Improving gap light index (GLI) to quickly calculate gap coordinates

2008 ◽  
Vol 38 (9) ◽  
pp. 2337-2347 ◽  
Author(s):  
Lile Hu ◽  
Jiaojun Zhu
Keyword(s):  
Canopy Gap ◽  
Canopy Height ◽  
Gap Size ◽  
Light Regimes ◽  
Light Levels ◽  
Understory Plants ◽  
Sampling Points ◽  
Hemispherical Photographs ◽  
Geometric Calculation

Understory light is essential to the establishment and growth of understory plants and varies temporally and spatially within gaps. The previously defined gap light index (GLI) is a good model for assessing understory light levels, but it is time-consuming to determine gap coordinates, which are crucial to GLI, for numerous points within a gap. This paper introduces the geometric calculation (GeoCalc) of gap coordinates. GeoCalc quickly obtains gap coordinates for any specified point within a canopy gap and takes into account the tridimensional profile of the gap and the slope and aspect of the ground. The GeoCalc-based GLI was validated by the GLI derived from hemispherical photographs taken at 93 sampling points within seven natural gaps. Our results demonstrate that GeoCalc-based GLI was strongly positively correlated and not significantly differed from the GLI derived from hemispherical photographs. Next, to analyze gap light regimes and the effects of gap size, canopy height, and topography, three natural gaps of various size were selected and simulated as nine gaps with 1 and 1.5 times canopy height or on the opposite slope. Finally, we have summarized characteristics of GeoCalc-based GLI and its application.

scholarly journals Influence of Gap Size and Position within Gaps on Light Levels

2009 ◽  
Vol 2009 ◽  
pp. 1-8 ◽  
Author(s):  
Benoit Gendreau-Berthiaume ◽  
Daniel Kneeshaw
Keyword(s):  
Temperate Forest ◽  
Light Level ◽  
Light Distribution ◽  
Gap Size ◽  
Maximum Light ◽  
The North ◽  
Light Levels ◽  
Hemispherical Photographs ◽  
Northern Edge ◽  
South Axis

The previous studies have reported maximum light levels at different positions within gaps but many of these studies are based on gaps of different size. The objective of this study is to evaluate the influence of gap size and position within gap on light distribution in gaps and under the canopy north of gaps in a mixedwood temperate forest. For three gap sizes, with gap widths ranging between 0.5 and 1.5 times the height of the surrounding stand, light was measured at different positions along the north-south axis in each gap using two different techniques (hemispherical photographs and instantaneous measurements). In small gaps, the position with the most light was close to the northern edge although not under the canopy north of the gap. For both methods, the position with the highest light level shifted from the north towards the center of gaps as gap size increased which clarifies some of the variability in light measurements previously observed in gap studies. Higher light levels in the northern part of small and medium gaps compared to the southern portion could allow management of a mixture of species with intolerant species in the northern portions of gaps and tolerant species to the south.

Light regimes beneath closed canopies and tree-fall gaps in temperate and tropical forests

1990 ◽  
Vol 20 (5) ◽  
pp. 620-631 ◽  
Author(s):  
Charles D. Canham ◽  
Julie S. Denslow ◽  
William J. Platt ◽  
James R. Runkle ◽  
Tom A. Spies ◽  
...  
Keyword(s):  
Tropical Forests ◽  
Photosynthetically Active Radiation ◽  
High Ratio ◽  
Canopy Height ◽  
Light Penetration ◽  
Forest Types ◽  
Active Radiation ◽  
Light Regimes ◽  
Single Tree ◽  
Light Levels

