Home/Ecosystems/ Mississippi Alluvial Plain Loess Slope Forest

Mississippi Alluvial Plain Loess Slope Forest

EVT 7509Mississippi River Alluvial Plain Dry-Mesic Loess Slope Forest

CES203.071GNRTreeHardwood

Summary

This system of dry-mesic upland forests occurs most extensively on west-facing loess slopes on southern Crowley's Ridge, with more limited occurrences on northern Crowley's Ridge and in the erosional slopes and hills that bound the Grand Prairie terrace of Arkansas and Macon Ridge in Louisiana and Arkansas. The vegetation is very distinctive from that of the adjacent alluvial plain, and the sites themselves, which occur on distinct slopes that rise above the alluvial plain surface, also contrast sharply with it. Occurrences of this system generally comprise dry-mesic forests that occupy west-facing slopes and narrow, "finger" ridgetops in a highly dissected landscape. In many cases, these slopes provide habitat for plant species that are uncommon in other parts of the alluvial plain. Forests on the ridgetops are dominated by Quercus alba, Quercus rubra (Crowley's Ridge only), Quercus falcata, Quercus pagoda, Quercus stellata, Carya texana, Quercus shumardii, and Quercus velutina.

Source: NatureServe Explorer

Vegetation

This system consists of forests that are typically dominated by oaks and other hardwoods. Depending upon local soil moisture and other factors, canopy composition can vary from Quercus stellata- and Quercus falcata-dominated on the driest sites to Quercus alba and other oaks on more mesic sites. Associated species in the subcanopy and understory vary along this moisture gradient.

Source: NatureServe Explorer

Environment

These forests occur on narrow ridgetops and slopes in a highly dissected environment. The system is best documented from southern Crowley's Ridge, Arkansas (Cross County south through Phillips County), with additional occurrences on the northern ridge, on the eastern border of the Grand Prairie terrace in Arkansas, on Macon Ridge (Louisiana/Arkansas) and probably on other upland sites within the alluvial plain, including Missouri and extreme western Kentucky and Tennessee. Loess soil is a characteristic and diagnostic component of the environment of this system.

Source: NatureServe Explorer

Dynamics

These are fire-maintained forests. In Arkansas, they generally lie to the east of hydroxeric Pleistocene terrace flatwoods or prairies (now usually converted to cropland) that burned frequently. Those fires would have continued into these dry to dry-mesic forests. There is presumably also some natural disturbance from the effects of windstorms and collapse of the fragile loess.

This loess forest type is Fire Regime Group III, surface fires with return intervals of 30 to 100 or more years. Mixed-severity fires will occur approximately every 100 years, opening the canopy with increased mortality. This effect may also be achieved by recurrent, severe insect defoliations or droughts. Straight-line winds or microbursts may cause blowdowns on a scale of 1 to 100 acres. Stand-replacement fires happen very infrequently (Landfire 2007a).

Source: NatureServe Explorer

Threats

Conversion of this type has primarily resulted from removal of the characteristic dominant hardwoods (primarily Quercus species and Carya species) through logging. This is also the most critical anthropogenic threat. This may result in a stand dominated by wind-blown or bird-dispersed tree species, including Acer rubrum, Celtis spp., Fraxinus americana, Juglans nigra, Juniperus virginiana, Liquidambar styraciflua, Liriodendron tulipifera, Prunus serotina, Robinia pseudoacacia, Sassafras albidum, Ulmus americana, and the exotic Ailanthus altissima. These and other fire-intolerant species persist and increase in the absence of fire (Edwards et al. 2013).

Aside from actual site conversion, feral hogs (Sus scrofa) represent one of the greatest threats to biodiversity in these forests (Engeman et al. 2007). In addition, invasive exotic species, including Ailanthus altissima, Macrothelypteris torresiana, Microstegium vimineum, Paulownia tomentosa, Phyllostachys aurea, and Pueraria montana var. lobata, can become dominant in the ground and shrub layers following canopy disturbance. For forests containing Fraxinus species, emerald ash borer (which as of October 2013 has been reported from southeastern Missouri) may also be (or become) a significant stressor.

