Single Tree Species Research Articles

The effect of single tree species on soil microbial activities related to C and N cycling in the Siberian artificial afforestation experiment

The effects of grassland conversion to forest vegetation and of individual tree species on microbial activity in Siberia are largely unstudied. Here, we examined the effects of the six most commonly dominant tree species in Siberian forests (Scots pine, spruce, Arolla pine, larch, aspen and birch) on soil C and N mineralization, N2O-reduction and N2O production during denitrification 30 years after planting. We also documented the effect of grassland conversion to different tree species on microbial activities at different soil depths and their relationships to soil chemical properties. The effects of tree species and grassland conversion were more pronounced on N than on C transformations. Tree species and grassland conversion did significantly alter substrate-induced respiration (SIR) and basal respiration, but the differences were not as large as those observed for N transformations. Variances in SIR and basal respiration within species were markedly lower than those in N transformations. Net N mineralization, net nitrification, and denitrification potential were highest under Arolla pine and larch, intermediate under deciduous aspen and birch, and lowest beneath spruce and Scots pine. Tree species caused similar effects on denitrification potential, net N mineralization, and net nitrification, but effects on N2O reduction rate were idiosyncratic, indicating a decoupling of N2O production and reduction. We predict that deciduous species should produce more N2O in the field than conifers, and that Siberian forests will produce more N2O if global climate change alters tree species composition. Basal respiration and SIR showed inverse responses to tree species: when basal respiration increased in response to a given tree species, SIR declined. SIR may have been controlled by NH4 + availability and related therefore to N mineralization, which was negatively affected by grassland conversion. Basal respiration appeared to be less limited by NH4 + and controlled mostly by readily available organic C (DOC), which was higher in concentration under forests than in grassland and therefore basal respiration was higher in forested soils. We conclude that in the Siberian artificial afforestation experiment, soil C mineralization was not limited by N.

Arthropods on islands: colonization, speciation, and conservation.

Islands have traditionally been considered to be any relatively small body of land completely surrounded by water. However, their primary biological characteristic, an extended period of isolation from a source of colonists, is common also to many situations on continents. Accordingly, theories and predictions developed for true islands have been applied to a huge array of systems, from rock pools, to single tree species in forests, to oceanic islands. Here, we examine the literature on islands in the broadest sense (i.e., whether surrounded by water or any other uninhabitable matrix) as it pertains to terrestrial arthropods. We categorize islands according to the features they share. The primary distinction between different island systems is "darwinian" islands (formed de novo) and "fragment" islands. In the former, the islands have never been in contact with the source of colonists and have abundant "empty" ecological niche space. On these islands, species numbers will initially increase through immigration, the rate depending on the degree of isolation. If isolation persists, over time species formation will result in "neo-endemics." When isolation is extreme, the ecological space will gradually be filled through speciation (rather than immigration) and adaptive radiation of neo-endemics. Fragment islands are fundamentally different. In these islands, the ecological space will initially be filled as a consequence of connection to the source of colonists prior to insularization. Species numbers will decrease following fragmentation through the process of relaxation. If these islands become more isolated, species will eventually arise through relictualization with the formation of "paleo-endemics." Given sufficient time, this process can result in generic level endemism on ancient fragment islands, a phenomenon well illustrated in Madagascar and New Zealand. Recognizing the distinction between the different kinds of islands is fundamental for understanding emerging patterns on each, in particular speciation, biodiversity (e.g., neo-endemics versus paleo-endemics), and conservation (e.g., naiveté in interactions with alien species).

