Showing papers on "Tree canopy published in 1992"

Transpiration and canopy conductance in a pristine broad-leaved forest of Nothofagus : an analysis of xylem sap flow and eddy correlation measurements

Abstract: Tree transpiration was determined by xylem sap flow and eddy correlation measurements in a temperate broad-leaved forest of Nothofagus in New Zealand (tree height: up to 36 m, one-sided leaf area index: 7). Measurements were carried out on a plot which had similar stem circumference and basal area per ground area as the stand. Plot sap flux density agreed with tree canopy transpiration rate determined by the difference between above-canopy eddy correlation and forest floor lysimeter evaporation measurements. Daily sap flux varied by an order of magnitude among trees (2 to 87 kg day-1 tree-1). Over 50% of plot sap flux density originated from 3 of 14 trees which emerged 2 to 5 m above the canopy. Maximum tree transpiration rate was significantly correlated with tree height, stem sapwood area, and stem circumference. Use of water stored in the trees was minimal. It is estimated that during growth and crown development, Nothofagus allocates about 0.06 m of circumference of main tree trunk or 0.01 m2 of sapwood per kg of water transpired over one hour.Maximum total conductance for water vapour transfer (including canopy and aerodynamic conductance) of emergent trees, calculated from sap flux density and humidity measurements, was 9.5 mm s-1 that is equivalent to 112 mmol m-2 s-1 at the scale of the leaf. Artificially illuminated shoots measured in the stand with gas exchange chambers had maximum stomatal conductances of 280 mmol m-2 s-1 at the top and 150 mmol m-2 s-1 at the bottom of the canopy. The difference between canopy and leaf-level measurements is discussed with respect to effects of transpiration on humidity within the canopy. Maximum total conductance was significantly correlated with leaf nitrogen content. Mean carbon isotope ratio was -27.76±0.27‰ (average ±s.e.) indicating a moist environment. The effects of interactions between the canopy and the atmosphere on forest water use dynamics are shown by a fourfold variation in coupling of the tree canopy air saturation deficit to that of the overhead atmosphere on a typical fine day due to changes in stomatal conductance.

Characteristics of dry forest in West Africa and the influence of fire

Abstract: . The climate, soil, structure and floristics of dry forests in West Africa are summarised. Data from Ghana show that these forests have two-peak annual rainfall between 850 and 1350 mm, with 6–10 dry months (< 100 mm rain) each year; by relatively nutrient-rich soils developed over a variety of rock types; by short stature (tallest trees 10-40 m) relatively high deciduousness in the upper canopy and evergreenness in the understorey; and by a distinctive flora which changes gradually towards areas of higher rainfall but abruptly at the forest-savanna boundary. Dry forests near the forest-savanna boundary form a distinctive sub-type as a result of occasional encroachment by litter fires which have become more common in the 1980's. Evidence is presented to suggest that many parts of the forest zone in West Africa may have been subject to fires most often in the dry forest types. Past fires are likely to have had a profound influence on the composition of the present forest canopy. Fire mortality is greatest in small trees, whilst drought (without fire) kills more large trees. This thinning process allows rapid recolonisation especially by Marantaceous and Zingiberaceous forbs and by pioneer trees. Seedlings of canopy trees grow beneath these colonising plants. Recurrent fires seriously impede the recovery of burnt forest and are a principal concern for the rehabilitation of dry forests.

Atmosphere-surface exchange of mercury in a forest: Results of modeling and gradient approaches

Abstract: We have modified recently published dry deposition models to estimate deposition velocities (Vd) for Hg in both fine aerosol and vapor form to forest canopy surfaces. Aerosol and total vapor phase Hg concentrations in air previously measured at Walker Branch Watershed in Tennessee have been used with model results to estimate dry deposition to a deciduous forest. The concentration data confirm that airborne Hg is dominated by vapor forms at this site and exhibits concentrations moderately above continental background levels. The modeled Vd values reflect published data which suggest that dry deposition of Hg vapor is strongly controlled by surface transport processes, notably stomatal and mesophyll resistances, the latter dominating. Weekly mean Vd values ranged from 0.006 (winter) to 0.12 (summer) cm s−1. We have also measured concentration gradients of Hg vapor in air above this forest to estimate air-surface exchange during short-term experiments. While the model results indicate that the canopy is a sink for Hg vapor, the concentration profiles suggest that the forest soils are a source during some periods, the combined effect of which is net Hg fluxes in the upward direction. Application of a detailed canopy turbulence model yielded soil emission rates of the order of 50 ng Hg m−2 h−1, ∼10% of which is deposited in the canopy. Our modeled dry deposition estimates plus limited measurements of wet deposition in this area suggest that dry and wet deposition may be comparable in magnitude.

