Vertical Canopy Research Articles

Canopy Structure of a Tropical Rain Forest and the Nature of an Unstratified Upper Layer

The two-dimensional distribution of foliage density was investigated in a vertical canopy section of forest in West Sumatra, using analysis of variance. No significant continuous upper canopy layer could be found. However, there was significant stratification with a dense foliage layer below 15 m. The structure of the upper canopy (higher than 15 m) had an erect structure rather than being stratified. Two hypotheses were examined to explain the unstratified upper canopy structure: it was due to incomplete growth in height of the trees, leading to an unstratified forest canopy even in mono-specific forest, or it was caused by a mixture of species with different potential for height growth. The latter hypothesis was supported by the observations on tree growth (...)

Leaf area dynamics of potato cultivars infected by Phytophthora infestans

The effect ofPhytophthora infestans on foliage growth and senescence of three potato cultivars was studied in two field experiments. Inoculum or fungicide was applied in different frequencies to establish a range of levels of disease. At weekly intervals leaf numbers were determined as well as vertical canopy profiles of senescent and lesion covered leaf and stem area. P. infestans reduced appearance of new leaves on the main stem only at the highest level of disease. The cultivars differed more in rate of primary infection of healthy leaves than in the subsequent increase in percentage lesion coverage of the infected leaves. Differences between cultivars in stem lesion coverage resembled the differences for leaf lesions, but in every cultivar stem lesions were most prominent in the top of the canopy, contrary to leaf lesions.P. infestans stimulated leaf senescence similarly in the different cultivars.

Sensitivity analysis of a forest succession model

Gap models can simulate forest structure, dynamics and succession. A sensitivity analysis is presented for a gap model, FORSKA. FORSKA was developed to simulate boreal forests and uses an explicit vertical canopy structure that allows self-pruning in response to shading of the lower crowns. A simulation of 190 years' succession in a old-growth stand dominated by pine ( Pinus sylvestris L.) and spruce ( Picea abies (L.) Karst.) was used as a basis for the analysis. These species differ in their shade-tolerance characteristics, leaf-area sapwood-area ratio and diameter/height relation. Response curves of the sensitivity of each species to all model parameters were determined by varying the standard values up and down by 10% and 50%. Sensitivity indices were estimated by regression. The most critical parameters proved to be those directly affecting growth rates, light availability within the canopy and the species' response to shading through deterministic algorithms. Other parameters, including many that are difficult to estimate precisely, had relatively little effect. Although the stochastic processes of recruitment and mortality are qualitatively important to the outcome of the simulation, the low sensitivity to the parameters of these processes suggest that the system is strongly buffered against natural variability in these parameters.

Competition in Heathland along an Experimental Gradient of Nutrient Availability

In a three year field experiment competition between Erica tetralix and Molinia caerulea and between Calluna vulgaris and Molinia was studied at four levels of nutrient (NPK) availability using replacement series. In the monocultures of the unfertilized control productivity of both Erica and Calluna exceeded that of Molinia by a factor two. At the highest fertilisation level the rank order of productivity was Erica 1) and Molinia was outcompeted. Only in the highest nutrient treatment was RYem smaller than 1 and Erica was outcompeted by Molinia. In all nutrient treatments Calluna was the superior competitor (RYcm > 1) and Molinia was outcompeted by Calluna, despite its higher potential growth rate and its greater maximum foliage height. The high competitive ability for light interception of Erica and Calluna with respect to Molinia can be attributed to their evergreen habit, which permits canopy closure early in the growing season. The results emphasize the importance of vertical canopy structure and timing of canopy development in competition for light. However, the abilities to compete for light and mineral nutrients are probably closely inter-dependent.

