Eucalypts PDF Article - January 2011

See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/285151045 Eucalypts Article · January 2011 CITATIONS READS 69...

See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/285151045 Eucalypts Article · January 2011 CITATIONS READS 69 706 2 authors: Marcel Rejmanek David Mark Richardson University of California, Davis Stellenbosch University 200 PUBLICATIONS 28,851 CITATIONS 776 PUBLICATIONS 84,057 CITATIONS SEE PROFILE SEE PROFILE All content following this page was uploaded by David Mark Richardson on 06 July 2020. The user has requested enhancement of the downloaded file.  SEE ALSO THE FOLLOWING ARTICLES (>740 species). Angophora and Corymbia are often treated Early Detection and Rapid Response / Endangered and Threatened as subgenera of Eucalyptus, sensu lato. The genus Eucalyp- Species / Herbicides / Invasion Economics / Islands / Lag Times / tus (sensu stricto) is currently divided into ten subgenera, Risk Assessment and Prioritization six of which are monotypic (having only one species). Naturalized eucalypts belong almost exclusively to the FURTHER READING two largest subgenera, Eucalyptus (Monocalyptus, >140 Clout, M. N., and P. A. Williams, eds. 2009. Invasive Species Management: species) and Symphyomyrtus (>360 species) (Table 1). A Handbook of Techniques. Oxford: Oxford University Press. Genovesi, P. 2007. Limits and potentialities of eradication as a tool for Most eucalypts are trees (10 to >50 m in height), some addressing biological invasions (385–400). In W. Nentwig, ed. Biological are “mallees” (multistemmed from ground level, usually Invasions. Ecological Studies, Vol. 193. Heidelberg: Springer-Verlag. 5.0; China: >2.0; Vietnam: To date, the total area of eucalyptus plantations has >1.0) been increasing exponentially. The global extent of euca- Americas 6.4 (Brazil: >3.6; Chile: >0.3; Argentina: lypt planting outside Australia reached 15.6 million ha in >0.2; Peru: >0.2) the 1990s—more than four times the global total in the Africa 2.2 (South Africa: >0.4; Angola: >0.2; Morocco: >0.2) 1970s. In 2008, the total area of eucalyptus plantations was Europe 1.3 (Portugal: >0.6; Spain: >0.5; estimated at 19.6 million ha. This is an area larger than the Italy: >0.07) state of Washington, or the nations of Austria and Hungary Oceania 0.9 together. Only one genus of trees is more extensively culti- note: http://git-forestry-blog.blogspot.com/2008/09/eucalyptus-global-map-2008- vated than eucalypts: Pinus (pines), with a global plantation cultivated.html and other sources. E U C A LY P T S 205 05_Simberloff10_E_p169-222.indd 205 9/13/10 10:02:33 AM  2.0 and 5.5 m s–1. Lower terminal velocity values mean that seeds can be carried by winds for longer distances. HIGH MORTALITY OF SEEDLINGS. As noted above, euca- lypts produce very small seeds (usually 360 species). Still, all velocities of seeds of all tested eucalypt species are between six species that can be classified as invasive in at least one 206 E U C A LY P T S 05_Simberloff10_E_p169-222.indd 206 9/13/10 10:02:33 AM  TABLE 4 Of all widely used plantation species, eucalypts have Eucalyptus Species with No Conclusive Evidence of Naturalization attracted by far the most criticism. There are four main Species Subgenus Regenerative Strategy concerns: (1) excessive water use and suppression of food acmenoides Eucalyptus (Monocalyptus) Lignotuber sprouter crops growing nearby, (2) suppression of ground vegetation bosistoana Symphyomyrtus Lignotuber sprouter (possible allelopathic effects) and resulting soil erosion, erythrocorys Eudesmia Lignotuber sprouter (3) increased fire hazard, and (4) generally poor wildlife fraxinoides Eucalyptus (Monocalyptus) Obligate seeder jacksonii Eucalyptus (Monocalyptus) Lignotuber sprouter value. There is some substance to each of these concerns. macranda Symphyomyrtus Lignotuber sprouter pauciflora Eucalyptus (Monocalyptus) Lignotuber sprouter preissiana Eucalyptus (Monocalyptus) Lignotuber sprouter pulverulenta Symphyomyrtus Lignotuber sprouter punctata Symphyomyrtus Lignotuber