Patterns of gap-phase replacement in a subalpine, old-growth forest

Abstract: Small-scale natural disturbances involving the death of one to a few trees and creating gaps in the forest canopy are key processes in the population and community ecology of many forests. I examined the patterns of replacement in gaps in a subalpine old-growth forest in southern coastal British Columbia to assess their role in the forest community. I found no evidence that self replacement or reciprocal replacement act to maintain the current community composition. Gapmaker-gapfiller comparisons indicated preferential replacement of all species by Pacific silver fir (Abies amabilis), suggesting that the community is undergoing successional change. Nor did gap size, location within a gap, or local canopy composition appear to exert a strong influence on the species composition of regeneration within the gap. The only circumstance where Pacific silver fir was not overwhelmingly dominant among gapfillers was on stumps, where almost all successful western hemlock (Tsuga heterophylla) gapfillers were located. These patterns suggest that neither species-specific interactions between gapmakers and gapfillers nor variability in gap environments is adequate to maintain the current composition of the forest canopy. How- ever, caution is indicated in projecting a long-term trend from this short-term assessment of community trajectory.

Spatial and temporal patterns of light and canopy structure in a lowland tropical moist forest

Abstract: Computer-assisted image processing of hemispherical photographs of the forest canopy was used to study the light environment of a mature lowland moist tropical forest in the Republic of Panama. Wet and dry-season measurements were made in 1983 and 1984 near ground level at 2.5 m intervals along two 1-km long transects; additional measurements were made at a single site at 5 heights from forest floor to above-canopy, and in 10 experimentally produced treefall gaps in which understory herb responses to gap formation were also monitored. Mean daily global radiation along the transects showed no distinct dichotomy corresponding to "gap" versus "understory" habitats. Light measurements showed the effect of seasonality in rainfall, and year-to-year correlation was low, indicating the need for frequent assessment of the light environment for long-term studies of plant responses. Various measures of total irradiance (e.g., canopy openness, minutes of potential sunflecks, total solar energy) were highly correlated. However, the correlation of canopy openness in the eastern and western octants of the hemispherical images was low, indicating that the time of day in which direct sunlight occurs may differentiate microsites with similar daily total light levels. In treefall gaps, the light environment was more heterogeneous one year after treefalls; but, two years after the treefall, light levels were both lower and more homogeneous. Both spatial and temporal complexity in the light environment suggest that "gap" versus "understory" characterizations are too simplistic.

Access to the Upper Forest Canopy with a Large Tower Crane

Abstract: Figure 1. Sketch of the canopy crane operating in a forest showing the tower (a), jib (b), counterjib and counterweight (c), the operator's cab (d), and the gondola (e) attached to the hook. The radius and height of the jib are 82 and 52 m, respectively. T he uppermost forest canopy is a frontier ofscientific research (Erwin 1983). It is the primary interface between the atmosphere and the forest and is a reservoir of biological diversity. But understanding of this important portion of the forest is far from adequate because of the difficulties in gaining access to the tops of trees. Most techniques currently available to study canopies provide limited flexibility and maneuverability, little safety, and almost no access to the important outermost canopy zone. The inability to study the functioning of the upper forest canopy in situ has stalled progress on a variety of critical research pursuits. For example, the examination of forest/atmosphere interactions (crucial to understanding global climate) and rigorous analyses of canopy biodiversity (an essential basis for conservation decisions) are both severely limited by the lack of controlled canopy access. A tower crane with a long horizontal jib brings the previously unreachable portions of forests within the range of scientific scrutiny. It allows repeatable observations and experimental manipulations on individual

The effects of tree canopy cover on soil fertility in a Nigerian savanna

Abstract: The effect of tree canopy cover on soil properties was studied over three periods: middry season (January), mid-growth period (August) and peak-growth period (October) in three 1 ha plots in savanna of north-west Nigeria. The objective was to find out whether tree canopies change the nutrient status of the soil under them relative to adjacent grasslands. Soils under tree canopies were found to have significantly higher levels of organic matter, calcium, magnesium, potassium, total exchangeable bases, cation exchange capacity and pH than those in open grasslands. Nitrogen and phosphorus were slightly higher in soils under tree canopies than those in the open grasslands. Trees 7 m and above had more influence on soil properties than smaller trees. Differences in soil properties among the study plots were due to differences in their soil texture. Seasonal trends were observed in organic matter, carbon: nitrogen ratio, cation exchange capacity, phosphorus, calcium, sodium, total exchangeable cations and percentage base saturation.

