Structure, productivity, and transpiration of a subtropical dry forest in Puerto Rico
Plants in the Guánica Forest (lat. 18° N) grew under the following climatic conditions: annual temperature, 25.8°C; annual rainfall, 929 mm; annual pan evaporation, 2074 mm; actual evapotranspiration, 722 mm; yearly runoff, 205 mm; and mean solar radiation, 4366 kcal/m{ostrok}/day. The climate was seasonal with most of the runoff between September and October. Soils normally exhibited water deficits during 10 months of the year. Shallow soils with frequent limestone out-cropping compounded the water-supply problem of plants. Four upland plant associations were studied. The scrub forest had a basal area (BA) of 4.2 m{ostrok}/ha and a complexity index (CI) of 2 calculated for trees with dbh > 5 cm. Its shallow soils were very sandy, or rocky. Succulent plants were common, and the canopy was open. The deciduous forest had a BA of 8 m{ostrok}/ha and a CI of 20. Its soils were deeper, and comprised of 64 percent sand and 33 percent silt. A taller and denser canopy developed in this forest. A mahogany plantation grew in semi-evergreen forest soils. There, soils were as deep as 1 m and rich in clay and silt. An ecotonal forest (between deciduous and semi-evergreen) had a BA of 10.7 m{ostrok}/ha and a CI of 20. The canopy of the ecotonal forest was relatively closed with a leaf area index (LAI) that varied seasonally between 1.2 and 4.2. Plant photosynthesis, respiration, transpiration, litter fall, and loose litter standing crop responded to moisture availability. Net daytime photosynthesis increased linearly with soil moisture availability (r = 0.76) and averaged 2.0 g/m{ostrok} leaf area/day for non-succulent plants. Nighttime respiration rates increased with decreasing soil moisture availability (r = 0.65) and averaged 0.36 g/m{ostrok} leaf area/day for non-succulent plants and 0.1 g/m{ostrok} photosynthetic area/day for succulent plants. Tree trunks respired during the dry season at a rate of 2.64 g/m{ostrok} surface area/day. Soil respiration was 4.74 g/m{ostrok}/day. Transpiration of succulent plants was 64 g H subíndice 2 O/m{ostrok} photosynthetic area/day, while for non-succulent plants it was 576 g H subíndice 2 O/m{ostrok} leaf area/day. Water-use efficiency was 6.2 for succulent plants and 1.8 for non-succulent plants. Succulent plants also exhibited nighttime or 24 hr C-uptake and water loss during early morning or late afternoon. Leaf fall and standing crop of loose litter increased with decreasing soil moisture availability. Mean litter-fall production for the scrub, deciduous forest, and mahogany plantation in g/m{ostrok}/day was: 0.28, 0.79 and 1.48, respectively. Mean litter fall and mean standing crop of loose litter for the forest as a whole were 0.66 g/m{ostrok}/day and 715 g/m{ostrok}, respectively. Mean annual litter turnover was 0.34. Gross primary productivity average 1.6 g/m{ostrok}/day and correlated linearly with soil moisture availability (r = 0.87). It is concluded that soil moisture availability (a function of shallow soils and low rainfall) is the factor that determines forest productivity, growth characteristics, water loss, and physiognomy.
| Main Authors: | , , , |
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| Format: | biblioteca |
| Published: |
1978
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| Subjects: | CARACTERISTICAS DEL SITIO, PRODUCTIVIDAD, ESTRUCTURA DEL BOSQUE, TRANSPIRACION, ENERGIA SOLAR, SUELO, INTERCAMBIO DE GASES, PUERTO RICO, |
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