Direct Site Factor Research Articles

Tree regeneration characteristics in limestone forests of the Cat Ba National Park, Vietnam

BackgroundThe ability of overstory tree species to regenerate successfully is important for the preservation of tree species diversity and its associated flora and fauna. This study investigated forest regeneration dynamics in the Cat Ba National Park, a biodiversity hotspot in Vietnam. Data was collected from 90 sample plots (500 m2) and 450 sub-sample plots (25 m2) in regional limestone forests. We evaluated the regeneration status of tree species by developing five ratios relating overstory and regeneration richness and diversity. By examining the effect of environmental factors on these ratios, we aimed to identify the main drivers for maintaining tree species diversity or for potential diversity gaps between the regeneration and the overstory layer. Our results can help to increase the understanding of regeneration patterns in tropical forests of Southeast Asia and to develop successful conservation strategies.ResultsWe found 97 tree species in the regeneration layer compared to 136 species in the overstory layer. The average regeneration density was 3764 ± 1601 per ha. Around 70% of the overstory tree species generated offspring. According to the International Union for Conservation of Nature’s Red List, only 36% of threatened tree species were found in the regeneration layer. A principal component analysis provided evidence that the regeneration of tree species was slightly negatively correlated to terrain factors (percentage of rock surface, slope) and soil properties (cation exchange capacity, pH, humus content, soil moisture, soil depth). Contrary to our expectations, traces of human impact and the prevailing light conditions (total site factor, gap fraction, openness, indirect site factor, direct site factor) had no influence on regeneration density and composition, probably due to the small gradient in light availability.ConclusionWe conclude that the tree species richness in Cat Ba National Park appears to be declining at present. We suggest similar investigations in other biodiversity hotspots to learn whether the observed trend is a global phenomenon. In any case, a conservation strategy for the threatened tree species in the Cat Ba National Park needs to be developed if tree species diversity is to be maintained.

How drought-induced forest die-off alters microclimate and increases fuel loadings and fire potentials

Forest die-offs associated with drought and heat have recently occurred across the globe, raising concern that associated changes in fuels and microclimate could link initial die-off disturbance to subsequent fire disturbance. Despite widespread concern, little empirical data exist. Following forest die-off in the Northern Jarrah Forest, south-western Australia, we quantified fuel dynamics and associated microclimate for die-off and control plots. Sixteen months post die-off, die-off plots had significantly increased 1-h fuels (11.8 vs 9.8 tonnes ha–1) but not larger fuel classes (10-h and 100-h fuels). Owing to stem mortality, die-off plots had significantly greater standing dead wood mass (100 vs 10 tonnes ha–1), visible sky (hemispherical images analysis: 31 vs 23%) and potential near-ground solar radiation input (measured as Direct Site Factor: 0.52 vs 0.34). Supplemental mid-summer microclimate measurements (temperature, relative humidity and wind speed) were combined with long-term climatic data and fuel load estimates to parameterise fire behaviour models. Fire spread rates were predicted to be 30% greater in die-off plots with relatively equal contributions from fuels and microclimate, highlighting need for operational consideration by fire managers. Our results underscore potential for drought-induced tree die-off to interact with subsequent fire under climate change.

EFFECT OF CANOPY GAPS A'ND TOPOGRAPHIC REGIMES IN SEEDLINGS PERFORMANCE IN SINHARAJA RAIN FOREST, SOUTHWEST SFU LANKA

Growth and survival of tree canopy dominant seedlings in the Sinharaja lowland rain forest insouthwest Sri Lanka were monitored. Twelve canopy gaps and closed canopy sites wereselected, as four of each on different topographic positions- valley, midslope and ridgetop.Measurements of height, number of leaves and mortality were recorded over a two-year period.Hemispherical canopy photographs were taken to calculate Indirect Site Factor (ISF), Direct SiteFactor (DSF), and canopy openness. Greatest canopy openness, highest DSF values wererecorded for ridgetop sites and smallest values were recorded for valley sites. Over the two-yearperiod sixty-six (11.45%) seedlings died in the ridge top, which indicated the highest mortalityrate. Survival of seedlings in the canopy gap ani .orest understorey declined on progressingfrom valley to ridgetop sites. Seedlings of Mesua ferrea had a higher survival than other speciesin the canopy opening and understorey conditions. Height growth and leaf number were greatestin the gap sites. A significant relationship was found between DSF and maximum height growth(33.05,P>O.OO) for Syzygium rubicundum. Shorea trapezlfolta, Shorea distich a and Syzygiumrubicundum showed greatest height increment .n the valley, midslope and ridgetop sitesrespectively. No relationship was found between DSF and leaf numbers in all seedlings exceptSyzygium rubicundum, where has increased with increasing DSF.