Tree regeneration after bamboo die‐back in Chinese Abies‐Betula forests

Abstract: . Gaps created by disturbance in the forest canopy are important sites for tree regeneration from seed but plants already established in gaps may slow gap-filling. This study deals with consequences of bamboo die-back for tree regeneration and the dynamics of Abies-Betula forests in southwest China. Bamboo dominates the forest understory impeding tree regeneration when in its vegetative phase. Populations of tree seedlings were sampled in 1984–85 and 1990 in two sets of permanent plots where bamboo had died back in 1983. Both Abies and Betula density increased after bamboo die-back, Betula more so than Abies, especially in gaps. Before bamboo die-back, seedlings were established on raised surfaces such as logs but afterwards seedlings became common on the forest floor. This reduced the intensity of clumping of seedling populations between 1984 and 1990. A tree by tree replacement model predicts an increase in Abies and a decrease in Betula after bamboo die-back. Life histories of tree species, gap characteristics, and the bamboo growth cycle (mature/die-back/building) interact to promote fluctuating dominance of Abies and Betula in old-growth forests.

Faidherbia albida and its effects on Ethiopian highland Vertisols

Abstract: On a Vertisol under 850 mm rainfall, at an altitude of 1850 m, Faidherbia albida trees that occurred at 6.52 trees ha−1, with a canopy cover that range from 97 m2 ha−1 to 229 m2 ha−1 were recorded. Studies on the lateral and vertical influence of the tree canopy on some physical and chemical properties of the soil, show apparent higher organic matter on the West side of the tree than the East due to accumulated wind blown litter by prevalent wind direction, and organic matter, N, P and K levels were higher under the tree canopy than outside for all directions and depths studied. Soil pH, exchangeable Na, Ca and Mg under the canopy and outside were similar. Available water capacity was 1.5 to 2 times more under than outside the tree. Noticeable increases in the silt fraction under the tree was recorded and discussed in relation to soil condition improvement and plant growth.

Pulse Release of Sugars and Polyols from Canopy Bryophytes in Tropical Montane Rain Forest (Guadeloupe, French West Indies)

Abstract: Nonvascular epiphytes within the canopy of tropical montane rain forest in Guadeloupe (French West Indies) are exposed to episodes of severe desiccation on more than 30 percent of all days each year. This exposure to wetting/drying cycles induces the accumulation of more than 950 kg ha #751 of sugars and polyols by epiphytic bryophytes within the cloud forest canopy. These sugars ate then released in pulse form during rewetting episodes and subsequently translocated by throughflow precipitation within the canopy. Sugars and polyols were measured by high-performance liquid chromatography and one- and two-dimensional proton and carbon-13 nuclear magnetic resonance spectroscopy (...)

Response of five deciduous forest herbs to partial canopy removal and patch size.

Abstract: -Forest canopy was partly removed [33% or 66% removal of canopy tree basal area (BA)] from patches of three sizes (0.015, 0.053, 0.196 ha) to determine whether the frequency of five deciduous forest herbs was affected by patch size. Herb frequency, irradiance and woody stem density were recorded after canopy removal and 2 yr later. Irradiance and woody stem density both increased more in large (0.196 ha) patches than in smaller patches (0.015 and 0.053 ha) with 33% and 66% of tree BA removed. In contrast, where 66% of tree BA was removed, the frequency of four herbs increased more in smaller patches than in large patches and the frequency of the fifth herb was unaffected by patch size. Where 33% of tree BA was removed, herb frequency also increased more in smaller patches than in large patches for one herb and by about the same amount in all patches for another herb. The remaining three herbs each increased more in medium-sized patches (0.053 ha) than in small or large patches. These results indicate that the frequency of perennial forest herbs does not increase more in large canopy openings than in smaller openings. Although irradiance was higher in large patches than in smaller patches, woody stem density was greater in large patches as well and competition from more woody plants in large patches may explain why herbs did not increase more in large patches than in smaller patches.

Ecology of beech forests in the northern hemisphere.

