Shrub Strata Research Articles

STRUCTURE AND DYNAMICS OF HARDWOOD SWAMPS IN THE NEW JERSEY PINE BARRENS: CONTRASTING PATTERNS IN TREES AND SHRUBS

The biomass, density, age structure, and dominance patterns of the tree and shrub populations in hardwood swamps of the New Jersey Pine Barrens are described and contrasted with each other. The total biomass of individual swamps ranges from 92,000 kg/ha to 194,000 kg/ha, depending on the age of the stand. These biomass values are similar to those reported for southern hardwood swamps. The Pine Barrens swamps are distinguished by very large populations of ericaceous and other shrubs, which range up to 13% of the total above‐ground biomass. The tree populations, composed principally of Acer rubrum, Nyssa sylvatica and Magnolia virginiana, are even‐aged; Acer is strongly dominating, with a minimum of 73% of the biomass, and species richness is associated with the availability of different microhabitats. The shrub populations, by contrast, are all‐aged, with the dominance patterns among the species and the stand biomasses varying with the degree of flooding of the stand. Differences in size and growth rate among the shrub species parallel their evident response to the flooding gradient. The shrub stratum has lower species richness than the comparable southern swamps and floodplains, but ranges up to higher biomass values.

Structure and Dynamics of Hardwood Swamps in the New Jersey Pine Barrens: Contrasting Patterns in Trees and Shrubs

The biomass, density, age structure, and dominance patterns of the tree and shrub populations in hardwood swamps of the New Jersey Pine Barrens are described and contrasted with each other. The total biomass of individual swamps ranges from 92,000 kg/ha to 194,000 kg/ha, depending on the age of the stand. These biomass values are similar to those reported for southern hardwood swamps. The Pine Barrens swamps are distinguished by very large populations of ericaceous and other shrubs, which range up to 13% of the total above-ground biomass. The tree populations, composed principally of Acer rubrum, Nyssa sylvatica and Magnolia virginiana, are even-aged; Acer is strongly dominating, with a minimum of 73% of the biomass, and species richness is associated with the availability of different microhabitats. The shrub populations, by contrast, are all-aged, with the dominance patterns among the species and the stand biomasses varying with the degree of flooding of the stand. Differences in size and growth rate among the shrub species parallel their evident response to the flooding gradient. The shrub stratum has lower species richness than the comparable southern swamps and floodplains, but ranges up to higher biomass values.

Allelopathic Inhibition of Nitrification and Nitrifying Bacteria in a Ponderosa Pine (Pinus ponderosa Dougl.) Community

The dynamics of ponderosa pine (Pinus ponderosa Dougl.) stands in western North Dakota were studied to determine the influence of plant-produced chemicals on nitrification rates and competitive interactions within the stands. Ponderosa pine accounted for more than 98% of all tree and shrub stratum stems in this climax community. Low levels of nitrate-nitrogen relative to ammonium-nitrogen and low numbers of Nitrosomonas and Nitrobacter in the soils indicated that nitrification rates were low. Inhibition of nitrification is often attributed to low soil pH in coniferous forests, but the slightly alkaline soils in this study (pH 7.25–7.75) suggested that another factor caused the low nitrification. Evidence obtained suggested that the reduction in nitrate synthesis was due to the production and subsequent transfer to the soil of secondary plant chemicals that were toxic to Nitrosomonas. Chemical inhibitors of nitrification, including caffeic acid, chlorogenic acid, quercitin, and condensed tannins, were found in extracts from ponderosa pine needles, bark, and A horizon soils. These extracts proved to be toxic to soil suspensions of Nitrosomonas causing reductions of from 68–93% of the control. These findings indicate that climax ponderosa pine communities minimize the conversion of ammonia-nitrogen to nitrate-nitrogen by chemically inhibiting nitrification.