sprouter radiata Eucalyptus (Monocalyptus) Lignotuber sprouter smithii Symphyomyrtus Lignotuber sprouter spathulata Symphyomyrtus Obligate seeder torquata Symphyomyrtus Lignotuber sprouter? note: Commonly cultivated Eucalyptus species with no conclusive evidence of naturalization. Species listed here are relatively commonly cultivated or tested, but the extent of their cultivation is still very limited when compared with many major plantation species listed in the Table 1. Therefore, “no conclusive evidence of naturalization” does not necessarily mean conclusive noninvasiveness. country belong exclusively to the subgenus Symphyomyr- tus. There seems also to be a somewhat larger proportion of subgenus Eucalyptus species among commonly planted eucalypts with no evidence of naturalization (Table 4). On average, seeds of species in the subgenus Symphyomyrtus are smaller (a notable exception, however, is E. globulus) than seeds of species in the second largest subgenus— Eucalyptus (>140 species). Therefore, terminal velocities of Symphyomyrtus seeds should be less, and they could be dispersed somewhat longer distances by wind. Also, none of the species classified as invasive in at least one country is a straight lignotuber sprouter (LS). This could also point to the primary importance of seed dispersal in invasive- FIGURE 2 Eucalyptus camaldulensis ness. Nevertheless, the more straightforward explanation is is invasive along hundreds of kilome- that species classified as invasive have been planted more ters of rivers in South Africa’s West- ern Cape province. The images show extensively (see notes in Table 1). Then, however, reasons (A) a general view of E. camdulensis for their extensive planting may be correlated with their established in the Berg River, (B) the growth and timber characteristics that are associated with extreme persistence of adult plants due to their ability to sprout from the particular regenerative strategies. roots, and (C) microsites for seedling establishment. (Photographs cour- ENVIRONMENTAL CONTROVERSIES AND tesy of D. M. Richardson.) CONTROL METHODS Considering the amount of planting, eucalypts are rela- tively noninvasive species. If their potential spread is the only concern, then eucalypts should not be planted near rivers and streams. Temporarily flooded or eroded banks are suitable habitats for spontaneous establishment of their seedlings (Fig. 2). Moreover, their seeds can be dispersed for long distances by running water. However, there are other concerns. E U C A LY P T S 207 05_Simberloff10_E_p169-222.indd 207 9/13/10 10:02:34 AM  Nevertheless, it is important to realize that in many tropi- cal countries, where eucalypts are grown on degraded soils unsuitable for continuing to support native trees (usually abandoned agricultural land), fuel and other products of resprouting eucalypts can greatly reduce the increasing human pressure on the remnants of natural forests. Even here, however, deleterious human practices associated with consecutive cutting cycles may eventually lead to yield decline and forest site degradation on a long-term basis. For long-term site quality and sustainability of biomass production, prolonging the cutting cycles and prohibiting or controlling litter raking appears to be imperative. Eucalypts may be a major source of both nectar and FIGURE 3 It is undeniable that unmanaged stands of some eucalypt pollen for honeybees. Because flowering of many euca- species can accumulate highly flammable dead material. To what lypts is abundant and lasts for long periods, some spe- extent Tasmanian blue gum (Eucalyptus globulus) groves contributed cies (particularly E. camaldulensis and E. cladocalyx) are to the intensity of the tragic Berkeley–Oakland Hills fire in 1991 remains very valuable for the honey industry. When compared a subject of bitter discussions. This hazy but dramatic photograph of the 1991 fire was shot by former fire captain Wayne Drager through a with native vegetation, usually significantly lower spe- plexiglass window, using a disposable camera