Light regimes beneath closed canopies and tree-fall gaps are compared for five temperate and tropical forests using fish-eye photography of intact forest canopies and a model for calculating light penetration through idealized gaps. Beneath intact canopies, analyses of canopy photographs indicate that sunflecks potentially contribute 37–68% of seasonal total photosynthetically active radiation. In all of the forests, potential sunfleck duration is brief (4–6 min), but the frequency distributions of potential sunfleck duration vary because of differences in canopy geometry and recent disturbance history. Analysis of the photographs reveals that incidence angles for photosynthetically active radiation beneath closed canopies are not generally vertical for any of the forests, but there was considerable variation both among and within sites in the contribution of overhead versus low-angle lighting. Calculations of light penetration through idealized single-tree gaps in old growth Douglas-fir – hemlock forests indicate that such gaps have little effect on understory light regimes because of the high ratio of canopy height to gap diameter. However, single-tree gaps in the other four forest types produce significant overall increases in understory light levels. There is also significant spatial variation in seasonal total radiation in and around single-tree gaps. Our results demonstrate that there can be significant penetration of light into the understory adjacent to a gap, particularly at high latitudes. As gap size increases, both the mean and the range of light levels within the gap increases, but even in large gaps (ca. 1000 m2) the potential duration of direct sunlight is generally brief (<4 h). The major differences in gap light regimes of the five forests are largely a function of canopy height and latitude. The effects of latitude should also result in differences in gap light regimes across the geographic range of individual forest types.

Distribution of epicormic branches and foliage on Douglas-fir as influenced by adjacent canopy gaps

2018 ◽  
Vol 48 (11) ◽  
pp. 1320-1330
Author(s):  
John W. Punches ◽  
Klaus J. Puettmann
Keyword(s):  
Branch Length ◽  
Canopy Gaps ◽  
Douglas Fir ◽  
Canopy Gap ◽  
Tree Age ◽  
Gap Size ◽  
Terminal Bud ◽  
Total Branch Length ◽  
A Minor ◽  
Epicormic Branches

The influence of adjacent canopy gaps on spatial distribution of epicormic branches and delayed foliage (originating from dormant buds) was investigated in 65-year-old coastal Douglas-fir (Pseudotsuga menziesii var. menziesii (Mirb.) Franco). Sample trees were selected across a broad range of local densities (adjacent canopy gap sizes) from a repeatedly thinned stand in which gaps had been created 12 years prior to our study. Lengths and stem locations of original and epicormic branches were measured within the south-facing crown quadrant, along with extents to which branches were occupied by sequential (produced in association with terminal bud elongation) and (or) delayed foliage. Epicormic branches, while prevalent throughout crowns, contributed only 10% of total branch length and 2% of total foliage mass. In contrast, delayed foliage occupied over 75% of total branch length, accounted for nearly 39% of total foliage mass, and often overlapped with sequential foliage. Canopy gap size did not influence original or epicormic branch length or location. On original branches, larger gaps may have modestly negatively influenced the relative extent of sequential foliage on branches and (or) slightly positively influenced delayed foliage mass. Delayed foliage appears to contribute substantially to Douglas-fir crown maintenance at this tree age, but canopy gap size had a minor influence, at least in the short term.

scholarly journals Productive and nutritional characteristics of Piatã-grass in integrated systems

2018 ◽  
Vol 19 (2) ◽  
pp. 144-156
Author(s):  
Jeskarlândia Silva Barros ◽  
Laura Cristina Souza Castro ◽  
Fabiane de Lima Silva ◽  
Fabiana Villa Alves ◽  
Roberto Giolo de Almeida ◽  
...  
Keyword(s):  
Leaf Blade ◽  
Dry Mass ◽  
Canopy Height ◽  
Neutral Detergent Fiber ◽  
Integrated Systems ◽  
In Vitro Digestibility ◽  
Significant Difference ◽  
Nutritional Characteristics ◽  
Sampling Points

