Review of the Gymnosperm Literature
This piece presents a brief review of the literature on gymnosperms as of 2013. The principal motivation for this review is simply that the Gymnosperm Database cannot present in-depth, or in many cases even very current, treatment of all gymnosperm taxa. This is because our knowledge of this group is so vast, and is increasing so rapidly, that as the years go by I find that increasingly I am merely maintaining a library of links that point to information, rather than presenting the information per se. Merely as an illustration, the backlog of digital data that is currently waiting to be assimilated to the Database now stands at 7.4 gigabytes, not counting several thousand pages of printed matter. In contrast, the online Database comprises 303 megabytes, and it has taken 16 years to get all that online (interestingly, both the backlog and the size of the Database increased five-fold in the seven years since I last revised this page in 2006).
The purpose of this review, then, is to provide you with some guidance about where to go to get survey-level information about all gymnosperm taxa. Most of the required documents can be found online, but for some, you will need access to a large research library (perhaps via interlibrary loan). The difficulty of acquiring these documents was one of the things that drove me to develop the Database in the first place. Most of the review focuses on conifers, which comprise well over 99% of the information base, and a concluding section addresses cycads, ginkgo, and the gnetophytes. You should also review the Links page for helpful sources of online information. You may also want to peruse the Bookstore page for those works that are still in print, and Google Scholar is a good source for finding journal articles (or at least their abstracts).
Conifers in general are very well introduced by Farjon (2008), a short (book-length) introduction to the conifers, focused on ecological topics and supported by a good bibliography.
The principal overview works are organized taxonomically. Eckenwalder (2009) and Farjon (2010) are both comprehensive treatments that attempt to include all conifer species, along with a number of introductory chapters addressing topics such as systematics, evolution, ecology, and conservation. Of the two, Farjon (2010) provides much more detail on each taxon, and is very well illustrated. Auders and Spicer (2012) also cover all the species, in the only recent comprehensive text that contains thorough treatments of cultivars. Debreczy and Rácz (2011) is less comprehensive than the preceding treatments, being limited to conifers native to temperate climates (broadly interpreted, e.g. boreal regions and subtropical Australia). However, a lengthy introductory section addresses the history of conifer discovery, conservation, systematics, morphology, distribution and climate, and paleontology; these chapters are superior to the introductory sections of any of the other books. It is also a superbly illustrated pair of volumes, with several thousand color photos.
Several other works are less comprehensive but still quite important. Bieleski and Wilcox (2009) is the only comprehensive volume addressing the Araucariaceae. Dozens of articles address topics in systematics, biochemistry, ecology, etc. Richardson (1998) is focused on the pines, which are the largest (about 100 species) and most economically important genus of conifers. The 22 chapters address subjects as diverse as systematics, late Quaternary population dynamics, the role of fire, the evolution of life histories, genetic variation, seed dispersal, ecophysiology, mycorrhiza and soils, diseases and insect interactions, cultivation, and the importance of pines as invasive species. Finally, Turner and Cernusak (2011) address the podocarps, which represent the third great family of the conifers but have primarily a southern hemisphere distribution, and are relatively neglected in conifer research, seldom studied but highly distinctive. This work is the first comprehensive study of podocarps in the tropical forest, reviewing their ecophysiology, mycorrhizal symbionts, evolutionary ecology, and other aspects of their surprising coexistence within angiosperm-dominated forests.
Aris G. Auders and Derek P. Spicer. 2012. Royal Horticultural Society Encyclopedia of Conifers: a Comprehensive Guide to Cultivars and Species. London: Royal Horticultural Society. ISBN 978-1-907057-15-1.
R. L. Bieleski and M. D. Wilcox, 2009. Araucariaceae. Dunedin, New Zealand: International Dendrology Society.
Z. Debreczy and I. Rácz, 2011. Conifers Around the World. Vols. 1-2. Budapest: DendroPress Ltd.
B. L. Turner and L. A. Cernusak (eds.). 2011. Ecology of the Podocarpaceae in tropical forests. Smithsonian Contributions to Botany No. 95. Washington, DC: Smithsonian Institution Scholarly Press.
