Forest Stature Research Articles

Patterns of Mangrove Forest Structure and Soil Nutrient Dynamics along the Shark River Estuary, Florida

The basal area and productivity of managrove wetlands are described in relation to selected soil properties to understand the general pattern of optimum forest stature at the mouth of estuaries in the Everglades, such as the Shark River Slough, Florida (U.S.). The basal area of mangroves decreases from 40.4 m2 ha−1 and 39.7 m2 ha−1 at two stations 1.8 km and 4.1 km from the estuary mouth to 20.7 m2 ha−1 and 19.6 m2 ha−1 at two sites 9.9 km and 18.2 km from the mouth, respectively. The gradient in basal area at these four sites is mostly the result of approximately 34 yr of growth since Hurricane Donna. Wood productivity is higher in the lower estuary (10.7 Mg ha−1 yr−1 and 12.0 Mg ha−1 yr−1) than in the upper estuary (3.2 Mg ha−1 yr−1 and 4.2 Mg ha−1 yr−1). Porewater salinity among these four mangrove sites during seasonal sampling in 1994 and 1995 ranged from 1.6 g kg−1 to 33.5 g kg−1, while sulfide was generally<0.15 mM at all sites. These soil values indicate that abiotic stress cannot explain the decrease in forest structure along this estuarine gradient. Concentrations of nitrogen (N) and phosphorus (P) are more closely related to patterns of forest development, with higher soil fertility at the mouth of the estuary as indicated by higher concentrations of extractable ammonium, total soil P, and available P, along with higher ammonium production rates. The more fertile sites of the lower estuary are dominated by Laguncularia racemosa, whereas the less fertile sites in the intermediate and upper estuary are dominated by Rhizophora mangle. Relative N mineralization per unit of total N is higher in the lower estuary and is related positively to concentrations of available P, indicating the importance of turnover rates and nutrient interactions to soil fertility. Concentrations of Ca-bound P per volume soil in the lower estuary is 40-fold higher than in the upper estuary, and along with an increase in residual P in the upper estuary, indicate a shift from mineral to organic P along the estuarine gradient. Mineral inputs to the mouth of Shark River estuary from the Gulf of Mexico (rather than upland inputs) apparently control the patterns of mangrove structure and productivity.

On the causes of gradients in tropical tree diversity

1 The number of woody species in tropical forests tends to increase with precipitation, forest stature, soil fertility, rate of canopy turnover and time since catastrophic disturbance, and decrease with seasonality, latitude, altitude, and diameter at breast height (d.b.h.). 2 A model is presented to account for these trends. Novel hypotheses include how increased rainfall and substrate fertility, and decreased seasonality, might (i) increase attacks by natural enemies, and thus the overall level of density-dependent plant mortality; (ii) increase shade tolerance, canopy turnover, and stem density of the species-rich understorey; and (iii) increase reliance on relatively sedentary forest-interior birds for seed dispersal, fostering high rates of speciation in understorey genera. 3 High rainfall and low seasonality in the tropics favour two key groups of natural plant enemies – insects and fungi – that are directly responsible for promoting high rates of density-dependent plant mortality. Lower rainfall, greater seasonality, soil infertility, or unfavourable rooting conditions favour greater allocation to anti-herbivore defences, and thus lead to lower rates of such mortality and thence to lower tree diversity. The increased number of individuals on rainier sites is a minor contributor to increased tree diversity, accounting for only about 17% of the 8.3-fold increase with rainfall in the lowland Neotropics. 4 Predictions of the model are consistent with many ecological patterns of variation in tropical tree diversity within regions, and may help explain the decrease in tree diversity with elevation and the accompanying decrease in horizontal patchiness (within-habitat β diversity). 5 Random drift over evolutionary time in the relative effectiveness of density-dependent control of individual tree species by specialized natural enemies may better account for the observed distribution of tropical tree abundance than a random walk of species abundance through ecological time.

Structure, composition and species diversity in an altitude-substrate matrix of rain forest tree communities on Mount Kinabalu, Borneo

We studied forest structure, composition and tree species diversity of eight plots in an environmental matrix of four altitudes (700, 1700, 2700 and 3100 m) and two types of geological substrates (ultrabasic and non-ultrabasic rocks) on Mount Kinabalu, Borneo. On both substrate series, forest stature, mean leaf area and tree species diversity (both ≥ 4.8 cm and ≥ 10 cm diameter at breast height [dbh]) decreased with altitude. The two forests on the different substrate series were similar at 700 m in structure, generic and familial composition and tree species diversity, but became dissimilar with increasing altitude. The decline in stature with altitude was steeper on the ultrabasic substrates than on the non-ultrabasic substrates, and tree species diversity was generally lower on ultrabasic substrates than on non-ultrabasic substrates at ≥ 1700 m. The forests on non-ultrabasic substrates at higher altitudes and those on ultrabasic substrates at the lower altitudes were similar in dbh versus tree height allometry, mean leaf area, and generic and familial composition at ≥ 1700 m. These contrasting patterns in forest structure and composition between the two substrate series suggested that altitudinal change was compressed on the ultrabasic substrates compared to the non-ultrabasic substrates. Tree species diversity was correlated with maximum tree height and estimated aboveground biomass, but was not with basal area, among the eight study sites. We suggest that forests with higher tree species diversity are characterized by greater biomass allocation to height growth relative to trunk diameter growth under more productive environment than forests with lower tree species diversity.

