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Papers by David Coomes

Seed Science Research, 1997

Mean seed dry mass values were determined for 27 species of trees and shrubs in Amazonian caating... more Mean seed dry mass values were determined for 27 species of trees and shrubs in Amazonian caatinga (a forest-type especially short of nitrogen) and for 11 species in adjacent much taller forest on less poor soil. The tall trees (>15 m) of caatinga have smaller seeds than the tall trees in adjacent forest on less infertile soil (both overall and in six taxonomically controlled comparisons), and than the tall trees in lowland rainforests elsewhere. The smaller seed size is interpreted in terms of a major advantage of keeping up seed number outweighing the marginal advantages of larger seed size. For trees of caatinga and adjacent forest considered together, there is a significantly greater concentration of P and Mg, and almost significantly greater concentration of N, in the embryo-cum-endosperm fraction of smallerseeded species, but the content per seed of N, P and Mg is smaller in smaller seeds. The mean contribution of the seed coat (including endocarp for pyrenes) was 17% for dry mass, 3% for content of P, 10% for N and Mg, 15% for K, and 30% for Ca.

Plant Ecology, 1996

Tall and short Amazonian caatinga at La Esmeralda (rainfall 2600 mm yr -1) are described and comp... more Tall and short Amazonian caatinga at La Esmeralda (rainfall 2600 mm yr -1) are described and compared with those at San Carlos de Rfo Negro (3600 mm yr-1). The tall forests have much in common: thin-boled trees, many with scleromorphic mesophylls, lack of thick-stemmed climbers and of herbs, species paucity in all life-forms, domination by Eperua, and a high proportion of Bombacaceae, Clusiaceae and Euphorbiaceae. The short caatingas are also structurally and floristically similar but at La Esmeralda the notophyll scrubland species are lacking. At La Esmeralda, the common tree species are autochorous, but the majority of plants (particularly understorey species) are zoochorous. Relatively high transmission of light to the floor of the tall caatinga (1.5% PAR) may explain how trees with light-demanding architecture regenerate in the understorey. The presence of Cecropia and 'weedy' species in the caatinga only at San Carlos may be the result of greater human interference there. The soils at San Carlos and La Esmeralda are similar: thick humus overlying bleached sand, waterlogged most of the year. The water table at La Esmeralda drops to > 1 m depth during the drier months, but tensiometers at 30 cm depth did not indicate significant water shortage. Soils are consistently wetter in the short caatinga than the tall. Shortage of nitrogen appears to determine the major structural and physiognomic features of the caatinga, and depth of aerated soil appears to determine its stature. Comparisons are made between tall caatinga, wallaba and swamp forest in the Guianas and heath forests of Malaysia. L e e u w e n b e r g , S. M o r i , T. P e n n i n g t o n , L. S k o g and J J . W u r d a c k . T h e r e s e a r c h w a s f u n d e d by the Natural E n v i r o n m e n t R e s e a r c h C o u n c i l with e x t r a s u p p o r t f r o m the D r u m m o n d F u n d o f G o n v i l l e a n d Caius College. T h e visits o f P J G to V e n e z u e l a w e r e f u n d e d partly by the U n i v e r s i t y o f C a m b r i d g e a n d M a g d a l e n e C o llege.

Trends in Ecology and Evolution, 2003

Impacts of Root Competition in Forests and Woodlands: A Theoretical Framework and Review of Experiments

Ecological Monographs, 2000

... 1965). Although some shade-tolerant trees may establish under pine, the process of succession... more ... 1965). Although some shade-tolerant trees may establish under pine, the process of succession is greatly slowed by the soil infertility, persistence of the early-successional species, and by fire and drought (Faliński 1994). We ...

