Undergrowth

About: Undergrowth is a research topic. Over the lifetime, 795 publications have been published within this topic receiving 11911 citations. The topic is also known as: understorey & underbrush.

Influence of Selective Logging on Bird Species Diversity in a Guianan Rain Forest

Abstract: The composition and structure of the bird com- munity were investigated in French Guiana (northeastern Amazonia) I year and 10 years after selective logging and compared with bird community composition and structure in undisturbed primary forest A point-count method was used in which 937 0.25-ha sample quadrats were censused for 20 minutes each. Whereas logging removed little more than 3 trees/ha, 38% of the forest undergrowth was destroyed and a higher proportion of the canopy was opened or dam- aged. An overall 27-33% decrease of species richness, fre- quency, and abundance occurred after logging with a less marked decline of diversity and evenness indices, a substan- tial increase in the proportion of dominant species, and a 45% difference in species composition, weighed by fre- quency, between logged and undisturbed forest communi- ties. Forty-two percent of the species from the primary forest decreased sharply or disappeared after logging and only 34% increased or remained unchanged. Microhabitat selection was the main correlate of sensitivity to disturbance. Most affected by logging were species associated with the under- story of tall mature stands especially terrestrial species, members of mixed flocks, and solitary sallying insectivores, all of which decreased by 70% to over 90%. Most birds as- sociated with canopy, small gaps, and vine tangles declined by only 10-30%. Small frugivores and species associated with clearings or edges increased. Among other factors, phys-

Forest Dimensions and Production in the Great Smoky Mountains

Abstract: Samples based on stand measurements and borings of trees, and clippings of undergrowth, were taken from 24 forests and forest heaths in the Great Smoky Mountains. Samples were taken also from heath balds and grassy balds and a California coastal redwood forest. Available information on ratios and regressions of forest tree and shrub dimensions were used to estimate stand biomass and net annual production above ground. Mature climax forests of mesic environments below 1,400 m are characterized by: wood basal areas of 50—64 m2/ha and basal area increments of 0.3—0.6 m2/ha/yr, stem wood volumes (parabolic estimate) of 750—900 m3/ha and estimated wood volume increments of 530—590 cm3/m2/yr, aboveground biomasses of 500—610 t/ha and aboveground net annual productions of 1,000—1,200 g/m2, and biomass accumulation ratios of 40—50. These and other stand dimensions decrease along the moisture gradient to xeric sites and decrease toward higher elevations. Above—ground net annual productions of forest heaths of xeric slopes and forests of highest elevations are 420—650 g/m2. Evergreen spruce—fir forests are more productive than deciduous forests above 1,400 m. Among mesic high—elevation beech and fir forests, production is higher on south slopes than on north slopes. Production and biomass of steady—state forests were estimated from multiple correlations using elevation and weighted—average index of site moisture as independent variables. Apart from some high—elevation stands, production is not significantly correlated with evergreen vs. deciduous foliage or with direction of exposure affecting incident sunlight. When unstable stands are excluded, production and biomass are strongly correlated with each other and with mean tree height and other stand dimensions. A wide range of temperate—zone climax forests of relatively favorable environments have net annual productions above and below ground of 1,200—1,500 g/m2. Productions of stable closed heath balds are lower, 700—1,200 g/m2, but productions of heath balds and less productive forests overlap broadly. Production of unstable forests, both successional stands and those opened by removal of large trees, exceeds that of steady—state forests of similar environments. Canopy coverage and light penetration are not strongly correlated with forest production. Light penetration to the herb stratum ranges from 1.4—7.0% of incident sunlight in more open forests and forest heaths to 0.3—0.9% in cove forests. Foliage live/dry ratios decrease along the moisture gradient from mesic to xeric stands–from about 5.0 to 2.8 in shrub clippings, 7.6 to 2.8 in herb clippings. Undergrowth production and biomass are trivial compared with the tree stratum in many forests. Shrub production is generally higher in xeric environments and is 20—145% of tree production in forest heaths. Herb production is higher at the extremes of the moisture gradient (exceeding 3% of total aboveground production in mesic and in open xeric stands) than in intermediate stands (below 1%). Apart from such differences, her and thallophyte biomass and production increase with elevation to maximum values in fir forests of the highest summits.