North America and China are large areas that together command a large fraction of total gymnosperm diversity, especially in the Coniferae and Ephedraceae. Excellent current descriptions of these taxa are presented the Flora of North America (1993) and the Flora of China (1999). The Flora of Australia (1998), Flora of Japan (1995), and Flora of New Caledonia (1972) cover three more areas of high gymnosperm diversity, although the New Caledonia flora is only available in French (it is slowly being translated and published on the Gymnosperm Database, though), and each of these floras only provides descriptive information, with very little ecology or ethnobotany. For New Zealand, Salmon (1996) provides a superb resource, with good descriptions supplemented by copious high-quality color photographs and additional information on each species' natural history. De Laubenfels (1988) covers the highly diverse conifer flora, dominated by Podocarps, of the vast area from the Malay Peninsula east to Fiji and from the Philippines south through New Guinea. These southern hemisphere reviews are nicely augmented by an outstanding text on the Ecology of the Southern Conifers by Enright and Hill (1990). Farjon and Styles (1997) and Perry (1991) provide very thorough treatment of the Mexican and Central American pines. Burns and Honkala (1990) provide detailed accounts of the biology, ecology and management of 65 species of economically important conifers native to North America.
Flora of North America Editorial Committee (eds.): Flora of North America North of Mexico, Vol. 2. Oxford University Press. This document is available online. Go to http://www.efloras.org and click on "Flora of North America."
Conifers predominate over angiosperms primarily in ecosystems where the limiting factors are abiotic: north temperate and boreal ecosystems, and mountains. Consequently many studies of conifers have focused on abiotic limitations to growth and on autecological adaptation to those limits. This general topic is well treated by Bond (1989), who broadly examines why conifers dominate some forests and angiosperms others. The causes, it turns out, are mainly related to physiology and the physical environment.
The literature on autecological adaptation focuses heavily on physiological ecology. Smith and Hinckley (1994) provide a fine compilation of review articles that clearly show the ways in which tree physiology is entwined with the ecological functions of conifer forests. Chapters explore the linkage between paleoecology and physiology, forest responses to air pollution and climate change, and many other topics. Gower and Richards (1990) give a more focused review explaining why a deciduous conifer, the larch, is ecologically successful in environments primarily dominated by evergreen conifers. Waring and Franklin (1979), in a classic paper, give the best concise explanation of why large, old conifers dominate the Pacific Northwest forests; the analysis works equally well for most other conifer forests in wet maritime climates, e.g. Japan, New Zealand, and Chile. Finally, Arno and Hammerly (1984), although now somewhat dated, still is the best review of conifers in alpine and arctic timberline ecosystems. The spatial scope is worldwide and a substantial part of the book consists of an inventory and travelogue of timberlines around the globe.
Arno, Stephen F. and Ramona Hammerly. 1984. Timberline: mountain and arctic forest frontiers. Seattle: The Mountaineers.
Bond, W. J. 1989. The Tortoise and the Hare: Ecology of Angiosperm Dominance and Gymnosperm Persistence. Biological Journal of the Linnean Society 36:227–249.
Gower, S. T. and J. H. Richards. 1990. Larches: deciduous conifers in an evergreen world. Bioscience 40(11):818-826.
Smith, William K. and Thomas M. Hinckley (eds.). 1994. Ecophysiology of Coniferous Forests. San Diego: Academic Press.
The literature on conifer paleoecology is vastly dominated by Quaternary studies, although occasional insights to pre-Quaternary paleoecology are scattered through the paleobotanical literature. A good example is Quirk et al. (2013), who show how models and inference can be used to set boundary conditions on a paleoecological problem, and also to inform projections of future ecosystem response under changed boundary conditions, e.g. climate change.
