Climate Change Could Severely Impact California's Unique Native Plants
http://www.sciencedaily.com/releases/2008/06/08062 [2008-6-26]
Tag : plant parts
Because endemic species - native species not found outside thestate - make up nearly half of all California's native plants, achanging climate will have a major impact on the state'sunparalleled plant diversity, the researchers warn.
"Our study projects that climate change will profoundly impactthe future of the native flora in California," said DavidAckerly, UC Berkeley professor of integrative biology. "Themagnitude and speed of climate change today is greater than duringpast glacial periods, and plants are in danger of getting killedoff before they can adjust their distributions to keep pace."
The researchers caution that their study can't reliably predict thefate of specific species. However, the trend is clear: Theresearchers project that, in response to rising temperatures andaltered rainfall, many plants could move northward and toward thecoast, following the shifts in their preferred climate, whileothers, primarily in the southern part of the state and in BajaCalifornia, may move up mountains into cool but highly vulnerablerefugia.
Coast redwoods may range farther north, for example, whileCalifornia oaks could disappear from central California in favor ofcooler weather in the Klamath Mountains along the California-Oregonborder. Many plants may no longer be able to survive in thenorthern Sierra Nevada or in the Los Angeles basin, while plants ofnorthern Baja California will migrate north into the San Diegomountains. The Central Valley will become preferred habitat forplants of the Sonoran desert.
"Across the flora, there will be winners and losers,"said first author Scott Loarie, a Ph.D. candidate at DukeUniversity's Nicholas School for the Environment who has workedwith Ackerly on the analysis for the past four years. "Innearly every scenario we explored, biodiversity suffers -especially if the flora can't disperse fast enough to keep pacewith climate change."
The authors identified several "climate-change refugia"scattered around the state. These are places where large numbers ofthe plants hit the hardest by climate change are projected torelocate and hang on. Many of these refugia are in the foothills ofcoastal mountains such as the Santa Lucia Mountains alongCalifornia's Central Coast, the Transverse Ranges separating theCentral Valley from Los Angeles and the San Gabriel Mountains eastof Los Angeles. Many of these areas are already under increasingpressure from encroaching suburban development.
"There's a real potential for sheltering a large portion ofthe flora in these refugia if they are kept wild and if plants canreach them in time," Loarie said. The authors argue that it'snot too early to prepare for this eventuality by protectingcorridors through which plants can move to such refugia, and maybeeven assisting plants in reestablishing themselves in new regions.
"Part of me can't believe that California's flora willcollapse over a period of 100 years," Ackerly said. "It'shard to comprehend the potential impacts of climate change. Wehaven't seen such drastic changes in the last 200 years of humanhistory, since we have been cataloguing species."
Ackerly, Loarie and colleagues at UC Berkeley, Duke University inDurham, N.C., California Polytechnic State University (Cal Poly) inSan Luis Obispo and Texas Tech University in Lubbock report theirfindings in the open-access journal PLoS One, which appears onlineJune 25.
The researchers spent four years mining the data from more than 16plant collections around the state, in particular from theUniversity and Jepson Herbaria of UC Berkeley, to assess theclimatic ranges of more than 2,000 California endemic plants. Theserepresent almost 40 percent of the 5,500 native plants in theCalifornia Floristic Province, which includes most of the stateexcept for the deserts and the Modoc Plateau in the northeast, andalso includes parts of southern Oregon and northern BajaCalifornia. The plants assessed include individual species, as wellas subspecies and varieties.
In collaboration with climate modeler Katharine Hayhoe of TexasTech, Loarie and Ackerly then employed two different climate models- one based at the U.S. National Center for Atmospheric Researchand the other at the United Kingdom Meteorological Office - thatpredict changes in temperature and precipitation through the year2100 for lower and higher greenhouse gas emissions scenarios. Theythen projected for each model and scenario where California'sendemic species would have to move in order to find themicroclimate they need to survive. One set of projections assumedthat plants can easily relocate, while another assumed that theycannot migrate at all by 2100, so their ranges will only shrink asclimate changes.
Loarie emphasized that there are many uncertainties in the analysis- for example, in the known range of individual plants; inknowledge of the microclimate each plant prefers; in how muchwarming can be expected based on best- and worst-case greenhousegas scenarios; in the direction and magnitude of changes inCalifornia rainfall; and in whether or not plants can migratesufficiently in 100 years to discover congenial habitat.
Despite these unknowns, the researchers said they are confident intheir approach, which has been used previously to predict globalwarming's effects on isolated species or plant families in placessuch as South Africa, Europe, the eastern U.S. and southernCalifornia.
"We can have confidence in the trends, if not in what happensto specific species," Loarie said. "There is a cleartrend despite the uncertainty."
