Quantifying the greenhouse benefits of the use of wood products in two popular house designs in Sydney, Australia

Purpose

As the average wood products usage per unit of floor area in Australia has decreased significantly over time, there is potential for increased greenhouse gas (GHG) mitigation benefits through an increased use of wood products in buildings. This study determined the GHG outcomes of the extraction, manufacture, transport, use in construction, maintenance and disposal of wood products and other building materials for two popular house designs in Sydney, Australia.

Methods

The life cycle assessment (LCA) was undertaken using the computer model SimaPro 7.1, with the functional unit being the supply of base building elements for domestic houses in Sydney and its subsequent use over a 50-year period. The key data libraries used were the Australian Life Cycle Inventory library, the ecoinvent library (with data adapted to Australian circumstances where appropriate) and data for timber production from an Australian study for a range of Australian forestry production systems and wood products. Two construction variations were assessed: the original intended construction, and a “timber-maximised” alternative. The indicator assessed was global warming, as the focus was on GHG emissions, and the effect of timber production, use and disposal on the fate of carbon.

Results and discussion

The timber maximised design resulted in approximately half the GHG emissions associated with the base designs. The sub-floor had the largest greenhouse impact due to the concrete components, followed by the walls due to the usage of bricks. The use of a “timber maximised” design offset between 23 and 25 % of the total operational energy of the houses. Inclusion of carbon storage in landfill made a very significant difference to GHG outcomes, equivalent to 40–60 % of total house GHG emissions. The most beneficial options for disposal from a GHG perspective were landfill and incineration with energy recovery.

Conclusions

The study showed that significant GHG emission savings were achieved by optimising the use of wood products for two common house designs in Sydney. The switch of the sub-floor and floor covering components to a “wood” option accounted for most of the GHG savings. Inclusion of end of life parameters significantly impacted on the outcomes of the study.     

Tree-rings and transportation in the New Zealand kauri (Agathis australis) timber industry: Investigating the time lag from tree to building

The interpretation of felling dates established by dendrochronological dating requires understanding of sample context and building practices, as well as knowledge of processes and timescales within the timber supply chain. In New Zealand (N.Z.), tree ring analysis of kauri from colonial-era (1840–1906) and early Dominion-era (1907–1920) buildings has been undertaken since 2000 and felling dates have been identified from several structures, providing a terminus post quem date for construction or modification of the building. What has been lacking is a good understanding of how long it took for a kauri tree to become timber used in a building or other structure. As a first estimate, felling dates from a small set of buildings were compared to documented construction dates, suggesting a delay of up to 5 years. To improve interpretation of felling dates, we investigated timescales associated with two stages of timber production within the 19th and early 20th century kauri timber industry: (a) transportation from stump to mill, and (b) seasoning of sawn timber. Documentary sources for ∼1850 until the 1920s were analysed, covering the development, expansion and decline of industrialised kauri timber production. The available evidence suggests that transportation to the sawmill was the most important variable. Logs could arrive within a few weeks of felling or potentially experience a delay of a year or more. Transportation times were affected by geography, weather, spatial differences and temporal changes in transportation methods and economic fluctuations. Seasoning of sawn timber probably contributed little to the time lag, as the balance of evidence suggests framing timber was not usually seasoned. In general, any delay associated with transportation and seasoning is unlikely to be more than a couple of years. The findings support the earlier use-date range of up to 5 years, but suggest it is generous. The dating of waney-edge timbers from buildings with accurate construction dates would help refine a use date range for kauri, as would further research into other stages of the production process including conversion of logs, transportation to market, and stockpiling in the timber yard and/or building site. The current study is also a starting point for further research in three related areas: (a) biography of timber; (b) technological change; and (c) trade networks.     

Boron impregnation treatment of Eucalyptus grandis wood

Eucalyptus grandis is suitable for small timber purposes, but its wood is reported to be non-durable and difficult to treat. Boron compounds being diffusible, and the vacuum-pressure impregnation (VPI) method being more suitable for industrial-scale treatment, the possibility of boron impregnation of partially dry to green timber was investigated using a 6% boric acid equivalent (BAE) solution of boric acid and borax in the ratio 1:1.5 under different treatment schedules. It was found that E. grandis wood, even in green condition, could be pressure treated to desired chemical dry salt retention (DSR) and penetration levels using 6% BAE solution. Up to a thickness of 50mm, in order to achieve a DSR of 5 kg/m(3) boron compounds, the desired DSR level as per the Indian Standard for perishable timbers for indoor use, it was found that neither the moisture content of wood nor the treatment schedule posed any problem as far as the treatability of E. grandis wood was concerned.     