The Quaternary studies usually inform with regard to a specific geography, e.g. Szeicz et al. (2003), who use of sediment and tree-ring data to reconstruct paleoenvironmental change in a temperate rainforest of the southern hemisphere. Other studies provide insight to the use of methods of investigation; the latter include pollen studies, macrofossils, tree rings, and inference based on historical accounts and archeological evidence. Miller and Wigand (1994) provide an example, showing how many different types of paleoecological data can be synthesized to track environmental change over a long period, and to infer consequences that can inform land management decisions. Since climate change became a cause célèbre, much of the paleoecological work uses climate models and considers implications for the future. For instance, Whitlock et al. (2003) show how paleoecological data can be combined with contemporary climate models to predict future environmental change, with management implications. Other studies explore implications for habitat restoration and other management objectives. Hessburg and Agee (2003), for instance, use a literature review focusing on historical sources to assemble a broad geographic analysis of fire regimes and their changes during historical time, with results that have clear implications for land management.
Paul F. Hessburg and James K. Agee. 2003. An environmental narrative of inland Northwest United States forests, 1800–2000. Forest Ecology and Management 178(1):23-59.
Richard F. Miller and P. E. Wigand. 1994. Holocene changes in semiarid pinyon-juniper woodlands. Response to climate, fire, and human activities in the US Great Basin. BioScience 44(7): 465–474.
Joe Quirk, Nate G. McDowell, Jonathan R. Leake, Patrick J. Hudson, and David J. Beerling. 2013. Increased susceptibility to drought-induced mortality in Sequoia sempervirens (Cupressaceae) trees under Cenozoic atmospheric carbon dioxide starvation. American Journal of Botany 100(3):582–591.
Julian M. Szeicz, Simon G. Haberle, and Keith D. Bennett. 2003. Dynamics of north Patagonian rainforests from fine-resolution pollen, charcoal and tree-ring analysis, Chonos Archipelago, southern Chile. Austral Ecology 28(4): 413–422.
Cathy Whitlock et al. 2003. The role of climate and vegetation change in shaping past and future fire regimes in the northwestern US and the implications for ecosystem management. Forest Ecology and Management 178:5-21.
The conifer literature on ecosystem processes tends to focus on limits in the physical environment. Principal areas of work include the nitrogen economy and succession. Nitrogen is a limiting nutrient in most conifer-dominated ecosystems, largely because their physiology is heavily nitrogen-dependent but no conifers have the ability to fix atmospheric nitrogen. The general principles of the nitrogen economy of the forest are best reviewed in standard textbooks on forest ecology (e.g. Kimmins 2004 or Perry et al. 2008). One interesting example study is a review of the importance of returning salmon as a source of forest nitrogen (Reimchen et al. 2003), which is also an example of how stable isotopes can be a powerful analytical tool. Another is a study of the "fir waves" of New England, a feedback system in which forest mediation of nitrogen availability determines the sites and rates of tree mortality in the forest; as such, a good example of the importance of limiting factors and biogeochemical cycling to forest ecosystems (Sprugel and Bormann 1991). The nitrogen economy, in turn, is a primary driver of net primary productivity in the forest. Vogt et al. (1986) provide a somewhat dated but still valuable analysis of above- and below-ground productivity in conifer forests, in particular showing that a remarkably large fraction of total forest productivity (i.e., fixed carbon) goes to feed mycorrhizal fungi that scavenge nitrogen for the trees.
Succession is a distinctive process among conifers because as a whole they tend to be early successional and to have adaptations to fire that maintain widespread early successional environments across the landscape (discussed below, “Disturbance Ecology”). Oliver and Larson (1996) provide a very sound analysis of how conifer forests develop on a site over time, and the management implications of that information. Franklin and Hemstrom (1981), although an older study, provides a great short introduction to principles of forest succession in temperate coniferous rainforests, including the predominate successional trajectories and the role of dead wood in succession.
Many conifers are important to ecosystem processes because many are keystone species due to their large size and dominance on the landscape; even after death, their remains perform diverse functions in the ecosystem. Fetherston et al. (1995) and Maser et al. (1988) both show this for aquatic ecosystems, and in the process show how the forest is tied to the stream network, and even to the oceans, in very substantial ways.