Control of Relative Abundance of Perennials in Chalk Grassland in Southern England. II. Vertical Canopy Structure

(1) The vertical distribution of leaves was recorded using a point quadrat, at intervals throughout 1981 and 1982 from grazed chalk grasslands in Sussex and Wiltshire; the data were analysed to describe the overtopping relationships between leaves of different species. (2) In most cases there was a positive correlation between the relative height of rosette leaves of each species ('relative leaf position') and their relative abundance. (3) Despite the short turf of these chalk grasslands (< 10 cm excluding inflorescence stalks) there is pronounced vertical structure; the tallest species (often graminoids) tend to be the most abundant, and the shortest species (often dicotyledons) the least abundant. (4) It is suggested that relative abundance is partly determined by competition for light and that there is a steady-state relationship between species with taller and with shorter rosette leaves. The balance between species is determined by grazing with taller species favoured between grazing events and the shorter species at the time of grazing. (5) In grazed chalk grasslands in southern England, the balance falls in favour of species with taller and widely spreading growth-forms because grazing intensity is low and there is often a long time between successive grazing periods. (6) The species with shorter growth-forms persist, and the species with taller growthforms do not come to ecological dominance, because of chronic, differential defoliation.

Height Growth and Site Index Curves for Cherrybark Oak and Sweetgum in Mixed, Even-Aged Stands on the Minor Bottoms of Central Mississippi

Abstract A combination of stem analysis and height-age plot data procedures was used to construct height growth and site index curves for cherrybark oak (Quercus falcata var. pagodifolia Ell.) and sweetgum (Liquidambar styraciflua L.) in natural, even-aged stands on the minor bottoms of central Mississippi. Height growth is initially greater in sweetgum than cherrybark oak in these mixed stands. However, cherrybark oak height exceeds that of sweetgum at 20 to 25 years of age. Cherrybark oak continues to outgrow sweetgum, resulting in vertical canopy stratification. Cherrybark oak site index curves for the minor bottoms are shown to be different from those previously published for the major bottoms of the Mississippi River, but sweetgum site index curves are essentially the same. South. J. Appl. For. 11(4):219-222.

Arthropod faunal similarity of Bornean rain forest trees

ABSTRACT. 1. Arthropod samples, collected by insecticide fogging ten Bornean lowland rain forest trees, were sorted to species and used to study some of the determinants of faunal similarity of these trees.2. Similarity indices were calculated between pairs of trees for guilds of beetles, beetle families and for different orders and other families of insects.3. Multiple regression analyses of five independent variables of the trees (taxonomic similarity, distance apart, vertical canopy overlap, similarity in tree height, epiphytic load) were carried out against these similarity indices.4. In eight of the eighteen insect groups analysed, taxonomic similarity of the trees is the most important variable affecting their species composition, accounting for a maximum of 29.4% of the variation.5. For the Homoptera, Gryllidae, Anthicidae, Chrysomeloidea and scavengers, distance between the trees and the similarity of the trees’epiphyte load have a greater effect on their faunal similarities than taxonomic similarity of the trees.6. The maximum variation accounted for by variables with significant T ratios was 38.6% in the Anthicidae. In four groups, the Formicidae, Heteroptera, Galerucinae and Corylophidae, none of the variables was significant.7. These data may support the view that for many insect groups there is less host‐specificity in the tropics than in temperate regions.

Light interception and distribution in horizontal and vertical canopies of red raspberries

SummaryLight interception by several plantations of horizontally (New Zealand canopy) and vertically trained red raspberries was recorded at the start of flowering and at harvest. The maximum daily light interception was 81% of incident light, achieved by a vertical system in rows 2.5 m apart. Measurements of light distribution within the canopy showed improved light penetration with the horizontal compared to the vertical training. Calculated values of light interception from a computer model showed close agreement with measured values. Using published data on the effect of between-row spacing on yield, yield was found to be a function of light interception, calculated from the model. The model was then used to define the row spacing of the horizontal canopy system which would attain equivalent levels of light interception to those of the vertical system. Results of a small shading trial indicated that the cropping of the horizontal canopy was unlikely to suffer from the shade cast by the vegetative cane...