ALLELOPATHIC INHIBITION OF NITRIFICATION AND NITRIFYING BACTERIA IN A PONDEROSA PINE (PINUS PONDEROSA DOUGL.) COMMUNITY

The dynamics of ponderosa pine (Pinus ponderosa Dougl.) stands in western North Dakota were studied to determine the influence of plant‐produced chemicals on nitrification rates and competitive interactions within the stands. Ponderosa pine accounted for more than 98% of all tree and shrub stratum stems in this climax community. Low levels of nitrate‐nitrogen relative to ammonium‐nitrogen and low numbers of Nitrosomonas and Nitrobacter in the soils indicated that nitrification rates were low. Inhibition of nitrification is often attributed to low soil pH in coniferous forests, but the slightly alkaline soils in this study (pH 7.25–7.75) suggested that another factor caused the low nitrification. Evidence obtained suggested that the reduction in nitrate synthesis was due to the production and subsequent transfer to the soil of secondary plant chemicals that were toxic to Nitrosomonas. Chemical inhibitors of nitrification, including caffeic acid, chlorogenic acid, quercitin, and condensed tannins, were found in extracts from ponderosa pine needles, bark, and A horizon soils. These extracts proved to be toxic to soil suspensions of Nitrosomonas causing reductions of from 68–93% of the control. These findings indicate that climax ponderosa pine communities minimize the conversion of ammonia‐nitrogen to nitrate‐nitrogen by chemically inhibiting nitrification.

Vegetative Structure of an Appalachian Oak Forest in Southwestern Virginia

Structural parameters were used to assess differences among major vegeta- tion types in an Appalachian oak forest in southwestern Virginia. Cluster analysis re- sulted in ordering stands along a moisture gradient determined from site topographic features. Position along the moisture gradient from mesic to xeric was reflected in a number of vegetative structural variables. For the overstory these included decreased canopy coverage, decreased stand height and decreased stem basal area. Trends in the shrub stratum (l-5m) tended to be the reverse of those in the overstory. The results indicate that vegetative structure is strongly influenced by site relationships reflecting differences in moisture regime. A number of investigators have demonstrated the importance of stand structure to analysis of forest ecosystems. Horn (1971, 1975) examined the relationship be- tween structural development and succession. Whittaker (1956), Mowbray and Oosting (1968) and Whittaker and Woodwell (1969) noted structural and com- positional changes in vegetation along a moisture gradient. Whittaker (1966) demonstrated a relationship between stand structure and forest production in the Great Smoky Mountains of Tennessee. MacArthur and MacArthur (1961), James and Shugart (1970) and Morse (1976) described the importance of vegetation structure in defining certain niche requirements of bird species. The present study attempts to add to existing knowledge of forest ecosystems by structural analysis of major vegetation types in the Appalachian Oak Forest Region of southwestern Virginia. A cluster analysis of vegetative structural attributes is employed to determine interstand distances associated with a topographically de- rived moisture gradient. The relationship between the vertical stratification of foliage in forest stands and the more traditional measures of stand structure is evaluated. Methods Nine sample areas were selected on the SE slope of Potts Mountain in Craig Co., Virginia, to represent a large area of forested land in the Ridge and Valley Province. The areas are noncontiguous and extend across 5.2 km of midslope at approximately 730 m elevation. Slopes vary from 8-45%, while aspect varies from E to SW. Soils are derived mainly from ortho-quartzite sandstone with some interbedded shale outcroppings. Sites range from dry to infertile on main slopes and spur ridges to relatively fertile and mesic in coves. According to Braun (1950), the site falls within the Ridge and Valley Section

A quantitative description of the forest vegetation on an altitudinal gradient in the Mount Field National Park, Tasmania, and a discussion of its history and dynamics