Kevin L. Fetherston, Robert J. Naiman, and R. E. Bilby. 1995. Large woody debris, physical process, and riparian forest development in montane river networks of the Pacific Northwest. Geomorphology 13:133-144.
Jerry F. Franklin and Miles A. Hemstrom. 1981. Aspects of succession in the coniferous forests of the Pacific Northwest. Pp. 212-229 in D. C. West, H. H. Shugart, and D. B. Botkin (eds.), Forest succession concepts and application. New York: Springer-Verlag.
J. P. Kimmins. 2004. Forest ecology (3rd ed.). New York: MacMillan. 596 p.
C. D. Oliver and B.C. Larson. 1996. Forest stand dynamics. New York: John Wiley & Sons. 537pp.
David A. Perry, R. Oren, and S. C. Hart. 2008. Forest ecosystems (2nd ed.). Johns Hopkins University Press. ISBN 978-0801888403.
T. E. Reimchen, D. D. Mathewson, M. D. Hocking, J. Moran, and D. Harris. 2003. Isotopic evidence for enrichment of salmon-derived nutrients in vegetation, soil, and insects in riparian zones in coastal British Columbia. Pp. 59-63 in American Fisheries Society Symposium 34, Nutrients in Salmonid Ecosystems. Bethesda, MD: American Fisheries Society.
Douglas G. Sprugel and F. H. Bormann. 1991. Natural disturbance and the steady state in high-altitude balsam fir forests. Science 211:390–393.
Kristina A. Vogt, Charles C. Grier, and Daniel J. Vogt. 1986. Production, turnover, and nutrient dynamics of above- and belowground detritus of world forests. Advances in Ecological Research 15(3):3-377.
Chris Maser, Robert F. Tarrant, James M. Trappe, and Jerry F. Franklin (eds.). 1988. From the forest to the sea: a story of fallen trees. General Technical Report PNW-GTR-229. USFS Pacific Northwest Forest and Range Experiment Station. 153 p.
Due to their role as keystone species, conifers are often central to community ecology studies, playing a role in various types of symbiotic relationships. One of the best examples is the mutualistic relationship between corvids and the “stone pines”, i.e. the pines that produce wingless seeds and thus rely upon birds for long-range dispersal (Lanner 1996). Other examples include the distinctive communities associated with forest canopies, with forest interior environments, and in the belowground environment. Sillett and Van Pelt (2007) provide a fine exposition of what we know about the canopy ecosystem of the coast redwood, which has perhaps the best-studied canopy of any forest type. Barbour and Billings (1988) are editors of a lengthy review volume that contains chapters on all the major North American biomes, many of which are dominated by conifer forests. Autecology and disturbance ecology are important themes, but the analyses focus most on the biological and functional diversity of these systems. Finally, Perry et al. (1989) give a short but engaging review of the mutualism between trees and their mycorrhizal associates. All conifers seem to be mycorrhizal, and all case studies in their review involve conifer forests.
M. G. Barbour and W. D. Billings (eds.). 1988. North American terrestrial vegetationu. Cambridge, England: Cambridge University Press.
David A. Perry, M. P. Amaranthus, J. G. Borchers, S. L. Borchers, and R. E. Brainerd. 1989. Bootstrapping in ecosystems. BioScience 39(4): 230–237.
It is the fate of all trees that they must fall, and as most trees are large ecosystem dominants, that falling has consequences for all organisms in the ecosystem. In the modern world, the most widespread and destructive agent of disturbance is human activity, a topic covered below (“Applied Ecology” and “Climate Change”). A more traditional view of disturbance in conifer forest, though, downplays the role of humans and focuses on natural processes. In this view, the principal modes of disturbance are episodic, where disturbance occurs but the forest goes on; and catastrophic, where the forest is destroyed and a new forest rises in its place.
Episodic disturbance is nicely covered by Pickett and White (1985) in an influential review and theoretical exposition of patch dynamics and related disturbances in forest ecosystems. Although not exclusive to conifer forests, these principles are widely applicable in most conifer forest systems where the successional trajectory is not primarily a response to catastrophic disturbance. Franklin et al. (1987) give a much briefer summary of the phenomenon of tree mortality with emphasis on the temperate conifer rainforests of the Pacific Northwest, where episodic disturbances predominate.
