An official website of the United States government
Abstract Forests around the world are experiencing changes due to climate variability and human land use. How these changes interact and influence the vulnerability of forests are not well understood. In the eastern United States, well‐documented anthropogenic disturbances and land‐use decisions, such as logging and fire suppression, have influenced forest species assemblages, leading to a demographic shift from forests dominated by xeric species to those dominated by mesic species. Contemporarily, the climate has changed and is expected to continue to warm and produce higher evaporative demand, imposing stronger drought stress on forest communities. Here, we use an extensive network of tree‐ring records from common hardwood species across ~100 sites and ~1300 trees in the eastern United States to examine the magnitude of growth response to both wet and dry climate extremes. We find that growth reductions during drought exceed the positive growth response to pluvials. Mesic species such asLiriodendron tulipiferaandAcer saccharum, which are becoming more dominant, are more sensitive to drought than more xeric species, such as oaks (Quercus) and hickory (Carya), especially at moderate and extreme drought intensities. Although more extreme droughts produce a larger annual growth reduction, mild droughts resulted in the largest cumulative growth decreases due to their higher frequency. When using global climate model projections, all scenarios show drought frequency increasing substantially (3–9 times more likely) by 2100. Thus, the ongoing demographic shift toward more mesic species in the eastern United States combined with drier conditions results in larger drought‐induced growth declines, suggesting that drought will have an even larger impact on aboveground carbon uptake in the future in the eastern United States.
more »
« less
The Drought Response of Eastern US Oaks in the Context of Their Declining Abundance
Abstract The oak (Quercus) species of eastern North America are declining in abundance, threatening the many socioecological benefits they provide. We discuss the mechanisms responsible for their loss, many of which are rooted in the prevailing view that oaks are drought tolerant. We then synthesize previously published data to comprehensively review the drought response strategies of eastern US oaks, concluding that whether or not eastern oaks are drought tolerant depends firmly on the metric of success. Although the anisohydric strategy of oaks sometimes confers a gas exchange and growth advantage, it exposes oaks to damaging hydraulic failure, such that oaks are just as or more likely to perish during drought than neighboring species. Consequently, drought frequency is not a strong predictor of historic patterns of oak abundance, although long-term climate and fire frequency are strongly correlated with declines in oak dominance. The oaks’ ability to survive drought may become increasingly difficult in a drier future.
more »
« less
- Award ID(s):
- 2006196
- PAR ID:
- 10364639
- Publisher / Repository:
- Oxford University Press
- Date Published:
- Journal Name:
- BioScience
- Volume:
- 72
- Issue:
- 4
- ISSN:
- 0006-3568
- Format(s):
- Medium: X Size: p. 333-346
- Size(s):
- p. 333-346
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Summary White oak (Quercus alba) is an abundant forest tree species across eastern North America that is ecologically, culturally, and economically important.We report the first haplotype‐resolved chromosome‐scale genome assembly ofQ. albaand conduct comparative analyses of genome structure and gene content against other published Fagaceae genomes. We investigate the genetic diversity of this widespread species and the phylogenetic relationships among oaks using whole genome data.Despite strongly conserved chromosome synteny and genome size acrossQuercus, certain gene families have undergone rapid changes in size, including defense genes. Unbiased annotation of resistance (R) genes across oaks revealed that the overall number of R genes is similar across species – as are the chromosomal locations of R gene clusters – but, gene number within clusters is more labile. We found thatQ. albahas high genetic diversity, much of which predates its divergence from other oaks and likely impacts divergence time estimations. Our phylogenetic results highlight widespread phylogenetic discordance across the genus.The white oak genome represents a major new resource for studying genome diversity and evolution inQuercus. Additionally, we show that unbiased gene annotation is key to accurately assessing R gene evolution inQuercus.more » « less
-