SUMMARY This study aimed to evaluate the pasture productive and nutritional characteristics of Brachiaria brizantha cv. BRS Piatã in integrated systems with different densities of trees. Considering as plot the systems: integrated crop-livestock-forest with rows of trees (eucalyptus) spaced at 14 m and 357 trees ha-1 (ICLF-14m), ICLF with rows of trees spaced at 22 m and 227 trees ha-1 (ICLF-22m) and the integrated crop-livestock (ICL) with five remaining native trees ha-1; period of the year as subplots, and sampling points as subsubplots (A, B C, D, and E) arranged perpendicular to trees alleys. It was evaluated the production of forage and leaf blade dry mass, leaf:stem ratio, soil coverage, radiation photosynthetically active interception, canopy height, crude protein (CP), neutral detergent fiber (NDF), in vitro digestibility of organic matter (IVDOM) of the leaf blade, and stem associated with the leaf sheath. There was a significant difference (P<0.05) for all variables due to the month within the integrated systems. Mainly in January and March, showing the forage and leaf blade dry mass reduction due to a higher trees density. System with higher trees density showed the lowest soil coverage and canopy height sampling points A and E in ICLF-22m showed lower forage and leaf blade dry mass production and soil coverage. The system with higher trees density showed lower value of NDF of the leaf blade, and higher CP contents. The IVDOM of the leaf blade was higher in ICLF systems. For the evaluated parameters the best results were for the ICLF-22m.

Forest Dynamics with Canopy Gap Expansion and Stochastic Ising Model

Fractals ◽  
1998 ◽  
Vol 06 (01) ◽  
pp. 81-86 ◽  
Author(s):  
Makoto Katori ◽  
Shinya Kizaki ◽  
Youichi Terui ◽  
Takuya Kubo
Keyword(s):  
Ising Model ◽  
Forest Dynamics ◽  
Ecological Study ◽  
Gibbs State ◽  
Canopy Gap ◽  
Barro Colorado Island ◽  
Gap Size ◽  
Stochastic Ising Model ◽  
Neotropical Forest ◽  
Gap Creation

Importance of the influence of neighboring canopy gaps upon new gap creation has been clarified by the ecological study of a neotropical forest on Barro Colorado Island (BCI), Panama. A stochastic lattice model for the forest dynamics with interacting canopy gap expansion was introduced by Kubo et al. We give a theorem showing a condition that this model can be regarded as a stochastic Ising model, and that its stationary state is exactly given by a Gibbs state. Using this theorem, we obtain a Gibbs state which remarkably well approximates the real gap-size distribution in BCI.

Modelling the contribution of benthic microbial mats to net primary production in Lake Hoare, McMurdo Dry Valleys

2005 ◽  
Vol 17 (1) ◽  
pp. 33-45 ◽  
Author(s):  
DARYL MOORHEAD ◽  
JAMIE SCHMELING ◽  
IAN HAWES
Keyword(s):  
Primary Production ◽  
Microbial Mats ◽  
Net Primary Production ◽  
Light Response ◽  
Light Extinction ◽  
Initial Slope ◽  
Model Parameters ◽  
Dry Valleys ◽  
Light Regimes ◽  
Light Levels

A model was used to simulate primary production of benthic microbial mats in Lake Hoare, southern Victoria Land, Antarctica, and to compare potential benthic to planktonic production. Photosynthetic and respiratory characteristics of mats from five depths in the lake were extrapolated across depth, surface area and time, to estimate whole-lake, annual net primary production. Variation in under-ice light regimes resulting from changes in ice thickness and transparency, and light extinction in the water column was examined, and an uncertainty analysis of key model parameters performed. Daily mat production estimates were 0.98–37.83 mg C m−2 d−1, depending on depth and PAR, whereas in situ production of phytoplankton averaged 15% of this. Annual patterns of mat production achieved maximum rates of 15–16 g C m−2 y−1 at 10 m depth when ≥ 5% of ambient PAR was transmitted through the ice covering the lake; observed transmittance values were usually ≤ 5%. Increasing underwater PAR had little effect above 5–7% transmittance, as photosynthesis became saturated at this level. Uncertainties in estimates of maximum photosynthetic rate (Pmax), initial slope of photosynthetic-light response (α) and maximum respiration rate (Rmax) explained 72–99% of uncertainty in model behaviour; Pmax was increasingly important at high light levels whereas α was more important at low light levels, however Rmax exerted the greatest influence under most conditions.

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