In the most optimistic scenario, in which global emissions ofcarbon dioxide return to near-1990 levels by the end of the centuryand plants are able to move into new habitats within a century,diversity of species in parts of California might actuallyincrease, especially along the northwest and central coast.Nevertheless, diversity in the northern Sierra and in southernCalifornia would decrease.
However, such an optimistic outcome is far less likely than moredire ones, Ackerly said. In the higher scenario - the greatestwarming, and plants unable to move in the 90- to-100-year timeframe of global warming - plant diversity will decrease everywhereby as much as 25 percent, even if no species actually becomeextinct. Similarly, 66 percent of all endemic species willexperience more than an 80 percent reduction in range.
If plants are able to disperse in time to find more suitablehabitat, the researchers found that ranges will shift by an averageof 150 kilometers (95 miles) under higher climate change, oftenwith no overlap between the old and new ranges. Paradoxically, thismay separate species that now live together: Substantial numbers offloral communities may be split up as some species move south anduphill while others move north and towards the coast.
Though the study did not look at the response of invasive ornon-native plants to climate change, Ackerly said that they likelywill expand their ranges at the expense of natives and endemics.And shifting and shrinking ranges of endemic species likely willaffect animal diversity as well. Ackerly noted that range changemay separate an animal from its major food source, or a pollinatorfrom its preferred plant.
With the shifting ranges of endemic species, species conservationbecomes a moving target, the researchers noted. Brent Mishler,director of the University and Jepson herberia and a professor ofintegrative biology, anticipates a big need for information onpossible plant movement among those people protecting, managing orrestoring natural areas around the state.
"They could really benefit by knowing what plants are indanger of being eliminated from their area, and maybe even moreimportantly, what plants to keep in mind that will be 'refugees'from other sites that will need to move into their area to avoidextinction," he said. "Planning for refugees will becomea new but important concept for natural reserves to thinkabout."
Coauthors with Loarie, Ackerly and Hayhoe are UC Berkeley graduatestudent Benjamin E. Carter; database specialist Richard Moe of UCBerkeley's University and Jepson herbaria; professor Charles A.Knight of Cal Poly; and statistician Sean McMahon of Duke. Loarie,who began the research project with Ackerly while working on hisB.S. at Stanford University, continued the project while earninghis Ph.D. at Duke, and will be starting a post-doctoral fellowshipat the Carnegie Institute of Washington's Department of GlobalEcology this summer.
Because endemic species - native species not found outside thestate - make up nearly half of all California's native plants, achanging climate will have a major impact on the state'sunparalleled plant diversity, the researchers warn.
"Our study projects that climate change will profoundly impactthe future of the native flora in California," said DavidAckerly, UC Berkeley professor of integrative biology. "Themagnitude and speed of climate change today is greater than duringpast glacial periods, and plants are in danger of getting killedoff before they can adjust their distributions to keep pace."
The researchers caution that their study can't reliably predict thefate of specific species. However, the trend is clear: Theresearchers project that, in response to rising temperatures andaltered rainfall, many plants could move northward and toward thecoast, following the shifts in their preferred climate, whileothers, primarily in the southern part of the state and in BajaCalifornia, may move up mountains into cool but highly vulnerablerefugia.
Coast redwoods may range farther north, for example, whileCalifornia oaks could disappear from central California in favor ofcooler weather in the Klamath Mountains along the California-Oregonborder. Many plants may no longer be able to survive in thenorthern Sierra Nevada or in the Los Angeles basin, while plants ofnorthern Baja California will migrate north into the San Diegomountains. The Central Valley will become preferred habitat forplants of the Sonoran desert.
"Across the flora, there will be winners and losers,"said first author Scott Loarie, a Ph.D. candidate at DukeUniversity's Nicholas School for the Environment who has workedwith Ackerly on the analysis for the past four years. "Innearly every scenario we explored, biodiversity suffers -especially if the flora can't disperse fast enough to keep pacewith climate change."
The authors identified several "climate-change refugia"scattered around the state. These are places where large numbers ofthe plants hit the hardest by climate change are projected torelocate and hang on. Many of these refugia are in the foothills ofcoastal mountains such as the Santa Lucia Mountains alongCalifornia's Central Coast, the Transverse Ranges separating theCentral Valley from Los Angeles and the San Gabriel Mountains eastof Los Angeles. Many of these areas are already under increasingpressure from encroaching suburban development.
"There's a real potential for sheltering a large portion ofthe flora in these refugia if they are kept wild and if plants canreach them in time," Loarie said. The authors argue that it'snot too early to prepare for this eventuality by protectingcorridors through which plants can move to such refugia, and maybeeven assisting plants in reestablishing themselves in new regions.
