Notes: The Trouble with Thypha (Cattail)

Introduction
The following are some of my notes from a lecture I attended at the headquarters to a national park in Indiana on wetland restoration and cattail invasion.  Wetlands are any area of land that is soaked with water for most of the year (but is not just open water such as in a lake).  Normally, wetlands have a diverse array of aquatic plants such as various grasses, sedges, waterlilies, etc.  Within the last few centuries, however, many wetlands - both natural and man-made - are quickly giving way to a monoculture of cattail (Thypha spp.), a reed that frequently grows in shallow water (see Figure 1).  This lecture I attended discusses how and why cattail has become an invasive species, what people can do to monitor the situation, and how to control the invasion of cattail reeds.

Figure 1:  Cattail reeds in a marsh.  Photo by Joy Marburger
  • Cattail considered invasive since the 1950s.
  • Cattail is in the Family Typhacea and its only genus is Typha.
  • Has wind-dispersed pollen and seeds (both are very small and easily airborne)
  • The structure of a cattail includes an extensive system of rhizomes.  The rhizomes from when a new plant is only about 6 inches in height!  It also consists of a root, steam, and a leaf (see Figure 2).  
Figure 2:  The basic structure of a cattail.
Figure 3: Thypha latifolia (a) and Typha angustifolia (b)
The native species of cattail, prevalent in pre-Colonial times, was Typha latifolia (Figure 3a).  The non-native species, likely introduced via the movement of ships from Europe to the United States, is T. angustifolia (Figure 3b).  The main morphological differences between the two species, as shown in Figure 3, is the gap that the native species has between the female inflorescence and the male section of the plant.  
  • The two species are now hybridizing.  
  • Hybrid species has highly variable features in terms of height, length, and where it grows.
  • Creates monocultures (Figure 1) and it changes the hydrology of wetland ecosystems, since cattails use up a lot of water and essentially dry out the marshes.  
Causes of Spread: Genetic Analysis
  • There are various causes for the spread of cattail.
  • Genetic analysis of cattail and cattail hybrids - a combination of genetic and environmental factors yield the plant's characteristics.  Phenotype = genotype + Environmental variables
  • Microsatellite DNA analysis used to determine parentage
  • Sequences (the different instances of the enzymes found in DNA) should match for a given species:
ABAB       CDCD
ABAB       CDCD
  • A hybrid would be expected to have a combination of two different species:
ABABCDCD

Causes of Spread: Seedbank Study
  • The introduction of T. angustifolia to North America gave it a good start
  • Disturbance from the industrial era and the movement of ships into the Great Lakes with contaminated ballast water
  • T. angustifolia has similar breeding mechanisms and same chromosome numbers to the native cattail (T. latifolia).  
  • Continues to spread across landscape via rhizomes and some fertile seeds
  • Extensive genetic intermixing - it is able to colonize various wetland habitats
  • Native cattail may go extinct through hybridization.  
  • Cattail more prevalent in seedbanks in some areas and not as much in other areas - despite similarities between two given localities.  
Cattail Management in Wetlands
  • Animal grazing is ineffective (muskrats cannot keep up with fast cattail growth)
  • Mechanical measures ineffective because of rhizomes
  • Hand pulling for small areas can work
  • Prescribed burning ineffective because it can cause peat fires and it does not neccesarily kill cattail rhizomes
  • Chemical control is used!  Glyphosate or diquat herbicide is used.  Both require the addition of a surfactant to stick to cattail plants and minimize damage to other plants and animals.  
Remedy?
  • Use prior research on cattails and cattail management
  • Develop historical documentation of what vegetation existed prior to invasion
  • Survey existing flora, fauna, seedbanks, soils, etc.
  • Develop restoration goals for where cattail will be controlled
  • Use restoration management techniques to restore pre-colonial vegetation communities, keeping in mind climate change.  
  • Use demonstration sites to create public awareness
  • Volunteer!  Sign on to the USGS's Cattail Volunteer Monitoring Project:  http://nwrcwebapps.cr.usgs.gov/cattail/

Cattail (seen just before treeline in background) encroaching into a native fen wetland in a national park in Ohio.  Photo by Joy Marburger.  


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