Loss of animal seed dispersal increases extinction risk in a tropical tree species due to pervasive negative density dependence across life stages
Caughlin, T.T. ; Ferguson, J.M. ; Lichstein, J.W. ; Zuidema, P.A. ; Bunyavejchewin, S. ; Levey, D.J. - \ 2015
Proceedings of the Royal Society. B: Biological Sciences 282 (2015)1798. - ISSN 0962-8452 - 9 p.
spatial-patterns - rain-forest - recruitment - consequences - neighborhood - defaunation - habitat - uncertainty - diversity - abundance
Overhunting in tropical forests reduces populations of vertebrate seed dispersers. If reduced seed dispersal has a negative impact on tree population viability, overhunting could lead to altered forest structure and dynamics, including decreased biodiversity. However, empirical data showing decreased animal-dispersed tree abundance in overhunted forests contradict demographic models which predict minimal sensitivity of tree population growth rate to early life stages. One resolution to this discrepancy is that seed dispersal determines spatial aggregation, which could have demographic consequences for all life stages. We tested the impact of dispersal loss on population viability of a tropical tree species, Miliusa horsfieldii, currently dispersed by an intact community of large mammals in a Thai forest. We evaluated the effect of spatial aggregation for all tree life stages, from seeds to adult trees, and constructed simulation models to compare population viability with and without animal-mediated seed dispersal. In simulated populations, disperser loss increased spatial aggregation by fourfold, leading to increased negative density dependence across the life cycle and a 10-fold increase in the probability of extinction. Given that the majority of tree species in tropical forests are animal-dispersed, overhunting will potentially result in forests that are fundamentally different from those existing now.
Can we infer plant facilitation from remote sensing? A test across global drylands
Xu, C. ; Holmgren, M. ; Nes, E.H. van; Maestre, F.T. ; Soliveres, S. ; Berdugo, M. ; Kefi, S. ; Marquet, P.A. ; Abades, S. ; Scheffer, M. - \ 2015
Ecological Applications 25 (2015)6. - ISSN 1051-0761 - p. 1456 - 1462.
positive interactions - vegetation patterns - spatial-patterns - ecosystems - desertification - distributions - environments - competition - dynamics - ecology
Facilitation is a major force shaping the structure and diversity of plant communities in terrestrial ecosystems. Detecting positive plant-plant interactions relies on the combination of field experimentation and the demonstration of spatial association between neighboring plants. This has often restricted the study of facilitation to particular sites, limiting the development of systematic assessments of facilitation over regional and global scales. Here we explore whether the frequency of plant spatial associations detected from high-resolution remotely-sensed images can be used to infer plant facilitation at the community level in drylands around the globe. We correlated the information from remotely-sensed images freely available through Google EarthTM with detailed field assessments, and used a simple individual-based model to generate patch-size distributions using different assumptions about the type and strength of plant-plant interactions. Most of the patterns found from the remotely-sensed images were more right-skewed than the patterns from the null model simulating a random distribution. This suggests that the plants in the studied drylands show stronger spatial clustering than expected by chance. We found that positive plant co-occurrence, as measured in the field, was significantly related to the skewness of vegetation patch-size distribution measured using Google EarthTM images. Our findings suggest that the relative frequency of facilitation may be inferred from spatial pattern signals measured from remotely-sensed images, since facilitation often determines positive co-occurrence among neighboring plants. They pave the road for a systematic global assessment of the role of facilitation in terrestrial ecosystems.
CTFS-ForestGEO: A worldwide network monitoring forests in an era of global change
Anderson-Teixeira, K.J. ; Davies, S.J. ; Bennett, A.C. ; Gonzalez-Akre, E.B. ; Muller-Landau, H.C. ; Wright, S.J. ; Abu Salim, K. ; Almeyda Zambrano, A.M. ; Jansen, P.A. ; Ouden, J. den - \ 2015
Global Change Biology 21 (2015)2. - ISSN 1354-1013 - p. 528 - 549.