The aim of this study was to describe the forest vegetation along an altitudinal transect running from 158 m to 1220 m (treeline) in the Mount Field National Park, Tasmania. Eighteen 1 ha plots were sampled along this transect, using a modified point-centred quarter method for species composition and density. Size frequency distributions were used to calculate basal areas. Estimates of relative density, frequency and basal area for each species were combined in to an importance value. The altitudinal ranges of all woody species were determined. The altitudinal temperature lapse rate was measured, and data on soil pH obtained. The initial ‘direct gradient’ analysis revealed relatively well marked discontinuities in the vegetation which were further examined by ordination and classification techniques. The latter provided a simple threefold classification into altitudinal zones. The lower zone reaches from the Park entrance (158 m) to between 600 and 670 m, and comprises tall open forest dominated by Eucalyptus regnans and/or E. obliqua and with a ‘wet sclerophyll’ understorey characterized by Olearia argophylla. The middle zone stretches from c. 670 to 940 m and comprises closed rainforest or ‘mixed’ forest (i.e. with senescent emergent eucalypts) dominated by Nothofagus cunning hamii and Atherosperma moschatum. This zone is characterized by the absence of O. argophylla and the presence of Phyllocladus aspleniifolius. The upper part of this zone constitutes an interdigitating transition to the subalpine forests, usually dominated by E. coccifera and occurring on suitable sites between c. 880 m and the timberline. The transition to subalpine forests is associated with a marked decline in basal area. Species richness (of woody plants) increases with altitude to reach a peak in the sub-alpine zone. This trend is the reverse of that normally encountered elsewhere in the world, and is mainly due to relatively high α and β diversities in the shrub stratum of this zone. The significance of fires, aspect and substrate is discussed in relation to the variations in composition within each zone. The low diversity of Nothofagus-dominated rainforest is thought to be due, in part, to the intense competitive thinning in the eucalypt re-growth phase following burning, and the subsequent ‘capture’ of the Eucalyptus niche by Nothofagus. It is speculated that, in Tasmania, the downhill migrations during the cooling phases of the Pleistocene were associated with extinctions of lowland forest taxa, while uphill migrations during warming phases were associated with speciation on the plateaux of the present subalpine zone. This hypothesis implies that the relative proportions of land area available at different altitudes, now and in the past, have determined the relative rates of speciation and extinction, and hence the altitudinal gradients of species richness.

Early Stages of Regeneration After Burning in Dry Sclerophyll Vegetation. II. Regeneration by Seed Germination

Following experimental burns in three dry sclerophyll communities, all except the geophytic species regenerated from seedlings in the first year. The annual and perennial species in the shrub strata regenerated from surviving seeds in the soil and ash, and the eucalypts from seeds released from the trees after burning. Although many seeds were destroyed during the fires, the germination of most species was higher in burnt than in unburnt plots. Fire appeared to stimulate germination through direct heat effects on the seeds, and by removing inhibitors present in the unburnt vegetation. Seedling mortality was highest during the first year. Many seedlings died while in the cotyledon stage, the main observed causes of mortality being desiccation, fungal disease and predation by insects. Seedling survival was enhanced by burning, owing to the removal of the litter and other fire-induced changes which made conditions more favourable for seedling establishment and/or growth. Two years after burning, the relative positions of dominance of the three major species in the tall shrub stratum had changed compared with the pre-burn status of each. Evidence suggests that such shifts in dominance depend on a number of interacting factors which selectively promote or inhibit the recovery of each species.

Vegetation succession after fire in sclerophyll woodland communities in south‐eastern Australia

AbstractThe dynamics of vegetation regeneration after burning were examined in three dry sclerophyll communities near Canberra, in south‐eastern Australia. Changes in seedling and regrowth populations were followed in permanent quadrats during the first two years after burning, compared with both the preburn vegetation and population changes over the same period in adjacent, unburnt plots.All species represented either by living plants in the tree and shrub strata and/or by seed in the soil and litter prior to burning regenerated during the first year after the fire treatments. No new species invaded the areas after burning. Species varied in their regenerative strategy and recovered after the fires either by germination of seed residual in the soil and ash or released from trees after burning, by regrowth from surviving vegetative organs, or by a combination of germination and regrowth. Both seedling input and the vegetative recovery of populations were higher during the first than second year after burning. The vegetative multiplication and seed gertnination of many species were stimulated by fire.It was concluded that the regeneration of the communities studied, as well as the post‐fire recovery of numerous different communities reported in the literature, closely resembled an initial floristic composition model. It is considered that the process of vegetation redevelopment after a disturbance (i.e. secondary succession) will be influenced greatly by the species composition at the time of disturbance, and by the type of disturbing agent. A single model would not be expected to adequately describe secondary succession following disturbance by agents imposing different stress conditions on a community.