Searching for Leverage to Conserve Forests: The Industrial Ecology of Wood Products in the United States

The forest and the creatures it shelters exemplify nature, and logging exemplifies the impacts of humans. In the 1990s Americans annually removed 70% more timber from the forest than in 1900. Since I900 population rose more than three times and gross domestic product (GDP) per person almost five. Despite more people, affluence, and logging, U.S. forest area remained constant. Since mid-century, standing timber volume me nearly 30%. Consumers, millers, and foresters, responding to changes in style, ethics, and technology, have contributed to these outcomes. We examine the role of each actor in the industrial ecology of forests for their leverage for sparing forests. Consumers lessened their use of wood products per GDP (Intensity of Use) during the century by 2.5% annually to offset expanding population and GDP per person, a trend that will level or lower timber consumption if population and affluence grow as expected. Millers became highly efficient at utilizing wood and recycled fiber for their material or energy, a success that limits their fcrture leverage. Foresters have leverage to grow trees faster and thus use less forest land to grow and harvest timber. Steady or declining demand for trees coupled to productive forests could spare more US. forest land for sequestering carbon, ecosystem services, and habit for nature.     

Impacts of Intensive Management and Landscape Structure on Timber and Energy Wood Production and net CO2 Emissions from Energy Wood Use of Norway Spruce

The aim of this study was to analyze the effects of intensive management and forest landscape structure (in terms of age class distribution) on timber and energy wood production (m³?ha^?1), net present value (NPV, ? ha^?1) with implications on net CO₂ emissions (kg CO₂ MWh^?1 per energy unit) from energy wood use of Norway spruce grown on medium to fertile sites. This study employed simulations using a forest ecosystem model and the Emission Calculation Tool, considering in its analyses: timber (saw logs, pulp) and energy wood (small-sized stem wood and/or logging residuals for top part of stem, branches, and needles) from the first thinning and harvesting residuals and stumps from the final felling. At the stand level, both fertilization and high pre-commercial stand density clearly increased timber production and the amount of energy wood. Short rotation length (40 and 60?years) outputted, on average, the highest annual stem wood production (most fertile and medium fertile sites), the 60?year rotation also outputted the highest average annual net present value (NPV with interest rates of 1?C4%). On the other hand, even longer rotation lengths, up to 80 and 100?years, were needed to output the lowest net CO₂ emissions per year in energy wood use. At the landscape level, the largest productivity (both for timber and energy wood) was obtained using rotation lengths of 60 and 80?years with an initial forest landscape structure dominated by older mature stands (a right-skewed age-class distribution). If the rotation length was 120?years, the initial forest landscape dominated by young stands (a left-skewed age-class distribution) provided the highest productivity. However, the NPV with interest rate of 2% was, on average, the highest with a right-skewed distribution regardless of the rotation length. If the rotation length was 120?years, normal age class distribution provided, on average, the highest NPV. On the other hand, the lowest emissions (kg CO₂ MWh^?1a^?1) were obtained with the left-skewed age-class distribution using the rotation lengths of 60 and 80?years, and with the normal age-class distribution using the rotation length of 120?years. Altogether, the management regimes integrating both timber and energy wood production and using fertilization provided, on average, the lowest emissions over all management alternatives considered.     

Short-term climate change and the extinction of the snail Rhachistia aldabrae (Gastropoda: Pulmonata)

The only known population of the Aldabra banded snail Rhachistia aldabrae declined through the late twentieth century, leading to its extinction in the late 1990s. This occurred within a stable habitat and its extinction is attributable to decreasing rainfall on Aldabra atoll, associated with regional changes in rainfall patterns in the late twentieth and early twenty-first century. It is proposed that the extinction of this species is a direct result of decreasing rainfall leading to increased mortality of juvenile snails.     

Host selection behaviour of deathwatch beetle, Xestobium rufovillosum: Oviposition preference choice assays testing old vs new oak timber, Quercus sp.

In a choice bio-assay adult female deathwatch beetles were offered two dendrochronologically dated wood blocks from oak timber to study oviposition preference behaviour. There was a clear preference for ovipositing on old wood dating from the 13th to 19th centuries rather than new wood from the 20th century. Control, same-century choice, experiments showed that beetles will oviposit on young wood and that the age of the wood does not alter the overall oviposition potential. Oviposition frequency varied with insect age. Fecundity of insects collected from an infested building was similar to that of insects maintained in culture.     