EFFECT OF SHADING ON SURViVAL AND GROWTH OF Mesua (CLUSIACEAE) AND Shorea (DIPTEOCARPACEAE) SEEDLINGS ACROSSTOPOGRAPHIC GRADIENT IN SINHARAJA RAIN FOREST, SOUTHWEST SRI lANKA

The effect of shading on survival and growth of two species of Mesua (Clusiaceae) andfour species of Shorea (Dipteocarpaceaeh planted seedlings were investigated at differenttopographic positions in Sinharaja rain forest All occur together as canopy dominant treesIII Sinharaja rain forest Twelve-understory sites were selected, four each on differenttopographic posilions valley, midslope and ridgetop. Measurements of height, number ofleaves, root collar diameter and the mortality were recorded over a five-year period.Hemispherical canopy photographs were taken to calculate Indirect Site Factor (ISF),Direct Site Factor (DSF), and the Leaf Area Index (LAI). Analysis of photographsdemonstrated that LAI decreased from valley to ridge top while DSF and ISF increasedfrom the valley to ridge top. After five years thirty-four (34 %) seedlings died in the ridgelop and the lowest mortality was recorded in the midslope. Seedlings of Mesua ferrea L.had the highest survival than other species in all understory conditions and the lowestsurvival rate recorded for Shorea trapezifolia (Thw.) Ashton. Results showed cleardifferences in survival and growth among species. These differences appeared related (0availability of soil moisture and understory radiation regimes.

Importance of light conditions for the height growth of underplatings in Norway spruce stands in the Oravské Beskydy Mts.

The study analyses the relationships between the components of relative irradiance and density of parent Norway spruce stand as well as the impact of light on height growth and crown architecture of beech and fir underplantings and natural regeneration of spruce. We observed three variants of regeneration: fir underplanting, beech underplanting and spruce natural regeneration. For each variant three circular research plots with the size 500 m2 were established. To determine the intensity of relative irradiance 15 hemispherical photographs in the height of 1.5 m were taken for each variant. The analysis confirmed a significant relationship only between indirect site factor (ISF) and basal area and partly stem number of parent stand. There is almost no influence of spruce overstorey density (within the observed range of basal area and stem number) on the values of total site factor (TSF) and its main component direct site factor (DSF). The relevant predictor for the height increments of underplanted saplings is ISF. Relationship between TSF and height increment is weak. Apical dominance ratio (ADR) that was used to characterize crown architecture is significantly correlated with ISF only for beech and fir. In the case of spruce, increase of light intensity in the observed range does not lead to a significant change of saplings crown architecture.

Near‐ground solar radiation along the grassland–forest continuum: Tall‐tree canopy architecture imposes only muted trends and heterogeneity

AbstractSolar radiation directly and indirectly drives a variety of ecosystem processes. Our aim was to evaluate how tree canopy architecture affects near‐ground, incoming solar radiation along gradients of increasing tree cover, referred to as the grassland–forest continuum. We evaluated a common type of canopy architecture: tall trees that generally have their lowest level of foliage high above, rather than close to the ground as is often the case for shorter trees. We used hemispherical photographs to estimate near‐ground solar radiation using the metric of Direct Site Factor (DSF) on four sites in north Queensland, Australia that formed a grassland–forest continuum with tree canopy cover ranging from 0% to 71%. Three of the four sites had tall Eucalyptus trees with foliage several metres above the ground. We found that: (i) mean DSF exceeded >70% of the potential maximum for all sites, including the site with highest canopy cover; (ii) DSF variance was not highly sensitive to canopy coverage; and (iii) mean DSF for canopy locations beneath trees was not significantly lower than for adjacent intercanopy locations. Simulations that hypothetically placed Australian sites with tall tree canopies at other latitude–longitude locations demonstrated that differences in DSF were mostly due to canopy architecture, not specific site location effects. Our findings suggest that tall trees that have their lowest foliage many metres above the ground and have lower foliar density only weakly affect patterns of near‐ground solar radiation along the grassland–forest continuum. This markedly contrasts with the strong effect that shorter trees with foliage near the ground have on near‐ground solar radiation patterns along the continuum. This consequence of differential tree canopy architecture will fundamentally affect other ecosystem properties and may explain differential emphases that have been placed on canopy–intercanopy heterogeneity in diverse global ecosystem types that lie within the grassland–forest continuum.

