Wetland Words
and What They Mean:
Vegetation
Published in The Forum, Volume 5 Number 1, Winter 1998
Barbara B. Beall, PWS
In the last two issues of the Forum Newsletter, we have focused
on hydrology and hydric soils and the technical terms associated
with these parameters in the federal wetland delineation methods.
In this article we will tackle the last parameter used in the Federal
Delineation Manual...vegetation.
To review, in order for an area to be identified as a wetland,
water must be present in the soil frequently enough and for long
enough duration to cause the soil to become anaerobic in the upper
part. All of the easily drained pore spaces are filled with water
and there are no pockets of oxygen for the plant's roots to tap
into for growth. As a result, many species of plants die under these
anaerobic conditions. Imagine trying to grow African violets in
a pot of soil that is saturated continuously for two weeks during
the year. Some plants however, have developed special adaptations
to live in these harsh growing conditions. These plants are called
hydrophytes, which in English means "water plants."
Adaptations that the plants make to live in these adverse conditions
can take many forms, but are generally grouped into morphological,
physiological and reproductive adaptations. Morphological adaptations
are changes in the structure or form of the plant which aid them
in growing in their particular environment. In wetlands, hydrophytes,
especially trees, may have buttressed bases which help provide additional
stability in soft wetland soils. They may have adventitious roots,
which are multiple root stems growing down from the main trunk.
Mangroves trees are an example of a plant with this adaptation.
Other plants have aerenchymous tissue, which is spongy hollow tissue
often found in the stems which increases the plant's buoyancy, and
the number of air spaces in the plant. This type of tissue may help
the leaves of the plant to float, and may store air for the plant
when it is under water. Wetland plants with floating leaves also
often have a waxy surface to protect the leaf from constant contact
with the water. Many of the emergent and floating aquatic plants,
such as water lilies, have this feature. Shallow root systems are
a morphological adaptation to provide additional stability to the
plant growing in wetland soils. Finally, some plants have developed
specialized cells to enhance the movement of oxygen to the roots
from the stems of the plants.
Physiological adaptations are methods which plants use to change
the metabolic pathways in which they process energy. Remember the
Krebs cycle in high school biology class? Accessing the deep recesses
of your brain? Do you remember that there were alternative pathways
through the Krebs cycle for anaerobic activity? To refresh your
memory, these anaerobic pathways are not as energy efficient as
aerobic pathways, and often cause the accumulation of chemicals
which may be toxic to biological processes. For those athletes out
there, it is kind of like when lactic acid builds-up in muscle tissue
during anaerobic exercise. Many wetland plants are thought to possess
alternative methods to handle the energy stresses and the build-up
of these chemicals from anaerobic respiration. For example, some
plants can store the accumulated chemicals in a non-toxic form in
their roots until a dry spell when the chemicals can be released.
Another adaptation is the ability to lower the rate in which metabolic
activity takes place under stressful conditions. The larch (Larix
laricina) is thought to possess this ability. Many plants can
transfer oxygen from the roots into the pore spaces of the soil
surrounding the roots, to minimize root degradation and to maintain
nutrient uptake under anaerobic soil conditions. Cattails (Typha
spp.) can maintain root growth under very low oxygen levels
in the soil, a condition which would end root growth in many other
plants.
Reproductive adaptations include prolonged seed viability in wet
conditions, and the ability of the seed to be triggered to grow
in dry conditions. Many wetland plants have seeds which can germinate
under low oxygen soil conditions, and have seedlings which can survive
low oxygen conditions during their early development.
Similar to the process used to develop the National Hydric Soils
List, a group of wetland botanists and ecologists representing the
four federal agencies involved in wetland regulations were assembled
to assess the probability of the common plants in the United States
to grow in wetland conditions. The scientists rated each plant's
likelihood of occurring in wetlands, and listed these plants in
the "National List of Plants that Occur in Wetlands,"
The list was further refined through the development of wetland
plant lists specific to various regions of the country. New York
State is in Region 1.
Indicator categories include Obligate Wetland (OBL) (occurs almost
always in wetlands (>99% of the time)); Facultative Wetland (FACW)
(usually occurs in wetlands (67% - 99% of the time) but may occur
in uplands), Facultative (FAC) (equally likely to occur in wetlands
or non-wetlands (34% to 66% in wetlands)); Facultative (FACU) (usually
occurs in non-wetlands (67% to 99%) but may occur in wetlands (1%
to 33%)); and Obligate Uplands (UPL) (occurs almost always in non-wetlands
(99% of time) in region listed). A + or - sign may also be included
on the indicator to further refine the probability of occurrence,
with a + sign indicating a higher probability of being found in
wetlands.
