Showing papers on "Tree canopy published in 1989"

A methodology for estimating canopy disturbance frequency and intensity in dense temperate forests

Abstract: Analysis of the frequency of past moderate and high-intensity disturbances has been hindered in forests of complex age structure by methodological problems. A methodology is proposed for developing a disturbance chronology in such stands by identifying the probable date of canopy accession for each sample tree. Canopy accession dates are based on an evaluation of radial growth pattern and early growth rates of existing canopy trees. Canopy disturbance intensity is defined as the percentage of sample trees with canopy accession events in each decade. Rotation periods for disturbances of various intensities are calculated from the chronology. The method was evaluated using 893 increment cores from 70 plots in northern hardwood stands of western Upper Michigan. The estimated average disturbance rate for all plots and decades was 5.7–6.9% of land area per decade, with an implied average canopy tree residence time of 145–175 years. These estimates are similar to those obtained by on-site estimates of canopy tr...

Observation of organized structure in turbulent flow within and above a forest canopy

Abstract: Ramp patterns of temperature and humidity occur coherently at several levels within and above a deciduous forest as shown by data gathered with up to seven triaxial sonic anemometer/thermometers and three Lyman-alpha hygrometers at an experimental site in Ontario, Canada. The ramps appear most clearly in the middle and upper portion of the forest. Time/height cross-sections of scalar contours and velocity vectors, developed from both single events and ensemble averages of several events, portray details of the flow structures associated with the scalar ramps. Near the top of the forest they are composed of a weak ejecting motion transporting warm and/or moist air out of the forest followed by strong sweeps of cool and/or dry air penetrating into the canopy. The sweep is separated from the ejecting air by a sharp scalar microfront. At approximately twice the height of the forest, ejections and sweeps are of about equal strength.

Low-Diversity Tropical Rain Forests: Some Possible Mechanisms for Their Existence

Abstract: Tropical rain forests do not always have a high diversity in tree species. In some cases, most of the trees in the canopy layer are a single species. This results in a low diversity among the other canopy tree species (fig. 1). Increasing dominance by one canopy species has little effect on the diversity of subcanopy trees (fig. 2). Such single-dominant forests are of two types: the dominant either persists at the site beyond one generation or it does not. In forests with a persistent dominant species (type I), one species may achieve dominance either by colonizing most of a large open patch and persisting thereafter or by gradually replacing the existing residents. The latter could take place either because the dominant is the species most resistant to deleterious physical or biotic conditions or because it is superior in competition to all others. One possible mechanism enabling one species to replace and exclude many others is the possession of an ectomycorrhizal (EM) association. Most tropical tree sp...

Arrival and Survival in Tropical Treefall Gaps

Abstract: Most tropical tree species require light from a treefall gap at some time during their lives to reach maturity. Responses to light conditions have been dichotomized as shade-intolerant pioneers or shade-tolerant climax species (e.g., Whitmore 1975, 1982, 1989). The former typically have small, widely dispersed seeds from which juveniles establish only in gaps, while the latter typically have larger seeds that can germinate beneath the forest canopy and can persist as suppressed juveniles or grow slowly until a gap forms. According to this framework, a new gap promotes shade-intolerant regeneration through germination and shade-tolerant regeneration through release of suppressed juveniles. Truly shade-tolerant species can grow to maturity beneath the forest canopy, but even these are likely to benefit from any increases in light levels beneath the canopy (Uhl et al. 1988, Canham 1989, Lieberman et al. 1989b, Martinez-Ramos et al. 1989). Although useful, we believe this dichotomy limits views of gap dynamics by implying that each species is constrained to a specific pathway to the forest canopy. In reality, all species recruit to differing degrees from dispersal into new gaps and from release of dormant seed or juvenile banks beneath the canopy (see Martinez-Ramos et al. 1989). The probability that a tree of a given species will enter the forest canopy is a function of the joint probabilities of arriving and surviving in particular habitats. We emphasize three issues that, for any species, define probable regeneration at a given site: (1) pattern of seed arrival in gaps and beneath the canopy, (2) proportion of forest area in gap vs. closed canopy, and (3) survival to reproductive maturity of seeds landing in gaps and beneath the canopy. This view enables recruitment of tropical trees to be interpreted from the perspective of relative advantages of given characteristics within the context of those environments in which individuals with those characteristics are located.