tropical tree community - long-term nitrogen - rain-forest - neotropical forest - functional traits - spatial-patterns - el-nino - phylogenetic structure - seedling recruitment - dispersal limitation
Global change is impacting forests worldwide, threatening biodiversity and ecosystem services including climate regulation. Understanding how forests respond is critical to forest conservation and climate protection. This review describes an international network of 59 long-term forest dynamics research sites (CTFS-ForestGEO) useful for characterizing forest responses to global change. Within very large plots (median size 25 ha), all stems =1 cm diameter are identified to species, mapped, and regularly recensused according to standardized protocols. CTFS-ForestGEO spans 25°S–61°N latitude, is generally representative of the range of bioclimatic, edaphic, and topographic conditions experienced by forests worldwide, and is the only forest monitoring network that applies a standardized protocol to each of the world's major forest biomes. Supplementary standardized measurements at subsets of the sites provide additional information on plants, animals, and ecosystem and environmental variables. CTFS-ForestGEO sites are experiencing multifaceted anthropogenic global change pressures including warming (average 0.61 °C), changes in precipitation (up to ±30% change), atmospheric deposition of nitrogen and sulfur compounds (up to 3.8 g N m-2 yr-1 and 3.1 g S m-2 yr-1), and forest fragmentation in the surrounding landscape (up to 88% reduced tree cover within 5 km). The broad suite of measurements made at CTFS-ForestGEO sites makes it possible to investigate the complex ways in which global change is impacting forest dynamics. Ongoing research across the CTFS-ForestGEO network is yielding insights into how and why the forests are changing, and continued monitoring will provide vital contributions to understanding worldwide forest diversity and dynamics in an era of global change.
Drought and grazing combined: Contrasting shifts in plant interactions at species pair and community level
Verwijmeren, M. ; Rietkerk, M. ; Bautista, S. ; Garcia Mayor, A.P. ; Wassen, M.J. ; Smit, C. - \ 2014
Journal of Arid Environments 111 (2014). - ISSN 0140-1963 - p. 53 - 60.
stress-gradient hypothesis - positive interactions - nurse plants - microhabitat amelioration - spatial-patterns - arid ecosystems - abiotic stress - semiarid plant - tree saplings - facilitation
The combined effects of drought stress and grazing pressure on shaping plant plant interactions are still poorly understood, while this combination is common in arid ecosystems. In this study we assessed the relative effect of grazing pressure and slope aspect (drought stress) on vegetation cover and soil functioning in semi-arid Mediterranean-grassland shrublands in southeastern Spain. Moreover, we linked these two stress factors to plant co-occurrence patterns at species-pair and community levels, by performing C-score analyses. Vegetation cover and soil functioning decreased with higher grazing pressure and more south-facing (drier) slopes. At the community level, plants at south-facing slopes were negatively associated at no grazing but positively associated at low grazing pressure and randomly associated at high grazing pressure. At north-facing slopes, grazing did not result in a shift in the direction of the association. In contrast, analysis of pairwise species co-occurrence patterns showed that the dominant species Stipa tenacissima and Anthyllis cytisoides shifted from excluding each other to co-occurring with increasing grazing pressure at north-facing slopes. Our findings highlight that for improved understanding of plant interactions along stress gradients, interactions between species pairs and interactions at the community level should be assessed, as these may reveal contrasting results. (C) 2014 Elsevier Ltd. All rights reserved.
Belowground biodiversity and ecosystem functioning
Bardgett, R.D. ; Putten, W.H. van der - \ 2014
Nature 515 (2014). - ISSN 0028-0836 - p. 505 - 511.
arbuscular mycorrhizal fungi - soil microbial communities - food webs - global patterns - ectomycorrhizal fungi - litter decomposition - neighboring plants - spatial-patterns - invasive plant - climate-change
Evidence is mounting that the immense diversity of microorganisms and animals that live belowground contributes significantly to shaping aboveground biodiversity and the functioning of terrestrial ecosystems. Our understanding of how this belowground biodiversity is distributed, and how it regulates the structure and functioning of terrestrial ecosystems, is rapidly growing. Evidence also points to soil biodiversity as having a key role in determining the ecological and evolutionary responses of terrestrial ecosystems to current and future environmental change. Here we review recent progress and propose avenues for further research in this field.