Spatial pattern and species richness of boreonemoral forest understorey and its determinants—A comparison of differently managed forests

We compared patterns of understorey vegetation and abiotic factors in old-growth forests with low management intensity and young forests with high management intensity. CCA showed that disturbance gradient was the main axis of community variation, while local light availability (ISF, indirect site factor) and soil conditions (nitrate content) were also of some importance. Young stands demonstrated a significantly higher heterogeneity of vegetation with increased pattern diversity (1 − Jaccard similarity among 1 m × 1 m plots, also called beta diversity), variation in species richness and variation in the cover of both vascular plants and bryophytes. Young stands also showed a higher variation of soil nitrate content and lower average vascular plant cover. We concluded that the understorey vegetation in young stands with high intensity management is, contrary to our literature-based expectation, more heterogeneous in space than that in old stands with low management intensity. The relationship between environmental heterogeneity and diversity has been discussed extensively, but there is a scarcity of quantitative relationships documented in natural vegetation. We found that species richness in 4 m × 4 m plots was positively dependent on the variability of light availability (ISF) within plot. Pattern diversity was positively dependent on the variation of microtopography and the availability of direct radiation (DSF, direct site factor).

A calibration method for the crown illumination index for assessing forest light environments

The crown illumination index (CII) is an ordinal scale frequently used to qualitatively assess the light environment within a forest. Although this method provides a simple and rapid approach, it can be subjective and needs to be calibrated against quantitative measurements of canopy structure. A study was undertaken in north-western Amazonia to provide a means to calibrate the CII in tropical forests. Hemispherical photographs were taken to represent each CII class, which were then analysed using HemiView 2.1 software in order to calculate light availability factors. The proportion of visible sky and indirect, direct and global site factors (the proportion of indirect, direct and total radiation reaching a point, compared to an open location) were all found to correlate strongly with CII class and therefore offer a viable method for calibration. CII classes could only be weakly defined with respect to leaf area index (LAI), however, and so conversion of CII to LAI or vice versa is problematic. The results of this study provide a quantified description of each index class, significantly improving interpretation of the crown illumination index.

Differences between structural and functional environmental heterogeneity caused by seed dispersal

Summary This paper explores the idea that functional heterogeneity (variability of a system property affecting ecological processes) is only a fraction of the available structural heterogeneity (variability of a property measured without reference to ecological effects) caused by non‐random propagule dispersal. We report the effect of acorn dispersal by jays on the light environment experienced by Holm Oaks (Quercus ilex L.) during early recruitment in a Mediterranean montane forest. Four light variables were estimated by studying hemispherical photographs: direct site factor (DSF); indirect site factor (ISF); and potential direct radiation during April (PDRApril) and August (PDRAugust). Means and variances of these variables were compared before and after the dispersal of acorns by jays. The landscape occupied by Holm Oaks was very heterogeneous, which translated into differences in the available light among microhabitats of up to one order of magnitude. Because of the spatial pattern of acorn dispersal, the light environment of the oaks during their establishment was much more homogeneous than that in the whole landscape. This demonstrates that the heterogeneity relevant for plant recruitment is not necessarily that of the landscape as a whole.

Light-related competitive effects of overstory trees on the understory conifer saplings in a subalpine forest

To clarify the mechanism by which overstory trees shade understory saplings, we investigated the relationships among light conditions of the saplings (measured as indirect site factor; ISF and direct site factor; DSF), the calculated competition effects of overstory trees on the saplings (W), and relative height growth rate of the saplings (RHGR). We calculated several W values in order to find a W value which can express the light conditions as appropriately as possible, and the results indicated that W explained only 21.9%–24.7% of the total variance of light conditions in the cases where W gave the best fit. In this study, W was calculated based on the basal areas of overstory trees. However, it is known that canopy structure also affects the light regimes in the forest understory, and this might yield the possible errors even within W representing the shading effects most adequately. Therefore, although W significantly represents the shading effect from overstory trees, a great proportion of the variance remained without being explained by W. RHGR was negatively correlated with W, and the W value which had the most adequate explanation of the shading effect also showed the best negative correlation with RHGR. This provides the evidence that the competitive effect of overstory trees on sapling growth is mediated by the shading effect, indicating that competition for light clearly exists within this forest. Such competition for light may closely relate to the well-known phenomenon of gap regeneration in subalpine forests in central Japan.

