOUL>2.0.ZU;2-V
Fonte:
ISI
Lingua:
ENG
Soggetto:
PLANT-SPECIES DIVERSITY; TROPICAL MOIST FOREST; TREEFALL GAP; SPATIAL AUTOCORRELATION; SOLAR-RADIATION; COSTA-RICA; ENVIRONMENTS; REGIMES; SIZE; DEFINITION;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Science Citation Index Expanded
Citazioni:
43
Recensione:
Indirizzi per estratti:
Citazione:
D.B. Clark et al., "LANDSCAPE SCALE EVALUATION OF UNDERSTORY LIGHT AND CANOPY STRUCTURE -METHODS AND APPLICATION IN A NEOTROPICAL LOWLAND RAIN-FOREST", Canadian journal of forest research, 26(5), 1996, pp. 747-757

Abstract

Light is a key resource controlling tree regeneration in the understory of closed-canopy old-growth forests. To evaluate the distribution of understory light environments at a landscape scale, we used stratified random sampling in a 500-ha stand of Costa Rican tropical rain forest. Fifteen 100 m long transects were placed using random coordinates within two soil-geomorphology units (flat alluvial terraces and dissected ridge-slope-swale terrain). At 2.5-m intervals we measured canopy height and slope angle, classified topographic position, and took canopy photographs with a fish-eye lens at 1 and 3 m above the ground (andat 0.6 and 5 m height at five stations per transect). Photographs were analyzed for global site factor (GSF), which is analogous to the percentage of full sun radiation reaching a point. Canopy height and GSF at 1 and 3 m above the ground were significantly autocorrelated (Moran's I) at 2.5-m intervals. The autocorrelation rapidly declined at greater intervals, reaching nonsignificance at ca. 20 m. Both canopy height and GSF at 3 m height had a weak tendency for negative autocorrelations at intervals of 25-50 m. Median canopy height (615 stations) was 23 m (range 0-37). Caps (canopy height less than or equal to 2 m, Brokaw 1982) were only 1.5% of sample points. Caps were more frequent on steep slopes than on terraces, ridgetops, swales, and gentle slopes. Canopy height varied significantly across this topographic gradient. At all four heights (0.6, 1, 3, and 5 m) median GSF was less than or equalto 2.4%. GSF values > 8% accounted for only 3% of the total sample (N= 1380). GSF was only weakly negatively correlated with canopy heightand the relation was not monotonic. Under canopies 13-19 m tall, nearly all GSF values were less than or equal to 5%. Higher GSFs were morefrequent under both shorter and taller canopies. Given the observed variance in GSF and canopy height, 100-200 points separated by intervals of greater than or equal to 20 m are necessary to measure the forest-wide means of these variables to +/- 10%. We discuss implications of these results for current approaches to modeling understory light based on canopy characteristics We compared the random background of lightenvironments from 1-3 m above the ground at La Selva with those occupied by saplings of pioneer and nonpioneer tree species. The two pioneers (Cecropia spp.) occurred in microsites significantly brighter than random sites, while sapling microsites of all five nonpioneer species were significantly darker than random. Comparing the landscape-scale distribution of key resources with species' actual distributions at similar scales offers a quantitative method for assessing plant life histories within and among forests.

ASDD Area Sistemi Dipartimentali e Documentali, Università di Bologna, Catalogo delle riviste ed altri periodici
Documento generato il 20/01/21 alle ore 05:22:26