The distribution of Phytophthora cinnamomi in victoria

The distribution of Phytophthora cinnamomi and the disease with which it is associated have been shown to originate in Victoria from the use of infected soil or gravel, or infected drainage water, and to have extended along roads and down gullies or table drains. The presence of the pathogen in soil frequently leads to disease in dry sclerophyll and coastal forests where most species, including dominants of the tree and shrub strata are highly susceptible. In shallow, poorly drained soil, disease may cause a complete change of plant community from shrubby sclerophyll forest to grassy woodland, with the extinction of a number of native species. Inoculation experiments with combinations of tolerant and sensitive eucalypt species in a controlled environment showed that susceptible species were rapidly eliminated from infected soil. Field inoculations using washed mycelium or infected topsoil have produced typical dieback disease in both strata of the forest. The disjunct distribution of the fungus and the susceptibility of the forest flora are evidence of the recent introduction of a pathogen that disturbs the equilibrium of the Victorian dry sclerophyll forest. Observations are not compatible with the view that P. cinnamomi is a common component of the soil microflora.

The Invasion of Native Forest by Phytophthora cinnamomi. III. Threat to the National Park, Wilson's Promontory, Victoria

Diseased vegetation was first reported from the northern slopes of the Vereker Range at Wilson's Promontory National Park in September 1970. Phytophthora cinnamomi was isolated from plants in diseased areas but not from unaffected localities. The pathogen has since invaded three types of plant community-dry sclerophyll woodland, heaths, and swamps-and can be isolated at all depths to 80 cm in deep sands. High inoculum potentials are found at depths of maximum root concentration, i.e, to about 32 cm. Except where free water occurs, the rate of extension of the disease is slow. Dominants of both tree and shrub strata are susceptible and have been killed. Highly susceptible shrubs of the understorey, such as Xanthorrhoea australis and Isopogon ceratophyllus, are destroyed first. These are followed 6-12 months later by less susceptible shrubs, and at least 12 months later symptoms appear in trees. This variation in time may be responsible for the characteristic mosaic appearance of diseased areas. Inoculation experiments on 9-month-old trees of Banksia serrata and Eucalyptus obliqua confirmed field observations of susceptibility and symptom expression. The origin of the disease at Wilson's Promontory and its ecological significance are examined. Experiments in control of the pathogen are reported and recommendations discussed for control within the National Park.

Lake Water Quality and Surrounding Vegetation in Dry Churiya Hills, Far-Western Nepal

Mudka, Bedkot and Jhilmila are natural lakes in dry sub-tropic Churiya hills of Kanchanpur in far-western Nepal. A study was carried out on these lakes to prepare baseline information on water quality, floristic and structural features of adjoining forest vegetation, socio-cultural importance and threats to help support their sustainable use. The study was conducted in March (pre-monsoon) and November 2008 (post-monsoon). A significant seasonal variation (p≤0.05) in the physico-chemical properties of the lake waters was recorded. Adjoining forests of Mudka contained 23 species at canopy, 13 species at shrub and 27 species at herb strata, while that of Bedkot had 31 species of plants at canopy, 9 species at shrub and 37 species at herb strata, and Jhilmila had 23 species at canopy, no species at shrub and 47 species at herb strata. The most frequently seen trees were Mallotus philippensis and Shorea robusta in the forests surrounding Mudka and Bedkot whereas Jhilmila's surrounding forests contained S. robusta, Semicarpus anacardium, Syzygium cumini and Anogeisus latifolius. At shrub stratum, in the forest surrounding Mudka, M. philippensis had the highest density (633.3 no./ha) whereas in case of Bedkot, Solanum erianthum had the highest density (144.0no./ha). At herb stratum, the species with highest coverage at the respective forest were Ageratum conyzoides (7.14%), Viburnum contifolium (8.5%) and Themeda triandra (16.09%). All three lakes possessed cultural values as the people visited the sites as pilgrimage and observed religious festivals mostly on full moon. However, unsustainable consumption of the resources from the surrounding forests is adding pressure on the condition of the lakes. Further, the area and depth of the lakes are diminishing due to the massive amount of sediments from fragile Churiya hills. This calls for the urgent conservation and good management of the lakes. Key words: conservation; forest characteristics; seasonal variation; socio culture DOI: 10.3126/njst.v11i0.4142Nepal Journal of Science and Technology 11 (2010) 181-188

