Showing papers on "Tree canopy published in 1981"

Gap Regeneration in Some Old-growth Forests of the Eastern United States

Abstract: Tree replacement in gaps was studied in old-growth mesic forest stands in western Pennsylvania, Ohio, and the southern Appalachian Mountains. Predictions of future overstory com- position, based on sapling composition in small gaps (average 200 M2), were compared to current canopy composition. Both Markov analyses and simple average sapling composition of gaps support the hypothesis that regeneration in small gaps was sufficient to perpetuate the current canopy species composition of the stands studied. In some cases the saplings most likely to replace a dead canopy tree were of the same species. In other cases, especially low-diversity beech-sugar maple stands, each species seemed to enhance significantly the success of the other species.

Effects of canopy modification and accumulated sediment on stream communities.

Abstract: Small streams differing in sediment composition were compared in logged and forested reaches to determine effects of accumulated fine sediment on stream communities under different trophic conditions. Three stages of forest community succession were studied in the Cascade Mountains: Recently clear-cut areas without forest canopy (5–10 years after logging); second-growth forest with deciduous canopy (30–40 years after logging); and old-growth coniferous forest (>450 years old). One stream with mostly coarse sediment (56–76% cobble) and one with more fine sediment (5–14% sand and 23–53% gravel) were contrasted for each successional stage. In general, streams traversing open clear-cuts had greater rates of microbial respiration, and greater densities or biomasses of aufwuchs, benthos, drift, salamanders, and trout than did the shaded, forested sites regardless of sediment composition. We conclude that for these small Cascade Range streams, changes in trophic status and increased primary productivity...

Canopy roots: convergent evolution in rainforest nutrient cycles.

Abstract: Accumulations of living and dead epiphytes in the canopy of rainforest trees provide an aboveground nutrient resource. A wide range of host tree species in both temperate and tropical rainforests gain access to these nutrients by putting forth extensive networks of adventitious roots beneath the epiphyte mats they support.

Long-Term Dynamics of Forest Ecosystems

Abstract: The fundamental data for understanding the dynamics of forests are the diameters and species of the trees that make up the forest. Tree diameter changes for an individual tree as the tree grows. Over a given area, the statistical distribution of tree diameters changes as a complex consequence of tree birth, growth, and death. Because a forest is composed of many trees and because the number of factors affecting the life of each tree is large, realistic models of forest dynamics based on individual trees have developed only as computing power has become available. In this paper, models that simulate forest dynamics are treated by calculating the competitive interrelationships among trees in a restricted spatial unit--typically the gap in a forest canopy created by the death or removal of a large canopy tree. For this reason they are called gap models. Computer simulation models, which allow for numerous seedlings and the long lives of large trees, predict how forests will respond to different management techniques.(KRM)

The Abundance and Seasonality of Forest Canopy Birds on Barro Colorado Island, Panama