Impact of single species tree plantations on nutrient cycling in West Africa

SUMMARY This paper evaluates the impact of plantation monocultures of fast-growing exotic species and indigenous tree species on nutrient cycling in West Africa. The rates of nutrient uptake and recycling to the soil vary with tree species and ecological zones. In general, single species tree plantations immobilize soil nutrients faster and return less nutrients to the soil than native forest and savanna vegetation. Hence, they deplete soil nutrients. Plantations of an indigenous species, Terminalia ivorensis, exert less deleterious effects on soil nutrient status than exotics such as teak and gmelina. Owing to their effects in destabilising the nutrient cycle in forest and savanna ecosystems, the plantation monocultures of fast-growing tree species are not likely to be sustainable in the long term. The widespread adoption of plantation forestry as an alternative to the natural regeneration of native forests as a strategy for increasing the wood resources of humid tropics is, therefore, indicative of an uncritical acceptance of the view that monocultural tree plantations are sustainable. There is need for caution in the rush to convert native ecosystems, especially rain forests, into plantations of fast-growing exotic trees.

NATURAL SELECTION ON SEED-BEETLE EGG SIZE IN NATURE AND THE LABORATORY: VARIATION AMONG ENVIRONMENTS

The size of eggs that evolves within a population will in theory reflect a balance between selection for large eggs and for increased fecundity. Theory also predicts that the intensity of selection for large eggs (via effects of egg size on progeny survival and growth) increases as environmental quality decreases. I took advantage of variation in seed quality among individuals within one population of a single tree species, Cercidium floridum, to (1) quantify variation in the magnitude of selection on seed beetle (Stator limbatus) egg size, and (2) test the hypothesis that the intensity of selection on egg size increases with decreasing host plant quality. The proportion of larvae that failed to penetrate the seed coat varied substantially among individual trees and was used as a measure of seed-coat resistance. The intensities of selection (i) on egg size also varied among trees. This measure i was positively correlated (among trees) with the resistance of seed coats to penetration by larvae of S. limbatus, indicating that that selection is greatest on trees upon which larval survivorship was lowest. This study thus demonstrates that the intensity of selection on egg size increases as larval environmental quality decreases.

Soil carbon, microbial activity and nitrogen availability in agroforestry systems on moderately alkaline soils in northern India

The present investigation aimed to analyze the role of agroforestry systems in improving soil organic matter status, microbial activity and nitrogen availability with a view to effective management of the fertility of moderately alkaline soils. The study site was located at Karnal (29°59′N, 76°51′E, 250 m.s.l.) and the systems were characterized by a rice–berseem crop rotation; agrisilvicultural systems of Acacia, Eucalyptus and Populus along with rice–berseem and single species tree plantations. Soil microbial biomass was measured using the fumigation extraction technique and nitrogen mineralization using the aerobic incubation method. Microbial biomass carbon was low in rice–berseem crops (96.14 μg g −1 soil) and increased in soils under tree plantations (109.12–143.40 μg g −1 soil) and agrisilvicultural systems (133.80–153.40 μg g −1 soil). Microbial biomass was higher by 42% (microbial C) and 13% (microbial N) in tree-based systems as compared to monocropping. Microbial biomass immobilized 2.32–2.57% of the soil carbon and 4.08–4.48% of the soil nitrogen in tree-based systems. Soil carbon increased by 11–52% due to integration of trees along with the crops for 6–7 years. Cropland management practices and tree species influenced CO 2-C production, biomass specific respiratory activity, and nitrogen mineralization rates. In tree-based systems, soil inorganic N levels were higher by 8–74% and nitrogen mineralization by 12–37% as compared to monocropping. On the basis of increased soil organic matter content, enlarged soil microbial biomass pool and greater soil N availability, agrisilvicultural systems have been found to be ecologically sustainable land-use systems for utilizing moderately alkaline soils.