ABSTRACT Forest composition is changing, yet the consequences for terrestrial carbon cycling are unclear. In the eastern United States, water‐demanding “mesophytic” tree species are replacing “xerophytic” oaks (Quercusspp.) and hickories (Caryaspp.), raising concerns that forest productivity will become increasingly sensitive to more frequent and severe drought conditions predicted for the region. However, we have a limited understanding of the extent to which the mortality risk of xerophytes versus mesophytes is coordinated with their growth sensitivity during drought. Here, we evaluated growth and mortality dynamics for 20 abundant eastern United States tree species following a severe drought in the summer of 2012. We synthesized data from ~4500 forest inventory plots and used an approach that quantified relative drought responses between co‐located trees to minimize impacts from environmental heterogeneity. We found that mesophytes were just as likely to perish as co‐occurring xerophytes but were more sensitive to drought in terms of diminished growth. These findings suggest that xerophytic decline is likely to lead to reduced carbon uptake during drought and that management efforts to conserve oak‐hickory stands will be decisive to sustain the carbon mitigation potential of these forests. However, we also found that growth‐mortality relationships differed between functional groups. Among xerophytes, growth and survival during drought were decoupled. Among mesophytes, there was a high degree of coordination, where species that experienced greater mortality also experienced greater growth reductions. Therefore, mesophytes with high growth sensitivity to water deficits are likely to be the most vulnerable to drought‐driven die‐off events moving forward.more » « less
-
null (Ed.)Eastern redcedar (Juniperus virginiana L., redcedar) encroachment is transitioning the oak-dominated Cross-Timbers of the southern Great Plain of the USA into mixed-species forests. However, it remains unknown how the re-assemblage of tree species in a semiarid to sub-humid climate affects species-specific water use and competition, and ultimately the ecosystem-level water budget. We selected three sites representative of oak, redcedar, and oak and redcedar mixed stands with a similar total basal area (BA) in a Cross-Timbers forest near Stillwater, Oklahoma. Sap flow sensors were installed in a subset of trees in each stand representing the distribution of diameter at breast height (DBH). Sap flow of each selected tree was continuously monitored over a period of 20 months, encompassing two growing seasons between May 2017 and December 2018. Results showed that the mean sap flow density (Sd) of redcedar was usually higher than post oaks (Quercus stellata Wangenh.). A structural equation model showed a significant correlation between Sd and shallow soil moisture for redcedar but not for post oak. At the stand level, the annual water use of the mixed species stand was greater than the redcedar or oak stand of similar total BA. The transition of oak-dominated Cross-Timbers to redcedar and oak mixed forest will increase stand-level transpiration, potentially reducing the water available for runoff or recharge to groundwater.more » « less
-
Frey, Jennifer (Ed.)Abstract Rodents play a key role in forest regeneration by dispersing seeds and interspecific differences in seed preferences could have important consequences for forest growth. The White-footed Mouse (Peromyscus leucopus) and Deer Mouse (Peromyscus maniculatus gracilis) are 2 closely related species that can exploit Red Oak (Quercus rubra) acorns but may display different preference levels due to the high tannin concentration present in these acorns. Here we investigated how White-footed Mice and Deer Mice differ in their ability to exploit Red Oak acorns. We conducted a cafeteria-style experiment where we offered mice (n = 61) acorns of Red Oak and Bur Oak (Q. macrocarpa; control seed with lower tannin levels) and video-recorded their preference and the acorn fate (consumed or cached). Using mixed-effects models, we found that both mouse species selected and consumed Bur Oak acorns at a high rate; however, White-footed Mice were 6.67 times more likely to select and consume Red Oak acorns than Deer Mice. Furthermore, White-footed Mice tended to cache Red Oak acorns near the surface where there is a higher chance of germination, while they usually consumed Bur Oak acorns. Our results suggest that Red Oaks have a better strategy for avoiding predation than Bur Oaks (i.e., high tannin levels leading to caching), and the strong interaction between the White-footed Mouse and Red Oak might be an important mechanism behind the current range expansion of both species in response to climate change.more » « less
