Changes in climate extremes and their impacts on the natural physical environment: An overview of the IPCC SREX report

What determines the number and size of the seeds produced by a plant? How often should it reproduce them? How often should a plant produce them? Why and how are seeds dispersed, and what are the implications for the diversity and composition of vegetation? These are just some of the questions tackled in this wide-ranging review of the role of seeds in the ecology of plants. The authors bring together information on the ecological aspects of seed biology, starting with a consideration of reproductive strategies in seed plants and progressing through the life cycle, covering seed maturation, dispersal, storage in the soil, dormancy, germination, seedling establishment, and regeneration in the field. The text encompasses a wide range of concepts of general relevance to plant ecology, reflecting the central role that the study of seed ecology has played in elucidating many fundamental aspects of plant community function.

The ecology of seeds

aLLiSon perry Reefs at Risk Revisited ContriButing inStitutionS Reefs at Risk Revisited is a project of the World Resources Institute (WRI), developed and implemented in close collaboration with The Nature Conservancy (TNC), the WorldFish Center, the International Coral Reef Action Network (ICRAN), the United Nations Environment Programme World Conservation Monitoring Centre (UNEP-WCMC), and the Global Coral Reef Monitoring Network (GCRMN). Many other government agencies, international organizations, research institutions, universities, nongovernmental organizations, and initiatives provided scientific guidance, contributed data, and reviewed results, including:

Reefs at Risk Revisited

▪ Abstract For many years biologists have debated whether mast seeding (the synchronous intermittent production of large seed crops in perennial plants) results from weather conditions or is an evolved plant reproductive strategy. In this review, we analyze the evidence for the underlying causes of masting. In the absence of selection for higher or lower variability, plants will vary in tandem with the environment (resource matching). Two selective factors often favor the evolution of masting: increased pollination efficiency in wind-pollinated species, and satiation of seed predators. Other factors select against masting, including animal pollination and frugivore dispersal. A survey of 570 masting datasets shows that wind-pollinated species had higher seed production coefficients of variation (CVs) than biotically pollinated ones. Frugivore-dispersed species had low CVs whereas predator-dispersed plants had high CVs, consistent with gaining benefits from predator satiation rather than dispersal. The glo...

MAST SEEDING IN PERENNIAL PLANTS: Why, How, Where?

The world’s coastal zones are experiencing rapid development and an increase in storms and flooding. These hazards put coastal communities at heightened risk, which may increase with habitat loss. Here we analyse globally the role and cost effectiveness of coral reefs in risk reduction. Meta-analyses reveal that coral reefs provide substantial protection against natural hazards by reducing wave energy by an average of 97%. Reef crests alone dissipate most of this energy (86%). There are 100 million or more people who may receive risk reduction benefits from reefs or bear hazard mitigation and adaptation costs if reefs are degraded. We show that coral reefs can provide comparable wave attenuation benefits to artificial defences such as breakwaters, and reef defences can be enhanced cost effectively. Reefs face growing threats yet there is opportunity to guide adaptation and hazard mitigation investments towards reef restoration to strengthen this first line of coastal defence.

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The effectiveness of coral reefs for coastal hazard risk reduction and adaptation

We developed a conceptual model for evaluating the benefits of wind pollination to mast-flowering species. The benefit that a plant population gains from mast flowering via increased wind pollination efficiency was predicted from how far pollination efficiency at mean seed crop size falls below the maximum. Species were most likely to benefit from mast seeding if mean reproductive effort in the field gave an intermediate level of pollination efficiency, regardless of the cost of unpollinated female structures. To quantify the benefits of different degrees of mast flowering, a simulation model was used to alter the seed production coefficient of variation (cv) and to calculate its effects on weighted mean pollination efficiency. The model was applied to seven real data sets for five species with pollination benefits from masting that ranged from relatively small (Chionochloa pallens), to moderate (Dacrydium cupressinum, Betula alleghaniensis), to large (Nothofagus solandri, N. menziesii).

Many studies have reported higher seed production coefficients of variation at higher altitudes and latitudes within a species. Our model showed that higher coefficients of variation are favored by reduced mean seed output per plant at higher altitudes. Data for N. solandri at three altitudes in one site showed much higher pollination benefits from masting at higher altitudes. Reduced plant density (e.g., through fragmentation), which also lowers mean flowering effort per unit area, resulted in large increases in masting benefits in N. solandri, but only small increases in C. pallens. These contrasting results were primarily due to differences between the two species in mean reproductive effort vs. wind pollination efficiency, rather than to differences in the effects of fragmentation and altitude.