Global Ecology and Biogeography, 2007

Aim Few studies have explicitly examined the influence of spatial attributes of forest fragments... more Aim Few studies have explicitly examined the influence of spatial attributes of forest fragments when examining the impacts of fragmentation on woody species. The aim of this study was to assess the diverse impacts of fragmentation on forest habitats by integrating landscape-level and species-level approaches.Location The investigation was undertaken in temperate rain forests located in southern Chile. This ecosystem is characterized by high endemism and by intensive recent changes in land use.Method Measures of diversity, richness, species composition, forest structure and anthropogenic disturbances were related to spatial attributes of the landscape (size, shape, connectivity, isolation and interior forest area) of forest fragments using generalized linear models. A total of 63 sampling plots distributed in 51 forest fragments with different spatial attributes were sampled.Results Patch size was the most important attribute influencing different measures of species composition, stand structure and anthropogenic disturbances. The abundance of tree and shrub species associated with interior and edge habitats was significantly related to variation in patch size. Basal area, a measure of forest structure, significantly declined with decreasing patch size, suggesting that fragmentation is affecting successional processes in the remaining forests. Small patches also displayed a greater number of stumps, animal trails and cow pats, and lower values of canopy cover as a result of selective logging and livestock grazing in relatively accessible fragments. However, tree richness and β-diversity of tree species were not significantly related to fragmentation.Main conclusions This study demonstrates that progressive fragmentation by logging and clearance is associated with dramatic changes in the structure and composition of the temperate forests in southern Chile. If this fragmentation process continues, the ability of the remnant forests to maintain their original biodiversity and ecological processes will be significantly reduced.

Ecological Modelling, 2008

Logistic regression Temperate forests Chile a b s t r a c t Forest fragmentation threatens biodiv... more Logistic regression Temperate forests Chile a b s t r a c t Forest fragmentation threatens biodiversity in one of the last remaining temperate rainforests that occur in South America. We study the current and future impacts of fragmentation on spatial configuration of forest habitats at the landscape level time in southern Chile. For this purpose, we identify the geophysical variables ("pattern drivers") that explain the spatial patterns of forest loss and fragmentation between 1976 and 1999 using both a GIS-based land-use change model (GEOMOD) and spatially explicit logistic regression. Then, we project where and how much forest fragmentation will occur in the future by extrapolation of the current rate of deforestation to 2010 and 2020. Both modeling approaches showed consistent and complementary results in terms of the pattern drivers that were most related to deforestation. Between 1976 and 1999, forest fragmentation has occurred mainly from the edges of small fragments situated on gentle slopes (less than 10 • ) and far away from rivers.

Biological Conservation, 2006

The temperate forests of Chile are classified a biological ''hotspot'' as a result of their high ... more The temperate forests of Chile are classified a biological ''hotspot'' as a result of their high species diversity and high endemism. However, they are being rapidly destroyed, with significant negative impacts on biodiversity. Three land-cover maps were derived from satellite imagery acquired over 25 years (1975, 1990 and 2000), and were used to assess the patterns of deforestation and forest fragmentation in the coastal range of south-central Chile. Between 1975 and 2000, there was a reduction in natural forest area of 67% in the study area, which is equivalent to an annual forest loss rate of 4.5% per year using a compound-interest-rate formula. Forest fragmentation was associated with a decrease in forest patch size, which was associated with a rapid increase in the density of small patches (<100 ha), and a decrease in area of interior forest and in connectivity among patches. Since the 1970s, native forest loss was largely caused by an expansion of commercial plantations, which was associated with substantial changes in the spatial configuration of the native forests. By 2000, most native forest fragments were surrounded by highly connected exotic-species plantations. The assessment of forest loss and fragmentation provides a basis for future research on the impacts of forest fragmentation on the different component of biodiversity. Conservation strategies and land use planning of the study area should consider the spatial configuration pattern of native forest fragments and how this pattern changes over time and space at landscape level.

Conservation Biology, 2003

There is currently great interest in restoring ecosystems affected by invasive organisms. In New ... more There is currently great interest in restoring ecosystems affected by invasive organisms. In New Zealand, deer were introduced during the nineteenth century, causing dramatic changes to the understory composition and structure of some forests. Deer prefer to browse on short tree species, mostly associated with early successional stands and moist-fertile sites, but many tall tree species are browsed only when other food sources are scarce. The government has invested heavily in control programs aimed at reducing deer numbers and thereby restoring forests to something approaching their preinvasion composition and structure, but have met with only limited success. Based on a literature review, we give several examples of situations in which deer impacts may not be reversible, including the following: (1) palatable species remaining highly browsed even at low deer densities as a result of diet switching; (2) occupation of vacated niches by plant species not eaten by deer; (3) local extinction of seed sources; (4) fundamental alterations to successional pathways; (5) shifts in ecosystem processes; (6) other exotic animals becoming naturalized and weakening the effectiveness of single-species control; and (7) exotic plants weakening the effectiveness of single-species control. We consider the contributions that scientific research can make to effective forest restoration, including empirically based forest-dynamics models that place regeneration in the context of other processes, such as disturbance, soil fertility, and multiple invasive organisms.