Nitrogen Turnover in Forest Floors of Coastal Douglas-Fir at Sites Differing in Soil Nitrogen Capital

Nitrogen cycling is generally considered to be more rapid on sites with high availability of N; this is usually associated with differences in tree species composition. We tested whether N cycling in stands of a single tree species increased with increasing mineral soil nitrogen capital. Rates of N cycling in nine stands of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) were estimated by measuring annual N input in litter, N content of the forest floor, and net N mineralization rate in the forest floor. Rates of C and N turnover were estimated from the litterfall:forest floor ratio. The amount of N returned in litter increased as soil N capital increased. The increase in litter N content resulted from both increased litter mass (C content) and increased N concentration in litter. Despite the greater litter input, forest floor mass was smaller at N-rich sites, indicating more rapid turnover of the forest floor on N-rich sites. There was a positive relationship between fractional annual loss of N from the forest floor and soil N capital. Therefore, even without changes in tree species composition, sites with greater soil N capital returned more N in annual litterfall and had faster turnover of N in the forest floor. Fractional annual loss of C also increased with increasing soil N capital, indicating faster decomposition on N-rich sites. The rate of net N mineralization during laboratory incubations of the forest floor was not correlated with soil N capital or N concentrations of litter, but was related to the C:N ratio of the forest floor. Net N mineralization was appreciable only at two sites where forest floor C:N ratios were <35. The rate of net N mineralization or C:N ratio of the forest floor were not good indicators of N availability at these sites. The results of this study are consistent with the hypothesis that rates of N cycling are faster on N-rich sites, and that this effect can occur in the absence of changes in tree species composition.

NITROGEN TURNOVER IN FOREST FLOORS OF COASTAL DOUGLAS-FIR AT SITES DIFFERING IN SOIL NITROGEN CAPITAL

Nitrogen cycling is generally considered to be more rapid on sites with high availability of N; this is usually associated with differences in tree species composition. We tested whether N cycling in stands of a single tree species increased with increasing mineral soil nitrogen capital. Rates of N cycling in nine stands of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) were estimated by measuring annual N input in litter, N content of the forest floor, and net N mineralization rate in the forest floor. Rates of C and N turnover were estimated from the litterfall:forest floor ratio. The amount of N returned in litter increased as soil N capital increased. The increase in litter N content resulted from both increased litter mass (C content) and increased N concentration in litter. Despite the greater litter input, forest floor mass was smaller at N-rich sites, indicating more rapid turnover of the forest floor on N-rich sites. There was a positive relationship between fractional annual loss of N from the forest floor and soil N capital. Therefore, even without changes in tree species composition, sites with greater soil N capital returned more N in annual litterfall and had faster turnover of N in the forest floor. Fractional annual loss of C also increased with increasing soil N capital, indicating faster decomposition on N-rich sites. The rate of net N mineralization during laboratory incubations of the forest floor was not correlated with soil N capital or N concentrations of litter, but was related to the C:N ratio of the forest floor. Net N mineralization was appreciable only at two sites where forest floor C:N ratios were <35. The rate of net N mineralization or C:N ratio of the forest floor were not good indicators of N availability at these sites. The results of this study are consistent with the hypothesis that rates of N cycling are faster on N-rich sites, and that this effect can occur in the absence of changes in tree species composition.

Tree Species Distributions in an Upper Amazonian Forest

Not a single tree species distribution in the Amazon basin has been reliably mapped, though speculation regarding such distributions has been extensive. We present data from a network of 21 forest plots in Manu National Park, Peru, totaling >36 ha and sited over an area of ∼400 km2, to explore how tree species are distributed across upper Amazonia at a variety of spatial scales. For each of 825 tree species occurring in the plots we asked three questions: (1) Does the species have a large or small geographic range? (2) Is the species restricted to a single forest type, or is it found in several? (3) Is the species locally abundant anywhere or is it scarce everywhere? The answers served to classify a subset of species under Rabinowitz’s classification scheme for rare species. Three main conclusions emerged. First, the great majority of tree species at Manu are geographically widespread. Every species identified to date occurs elsewhere in South America, outside the department of Madre de Dios; more than two-thirds of them have been collected 1500 km away in Amazonian Ecuador. Second, 15–26% of species appear to be restricted to a single forest type, when forest types are defined by historical river dynamics (i.e., terra firme forest, mature floodplain forest, swamp forest, and primary successional floodplain forest). The proportion of restricted species declined with increasing sampling effort, making 15% a more reliable figure. Third, while 88% of species occurred at densities of <1 individual/ha over the entire network of plots, at least half occurred somewhere at densities of >1.5 individuals/ha. Extrapolating these results provides a first guess at how tree species are distributed across the western portion of the Amazon basin. We conclude with the suggestion that most tree species in the region are habitat generalists occurring over large areas of the Amazonian lowlands at low densities but large absolute population sizes.