Gap light regimes influence canopy tree diversity.

Abstract: In old-growth deciduous forests of the eastern United States, where light levels beneath intact canopies are about 1% of full sunlight (Canham 1988b), gaps result in locally elevated light levels. Such increases in light appear necessary for almost all tree species to attain canopy status (e.g., Barden 1980, Runkle 1981, Canham 1989). While patterns and mechanisms of replacement among the two species most often codominant in these forests, American beech (Fagus grandifolia) and sugar maple (Acer saccharum), have been intensively studied (Cain 1935, Fox 1977, Woods 1979, Donnelly 1986, Canham 1988a), relationships among rates and types of treefall, variability in light levels, and species' responses have not been studied. We have studied populations of tree species in one old-growth Eastern deciduous forest (Warren Woods, Michigan, USA) for the past 15 yr. We have followed the more abundant canopy species under different spatial and temporal patterns of increased light levels associated with different rates of gap formation (Poulson and Platt 1981, 1988, unpublished manuscript). Here we summarize our results to show how size and compass orientation of gaps determine light regimes and how light regimes interact with sapling architecture to influence the diversity of species that reach the canopy. We contrast small, isolated treefalls with small, overlapping treefalls and contrast small, overlapping gaps oriented north-south (N-S) with those oriented eastwest (E-W). In addition, we describe patterns to zonation of species in large, multiple treefalls. We conclude our essay by discussing how changes in latitude influence gap light regimes and, hence, replacement patterns of canopy trees in temperate and tropical forests.

Canopy organization and foliage photosynthetic capacity in a broad-leaved evergreen montane forest

Abstract: The spatial and physical characteristics of foliage varied systematically with canopy height in a broad-leaved evergreen forest of Nothofagus solandri var. cliffortioides (Hook.f.) Poole (mountain beech) in the Craigieburn Range, South Island, New Zealand. Leaf inclination angle, leaf weight per unit area, leaf nitrogen concentration, leaf photosynthetic capacity and leaf reflectance of photosynthetically active radiation all decreased with depth in the canopy. These changes will result in a more uniform distribution of photosynthetically active radiation through the canopy and a greater canopy carbon gain than possible in canopies composed of randomly oriented leaves with constant physical properties. The mean leaf area index of the Nothofagus solandri var. cliffortioides foliage was 6 7 and mean branch silhouette area index was 1 4. Mistletoe (Alepisflavida [Hook.f.] Tiegh) was present in the canopy and had a leaf area index of 0-14, and a stem silhouette area index of 0-02. Total beech and mistletoe foliage biomass was 1183 and 36g m-2 respectively and total beech and mistletoe foliage nitrogen mass was 12 3 and 037g m2. Key-words: Leaf orientation, leaf area index, leaf nitrogen, Nothofagus, photosynthetic capacity, mistletoe

Competition and patterns of resource use among seedlings of five tropical trees grown at ambient and elevated CO2.

Abstract: Seedlings of five tropical trees, Cecropia obtusifolia, Myriocarpa longipes, Piper auritum, Senna multijuga and Trichospermum mexicanum, were grown both as individuals, and in competition with each other at ambient (350) and two levels of elevated CO2 (525 and 700 μl l-1) for a period of 111 days. Growth, allocation, canopy architecture, mid-day leaf water potential and soil moisture content were assessed three times over this period for individually grown plants, and at the end of the experiment for competitively grown plants. In addition, leaf photosynthesis and conductance were assessed for the individually grown plants midway through the experiment, and light profile curves were determined for the competitive arrays at three stages of development. Elevated CO2 did not affect photosynthesis or overall growth of the individually-grown plants but did affect canopy architecture; mean canopy height increased with CO2 in Piper and Trichospermum and decreased in Senna. Stomatal conductance decreased slightly as CO2 increased from 350 to 525 μl l-1 but this had no significant effect upon whole plant water use of leaf water potential. Soil moisture content for the individuals increased marginally as CO2 increased, but this did not occur in the competitive arrays. There was a marked effect of CO2 upon species composition of the competitive arrays; Senna decreased in importance as CO2 increased while Cecropia, Trichospermum and Piper increased in importance. Stepwise regression analysis using competitive performance as the independent variable, and the various morphological and physiological parameters measured on the individually grown plants as independent variables, suggested that canopy height was the single most important variable determining competitive ability. Also significant were photosynthetic rate (particularly at low light levels) and allocation to roots early in the experiment. Light profiles in the canopy revealed that less than 15% of incident light penetrated to the level of mean canopy height. Results suggest that competition for light was the major factor determining community composition, and that CO2 affected competitive outcome through its affect upon canopy architecture.