The principal agents of catastrophic (and sometimes episodic) disturbance, which often work interdependently, are disease, insect attack, and fire. Castello et al. (1995) give a good brief introduction to the role of pathogens in forest ecosystems, and Holdenrieder (2004) offers a thought-provoking review of dominant themes in the landscape ecology of forest pathogens, addressing topics such as the importance of species introductions, the monocultures created by managed forests, and the role of predisposing factors such as soils and climate in determining the risk of pathogen-induced mortality. The problem of forest pests has had a thorough recent treatment by Wainhouse (2005), who addresses both natural and managed forests and acknowledges the growing importance of introduced pests. Prevention and both biological and chemical controls are reviewed in the context of an Integrated Pest Management strategy. A good case study of a forest pest is given by Orwig and Foster (1998), who discuss one of the most important introduced conifer pests in North America, the hemlock wooly adelgid.
The most-studied disturbance in conifer forests is wildfire. Agee (1993) gives a comprehensive review of fire ecology, strongly focused on conifer systems ranging from dryland pines to temperate rainforest. Agee is one of the most-published authors in the field, and Hessburg and Agee (2003), cited above in “Paleoecology”, is also well worth a read. Most of the literature, though, is highly focused on particular ecosystems. For instance, McKelvey et al. (1996) provide a good review of the ecological role of fire in the Sierra Nevada of California, where a broad spectrum of fire regimes are expressed across the landscape. Noss et al. (2006) give an influential review of the ecological science relevant to developing and implementing fire and fuel management policies for forests before, during, and after wildfires, and provide recommendations for restoration and management of fire-prone forests.
James K. Agee. 1993. Fire ecology of Pacific Northwest forests. Washington, DC: Island Press.
J. D. Castello, D. J. Leopold, and P. J. Smallidge. 1995. Pathogens, patterns, and processes in forest ecosystems. BioScience 45(1):16-24.
Jerry F. Franklin, H. H. Shugart, and Mark E. Harmon. 1987. Tree death as an ecological process. BioScience 37(8):550–556.
O. Holdenrieder. 2004. Tree diseases and landscape processes: the challenge of landscape pathology. Trends in Ecology & Evolution 19(8):446–452.
K. S. McKelvey, C. N. Skinner, C. R. Chang, D. C. Erman, S. J. Husari, D. J. Parsons, and C. P. Weatherspoon. 1996. Fire and fuels. Vol. 1, pp. 61-71 in Sierra Nevada ecosystem project: final report to Congress.
Reed F. Noss, Jerry F. Franklin, W. L. Baker, T. Schoennagel, and Peter B. Moyle. 2006. Managing fire-prone forests in the western United States. Frontiers in Ecology and the Environment 4(9):481-487.
D. A. Orwig and D. R. Foster. 1998. Forest response to the introduced hemlock woolly adelgid in southern New England, USA. Journal of the Torrey Botanical Society 125(1):60-73.
S. T. A. Pickett and P. S. White. 1985. The ecology of natural disturbance and patch dynamics Orlando, FL: Academic Press.