Abstract: Beech forests are dominated or codominated by at least one Fagus species The beeches are a homogeneous group of 11 deciduous tree species growing in the Northern Hemisphere (Figure 11) They often dominate forest ecosystems throughout their ranges The optimum for beech is on acidic and mesic loam soils The ranges are limited by summer water deficits in continental and southern climates, and low winter temperatures and late spring frost in the north The purpose of my research was to find out why beeches are such widespread successful trees I tried to answer several questions: 1 Do these beech species have something in common as forest organisms? What makes them different from codominant trees? In Chapter 3, I selected radial growth and size parameters for such comparisons among trees Size parameters were tree height, stem diameter and crown projection 2 What are common characteristics of beech forests over the whole range? In Chapter 4, I analyzed geographical trends in woody species composition and forest architecture Within each site, I compared tree-height distribution and tree regeneration and related them to forest architecture 3 Are there common characteristics in the dynamics of beech forests? The relation between suppressed and released growth in trees, as well as release frequency, yields information about stability and change in the forest In Chapter 5, I compared suppression and release in tree-ring chronologies of trees in different study sites The per tree number of major releases was counted over one century For each study site, I used this parameter to calculate the per year per tree probability of a major release In Chapter 2, I described the 16 study sites (Figure 21, Table 21) which were representative of beech forests in different geographic areas They were selected in sites with minimal human influences In each study site, I selected at least two plots The plots included different phases of forest development and were between 300 and 2400m 2in size Tree height and stem diameter were measured in trees taller than 5m, and in a subplot, trees between 05m and 5m were measured Their stem position and crown projection were mapped Among plants lower than 05m, I recorded abundance of beech seedlings and estimated percentage cover of important plant species Increment cores were taken from trees growing in the forest canopy, in canopy gaps and in the understory Generally, beeches are more shade-tolerant than their deciduous broad-leaved codominants and less shade-tolerant than their evergreen broad-leaved codominants During its lifecycle a beech tree can pass several periods of suppression (Table 37) Compared with beech, height/stem-diameter ratios were relatively higher in deciduous and lower in evergreen broad-leaved codominants With the exception of Acer saccharum and Cyclobalanopsis multinervis, beeches had more variable height/ stem-diameter relationships than any codominant analyzed (Table 33) Beech had a more flexible growth strategy than codominant tree species The architecture of beech forests was most simple in some European beech forests and became increasingly complex in eastern Asiatic beech forests (Chapter 4) The eastern Asiatic beech forests were richest in woody species and had the highest ratio of evergreen vs deciduous broad-leaved tree species In each study site, the forest canopy covered about 70% of the area and potential trees dominated in the canopy gaps Exceptions were some Asiatic sites where medium-tall tree species or shrub and dwarf bamboo species dominated in the canopy gaps, and beech seedlings could not establish themselves, Beech juveniles were also absent from Chinese study sites where evergreen broad-leaved trees were abundant in the understory The beech forests are very different in architecture and species composition There was a relationship between per year per tree probability of major release and the codominance of other tree species (Chapter 5) High probabilities of major release in the study sites where deciduous broad-leaved tree species could occur, favored these tree species over beech Low probabilities of major release in the study sites where evergreen broad-leaved tree species could occur, favored these tree species over beech In the study sites with evergreen broad-leaved trees, codominance of beech is probably maintained through infrequent and large-scale major releases The interval between changes in the forest architecture, and consequently light levels in the forest, is important in determining the dominance of beech The Fagus species form an ecologically homogeneous group of tree species that are successfully dominating or codominating the forest ecosystems where they occur Shade tolerance and flexible growth strategies form the basis for the success of beech Beeches have a wide tolerance for macroclimate and soil as long as these are sufficiently humid, however the extent of their dominance is determined by the frequency of wind impacts

The Snowmelt and Heat Balance in Snow-covered Forested Areas

Abstract: The snowmelt and heat balance in snow-covered formed areas have been studied with the use of a canopy model. It was found that, in general, as the canopy density increased the snowmelt decreased. However, with conditions of high air temperature, weak winds, and large snow albedo, a greater degree of snowmelt occurred under a dense canopy due to infrared radiation from the canopy elements than under a sparse canopy. Although the snow temperature was never higher than 0°C while the air temperature was greater than 0°C, an upward sensible heat flux was supplied from the forest canopy, resulting in the atmospheric heating.

Seed dispersal ecology of a wind dispersed rain forest tree in the Western Ghats, India

Abstract: Fecundity and seed dispersal of Lophopetalum wightianum, Wight (Celastraceae), a wind dispersed canopy tree species, were studied in the rain forests of the Western Ghats, India. The effects of fruit crop size, seed characteristics, tree height, and wind speed on seedfall and dispersal distances were investigated. Fruiting was synchronous and fruits were produced between February and April. Smaller fruits suffered more predispersal predation. The majority of seeds, described as rolling autogyros were dispersed near the parent. The rate of descent of seeds was related to the square root of wing-loading. However, wind speed significantly decreased the rate of descent and increased dispersal distances. Taller trees dispersed seeds more evenly. Large trees had a significant dispersal advantage since they were more fecund and dispersed seeds further away and more evenly, thereby decreasing the probability of mortality due to density and distance dependent predation. These results show that there is convergence in dispersal strategies of Lophopetalum wightianum with wind dispersed trees studied in the neotropics.