Vaccines for the twenty-first century society

Vaccines have been one of the major revolutions in the history of mankind and, during the twentieth century, they eliminated most of the childhood diseases that used to cause millions of deaths. In the twenty-first century, vaccines will also play a major part in safeguarding people's health. Supported by the innovations derived from new technologies, vaccines will address the new needs of a twenty-first century society characterized by increased life expectancy, emerging infections and poverty in low-income countries.     

Tracking Construction Material over Space and Time: Prospective and Geo‐referenced Modeling of Building Stocks and Construction Material Flows

Construction material plays an increasingly important role in the environmental impacts of buildings. In order to investigate impacts of materials on a building level, we present a bottom‐up building stock model that uses three‐dimensional and geo‐referenced building data to determine volumetric information of material stocks in Swiss residential buildings. We used a probabilistic modeling approach to calculate future material flows for the individual buildings. We investigated six scenarios with different assumptions concerning per‐capita floor area, building stock turnover, and construction material. The Swiss building stock will undergo important structural changes by 2035. While this will lead to a reduced number in new constructions, material flows will increase. Total material inflow decreases by almost half while outflows double. In 2055, the total amount of material in‐ and outflows are almost equal, which represents an important opportunity to close construction material cycles. Total environmental impacts due to production and disposal of construction material remain relatively stable over time. The cumulated impact is slightly reduced for the wood‐based scenario. The scenario with more insulation material leads to slightly higher material‐related emissions. An increase in per‐capita floor area or material turnover will lead to a considerable increase in impacts. The new modeling approach overcomes the limitations of previous bottom‐up building models and allows for investigating building material flows and stocks in space and time. This supports the development of tailored strategies to reduce the material footprint and environmental impacts of buildings and settlements.     

Dealing with heteroconnections and short tree-ring series at different levels of dating in the dendrochronology of the Southwest German pile-dwellings

Within the field of pile-dwelling research in SW Germany, the application of a dendroarchaeological approach to the study of young wood among large timber series has allowed a better understanding of the short-term development of settlement showing high variations of building activity coupled with varying strategies of timber supply and woodland use. This is illustrated by systematic tree-ring investigations at the Neolithic lake-shore site of Hornstaad-Hörnle I, which have demonstrated an occupation of 20 years around 3900 BC. On specific levels of dendrodating and on the basis of heteroconnections, short alternating building phases with specific choice of timber have been found, showing a wave-like development of the settlement. Repeated short-term repairs also give an estimation of the time spans during which the houses were in use. Furthermore, the timber supply seems to have been based principally on coppicing and the defoliation damages caused by the cyclic development of the cockchafer can be detected in the young oak series. Particularly interesting are the alternating building phases with ash (Fraxinus excelsior L.) on one side, and oak (Quercus robur L./Quercus petraea [Matt] Liebl.) and beech (Fagus sylvatica L.) on the other side. After an initial building phase with ash wood gained from the azonal vegetation, the strong development of the village was accompanied by the systematic use of timber from an oak and beech mixed stand located in the mesophile deciduous forest. In our interpretation, this alternance seems to be linked with a shifting cultivation system at the beginning of the Neolithic lake-shore site occupation at Lake Constance. Oak and beech building phases correspond to a short period of greater concentration of occupation, probably with increasing agricultural activities whereas the use of ash wood gained from the hydrophilous vegetation belt behind the village, occurred in the phases of installation or dissolution of the community. In comparison, later settlement development in the whole region shows a greater stability in the building activity as well as in the woodland use.     