Forest dynamics. SILVI-STAR: a comprehensive monitoring system.

Abstract: To learn about the interactions between individual trees and between trees and other forest organisms, long-term monitoring of spontaneous forest development is necessary. A complete monitoring system has been developed including a computer package for analysis of long-term forest dynamics observations. A method of nested plot data collection on forest architecture and plant species composition has been worked out for monitoring purposes. The spatial and temporal relations between data are numerically expressed. Therefore a three-dimensional single-tree architectural model has been worked out to describe asymmetric tree shapes with a minimum of measured data points. Time series of forest development at different sites are built up on the basis of a digital descriptive model of the complex reality of forest structure and species composition. To guarantee continuity in data storage and data query a commercially available database and a geographical information system were used in the design of the information system. A visual interpretation of data is enabled by graphical system outputs such as profiles and ground plans of tree crown projections, providing substitutes for traditional profile drawings and maps. Application programs were developed to solve specific problems, as a step towards predictive models. In an application program, for integration with remote sensing studies, an aerial view of the forest canopy is simulated on the basis of measured plot data. This view provides a ground-truth reference for the training and interpretation of remote sensing images. To explain the growth of individual trees and the distribution patterns of herbs and tree regeneration on the forest floor, another application was developed, simulating the penetration of direct and of diffuse light. For the reconstruction of forest growth with tree ring data, a technique of animation was elaborated facilitating a visual interpretation of the forest development. The system is applied to demonstrate forest development in some European forest reserves using forest architectural descriptions and vegetation releves, tree ring data and historical sources.

An evaluation of imaging spectrometry for estimating forest canopy chemistry

Abstract: High spectral resolution Airborne Imaging Spectrometer (AIS) data were acquired over 20 well-studied Wisconsin forest sites to evaluate the potential of remote sensing for estimating forest canopy chemistry. Intensive nutrient cycling research in these forests demonstrates that canopy lignin content is strongly related to measured annual nitrogen mineralization at the undisturbed sites and may serve as an accurate index for nitrogen cycling rates. Ground measurements were made of foliar biomass and canopy nitrogen and lignin content, the latter within two weeks of the AIS overflight. The spectral data were transformed using derivative techniques modified from laboratroy spectroscopy. Stepwise regression assisted in determining combinations of wavelengths most highly correlated with canopy chemistry and biomass. Strong correlations between AIS data and total canopy lignin content in deciduous forests and canopy lignin concentration (total lignin/biomass) in both deciduous and coniferous stands indicate that imaging spectrometry can be used to estimate canopy lignin content and, from that, the spatial distribution of annual nitrogen mineralization rates.

Factors affecting the spectral response of forest canopies: A review

Abstract: Interpreting remote sensing data on forest canopies demands an adequate knowledge of factors affecting their optical properties. After a short analysis of the optical properties of a forest canopy, a review of the factors acting on the forest reflectance is presented. These factors can be external or internal. The five external factors considered are: size of the viewed area, orientation and inclination of the view axis, sun elevation, nebulosity and wind speed. Three internal factors can also affect forest reflectance: row orientation (for young artificial forests), optical properties of the background (soil and understory), and canopy geometry. The effects of these different factors are analysed and discussed.