D. Wainhouse. 2005. Ecological methods in forest pest management. Oxford University Press.
Applied ecology is simply the willful modification of ecosystems to achieve management objectives. It is easy to forget that applied ecology has been going on for thousands of years, in the context of traditional ecological knowledge, under which science and religion were often indistinguishable. Hageneder (2007) traces much of that history as it applied to the European experience of Taxus baccata, the common yew. In modern times, applied ecology ranges from timber production, through such varied topics as management for fish and wildlife habitat, correction of forest changes wrought by a failed policy of fire suppression, restoration of lands degraded by changes such as strip mining or desertification, and sequestration of atmospheric carbon dioxide. Timber management, sometimes called "new forestry" in recognition of its ecological perspective, is briefly explained by Gillis (1990), or in a book-length treatment by Smith et al. (1997), who surveys silvicultural practice for various objectives: wood production, watershed management, agroforestry, etc. Wuerthner (2006) has edited a very large and comprehensive treatment of one of the great ecological stories of North America in the past century: the management of wildfire by attempting to suppress it entirely, and the ecological consequences of this strategy on a conifer-dominated landscape that formerly burned quite frequently. Wuerthner adeptly traces that history and its consequences, and the emergence of a new ethic for wildfire management. A website, Reforestation, Nurseries, & Genetics Resources, provides numerous resources related to managing conifers for diverse objectives. Finally, the utility of forests in carbon sequestration is currently an active and controversial research topic. Harmon et al. (2010) provide a good summary of the issues, describing the forest carbon cycle, presenting an array of sequestration strategies, discussing carbon offsets and credits, and describing principal sources of uncertainty.
A. M. Gillis. 1990. The new forestry: an ecosystem approach to land management. Bioscience 40(8):558-562.
Fred Hageneder. 2007. Yew, a history. Stroud, UK: Sutton Publishing.
M. E. Harmon, M. E., Birdsey, R. A., Giardina, C. P., Heath, L. S., Houghton, R. A., Jackson, R. B., and Skog, K. E. 2010. A synthesis of the science on forests and carbon for US forests. Issues in Ecology No. 13. Ecological Society of America.
D. M. Smith, B. C. Larson, M. J. Kelty, and P. M. S. Ashton. 1997. The practice of silviculture: applied forest ecology (9th Ed.). Wiley and Sons, Inc. 537 p.
G. Wuerthner (ed.). 2006. The wildfire reader: a century of failed forest policy. Washington, DC: Island Press.
Until approximately 1995, studies of climate change focused primarily on paleoecological data sources and are addressed above under “Paleoecology.” Current studies focus on impacts, mitigation, and adaptation to current and forecast climatic change; in practice, nearly all work to date concerns impacts. There have been a lot of good reviews of this topic in recent years. Allen et al. (2010) provide a global perspective in a pivotal paper that showed climate change was altering forests worldwide in a manner that significantly increased tree mortality rates. Ryan and Archer (2008) focus on anticipated climate change effects on forest lands in the U.S., with many particulars applicable to conifer forests. One of the most discussed consequences of climate change for forests of western North America has been its effects on bark beetle irruptions and associated ecological and economic damage. Bentz et al. (2010) provide a good, brief overview of the subject. A literature that synthesizes the various types of climate change impacts and shows how they act synergistically or in opposition is only beginning to emerge; the best work to date is by McKenzie et al. (2009).
Climate change adaptation and mitigation are a nascent field as far as conifers are concerned, but Vose et al. (2012) do an excellent synthesis of research to date on climate change effects on U.S. forests, along with a review of climate change adaptation and mitigation options and needs for further research.
Craig D. Allen, A. K. Macalady, H. Chenchouni, D. Bachelet, N. McDowell, M. Vennetier, and N. Cobb. 2010. A global overview of drought and heat-induced tree mortality reveals emerging climate change risks for forests. Forest Ecology and Management 259(4):660-684.
B. J. Bentz, J. Régnière, C. J. Fettig, E. M. Hansen, J. L. Hayes, J. A. Hicke, and S. J. Seybold. 2010. Climate change and bark beetles of the western United States and Canada: direct and indirect effects. BioScience 60(8):602-613.
D. McKenzie, D. L. Peterson, and J. J. Littell. 2009. Global warming and stress complexes in forests of western North America. Pp. 317-337 in A. Bytnerowicz, M.J. Arbaugh, A.R. Riebau, and C. Andersen (eds.), Wildland fires and air pollution. The Hague, Netherlands: Elsevier Publishers: 317–337.
M. G. Ryan and S. R. Archer. 2008. Land resources: forests and arid lands. Pp. 75-120 in P. Backlund, A. Janetos, and D. Schimel, The effects of climate change on agriculture, land resources, water resources, and biodiversity in the United States. Final report, synthesis and assessment product 4.3. A report by the U.S. Climate Change Science Program and the Subcommittee on Global Change Research. Washington, DC: U.S. Environmental Protection Agency.
