Relative Canopy Research Articles

VOLUME OF FLUID MODEL FOR NUMERICAL SIMULATION OF VEGETATED FLOWS

ABSTRACT Aquatic vegetation controls the mean and turbulent flow characteristics in rivers, streams and in coastal regions. Volume of fluid modelling approach is applied for vegetated flows idealizing vegetation as two-dimensional arrays of cylinders. The present modelling technique validated well with results obtained from flume experiments as reported in literature. Simulations were carried out for studying the effect of relative canopy submergence on mean flow and other flow parameters. Further, present simulations show that the interface flow structure resembles more of a mixing layer than a shear layer as seen for atmospheric terrestrial flows.

Effects of a nurse shrub on seed deposition and seedling recruitment of the annual <i>Agriophyllum squarrosum</i>

Abstract. The shrub Artemisia halodendron and the annual herb Agriophyllum squarrosum, which typically co-occur in a mobile sandy habitat in eastern inner Mongolia, China, were used to determine whether the presence of A. halodendron influences seed deposition and seedling recruitment of A. squarrosum under and around the shrub canopy in relation to wind direction, sampling position (windward vs. leeward sides) and distance from the shrub. The numbers of seeds deposited, seedlings emerged, and individuals recruited of A. squarrosum around adult shrubs were sampled along four transects aligned to the four main wind directions at 0.5, 1, 2, 3, 4.5 and 6 m from the shrub base on both windward and leeward sides of each transect. Spatial pattern of seed deposition was strongly altered by the presence of shrubs, but effects varied with wind direction, sampling position and distance from shrubs. Significantly more seeds tended to deposit on the leeward than on the windward sides in all four transects, with the exception of transects along the least prevailing wind direction. The presence of shrubs as nursing plants caused a marked variation in seed deposition across sampling locations, but this effect was detected only in the most, secondary and third most prevailing wind directions, but not in the least prevailing wind direction. In general, the shrub’s influence was within a 2 m radius from the shrub, despite some differences among transects. Although seed bank density had no direct effect on A. squarrosum recruitment patterns, it contributed to the observed variation in recruitment indirectly through density-dependent emergence of seedlings. Our findings provide further evidence of shrubs as a source of spatial heterogeneity in seed availability and thereby a common factor determining population dynamics of understorey herbaceous species.

Spatial Distribution of Leaf Area Index and Leaf N Content In Relation To Grain Yield and Nitrogen Uptake in Rice

Exploring Approaches To Optimizing Spatial Distributions of Leaf Area index (Lai) and Leaf Nitrogen Content (Lnc) Should Be Useful For increasing Grain Yield in Rice (Oryza Sativa). THe Primary Objective of This Study Was ToCharacterize The Variation of Lai and Lnc Distributions Within The Canopy in Relation To Grain Yield and N Uptake in Rice.Two Experiments With Different N Fertilization Rates Under Conventional and intermittent Irrigation (Ci and Ii, Respectively) Were Conducted in 2002 and 2003, Using Japonica Rice Cultivar Wuyujing9. The Results Showed That Grain Yield and N Uptake Were Significantly Different Among Application Rates of N (N Rates), But Did Not Differ Between Ci and Ii. Lai Distribution At Full Heading Was Affected Significantly By N Rate But Hardly By The Irrigation Method. individual Lai increased With The N Rate. To Achieve A High Yield, The Proper Distribution of Lai in The Canopy Can Be Designed As The Largest in The 2Nd Leaf From The Top, Followed By The 3Rd and 4Th Leaves, and The Smallest in The Top Leaf. Lnc On The Base of Both Area and Dry Matter At 15 Days After Full Heading Decreased From The Top To Lower Leaves in The Canopy, and Significantly increased With The N Rate. Grain Yield Was Enhanced Linearly With The increasing N Content of The Upper Two Leaves, But Hindered By The High N Content of Lower Leaves. These Results indicate That The Spatial Distributions of Both Lnc and Lai Could Be Optimized To Achieve Maximum Canopy Photosynthesis and Grain Yield in Rice.