Journal of Ecology, 2005

1 Angiosperm trees often dominate forests growing in resource-rich habitats, whereas conifers are... more 1 Angiosperm trees often dominate forests growing in resource-rich habitats, whereas conifers are generally restricted to less productive habitats. It has been suggested that conifers may be displaced by angiosperms except where competition is less intense, because conifer seedlings are inherently slow growing, and are outpaced by faster-growing angiosperm species. Here we investigate whether competition with ferns and deeply shading trees also contributes to a failure of conifers to regenerate in resource-rich habitats.

Forest Ecology and Management, 2002

The United Nations framework convention on climate change (FCCC) commits signatory nations to mon... more The United Nations framework convention on climate change (FCCC) commits signatory nations to monitor changes in all 14 fluxes and sinks of carbon, including those related to vegetation and soil. This paper describes a system for monitoring carbon 15 in New Zealand's forests and shrublands (6.3 and 2.6 million ha, respectively), which was tested on a 60 km-wide transect 16 across the South Island. A 9 km 2 grid was superimposed onto a land-cover map (SPOT imagery) to obtain 62 ground-sampling 17 points. New permanent plots were established at 43 of these points and 18 existing plots were revisited (one site was 18 inaccessible). On each plot, the dimensions of all trees, shrubs and coarse woody debris (CWD) were measured, and these 19 measurements converted to per-hectare C-stocks using regression relationships. C-stocks in fine litter and mineral soil were 20 quantified using data from New Zealand's national soil-C monitoring system that quantifies national-scale soil-C stocks using 21 a soil-C database stratified by soil type, climate, and land-cover; we used these data to derive values for the transect.

Enquist and Niklas propose that trees in natural forests have invariant size-density distribution... more Enquist and Niklas propose that trees in natural forests have invariant size-density distributions (SDDs) that scale as a )2 power of stem diameter, although early studies described such distributions using negative exponential functions. Using New Zealand and ÔglobalÕ data sets, we demonstrate that neither type of function accurately describes the SDD over the entire diameter range. Instead, scaling functions provide the best fit to smaller stems, while negative exponential functions provide the best fit to larger stems. We argue that these patterns are consistent with competition shaping the small-stem phase and exogenous disturbance shaping the large-stem phase. Mortality rates, estimated from repeat measurements on 1546 New Zealand plots, fell precipitously with stem size until 18 cm but remained constant after that, consistent with our arguments. Even in the small-stem phase, where SDDs were best described by scaling functions, the scaling exponents were not invariantly )2, but differed significantly from this value in both the ÔglobalÕ and New Zealand data sets, and varied through time in the New Zealand data set.

Journal of Ecology, 2007

Understanding the factors influencing tree growth is central to forest ecology because of the sig... more Understanding the factors influencing tree growth is central to forest ecology because of the significance of growth to forest structure and biomass. One of the simplest, yet most controversial growth models, proposed by Enquist and colleagues, predicts that stem-diameter growth scales as the one-third power of stem diameter. Recent analyses of large-scale data sets have challenged the generality of this theory and highlighted the influence of resource competition on the scaling of growth with size.

Ecology Letters, 2003

Enquist and Niklas propose that trees in natural forests have invariant size-density distribution... more Enquist and Niklas propose that trees in natural forests have invariant size-density distributions (SDDs) that scale as a −2 power of stem diameter, although early studies described such distributions using negative exponential functions. Using New Zealand and ‘global’ data sets, we demonstrate that neither type of function accurately describes the SDD over the entire diameter range. Instead, scaling functions provide the best fit to smaller stems, while negative exponential functions provide the best fit to larger stems. We argue that these patterns are consistent with competition shaping the small-stem phase and exogenous disturbance shaping the large-stem phase. Mortality rates, estimated from repeat measurements on 1546 New Zealand plots, fell precipitously with stem size until 18 cm but remained constant after that, consistent with our arguments. Even in the small-stem phase, where SDDs were best described by scaling functions, the scaling exponents were not invariantly −2, but differed significantly from this value in both the ‘global’ and New Zealand data sets, and varied through time in the New Zealand data set.