A common misperception about this rating system is that the wetland
indicator status of a plant serves to establish a "wetland
plant gradient" or describes how wet an area a plant will grow
in. This is not true and not the intention of this list. For example,
a silver maple (Acer saccharinum, FACW) will grow
in an upland yard very well.
In order for the "vegetation parameter" to be met for
the purposes of delineating wetlands, the wetland plant community
present in that location must be dominated by hydrophytes. To make
this assessment, a wetland scientist will examine the whole plant
community, and assess which plants are dominant in each layer. This
includes the tree layer, the shrub layer, the herbaceous layer and
any vines layer. Trees are defined as woody plants greater than
3 inches in diameter at breast height. In a typical wetland delineation,
a visual estimate is made to determine which plants dominate the
community in each layer. The dominant plants are recorded, and rated
according to their probability of occurrence in wetlands. When the
delineation needs to have more rigorous documentation, a comprehensive
delineation is conducted, which includes physical measurements of
the plant coverage for each layer, and a more complex rating system.
Regardless of the method used, the area must be dominated by hydrophytes
(plants rated as FAC, FACW or OBL) in order for that location to
meet the vegetation parameter under the federal delineation method.
For the visual assessment, this means that more than 50% of the
plant species recorded must be FAC, FACW or OBL. The comprehensive
system often uses an "importance value" system which multiplies
the percent dominance of each plant by a numeric rating for each
indicator status, and then divides by the number of plant species
to obtain an average indicator status rating for the plant community.
References
Environmental Laboratory. 1987. Corps of Engineers Wetlands
Delineation Manual, Technical Report Y-87-1, US Army Engineer
Waterways Experiment Station, Vicksburg, Miss.
Reed, P.B., Jr. 1988. National list of plant species that occur
in wetlands: Northeast (Region 1). U.S. Fish Wildl. Serv. Biol.
Rep. 88 (26.1). 111 pp.
4
Youngs Place
P.O. Box 1351
Latham, NY 12110-1351
518-783-1322
Fax: 518-783-1258
info@wetlandsforum.org
Wetland Words
and What They Mean:
Vegetation
Published in The Forum, Volume 5 Number 1, Winter 1998
Barbara B. Beall, PWS
In the last two issues of the Forum Newsletter, we have focused on hydrology and hydric soils and the technical terms associated with these parameters in the federal wetland delineation methods. In this article we will tackle the last parameter used in the Federal Delineation Manual...vegetation.
To review, in order for an area to be identified as a wetland, water must be present in the soil frequently enough and for long enough duration to cause the soil to become anaerobic in the upper part. All of the easily drained pore spaces are filled with water and there are no pockets of oxygen for the plant's roots to tap into for growth. As a result, many species of plants die under these anaerobic conditions. Imagine trying to grow African violets in a pot of soil that is saturated continuously for two weeks during the year. Some plants however, have developed special adaptations to live in these harsh growing conditions. These plants are called hydrophytes, which in English means "water plants."
Adaptations that the plants make to live in these adverse conditions can take many forms, but are generally grouped into morphological, physiological and reproductive adaptations. Morphological adaptations are changes in the structure or form of the plant which aid them in growing in their particular environment. In wetlands, hydrophytes, especially trees, may have buttressed bases which help provide additional stability in soft wetland soils. They may have adventitious roots, which are multiple root stems growing down from the main trunk. Mangroves trees are an example of a plant with this adaptation. Other plants have aerenchymous tissue, which is spongy hollow tissue often found in the stems which increases the plant's buoyancy, and the number of air spaces in the plant. This type of tissue may help the leaves of the plant to float, and may store air for the plant when it is under water. Wetland plants with floating leaves also often have a waxy surface to protect the leaf from constant contact with the water. Many of the emergent and floating aquatic plants, such as water lilies, have this feature. Shallow root systems are a morphological adaptation to provide additional stability to the plant growing in wetland soils. Finally, some plants have developed specialized cells to enhance the movement of oxygen to the roots from the stems of the plants.