Canopy Development and Leaf Nitrogen Distribution in a Stand of Carex Acutiformis

Abstract: Seasonal changes in leaf nitrogen distribution were examined in the canopy of a Carex acutiformis stand in a wet meadow area Although there was a tendency for leaf nitrogen concentration to decrease with increasing leaf age in any one layer of the canopy, nitrogen concentration increased significantly with plant height despite increasing age of leaf portions higher in the canopy This suggests a predominant effect of the light climate on the nitrogen distribution within the canopy During the growing period, standing crop dry mass increased significantly, while the increase in the standing crop of nitrogen was marginal The amount of nitrogen decreased in the lower layers and increased in the upper layers, and a strongly decreasing gradient of nitrogen concentration developed from the top to the bottom of the canopy It is suggested that this gradient resulted mainly from leaf tips with high nitrogen concentrations being lifted to higher positions because of growth at the base, with some retranslocation of nitrogen downwards from senescing tips to active parts The distribution of nitrogen concentration became less uniform during the growing period, thus supporting the prediction that nitrogen concentration should become less uniformly distributed with development of the canopy

Vertical profile and canopy organization in a mixed deciduous forest

Abstract: A combination of optical measurements of leaf heights and observations on litterfall provided a vertical and temporal description of the leaf community structure in a tall, Liriodendron forest on the Maryland coastal plain. Leaf area, mass, and number were bimodally distributed with height. Median leaf number occurs far below (7–8 m) and median leaf mass far above (22–23 m) the median leaf area (18–19 m). Tree species exhibited leaf stratification into 3 height levels: understory (0–10 m), mid canopy (10–25 m), and overstory (25–37 m). Species leaf area in litterfall was related to the species basal area, although representation of leaf number in litterfall was not correlated with stem numbers for species in the stand. Species also showed a clear phenological sequence of leaf fall.

Leaf and canopy responses of Lolium perenne to long-term elevated atmospheric carbon-dioxide concentration

Abstract: The relationship between leaf photosynthetic capacity (pn, max), net canopy CO2- and H2O-exchange rate (NCER and Et, respectively) and canopy dry-matter production was examined in Lollium perenne L. cv. Vigor in ambient (363±30 μl· l-1) and elevated (631±43 μl·l-1) CO2 concentrations. An open system for continuous and simultaneous regulation of atmospheric CO2 concentration and NCER and Et measurement was designed and used over an entire growth cycle to calculate a carbon and a water balance. While NCERmax of full-grown canopies was 49% higher at elevated CO2 level, stimulation of pn, max was only 46% (in spite of a 50% rise in one-sided stomatal resistance for water-vapour diffusion), clearly indicating the effect of a higher leaf-area index under high CO2 (approx. 10% in one growing period examined). A larger amount of CO2-deficient leaves resulted in higher canopy dark-respiration rates and higher canopy light compensation points. The structural component of the high-CO2 effect was therefore a disadvantage at low irradiance, but a far greater benefit at high irradiance. Higher canopy darkrespiration rates under elevated CO2 level and low irradiance during the growing period are the primary causes for the increase in dry-matter production (19%) being much lower than expected merely based on the NCERmax difference. While total water use was the same under high and low CO2 levels, water-use efficiency increased 25% on the canopy level and 87% on a leaf basis. In the course of canopy development, allocation towards the root system became greater, while stimulation of shoot dry-matter accumulation was inversely affected. Over an entire growing season the root/shoot production ratio was 22% higher under high CO2 concentration.

Strontium isotope studies of atmospheric inputs to forested watersheds in New Mexico

Abstract: Stable isotopes of strontium provide a unique quantification of ecosystem processes because organisms do not differentiate between them. For landscapes with contrasting geologies, these isotopes can identify atmospheric source material from local weathered material. This study quantified the input of strontium, distribution within the ecosystem, canopy capture versus leaf leachate, canopy loss, and Sr increment in biomass from an atmospheric origin. Forest ecosystems were studied along an elevational gradient in New Mexico. Spruce forests had a much greater capacity for capturing atmospheric Sr than aspen forests; however, aspen contained more total atmospheric Sr in their tissues because of greater uptake rates and the ability to utilize atmospheric deposited Sr before the initiation of the aspen forest. This technique has excellent capabilities for estimating the relative importance of atmospheric and weathering inputs to certain ecosystems.