Negative density dependence of seed dispersal and seedling recruitment in a Neotropical palm
Jansen, P.A. ; Visser, M.D. ; Joseph Wright, S. ; Rutten, G. ; Muller-Landau, H.C. - \ 2014
Ecology Letters 17 (2014)9. - ISSN 1461-023X - p. 1111 - 1120.
scatter-hoarding rodent - tropical tree - spatial-patterns - plant diversity - forest - competition - removal - consequences - mechanisms - herbivores
Negative density dependence (NDD) of recruitment is pervasive in tropical tree species. We tested the hypotheses that seed dispersal is NDD, due to intraspecific competition for dispersers, and that this contributes to NDD of recruitment. We compared dispersal in the palm Attalea butyracea across a wide range of population density on Barro Colorado Island in Panama and assessed its consequences for seed distributions. We found that frugivore visitation, seed removal and dispersal distance all declined with population density of A. butyracea, demonstrating NDD of seed dispersal due to competition for dispersers. Furthermore, as population density increased, the distances of seeds from the nearest adult decreased, conspecific seed crowding increased and seedling recruitment success decreased, all patterns expected under poorer dispersal. Unexpectedly, however, our analyses showed that NDD of dispersal did not contribute substantially to these changes in the quality of the seed distribution; patterns with population density were dominated by effects due solely to increasing adult and seed density.
Carbon storage in tropical forests correlates with taxonomic diversity and functional dominance on global scales
Cavanaugh, K.C. ; Gosnell, S. ; Davis, S.L. ; Ahumada, J. ; Boundja, P. ; Clark, D.B. ; Mugerwa, B. ; Jansen, P.A. ; O'Brien, T.G. ; Rovero, F. ; Sheil, D. ; Vasquez, R. ; Andelman, S. - \ 2014
Global Ecology and Biogeography 23 (2014)5. - ISSN 1466-822X - p. 563 - 573.
ecosystem function - species richness - plant diversity - wood density - aboveground biomass - amazonian forest - spatial-patterns - multiple traits - productivity - biodiversity
We examined (1) the relationships between aboveground tropical forest C storage, biodiversity and environmental drivers and (2) how these relationships inform theory concerning ecosystem function and biodiversity. Experiments have shown that there is a positive relationship between biodiversity and ecosystem functioning, but intense debate exists on the underlying mechanisms. While some argue that mechanisms such as niche complementarity increase ecosystem function, others argue that these relationships are a selection effect.
Effects of sampling scale on patterns of habitat association in tropical trees
Garzon-Lopez, C.X. ; Jansen, P.A. ; Bohlman, S.A. ; Ordonez, A. ; Olff, H. - \ 2014
Journal of Vegetation Science 25 (2014)2. - ISSN 1100-9233 - p. 349 - 362.
rain-forest trees - spatial-patterns - environmental heterogeneity - recruitment limitation - mesoscale distribution - ecological community - neotropical forest - neutral theory - landscape - distributions
Questions: Niche differentiation is a central explanation for the co-existence and distribution patterns of numerous tree species in tropical forests, but functional equivalence leading to neutral dynamics has been proposed as an alternative explanation. This niche vs neutral debate is fuelled by the highly variable results yielded by studies of the association between tree species distributions and environmental factors, where some studies find strong associations but others do not. Here, we ask how differences in sampling scale between studies contribute to this variation. Location: Barro Colorado Island, Panama. Methods: Using distribution maps of canopy-statured individuals, we evaluated patterns of habitat association in five tropical tree species on Barro Colorado Island across a wide range of sampling scales (from 50 to 1600 ha). We investigated the scale-dependency of species clumping patterns (Ripley's K) and the association of species distributions with important environmental variables (forest age, topography and geological formation) using point pattern analyses. Results: Clump size and clump density had high variances within and among spatial scales. Significant habitat associations were found in all five species, with the number of habitat associations generally increasing with the sampling scale. Ignoring dispersal constraints inflated the number of significant habitat associations. Conclusions: We found that patterns of habitat association (and hence conclusions on the importance of niche vs neutral processes) are strongly affected by the choice of sampling scale and location. Explicit inclusion of the effect of spatial scale is critical for studies of habitat association and the main processes that structure communities of tropical trees.
Large trees drive forest aboveground biomass variation in moist lowland forests across the tropics
Slik, J.W.F. ; Paoli, G. ; McGuire, K. ; Amaral, I. ; Barroso, J. ; Bongers, F. ; Poorter, L. - \ 2013
Global Ecology and Biogeography 22 (2013)12. - ISSN 1466-822X - p. 1261 - 1271.