Light environment and tree strategies in a Bolivian tropical moist forest: an evaluation of the light partitioning hypothesis

Light partitioning is thought to contribute to the coexistence of rain forest tree species. This study evaluates the three premises underlying the light partitioning hypothesis; 1) there is a gradient in light availability at the forest floor, 2) tree species show a differential distribution with respect to light, and 3) there is a trade-off in species performance that explains their different positions along the light gradient. To address these premises, we studied the light environment, growth, and survival of saplings of ten non-pioneer tree species in a Bolivian moist forest. Light availability in the understorey was relatively high, with a mean canopy openness of 3.5% and a mean direct site factor of 6.8%. Saplings of two light demanding species occurred at significantly higher light levels than the shade tolerant species. The proportion of saplings in low-light conditions was negatively correlated with the successional position of the species. Light-demanding species were characterised by a low share of their saplings in low-light conditions, a high sapling mortality, a fast height growth and a strong growth response to light. These data show that all three premises for light partitioning are met. There is a clear gradient in shade-tolerance within the group of non-pioneer species leading to a tight packing of species along the small range of light environments found in the understorey.

Effects of potential PAR on shoot extension in juveniles of the main tree species in a Japanese temperate forest

We studied the relationship between potential photosynthetically active radiation (PAR), estimated from hemispherical photographs, and shoot extension rates of juveniles of 12 seral tree species. We distinguished between direct light site factor (DIR), diffuse light site factor (DIF), and gap light index (GLI). We used a log‐linear model to relate growth to DIR, DIF and GLI. Potential PAR explained shoot growth rates significantly in 33 cases out of 36 (12 species × 3 PAR). DIF explained the shoot extension rates better than DIR and GLI for 10 of the 12 species. The mean values of maximum shoot extension rates of the tolerant, the intermediate and the intolerant species were 52.4 cm year–1, 64.3 cm year–1 and 87.7 cm year–1, respectively. The maximum shoot extension rates of the tolerant and the intolerant species were recorded in about 50% DIF and more than 70% DIF, respectively. The minimum light level for seedling establishment of the intermediate and intolerant species was more than 20% DIF. We explained distribution characteristics and shoot extension of the species in relation to light in terms of shade tolerance. Predictions based on light‐growth curves and maximum growth curves were similar to field observations made elsewhere, suggesting that these models may be useful to predict extension growth of juvenile trees in mixed species stands.

Tree seedling performance in canopy gaps in a tropical rain forest at Nouragues, French Guiana

The effect of natural canopy gaps on the performance of naturally occurring tree seedling populations was studied in a tropical rain forest in French Guiana. This was done at two levels of scale. Firstly, on a 20 m × 250 m forest transect intersecting four canopy gaps, it was investigated how patterns of recruitment, growth and survival of seedlings of Cecropia obtusa, Dicorynia guianensis and Pourouma bicolor differed between canopy gaps and closed forest. Secondly, for one large natural canopy gap, performance of seedling cohorts established before (‘pre-gap’ cohorts) and after (‘post-gap’ cohorts) gap formation was studied in relation to environmental heterogeneity. The direct site factor (DSF) was used as an indicator of light availability in the gap zone. Cecropia specialised in large gaps, and also in specific sites within the large gap: seedling performance was increased by light, and by dead wood. Pourouma mainly germinated under closed forest conditions, where it can survive for a long period until a canopy gap is formed nearby. Pourouma seedlings adjusted well to the new gap environment but they did not specialise in specific places within the gap. Seedling location of Pourouma seedlings was mainly determined by accidental positioning before gap formation. Dicorynia was able to germinate both in gaps and under closed forest conditions. Although the number of gaps studied in this study was low, the results show that seedling establishment, early growth and survival of the three tree species were affected by canopy gaps and by the environmental heterogeneity within a large gap.