Journal of Ecology, 2007

1Tree-size distributions are changing in many natural forests around the world, and it is importa... more 1Tree-size distributions are changing in many natural forests around the world, and it is important to understand the underlying processes that are causing these changes. Here we use a classic conceptual framework – the shifting mosaic of patches model – to explore the ways in which competitive thinning and disturbance influence tree-size distributions, and to consider the effects of temporal variability in disturbance frequency on the size structure of forests.2We monitored 250 stands of Nothofagus solandri var. cliffortiodes (mountain beech), randomly distributed over 9000 hectares, for 19 years. Mountain beech is a light-demanding species that forms monospecific forests in New Zealand mountains. For the purposes of our model, we assumed that each stand functions as an even-aged population: it is initiated by a pulse of recruitment, undergoes competitive thinning as it matures, and is eventually destroyed by a disturbance event. The tree-size distribution of the whole forest is driven partly by the frequency and temporal patchiness of disturbance events and partly by competitive processes within the constituent stands.3Temporal changes in stem density and mean tree size were observed to be remarkably similar in all young stands, indicating that a consistent packing rule operates during this phase of stand development. A popular idea in the self-thinning literature is that the maintenance of constant leaf area index (LAI) provides the mechanism for this packing rule, but our analyses suggest that LAI increased by about 30% during the thinning phase. We use leaf economic theory to develop a new packing rule based on light interception, and argue that LAI increases with stand age because of changes in canopy organisation.4Smaller trees were significantly more likely to die than larger trees within the young stands. Tree-diameter distributions within young stands were left skewed but those of older populations were normally distributed. These observations are consistent with asymmetric competition winnowing out small, suppressed trees from young stands but having less effect in older stands.5Large-scale disturbances created gaps of sufficient size to allow mass recruitment of seedlings in about 0.8% of stands each year. Older stands were most susceptible to such large-scale disturbance, but the trend was weak.6The diameter-distribution of the whole Nothofagus forest was found to be approximately exponential in form. Simulation models only produced realistic diameter distributions when competitive packing rules and disturbance were included. Therefore, the shifting mosaic model provides a general framework for understand the ways in which these mortality processes determine forest size structure.7The diameter distribution of the forest was not in equilibrium over the 19-year study. Using simulation models, we show that temporal variability in disturbance frequency can generate enormous deviations in tree-diameter distributions away from the long-term mean, leading us to conclude that modern-day disequilibrium in natural forests may be the legacy of past disturbance events.Tree-size distributions are changing in many natural forests around the world, and it is important to understand the underlying processes that are causing these changes. Here we use a classic conceptual framework – the shifting mosaic of patches model – to explore the ways in which competitive thinning and disturbance influence tree-size distributions, and to consider the effects of temporal variability in disturbance frequency on the size structure of forests.We monitored 250 stands of Nothofagus solandri var. cliffortiodes (mountain beech), randomly distributed over 9000 hectares, for 19 years. Mountain beech is a light-demanding species that forms monospecific forests in New Zealand mountains. For the purposes of our model, we assumed that each stand functions as an even-aged population: it is initiated by a pulse of recruitment, undergoes competitive thinning as it matures, and is eventually destroyed by a disturbance event. The tree-size distribution of the whole forest is driven partly by the frequency and temporal patchiness of disturbance events and partly by competitive processes within the constituent stands.Temporal changes in stem density and mean tree size were observed to be remarkably similar in all young stands, indicating that a consistent packing rule operates during this phase of stand development. A popular idea in the self-thinning literature is that the maintenance of constant leaf area index (LAI) provides the mechanism for this packing rule, but our analyses suggest that LAI increased by about 30% during the thinning phase. We use leaf economic theory to develop a new packing rule based on light interception, and argue that LAI increases with stand age because of changes in canopy organisation.Smaller trees were significantly more likely to die than larger trees within the young stands. Tree-diameter distributions within young stands were left skewed but those of older populations were normally distributed. These observations are consistent with asymmetric competition winnowing out small, suppressed trees from young stands but having less effect in older stands.Large-scale disturbances created gaps of sufficient size to allow mass recruitment of seedlings in about 0.8% of stands each year. Older stands were most susceptible to such large-scale disturbance, but the trend was weak.The diameter-distribution of the whole Nothofagus forest was found to be approximately exponential in form. Simulation models only produced realistic diameter distributions when competitive packing rules and disturbance were included. Therefore, the shifting mosaic model provides a general framework for understand the ways in which these mortality processes determine forest size structure.The diameter distribution of the forest was not in equilibrium over the 19-year study. Using simulation models, we show that temporal variability in disturbance frequency can generate enormous deviations in tree-diameter distributions away from the long-term mean, leading us to conclude that modern-day disequilibrium in natural forests may be the legacy of past disturbance events.