Determining the Relative Canopy Coverage with a Digital Image and Adobe Photoshop®: A Pilot Project to Introduce a Low Cost Technique

Determining canopy coverage in rice (Oryza sativa L) between the 4th tillering stage to internode elongation to harvest allows the assessment of the degree of tillering and indicates the adequacy of the nitrogen fertilization program. This investigation is a technique project to determine if images obtained from moderately priced digital cameras ($200–$300 range) and commercially available imaging processing software (Abode Photos hop®) may effectively estimate the percent canopy coverage. The image analysis is performed using the “magic wand” feature in the software package to isolate and then recolor the soil using the “paint bucket” feature to enhance the color contrast. The second procedure involves overlaying the image with a grid so the percent canopy cover area can be estimated for the area of the photograph. Preliminary work in the field shows that this technique can discriminate canopy coverage in high and low nitrogen plots in rice.

Illumination–size relationships of 109 coexisting tropical forest tree species

1 Competition for light is a central issue in ecological questions concerning forest tree differentiation and diversity. Here, using 213 106 individual stem records derived from a national survey in Ghana, West Africa, we examine the relationship between relative crown exposure, ontogeny and phylogeny for 109 canopy species. 2 We use a generalized linear model (GLM) framework to allow interspecific comparisons of crown exposure that control for stem-size. For each species, a multinomial response model is used to describe the probabilities of the relative canopy illumination classes as a function of stem diameter. 3 In general, and for all larger stems, canopy-exposure increases with diameter. Five species have size-related exposure patterns that reveal local minima above 5 cm d.b.h., but only one, Panda oleosa, shows a local maximum at a low diameter. 4 The pattern of species exposures at 10 cm diameter is consistent with two overlapping groups, of which the smaller (21 species, including most pioneers) is generally better exposed. 5 Relative illumination rankings amongst species are significantly maintained over a wide range of stem sizes. Species that are well exposed at small diameters are therefore also more likely to be well exposed at larger diameters, although two species in the most exposed 25% of species at 10 cm d.b.h. drop to the lowest illumination quartile at 40 cm d.b.h., and three demonstrate the opposite (low-to-high) pattern. 6 Species capable of achieving the largest diameters are generally recorded less frequently in shade than are smaller species, even when compared as saplings, suggesting that species achieving large mature sizes are generally shade intolerant when small. Controlling for phylogeny reveals that this relationship holds across independent lineages. 7 We also find evidence that the range of strategies encountered is influenced by disturbance regimes. 8 We interpret our results as indicating a continuum of strategies that reflect an evolutionary trade-off between a species’ mature size and its general shade-tolerance, in combination with differentiation based on disturbance based opportunities. Species that appear similar can therefore remain ecologically distinct over their lifetimes.

Vertical distribution and seasonal dynamics of arboreal collembolan communities in a Japanese cedar ( Cryptomeria japonica D. Don) plantation

Summary We discuss the spatial distributions and seasonal dynamics of arboreal collembolan communities in a Cryptomeria japonica D. Don plantation and their spatiotemporal patterns and processes of stratification between the canopy and soil in relation to the vertical structure of the forest. We sampled dead branches with foliage in the canopy (canopy litter) and forest-floor litter (soil litter) and extracted 6 species of arboreal collembolans from both. The species composition of the collembolan community differed greatly between the canopy litter and soil litter. The density of all collembolans per unit litter mass showed a unimodal seasonal pattern, and ranged from 0.98 to 17.25 g−1 dry weight (canopy) and from 1.42 to 30.87 g−1 dry weight (soil) during the study period. Collembolan species dominant in the canopy were divided into two groups: species collected from both the canopy litter and soil litter, and species only collected from the canopy litter. The component species of these collembolan communities presented different temporal distributions in one or both habitats. Both the vertical and seasonal patterns indicated that the spatiotemporal distributions of arboreal collembolans in the C. japonica forest were highly species-specific.