on a bumpy helicopter cies diversity of arthropods, small mammals, and birds is flight. (Photograph courtesy of Wayne Drager.) reported from eucalyptus stands. For example, in Angel Island State Park, California, 41 species of birds were observed in native vegetation, but only 30 species in the Because of accumulated litter, dense eucalypt stands are eucalyptus forest. However, there may be also some other extremely flammable. The situation is exacerbated after trends: approximately three times more California slender winter freezes, when trees drop dead branches and foliage. salamanders (Batrachoseps attenuatus) were found in euca- During the last two weeks of 1990, a mass of frigid arctic air lyptus vegetation than in native. Even more importantly, moved into California, and temperatures plunged to record in California, eucalypts are major providers of shelter and lows along the Pacific Coast. It is very likely that fuel accu- nectar to the migrating monarch butterfly (Danaus plex- mulation in unmanaged eucalyptus stands contributed to ippus) during winter months. the intensity of the tragic fire in the Berkeley–Oakland Hills Allelopathic effects of eucalypts on native species are area in October 1991 (Fig. 3). widely reported. Such reports are mostly based on labo- In arid and semiarid countries, where shortage of water ratory bioassays. However, some field trials also point to is a big concern, benefits of eucalypt plantations may be decline of seed germination and increase of seedling mor- outweighed by their negative environmental impacts: tality of some native species. If not chemical inhibition, namely, their high water consumption. In South Africa, then at least accumulation of dead material on the floor of invasive eucalypts have been cleared over large areas as eucalypt plantations retards regeneration of native species. part of a national restoration program called Working for Mixed-species plantations of eucalypts with native (mainly Water. In most areas, standing trees are felled and, where nitrogen-fixing) species have the potential to increase pro- it is practically possible, their timber is harvested. Where ductivity while maintaining soil fertility and biodiversity. recovery of the timber is impractical, felled plants are often Tasmanian blue gums (E. globulus) were planted in the stacked and burned. The most challenging management San Francisco area of California as early as the second half operations involve clearing river banks in large parts of of the nineteenth century. Having been in this landscape the Western Cape province of dense stands of invasive E. for such a long time, many old eucalypts are now treated camaldulensis. Clearing alone often causes destabilization as trees with “historical value” or as “heritage trees.” Many of the river banks, and research is under way to determine people feel that eucalypts give California a “unique exotic the most effective ways of thinning the invasive stands flavor” lacking in other parts of the United States. This is gradually while simultaneously reintroducing key native the reason why removal of eucalypts on Angel Island in the plants to stabilize the sites and launch succession toward a San Francisco Bay (1990–1996) sparked a raging contro- sustainable community dominated by native plants. versy. In a very balanced way, the history of this episode was The fact that eucalypt seeds do not have dormancy, with described by Peter Coates. seed storage in the soil lasting less than a year, makes local 208 E U C A LY P T S 05_Simberloff10_E_p169-222.indd 208 9/13/10 10:02:35 AM  eradication an achievable goal. However, resprouting of cut trees from stumps or lignotubers, which is advantageous in some situations, makes control of eucalypts difficult. Con- tinuously cutting back the regrowth can eventually kill the tree, but this is a labor-intensive and expensive control method. Herbicide applications (triclopyr or glyphosate) to freshly cut stumps can greatly reduce resprouting. Because eucalypts are valued as timber and ornamental trees in many