The most significant potential climate change effects over the next 50 years include an increase in storms, which would contribute to severe erosion of the fragile loess substrate. Climate change may also bring increased periods of drought, which will affect the health and survival of the trees, as well as increase the probability of damaging wildfire.

Source: NatureServe Explorer

Distribution

This system is endemic to well-drained sites on Crowley's Ridge (Arkansas, Missouri) and Macon Ridge (Louisiana/Arkansas), along the eastern slopes of the Grand Prairie terrace in Arkansas, and perhaps other such sites in the Mississippi River Alluvial Plain, including Missouri and extreme western Kentucky and Tennessee.

Source: NatureServe Explorer

Ecologically Associated Plant Species

Plant species that characterize this ecosystem type, organized by vegetation stratum. These are species ecologically associated with the ecosystem, not confirmed present in any specific area.

Tree canopy

Carya texana, Ostrya virginiana, Quercus alba, Quercus falcata, Quercus pagoda, Quercus rubra, Quercus shumardii, Quercus stellata, Quercus velutina

Source: NatureServe Ecological System assessment

Ecologically Associated Animals (4)

Animal species ecologically associated with this ecosystem type based on NatureServe assessment. These are species whose habitat requirements overlap with this ecosystem, not confirmed present in any specific roadless area.

Reptiles (3)

Common Name	Scientific Name	G-Rank
Common Five-lined Skink	Plestiodon fasciatus	G5
Eastern Fence Lizard	Sceloporus undulatus	G5
Little Brown Skink	Scincella lateralis	G5

Other Invertebrates (1)

Common Name	Scientific Name	G-Rank
American Box Turtle	Terrapene carolina	G5

Source: NatureServe Ecological System assessment

Component Associations (3)

Plant community associations that occur within this ecological system. Associations are the finest level of the U.S. National Vegetation Classification (USNVC) and describe specific, repeating assemblages of plant species. Each association represents a distinct community type that may be found where this ecosystem occurs.

Name	G-Rank
Pinus echinata Crowley's Ridge Forest	G3	NatureServe
Quercus alba - Quercus falcata - Quercus velutina / Ostrya virginiana Forest	G1	NatureServe
Quercus stellata - Quercus falcata / Ostrya virginiana Forest	G1	NatureServe

State Conservation Ranks (5)

Subnational conservation status ranks (S-ranks) assigned by Natural Heritage Programs in each state where this ecosystem occurs. S1 indicates critically imperiled at the state level, S2 imperiled, S3 vulnerable, S4 apparently secure, and S5 secure. An ecosystem may be globally secure but imperiled in specific states at the edge of its range.

State	S-Rank
AR	SNR
KY	SNR
LA	SNR
MO	SNR
TN	SNR

Methodology and Data Sources

Ecosystem classification: Ecosystems are classified using the LANDFIRE 2024 Existing Vegetation Type (EVT) layer, mapped to NatureServe Terrestrial Ecological Systems via a curated crosswalk. Each EVT is linked to the USNVC (U.S. National Vegetation Classification) hierarchy through pixel-level co-occurrence analysis of LANDFIRE EVT and NatureServe IVC Group rasters across all roadless areas.

Vegetation coverage: Coverage percentages and hectares are derived from zonal statistics of the LANDFIRE 2024 EVT raster intersected with roadless area boundaries.

Ecosystem narratives and community species: Sourced from the NatureServe Explorer API, representing professional ecological assessments of vegetation composition, environmental setting, dynamics, threats, and characteristic species assemblages.

IVC hierarchy: The International Vegetation Classification hierarchy is sourced from the USNVC v3.0 Catalog, providing the full classification from Biome through Association levels.

Component associations: Plant community associations listed as components of each NatureServe Ecological System. Association data from the NatureServe Explorer API.

State ranks: Conservation status ranks assigned by NatureServe member programs in each state where the ecosystem occurs.