TREE SPECIES DISTRIBUTIONS IN AN UPPER AMAZONIAN FOREST

Not a single tree species distribution in the Amazon basin has been reliably mapped, though speculation regarding such distributions has been extensive. We present data from a network of 21 forest plots in Manu National Park, Peru, totaling >36 ha and sited over an area of -400 km2, to explore how tree species are distributed across upper Amazonia at a variety of spatial scales. For each of 825 tree species occurring in the plots we asked three questions: (1) Does the species have a large or small geographic range? (2) Is the species restricted to a single forest type, or is it found in several? (3) Is the species locally abundant anywhere or is it scarce everywhere? The answers served to classify a subset of species under Rabinowitz's classification scheme for rare species. Three main conclusions emerged. First, the great majority of tree species at Manu are geographically widespread. Every species identified to date occurs elsewhere in South America, outside the department of Madre de Dios; more than two-thirds of them have been collected 1500 km away in Amazonian Ecuador. Second, 15-26% of species appear to be restricted to a single forest type, when forest types are defined by historical river dynamics (i.e., terra firme forest, mature floodplain forest, swamp forest, and primary successional floodplain forest). The proportion of restricted species declined with increasing sampling effort, mak- ing 15% a more reliable figure. Third, while 88% of species occurred at densities of 1.5 individuals/ha. Extrapolating these results provides a first guess at how tree species are distributed across the western portion of the Amazon basin. We conclude with the suggestion that most tree species in the region are habitat generalists occurring over large areas of the Amazonian lowlands at low densities but large absolute population sizes.

Spatial patterns of ground vegetation, soil microbial biomass and activity in a mixed spruce‐birch stand

Trees directly and indirectly influence the above‐ and below‐ground environment, and can be expected to modify the spatial patterns of organisms associated with the forest floor. This study aimed to examine the effects of a coniferous (Picea abies) and a broad‐leaved (Betula pubescens) tree species on the spatial pattern of ground vegetation and soil microbial properties in a mixed stand in central Sweden. I have characterised the species composition of ground vegetation, soil microbial biomass and activity, photosynthetic active radiation (PAR), soil water content and soil pH in the stand, and tested whether the spatial patterns of these variables were related to the positioning of trees. Geostatistics were used to describe the spatial variation in ground vegetation, soil mirobiological properties and the soil surface environment. PAR, soil water content and the cover of the moss Brachytecium reflexum and associated herb species decreased with the influence of spruce trees. Microbial biomass, measured as the amount of phospholipid fatty acids, decreased with spruce influence but increased with the influence of birch trees. Microbial respiration was not affected by spruce but increased with the influence of birch. Ground vegetation and microbial respiration, which were influenced by one tree species only, aggregate on a scale of 4‐5 m, corresponding fairly well with patches of a single tree species. Soil microbial biomass, which was affected by both tree species, aggregated on a scale of 7‐8 m. roughly corresponding to the distance between patches of spruce and birch trees respectively. I suggest that spruce trees influenced vegetation mainly through shading, and that a difference in the availability of organic matter under birch and spruce trees caused spatial variation in microbial biomass and activity. Thus, spatial patterns in ground vegetation and soil microbial properties may develop in a mixed forest of coniferous‐broad leaved trees, as a result of the difference in influence of tree species and nested variation associated with the arrangement of the trees.