Comparisons of Structure Among Mixed Dipterocarp Forests of North-Western Borneo

Relationships between lowland rain-forest structure, dynamics and site conditions were examined by the establishment of plots and profile diagrams within mature-phase forest at 13 sites and with permanent plots at three of these sites where trees have been enumerated over 20 years. Most forest structural measures were intercorrelated but forest stature was uncorrelated with HCl-extractable soil nutrient concentrations and was apparently related to topography, soil depth and soil water. The relationship between diameter and height varied between forests and was correlated with HCl-extractable P and Mg for dry-land sites (...)

Structure and dynamics of a tropical dry forest in Ghana

Forest under low rainfall (averaging 745 mm yr- 1) on the Shai Hills in S.E. Ghana has redeveloped following cessation of farming in the 1890s. Forest stature is low, with a canopy at about 11 m, principally of three species, Diospyros abyssinica, D. mespiliformis and Millettia thonningii. Drypetes parvifolia and Vepris heterophylla are common understorey trees. Twelve species of woody liane were recorded. Species of thicket vegetation in the area were also present at low density. Most species are evergreen. Tree mortality averaged 2.3~o yr ~ and exceeded recruitment (1.5~ yr-1). Differences between species in mortality and recruitment were pronounced: canopy species showed a small decline in density; understorey species increased markedly and the thicket species declined. Seed production was very variable, but seedling establishment was very poor for all species. Seedling mortality was high (11 ~o yr - 1 ) especially for small seedlings. These population trends probably represent the latter stages of succession of forest regrowth after farming about 100 years ago. Compared with tropical rain forest, Shai Hills forest has similar relative tree diameter growth (1-3.5 ~o yr- 1), mortality and recruitment rates, and small-litter fall (5.52 t ha-1 yr- 1). Shai Hills forest differs from rain forest by its short stature, relatively few (evergreen) tree species, poor regeneration from seed, high soil nutrient status and low rainfall. Similar forests have been reported in east Africa and in parts of New Guinea. Abbreviations: dbh = diameter at breast height (1.3 m), gbh = girth at breast height. Nomenclature: follows Hutchinson & D alziel (1954-72), except where authorities are given.

Variability of Mangrove Ecosystems along the Brazilian Coast

Brazilian mangroves extend from 4°30′N to 28°30′S, varying greatly in growth form, species distribution patterns, and stand structure, in spite of a limited floristic diversity. We divided the Brazilian coastline into eight units, within which physiographic and climatic conditions are relatively uniform, and described mangrove occurrence, species distribution and structural attributes characteristic of each segment. In general, greates mangrove coverage and greatest forest stature are found in areas with a large surplus of rainfall over potential evapotranspiration and macrotidal regimes. An exception was the segment containing the mouth of the Amazon river, where freshwater systems dominate over brackish or marine associations. We believe that the variability in species associations and the dominance of each in a given environment is predominantly determined by the characteristics of the landforms that can be colonized by each species in a given region. The type, size, and frequency of occurrence of available landforms is a function of the particular mix of fluvial, tidal, and wave energies found in a region. Different species colonize these sites depending on their adaptations and edaphic preferences. Climate affects mangrove colonization and growth. We suggest that Brazilian mangroves play a minor role in modifying the geomorphic setting; the spatial arrangement of the various forest types is a response to the underlying topography and edaphic conditions, and to the constraints imposed by climatic and hydrologic factors. The spatial arrangement of species does not necessarily show successional processes, but may be the result of direct and differential colonization on appropriate substrates.

Avian species richness in tropical South America

The most extensive biomes of tropical South America, in particular the Amazonian Forest, are the richest in total number of bird species and number of endemic species. On the other hand, relative diversity of species and endemic species (number of species per 10,000 km2 of biome) is highest in areally restricted and/or isolated biomes like the Pacific Colombian‐Ecuadorian Forest, the Andean Montane Forest and the Pantepui Montane Forest. Local species richness is highest in Amazonia, especially in upper Amazonia where 400 to 430 forest bird species (over 500 species, if water‐birds and migrants are included) occur at individual localities. Very high species richness characterizes also the avifaunas of the forests which extend, from upper Amazonia, far eastward in the hilly country both to the north and to the south of the central Amazon Valley. By contrast, local species diversity is considerably reduced in central Amazonia. The avifaunas at individual Amazonian localities are five to six times richer in species than north Temperate Zone avifaunas. “Excess” tropical species richness is explained by several factors, viz. tighter species packing, additional tropical guilds and increased size ranges of tropical guilds. Interspecific competition has a prominent role in determining the range limits of numerous parapatric bird species in the lowlands as well as along the slopes of the Andes. The total number of forest bird species at individual sites decreases with elevation in the Andes closely paralleling a similar trend of decreasing forest stature. During Cenozoic time (Tertiary‐Quaternary), tropical and high latitude avifaunas have been affected by similar vicariance processes (which probably caused extensive faunal diversification), viz. paleogeographic changes in the distribution of land and flooded areas, separation by broad rivers, and climatic‐vegetational fluctuations (leading to the isolation of restricted populations in temporal ecological refugia).