rain-forest - wood density - species composition - spatial-patterns - landscape-scale - carbon stocks - amazon - diversity - climate - monodominance
Aim - Large trees (d.b.h.¿=¿70¿cm) store large amounts of biomass. Several studies suggest that large trees may be vulnerable to changing climate, potentially leading to declining forest biomass storage. Here we determine the importance of large trees for tropical forest biomass storage and explore which intrinsic (species trait) and extrinsic (environment) variables are associated with the density of large trees and forest biomass at continental and pan-tropical scales. Location - Pan-tropical. Methods - Aboveground biomass (AGB) was calculated for 120 intact lowland moist forest locations. Linear regression was used to calculate variation in AGB explained by the density of large trees. Akaike information criterion weights (AICc-wi) were used to calculate averaged correlation coefficients for all possible multiple regression models between AGB/density of large trees and environmental and species trait variables correcting for spatial autocorrelation. Results - Density of large trees explained c. 70% of the variation in pan-tropical AGB and was also responsible for significantly lower AGB in Neotropical [287.8 (mean)¿±¿105.0 (SD) Mg ha-1] versus Palaeotropical forests (Africa 418.3¿±¿91.8 Mg ha-1; Asia 393.3¿±¿109.3 Mg ha-1). Pan-tropical variation in density of large trees and AGB was associated with soil coarseness (negative), soil fertility (positive), community wood density (positive) and dominance of wind dispersed species (positive), temperature in the coldest month (negative), temperature in the warmest month (negative) and rainfall in the wettest month (positive), but results were not always consistent among continents. Main conclusions - Density of large trees and AGB were significantly associated with climatic variables, indicating that climate change will affect tropical forest biomass storage. Species trait composition will interact with these future biomass changes as they are also affected by a warmer climate. Given the importance of large trees for variation in AGB across the tropics, and their sensitivity to climate change, we emphasize the need for in-depth analyses of the community dynamics of large trees
Mapping tropical forest trees using high-resolution aerial digital photographs
Garzon-Lopez, C.X. ; Bohlman, S.A. ; Olff, H. ; Jansen, P.A. - \ 2013
Biotropica 45 (2013)3. - ISSN 0006-3606 - p. 308 - 316.
rain-forest - spatial-patterns - scale - dispersal - imagery - identification - biodiversity - limitation - management - dynamics
The spatial arrangement of tree species is a key aspect of community ecology. Because tree species in tropical forests occur at low densities, it is logistically challenging to measure distributions across large areas. In this study, we evaluated the potential use of canopy tree crown maps, derived from high-resolution aerial digital photographs, as a relatively simple method for measuring large-scale tree distributions. At Barro Colorado Island, Panama, we used high-resolution aerial digital photographs (~0.129 m/pixel) to identify tree species and map crown distributions of four target tree species. We determined crown mapping accuracy by comparing aerial and ground-mapped distributions and tested whether the spatial characteristics of the crown maps reflect those of the ground-mapped trees. Nearly a quarter (22%) of the common canopy species had sufficiently distinctive crowns to be good candidates for reliable mapping. The errors of commission (crowns misidentified as a target species) were relatively low, but the errors of omission (missed canopy trees of the target species) were high. Only 40 percent of canopy individuals were mapped on the air photographs. Despite failing to accurately predict exact abundances of canopy trees, crown distributions accurately reproduced the clumping patterns and spatial autocorrelation features of three of four tree species and predicted areas of high and low abundance. We discuss a range of ecological and forest management applications for which this method can be useful.
Directed seed dispersal towards areas with low conspecific tree density by a scatter-hoarding rodent
Hirsch, B.T. ; Kays, R. ; Pereira, V.E. ; Jansen, P.A. - \ 2012
Ecology Letters 15 (2012)12. - ISSN 1461-023X - p. 1423 - 1429.
chipmunks tamias-amoenus - tropical forests - spatial-patterns - dependent survival - cache protection - fox squirrels - recruitment - pilferage - abundance - ecology
Scatter-hoarding animals spread out cached seeds to reduce density-dependent theft of their food reserves. This behaviour could lead to directed dispersal into areas with lower densities of conspecific trees, where seed and seedling survival are higher, and could profoundly affect the spatial structure of plant communities. We tested this hypothesis with Central American agoutis and Astrocaryum standleyanum palm seeds on Barro Colorado Island, Panama. We radio-tracked seeds as they were cached and re-cached by agoutis, calculated the density of adult Astrocaryum trees surrounding each cache, and tested whether the observed number of trees around seed caches declined more than expected under random dispersal. Seedling establishment success was negatively dependent on seed density, and agoutis carried seeds towards locations with lower conspecific tree densities, thus facilitating the escape of seeds from natural enemies. This behaviour may be a widespread mechanism leading to highly effective seed dispersal by scatter-hoarding animals.
