Kai Zhu

Global Change Biology across Space and Time

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Migration paper cited by IPCC

Zhu K., Woodall C.W., Clark J.S. (2012). Failure to migrate: lack of tree range expansion in response to climate change. Global Change Biology, 18, 1042-1052.

The Intergovernmental Panel on Climate Change (IPCC) is a scientific intergovernmental body under the auspices of the United Nations. The IPCC provides an internationally accepted authority on climate change, producing reports which have the agreement of leading climate scientists and the consensus of participating governments. For the efforts to build up and disseminate knowledge about climate change, the IPCC was awarded the 2007 Nobel Peace Prize.

The newly released IPCC Fifth Assessment Report (AR5) Working Group II (WGII: Impacts, Adaptation and Vulnerability) Chapter 4 (Terrestrial and Inland Water Systems) cites the Global Change Biology article in the section of Observed Changes in Species Range, Abundance and Extinction.

Observed species range shifts – The number of studies looking at observed range shifts and the breadth of species examined has greatly increased since AR4. The most important advances since AR4 concern improvements in understanding the relationship between range shifts and changes in climate over the last several decades. The “uphill and poleward” view of species range shifts in response to recent warming (Parmesan and Yohe, 2003; Parmesan, 2006; Fischlin et al., 2007; Chen et al., 2011) is a useful simplification of species responses; however, responses to warming are conditioned by changes in precipitation, land use, species interactions and many other factors. Investigations of the mechanisms underlying observed range shifts show that climate signals can often be detected, but the impacts of and interactions between changing temperature, precipitation and land use often result in range shifts that are downhill or away from the poles (Rowe et al., 2010; Crimmins et al., 2011; Hockey et al., 2011; McCain and Colwell, 2011; Rubidge et al., 2011; Pauli et al., 2012; Tingley et al., 2012; Zhu et al., 2012). There are large differences in the ability of species groups (i.e., broad taxonomic categories of species) and species within these groups to track changes in climate through range shifts (Angert et al., 2011; Mattila et al., 2011; Chen et al., 2011). For example, butterflies appear to be able track climate better than birds (community shifts: Devictor et al., 2012; but see Chen et al., 2011 for range shifts) while some plants appear to be lagging far behind climate trends except in mountainous areas (Bertrand et al., 2011; Doxford and Freckleton, 2012; Gottfried et al., 2012; Zhu et al., 2012; Telwala et al., 2013). There is growing evidence that responses at the “trailing edge” of species distributions (i.e., local extinction in areas where climate has become unfavourable) are often less pronounced than responses at the “leading edge” (i.e., colonization of areas where climate has become favourable), which may be related to differences in the rates of local extinction vs. colonization processes (Doak and Morris, 2010; Chen et al., 2011; Brommer et al., 2012; Sunday et al., 2012) and difficulties in detecting local extinction with confidence (Thomas et al., 2006).

Turnover paper published in Global Change Biology

Zhu K., Woodall C.W., Ghosh S., Gelfand A.E., Clark J.S. (2014). Dual impacts of climate change: forest migration and turnover through life history. Global Change Biology, 20, 251-264. News release below.

CLIMATE WARMING MAY SPEED UP FORESTS’ LIFE CYCLES

DURHAM, N.C. – Many climate studies have predicted that tree species will respond to global warming by migrating via seed dispersal to cooler climates. But a new study of 65 different species in 31 eastern U.S. states finds evidence of a different, unexpected response.

Nearly 80 percent of the species aren’t yet shifting their geographic distributions to higher latitudes. Instead, they’re staying in place – but speeding up their life cycles.

The Duke University-led study, published today in the peer-reviewed journal Global Change Biology, is the first to show that a changing climate may have dual impacts on forests. It adds to a growing body of evidence, including a 2011 study by the Duke team, that climate-driven migration is occurring much more slowly than predicted, and most plant species may not be able to migrate fast enough to stay one step ahead of rising temperatures.

“Our analysis reveals no consistent, large-scale northward migration is taking place. Instead, most trees are responding through faster turnover – meaning they are staying in place but speeding up their life cycles in response to longer growing seasons and higher temperatures,” said James S. Clark, H.L. Blomquist Professor of Environment at Duke’s Nicholas School of the Environment

Anticipating the impacts of this unexpected change on U.S. forests is an important issue for forest managers and for the nation as a whole, Clark said. It will have far-reaching consequences for biodiversity and carbon storage.

To test whether trees are migrating northward, having faster turnover, or both, the scientists went through decades of data on 65 dominant tree species in 31 eastern states, compiled by the USDA Forest Service’s Forest Inventory and Analysis program. They used computer models to analyze the temperature and precipitation requirements of the trees at different life stages, and also considered factors like reproductive dependence of young and adult trees.