ECOLOGICAL CONSTRAINTS ON WOOD DENSITY IN A TROPICAL MONTANE RAIN FOREST

In a Costa Rican tropical lower montane rain forest the wood densities of canopy tree species are related to the windiness of their preferred habitats, and to their abilities to tolerate shade. Shade‐intolerant species tend to have less dense wood than shade‐tolerant species from the same habitat. Species characteristic of windy sites tend to have denser wood than species characteristic of sheltered habitats. Stand mean wood density, the average of species’ wood densities weighted by their proportional contributions to stand basal area, increases with exposure to the wind. These trends in wood density should at least partially counteract the damaging effects of wind on exposed sites. Since investment in wood must come at the expense of growth elsewhere, such trends in wood density may help explain the small stature of elfin forest and montane thicket formations in tropical mountains.

Inputs and Cycling of Mineral Nutrients in a Coastal Subtropical Eucalypt Forest

(1) Nutrient budgets have been estimated for eleven elements in a Eucalyptus signatadominated forest 15 m tall, growing on infertile podzolized sands on North Stradbroke Island in subtropical Australia. (2) No single component of the ecosystem rainfall, salt spray, soil or litter mass is sufficient to provide all the net annual nutrient demands of the forest. Although recirculation of mineral nutrients is therefore essential to the maintenance of the forest, turnover of nutrients from the vegetative standing stock is slow relative to deciduous forests on more fertile soils. (3) Rainfall and salt spray provide significant inputs to the forest, especially of chloride, manganese, nitrogen and sodium. Substantial quantities of mineral nutrients from salt spray are subsequently transferred to the forest floor with throughfall (68% of rainfall volume) and stem-flow (677%), but these evergreen trees appear more resistant to leaching losses than deciduous trees observed in temperate regions. (4) The forest dominant exhibits advantageous patterns of nutrient flow relative to its major competitors, by assimilating a smaller amount of nutrients relative to its mass, and by channelling more salt-laden waters to its roots via stem-flow. (5) The decrease in forest stature on older dunes on North Stradbroke Island (500 000 years old or more) may be due in part to gradual loss of nutrients from the ecosystem. Supplies of exchangeable potassium and available phosphorus, for example, are very low relative to uptake demands in the younger pyric-climax forest studied.

Bird Species Diversity on an Andean Elevational Gradient

This paper analyzes patterns of bird species diversity on an elevational transect of the Cordillera Vilcabamba, Peru. Major changes in climate and vegetation are encompassed by the transect which extended from the Apurimac Valley floor at 500 m to the summit ridge of the range at &gt;3,500 m. Four vegetation zones are easily discerned–lowland rain forest, montane rain forest, cloud forest, and elfin forest. In progressing upwards there is a monotonic trend toward decreasing canopy stature and reduced number of plant strata. The vegetation gradient provided the opportunity to examine the relation between bird species diversity and habitat complexity in an entirely natural setting. The decrease in forest stature with elevation was closely paralleled by decreasing avian syntopy (the total number of bird species cohabiting the forest at a given elevation). Bird species diversity was shown to be highly correlated with foliage height diversity, using either four or five layers in the foliage height diversity calculation (r = .97), and less well correlated using three layers, as defined previously by MacArthur (r = .84). At this superficial level the trend in bird species diversity seemed to be adequately explained as a response to the vegetation gradient. This preliminary conclusion was found to be illusory when the elevational trend in syntopy was reexamined separately for three major trophic subdivisions of the fauna. The number of insectivores decreased 5.2—fold from the bottom to the top of the gradient, frugivores decreased by a factor of 2.3, and nectarivores showed no change. It was now clear that the diversity in each of these trophic categories was responsive to environmental influences other than, or in addition to, the gradient in habitat structure. Additional factors implicated by the available evidence are competitive interactions with other taxa at the same trophic level, changing composition of the resource base as a function of elevation, and declining productivity at high elevations. Analysis of netted bird samples revealed an unexpected diversity maximum in the lower cloud forest zone. The immediate cause of this was a relaxation of the vertical stratification of foraging zones, such that an anomalously large fraction of the species present entered the nets. The excess diversity was found to consist almost entirely of insectivores. Several factors appear to contribute to the ultimate causes of the diversity maximum: greater patchiness of the montane forest due to the rugged topography, a higher density of foliage near the ground, and possibly increased resource productivity. A correlation between diversity and density in the netting results suggested a causal connection mediated via resource levels. The conclusion in that diversity is a complex property that is responsive to many types of influences beyond simply the structure of the habitat.