Characteristics of Bird Assemblages along Linear Riparian Zones in Western Montana

Bird populations occupying two narrow, linear riparian zones in Mon- tana were studied in 1968 and 1980. The two areas differed in several vegetative parameters such as vertical layering, riparian width, and canopy cover. Bird densities ranged from 355 to 475 pairs per 40 ha. Riparian width, height of vegetation layers 1 and 2, and cover in layer 2 were the most significant variables in male territory location for some bird species. Some species such as the Winter Wren and American Redstart were absent in 1980 from one study area, whereas the populations of most other species were similar between years. Although there have been many studies dealing with the relationships between bird communities and vegetation structure, few have been conducted in narrow, linear ri- parian zones in coniferous forests. Such riparian zones usually have a more diverse bird community, significantly higher total bird density, and more breeding bird species than are found in the surrounding forest (Stevens et al. 1977). During an earlier study (Manuwal 1968) I was impressed with the observation that although the two riparian zones reported in this study were very similar in the general types of vegetation and structural features, there were substantial differences in breed- ing bird species composition. This study was conducted in an attempt to determine why such differences in the avifauna existed. To accomplish this, I tested the hypothesis that bird species richness and density are proportional to the complexity and extent of riparian vegetation. STUDY AREA AND METHODS I conducted this study at Elk Creek and its tributary (the North Fork of Elk Creek) which are located in the Lubrecht Experimental Forest, approximately 64 km NE of Missoula, Montana. The surrounding coniferous forest was a typical mixture of ponderosa pine (Pinus ponderosa), lodgepole pine (P. contorta), Douglas-fir (Pseudotsuga menziesii), and western larch (Larix occidentalis) (Manuwal 1983). I sampled vegetative cover by placing 1-m2 quadrats made of plastic PVC tubing every 30 m along a transect paralleling each side of the creek. At each sample point I recorded percent cover and height of vegetation layers in a vertical column above the quadrat, the species of trees and shrubs (> 1 cm dbh) nearest the quadrat in each cardinal direction, the height of taller trees inter- cepting the sampling column, and width of the riparian strip. I measured the latter two variables with a range finder. I used the spot-map method (Williams 1936, Hall 1964) to determine territorial male density and delineate territory boundaries. I marked the riparian strips either with numbered lath stakes (1968) or numbered plastic flagging (1980) to facilitate the mapping of the exact location of each bird on a map of the study areas.

An evaluation of the structure and function of tropical homegardens

Homegardens represent land use systems involving deliberate management of multipurpose trees and shrubs in intimate association with annual and perennial agricultural crops and, invariably, livestock, within the compounds of individual houses, the whole crop-tree-animal unit being intensively managed by family labour. Known by different names in various places, these agroforestry systems are common in all ecological regions of the tropics and subtropics, especially in humid lowlands with high population density. An analysis of the structural and functional aspects of ten selected homegarden systems from different ecological and geographical regions shows that the average size of the homegarden units is less than 0·5 ha; yet they are composed of a large number of woody and herbaceous species, carefully structured to form 3–5 vertical canopy strata, with each component having a specific place, as well as function. Food production is the primary function of most homegardens, the vast majority of them being subsistence production systems. While there is a remarkable similarity among the different homegardens with respect to the type and nature of the herbaceous crops, the nature of woody perennials varies, depending on environmental and ecological factors. In general, most woody components produce fruits or other types of food in addition to other outputs such as fuelwood, timber, etc. These various food products provide a substantial proportion of nutritive and energy requirements of the local diet. Moreover, the species diversity and varying production cycles of the different components ensure continuous production throughout the year from the homegarden unit. Little or no research has been done to improve homegarden systems. Structural complexity, species diversity, multiple output nature, tremendous variability from farm to farm, etc., are some of the main characteristics that make the homegardens extremely difficult models to work with according to the currently available research procedures.

Selective Harvesting of Valencia Oranges with a Vertical Canopy Shaker

Selective Harvesting of Valencia Oranges with a Vertical Canopy Shaker