Thieving rodents as substitute dispersers of megafaunal seeds
Jansen, P.A. ; Hirsch, B.T. ; Emsens, W.J. ; Zamora-Gutierrez, V. ; Wikelski, M. ; Kays, R. - \ 2012
Proceedings of the National Academy of Sciences of the United States of America 109 (2012)31. - ISSN 0027-8424 - p. 12610 - 12615.
palm astrocaryum-standleyanum - tropical forests - spatial-patterns - acorn dispersal - rain-forest - agouti - recruitment - predation - tracking - survival
The Neotropics have many plant species that seem to be adapted for seed dispersal by megafauna that went extinct in the late Pleistocene. Given the crucial importance of seed dispersal for plant persistence, it remains a mystery how these plants have survived more than 10,000 y without their mutualist dispersers. Here we present support for the hypothesis that secondary seed dispersal by scatter-hoarding rodents has facilitated the persistence of these large-seeded species. We used miniature radio transmitters to track the dispersal of reputedly megafaunal seeds by Central American agoutis, which scatter-hoard seeds in shallow caches in the soil throughout the forest. We found that seeds were initially cached at mostly short distances and then quickly dug up again. However, rather than eating the recovered seeds, agoutis continued to move and recache the seeds, up to 36 times. Agoutis dispersed an estimated 35% of seeds for >100 m. An estimated 14% of the cached seeds survived to the next year, when a new fruit crop became available to the rodents. Serial video-monitoring of cached seeds revealed that the stepwise dispersal was caused by agoutis repeatedly stealing and recaching each other's buried seeds. Although previous studies suggest that rodents are poor dispersers, we demonstrate that communities of rodents can in fact provide highly effective long-distance seed dispersal. Our findings suggest that thieving scatter-hoarding rodents could substitute for extinct megafaunal seed dispersers of tropical large-seeded trees.
Human impacts on fire occurrence: a case study of hundred years of forest fires in a dry alpine valley in Switzerland
Zumbrunnen, T. ; Menéndez, P. ; Bugmann, H. ; Conedera, M. ; Gimmi, U. ; Bürgi, M. - \ 2012
Regional Environmental Change 12 (2012)4. - ISSN 1436-3798 - p. 935 - 949.
generalized additive-models - smoothing parameter-estimation - climate-change - southern-california - land abandonment - united-states - swiss alps - landscape dynamics - spatial-patterns - national-park
Forest fire regimes are sensitive to alterations of climate, fuel load, and ignition sources. We investigated the impact of human activities and climate on fire occurrence in a dry continental valley of the Swiss Alps (Valais) by relating fire occurrence to population and road density, biomass removal by livestock grazing and wood harvest, temperature and precipitation in two distinct periods (1904–1955 and 1956–2006) using generalized additive modeling. This study provides evidence for the role played by humans and temperature in shaping fire occurrence. The existence of ignition sources promotes fire occurrence to a certain extent only; for example, high road density tends to be related to fewer fires. Changes in forest uses within the study region seem to be particularly important. Fire occurrence appears to have been negatively associated with livestock pasturing in the forest and wood harvesting, in particular during the period 1904–1955. This study illustrates consistently how fire occurrence has been influenced by land use and socioeconomic conditions. It also suggests that there is no straightforward linear relationship between human factors and fire occurrence.
Quantifying seed dispersal kernels from truncated seed-tracking data
Hirsch, B.T. ; Visser, M.D. ; Kays, R. ; Jansen, P.A. - \ 2012
Methods in Ecology and Evolution 3 (2012)3. - ISSN 2041-210X - p. 595 - 602.