Abstract: The outer canopy of a lowland tropical forest has a less buffered microclimate and more seasonal leaf phenology than the understory. Censuses were conducted from a canopy tower on Barro Colorado Island, Panama, to assess the composition and degree of seasonality of the canopy avifauna. The canopy avifauna shares many species with scrubby second growth; many common canopy species were also found frequently in more open areas. The rarest visitors to the canopy were primarily those from lower strata. Most common species were omnivorous, and restricted insectivores were poorly represented when compared to lower strata. This distribution is correlated with a taxonomic shift from the antbirdwoodcreeper-dominated understory to a tanager-dominated canopy avifauna. A majority of common canopy species was significantly seasonal in abundance; the most seasonal resident species tending to be the omnivores. Two sources of overall fluctuation in birds using the outer canopy were an influx of small omnivorous tanagers in the early dry to early wet season, and the presence of temperate-zone migrants, mainly Dendroica castanea, from late wet through the dry season. THE OUTER CANOPY OF A TROPICAL FOREST is a world distinct from the somber understory it shades. The protective shell formed by the foliage of massive trees receives the full brunt of the weather: wind speeds are higher, solar radiation and rainfall are most intense (Allee 1923), and temperatures average 2-5? C warmer than in the understory only 5 m below (Smithsonian Environmental Sciences Program, unpubl.). The biotic environment also differs markedly; large trees cover areas that might have supported many small plants on the forest floor, creating patches of young leaves, flowers, and fruits on a larger scale in the canopy than in the understory below. Furthermore, canopy trees display more pronounced seasonality in leaf loss than understory shrubs in semideciduous tropical forests (Croat 1978, Leigh and Smyth 1979). As Karr (1976b) argued, birds using different levels of a tropical woodland face radically different seasonal regimes, and the diversity and seasonality of the avifauna of each stratum should differ accordingly. Karr (1976b) showed that in a late scrub community in Panama, the upper strata had a less diverse and more fluctuating bird population than lower strata. Various authors (Orians 1969, Pearson 1971) have noted the taxonomic affinity of canopy and clearing avifaunas and the dissimilarity between canopy and understory birds. These observations suggest that the influence of differences in phenology, microclimate, or foliage structure of different forest strata may be profound. Few data are available on the abundance and seasonality of species in the outer canopy. The major problem in analyzing bird use of a tropical forest canopy is the difficulty of observing birds 25-40 m above ground. This difficulty is exacerbated by the similarity of the high sibilant calls of many small tanagers. One solution to this problem is to census birds from a canopy tower or walkway. Lovejoy (1975) censused from such a tower in the Brazilian Amazon but did not separate canopy census results in his published analysis. In this paper I present an analysis of census data taken from a 40 m canopy tower in secondary forest of Barro Colorado Island, Panama (BCI). Censuses were conducted to quantify the seasonal use of a small piece of outer canopy.

The tropical rainforest canopy : a method of providing total access

Abstract: An aerial rope network was constructed, using three emergent trees as supports, which provides access to a large volume of tropical rain forest from ground level to above the canopy's upper surface. The virtually unexplored canopy community thus becomes accessible for a broad range of scientific research. THE CANOPY OF THE TROPICAL FOREST possesses one of the most complex and diverse communities on the earth, yet there have been few effective methods for studying this aerial zone, and none of these provides comprehensive access to a large volume of forest. To observe the canopy, which varies in height from about 15 meters to above 60 meters, early investigators built towers and platforms in tall trees (Hingston 1932, Bates 1944, McClure 1966). Immobile structures such as these proved to be biased observation posts due to the high spatial heterogeneity in plant species and associated animal activities of tropical forests (Elton 1973). The usefulness of treetop platforms was expanded by Muul and Liat (1970), who built transects of catwalks extending hundreds of meters at various heights in the canopy. This method faciliated observations, but access to surrounding vegetation was severely limited. Further, catwalks were not ecologically benign since they offered new routes for canopy animals that in turn could influence colonization patterns on nearby limbs by epiphytes (Perry 1978b). Using advances made by Denison et al. (1972), Perry (1978a) developed highly mobile tree-climbing methods that made the peripheral regions of every strong tree and the volume of forest under its crown accessible to investigation. Nevertheless, important regions of the forest remained inaccessible: i.e., the upper surface of the canopy with its high activity of insect and bird species, and a large fraction of the forest which is composed of weak trees unsafe for climbing, whose heights commonly reach 30 meters. To gain complete access to the latter regions for studies of pollination biology, we developed an aerial network of ropes, which provided access to about an acre of forest from ground level to above the historically inaccessible upper surface. The study site was Finca La Selva, a field station owned by the Organization for Tropical Studies, located near Puerto Viejo, Heredia Province, Costa Rica. The work required only two people and was begun on 8 March, and ended on 1 April 1979. Following the lead of Muul and Liat (1970), who used trees as structural supports for their catwalks in a Malaysian forest, our minimum canopy research facility was constructed using three emergent trees in undisturbed lowland rain forest of the southeast corner of the University of Washington Research Plot I. The trees formed a triangle of approximately 100 meters on a side. Each was taller than the surrounding canopy by about 15 meters, a height that was essential to the function of the web. A small platform was constructed in one tree at a height of 32 meters which serves for sleeping, equipment storage, and access to the web. From the platform we shot 20 lb. test monofilament lines, using a crossbow and arrows, to and between the two opposite trees, making a continuous loop (fig. 1). The position of these initial lines was adjusted to avoid abrasion against limbs, which would weaken the ropes when the web was in operation. The lines were replaced by 200 lb. test braided Nylon cords that were strong enough for use in pulling the 8600 lb. test, 1/2 inch in diameter, perimeter rope into place. The rope brand is Continental Dacron over Dacron, and is available through Continental Western Corporation, 2931 South Avil Avenue, Commerce, California 90040. Dacron was selected because it is nearly stretch-free and resistant to sunlight, though this rope does abrade easily. Because of this hazard, all ropes, especially where they extend into a tree crown, should be clearly visible so they can be inspected regularly. Rodents should not be overlooked as a source for abrasion since they may BIOTROPICA 13(4): 283-285 1981 283 This content downloaded from 157.55.39.72 on Wed, 14 Sep 2016 06:13:03 UTC All use subject to http://about.jstor.org/terms