J. M. Vose, D. L. Peterson, and T. Patel-Weynand (eds.). 2012. Effects of climatic variability and change on forest ecosystems: a comprehensive science synthesis for the US. USFS Pacific Northwest Research Station General Technical Report PNW-GTR-870.
In some ecosystems, conifers are regarded as invasive species. In many cases this is simply a management complaint in response to natural regeneration by native species, but there are regions where conifers constitute invasive nonnative species. Usually this happens when a conifer has been introduced as a timber species, or less commonly as an ornamental, and then becomes naturalized (Richardson and Rejmánek 2004). Most examples involve species of the Pinaceae in the southern hemisphere (Richardson and Higgins 1998, Richardson et al. 2008, Simberloff et al. 2010). Invasive conifers are a particularly severe problem in New Zealand, where they are called “wilding” conifers and are represented by 10 species in the Pinaceae. A compilation of papers by Hill et al. (2004) provides a good overview of the problem. One chapter addresses wilding conifers in South Africa. An effective management response to conifer invasions is often imperative in order to minimize modification of native natural communities; Hill et al. (2004), Richardson et al. (2008), and Simberloff et al. (2010) all provide suggestions.
R. L. Hill, S. M. Zydenbos and C. M. Bezar (eds.). 2004. Managing wilding conifers in New Zealand: present and future. Christchurch: New Zealand Plant Protection Society. ISBN 0-478-10842-7.
David M. Richardson and S. I. Higgins. 1998. Pines as invaders in the southern hemisphere. Pp. 450–474 in D. M. Richardson (ed.), Ecology and biogeography of Pinus. Cambridge University Press.
David M. Richardson and Marcel Rejmánek. 2004. Conifers as invasive aliens: a global survey and predictive framework. Diversity and Distributions 10(5-6):321–331.
David M. Richardson, Brian W. van Wilgen, and Martin A. Nuñez. 2008. Alien conifer invasions in South America: short fuse burning? Biological Invasions 10:573–577.
D. Simberloff, M. A. Nuñez, N. J. Ledgard, A. Pauchard, D. M. Richardson, M. Sarasola, B. W. van Wilgen, S. M. Zalba, R. D. Zenni, R. Bustamente, E. Peña, and S. R. Ziller. 2010. Spread and impact of introduced conifers in South America: lessons from other southern hemisphere regions. Austral Ecology 35(5): 489-504.
Currently, about a third of all conifer species are listed as species of conservation concern. They include some of the world’s most endangered species; some species have fewer than 10 known individuals, and many are restricted to one or two small populations (Farjon and Page 1999, Farjon 2008). Farjon and Page (1999) was the first published assessment of the conservation status of all gymnosperm species. Chapters provide a global assessment of conifer diversity and threats, a summary of conservation issues, regional accounts addressing the global hot spots of conifer diversity, and some species accounts. Farjon has continued to play a central role in this issue and is the lead scientist behind conifer assessments prepared by the IUCN Red List, which is a comprehensive online database maintained by the international organization that assesses and rates species conservation status worldwide. In 2013 this site was largely superseded by Threatened Conifers of the World, assembled and maintained by the International Conifer Conservation Programme out of the Royal Botanical Garden, Edinburgh, which provides species-specific accounts of the status of all conifer species. Most accounts include general ecological information (photographs in habitat, distribution, ecology) as well as a conservation assessment that covers status, threats, and conservation actions. Sources are cited.
The general conservation biology literature also treats conifers occasionally. One full-length book by Lindenmayer and Franklin (2002) is more closely focused on conifer forests and which was, at the time of its publication, the first comprehensive study of how to manage forests to optimize biological diversity, a topic that has since become a dominant theme in forest management.