tropical forests - plant-populations - spatial-patterns - wind dispersal - rain-forest - shadows - consequences - recruitment - dependence - behavior
1. Seed dispersal is a key biological process that remains poorly documented because dispersing seeds are notoriously hard to track. While long-distance dispersal is thought to be particularly important, seed-tracking studies typically yield incomplete data sets that are biased against long-distance movements. 2. We evaluate an analytical procedure developed by Jansen, Bongers & Hemerik (2004) to infer the tail of a seed dispersal kernel from incomplete frequency distributions of dispersal distances obtained by tracking seeds. This ‘censored tail reconstruction’ (CTR) method treats dispersal distances as waiting times in a survival analysis and censors nonretrieved seeds according to how far they can reliably be tracked. We tested whether CTR can provide unbiased estimates of longdistance movements which typically cannot be tracked with traditional field methods. 3. We used a complete frequency distribution of primary seed dispersal distances of the palm Astrocaryum standleyanum, obtained with telemetric thread tags that allow tracking seeds regardless of the distance moved. We truncated and resampled the data set at various distances, fitted kernel functions on CTR estimates of dispersal distance and determined how well this function approximated the true dispersal kernel. 4. Censored tail reconstruction with truncated data approximated the true dispersal kernel remarkably well but only when the best-fitting function (lognormal) was used. We were able to select the correct function and derive an accurate estimate of the seed dispersal kernel even after censoring 50–60% of the dispersal events. However, CTR results were substantially biased if 5% or more of seeds within the search radius were overlooked by field observers and erroneously censored. Similar results were obtained using additional simulated dispersal kernels. 5. Our study suggests that the CTR method can accurately estimate the dispersal kernel from truncated seed-tracking data if the kernel is a simple decay function. This method will improve our understanding of the spatial patterns of seed movement and should replace the usual practice of omitting nonretrieved seeds fromanalyses in seed-tracking studies
Eco-Morphological Problems in the Yangtze Estuary and the Western Scheldt
Vriend, H.J. de; Wang, Z.B. ; Ysebaert, T. ; Herman, P.M.J. ; Ding, P.X. - \ 2011
Wetlands 31 (2011)6. - ISSN 0277-5212 - p. 1033 - 1042.
sedimentation patterns - changjiang yangtze - salinity gradient - chongming dongtan - spatial-patterns - river estuary - nw-europe - china - netherlands - waters
This paper compares the Yangtze Estuary in China and the Western Scheldt Estuary in The Netherlands by their morphodynamic and ecological systems, their engineering works and estuarine management issues, and the major challenges in studying them. Physically speaking, the two estuaries are very different. The Yangtze Estuary is much larger and much more influenced by the upstream river than the Western Scheldt. Yet, they also have a number of morphological and ecological features in common. Both estuaries have a multi-channel system and extensive intertidal flats and wetlands with ecologically valuable flora and fauna. These eco-morphological systems are influenced by similar societal developments and human activities. Examples of the latter are engineering works and dredging activities for improving and maintaining the navigation channels, and shoreline management activities including land reclamations and setbacks. The fundamental eco-morphological phenomena that remain to be analysed and understood are the same for the two estuaries and will be discussed in this paper.
Height-diameter allometry of tropical forest trees
Feldpausch, T.R. ; Banin, L. ; Phillips, O.L. ; Baker, T.R. ; Lewis, S.L. ; Quesada, C.A. ; Affum-Baffoe, K. ; Arets, E.J.M.M. ; Berry, N.J. ; Bird, M. ; Brondizio, E.S. ; Camargo, P. de; Chave, J. ; Djagbletey, G. ; Domingues, T.F. ; Drescher, M. ; Fearnside, P.M. ; Franca, M.B. ; Fyllas, N.M. ; Lopez-Gonzalez, G. ; Hladik, A. ; Higuchi, N. ; Hunter, M.O. ; Iida, Y. ; Salim, K.A. ; Kassim, A.R. ; Keller, M. ; Kemp, J. ; King, D.A. ; Lovett, J.C. ; Marimon, B.S. ; Marimon-Junior, B.H. ; Lenza, E. ; Marshall, A.R. ; Metcalfe, D.J. ; Mitchard, E.T.A. ; Moran, E.F. ; Nelson, B.W. ; Nilus, R. ; Nogueira, E.M. ; Palace, M. ; Patino, S. ; Peh, K.S.H. ; Raventos, M.T. ; Reitsma, J.M. ; Saiz, G. ; Schrodt, F. ; Sonké, B. ; Taedoumg, H.E. ; Tan, S. ; White, L. ; Wöll, H. ; Lloyd, J. - \ 2011
Biogeosciences 8 (2011). - ISSN 1726-4170 - p. 1081 - 1106.