Food Habits of Hand-Reared Caribou Rangifer tarandus L. in Newfoundland

Three caribou Rangifer tarandus were hand-reared from birth till 3-years-of-age. The food preferences of these animals was determined by allowing them to feed ad lib. (4 hours per week throughout 1 year) in natural, ungrazed habitats and recording the seconds of feeding time per plant species. The caribou took a wide variety of plants but appeared to prefer green growing plants. They appeared unable to detect ground lichens in the absence of a shrub stratum through 18 cm of snow.

Dimension and Production Relations of Trees and Shrubs in the Brookhaven Forest, New York

Extensive tracts of oak-pine forest grow on the level, sandy soils of glacial outwash derivation on Long Island, New York (Conard 1935). The forests are small and unimpressive to a forester. In mature stands older and larger pines (Pinus rigida Mill.) rise above a canopy of oaks (Quercus alba L., Q. coccinea Muench, and few Q. velutina Lam. and other species). The canopy is open, with light intensity below the trees sufficient to support a shrub stratum of small Vacciniaceae of high coverage (Reiners 1965). These forests are floristically related to the pine forests of New Jersey and the Coastal Plain southward, and to the pine heaths of the Great Smoky Mountains (Whittaker 1956), with which they share a number of major species. All of these forests have been subject to repeated fires, and dense, immature successional stands with Pinus rigida and scrub oak (Qtiercus ilicifolia Wang.) occur over extensive areas. The small size of the trees at Brookhaven has facilitated development of a system of detailed dimension analysis useful for various problems related to forest volume, biomass, production, surface and nutrient circulation. The methods are developments from forest measurements used by Burger (1929, 1953), Boysen Jensen (1932), Moller (1945, 1947), Ovington (1957), Ovington & Madgwick (1959a, b) and others, but are intended to advance beyond those measurements in important respects. They use the wood rings and bud-scale scars which mark annual increments of growth in some climates for assessment of current net production and nutrient movement in forests. They are designed specifically to deal with the complexities of many-aged stands including climaxes, as distinguished from plantations. The work is part of a long-term study of various aspects of the Brookhaven forest as an ecosystem, a study which includes experimental irradiation of a segment of the forest with gamma radiation from a cesium soturce (Woodwell 1962, 1965). The plants of the present study have been taken from the forest outside the area of radiation effects. Included in this report are results of dimension analysis of trees and shrubs as a first phase of the research on bio mass, production and nutrient circulation.

Ecology of a Northeastern Outlying Stand of Pinus Flexilis

A small stand (208 acres) of limber pine (Pinus flexilis) occurs in association with Juniperus scopulorum in southwestern North Dakota, about 12 miles north of Marmarth, and at an average elevation of 2,850 feet in typical "Badlands" terrain. Both P. flexilis and J. scopulorum are reproducing well, although the pine shows greater relative density and a higher frequency index in the larger size classes, indicating site dominance. The total foliage cover of the shrub stratum was only 7.6% however, the dominance of one shrub, Rhus trilobata is of particular importance. From increment borings of 50 Pinus flexilis trees the oldest tree was 238 years old at breast height. The greatest diameter was 17.2 in. at breast height, and the greatest height was 26 ft. The average diameter growth was .11 in. per year. The trees growing on the knolls showed the greatest growth rate. Sectioned trunks showed a definite pattern of radial eccentricity, with growth the least on the south side and increasing toward the northeast side. This small stand of Pinus fexilis may have been seeded, either accidentally or purposely, by Indians camping in the area before settlement by the white man.

