Ghost forests consisting of dead trees adjacent to marshes are striking indicators of climate change, and marsh migration into retreating coastal forests is a primary mechanism for marsh survival in the face of global sea‐level rise. Models of coastal transgression typically assume inundation of a static topography and instantaneous conversion of forest to marsh with rising seas. In contrast, here we use four decades of satellite observations to show that many low‐elevation forests along the US mid‐Atlantic coast have survived despite undergoing relative sea‐level rise rates (RSLRR) that are among the fastest on Earth. Lateral forest retreat rates were strongly mediated by topography and seawater salinity, but not directly explained by spatial variability in RSLRR, climate, or disturbance. The elevation of coastal tree lines shifted upslope at rates correlated with, but far less than, contemporary RSLRR. Together, these findings suggest a multi‐decadal lag between RSLRR and land conversion that implies coastal ecosystem resistance. Predictions based on instantaneous conversion of uplands to wetlands may therefore overestimate future land conversion in ways that challenge the timing of greenhouse gas fluxes and marsh creation, but also imply that the full effects of historical sea‐level rise have yet to be realized.
The impacts of climate change on ecosystems are manifested in how organisms respond to episodic and continuous stressors. The conversion of coastal forests to salt marshes represents a prominent example of ecosystem state change, driven by the continuous stress of sea‐level rise (press), and episodic storms (pulse). Here, we measured the rooting dimension and fall direction of 143 windthrown eastern red cedar (
- NSF-PAR ID:
- 10443847
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Ecology
- Volume:
- 102
- Issue:
- 10
- ISSN:
- 0012-9658
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract We experimentally increased salinities in a tidal freshwater marsh on the Altamaha River (Georgia, USA) by exposing the organic rich soils to 3.5 yr of continuous (press) and episodic (pulse) treatments with dilute seawater to simulate the effects of climate change such as sea level rise (press) and drought (pulse). We quantified changes in root production and decomposition, soil elevation, and soil C stocks in replicated (
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Abstract Ghost forests, consisting of dead trees adjacent to marshes, are a striking feature of low-lying coastal and estuarine landscapes, and they represent the migration of coastal ecosystems with relative sea-level rise (RSLR). Although ghost forests have been observed along many coastal margins, rates of ecosystem change and their dependence on RSLR remain poorly constrained. Here, we reconstructed forest retreat rates using sediment coring and historical imagery at five sites along the Mid-Atlantic coast of the United States, a hotspot for accelerated RSLR. We found that the elevation of the marsh-forest boundary generally increased with RSLR over the past 2000 yr, and that retreat accelerated concurrently with the late 19th century acceleration in global sea level. Lateral retreat rates increased through time for most sampling intervals over the past 150 yr, and modern lateral retreat rates are 2 to 14 times faster than pre-industrial rates at all sites. Substantial deviations between RSLR and forest response are consistent with previous observations that episodic disturbance facilitates the mortality of adult trees. Nevertheless, our work suggests that RSLR is the primary determinant of coastal forest extent, and that ghost forests represent a direct and prominent visual indicator of climate change.more » « less
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Coastal forests in the Mid-Atlantic region are threatened by sea level rise through chronic and episodic salinization and hydrologic alterations, leading to inland marsh migration and the occurrence of ghost forests. This study uses dendrochronology to explore the impact of rising sea level on the annual growth of Juniperus virginiana (the Eastern red cedar) at the St. Jones component of the Delaware National Estuarine Research Reserve in Dover, DE. Chronologies from low and high elevations were developed, and a difference chronology (high–low) was generated. A rapid field assessment of tree stress indicated greater stress in low elevation trees, and low elevation soil tests showed higher soil moisture and salt content compared to samples from high elevation. Ring width indices were analyzed in relation to water level, precipitation, the Standardized Precipitation Evapotranspiration Index, and temperature, with Pearson’s correlation analysis. Trees growing at low elevation showed greater climate sensitivity and responded favorably to cool, wet summers. Over time, correlations between growth and climate variables decreased, while negative correlations with tidal water level increased—a pattern that presented nearly a decade earlier in the low elevation system. Given the widespread distribution of the Eastern red cedar and its sensitivity to changes in sea level, this species may be particularly useful as a sentinel of change in coastal landscapes as sea levels rise.more » « less
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Abstract Greater tree density and forest productivity at the tundra–taiga ecotone (TTE) are expected with climate warming, with potential feedbacks to the climate system. Yet, competition for nitrogen (N) may impact TTE dynamics. Greater tree density will likely increase N demand, while reducing N supply through soil shading and slower decomposition rates. We explored whether characteristics of roots and root‐associated fungi important to N acquisition responded to changes in density at the TTE and were related to above‐ground stand productivity and N cycling.
We measured rooting depth, uptake of N forms among soil layers and ectomycorrhizal (EcM) colonization and composition along a natural tree density gradient of monodominant larch
Larix cajanderi in northeastern Siberia. We tested relationships between larch root and fungal characteristics, above‐ground productivity and stand‐level N cycling parameters.Overall, there was preferential uptake of ammonium compared to glycine or nitrate. Nitrogen uptake was greatest in shallow soils of the organic horizon and related to root chemistry, root‐associated fungi and above‐ground N cycling parameters, but the direction of these relationships depended on N form. Uptake of different N forms, rooting depth and EcM colonization and composition were not related to tree density, but fungal composition was correlated with root N chemistry and above‐ground N cycling parameters. In addition to EcM, the abundance of dark septate endophytes and other ascomycetous taxa was positively related to N uptake and above‐ground N cycling parameters.
Synthesis . There was little impact of tree density on root and fungal parameters related to N acquisition suggesting intraspecific larch competition for N was not amplified with increased density. There was, however, a strong impact of root‐associated fungi on N uptake and stand N dynamics regardless of tree density. Together, this suggests an important role of root‐associated fungi on broadscale patterns of N cycling in TTE larch forests independent of changes in tree density expected with climate warming.