“The patterns we were able to see from this massive study are consistent with forests having faster turnover, where young trees tend to be more abundant than adult trees in warm, wet climates. This pattern is what we would expect to see if populations speed up their life cycle in warming climates,” said Kai Zhu, a doctoral student of Clark’s at Duke, who was lead author of the study. “This is a first sign of climate change impacts, before we see large-scale migrations. It gives a very different picture of how trees are responding to climate change.”

The fact that most trees are not yet showing signs of migration “should increase awareness that there is a significant lag time in how tree species are responding to the changing climate,” Zhu said.

The study was funded by the National Science Foundation (NSF), and Zhu was supported by an NSF Doctoral Dissertation Improvement Grant.

Christopher W. Woodall, research forester at the U.S. Forest Service’s Northern Research Station in St. Paul, Minn., Souparno Ghosh, a postdoctoral researcher in Duke’s Department of Statistical Science, and Alan E. Gelfand, J.B. Duke Professor of Statistics and Decision Sciences in Duke’s Department of Statistical Science, were co-authors of the study. Clark also holds an appointment as professor in the Department of Statistical Science.

 

Awarded NSF grant

The National Science Foundation (NSF) awards a Doctoral Dissertation Improvement Grant (DDIG) to James S. Clark (Principal Investigator) and Kai Zhu (Co-Principal Investigator) for support of the project entitled “DISSERTATION RESEARCH: Forest climate requirements change through species life history.” This award is effective May 1 , 2013 and expires April 30, 2014. See details on the NSF website. Abstract below.

Global warming is expected to have strongly negative effects on many species. One way these effects might be reduced is if species can change their geographical ranges as climate changes; if species can migrate to cooler places such as higher latitudes or elevations as temperature rises, they may be able to stay in the same climate by changing place. However, the preliminary research for this project shows that species of trees in the eastern U.S. have not moved northward. The project will test two alternative hypotheses to explain this, both based on whether young and adult trees differ in their ability to tolerate a wide range of environmental conditions. Researchers will expand a current species distribution model to include more explicit effects of juvenile and adult responses to temperature, and use data from a national forest inventory and climate measurements to compare the abundances of juveniles and adults.

Anticipating the impacts of climate change on U.S. forests is an important issue for forest managers and for the nation as a whole. Results from this project will help plan strategies for maintaining forest productivity and for substitutions of alternative land uses. The project will also strengthen collaboration between Duke University and the USDA Forest Service, and train a Ph.D. student and an undergraduate student.

Received ESA Award

The Ecological Society of America (ESA) has named Kai Zhu, a doctoral student at Duke University’s Nicholas School of the Environment, the recipient of its prestigious 2012 Outstanding Research in Ecology by a Graduate Student Award on August 7 at the ESA annual meeting in Portland, OR. Press release below.

PhD Student Kai Zhu Receives ESA Award for Outstanding Research

DURHAM, NC – The Ecological Society of America (ESA) has named Kai Zhu, a doctoral student at Duke University’s Nicholas School of the Environment, the recipient of its prestigious 2012 Outstanding Research in Ecology by a Graduate Student Award.

Zhu, whose research focuses on forest biodiversity in a changing climate, received the award August 7 at the ESA annual meeting in Portland, Ore.

In selecting Zhu for the honor, the award jury cited his work to develop innovative new approaches to modeling forest biodiversity in response to climate change, and his lead authorship of the groundbreaking paper, “Failure to Migrate: Lack of Tree Range Expansion in Response to Climate Change,” which was published in the peer-reviewed journal Global Change Biology in October 2011.

That study, funded by the National Science Foundation, found that more than half of eastern U.S. tree species aren’t adapting to climate change as quickly or consistently as predicted.  Many models have predicted that trees will migrate rapidly to higher latitudes and elevations in response to warming temperatures, but Zhu and his colleagues’ large-scale analysis found no evidence that a consistent, climate-driven northward migration is occurring.

Earlier this year, Zhu also was named winner of the Nicholas School’s 2012 Dean’s Award for the Outstanding PhD Student Manuscript for the study.

James S. Clark, H.L. Blomquist Professor of Environment and professor of biology and statistics, is Zhu’s faculty advisor.

Zhu received his Master of Science degree in 2009, and his Bachelor of Science degree in 2006, both from Beijing Normal University.

Winning Dean’s Award

Dean's AwardKai Zhu was named a recipient of the 2012 Dean’s Award for Outstanding PhD Student Manuscript of Duke University’s Nicholas School of the Environment for his paper, “Failure to migrate: lack of tree range expansion in response to climate change,” which was published in October 2011 in the peer-reviewed journal Global Change Biology. Press release highlights below.