Virgin Hemlock Forest Segregates in the Joyce Kilmer Memorial Forest of Western North Carolina

1. Two segregates can be readily distinguished in the virgin hemlock forest which occupies the flats and lower slopes in the Joyce Kilmer Memorial, a part of the Nantahala National Forest in western North Carolina. The first of these types, restricted to the flats and lowermost parts of the slopes along the streams, is characterized by a dense undergrowth of Rhododendron and a sparse herb layer. The other type, occurring higher up on the slopes, has a very open shrub stratum but a fairly dense and diversified herb layer. 2. Tsuga canadensis is the dominant tree species in both types, with Fagus grandifolia, Tilia americana, Betula lenta, Fraxinus pennsylvanica, and Halesia carolina as almost constant associates. Liriodendron tulipifera and Acer saccharum are more abundant in the Herb type, while Betula lutea is restricted to the Rhododendron type. The total tree density is lower, but the BA is greater in the latter type (60% more). Hemlock reproduction is about equivalent at the seedling stage, but saplings are considerably less numerous in the Rhododendron type. Age-diameter relationships in hemlock indicate that the species is able to stand suppression relatively well but not so long as some other climax conifers. 3. Herbs which are constants for both types include Mitchella repens and Viola rotundifolia, observed in every stand, and Tiarella cordifolia, Laportea canadensis, Trillium sessile, Dryopteris spinulosa var. intermedia, and Oxalis montana, with lower presence values. In spite of their general distribution, these are the important herbs of the Rhododendron type. The characteristic herbs of the Herb type are therefore those numerous additional species which appear. Among these, Carex plantaginea, Medeola virginiana, Adiantum pedatum, and Polygonatum pubescens are exclusive and constant. 4. The soils are very similar under both types. They are sandy loams with an A-C profile, good incorporation of organic matter, and good structure. The better growth of dominant components in the Rhododendron type is attributed to better soil-water relations, owing to topography and possibly to microclimatic differences. 5. A comparison is made with the two types (Rhododendron and Polycodium) of virgin hemlock forest found in Ravenel's Woods. Differences in species composition and in growth of hemlock lead to the conclusion that there are at least four types of hemlock cove forest, which are believed to be relic association-segregates of Braun's Tertiary Mesophytic Climax. The considerably greater BA of hemlock in Ravenel's Woods and the differences in associated species are attributed to differences in general climate (higher precipitation and lower temperature). 6. The sampling method used in this study is discussed. It consists of a strip random sampling in which each strip is in turn systematically subsampled at a 50% intensity.

Notes on Some Plant Communities in the Northern Mackenzie Basin, Canada

Selected examples illustrating a number of the plant communities in the Mackenzie District between 60⚬50' N. Lat. and 69⚬20' N. Lat., excepting mesic forest sites, are described. Five distinct moist tundra communities on sand, determined by exposure and drainage conditions, form an intimate mosaic. In the transition spruce forest farther southeast, a very large type of raised-center polygon has the center dominated by a flat stand of Cladonia and Cetraria, dotted with hummocks of Sphagnum and low ericaceous shrubs. An inland saline meadow exemplifies a habitat unique in this region. Bogs with true floating mats rarely occur; consequently, Sphagnum is far less important in low wet sites than Camptothecium, Aulacomnium, and Dicranum. Where frequent stream flooding brings in silt, and on pond borders, reed-marsh communities are very prevalent. Their dense emergent growth, dominated by Carex aquatilis, C. rostrata, or Equisetum limosum, initiates peat accumulation. Communities upon deeper organic deposits include (a) tussock-sedge low-willows, (b) ground-birch muskeg, (c) tall clumped willows, and (d) closed stands of tall willow and paper birch. These are not all related successionally. The black spruce and tamarack dominate mature bogs in both the northern transition forest of the Pre-Cambrian Shield and the Mackenzie Lowlands region. Such bogs have a shrub stratum of low, mostly ericaceous chamaephytes, and a ground cover of non-Sphagnum mosses and Equisetum scirpoides.