Effects of Habitat, Plant Size, and Floral Display on Male and Female Reproductive Success of the Neotropical Orchid Brassavola nodosa

We examined correlatively the joint effects of light, supporting plant characteristics, plant size, and floral display on pollinia removal and fruit production of 103 individuals of the orchid Brassavola nodosa (L.) Lindl. at Peter Douglas Cay, Belize, Central America. This orchid is epiphytic on red mangroves (Rhizophora mangle L. [Rhizophoraceael), and grows from 1-300 cm above ground. Light levels above each orchid, measured as direct site factor using hemispherical canopy photography, were 6-46 percent of potential direct sunlight. To characterize plant size, we counted the number of leaves of each plant and measured its longest leaf and the leaf subtending each inflorescence. The largest orchids were found in areas of high light availability, high above ground, and on large support structures. From June through early August 1993, and again in December 1993, orchids were surveyed every 3-4 days for reproductive status and success (removal of pollinia and/or fruit production). The 48 plants that flowered during these 7 months had more and longer leaves than the 55 plants that did not flower at any time in this time period. Plants flowered continuously throughout the summer; a complete reproductive cycle (bud appearance to fruit set) lasts 2-5 weeks. Pollinia were removed from 12 percent, and fruits were set by 30 percent, of the flowers produced in the summer. Because fruit set was much lower in the fall, the total proportion of fruit production relative to flower production over the 7-month study period was only 13 percent. Path analysis indicated that direct site factor, height above ground, and diameter of supporting structures significantly contributed to plant size and floral display area. In turn, floral display significantly affected both male and female reproductive success. We condude that resources limit flower production and components of floral display, whereas pollinator availability likely limits reproductive success in Brassavola nodosa.

Light environments and floristic composition across an open forest‐rainforest boundary in northeastern Queensland

Abstract This paper demonstrates the changes in structure, floristics and forest floor light regimes across the boundary between open forest and rainforest at Kirrama in northeastern Queensland. Hemispherical photographs of the canopy were used to estimate spatial and temporal variations in potential (clear‐sky) direct and diffuse photosynthetic photon flux density (PPFD = 400–700 nm) across the boundary. Five vegetation zones were identified across the boundary: (A) open forest, (B) tall open forest, (C) tall open forest with a rainforest under‐storey, (D) young rainforest, and (E) mature rainforest. During the summer (September–March) direct PPFD declined semi‐exponentially across the boundary, while in the winter (April–August), the decline was more linear. However, the decline in diffuse PPFD across the boundary was linear throughout the year. Mean per cent grass cover was positively correlated and mean per cent shrub cover negatively correlated with annual average total PPFD across the boundary. Mean percentages of diffuse radiation relative to that above the forest (diffuse site factors) ranged from 9.8% in the mature rainforest to 66.4% in the open forest, while mean percentages of direct radiation relative to that above the forest (direct site factors) ranged from 2.9–38.3% at the same sites, respectively. Daily PPFD in the rainforest understorey is probably insufficient for the shade intolerant (pioneer) species which prefer the more open environments on the rainforest margin where light intensities and soil temperatures are higher. Towards the rainforest end of zone C, light conditions appear to be similar to those experienced within small treefall gaps in rainforests. Typically, such light conditions are preferred by shade tolerant (primary) tree species that are unable to grow and reproduce successfully in the adjacent shaded understorey and to compete with the fast growing pioneer tree species in the more open end of zone C.

Understorey light environments in a north-east Australian rain forest before and after a tropical cyclone

ABSTRACTThis paper describes estimates of canopy openness and associated light availability in the understorey of a north-east Australian rain forest before and immediately after a tropical cyclone. On the basis of 20 hemispherical (fisheye) canopy photographs it was shown that direct, diffuse and total site factors increased significantly as a result of the slight-to-moderate canopy disturbance caused by the cyclone. In the understorey, median total site factors ranged from 2.5–3.4% before the cyclone and from 6.0–8.6% after the cyclone, representing a 2- to 3-fold increase in potential light availability. Following the cyclone, mean relative gap frequencies increased substantially at all altitudes but particularly at canopy positions more than 70° above the horizon. Cyclone-induced canopy disturbance not only reduced the complexity of the understorey light regime but may have also increased the seasonal variability of light within the understorey of the forest during the interval of canopy recovery. The implications of these results for the ecophysiology of understorey tree seedlings and saplings at several temporal scales are discussed.