Changes in bird communities following conversion of lowland forest to oil palm and rubber plantations in southern Thailand

Abstract: This paper describes changes in bird communities following the conversion of lowland forest to commercial oil palm and rubber plantations. Conversion of forest to plantations resulted in a reduction in species richness of at least 60%, with insectivores and frugivores suffering greater losses than more omnivorous species. Of the 128 species recorded across all habitats, 84% were recorded in forest, and 60% were recorded only in that habitat. Of the 16 Globally Threatened or Near-Threatened species recorded in the study, 15 were recorded only in forest. Species occurring in plantations were significantly more widespread in Thailand than species recorded only in forests and had a tendency towards smaller body size. Species richness in plantations was unaffected by plantation age or distance from nearest forest edge, but was significantly greater where undergrowth was allowed to regenerate beneath the crop trees. Bird communities in oil palm and rubber plantations were extremely similar, and there was a strong positive correlation across species in their relative abundance in each plantation type. The results indicate that a high proportion of species formerly present in the region are unable to adapt to conversion of forest to oil palm and rubber plantations, resulting in large losses of bird species and family richness and the replacement of species with restricted ranges and high conservation status by those with extensive ranges and low conservation status. Initiatives that reduce pressure to clear new land for plantations, for example by increasing productivity in existing plantations and improving protected area networks, are likely to be more effective in conserving threatened forest birds than initiatives to improve conditions within plantations, though both should be encouraged.

Habitat Selection and Environmental Gradients: Dynamics in the "Stable" Tropics

Abstract: Both physical and biological processes shape species assemblages (communities) For birds, vegetation structure has long been assumed to be the dominant factor in habitat selection, especially along successional gradients While vegetation may be important as a proximate factor, detailed knowledge of ultimate factors governing habitat selection is required Gradients of microcli- mate, especially temperature and moisture, may be such an ultimate factor through direct physiolog- ical pressures on birds or indirectly through distribution and availability of food resources We doc- umented the existence of gradients of both vegetation structure and microclimate in the undergrowth of seasonally humid forest in central Panama To assess the relative importance of these gradients in shaping local avian distribution, birds were netted in undergrowth (up to 3 m above ground) during 2-wk periods in dry (March) and wet (July) season for 4 yr (1979-1982) A total of 3037 captures of 95 species was recorded during that period Although patterns of species richness and capture rate are relatively simple, species composition and other assemblage attributes are complex and difficult to interpret without careful evaluation of the dynamics of individual species The variety of activity patterns exhibited by birds on moisture and vegetation gradients clearly demonstrates the complexity of dynamics that affect assemblage attributes Overall, birds are more active at dry sites and at sites with intermediate shrub density However, activity levels change with time, suggesting that avian activity reflects a dynamic process of habitat selection Though no food resource data are available at present, the general pattern of habitat use on diurnal time scales for several guilds suggests that birds track microclimatic optima for physiological reasons Habitat selection processes are both ex- tremely complex and variable in time and space for the avifauna of tropical forest undergrowth Indeed, the scale of study in space and time is important in determining the conclusion of a study The recent perception of a dichotomy between equilibrium (deterministic) and nonequilibrium (stochastic) assemblages is undermined by these results Habitat selection in birds produces dynamic (nonequilibrium) assemblages in space and time However, these are not stochastic assemblages Each species seeks habitat optima in the context of current environmental conditions on diurnal, seasonal, and between-year time scales Thus, instead of nonequilibrium and stochastic assemblages, the avifaunas of tropical forest undergrowth are nonequilibrium but relatively predictable from knowl- edge of current environmental conditions

Present Composition of Some Stands of the Former Oak-Chestnut Forest in the Southern Blue Ridge Mountains

Abstract: Chestnut blight, caused by the Ascomycete Endothia parasitic, was first discovered in the United States in 1904 in New York City and spread rapidly northeast, west, and southwest. By 1910 it had spread as far south as southeastern Pennsylvania and in 1920 the "80 per cent infection zone" extended along the Blue Ridge mountains to central Virginia. In 1926 local infections had been reported in western North Carolina, northern Georgia, and northwestern South Carolina. In 1930 Gravatt and Gill reported that infection in western North Carolina showed eighty to ninety-nine per cent. Owners of chestnut timber in the newly infected areas of the Carolinas and Georgia quickly cut as much of that lumber as possible. Most of the remaining chestnut (Castanea dentata)lt trees, dead or alive, have been gradually removed, until now, twenty years after the blight reached its peak, there are only a few scattered ghost trees left to indicate the once relatively great importance of the species. The removal of a species which made up more than 40 per cent of the overstory trees in the climax forests of an area would certainly be expected to produce changes in the composition of the vegetation of the region. It is possible that species co-dominant with chestnut would advance in rank and become the most important species in the new climax. It is also possible, as Braun (1950) suggests, that the opening of the canopy, the release of undergrowth trees, and the resulting changes in the humus layer may cause