amazon rain-forest - elfin cloud forest - leaf gas-exchange - montane forest - aboveground biomass - spatial-patterns - hydraulic architecture - altitudinal transect - environmental-change - neotropical forest
Tropical tree height-diameter (H:D) relationships may vary by forest type and region making large-scale estimates of above-ground biomass subject to bias if they ignore these differences in stem allometry. We have therefore developed a new global tropical forest database consisting of 39 955 concurrent H and D measurements encompassing 283 sites in 22 tropical countries. Utilising this database, our objectives were: 1. to determine if H:D relationships differ by geographic region and forest type (wet to dry forests, including zones of tension where forest and savanna overlap). 2. to ascertain if the H:D relationship is modulated by climate and/or forest structural characteristics (e.g. stand-level basal area, A). 3. to develop H:D allometric equations and evaluate biases to reduce error in future local-to-global estimates of tropical forest biomass. Annual precipitation coefficient of variation (PV), dry season length (SD), and mean annual air temperature (TA) emerged as key drivers of variation in H:D relationships at the pantropical and region scales. Vegetation structure also played a role with trees in forests of a high A being, on average, taller at any given D. After the effects of environment and forest structure are taken into account, two main regional groups can be identified. Forests in Asia, Africa and the Guyana Shield all have, on average, similar H:D relationships, but with trees in the forests of much of the Amazon Basin and tropical Australia typically being shorter at any given D than their counterparts elsewhere. The region-environment-structure model with the lowest Akaike's information criterion and lowest deviation estimated stand-level H across all plots to within amedian -2.7 to 0.9% of the true value. Some of the plot-to-plot variability in H:D relationships not accounted for by this model could be attributed to variations in soil physical conditions. Other things being equal, trees tend to be more slender in the absence of soil physical constraints, especially at smaller D. Pantropical and continental-level models provided less robust estimates of H, especially when the roles of climate and stand structure in modulating H:D allometry were not simultaneously taken into account.
The effect of feeding time on dispersal of Virola seeds by toucans determined from GPS tracking and accelerometers
Kays, R.W. ; Jansen, P.A. ; Knecht, E. ; Vohwinkel, R. ; Wikelski, M. - \ 2011
Acta Oecologica-International Journal of Ecology 37 (2011)6. - ISSN 1146-609X - p. 625 - 631.
spatial-patterns - animal movement - forest - ecology - models - panama - birds - wild - frugivore - behavior
Seed dispersal is critical to understanding forest dynamics but is hard to study because tracking seeds is difficult. Even for the best-studied dispersal system of the Neotropics, Virola nobilis, the dispersal kernel remains unknown. We combined high-resolution GPS/3D-acceleration bird tracking, seed-retention experiments, and field observations to quantify dispersal of V. nobilis by their principal dispersers, Ramphastos toucans. We inferred feeding events from movement data, and then estimated spatio-temporally explicit seed-dispersal kernels. Wild toucans moved an average of 1.8 km d-1 with two distinct activity peaks. Seed retention time in captive toucans averaged 25.5 min (range 4–98 min). Estimated seed dispersal distance averaged 144 ± 147 m, with a 56% likelihood of dispersal >100 m, two times further than the behaviour-naive estimate from the same data. Dispersal was furthest for seeds ingested in the morning, and increased with seed retention time, but only up to 60 min after feeding. Our study supports the long-standing hypothesis that toucans are excellent dispersers of Virola seeds. To maximize seed dispersal distances trees should ripen fruit in the morning when birds move the most, and produce fruits with gut-processing times around 60 min. Our study demonstrates how new tracking technology can yield nuanced seed dispersal kernels for animals that cannot be directly observed.
A common dominant scale emerges from images of diverse satellite platforms using the wavelet transform
Pittiglio, C. ; Skidmore, A.K. ; Bie, C.A.J.M. de; Murwira, A. - \ 2011
International Journal of Remote Sensing 32 (2011)13. - ISSN 0143-1161 - p. 3665 - 3687.
spatial-patterns - ecological data - landscape - decomposition - vegetation - resolution - fusion - heterogeneity - avhrr - zone
In this article we investigate the scale dependence of spatial heterogeneity in multiresolution and multisensor data using the wavelet transform. The landscape analysed with the wavelets retains the same dominant pattern irrespective of the original pixel size of the image. In agricultural areas, typically characterized by a mosaic of cultivated fields, the wavelet transform quantified consistently a median dominant scale of 512 m in the Orthophoto, Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) and Landsat Enhanced Thematic Mapper Plus (ETM+). The dominant scale represented the dominant field size of cultivated areas. The shape of the average wavelet energy curves was also similar among the images. In semi-natural areas the wavelet transform quantified consistently a median dominant scale of 128 m in the Orthophoto and ASTER. The median dominant scale of ETM+ was slightly smaller and located at 64 m. We characterized the spatial heterogeneity of agricultural and semi-natural areas in Andalucia (Spain) using multisensor data not time coincident ranging from 1 m (Orthophoto), to 15 m (ASTER) to 28.5 m (ETM+). The contrast in vegetation cover was measured using Normalized Difference Vegetation Index (NDVI) in ASTER and ETM+ and red band in Orthophoto. We performed a multiresolution analysis using a Haar two-dimension discrete wavelet transform to quantify and compare the intensity (maximum degree of contrast in vegetation cover), the dominant scale (the scale at which the maximum intensity occurs) and the wavelet energy curve (intensity plotted as a function of the scale) of different images at intervals of power of 2 within the scale range from 2 to 4096 m
Strict mast fruiting for a tropical dipterocarp tree: a demographic cost–benefit analysis of delayed reproduction and seed predation
Visser, M.D. ; Jongejans, E. ; Breugel, M. van; Zuidema, P.A. ; Chen, Y.Y. ; Kassim, A.R. ; Kroon, H. de - \ 2011
Journal of Ecology 99 (2011)4. - ISSN 0022-0477 - p. 1033 - 1044.