"Part of me can't believe that California's flora willcollapse over a period of 100 years," Ackerly said. "It'shard to comprehend the potential impacts of climate change. Wehaven't seen such drastic changes in the last 200 years of humanhistory, since we have been cataloguing species."
Ackerly, Loarie and colleagues at UC Berkeley, Duke University inDurham, N.C., California Polytechnic State University (Cal Poly) inSan Luis Obispo and Texas Tech University in Lubbock report theirfindings in the open-access journal PLoS One, which appears onlineJune 25.
The researchers spent four years mining the data from more than 16plant collections around the state, in particular from theUniversity and Jepson Herbaria of UC Berkeley, to assess theclimatic ranges of more than 2,000 California endemic plants. Theserepresent almost 40 percent of the 5,500 native plants in theCalifornia Floristic Province, which includes most of the stateexcept for the deserts and the Modoc Plateau in the northeast, andalso includes parts of southern Oregon and northern BajaCalifornia. The plants assessed include individual species, as wellas subspecies and varieties.
In collaboration with climate modeler Katharine Hayhoe of TexasTech, Loarie and Ackerly then employed two different climate models- one based at the U.S. National Center for Atmospheric Researchand the other at the United Kingdom Meteorological Office - thatpredict changes in temperature and precipitation through the year2100 for lower and higher greenhouse gas emissions scenarios. Theythen projected for each model and scenario where California'sendemic species would have to move in order to find themicroclimate they need to survive. One set of projections assumedthat plants can easily relocate, while another assumed that theycannot migrate at all by 2100, so their ranges will only shrink asclimate changes.
Loarie emphasized that there are many uncertainties in the analysis- for example, in the known range of individual plants; inknowledge of the microclimate each plant prefers; in how muchwarming can be expected based on best- and worst-case greenhousegas scenarios; in the direction and magnitude of changes inCalifornia rainfall; and in whether or not plants can migratesufficiently in 100 years to discover congenial habitat.
Despite these unknowns, the researchers said they are confident intheir approach, which has been used previously to predict globalwarming's effects on isolated species or plant families in placessuch as South Africa, Europe, the eastern U.S. and southernCalifornia.
"We can have confidence in the trends, if not in what happensto specific species," Loarie said. "There is a cleartrend despite the uncertainty."
In the most optimistic scenario, in which global emissions ofcarbon dioxide return to near-1990 levels by the end of the centuryand plants are able to move into new habitats within a century,diversity of species in parts of California might actuallyincrease, especially along the northwest and central coast.Nevertheless, diversity in the northern Sierra and in southernCalifornia would decrease.
However, such an optimistic outcome is far less likely than moredire ones, Ackerly said. In the higher scenario - the greatestwarming, and plants unable to move in the 90- to-100-year timeframe of global warming - plant diversity will decrease everywhereby as much as 25 percent, even if no species actually becomeextinct. Similarly, 66 percent of all endemic species willexperience more than an 80 percent reduction in range.
If plants are able to disperse in time to find more suitablehabitat, the researchers found that ranges will shift by an averageof 150 kilometers (95 miles) under higher climate change, oftenwith no overlap between the old and new ranges. Paradoxically, thismay separate species that now live together: Substantial numbers offloral communities may be split up as some species move south anduphill while others move north and towards the coast.
Though the study did not look at the response of invasive ornon-native plants to climate change, Ackerly said that they likelywill expand their ranges at the expense of natives and endemics.And shifting and shrinking ranges of endemic species likely willaffect animal diversity as well. Ackerly noted that range changemay separate an animal from its major food source, or a pollinatorfrom its preferred plant.
With the shifting ranges of endemic species, species conservationbecomes a moving target, the researchers noted. Brent Mishler,director of the University and Jepson herberia and a professor ofintegrative biology, anticipates a big need for information onpossible plant movement among those people protecting, managing orrestoring natural areas around the state.
"They could really benefit by knowing what plants are indanger of being eliminated from their area, and maybe even moreimportantly, what plants to keep in mind that will be 'refugees'from other sites that will need to move into their area to avoidextinction," he said. "Planning for refugees will becomea new but important concept for natural reserves to thinkabout."
Coauthors with Loarie, Ackerly and Hayhoe are UC Berkeley graduatestudent Benjamin E. Carter; database specialist Richard Moe of UCBerkeley's University and Jepson herbaria; professor Charles A.Knight of Cal Poly; and statistician Sean McMahon of Duke. Loarie,who began the research project with Ackerly while working on hisB.S. at Stanford University, continued the project while earninghis Ph.D. at Duke, and will be starting a post-doctoral fellowshipat the Carnegie Institute of Washington's Department of GlobalEcology this summer.
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