Patterns Of Light Attenuation Research Articles

Vertical and horizontal light heterogeneity along gradients of secondary succession in cool- and warm-temperate forests.

Light availability varies drastically in forests, both vertically and horizontally. Vertical light heterogeneity (i.e., patterns of light attenuation from the forest canopy to the floor) may be related to light competition among trees, while horizontal light heterogeneity (i.e., variations in light intensity at a given height within forests) may be associated with light-niche partitioning among tree species. However, light heterogeneity in vertical and horizontal directions and their associations with forest structure are rarely studied to date. Here we report the first comprehensive study to compare the vertical and horizontal light heterogeneity in differently aged forests in two forest types. Twelve forest stands of different ages in cool-temperate forests (consisting of deciduous broad-leaved trees) and five of different ages in warm-temperate forests (evergreen conifer and deciduous broad-leaved trees) in Japan. We measured vertical light profiles at 1-m intervals from the understorey (1m above the ground) to the top canopy (12-22 m depending on stands) at 16 locations for each stand (20 m × 20 m). We also measured structural parameters (diameter at breast height, height, and crown dimensions) for all major trees in these stands. Along the secondary successional gradients, the vertical and horizontal light heterogeneity changed in a systematic manner in both forests. The vertical light attenuation rate was steeper in early succession and more gradual in late succession, and the horizontal light heterogeneity was relatively small in early succession and more pronounced in late succession. The vertical light attenuation rate was different between the two forest types; the light intensity dropped more sharply from the canopy surface in the cool-temperate forests due to the crown being vertically shorter and denser (i.e., higher leaf density per unit volume). In early succession, a steeper light attenuation rate is likely related to the strong light competition among co-occurring trees and thus a self-thinning process. In late succession, the high spatial light heterogeneity in forests (i.e., larger horizontal light heterogeneity and gradual light attenuation rate) may allow more species to partition light, and thus may enhance species coexistence and diversity.

Effects of Understory Foliage on Patterns of Light Attenuation near the Forest Floor

ABSTRACTUnderstory light availability is an important component of the environment for canopy tree seedlings. Understanding what generates variation in Understory light availability represents one step in understanding processes regulating seedling banks, the beginning capital of regeneration in tropical forests. Near the forest floor, variation in light availability may be strongly influenced by the structure and composition of the understory. I examined abundance of Understory foliage and patterns of light attenuation in five Neotropical forests (La Selva Biological Station, Costa Rica = LS; Barro Colorado Nature Monument, Panama = BCI; Cocha Cashu Biological Station, Manu National Park, Peru = CC; Kilometer 41, Manaus, Brazil = KM41; and Nouragues, French Guiana = NG). I used hemispherical canopy photos to estimate light availability at two heights (0.65 and 1.7 m) above the forest floor and counted foliage between these heights. Light availability differed significantly among sites, and site rankings depended on measurement height. At 0.65 m, NG had significantly lower mean light availability than CC, with KM41, LS, and BCI equivalent and intermediate. At 1.7 m, light availability was still lowest at NG, and highest at CC, but LS had levels similar to CC while KM41 and BCI remained intermediate. Across sites, light attenuation was positively related to foliage density. LS had the most understory foliage and the highest light attenuation between 0.65 and 1.7 m. KM41, NG and CC had intermediate amounts of foliage and intermediate light attenuation. BCI had the lowest density of understory foliage and no difference between light at the two measurement heights. My results show significant effects of understory foliage on understory light and indicate that the selective environment of canopy tree seedlings differs among sites.RESUMENLas condiciones lumínicas en el sotobosque son un componente importante del ambiente selectivo de las pláintulas de árboles del dosel. Entender los factores que regulan la variación en la cantidad del luz que llega a un punto dado del sotobosque representa un paso en la comprensión de los procesos que regulan la regeneratión avanzada en bosques tropicales. Cerca del suelo del bosque, la variación en el ambiente lumínico puede verse afectado más por la estructura la compositión del sotobosque que por el dosel. Para evaluar esta hipótesis, examiné la abundancia del follaje del sotobosque y los patrones de la atenuación de luz en cinco bosques neotrópicales (Estación Biológica La Selva, Costa Z Rica = LS; Monumento Natural de Barro Colorado, Panamá= BCI; Estación Biológica Cocha Cashu, Parque Nacional Manu, Perú= CC; Kilómetro 41, Manaus, Brasil = KM41; y Nouragues, French Guiana = NG). Estimé la disponibilidad de luz con fotos hemisphericas (lente “ojo de pez”) tornados en dos alturas (0.65 y 1.7 m desde el suelo). Medí un perfil de follaje entre las alturas focales. Los sitios difirieron significativamente en la cantidad de luz. Además, el orden del los sitios en cuanto a condiciones luminícas varió con la altura de la medida. A 0.65 m, NG mostró la menor disponibilidad de luz seguido por KM41, LS, y BCI (similares) y finalmente CC. A 1.7 m, NG todavía mostró la menor disponibilidad del luz seguido por KM41 y BCI, y ambos fueron más bajos que LS o CC (similares y las mayores cantidades). La attenuatión de luz se relacionó positivamente con la densidad del follaje en el sotobosque. En LS observé la mayor cantidad del follaje del sotobosque y la mayor atenuación de luz entre alturas de medida. En KM41, CC, y NG observé cantidades intermedios del follaje y atenuación de la luz. BCI mostró las menores cantidades del follaje del sotobosque y ninguna diferencia entre la luz en las dos alturas medidas. Mis resultados muestran los efectos fuertes de la vegetatión del sotobosque por el ambiente lumínico y indican que el ambiente selectivo de las plántulas de los árboles del dosel puede diferir entre sitios.