Effect of Quercus douglasii (Fagaceae) on herbaceous understory along a rainfall gradient

Abstract: Variation in effect of approximately 50% Quercus douglasii (blue oak) cover on herbaceous understory biomass and composition was studied along a rainfall gradient between five sites. Biomass and composition were compared between understory and adjacent open grassland at each site to evaluate changes in canopy effect along the gradient. Biomass was measured at the time of greatest standing biomass (PEAK) in 1986 and 1987. Composition was measured at PEAK 1986. Annual rainfall was above average in 1985-1986, and below average in 1986-1987. In both years PEAK biomass was greater in grassland than understory at sites with >50 cm yr_1 average rainfall, and no difference was apparent at sites with <50 cm yr_1 rainfall. Variation in species composition between grassland and understory was independent of rainfall gradient. Differences in individual species presence and abundance between grassland and understory were found at all sites. We conclude that variation in canopy effect on biomass resulted from changes in relative production between understory and open grassland, not from differences in relative composition. Winter deciduous Quercus douglasii Hook. & Arn. (blue oak) forms a patchy canopy over and within a continuous annual herbaceous layer on more than a million hectares in California (McClaran and Bartolome 1989). Average rainfall in blue oak woodland varies geographically from 30 to 100 cm yr_1 (Griffin 1977). In high rainfall areas understory biomass was lower than open grassland (Bartolome 1 986; Jansen 1987), and understory biomass increased after thinning or removal of oak canopy (Johnson et al. 1959; Heady and Pitt 1 979; Kay 1 987). In low rainfall areas understory biomass was greater than in open grassland (Duncan and Reppert 1960; Holland 1980). Composition differences between grassland and understory were reported for several sites (Heady and Pitt 1979; Holland 1980; Bartolome 1986; Jansen 1987). Because Q. douglasii cover was not constant among these study sites, relative influence of rainfall and tree cover on herbaceous biomass and composition cannot be interpreted. Madrono, Vol. 36, No. 3, pp. 141-153, 1989 This content downloaded from 157.55.39.112 on Wed, 07 Sep 2016 05:32:13 UTC All use subject to http://about.jstor.org/terms 142 MADRONO [Vol. 36 In general, differences between understory and grassland composition have been attributed to negative competition effects or positive site modification effects (e.g., Parker and Muller 1982; Yavitt and Smith 1983; Schott and Pieper 1985). Biomass differences between understory and grassland also have been attributed to these positive and negative effects. Examples of positive effects described for relatively xeric areas (e.g., Tiedemann and Klemmedson 1977; Patten 1978), contrast with negative effects in mesic regions (e.g., Halls and Schuster 1965; Jameson 1967; Ford and Newbould 1977). Negative effects of light and water competition were suggested in tree-grass models (Walker et al. 1981; McMurtie and Wolf 1983) and the interpretation of empirical biomass data (Knoop and Walker 1985). The suggestion that species interactions vary along environmental gradients (Begon et al. 1986) provides a framework to organize the diversity of canopy effects by Quercus douglasii. We used this framework to identify our objective and generate a null hypothesis. To evaluate effects of rainfall and Q. douglasii canopy on herbaceous understory, we used the null hypothesis that the effect of 50% Q. douglasii canopy on the similarity of grassland and understory biomass and composition does not vary along a rainfall gradient.