Dendroprovenancing: A preliminary assessment of potential to geo-locate kauri timbers in northern New Zealand

After 1840, New Zealand kauri (Agathis australis) became the focus of a large-scale timber industry in the upper North Island, which converted trees into timber that was then used in construction. Cities such as Auckland and Wellington relied on importing kauri to meet local demand for construction and other uses. Kauri timbers from buildings and in-ground features, mostly in Auckland city, have been collected for tree-dating and master chronology development. Although the use of timber at archaeological sites is understood, the geographic origin of the timber from within the natural range of kauri (north of 38 °S) is largely unknown. This limits interpretation of archaeological wood and constrains use of the tree-ring data in dendroclimatology. In this paper, we consider the potential to provenance kauri timbers used in 19^th and early 20^th century New Zealand buildings, using a combination of documentary sources, t-value mapping, and refined statistical matching using spatial patterns of correlations. Analysis of documentary sources for a test period of 1861–1865 CE indicates that there is sufficient information about the kauri timber industry to provide a geographic context for provenancing kauri in the upper North Island. The use of t-values for provenancing may be confounded by the relatively small size of the kauri growth region and a lack of sufficient spatial differentiation in growth patterns between the sub-regions. However, a new approach of using indexed residual chronologies and field correlations has promise for geo-locating timber in a relatively small region. The research highlights the value of establishing kauri provenance to New Zealand dendroclimatology, dendroarchaeology and environmental history.     

The weight of islands: Leveraging Grenada's material stocks to adapt to climate change

The building stock consumes large amounts of resources for maintenance and expansion which is only exacerbated by disaster events where large‐scale reconstruction must occur quickly. Recent research has shown the potential for application of material stock (MS) accounts for informing disaster risk planning. In this research, we present a methodological approach to analyze the vulnerability of the material stock in buildings to extreme weather events and sea‐level rise (SLR) due to climate change. The main island of Grenada, a Small Island Developing State (SIDS) in the Caribbean region, was used as a case study. A bottom‐up approach based on a geographic information system (GIS) is used to calculate the total MS of aggregate, timber, concrete, and steel in buildings. The total MS in buildings in 2014 was calculated to be 11.9 million tonnes (Mt), which is equivalent to 112 tonnes per capita. Material gross addition to stock (GAS) between 1993 to 2009 was 6.8 Mt and the average value over the time period was 4.0 tonnes per capita per year. In the year following Hurricane Ivan (2004), the per capita GAS for timber increased by 172%, while for other metals, GAS spiked by 103% (compared to average growth rates of 11% and 8%, respectively, between 1993 and 2009). We also ran a future “Ivan‐II” scenario and estimated a hypothetical loss of between 135 and 216 kilotonnes (kt) of timber from the building stock. The potential impact of SLR is also assessed, with an estimated 1.6 Mt of building material stock exposed under a 2‐m scenario. We argue that spatial material stock accounts have an important application in planning for resilience and provide indication of the link between natural disaster recovery and resource use patterns.     

Seeing the forest for the trees: New approaches and challenges for dendroarchaeology in the 21st century

The application of tree-ring research to the study of cultural heritage has seen important conceptual and methodological developments in the 21 st century. Following the breakthrough discovery in the 1980s of the importation of timber from the south-eastern Baltic to the Low Countries for panel paintings, the historical timber trade acquired paramount relevance in European dendrochronology. The improvement of methods and tools to locate the area of origin of the wood has since become a focal line of research. Reference chronologies of different variables (ring width, earlywood, latewood, earlywood vessel size in oak, latewood density in conifers, stable isotope chronologies of δ¹³C, δ¹⁸O) are now being developed in areas formerly (and currently) exploited for timber production, and isotopic signatures of ⁸⁷Sr/⁸⁶Sr are being mapped to provide a geochemical reference. In parallel, novel techniques to identify wood species (automated wood identification, chemical biomarkers, DNA barcoding) and their application on historical and ancient wood are being explored, given that this could sometimes help narrow down the timber source area. Modern technology is playing a key role in the study of wooden objects through non-invasive methods, and collaboration with (art) historians, mathematicians, engineers and conservators has proven essential in current achievements. Tree-ring series can now be retrieved from high resolution X-ray computed tomography images, allowing the research of otherwise inaccessible pieces. This paper reviews recent advances in those fields (tree-ring based dendroprovenancing, wood species identification, chemical fingerprinting, use of genetic markers, isotopic signatures, and non-invasive methods), and discusses their implementation and challenges in dendroarchaeological studies.     