rain-forest - evolutionary ecology - spatial-patterns - resource-allocation - woody-plants - el-nino - recruitment - dispersal - dynamics - impact
1. Masting, the production of large seed crops at intervals of several years, is a reproductive adaptation displayed by many tree species. The predator satiation hypothesis predicts that starvation of seed predators between mast years and satiation during mast years decreases seed predation and thus enhances tree regeneration. 2. Mast fruiting comes at demographic costs such as missed reproduction opportunities and increased density-dependence of recruits, but it remains unknown if predator satiation constitutes a sufficiently large benefit for masting to evolve as a viable life-history strategy. So far, no studies have quantified the net fitness consequences of masting. 3. Using a long-term demographic data set of the dipterocarp Shorea leprosula in a Malaysian forest, we constructed stochastic matrix population models and performed a demographic cost–benefit analysis. 4. For observed values of mast frequency and seed predation rates, we show that strict masting strongly increases fitness compared with fruiting annually. Model results also show that the demographic costs of mast fruiting are very low compared to the demographic losses due to seed predation in a scenario of annual fruiting. Finally, we find that mast fruiting would still be selected for even at low levels of seed predation and when including additional costs such as decreased adult growth rates, limiting crop size and density-dependent seedling survival. 5. Synthesis. Our results are consistent with the predictions of the predator satiation hypothesis: mast fruiting increases fitness for a range of seed predation levels. Under seed predation pressure annually fruiting species are at a strong disadvantage and as a result a mast fruiting strategy may swiftly confer a fitness advantage. Our study shows that demographic modelling allows the weighing of fitness benefits and costs of life-history phenomena such as strict masting.
Prunus serotina unleashed: invader dominance after 70 years of forest development
Vanhellemont, M. ; Wauters, L. ; Baeten, L. ; Bijlsma, R.J. ; Frenne, P. De; Hermy, M. ; Verheyen, K. - \ 2010
Biological Invasions 12 (2010)5. - ISSN 1387-3547 - p. 1113 - 1124.
black-cherry - propagule pressure - agricultural landscape - biotic invasions - tropical forests - spatial-patterns - acer-platanoides - seed dispersal - tree - temperate
Propagule pressure and disturbance have both been found to facilitate invasion. Therefore, knowledge on the history of introduction and disturbance is vital for understanding an invasion process, and research should focus on areas in which the invasive species has not been deliberately introduced or managed to study unconfounded colonization patterns. Comparing the outcome of such spontaneous colonization processes for different ecosystems might provide a useful framework for setting management priorities for invasive species that enter new, uninvaded areas. We focused on the 70-year spontaneous spread of the invasive tree species Prunus serotina in a pine forest in the Netherlands. To reconstruct the invasion pattern, we combined historical maps, tree ring analysis, spatially explicit tree inventory data, seed density data, and regeneration data for both native and non-native species. Prunus serotina was the only species that showed successful regeneration: the species was present throughout the forest in the tree, shrub, and herb layer. Native species were not able to outgrow the seedling stage. Our data demonstrate that P. serotina is a gap-dependent species with high seed production that builds up a seedling bank. We also compared the results of this study with a similar study on P. serotina colonization in a deciduous forest in Belgium, where P. serotina invasion was not successful. The sharp contrast between the outcomes of the two invasion processes shows the importance of studying an invasive species and the recipient ecosystem jointly and made us raise the hypothesis that herbivore pressure may facilitate P. serotina invasion