Correlations Between Biomass Allocation, Relative Growth Rate and Light Environment in Tropical Forest Saplings

The growth rates and patterns of aboveground biomass allocation were determined for saplings of nine species of a wet tropical forest in Costa Rica. Relative growth rate and allocation were calculated by remeasuring the dimensions of forest-grown saplings and using biomass-dimension relationships derived from harvested saplings to convert linear dimensions to biomass estimates. The light environment of each sapling was characterized in terms of direct and indirect site factors calculated from hemispherical 'fisheye' photographs of the canopy. Relative growth rate (RGR) was significantly correlated with both direct and indirect site factors. A significant negative correlation was found between ln(% leaf allocation) and RGR for six species, but no such correlation occurred for the three species most highly associated with canopy gaps. Thus, shade-tolerant saplings shift most of their above-ground growth to leaf replacement when heavily shaded, while gap-associated species allocate about 2/3 of aboveground growth to the stem and branches under all measured conditions. This differential plasticity in leaf vs wood allocation may be an important factor in determining the shade tolerance and successional status of woody species. Key-words: Allocation, growth, light, sapling, tropical

Tree Seedling Growth and Survival in a Malaysian Rain Forest

Growth and survival of tree seedlings were observed in lowland, evergreen, tropical rain forest in Pantai Aceh Forest Reserve, Penang, Peninsular Malaysia. Four natural gaps and two closed-canopy sites were used. In each site twenty 1 m2 plots were laid out at random and all the seedlings in them were identified, tagged, mapped, and measured for height and basal stem diameter, and the number of leaves were counted. After six months four of the sites were revisited, and after 16 months they were all revisited. Hemispherical canopy photographs were taken to calculate diffuse and direct site factors. At the start of the observations 1287 seedlings of 116 species were tagged. Over 16 months 251 (19.5%) seedlings died. Mortality was inversely correlated with seedling height. Potential direct radiation had no affect on seedling mortality. For the five common species the mortalities were: Shorea multiflora 6.2 percent, Hopea pedicellata 6.8 percent, Shorea curtisii 13.4 percent, Hopea beccariana 14.1 percent and Gluta curtisii 22.7 percent. The mortality of recruits from seed was: Shorea multiflora 19.0 percent, Shorea curtisii 29.1 percent and Gluta curtisii 29.5 percent. The seedlings grew very little over the 16 months. Height growth was greater in gap sites. There was a significant relationship between direct site factor and plot maximum height growth (r, = 0.399, P < 0.01) but its predictive value was poor (r2 = 0. 188). Gluta curtisii was the only species to show a significant relationship between direct site factor and height growth. Shorea multiflora and Gluta curtisii showed a significantly greater rate of height growth in the plots with above-median direct site factor compared to plots with below-median values. Shorea multiflora is a

Analysis of forest light environments part I. Computerized estimation of solar radiation from hemispherical canopy photographs

A microcomputer based system for the semi-automatic analysis of hemispherical canopy photos is described and evaluated. Images are transferred from film by a video camera to a digitizer for processing. Our program calculates diffuse and direct site factors (proportions of unobstructed radiation) according to Anderson's methods. These factors are used to estimate absolute amounts of radiation on a horizontal, subcanopy surface from measured or estimated values in the open. Additional indices calculated include the proportion of open canopy in the entire image and in the solar band, the cardinal octants, and 20 concentric rings plus a frequency histogram of potential sunfleck duration. About 20 photos can be processed in an hour. The program was designed for large-scale studies correlating plant biology and distribution or animal behavior with radiation regimes where time scales of several weeks or longer are of interest. Consistency and accuracy of estimates of mean daily global radiation by different operators permit meaningful intersite comparisons.

Photographic estimation of photosynthetically active radiation: evaluation of a computerized technique.

We describe a computerized technique for the analysis of hemispherical photographs of sites within plant canopies. The analysis yields estimates of canopy openness, a summary of the spatial distribution of canopy openings, estimates of direct and diffuse site factors, predicted times and durations of sunflecks for any date, and predicted daily courses of photosynthetically active photon flux density (PFD) for any date and for horizontal as well as inclined surfaces. By comparing estimates from photographs with measured values in 32 tropical forest microsites, we evaluate this technique and assess its potential and limitations. In sites of widely varying light availability, and with predictions specific to leaves at various angles, measured daily PFD correlated strongly (r=0.908) with predictions from photographs. Measured daily PFD was also closely correlated with estimates, from the photographs, of diffuse and direct site factors (r>0.8). Differences between predictions and measurements were proportionately largest in heavily shaded sites. Under clear conditions, this technique reliably predicted both daily PFD and the temporal pattern of PFD including predicting suflecks lasting more than a few minutes. However, temporal patterns of PFD predicted from photographs differ in potentially important details from measured patterns.