Elevation-specific tree-ring chronologies of Norway spruce and Silver fir in Southern Germany

Tree-ring (TR) chronologies are important instruments for the dating and provenance analyses of historical wood, as well as for climate reconstructions. However, radial growth patterns differ between tree species and growing environments. Therefore chronologies are more or less specific for a certain tree species, region and elevation. Chronologies that are restricted to more confined regions could extend the possibilities for dating, dendroprovenancing and regional climate reconstructions.In Southern Germany, the transport of wood by raft – for the supply of towns and cities with timber – has been documented since early mediaeval times. Consequently, not only local timber from the lowlands was used for construction purposes, but also alpine wood originating from sites up to the timberline. Since pronounced altitudinal gradients cause distinct climate differences, elevation-specific chronologies have the potential to improve dating precision in this region.In this contribution, a model is presented and applied in order to separate elevation-specific provenances of Norway spruce (Picea abies L. Karst) and Silver fir (Abies alba Mill.) in Southern Germany. The model is derived from more than 2100 living TR series originating from sites between 200 and 1710 m above see level. Absolute (mean, maximum) ring-width values and the variation of ring-widths (mean sensitivity) show distinct correlations with their altitudinal provenance, reflecting improvements in growth conditions as well as the increase of their yearly variation from high over intermediate to low elevation sites. Mean ring widths and mean sensitivity values were used as independent parameters in an exponential regression model which exhibits a coefficient of determination (r²) of 77% for spruce and 74% for fir. The prediction accuracy of the elevation amounts ±300 m for spruce and ±200 m for fir within the 95% confidence interval.The model was used to estimate the elevation origin of around 5000 historical spruce and 800 historical fir series from buildings located in Southern Germany. The historical TR series covering the AD 990–1800 period were allocated by the model to elevations between 120 and 2090 m. In a second step the individual TR series were combined to elevation-specific chronologies representing low, intermediate, and high altitudinal belts. The chronologies show distinct differences among the altitudinal belts in terms of signatures and pointer years, especially for spruce. Elevation-specific chronologies are assumed to amplify the dating possibilities of ancient timber, to provide valuable evidences for the origin of historical wood, and to offer more specific proxy data for regional climate reconstructions.     

Environmental Impact Assessment of Wood Use in Japan through 2050 Using Material Flow Analysis and Life Cycle Assessment

In this study, we used material flow analysis and life cycle assessment to quantify the environmental impacts and impact reductions related to wood consumption in Japan from 1970 to 2013. We then conducted future projections of the impacts and reductions until 2050 based on multiple future scenarios of domestic forestry, wood, and energy use. An impact assessment method involving characterization, damage assessment, and integration with a monetary unit was used, and the results were expressed in Japanese yen (JPY). We found that environmental impacts from paper consumption, such as climate change and urban air pollution, were significant and accounted for 56% to 83% of the total environmental impacts between 1970 and 2013. Therefore, reductions of greenhouse gas, nitrogen oxide, and sulfur oxide emissions from paper production would be an effective measure to reduce the overall environmental impacts. An increase in wood use for building construction, civil engineering, furniture materials, and energy production could lead to reductions of environmental impacts (via carbon storage, material substitution, and fuel substitution) amounting to 357 billion JPY in 2050, which is equivalent to 168% of the 2013 levels. Particularly, substitution of nonwooden materials, such as cement, concrete, and steel, with wood products in building construction could significantly contribute to impact reductions. Although an increase of wood consumption could reduce environmental impacts, such as climate change, resource consumption, and urban air pollution, increased wood consumption would also be associated with land‐use impacts. Therefore, minimizing land transformations from forest to barren land will be important.     

Evaluation of Modeling Approaches to Determine End‐of‐Life Flows Associated with Buildings: A Viennese Case Study on Wood and Contaminants

Dynamic material flow analysis enables the forecasting of secondary raw material potential for waste volumes in future periods, by assessing past, present, and future stocks and flows of materials in the anthroposphere. Analyses of waste streams of buildings stocks are uncertain with respect to data and model structure. Wood construction in Viennese buildings serve as a case study to compare different modeling approaches for determining end‐of‐life (EoL) wood and corresponding contaminant flows (lead, chlorine, and polycyclic aromatic hydrocarbons). A delayed input and a leaching stock modeling approach are used to determine wood stocks and flows from 1950 until 2100. Cross‐checking with independent estimates and sensitivity analyses are used to evaluate the results’ plausibility. In the situation of the given data in the present case study, the delay approach is a better choice for historical observations of EoL wood and for analyses at a substance level. It has some major drawbacks for future predictions at the goods level, though, as the durability of a large number of historical buildings with considerably higher wood content is not reflected in the model. The wood content parameter differs strongly for the building periods and has therefore the highest influence on the results. Based on this knowledge, general recommendations can be derived for analyses on waste flows of buildings at a goods and substance level.     