Zhu’s study finds that more than half of eastern U.S. tree species aren’t responding as predicted to climate change. Many models have predicted that trees will migrate rapidly to higher latitudes and elevations in response to warming temperatures, but Zhu and his colleagues’ large-scale analysis finds no evidence that a consistent, climate-driven northward migration is occurring.

Zhu will be acknowledged at the Nicholas School Recognition Ceremony on May 12, and receive a check for $1,500.

 

Migration paper recommended by F1000

Zhu K., Woodall C.W., Clark J.S. (2012). Failure to migrate: lack of tree range expansion in response to climate change. Global Change Biology, 18, 1042-1052.

Faculty of 1000 (F1000), a post-publication peer review service, places the above work in the library of the top 2% of published articles in biology and medicine. The service is widely used to find significant new research articles, and the inclusion of the article should significantly increase its visibility.

It is recommended as a “Must Read” “New Finding” by Luke McCormack and Erica Smithwick from Pennsylvania State University. Full comment below (also available on F1000 website).

This paper examines critically the assumption of northward range expansion (and southern contraction) of tree species in response to climate change. The results indicate that these responses are heterogeneous and variable across species and are inconsistently related to direct changes in temperature or seeding characteristics. Renewed efforts to monitor tree responses to climate are needed. Whether tree species will keep pace with a changing climate is a central question in ecology. In this paper, Zhu, Woodall and Clark use a relatively simple and elegant approach to analyze forest inventory analysis (FIA) data to test for range expansion and contraction at the southern and northern extremes of 92 temperate tree species in the eastern United States. The current paradigm assumes that most species will expand their ranges north and perhaps contract their southern range, tracking increasing temperate in the future. In line with this expectation, many previous publications, including modeling efforts and previous interpretations of FIA data, have suggested directly or indirectly this to be the case. However, work by Zhu, Woodall and Clark suggests a more complicated relationship between geography, species’ ranges and climate change. Of the 92 species examined in the study only 19 showed the expected northward expansion, while over 50 showed evidence for a general range contraction. Of particular importance is the authors’ honest acknowledgement of limitations in their approach and dataset. Despite these limitations, the work is a valuable contribution and gives sufficient evidence that range responses of trees to climate change will not be as simple as a little bump to the north, even in areas where geography, land use, and seed dispersal aren’t already making migration difficult.

Migration paper published in Global Change Biology

Zhu K., Woodall C.W., Clark J.S. (2012). Failure to migrate: lack of tree range expansion in response to climate change. Global Change Biology, 18, 1042-1052.

Failure to Migrate

Trees can’t migrate – but forests can. Indeed, many climate scientists have predicted that as temperatures warm, plant populations will respond by shifting to higher elevations and poleward toward cooler, higher latitudes. Now, a new study examines whether U.S. forests are indeed migrating north, and comes up with some potentially worrying findings.

The migration concept comes down to seeds and seedlings, Kai Zhu and James S. Clark of Duke University in North Carolina and Christopher W. Woodall of the U.S. Forest Service’s Northern Research Station in Minnesota note in Global Change Biology. As temperatures warm, for example, the southern edge of the range for some tree species could begin to erode as adult trees die and seeds left behind in the soil can’t sprout. In contrast, at the northern edge, the species could begin to creep north, as seedlings are able to gain a root-hold in a newly favorable climate. Although warm zones appear to have shifted north by up to 100 kilometers in parts of the United States, however, previous studies have failed to find forests moving north – although there are signs that some trees are shifting to higher elevations.

To take a fresh look for migrating forests, the researchers turned to a massive data set compiled by the Forest Service’s Forest Inventory and Analysis program. They focused on data on 92 tree species found in more than 43,000 inventory plots in 31 eastern states. Then, they looked at the relative distributions of seedlings, saplings and large trees, and factored in things like seed characteristics, and changes in climate and precipitation.

Although the results come with plenty of caveats, they suggest that forests are failing to migrate. Instead, nearly 59% of the tree species showed “the pattern expected for a population undergoing range contraction, rather than expansion, at both northern and southern boundaries.” About 21% appeared to be shifting northward, while about 16% appeared to be shifting southward. Just over 4% appeared to be expanding both north and south. In addition, there was “no consistent evidence that population spread is greatest in areas where climate has changed most; nor are patterns related to seed size or dispersal characteristics.”

The “evidence for climate-driven migration is essentially absent in this large analysis,” they conclude. “Patterns are more consistent with range contraction of eastern U.S. tree species than with northward migration.” And that should be “cause for concern,” they add, “given the temperature trends already underway during the 20th century.” Taken together, they write, the results “do not inspire confidence that tree populations are tracking contemporary climate change.”

 

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