The relative effects of masting on pollination, insect seed predation, and bird seed predation were modeled in B. alleghaniensis. Masting produced a small economy of scale from insect predator satiation, but an almost equivalent diseconomy of scale resulted from increased levels of bird seed predation. Efficiency of wind pollination improved moderately with increasing cv, providing some overall benefits from masting in this species. Accordingly, we propose that masting can be favored by either one dominant economy of scale (such as wind pollination efficiency in N. solandri or predator satiation in C. pallens), or a balance among several factors (such as pollination, predator satiation, and predator attraction in B. alleghaniensis). We predict that, in the absence of any selective benefits or disadvantages of masting, plants would be expected to have coefficients of variation in the range 0.85–1.35.

Evaluating the wind pollination benefits of mast seeding

Spatial and temporal variations in wave characteristics across a reef platform, Warraber Island, Torres Strait, Australia

[1] Low-lying reef islands appear particularly threatened by anticipated sea-level rise, and determining how they formed and whether they are continuing to accumulate sediment is essential for their sustainable management. Depositional chronology of Warraber Island, a small sand cay in Torres Strait, Australia, is re-examined based on AMS radiocarbon dating of specific skeletal components. Whereas radiometric dating of bulk sand samples indicated one or more discrete phases of mid-late Holocene deposition, component-specific AMS radiocarbon dating of sand grains indicates sustained incremental growth over the past 3000 years. Ages on gastropods that lived on the reef flat around the island indicate continuing sediment production and island progradation, in contrast to bulk ages and other components produced at greater distances. Growth of sand cays depends on the rate and pattern of sediment supply, which are functions of the local ecology of the surrounding reef and reef flat, and hydrodynamic constraints.

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Incremental accretion of a sandy reef island over the past 3000 years indicated by component-specific radiocarbon dating

Complex relationships exist between tropical reef ecology, carbonate (CaCO3) production and carbonate sinks. This paper investigated census-based techniques for determining the distribution and carbonate production of reef organisms on an emergent platform in central Torres Strait, Australia, and compared the contemporary budget with geological findings to infer shifts in reef productivity over the late Holocene. Results indicate that contemporary carbonate production varies by several orders of magnitude between and within the different reef-flat sub-environments depending on cover type and extent. Average estimated reef-flat production was 1.66 ± 1.78 kg m−2 year−1 (mean ± SD) although only 23% of the area was covered by carbonate producers. Collectively, these organisms produce 17,399 ± 18,618 t CaCO3 year−1, with production dominated by coral (73%) and subordinate contributions by encrusting coralline algae (18%) articulated coralline algae, molluscs, foraminifera and Halimeda (<4%). Comparisons between the production of these organisms across the different reef-flat zones, surface sediment composition and accumulation rates calculated from cores indicate that it is necessary to understand the spatial distribution, density and production of each major organism when considering the types and amounts of carbonate available for storage in the various reef carbonate sinks. These findings raise questions as to the reliability of using modal production rates in global models independent of ecosystem investigation, in particular, indicating that current models may overestimate reef productivity in emergent settings.

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Carbonate production of an emergent reef platform, Warraber Island, Torres Strait, Australia

Airborne light detection and ranging (LiDAR) data were acquired over the coastal city of Christchurch, New Zealand, prior to and throughout the 2010 to 2011 Canterbury Earthquake Sequence. Differencing of pre- and post-earthquake LiDAR data reveals land surface and waterway deformation due to seismic shaking and tectonic displacements above blind faults. Shaking caused floodplain subsidence in excess of 0.5 to 1 m along tidal stretches of the two main urban rivers, greatly enhancing the spatial extent and severity of inundation hazards posed by 100-year floods, storm surges, and sea-level rise. Additional shaking effects included river channel narrowing and shallowing, due primarily to liquefaction, and lateral spreading and sedimentation, which further increased flood hazard. Differential tectonic movement and associated narrowing of downstream river channels decreased channel gradients and volumetric capacities and increased upstream flood hazards. Flood mitigation along the large regional Waimakariri River north of Christchurch may have, paradoxically, increased the long-term flood hazard in the city by halting long-term aggradation of the alluvial plain upon which Christchurch is situated. Our findings highlight the potential for moderate magnitude (MW 6-7) earthquakes to cause major topographic changes that influence flood hazard in coastal settings.

Deirdre E. Hart

Papers

Evaluating the wind pollination benefits of mast seeding

Spatial and temporal variations in wave characteristics across a reef platform, Warraber Island, Torres Strait, Australia

Incremental accretion of a sandy reef island over the past 3000 years indicated by component-specific radiocarbon dating

Carbonate production of an emergent reef platform, Warraber Island, Torres Strait, Australia

The sinking city: Earthquakes increase flood hazard in Christchurch, New Zealand