Reconstructing the oaks’ growth patterns in Greece with the use of historical timber: Case studies from Western Peloponnese

Southern Greece is a region where available oak reference chronologies are still missing, making dendroarchaeology and dating of historical buildings rather challenging, if not impossible. In the current study we performed wood identification and dendroarchaeological analysis on timber from three historical buildings: the castles of Androusa and Koroni and the Church of Agios Dimitrios, in Western Peloponnese. The three monuments represent buildings of different uses covering different periods, but also sharing a common characteristic: oak was the only timber used in their construction, while the number of preserved timber elements is very limited. A dendroarchaeological examination of these three historical buildings, together with radiocarbon and wiggle-matching analysis, provided valuable chronological information for the local archaeologists, historians, and other scientists. Application of dendrochronological techniques has helped place the three buildings under study into the Ottoman period. Our results also show that timber was acquired most probably from local non-managed forests, which suggests that oak forests were present in the broader area at least from the late 15th to the first half of the 18th centuries. The discordance between dendrochronological and radiocarbon dates in one of the three cases highlights the need for further exploration of the study area through a combined implementation of both dendrochronological and radiocarbon dating analyses in order to develop well-replicated local oak chronologies. Our study also shows that dendroarchaeology can contribute significantly to the cultural and landscape history of Western Peloponnese even with an examination of limited number of preserved timber elements from historical buildings.     

Buildings and wood trade in Aix-en-Provence (South of France) during the Modern period

Many buildings are being restored in the city of Aix-en-Provence, southeastern France and allowed systematic dendrochronological analyses. 144 fir timbers (Abies alba Mill.) were examined and dated between 1303 and 1933. They highlight three felling phases (Medieval period, 17th-18th century, and 19th century). The best documented one corresponds to the 17th-18th centuries and coincides with significant building activity connected to the status of Aix, which is the parliamentary capital of Provence. Around Aix-en-Provence, it is difficult to find timbers with good dimensions. Our results show that timbers were transported from the Alps to Aix’s buildings. Potential testimonies of this timber trade have been found, such as raft assemblage marks, and carved signs and letters. A dendroprovenancing case study shows that between 1810 and 1890, some of Aix’s timbers could have come from the Northern French Alps or the Verdon-Durance region. Finally, the lack of timbers with good dimension and the difficulties of timber supply contributed to the development of reuse economy and technical innovation. These results are the foundation of a future well-established dendroprovenancing approach in the Southern Alps.     

长江流域林木资源的重要性及种质资源保护

中国长江流域有着丰富的林木资源, 包含极高水平的物种多样性、特有性和遗传多样性。根据考古证据, 在旧石器和新石器时代长江文明早期的孕育与发展中, 林木在食物、能源、工具、建筑和舟船中的应用起到了关键作用。现在, 长江流域和珠江流域逐渐成为国内木材供给的热点地区。面对木材供给总量不足和大径级木材结构性短缺问题, 长江流域林木资源将是未来国内木材安全的重要保障。这使得林木种质资源的保护更加迫切。针对长江流域林木种质资源保护存在的家底不清和保存体系不完善问题, 我们应尽快完成林木种质资源的全面调查和重要树种的多样性分析; 完善原地、异地和设施保存相结合的保存体系。     

Milestones and rates of growth in the development of biology.

An attempt has been made to examine the exponetial rate of increase of the great discoveries, the "milestones," in the rise of biology from the beginning of the seventeenth century, and particularly in the rise of genetics from the beginning of the twentieth century. The biological sciences in general, during the three centuries named, exhibit a doubling of the number of great discoveries in each fifty years. Genetics, in the twentieth century, has risen much faster. Its doubling time for the most significant discoveries has been about twenty-two and a half years. Either of these rates is of course far slower than the exponential rise in the total output of biological science, the number of scientists, or the cost of science, which have been generally reported to double about every ten years or less. It follows that, as time passes, and until these exponetial rates become considerably altered, a relationship of diminishing returns is quite evident. As time passes, even though the most significant discoveries continue to increase exponetially, it takes a greater total output, a greater number of (assisting?) scientists, and greater amounts of money to yield a set quantity of major new findings. The rapid rise of the life sciences cannot continue its present course into the twenty-first century without meeting ineluctable limits to expansion. It may be argued that as in other human spheres of activity, so too in natural science there are limits to growth which we are rapidly approaching. From the predictable asymptote only unpredictable breakthroughs might deliver us.