The timing of flush development affects the flowering of avocado (Persea americana) and macadamia (Macadamia integrifolia × tetraphylla)

Orchard trees of A4 macadamia (Macadamia integrifolia × tetraphylla) and Hass avocado (Persea americana) were thinned and tip-pruned at different times to generate a range of trees with different stages of leafy flush development. The stagger in the start of the first flush following pruning was repeated in the start of subsequent flushes, so pruning was an effective means of changing the phase of the cycle of flush development. The difference in phase affected flowering. In macadamia, over 80% of the variance in flowering was explained by regression against pruning time. Flowering ranged from 0 to 43% of tip-pruned branches, with the most profuse flowering on flushes appearing in July. In avocado, over 45% of the variance in flowering of the first flush following pruning, and over 35% of the second flush, was explained by regression against pruning time, with more flowering on those flushes starting nearer to the winter solstice. The control trees flowered better than the pruned trees but there was too little information to explain the difference. The macadamia control trees had less synchronised flushing than the pruned trees, and were not subject to internal thinning. The avocado control trees appeared to have a phase of flush development different from the pruned trees, with a summer flush commencing before the first pruning date and maturing before the maturation of the first post-pruning flushes. More research is needed for related canopy management guidelines.

Roller Chopping Effects on Tamaulipan Scrub Community Composition

Palatability of shrub sprouts to white-tailed deer (Odocoileus virginianus Raf.) differs among species, which causes selective browsing and can shift shrub species composition to dominance by less palatable species. The hypothesis was tested that differences in palatability of new sprouts among shrub species following roller chopping small (4 ha) patches within a shrubland matrix would result in a shift in shrub species composition within the patches toward less palatable species. Relative density and relative canopy cover of all woody species in plots 9 years after 1 roller chopping treatment, in plots 3 years after 2 roller chopping treatments, and in untreated plots were estimated. Relative density of blackbrush acacia (Acacia rigidula Benth.) was 3 times greater and relative canopy cover was 12 times greater 9 years after the first roller chopping treatment compared to untreated plots, but relative density and relative canopy cover of blackbrush acacia in roller chopped plots were similar to relative density and relative canopy cover in untreated plots 3 years after the second roller chopping treatment. Relative canopy cover of spiny hackberry (Celtis pallida Torr.) in plots roller chopped in 1989 and 1995 was higher than in untreated plots. Relative density and canopy cover of all other species were similar between roller chopped and untreated plots. Shrub community composition 9 years after 1 roller chopping treatment or 3 years after 2 roller chopping treatments in the subtropical thornscrub communities in southern Texas did not shift toward greater dominance of less palatable species. DOI:10.2458/azu_jrm_v56i6_schindler

Some quantitative relationships between leaf area index and canopy nitrogen content and distribution.

In a previous study (Yin et al. 2000. Annals of Botany 85: 579-585), a generic logarithmic equation for leaf area index (L) in relation to canopy nitrogen content (N) was developed: L=(1/ktn)1n(1+ktnN/nb). The equation has two parameters: the minimum leaf nitrogen required to support photosynthesis (nb), and the leaf nitrogen extinction coefficient (ktn). Relative to nb, there is less information in the literature regarding the variation of ktn. We therefore derived an equation to theoretically estimate the value of ktn. The predicted profile of leaf nitrogen in a canopy using this theoretically estimated value of ktn is slightly more uniform than the profile predicted by the optimum nitrogen distribution that maximizes canopy photosynthesis. Relative to the optimum profile, the predicted profile is somewhat closer to the observed one. Based on the L-N logarithmic equation and the theoretical ktn value, we further quantified early leaf area development of a canopy in relation to nitrogen using simulation analysis. In general, there are two types of relations between L and N, which hold for canopies at different developmental phases. For a fully developed canopy where the lowest leaves are senescing due to nitrogen shortage, the relationship between L and N is described well by the logarithmic model above. For a young, unclosed canopy (i.e. L < 1.0), the relation between L and N is nearly linear. This linearity is virtually the special case of the logarithmic model when applied to a young canopy where its total nitrogen content approaches zero and the amount of nitrogen in its lowest leaves is well above nb. The expected patterns of the L-N relationship are discussed for the phase of transition from young to fully developed canopies.