Physiological adaptations are methods which plants use to change the metabolic pathways in which they process energy. Remember the Krebs cycle in high school biology class? Accessing the deep recesses of your brain? Do you remember that there were alternative pathways through the Krebs cycle for anaerobic activity? To refresh your memory, these anaerobic pathways are not as energy efficient as aerobic pathways, and often cause the accumulation of chemicals which may be toxic to biological processes. For those athletes out there, it is kind of like when lactic acid builds-up in muscle tissue during anaerobic exercise. Many wetland plants are thought to possess alternative methods to handle the energy stresses and the build-up of these chemicals from anaerobic respiration. For example, some plants can store the accumulated chemicals in a non-toxic form in their roots until a dry spell when the chemicals can be released. Another adaptation is the ability to lower the rate in which metabolic activity takes place under stressful conditions. The larch (Larix laricina) is thought to possess this ability. Many plants can transfer oxygen from the roots into the pore spaces of the soil surrounding the roots, to minimize root degradation and to maintain nutrient uptake under anaerobic soil conditions. Cattails (Typha spp.) can maintain root growth under very low oxygen levels in the soil, a condition which would end root growth in many other plants.
Reproductive adaptations include prolonged seed viability in wet conditions, and the ability of the seed to be triggered to grow in dry conditions. Many wetland plants have seeds which can germinate under low oxygen soil conditions, and have seedlings which can survive low oxygen conditions during their early development.
Similar to the process used to develop the National Hydric Soils List, a group of wetland botanists and ecologists representing the four federal agencies involved in wetland regulations were assembled to assess the probability of the common plants in the United States to grow in wetland conditions. The scientists rated each plant's likelihood of occurring in wetlands, and listed these plants in the "National List of Plants that Occur in Wetlands," The list was further refined through the development of wetland plant lists specific to various regions of the country. New York State is in Region 1.
Indicator categories include Obligate Wetland (OBL) (occurs almost always in wetlands (>99% of the time)); Facultative Wetland (FACW) (usually occurs in wetlands (67% - 99% of the time) but may occur in uplands), Facultative (FAC) (equally likely to occur in wetlands or non-wetlands (34% to 66% in wetlands)); Facultative (FACU) (usually occurs in non-wetlands (67% to 99%) but may occur in wetlands (1% to 33%)); and Obligate Uplands (UPL) (occurs almost always in non-wetlands (99% of time) in region listed). A + or - sign may also be included on the indicator to further refine the probability of occurrence, with a + sign indicating a higher probability of being found in wetlands.
A common misperception about this rating system is that the wetland indicator status of a plant serves to establish a "wetland plant gradient" or describes how wet an area a plant will grow in. This is not true and not the intention of this list. For example, a silver maple (Acer saccharinum, FACW) will grow in an upland yard very well.
In order for the "vegetation parameter" to be met for the purposes of delineating wetlands, the wetland plant community present in that location must be dominated by hydrophytes. To make this assessment, a wetland scientist will examine the whole plant community, and assess which plants are dominant in each layer. This includes the tree layer, the shrub layer, the herbaceous layer and any vines layer. Trees are defined as woody plants greater than 3 inches in diameter at breast height. In a typical wetland delineation, a visual estimate is made to determine which plants dominate the community in each layer. The dominant plants are recorded, and rated according to their probability of occurrence in wetlands. When the delineation needs to have more rigorous documentation, a comprehensive delineation is conducted, which includes physical measurements of the plant coverage for each layer, and a more complex rating system.
Regardless of the method used, the area must be dominated by hydrophytes (plants rated as FAC, FACW or OBL) in order for that location to meet the vegetation parameter under the federal delineation method. For the visual assessment, this means that more than 50% of the plant species recorded must be FAC, FACW or OBL. The comprehensive system often uses an "importance value" system which multiplies the percent dominance of each plant by a numeric rating for each indicator status, and then divides by the number of plant species to obtain an average indicator status rating for the plant community.
References
Environmental Laboratory. 1987. Corps of Engineers Wetlands Delineation Manual, Technical Report Y-87-1, US Army Engineer Waterways Experiment Station, Vicksburg, Miss.
Reed, P.B., Jr. 1988. National list of plant species that occur in wetlands: Northeast (Region 1). U.S. Fish Wildl. Serv. Biol. Rep. 88 (26.1). 111 pp.
4
Youngs Place
P.O. Box 1351
Latham, NY 12110-1351
518-783-1322
Fax: 518-783-1258
info@wetlandsforum.org