Vertical variation in stemflow generation

Abstract: (1) Stemfiow production rates of Douglas fir were examined in the field in relation to crown volume and canopy architecture. (2) Experimentally controlled precipitation was applied to the tree, and stemflow monitored at four points down the trunk below major whorls. (3) Total stemflow production was less than 2% of total precipitation, with 98% of the stemflow being produced in the upper half of the canopy volume. (4) The results suggest that the sheltered, depressed branches of the lower canopy contribute little to stemflow production, despite having 31% of the branch interception area. density, stand structure, tree species, and precipitation duration and intensity on interception and net rainfall. Interception is usually measured indirectly as the difference between gross (above the canopy) and net (below the canopy) rainfall. The latter is calculated by summing the total throughfall (_ canopy drip) and stemflow (Kittredge 1948; Leonard 1961; Rothacker 1963; Rutter 1963; Geiger 1965; Helvey & Patric 1965; Zinke 1967; Brown & Barker 1970; Orr 1972; Swank, Geobel & Helvey 1972; Tajchman, Lee & Repa 1979). From the established relations it is possible to develop estimates of the budgetary terms in the form of linear regression equations that are of practical value to the forest and water manager. A rather different approach to the analysis of the forest water budget is that of Robins (1974), and Rutter et al. (1971, 1975). In their work empirically-derived, species-specific estimates of canopy storage capacity, canopy drainage and stemflow, and predicted evaporation rates (based on wind speed, atmospheric humidity and the aerodynamic resistance of the canopy) are used to calculate canopy water balance. In both these approaches the individual tree or forest stand forms the unit of investigation, but little account is taken of the hydrological response of different parts of a given tree. The objective of this study is to examine one response variable (stemflow) in a partitioned tree canopy, and to relate stemflow production to canopy storage capacity and canopy morphology.

Leaf Turnover Rates and Natural History of the Central American Tree Fern Alsophila salvinii

Abstract: There are few studies of growth rates of tropical trees. Moreover, the growth of tree ferns in their native habitats has seldom, if ever, been studied because of their slow growth and the need to make observations over a long period of time. As a Peace Corps volunteer in El Salvador I had the chance to study the growth of the cloud forest tree fern Alsophila salvinii Hooker (Cyatheaceae). Bosque Montecristo is a cloud forest that covers about 15 km2 and is located at the common borders of El Salvador, Guatemala, and Honduras. Approximately 60 percent of the forest is in El Salvador and has been set aside as a national park and wildlife preserve. The highest point in the forest, the summit of Cerro Montecristo, has an altitude of 2414 meters. Bosque Montecristo receives an average of 2250 mm of rain annually. Fog drip during the night deposits about the same amount of water on the forest (Reyna, 1979). March and April are the driest months. The rainy season begins in mid-May or early June and continues until December. Bosque Montecristo is a subtropical, lower montane, very humid forest according to the Holdridge life zone classification (Holdridge, 1975). The cloud forest proper begins at ca. 2100 m and extends to ca. 2350 m, where it is replaced by an ericaceous shrub association on the mountain summits. The ecotone between the cloud forest and the pine-cypress association below occurs between 1900 and 2100 meters. Secondary forest is found in the whole zone wherever there has been logging (Reyna, 1979). The majority of the trees in the cloud forest are evergreen. The emergent trees in the forest canopy are principally oaks, which are thickly covered with epiphytes (Reyna, 1979). Tree trunks near the forest floor support lush growths of mosses, filmy ferns, and many other ferns such as Asplenium, Grammitis, and Elaphoglossum. Reyna (1979) reports 175 species of trees in the Montecristo area and 71 species from the cloud forest proper. In the area where the present study was undertaken three tree ferns are common: Dicksonia gigantea Karst., Trichopteris schiedeana (Presl) Tryon, and Alsophila salvinii Hooker. Alsophila salvinii is a cloud forest tree fern known from southern Mexico, Guatemala, Honduras, and El Salvador (Stolze, 1976). It is one of the most conspicuous ferns in Bosque Montecristo and is the most common tree fern. In very wet parts of the forest, A. salvinii forms large, dense thickets, often in areas where a large tree or branch has fallen. The thicket shown in Fig. I is brightly lit during the morning from holes in the forest canopy. The thicket appears to be perpetuating itself, as there are hundreds of very young tree ferns present with trunks as yet undeveloped. Fronds of these are only about 30 cm long, whereas fronds of adults are about 2.5 m long. Alsophila salvinii is also found in relatively dry, open secondary forest at ca. 2050 meters in Bosque Montecristo. The ferns in the secondary forest don't form dense

