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RESPONSES OF JUVENILE TREES TO ABOVE‐ AND BELOWGROUND COMPETITION IN NUTRIENT‐STARVED AMAZONIAN RAIN FOREST
Author(s) -
Coomes David A.,
Grubb Peter J.
Publication year - 1998
Publication title -
ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.144
H-Index - 294
eISSN - 1939-9170
pISSN - 0012-9658
DOI - 10.1890/0012-9658(1998)079[0768:rojtta]2.0.co;2
Subject(s) - understory , nutrient , biology , agronomy , competition (biology) , rainforest , biomass (ecology) , soil water , environmental science , soil fertility , ecology , canopy
In several tropical lowland rain forests, removal of root competition by trenching around seedlings and saplings has been shown to have little or no impact on growth rate. However, we found that trenching increased the aboveground growth rate of saplings and seedlings of a wide variety of species in an Amazonian caatinga. This low‐statured forest develops on waterlogged, humus‐rich, white‐sand soil that is extremely low in available nitrogen. Analysis of foliar nutrient concentrations and a fertilizer experiment confirmed previous findings that nitrogen is limiting, while measures of soil moisture potential and stomatal resistance gave no indication of water shortage. We suggest that belowground competition has an impact on growth rate because (1) established trees allocate a large proportion of biomass to fine‐root production, further reducing the availability of nutrients in an inherently poor soil, and (2) penetration of daylight to the sapling layer is greater than under other tropical lowland rain forests (1–3% vs. 0.5–1%). Although trenching had no effect on percentage mortality (12% over 18 mo), it reduced the percentage of naturally regenerating seedlings exhibiting net leaf loss from 28 to 8%. Surprisingly, the magnitude of response was similar in gaps and understory and was similar among species, suggesting that trenching had a larger effect on allocation than on the rate of photosynthesis or respiration.