Roller chopping effects on tamaulipan scrub community composition

Palatability of shrub sprouts to white-tailed deer (Odocoileus virginianus Raf.) differs among species, which causes selective browsing and can shift shrub species composition to dominance by less palatable species. The hypothesis was tested that differences in palatability of new sprouts among shrub species following roller chopping small (4 ha) patches within a shrubland matrix would result in a shift in shrub species composition within the patches toward less palatable species. Relative density and relative canopy cover of all woody species in plots 9 years after 1 roller chopping treatment, in plots 3 years after 2 roller chopping treatments, and in untreated plots were estimated. Relative density of blackbrush acacia (Acacia rigidula Benth.) was 3 times greater and relative canopy cover was 12 times greater 9 years after the first roller chopping treatment compared to untreated plots, but relative density and relative canopy cover of blackbrush acacia in roller chopped plots were similar to relative density and relative canopy cover in untreated plots 3 years after the second roller chopping treatment. Relative canopy cover of spiny hackberry (Celtis pallida Torr.) in plots roller chopped in 1989 and 1995 was higher than in untreated plots. Relative density and canopy cover of all other species were similar between roller chopped and untreated plots. Shrub community composition 9 years after 1 roller chopping treatment or 3 years after 2 roller chopping treatments in the subtropical thornscrub communities in southern Texas did not shift toward greater dominance of less palatable species.

Survival and Growth of Transplanted Large-And Small-Caliper Red Oaks

Red oak (Quercus rubra L.) of 2 caliper sizes, 8.4 and 3.6 cm (3.3 and 1.4 in.), and 2 vigor classes (high and low) within the small-caliper trees, were transplanted to compare growth and establishment over a 4-year period. Possible confounding factors such as pre-transplant vigor, genetics, relative root-ball to backfill volume, and relative canopy to root-ball volume were controlled to determine whether small-caliper trees establish more rapidly than large-caliper trees. Large-caliper trees had high mortality, 58%, while no small-caliper trees died. Based on trunk caliper and height growth after transplanting, surviving large-caliper trees established faster than small-caliper trees—demonstrating that transplanted large-caliper red oaks can establish as rapidly as small-caliper red oaks.

Ocular estimates of understory vegetation structure in a closed Picea glauca/Betula papyrifera forest

Abstract. Horizontal/vertical profiling is a method used to assess vegetation space occupancy. This study investigated consistency and repeatability of measurements made on plots designed to describe forest understory vegetation structure. 20 circular, 100‐m2 plots were measured by six independent observers, three times during the summer of 1997. The plots, located in south‐central Alaska, were established in a closed Picea glauca (white spruce)/Betula papyrifera (paper birch) forest. Consistency and repeatability of measurements were evaluated by examining components of variance. Response variables were absolute and relative canopy cover. Results indicate that observers were not consistent relative to each other estimating vegetative cover from one plot to the next and from one measurement period to the next, making measurements unrepeatable.

Oviposition Site Selection by the Regal Fritillary, Speyeria idalia, as Affected by Proximity of Violet Host Plants

Selection of oviposition sites by female regal fritillary butterflies, Speyeria idalia (Drury), in relation to the location and abundance of their larval food plant, Viola pedatifida G. Don, was studied in Kansas tallgrass prairie. To identify potential cues that females use to select oviposition microsites, we compared plots in which eggs were laid with paired control plots in terms of violet abundance, distance from plot center to the nearest violet plant, plant species composition and relative abundance, plant diversity (Shannon's index), and average plant canopy height. No significant differences occurred between control and oviposition sites for any of these variables (P > 0.15). Violets were present in only 30% of the 1-m-diameter oviposition plots, compared with 24% of the corresponding controls. Furthermore, eggs were never laid directly on violets even when they were present nearby. These data imply that S. idalia females do not preferentially orient to or oviposit on their larval food plant. Nevertheless, female S. idalia did not oviposit randomly, for they invariably chose microsites near the ground that were shaded by the grass/forb overstory and usually deposited eggs on the underside of dead vegetation. We speculate that environmental stresses such as high temperatures and intense solar insolation during the egg stage or harsh overwintering conditions experienced by first-instar larvae impact survival and influence choice of oviposition sites. High fecundity (more than 2000 eggs in some individuals) may allow this species to use a conditional, “sweepstakes” strategy, i.e., producing and spreading many eggs over prairie that harbors host plants to compensate for low egg and larval survivorship.