Influence of acid deposition on element cycling in mature sugar Maple Forest, Algoma, Canada

Abstract: Forestry studies were undertaken within the Turkey Lakes Watershed to determine the impact of long-range transport of air pollutants on biogeochemical processes in old-growth sugar maple forest on shallow Precambrian-derived till soils in the Algoma District of Ontario, Canada. Distributions of organic matter and macroelements were determined in the tree- and field-layer vegetation, the forest floor and the mineral soil of the study site. Annual tree growth was largely offset by mortality, resulting in a relatively stable standing stock of ca. 245 t ha−1. Annual aboveground litter production averaged 3.7 t ha−1 yr−1, chiefly in the form of deciduous leaf fall. The average pH of the precipitation (4.3) was reduced considerably by contact with the forest canopy. Throughfall was enriched with other elements, principally K and, to a lesser extent, Ca and Mg. The cationic composition of the forest-floor percolates, on the other hand, was dominated primarily by Ca and only to a lesser extent by Mg and K. The stand receives moderate acid deposition, mainly from average inputs of 33–36 kg ha−1 yr−1 of SO4 2− and 24–29 kg ha−1 yr−1 of NO3 − distributed throughout the year. Atmospheric inputs add to substantial natural NO3 − production, notably within the forest floor and upper mineral soil, and contribute to leaching of bases, principally Ca and Mg, from the rooting zone. Active recycling of elements together with weathering of primary minerals should assist in preserving the base status of the site.

Three-dimensional dispersion of drosophilid flies in a cool temperate forest of northern Japan

Abstract: Three-dimensional dispersion of drosophilid flies was studied within a secondary broad-leaved forest in relation to forest structure. The survey area included the forest margin and old canopy gaps and varied in the foliage height profile from place to place. Using multivariate analyses on the data of drosophilid dispersion, five microhabitats which were different from one another for drosophilids were recognized: (i) canopy layer; (ii) middle layer; (iii) floor layer of forest interior; (iv) upper layer of forest margin; and (v) herbaceous layer of forest margin and gap. The height of living space of canopy species was remarkably lowered at the forest margin. The forest edge was richer in both numbers of individuals and species than the forest interior from the overlap of the grassland and the forest canopy subcommunities and the addition of invaders from other habitats. However, no ‘edge’ species, which were mostly restricted to or spend most of their time in ecotones, were found. It is hypothesized that the above-ground forest structure consists fundamentally of three zones: (i) the canopy; (ii) the floor; and (iii) the edge. A significant positive correlation was found between the foliage height diversity and the degree of vertical habitat segregation among drosophilid species. The patchiness of vegetation structure influential to the three-dimensional dispersion in a forest drosophilid community was estimated to be on the scale of 110–450 m2. This scale of subjective habitat patchiness or ‘ecological neighbourhood’ corresponds well with the most prevalent size of canopy gaps occurring in various forests.

Recovery of a mixed-species mangrove forest in South Florida following canopy removal

Abstract: In October 1982, the upper structure and canopy of a 0.09 ha area of mixed species mangrove forest (654 trees) in southeast Florida was removed by tree trimmers. This represented a reduction in mean forest height from 7.1 to 4.8 m. In February 1983, recovery studies were initiated based in part on comparisons with a contiguous untouched mangrove forest. Of some 148 tall Rhizophora mangle trees with an original mean height of 9.0 m, 110 (74%) died within 3 years. Mortality of R. mangle was highest among tall single-boled trees with a concentration of foliage above 4.8 m. All individuals of Avicennia gerrninans and Laguncularia racemosa recovered quickly by releafing, coppicing, and initiating trunk sprouts. Based on comparative light transmission measurements, the time estimated for forest canopy reclosure was 50 months although it varied from 72 to 118 months in the R. mangle zone, to < 1 to 24 months in the zone dominated by L. racemosa .

Radar Measurement of Forested Areas During Otter

Abstract: To test a forest ecosystem model in the OTTER (Oregon ecosystem research) project, it is desirable to find forest canopy parameters via radar remote sensing measurements. Conventionally, forest biomass, along with quantities such as the leaf area index, drive the model. It is shown that the radar backscatter is not uniquely related to biomass. A sensitivity study is carried out using a forward scattering model to determine the variation of radar cross section as a function of several forest parameters. The results are used to find suitable quantities to recover via radar experiments. A parameter estimation scheme is developed to calculate some preliminary statistical properties of the forest.