Modelling the risk of snow damage to forests under short-term snow loading

Regression models are developed to assess the risk of snow damage to Scots pine ( Pinus sylvestris L.), Norway spruce ( Picea abies (L.) Karst) and birch ( Betula spp.) stands based on simulated data, employing a mechanistic wind and snow damage model developed by Peltola et al., 1998a. The risk is predicted in terms of the critical windspeed needed to cause stem breakage and uprooting of trees at forest edges under short-term snow loading. Separate regression models are developed for each tree species using stem taper (breast height diameter of stem relative to tree height, d 1.3/ h), stand density, snow loading and distance from the stand edge as variables, and a general model for stem breakage and uprooting is also proposed having tree species as an additional dummy variable. The overall risk of stem breakage and uprooting is shown to increase with snow loading and decrease with increasing stem taper and stand density for all three tree species, although Scots pines and Norway spruces are predicted to be much more susceptible to snow damage than birches, which, being leafless, had much less crown area for snow attachment and wind loading. The greatest susceptibility to stem breakage and uprooting is seen at the stand edge, where the risk due to wind loading is much greater than inside the stand. Under these circumstances, slightly tapering Scots pines and Norway spruces are found to be the most vulnerable under a snow load of 60 kg m −2, suffering damage at windspeeds of <9 m s −1 at a constant height of 10 m above the ground, i.e. these windspeeds enhance the risk, whereas higher speeds can be expected to dislodge the snow from the crowns. Birches will only exceptionally be broken and uprooted at windspeeds of <9 m s −1 according to the models developed here. Since the general models give rise to somewhat greater residuals compared with the simulated data than do the single tree species models, it seems that the latter will give more reliable predictions of the risk of snow damage. The models could be useful when discussing the risk of snow damage in connection with alternative forms of stand management, especially in high risk areas, enabling high-risk trees to be removed during thinning.

Coffee Growing: Sun or Shade?

Sun cultivation of coffee (Laura Tangley, Research News, [22 Nov., p. 1299][1]) is not only a potentially bad thing for birds, but lethal for coffee itself in habitats with a distinct dry season. Despite observing an initial spike in coffee-berry production, we have documented severe damage or “ Mal de Vinas” in Guatemala ([1][2]) from insufficient shade, which leads to massive coffee tree death, often in less than a year. Similar problems occur elsewhere in Central America ([2][3]). Not only do plants suffer from drought stress, elevated ambient temperature, soil erosion, and loss of soil organic matter, but they experience leaf tissue damage and altered carbohydrate metabolism ([3][4]). Coffea arabica 's evolutionary origin as an understory plant favors low light ([4][5]) and presents distinct limits to breeding for heavy flowering and fruiting under full sun. Large plantations in Guatemala that converted to open-sun cultivation in the 1980s are now restoring shade tree growth. The fact that sun cultivation fails in some regions but is successful in others is a complex and poorly understood problem that relates to local rainfall, cloud cover, and the species under cultivation ( C. robusta is more tolerant of high light and temperature than C. arabica ). The question of labeling coffee as “environmentally friendly” is also tricky. Open-sun plantations are structurally and biologically depauperate, and they require much higher agrochemical inputs (primarily fertilizer) than traditional shaded coffee. It may be true, as Robert Rice speculates, that a plantation with a single species of shade tree and heavy pesticide use is no more friendly than a sun plantation. But the main difference in agrochemical use between sun and shade plantations is not in pesticide, but fertilizer use. Herbicide use also increases with the degree of sun exposure because of increased weed growth, and chemical elimination of flowering plants can affect nectar-feeding arthropods more than conventional manual weeding. Arthropod diversity and herbivore pressure on coffee are notoriously low relative to what occurs in the shade tree canopy ([5][6]). Even in plantations with just one or two species of shade tree ( Inga spp., for example) we have found most of the arthopod prey base for birds concentrated in the overstory ([5][6]). Chemical applications occur in the coffee shrub understory. On the other hand, soil-dwelling species such as the cicada nymphs mentioned by Young (Letters, [3 Jan., p. 12][7]) or the larvae of scarab beetles are at risk, and these may be significant food resources for birds. The ecological intricacies of coffee management systems must be studied with sound quantitative methods before generalizations about “friendliness” can be made. 1. 1.[↵][8]1. C. MacVean, 2. M. Krigsvold, 3. M. Dix, 4. M. Braeuner, 5. O. Arjona , “Causas y naturaleza del Mal de Vinas en cafetos de Guatemala” (Instituto de Investigaciones, Universidad del Valle de Guatemala, Guatemala, 1992). 2. 2.[↵][9]1. R. Rice , Agroecol. Neotropi. 2, 1 (1991). [OpenUrl][10] 3. 3.[↵][11]1. K. Tay, 2. C. MacVean , unpublished data. 4. 4.[↵][12]1. M. N. Clifford, 2. K. C. Wilson 1. M. G. R. Cannell , in Coffee: Botany, Biochemistry and Production of Beans and Beverage, M. N. Clifford, K. C. Wilson, Eds. (Croom Helm, Beckenham, Kent, United Kingdom, 1987), pp. 108-133. 5. 5.[↵][13]1. C. MacVean, 2. R. Greenberg , unpublished observations. [1]: /lookup/volpage/275/1299 [2]: #ref-1 [3]: #ref-2 [4]: #ref-3 [5]: #ref-4 [6]: #ref-5 [7]: /lookup/doi/10.1126/science.275.5296.11 [8]: #xref-ref-1-1 View reference 1. in text [9]: #xref-ref-2-1 View reference 2. in text [10]: {openurl}?query=rft.jtitle%253DAgroecol.%2BNeotropi.%26rft.volume%253D2%26rft.spage%253D1%26rft.atitle%253DAGROECOL%2BNEOTROPI%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx [11]: #xref-ref-3-1 View reference 3. in text [12]: #xref-ref-4-1 View reference 4. in text [13]: #xref-ref-5-1 View reference 5. in text