Effects of Understory Foliage on Patterns of Light Attenuation near the Forest Floor1

Understory light availability is an important component of the environment for canopy tree seedlings. Understanding what generates variation in understory light availability represents one step in understanding processes regulating seedling banks, the beginning capital of regeneration in tropical forests. Near the forest floor, variation in light availability may be strongly influenced by the structure and composition of the understory. I examined abundance of understory foliage and patterns of light attenuation in five Neotropical forests (La Selva Biological Station, Costa Rica = LS; Barro Colorado Nature Monument, Panama = BCI; Cocha Cashu Biological Station, Manu National Park, Peru = CC; Kilometer 41, Manaus, Brazil = KM41; and Nouragues, French Guiana = NG). I used hemispherical canopy photos to estimate light availability at two heights (0.65 and 1.7 m) above the forest floor and counted foliage between these heights. Light availability differed significantly among sites, and site rankings depended on measurement height. At 0.65 m, NG had significantly lower mean light availability than CC, with KM41, LS, and BCI equivalent and intermediate. At 1.7 m, light availability was still lowest at NG, and highest at CC, but LS had levels similar to CC while KM41 and BCI remained intermediate. Across sites, light attenuation was positively related to foliage density. LS had the most understory foliage and the highest light attenuation between 0.65 and 1.7 m. KM41, NG and CC had intermediate amounts of foliage and intermediate light attenuation. BCI had the lowest density of understory foliage and no difference between light at the two measurement heights. My results show significant effects of understory foliage on understory light and indicate that the selective environment of canopy tree seedlings differs among sites.

Influence of leaf area density and trellis/training system on the light microclimate within grapevine canopies

The influence of leaf area density and canopy configuration on the light microclimate within 6 wine grape trellis/ training systems commonly used in California (single curtain, double curtain, vertically shoot positioned, lyre, Smart-Henry and Smart-Dyson) was examined in two experimental vineyards (Oakville and Parlier). Mean canopy leaf area density varied considerably among the systems, ranging from approximately 2.8 m 2 m - 3 for the Wye to 10.1 m 2 m - 3 for the VSP. Non-positioned systems were characterized by a layer of relatively high leaf area density in their outer envelope and lower leaf area densities in their interior. In contrast, leaf area density in positioned systems increased from the top of the canopy moving downward to the fruit zone. Mean leaf area density within the fruit zone ranged from near 6 m 2 m - 3 in the DC to over 12 m 2 m - 3 in the VSP and LYR. The pattern of light attenuation within the canopy was generally similar among the systems, with PPF reaching its lowest level in or near the fruit zone. Fruit zone PPF was >10 % of ambient sunlight in low density canopies and <5 % in high density canopies. A gradual decline in fruit zone PPF was found as leaf area density increased in positioned systems. PPF decreased sharply in the fruit zone of non-positioned systems as leaf area density increased from 2 to 4 m 2 m - 3 , then leveled as leaf area density exceeded 6 m 2 m - 3 . Fruit zone PPF decreased as the leaf area density of divided systems increased from 2 to 4 m 2 m - 3 , then declined gradually as leaf area density approached 6 m 2 m - 3 . Fruit zone PPF in non-divided systems was initially lower, and declined more gradually as leaf area density increased, compared to divided systems. Compared to positioned systems, leaf layer number in the fruit zone rose more sharply in non-positioned systems as leaf area density increased. Leaf layer number was greater in nondivided systems compared to divided systems, but declined at similar rates in both systems as leaf area density increased. Shoot-positioned systems achieved well-exposed fruit zones at higher leaf area densities, but lower leaf layer numbers, compared to non-positioned canopies.

Light attenuation in a small tropical reservoir (Solomon Dam, North Queensland): seasonal changes and the effects of artificial aeration

Seasonal changes in light attenuation are described for a small tropical reservoir (Solomon Dam) at Palm Island, north Queensland, and the attenuation characteristics are compared with those reported for other Australian water bodies. The major components of the water column that affect attenuation of photosynthetically available radiation (PAR) were studied over a 4-year period, including 16 months when the reservoir was artificially aerated. The pattern of light attenuation varied at different times of the year, depending largely on the stratification conditions and on the dominant phytoplankton species. The vertical attenuation coefficient for PAR varied on a seasonal basis, the major peaks being related to periods of high phytoplankton densities. The only time tripton contributed significantly to attenuation of PAR was coincident with the start of artificial aeration. Gilvin concentrations in Solomon Dam were moderately high, especially in the hypolimnion of the strongly stratified reservoir. Artificial aeration moderated the range of seasonal fluctuations in light attenuation, by reducing the density of phytoplankton in the surface layers.