Sexual dimorphism, sex ratio and spatial distribution of male and female shrubs in the dioecious speciesPistacia lentiscus L.

The population sex ratio, spatial distribution, relative growth rate, canopy size and morphology, and nitrogen content of leaves of male and female individuals were compared in seven populations of the dioecious shrubPistacia lentiscus L. occurring in different localities of the Serra da Arrabida Natural Park, Portugal. The expected pattern of male preponderance in stressful habitats was tested.

Impact of forest canopy on quality and accuracy of GPS measurements

Global Positioning System (GPS) technology has become an essential tool in the Earth observation field for georeferencing, classification and accuracy assessment activities. While it was developed to be employed primarily in the open, many users nowadays operate GPS receivers in less favourable conditions. We investigated the impact of varying types and degrees of forest cover overstorey on GPS data collection, accuracy and precision. While the occurrence of canopy overhead may degrade the positional precision by one order of magnitude, it is the presence of the foliage itself (leaf-on condition) that plays a major role in the signal reception and the positional accuracy. The relationship is inverse, with increasing relative canopy closure resulting in decreasing logging efficiency and accuracy. We also found that under larger forest canopy the Position Dilution of Precision (PDOP) values may improve signal reception without deteriorating accuracy. Moreover, the relationship between degree of canopy closure and the accuracy RMSE follows an exponential pattern with small increases in relative canopy closure leading to huge increases in positional error. Averaging proved to be a powerful way to diminish residual positional error under forest cover, 300 fixes being proposed as a good number for GPS data acquisition under mature canopy conditions. Ultimately, we judged that PDOP is not as good an indicator for positional accuracy under forest canopy as is universally acclaimed.

Factors Influencing the Establishment of Seedlings of the Mallee, Eucalyptus luehmanniana (Myrtaceae)

Factors influencing the survival of seedlings of the wet mallee-eucalypt Eucalyptus luehmanniana F.Muell. were examined using seedlings germinated in the laboratory and planted into the field. The effects of time since fire (0, 13 and 26 years), predation and position relative to adult canopy on seedling survival and growth in the first year after establishment were tested experimentally. Drought, predation by invertebrates and burial in leaf litter were identified as factors causing seedling mortality. Seedlings were most susceptible to predation at unburnt sites. Seedlings planted at burnt sites were more susceptible to drought, although a small percentage were killed by invertebrate predators. Burial of seedlings in leaf litter was most common under eucalypt canopies. After 200 days, seedlings in burnt sites were significantly more advanced in height, leaf area and leaf number than those in unburnt sites. It is predicted that E. luehmanniana seedlings are unlikely to achieve fire tolerance before fire occurs (assuming a fire interval of 10–20 years) unless they establish immediately after fire. The results suggest that mass establishment cued by fire allows seedlings to avoid predation, however mortality due to drought was greater at burnt sites than mortality due to predation at unburnt sites.

Influence of different Taxodium ascendens stands on the open ranges and system performance in Jiangsu Province, China

This paper reveals the results of an eight-year experiment set up to identify the effects of four tree spacing configurations (1.5 × 4 m, 1.2 × 5 m, 2 × 3 m and 1.5 × 2 × 6 m) on open ranges and the relationship between open ranges and species coexistence in Taxodium ascendens-intercrop systems. Relative interrow open ranges and relative interplant open ranges were significantly different among four tree spacings. All relative open ranges (relative interrow open ranges, relative interplant open ranges, relative canopy open ranges and relative space-volumed open ranges) decreased with increasing age. The wider interrow or interplant spacings of trees offered wider (relative) interrow or interplant open ranges for intercrops. All of the tree spacings, except spacing 2 × 3 m, had negative relative interplant open ranges in nine-year-old stands, suggesting that the canopies between a plant and its neighbouring plant were in direct competition, and no interplant open range existed between two individual trees. Up to age nine, spacing 1.5 × 2 × 6 m showed no marked disadvantage in growth performance as compared to the other three spacings, but provided wider interrow open ranges for intercrops. Starting with tree stands of age four years, the yields of interplanted wheat (Triticum aestivum), soybean (Glyciae max) and rape (Brassica napus) decreased significantly as a result of the decrease of open ranges in tree stands. The yields of wheat, soybean and rape were lower in tree spacing 2 × 3 m than in other spacings. There was a positive correlation between wheat yields and canopy open ranges.