settings, biological control is very unlikely as an option. SEE ALSO THE FOLLOWING ARTICLES Allelopathy / Fire Regimes / Forestry and Agroforestry / Invasiveness / Mycorrhizae / Propagule Pressure / Trees and Shrubs FURTHER READING FIGURE 1 The impacts of eutrophication on aquatic ecosystems. (Figure developed by the Integration and Application Network of the Coates, P. 2006. American Perceptions of Immigrant and Invasive Species. University of Maryland Center for Environmental Science.) Berkeley: University of California Press. Díez, J. 2005. Invasion biology of Australian ectomycorrhizal fungi intro- duced with eucalypt plantations into the Iberian Peninsula. Biological Invasions 7: 3–15. Doughty, R. W. 2000. The Eucalyptus: A Natural and Commercial History contain less than 5–10 µg L-1 phosphorus and less than 250– of the GumTree. Baltimore: The Johns Hopkins University Press. 600 µg L-1 nitrogen. These nutrient concentrations are at Keane, P. J., G. A. Kile, F. D. Podger, and B. N. Brown, eds. 2000. Dis- eases and Pathogens of Eucalypts. Collingwood, Australia: CSIRO least 2 to 10 times as high in eutrophic waters and can have Publishing. major effects on biotic communities, including the loss of Nicolle, D. 2006. A classification and census of regenerative strategies in biodiversity and the invasion of nonnative species (Fig. 1). the eucalypts (Angophora, Corymbia and Eucalyptus—Myrtaceae), with special reference to the obligate seeders. Australian Journal of Botany 54: 391–407. NATURAL AND ANTHROPOGENIC Poore, M. E. D., and C. Fries. 1985. The Ecological Effects of Eucalyptus. EUTROPHICATION FAO Forestry Paper 59: 1–87. Rome: FAO. Rejmánek, M., D. M. Richardson, S. I. Higgins, M. J. Pitcairn, and E. Eutrophication is a slow natural process. The slow accu- Grotkopp. 2005. Ecology of invasive plants: State of the art (104–161). mulation of nutrients is especially prevalent in deposi- In H. A. Mooney, R. N. Mack, J. A. McNeely, L. E. Neville, P. J. Schei, tional environments, such as lakes and wetlands, where and J. K. Waage, eds. Invasive Alien Species: A New Synthesis. Washington, DC: Island Press. nutrients and sediments derived from a watershed are Ritter, M., and J. Yost. 2009. Diversity, reproduction, and potential for collected in a basin and permanently or temporarily invasiveness of Eucalyptus in California. Madroño (in press). immobilized and stored. For example, estuaries are natu- Slee, A. V., M. I. H. Brooker, S. M. Duffy, and J. G. West. 2006. Euclid: Eucalypts of Australia, 3rd ed. Collingwood, Australia: CSIRO. rally eutrophic, and hence very productive, because they Williams, J., and J. Woinarski, eds. 1997. Eucalypt Ecology: Individuals to receive nutrients derived from watersheds and tidal flows. Ecosystems. Cambridge: Cambridge University Press. Lakes accumulate sediments and organic matter and over time convert into productive and nutrient-rich shallow lakes and emergent marshes. Other naturally eutrophic systems are areas along the coast where upwelling con- EUTROPHICATION, veys nutrient-rich water to the surface. As an ecosystem’s nutrient status changes over millennial time scales, so AQUATIC does its community structure, with local extinction and colonization of new species working in concert to pro- KATHARINA A. M. ENGELHARDT duce species-rich and productive ecosystems. University of Maryland Center for Environmental Science, However, the process of eutrophication can be greatly Frostburg accelerated by human activities, such as runoff of excess fer- tilizer, sewage effluent, and stormwater runoff. In Australia, Eutrophication is the natural or anthropogenic accumula- for example, sites affected by human activity have mean lev- tion of nutrients in soil or water (from Greek eu = “well” and els of 780 µg L-1 N and 95 µg L-1 P compared to 300 µg L-1 trophe = “nourished”). Oligotrophic (low-nutrient) waters N and 21 µg L-1 P at less impacted sites. Because estuaries E U T R O P H I C AT I O N , A Q U AT I C 209 05_Simberloff10_E_p169-222.indd 209 9/13/10 10:02:36 AM View publication stats