Modelling Photosynthesis in Monocultures and Mixtures

Abstract: A comparison is made between two models of canopy photosynthesis for monocultures that differ in their treatment of the variation of the rate of single-leaf photosynthesis in response to the irradiance in which the leaves have grown. Both are shown to be deficient, and a simple modification to one that results in a much improved performance is presented. The theory uses the non-rectangular hyperbola for the rate of single-leaf photosynthesis and incorporates the Monsi-Saeki approach for the light-intercepting characteristics of the canopy. The model is then extended to describe the photosynthesis of mixed canopies, which requires knowledge of the relative position of each leaf-area component within the sward. Analytical expressions can be derived for the case where the leaf-area components are homogeneously distributed relative to each other through the depth of the canopy. This is shown to be a good representation of leaf-area distributions in continuously grazed temperate grass-clover swards as well as frequently cut tropical grass-legume swards, and so is an important special case.

Stomatal control of transpiration from a developing sugarcane canopy

Abstract: . Stomatal conductance of single leaves and transpiration from an entire sugarcane (Saccharum spp. hybrid) canopy were measured simultaneously using independent techniques. Stomatal and environmental controls of transpiration were assessed at three stages of canopy development, corresponding to leaf area indices (L) of 2.2, 3.6 and 5.6. Leaf and canopy boundary layers impeded transport of transpired water vapour away from the canopy, causing humidity around the leaves to find its own value through local equilibration rather than a value determined by the humidity of the bulk air mass above the canopy. This tended to uncouple transpiration from direct stomatal control, so that transpiration predicted from measurement of stomatal conductance and leaf-to-air vapour pressure differences was increasingly overestimated as the reference point for ambient vapour pressure measurement was moved farther from the leaf and into the bulk air. The partitioning of control between net radiation and stomata was expressed as a dimensionless decoupling coefficent ranging from zero to 1.0. When the stomatal aperture was near its maximum this coefficient was approximately 0.9, indicating that small reductions in stomatal aperture would have had little effect on canopy transpiration. Maximum rates of transpiration were, however, limited by large adjustments in maximum stomatal conductance during canopy development. The product of maximum stomatal conductance and L. a potential total canopy conductance in the absence of boundary layer effects, remained constant as L increased. Similarly, maximum canopy conductance, derived from independent micrometeorological measurements, also remained constant over this period. Calculations indicated that combined leaf and canopy boundary layer conductance decreased with increasing L such that the ratio of boundary layer conductance to maximum stomatal conductance remained nearly constant at approximately 0.5. These observations indicated that stomata adjusted to maintain both transpiration and the degree of stomatal control of transpiration constant as canopy development proceeded.

Stand microclimate and physiological activity of tree leaves in an oak-hornbeam forest. I : Stand microclimate

Abstract: The photosynthetic activity of the Turkey oak (Quercus cerris L., height 22 m) and common hornbeam (Carpinus betulus L., height 17 m) in a deciduous forest stand was analysed. Trees studied grew in an uneven-aged forest (80 years old on average, main canopy surface at a height of 18m) forming the former IBP forest research site at Bab, SW Slovakia (Czechoslovakia). The average photosynthetic rate of oak foliage was higher than that of hornbeam. Net photosynthetic rate at saturating photon flux rate (PNmax) of hornbeam amounted to only 60% of that of oak for the leaves of the upper canopy layer (UCL) and to 67% for the leaves of the lower canopy layer (LCL). In the summer months the main photosynthetic activity of this deciduous stand was focused upon the UCL leaves and oak species. The relationship between PN and photon flux rate, as well as the diurnal course of PN and stomatal conductance (gs), was calculated using a mathematical model. The diurnal course of PN and gs were similar for both tree species and both types of leaf. Maximal gs values were observed at noon. The lower values of compensation photon flux rate (Γ1) and photosynthetic efficiency (α) but higher values of the maintenance respiration rate (RM), confirmed the higher shade tolerance of the hornbeam. The dark respiration rate (RD) of the UCL leaves was higher than that (RD) of the LCL leaves. Various photosynthetic features and production capacity of the above-mentioned types of leaf expressed the adaptation pressures to radiation conditions. In the stand studied, the primary production of the greater part of the crown depended on the vertical foliage distribution and on light penetration during the midday hours.

