Sudden opening and slow changes in canopy coverage modulate acclimation, survival and growth of a shade-tolerant rainforest tree species

MORETTI, ANA PAULA; OLGUIN, FLAVIA Y; GAUNA, JUAN MARCELO; GRACIANO CORINA

Journal of Forestry Research

Springer

Año: 2023

1007-662X

Disturbances at gap levels are one of the most important events for the regeneration and establishment of fast-growing intermediate species that initially established in the understory, but then require more light to grow and reach the upper strata. However, sudden changes in light could affect the survival and growth of plants established in the understory that fail to acclimate to the new microenvironment. Sudden canopy removal exposes plants to high light intensity and high evaporative demands that stress shade-acclimated plants. On the other hand, the slow closure of gaps reduce light availability to young plants established when the incident irradiation was higher. The aim of this work was to evaluate the morphological and physiological acclimation of Cabralea canjerana (Vell) Mart. young plants to sudden and slow changes in canopy coverage. We carried out a pot experiment with plants exposed to a sudden opening of the natural canopy coverage (light shock) and another field experiment with plants planted in a natural coverage gradient in rainforest gaps. In the pot experiment, few days after the light shock, plants rapidly increased photosynthetic rate and decreased leaf water potential. After two months, plants activated physiological responses at leaf level and whole plant level to high light and water stresses, like increase stomatal conductance, stomatal index and reduction of leaf: fine roots ratio and chlorophyll. After seven months, plants increased hydraulic conductivity of petioles and the whole leaf hydraulic conductance, and growth was much higher than plants that remained under the canopy. In the field experiment, plants acclimated to all canopy coverage intensities, as environmental conditions were intermediate to those in the pot experiment. Seven years after planting, plant growth was maximal when trees were planted in open microenvironments within the gaps, even if the canopy closed during the first 20 months after planting. In conclusion, if the species is planted to enrich the rainforest, the positions within the gaps with lower canopy coverage should be chosen, and gap closure will not affect plant growth. To manage C. canjerana natural regeneration, the opening of gaps and removal of understory will increase plant survival and growth, without the risk that the stress caused by these sudden opening could lead to the death of young plants. Finally, combining pot and field experiments is useful to understand the autoecology of trees with particular ecological interest, and to build restoration practices with scientific knowledge.