Plant Ecology, 2002

Many studies have investigated the density-dependent regulation ofannual-plant populations on coa... more Many studies have investigated the density-dependent regulation ofannual-plant populations on coastal sand dunes, but few have explored theconsequences of competition for the coexistence of plants in these simplecommunities. We used neighbourhood techniques to parameterize competition anddispersal functions from field data collected for two species of dune annual(Aira praecox and Erodium cicutarium)over three successive years, and then combined these functions into spatiallyexplicit simulation models. The population size of Airavaried enormously between years, while Erodium remainedsteady. Competition with neighbours reduced the spike length ofAira plants only in one of the three years (when itspopulation density was highest), while competition with neighbouringErodium plants appeared to result in the local death ofAira plants. However, these density-dependent effects werefar too weak to generate the observed changes in the population size ofAira among years, or to maintain populations below theupper limits observed. The large-seeded Erodium wasaffected by intraspecific competition but was unaffected by small-seededAira plants. Therefore, the larger-seeded species wascompetitively superior to the smaller-seeded species, an affect that couldpromote coexistence (albeit weakly) by a competition-colonisation trade-off.Modal dispersion distances of Aira andErodium were 45 and 60 mm respectively,greater than the radius within which competitive interactions occurred (40mm). Theoretical studies suggest that under these conditions thespatial arrangement of plants should be nearly random. In factAira was spatially aggregated, especially when rare,suggesting that patchy mortality across the dunes was important in generatingspatial structure. The study suggests that density dependence only weaklyregulates dune annual communities, while year-to-year environmental variationexert major influences on population sizes and spatial structures.

Oikos, 2002

. Are differences in seed mass among species important in structuring plant communities? Evidence... more . Are differences in seed mass among species important in structuring plant communities? Evidence from analyses of spatial and temporal variation in dune-annual populations. -Oikos 96: 421-432. We analyse the population and spatial structures of coastal annual-plant communities, across ten dunes and three years, to explore the role of seed mass in structuring these communities. One suggestion is that annual-plant communities are structured by competition-colonization trade-offs driven by difference among species in seed-allocation strategies, while another perspective is that seed mass influences the ways in which species respond to environmental variation. In support of the competition-colonization trade-off, the two largest-seeded species found on the dunes (Erodium cicutarium and Geranium molle) were negatively associated with the other guild members at the 10-mm scale in 1995, suggesting they locally excluded smaller-seeded species in that year (when population densities were high). In support of the environmental response hypothesis, populations of annual plants declined between 1995 and 1996 on eight of the ten dunes, underscoring the importance of year-to-year environmental fluctuations in determining population sizes. The species that became relatively uncommon also became more aggregated in space, and this effect was most pronounced among the small-seeded species. Thus, small-seeded species may be forced to retreat into refuges when conditions are unfavourable, where reduced frequencies of interspecific contacts may increase their chances of persistence. We also show that small-seeded species sometimes reach much higher population densities than larger-seeded species, consistent with earlier findings, but reason that this abundance/seed mass relationship could have resulted from either a competition-colonization trade-off or from different responses of small-and large-seeded species to environmental variation. We conclude that dune-annual species with contrasting seed masses respond differently to environmental variation, while the competition-colonization trade-off plays a lesser role in community dynamics than previously considered.