Finally, some species are conspicuous on the cultural landscape and thus attract a disproportionate share of attention. I offer two examples in the North American literature, while noting that other instances occur in other nations that have iconic conifers, such as England (yew), New Zealand (kauri), Japan (hinoki), Mexico (ahuehuete), or Viet Nam (several species). Earley (2004) is an engrossing study of the history of humans and longleaf pine, which formerly comprised one of the most extensive pine forests on earth, now diminished by more than 99%. The author gives case histories of a variety of innovative efforts now underway to restore the longleaf forest and its ecological functions. Tomback et al. (2000) attend to the plight of whitebark pine, an iconic species of western North America that has attracted a great deal of attention and is now proposed for listing as an endangered species. The book provides a snapshot of the knowledge concerning its ecology and restoration, and papers therein are cited by most current publications on the subject.
The scientific literature contains few acknowledgements of the spiritual and emotional importance of trees, even though this significance is one of the principal drivers that motivates the protection and preservation of these plants. In a landmark paper, Dwyer et al. (1991) discuss the human values surrounding trees in an urban environment.
John F. Dwyer, Herbert W. Schroeder, and Paul H. Gobster. 1991. The significance of urban trees and forests: toward a deeper understanding of values. Journal of Arboriculture 17(10):276–284.
Lawrence S. Earley. 2004. Looking for longleaf. Chapel Hill and London: University of North Carolina Press. 322pp.
D. B. Lindenmayer and Jerry F. Franklin. 2002. Conserving forest biodiversity: a comprehensive multiscaled approach. Washington, DC: Island Press.
Diana F. Tomback, Stephen F. Arno and Robert E. Keane (eds). 2000. Whitebark pine communities: ecology and restoration. Washington, DC: Island Press.
Compared to the conifers, little work has been done on the other gymnosperms. The best reviews of the cycads are those by Jones (2002), Norstog and Nicholls (1997), and Whitelock (2002). Whitelock gives the most comprehensive treatment of the species of Cycadales, presenting information on every species and in nearly every case complementing his descriptions with color photographs and ecological information. A series of appendices provide useful horticultural information as well. The second edition of Jones (2002) is also very good, a comprehensive review of cycads that includes ten introductory chapters that address cycad evolution and systematics, relationship with fire, economic importance, and conservation. Finally, Norstog and Nichols (1997) give an excellent introduction to cycad biology, with chapters on both general topics in biology and on the biology of particular species groups.
Until 2012, there wasn’t even compelling evidence that ginkgo existed in the wild. Tang et al. (2012) settle that question, and also discuss most of what is known of its ecology. See Ginkgo biloba for more literature on this species.
For the Gnetales, I am not aware of any good recent treatments. You could go to Pearson 1929, which is archaic, but comprehensive for its time. There's a good survey of the Ephedraceae by Stevenson (1993), and the many Chinese species are described in Wu and Raven (1999). Against this dusty literature, Loera et al. (2012) is a breath of fresh air, providing insights into the evolution and ecology of Ephedra.
For the Gnetaceae, the best treatment I know of is by Maheshwari and Vasil (1961), which is sorely dated and in any event is heavily focused on fine anatomical details of a few salient species. More current taxonomic information can be gleaned from the works on wood anatomy by Carlquist (1996a, 1996b). A fine and gratifyingly recent review by Feild and Balun (2008) explores the autecology of Gnetum, and provides answers to the question of how a gymnosperm can succeed in a forest so completely dominated by angiosperms.
For the Welwitschiaceae, see my treatment of Welwitschia.
Taylor S. Feild and Lawong Balun. 2008. Xylem hydraulic and photosynthetic function of Gnetum (Gnetales) species from Papua New Guinea. New Phytologist 177(3): 665–675.
Israel Loera, Victoria Sosa, and Stefanie M. Ickert–Bond. 2012. Diversification in North America arid lands: niche conservatism, divergence and expansion of habitat explain speciation in the genus Ephedra. Molecular Phylogenetics and Evolution 65(2):437-450.
Cindy Q. Tang, Yongchuan Yang, Masahiko Ohsawa, et al. 2012. Evidence for the persistence of wild Ginkgo biloba (Ginkgoaceae) populations in the Dalou Mountains, southwestern China. American Journal of Botany 99(8):1408–1414.
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