Light Acclimation of Four Native Tree Species in Felling Gaps within a Tropical Mountain Rainforest

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This article addresses the decline of Ecuadorian mountain rainforests by evaluating the success fo enrichment planting of native tree species in forest gaps to prote native tree abundance and biodiversity.

Research Goals & Methods

In this experiment, two mid-successional native tree species (C. montana and T. chrysantha), and two late-successional native tree species (N. membranacea and P. sprucei) were planted along felling gaps in a primary montane forest in Ecuador. A 4 hectare area was divided into 16 equal plots within which an average of 8 trees per plot was cut down to create canopy gaps varying in size between 80m2 and 100m2. Seedlings of the four native tree species were planted within 8 randomly selected felling gaps in belt transects. Light conditions were assessed based on canopy openness, the average daily photosynthetic photon flux density (PPFD), and the total site factor (the percentage of PPFD at the forest floor relative to the PPFD above the canopy). Photosynthetic light response, photosynthetic performance, total leaf area per individual and plant height were also recorded.

Conclusions & Takeaways

Across gaps, the highest light intensities were recorded at the center, and the lowest were recorded in the adjacent primary forest, with a mean light gradient within the gaps ranging from 6% to 24%. The heights of C. montana, P. sprucei,andT. chrysantha were positively correlated up to a measure of 30% canopy openness, at which point all three species showed diminishing growth rates, especially C. montana. P. spruceiwas the most sensitive to higher light levels. Overall, T. chrysantha had the highest growth rates at all light levels, followed by C. montana, P. sprucei, and N. membranacea. The mean total leaf area was highest for T. chrysantha, and decreased significantly in the other three species. Significant increases in total leaf area did not result from increases in canopy openness. The photosynthetic acclimation potential of N. membranacea was very high despite low growth levels. The authors conclude that all four species may be planted within the same felling gaps along existing light gradients, and suggest that T. chrysantha be planted in the center of the gap and that P. sprucei be planted in the understory adjacent to the gap.