Journal of Ecology, 2007

1We quantify the effects of spatial structure on individual, population and community biomass wit... more 1We quantify the effects of spatial structure on individual, population and community biomass within a natural community of annuals for two years (1994 and 1996) in which competition operated differently.2Using field-parameterized neighbourhood models in which we had previously estimated the spatial scale and magnitude of competitive effects, we perform virtual experiments in which we manipulate spatial structure relative to that observed. We first remove segregation by randomly re-labelling all annual plants in a focal plant's neighbourhood and then give individuals of all species the same average number of neighbours by re-locating individuals within the overall pattern of annuals.3The natural spatial structure generally acted to promote species coexistence. In 1994, when the strength of individual-level competition within species was already greater than that between species, the natural spatial structure enhanced this effect for six out of seven species by increasing the relative frequency of intraspecific contacts. Average plant biomass increased by 0.24–38% when spatial locations were randomized.4In 1996, when a single competitive hierarchy operated, the natural spatial structure systematically benefited small-seeded, weakly competitive species while having weak negative effects on large-seeded, strong competitors. Randomizing spatial locations decreased the biomass of the species with the smallest seeds by 12% but increased the biomass of the species with the largest seeds by < 1%. This asymmetry increased dramatically when we used the model to increase the competitive advantage of large seeds artificially. Randomizing spatial locations decreased the biomass of the species with the smallest seeds by 37% but increased the biomass of the species with the largest seeds by only 2.7%.5Effects of spatial structure on total community biomass were always small (maximum 7%). This was because common species always have weak spatial structure, and they draw down the effect on the community as a whole.6Our analysis, for the first time, quantifies the magnitude and direction of the effects of spatial structure in a natural community, and supports the conclusions of theoretical models that spatial structure can have substantial impacts on component species and community dynamics.We quantify the effects of spatial structure on individual, population and community biomass within a natural community of annuals for two years (1994 and 1996) in which competition operated differently.Using field-parameterized neighbourhood models in which we had previously estimated the spatial scale and magnitude of competitive effects, we perform virtual experiments in which we manipulate spatial structure relative to that observed. We first remove segregation by randomly re-labelling all annual plants in a focal plant's neighbourhood and then give individuals of all species the same average number of neighbours by re-locating individuals within the overall pattern of annuals.The natural spatial structure generally acted to promote species coexistence. In 1994, when the strength of individual-level competition within species was already greater than that between species, the natural spatial structure enhanced this effect for six out of seven species by increasing the relative frequency of intraspecific contacts. Average plant biomass increased by 0.24–38% when spatial locations were randomized.In 1996, when a single competitive hierarchy operated, the natural spatial structure systematically benefited small-seeded, weakly competitive species while having weak negative effects on large-seeded, strong competitors. Randomizing spatial locations decreased the biomass of the species with the smallest seeds by 12% but increased the biomass of the species with the largest seeds by < 1%. This asymmetry increased dramatically when we used the model to increase the competitive advantage of large seeds artificially. Randomizing spatial locations decreased the biomass of the species with the smallest seeds by 37% but increased the biomass of the species with the largest seeds by only 2.7%.Effects of spatial structure on total community biomass were always small (maximum 7%). This was because common species always have weak spatial structure, and they draw down the effect on the community as a whole.Our analysis, for the first time, quantifies the magnitude and direction of the effects of spatial structure in a natural community, and supports the conclusions of theoretical models that spatial structure can have substantial impacts on component species and community dynamics.

Journal of Ecology, 2004

1 We used neighbourhood modelling to estimate individual-level competition coefficients for seven... more 1 We used neighbourhood modelling to estimate individual-level competition coefficients for seven annuals growing in limestone grassland over 2 years. We calculated the relative strength of intra-and interspecific competition and related this to differences in seed size and plant size between targets and neighbours. 2 Significant differences in the impact of neighbours on each target species were observed in half the models fitted, allowing us to reject a null hypothesis of competitive equivalence.

Seed Science Research, 1997

Plant Ecology, 1996

Trends in Ecology and Evolution, 2003

Impacts of Root Competition in Forests and Woodlands: A Theoretical Framework and Review of Experiments

Ecological Monographs, 2000

Global Ecology and Biogeography, 2007

Ecological Modelling, 2008

Biological Conservation, 2006

Conservation Biology, 2003

Journal of Ecology, 2005

Forest Ecology and Management, 2002

Journal of Ecology, 2007

Ecology Letters, 2003

Enquist and Niklas propose that trees in natural forests have invariant size-density distribution... more Enquist and Niklas propose that trees in natural forests have invariant size-density distributions (SDDs) that scale as a −2 power of stem diameter, although early studies described such distributions using negative exponential functions. Using New Zealand and ‘global’ data sets, we demonstrate that neither type of function accurately describes the SDD over the entire diameter range. Instead, scaling functions provide the best fit to smaller stems, while negative exponential functions provide the best fit to larger stems. We argue that these patterns are consistent with competition shaping the small-stem phase and exogenous disturbance shaping the large-stem phase. Mortality rates, estimated from repeat measurements on 1546 New Zealand plots, fell precipitously with stem size until 18 cm but remained constant after that, consistent with our arguments. Even in the small-stem phase, where SDDs were best described by scaling functions, the scaling exponents were not invariantly −2, but differed significantly from this value in both the ‘global’ and New Zealand data sets, and varied through time in the New Zealand data set.

Journal of Ecology, 2007

Plant Ecology, 2002

Oikos, 2002

Journal of Ecology, 2007

Journal of Ecology, 2004