The use of imaging radars for ecological applications—A review

At the behest of NASA's Mission to Planet Earth, the National Research Council recently conducted a review on the current status and future directions for earth science information provided by spaceborne synthetic aperture radars. As part of this process, a panel of 16 scientists met to review the utility of SAR for monitoring ecosystem processes. The consensus of this ecology panel was that the demonstrated capabilities of imaging radars for investigating terrestrial ecosystems could best be organized into four broad categories: 1) classification and detection of change in land cover; 2) estimation of woody plant biomass; 3) monitoring the extent and timing of inundation; and 4) monitoring other temporally-dynamic processes. The major conclusions from this panel were: 1) Multichannel radar data provide a means to classify land-cover patterns because of its sensitivity to variations in vegetation structure and vegetation and ground-layer moisture. The relative utility of data from imaging radars versus multispectral scanner data has yet to be determined in a rigorous fashion over a wide range of biomes for this application. 2) Imaging radars having the capability to monitor variations in biomass in forested ecosystems. This capability is not consistent among different forest types. The upper levels of sensitivity for L-band and C-band systems such as SIR-C range between <100 t ha −1 for complex tropical forest canopies to ∼250 t ha −1 for simpler forests dominated by a single tree species. Best performance for biomass estimation is achieved using lower frequency ( P- and L-band) radar systems with a cross-polarized (HV or VH) channel. 3) Like-polarized imaging radars (HH or VV) are well suited for detection of flooding under vegetation canopies. Lower frequency radars ( P- and L-band) are most optimal for detecting flooding under forests, whereas higher frequency radars ( C-band) work best for wetlands dominated by herbaceous vegetation. 4) It has been shown that spaceborne radars that have been in continuous operation for several years [such as the C-band (VV) ERS-1 SAR] provide information on temporally dynamic processes, such as monitoring a) variations in flooding in nonwooded wetlands, b) changes in the frozen/thawed status of vegetation, and c) relative variations in soil moisture in areas with low amounts of vegetation cover. These observations have been shown to be particularly important in studying ecosystems in high northern latitudes.

