Tesis Maestría en Ciencias en Recursos Naturales y Desarrollo Rural El Colegio de la Frontera Sur 2000

Bibliografía: hojas 19-25

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We evaluated the light conditions of points in small gaps (64-175 m2) and in surrounding forested areas with hemispheric photographs, and its relationship with growth variables in 605 transplanted individuals (2.5 x 3.0 m from each other) of five native tree species: Almis acuminata, Cornus excelsa, Liquidambar styraciflua, Persea americana and Ouercus laurina. We assumed that spatial light contrasts between open and forested habitats have decreased with recent rising of disturbance levels. Plant performance variables were related (after 15 months) to direct sunlight (RDS) al the transplant point, and with spatial light contrast indices (LCl) constructed with RDS values in neighboring points. Positive contrasts included relatively highlight points surrounded by shaded areas; negative constrasts represented shaded points in the middle of more illuminated spots. Study plots showed a large heterogeneity of light enviromiients. Highest negative contrasts occurred when RDS < 15%; an asymptote (LCl = 0) was associated to canopy openings with RDS> 35%. Multiple linear regression indicated that RDS was related to shoot height of Liquidambar (P < 0.007) after removing the effect of their initial measurements. With only negative contrast points in the regression, height was related to RDS in Alnus (P < 0.05), Cornus (P < 0.045), and Liquidambar (P < 0.009), and stem diameter in Persea (P < 0.041). Basal stem diameter in Liquidambar (P < 0.039) and leaf size in Ouercus (P < 0.002) were explained by RDS under positive contrasts. Taller and thicker plants of Ouercus (P < 0.016) were related to high contrasts under high-light conditions. The results indicate that plant performance may depend on relative conditions of the light environment in addition to point-level values. Further criteria and indicators of forest sustainability and functional classification of tree species may consider the heterogeneity of light environments as represented by spatial light contrasts. Inglés

Manejo y Conservación de Recursos Naturales