Canopy dynamics and light climates in a tropical moist deciduous forest in India

Abstract: The canopy dynamics and light climates within a 20 by 60 m quadrat were studied in a disturbed moist deciduous forest near Bombay, India. A map was drawn of individual trees within the quadrat, the taxa were identified, and their phenology was followed from November 1984 to July 1985. The quadrat contained 14 species, the most common being Tectona grandis, Terminalia tomentosa, Butea monosperma, Mitragyne parviflora and Albizia procera. Some individuals were in leaf at all times, more so at the moister east end of the quadrat. In November at the end of the rainy season, light measurements documented percentages of total daily photosynthetic photon fluence (PPF) at 10.0% of full sunlight; 44% of this flux was due to sun-flecks whose duration was approximately 17% of the daytime hours. Values for six sites were similar to mid-day measurements along a 40 m transect, and consistent with the 94% canopy cover of the sites, photographed with a fish-eye lens. The March dry season measurements revealed a more intense radiation environment (54% of solar PPF), and 59% of the photosynthetic photon flux density at mid-day along the transect. Canopy openings were increased to a mean of 59.4%. Light in the understorey in November was spectrally altered, with typical R:FR ratios of 0.30, compared to March values identical to those of sunlight, at 1.10.

Root and Mycorrhizal Development in Healthy and Declining Norway Spruce Stands

Abstract: Roots link the soil-plant-continuum. Their health depends on both, soil environment and tree canopy function. Changes in any one of these compartments lead to a root response (Persson 1980). The health status of the root in return determines multiple aboveground plant functions, such as water and nutrient exchange (Chapin 1980), growth (Ingestad 1982), and hormonal root/shoot interactions (Schulze 1986). Figure 1 illustrates the interrelationships between the tree canopy and the root system. The canopy supplies carbohydrates for root growth (Marshall and Waring 1985) while roots supply water and nutrients to the canopy. However, root growth, mineral concentration, and the formation of root tips are determined by such soil chemical and physical properties as the nitrogen supply (Meyer 1985) and soil acidification. Soil acidification processes change molar ratios of Ca:Al and Ca:protons in the root environment (Ulrich 1981; Rost-Siebert 1985).

Implications of Tropical Deforestation for Climate: A Comparison of Model and Observational Descriptions of Surface Energy and Hydrological Balance

Abstract: Quantitative estimates of the impacts of tropical deforestation on climate can only be considered through use of models of climate that contain adequate treatments of both the land and atmospheric components. Recent global climate model (GCM) calculations by Dickinson & Henderson-Sellers of the effect of removing the Amazon forest attempted to include a detailed canopy model of the forest and the assumed grass replacement. An important role for the structure of the forest canopy was suggested by this study. However, data of Shuttleworth on the seasonal variation of Amazon evapotranspiration show much lower values during the wet season than were obtained in the GCM study and, consequently, much less seasonal variation. The reason for this discrepancy is examined by using results both from the GCM used in the deforestation study and a three-year simulation with a more recent version. The major source of the discrepancy is found to be a large excess of net surface radiation in the GCM simulations, and an excess rainfall interception loss, which is a consequence of this excess radiation. The modelled transpiration appears to agree with the observations.

Influence of tree canopies on the quantity of water and amount of chemical elements reaching the peat surface of a basin mire in the Midlands of England

Abstract: (1) The influence of three different tree canopies on the quantity and chemical composition of rainfall was studied at a small forested basin mire for two years. (2) Percentage throughfall of incident precipitattion under pine, fen and mixed broadleaved woodlands was 68%, 79%, and 80%, respectively. Marked variation was also observed over time. (3) Substantial quantities of plant nutrient elements reach the mire surface in rainfall which is supplemented in passing through the tree layer. The order of increase in total chemical complement of throughfall is: pine woodland > fen woodland > mixed woodland. (4) Comparison is made with rainfall and throughfall data collected at other forest sites in Britain and elsewhere. The ways in which vegetation canopies may change the chemical content of rainfall are discussed and the external sources of nutrient enrichment to rainfall are considered. (5) Of the ions studied, those which show greatest increase in passing through the tree canopies are sodium, potassium, calcium, magnesium, ammonium, sulphate and chloride. The highest input occurs during the winter months when rainfall is maximal.