Maize Response to Urea and Superphosphate in Pot Experiment with Soils Derived from Alley Cropping

Abstract A pot culture experiment was conducted to evaluate the urea and single superphosphate (SSP) fertilizer requirements of maize (Zea mays L.) using soils collected from a three-year-old agroforestry plot in the Southern Guinea Savanna Zone of Nigeria. The agroforestry plot carried various combinations ranging from mixed silviculture hedgerows of Leucaena and Gmelina and Parkia and Gmelina to single hedgerow tree species of either Leucaena, or Parkia or Gmelina. Maize had also been grown for four cropping seasons in the alleys provided by the various hedgerow tree species before this investigation. Although soils from all the various combinations would require some urea and SSP fertilizer for optimal maize production, the degree varies. Maize responded more to N and P on soils from the Parkia-based cropping system than on soils from Leucaena's. Nitrogen and P reduced the number of days to tasselling and silking in maize. The paper advocates the integration of mixed silviculture of Leucaena, Parkia an...

Species diversity and ecosystem response to carbon dioxide fertilization: conclusions from a temperate forest model

AbstractThis paper explores how the response of a temperate forest ecosystem to climate change might depend on species diversity and community change. In particular, we look at the dynamics of a model of temperate forest growth under doubled CO2. We combine a detailed, field‐calibrated model of forest dynamics (Pacala et al 1993) with greenhouse data on the range of seedling biomass growth response to doubled CO2 concentrations (Bazzaz et al. 1990; Bazzaz &amp; Miao 1993). Because total ecosystem response to climate change depends delicately on many environmental variables other than CO2, we isolate the effects of community change by comparing runs of the regular model, allowing dynamic community change, with runs of a reduced model that holds species composition static by using a single tree species with average parameters. Simulations that allowed community change instead of holding species composition constant showed a roughly 30% additional increase in total basal area over time scales of 50‐150 years. Although the model omits many possible feedbacks and mechanisms associated with climate change, it suggests the large potential effects that species differences and feedbacks can have in ecosystem models and reinforces the possible importance of diversity to ecosystem function (Naeem et ai 1994; Tilman &amp; Downing 1994) over time scales within the planning horizon for global change policy.

The Influences of Tree Biology and Fire in the Spatial Structure of the West African Savannah

Using a spatially explicit cellular automaton model we explore the effects of tree demography, fire-induced mortality, and seed dispersal on the spatial spread of a single tree species in a humid savanna at Lamto in West Africa. The model system is described by six parameters and consists of a grass-surrounded square grid of connecting cells, each being either inhabited by grass alone or by grass and an individual tree. In the baseline numerical simulations the tree can only recruit seedlings in immediately adjacent cells. These seedlings may perish from annual grass fires in their first year of life if they are not protected from the advancement of the fire by neighbouring reproductively mature trees (...)

Gene Trees and Species Trees: Molecular Systematics as One-Character Taxonomy

Reconstruction of phylogenies from molecular data has become an important and increasingly common approach in systematics. The product of such studies is a gene tree, hypoth- esizing relationships among genes or genomes. This gene tree may be fundamentally incongruent with the true species phylogeny, due to various biological phenomena such as introgression, lineage sorting, or mistaken orthology. In such circumstances all of the gene tree characters defining the relationships of molecular taxa (haplotypes) may be necessarily correlated, and the gene or genome may behave as a single species tree character. In these circumstances robustness of the gene hypoth- esis is meaningless as a measure of confidence in the species phylogenetic hypothesis. Incongruence between a phylogenetic hypothesis based on numerous, presumably independent, non-molecular characters and a single gene tree should not be assumed to be due to noise in non-molecular data. As with other characters, a character phylogeny, in this case a gene tree, can be tested best by a parsimony analysis in which other characters are included. If independence of molecular characters is assumed, then each is an equivalent phylogenetic hypothesis, as is each non-molecular character, leading to the suggestion that direct combination is appropriate. Swamping becomes an issue when a large molecular data set may be behaving as a single character. To alleviate this problem, a gene tree may be treated as a single multistate character, either ordered or unordered, and included with non-molecular data to obtain a globally parsimonious result. An example is given using published molecular and non-molecular data from the Asteraceae.