Changes in foliage distribution with relative irradiance and tree size: Differences between the saplings of Acer platanoides and Quercus robur

AbstractDependencies of foliage arrangement and structure on relative irradiance and total height (TH) were studied in saplings of Acer platanoides and Quercus robur. The distribution of relative foliar area and dry weight (leaf area and weight in a crown layer per total tree leaf area and weight, respectively) were examined with respect to relative height (RH, height in the crown per TH) and characterized by the Weibull function. The distributions of relative area and weight were nearly identical, and the differences between them were attributable to a systematic decline in leaf dry weight per area with increasing crown depth. Foliage distribution was similarly altered by tree size in both species; RH at foliage maximum was lower and relative canopy size (RCS, length of live crown per TH) greater in taller trees. However, the distribution was more uniform in A. platanoides than in Q. robur. Apart from the size effects, relative irradiance also influenced canopy structure; RCS increased in Q. platanoides and decreased in Q. robur with increasing irradiance. As crown architecture was modified by irradiance, foliage distribution was shifted upwards with decreasing irradiance in A. platanoides, but it was independent of irradiance in Q. robur. Higher foliage maximum at lower irradiance in more shade‐tolerant A. platanoides is likely to contribute towards more efficient foliar display for light interception and increase the competitive ability of this species in light‐limited environments. Consequently, these differences in crown architecture and foliage distribution may partly explain the superior behavior of A. platanoides in understory.

Vegetation Responses to 2 Brush Management Practices in South Texas

Brush management for improving wildlife habitat in South Texas is important because of the economic value of wildlife. We determined vegetation responses to (1) roller chopping of guajillo (Acacia berlandieri Benth.)-blackbrush acacia (A. rigidula Benth.)-dominated rangeland and (2) heavy discing of whitebrush (Aloysia lycioides Cham.)-dominated rangeland to improve white-tailed deer (Odocoileus virginianus Raf.) habitat. Canopy cover of vegetation was estimated seasonally during August 1988 to April 1990. Both treatments reduced brush canopy cover, but herbaceous response depended on rainfall. Mean herbaceous cover was 65 and 136% higher on roller chopped sites than on untreated sites when averaged across all sampling dates. Heavy discing reduced relative canopy cover of whitebrush but increased cover of spiny hackberry (Celtis pallida Torr.), an important browse species. Forb species richness was higher on roller chopped and disced sites than on untreated sites, but species diversity was similar. Because herbaceous response to brush removal may depend on rainfall, other factors such n effects on browse availability and nutritional quality may need to be considered when planning brush management strategies to improve white-tailed deer habitat.

The impact of the provision of water for game on the woody vegetation around a dam in the Kruger National Park

Quantitative inventory surveys were done on the woody vegetation in permanently marked plots at distance intervals from the Wik-en-Weeg Dam, Kruger National Park, in 1973. The surveys were repeated in 1990 so that changes in the community composition, the density and the canopy cover and the survival of the woody vegetation could be determined in relation to distance from the dam. Relationships with distance from the dam were shown for the relative density ofCombretumapiculatum in all height classes, the relative canopy cover of the second height class of woody plants, the relative canopy cover of C. apiculatum plants, the survival of all height classes of woody plants and the survival of C. apiculatum and Colophospermum mopane plants. It was concluded that the provision of water for game at the Wik-en-Weeg Dam had an impact on the woody vegetation in the vicinity. The relationships of parameters of the two dominant species, Combretum apiculatum and Colophospermum mopane, with distance from the dam were compared. Combretum apiculatum parameters were more sensitive to impact associated with the dam than those of Colophospermum mopane.