Comments on Measuring Turbulent Exchange Within and Above Forest Canopy

Abstract: Actual problems of measuring the turbulent exchange in and above forests (e.g., site requirements of micrometeorological observations, aerodynamic characteristics of forests, observations of the crown-produced mixing layer, flux-profile relationships above forests, and some experimental difficulties) are discussed. The present state of knowledge regarding the micrometeorology of forests is poor, and there are good opportunities for experimental and theoretical research. A wider participation of universities and research institutes (in forest meteorological research) and their international coordination is needed.

Forest vegetation as a sink for atmospheric particulates: Quantitative studies in rain and dry deposition

Abstract: Radionuclides in the atmosphere are associated with nonradioactive air particulates and hence serve to trace the fluxes of air particulates to various surfaces. Natural and artificial radioactivities found in the atmosphere have been measured in vegetation for 10 years to elucidate some of the mechanisms of acquirement by forest trees of atmospheric particulates. Whole tree analysis, in conjunction with soil assay, have served to establish the fraction of the flux of radionuclides retained by above-ground tissues of a forest stand. Interpretation is facilitated because most radionuclides in the atmosphere are superficially acquired. Typically 5--20% of the total open field flux is retained by the forest canopy in a moderately rainy climate (120 cm/year). Short-lived daughters of radon give a dry deposition velocity of particulates in the Aitken size range of 0.03--0.05 cm/s, thus permitting an estimate of transient removal by forest canopies by dry deposition of this size fraction.

The Energy and Mass Exchange Characteristics of a Loblolly Pine Plantation

Abstract: (1) Energy balance measurements based on Bowen ratio techniques were used in conjunction with the big-leaf model to characterize energy and mass exchange between the atmosphere and the forest canopy in a loblolly pine plantation. (2) The partitioning of net radiation into latent and sensible heat by the Bowen ratio varied greatly with time of day and from day to day even when measured at the same time of day. Such variation results from variations in net radiation, canopy resistance, and air vapour density deficit. The maximum Bowen ratio during daylight hours was 2.3 and the minimum 0.1 1. (3) Canopy conductance was significantly correlated with solar radiation flux density in the canopy. (4) Significant correlations were found between average stomatal conductance (calculated from canopy resistance and leaf area index) and leaf temperature, vapour density deficit, and solar radiation flux in the canopy.

Effect of forest canopy closure on incoming solar radiance

Abstract: In order to better understand the physical processes involved in defoliation assessment from remotely sensed data, a field study was designed to investigate the effect of forest canopy closure and other environmental variables on incoming solar radiation. Diffuse radiation measurements were recorded in red, infrared, and middle infrared wavelengths using the Mark 2 three band field radiometer. Results to date indicate that the percent canopy closure is the single most important variable affecting incoming solar radiation. In the visible and near infrared regions, interaction between time of day and date (defined later as solar zenith angle) also affect radiometric response. Aspect has only limited influence on radiance response. These same variables do not influence middle infrared response, however. Uniformity of the forest canopy appears to be more important. These results are compared to LANDSAT MSS classification results of gypsy moth defoliation.