Tree Species Distribution Across a Seasonally Flooded Elevation Gradient in the Australian Monsoon Tropics

A grid of 447 50x50 m cells was established across a monsoon forest-treeless floodplain transition near the Adelaide River, northern Australia. The grid was surveyed to the nearest 0.5 m, to reveal a gradual elevation gradient of less than 7 m over about 1000 m of horizontal distance. Half of the gradient was flooded by freshwater in the wet season. Three soil types were identified across the grid, and with the exception of cracking clays on the floodplain they showed no obvious relationship with elevation. The ecological response of most major (basal area >0.1 m 2 ha -1 ) tree species was skewed and unimodal and is thought to be primarily determined by degree of inundation. The peaks ot abundance of the forty-three major species were clumped in two groups across the gradient. The abundances of 81% of the seventy-eight tree species were significantly correlated (P<0.0001) to the abundance of at least one other species. Most of these species formed tight, independent clusters and are considered to be components of four intergrading forest communities. Tree species richness and stem density increased linearly up the elevation gradient, total basal area had a skewed unimodal response, and dominance of a single tree species occurred only on the boundary with treeless vegetation. Unlike complex rainforest the monsoon rainforest community was relatively bereft of species, possibly because of the overwhelming influence of climatically induced Pleistocene extinctions on the original Australian rainforest flora.

Population Densities and Patterns of Habitat Use Among Anthropoid Primates of the Ituri Forest, Zaire

The Ituri Forest of Eastern Zaire contains the richest recorded assemblage of anthropoid primates in the world (13 sympatric species), the behavior and ecology of which have not previously been studied. This study reports the result of line transect censuses at seven locations in the northern and central Ituri, and presents analyses of primate habitat use according to forest type, treefall gaps, tree species in which primates were observed, and height of primates in the vegetation. Estimated total anthropoid primate density is 112 ind/km2, corresponding to a biomass of 715 kg/ km2. Three common species of frugivorous/insectivorous Cercopithecus monkeys (C. ascanius, C. mitis, C. pogonius) showed pronounced habitat preferences for secondary forest, as did one folivore, Colobus guereza. The two more abundant colobine monkeys (Colobus angolensis and C. badius) were seen mainly in mature mixed forest. Very few primates of any species were observed in areas of mbau forest, a forest type dominated by the single tree species Gilbertiodendron dewevrei. The smallest Cercopithecus monkey, C. ascanius, was frequently observed in and around treefall gaps, and may be a gap-specialist in this species-rich primate community. The abundance of common Cercopithecus monkeys in secondary forest may be a response to continuous fruiting of pioneer tree species which constitute a dependable but low-quality resource during the seasonal hiatus of fruit availability in primary forest.

Feeding ecology of spider monkeys (Ateles geoffroyi) at Tikal, Guatemala

Field study in tropical dry forest in Tikal National Park, Guatemala, revealed that spider monkeys (Ateles geoffroyi) devoted about 57% of feeding time to fruit (pulp), 20% to the unripe seeds of a single tree species, and the remainder largely to leaves and buds. Fruit, seeds, flowers and leaves ofBrosimum alicastrum (Moraceae) accounted for 56% of the diet, and there was very little predation on invertebrates. A severe drought occurred during 1975, the first year of the study, and a comparison between July of that year with July, 1978 shows that in the drought year there was heavier than normal reliance on fruit of the genusFicus (46% versus 14%) and depressed consumption ofBrosimum (11% vs. 54%). Dietary species diversity (Shannon's measureH) and evenness (Hill'sE) were markedly higher during the drought July than the normal July.