Sericea Lespedeza

Sericea lespedeza presents quite a paradox. It has long been, and continues to be, acclaimed as a highly valuable erosion control and reclamation plant. It has recently become widely recognized as an invasive weedy species, while also being considered an underutilized forage plant. In contrast to kudzu, seed of sericea lespedeza continues to be commercially marketed and rather widely recommended for continued planting in the southeastern U.S. Agronomically, sericea lespedeza is recognized as difficult to establish and easily lost with excessive defoliation. Ecologically, sericea lespedeza is increasingly recognized as highly invasive and difficult to control. From combined contributions of these rather divergent perspectives, aspects of population dynamics from plant establishment to dominance and eventual population depletion are being discerned. Establishment limitations include hardseededness which adversely affects immediate germination and establishment but enhances opportunity for multiple establishment events beneficial to colonization of unpredictable and unmanaged environments. Initial vegetative growth of improved varieties each growing season is reported to be generally acceptable to grazing livestock and of good nutritive value despite moderate tannin levels. Rapid stem development during the growing season decreases palatability and often leads to the impression that the plant lacks forage value.

Sericea lespedeza is considered a semi-woody, upright-growing herb. Although seedlings are single-stemmed, mature plants can produce numerous upright stems from the perennating plant crown. In pure stands, a dense leaf canopy can develop to shade the soil surface and exclude other plants below this canopy. Senescence of leaves in the lower canopy of undefoliated plants late in the growing season can produce a layer on the soil surface which further excludes other plant species. In undisturbed stands, this layer can build up over a period of years [Baldridge, 1957]. With a canopy height of 1.5 to 2 m, sericea lespedeza is highly competitive with plants below this height, but it is vulnerable to competition from dense-growing plants above this height. Partial shade along forest roads in Louisiana appears to moderate sericea lespedeza with sparse populations existing as non-dominant community components in some instances for decades. Such partial shade from a forest canopy has also been noted to suppress vegetative competition and enhance establishment of sericea lespedeza planted on Louisiana Coastal Plain sites [Pitman, 2006]. Vegetative spread, other than increases in size of plant crowns and number of stems per crown, does not occur to effectively increase populations. Population increase is exclusively from seed, which can exceed 1,000 seeds per stem annually [Ohlenbusch et al., 2001] or several hundred kilograms per hectare of seed under cultivation. Seed are small (approximately 860,000 seed per kilogram), and seedlings are typically slow to develop. They are, therefore, vulnerable to competition, especially from rapidly developing, early colonizing annual grasses in humid environments.

Despite lack of seedling vigor, the ability of sericea lespedeza to spread from test plantings and volunteer in nearby areas was evident from observations of an 1899 planting in Virginia [Henson, 1957; Cope, 1957]. This ability to volunteer has been recognized as a desirable characteristic in pastures of the southeastern U.S. [Ball and Mosjidis, 1995]. Along with the ability to spread under certain conditions, limited palatability or requirement for a period of adjustment to sericea lespedeza by grazing livestock was recognized during early evaluations [Baldridge, 1957]. These indications of potential weediness and resistance to grazing were, however, countered by the establishment limitations and stand loss in heavily defoliated pastures and hay fields. Varieties of sericea lespedeza which were developed for reclamation rather than forage produced stands that were dominant and eventually recognized as inadequate for most economic uses such as livestock production in the coal-mining region of Appalachia. By the early 1980s, research was in progress to develop strategies to convert these dense stands of planted sericea lespedeza to better forage species [Dove et al., 1997]. During this same time period, widespread and increasing occurrence of sericea lespedeza was being reported in Oklahoma and Kansas [Koger and Stritzke, 2004]. The rapid expansion in Kansas was attributed at least in part to large-scale planting of native grass seed contaminated with sericea lespedeza seed as part of the Conservation Reserve Program [Kilgore et al., undated]. In Georgia and north Florida during this same time period, instances of undesired spread of this plant were also noted as illustrated by Landers and Mueller [1986]. From these and other similar divergent reports of the spread of, dominance by, and previously unappreciated limitations of this plant, sericea lespedeza became widely labeled as an undesirable invasive species. Only in the current century, however, have the various aspects of sericea lespedeza distribution, colonization, and dominance been evaluated in terms of ecological and anthropogenic relationships and their interactions.

Brandon et al. [2004] evaluated the mechanisms involved in dominance of an early successional, old field community by sericea lespedeza. They reported that mowing in spring or spring and fall increased sericea lespedeza, while nutrient enrichment (fertilization with nitrogen, phosphorus, and potassium) decreased cover, stem density, and biomass of this plant. The increase in sericea lespedeza with mowing was at least partially due to indirect effects since mowing prevented dominance by a taller growing woody species which shaded and out-competed the sericea lespedeza in un-mowed treatments. Brandon et al. [2004] concluded that light exclusion was the primary mechanism allowing sericea lespedeza to dominate adjacent herbaceous plants and also to be dominated by a dense-growing taller woody plant. The competitive advantage of sericea lespedeza in low nutrient environments was offset by fertilization providing opportunities for species more responsive to higher nutrient levels. Relationships of sericea lespedeza population dynamics to mowing have been further explored [Munger, 2004; Smith et al., 2001] with effects dependent on timing and subsequent treatments. Early spring defoliation, whether by mowing or burning, can remove old vegetation and enhance germination and seedling growth of sericea lespedeza when the soil seedbank includes this species. Repeated mowing or grazing at this time can decrease survival of these seedlings and be used to deplete soil seed reserves. Fall mowing, when seed have matured but not shattered, can effectively disperse the seed with limited effects on the senescent plants. According to Smith et al. [2001], the most effective time to mow for control of sericea lespedeza is during the late bud stage from mid July to late August. Mowing at this stage, particularly for two or three consecutive years, can effectively deplete stored energy because reserves have already been mobilized for reproductive development and will be further depleted to support vegetative regrowth.

The mechanisms of light control by means of a dominant canopy, competitive advantage for limited nutrients, and responsiveness to timing of defoliation or other disturbance providing opportunity for seed dispersal or germination and seedling development appear to be key aspects of developing and maintaining dominance by sericea lespedeza. Successional processes may be arrested indefinitely where a dense canopy of this species develops in resource-limited environments without potential for taller-growing species. In environments where resources can support shrub or forest communities, successional processes may be substantially delayed by a dense population of sericea lespedeza, but disturbance and edge effects will eventually allow increase of woody plants and suppression of sericea lespedeza as the overstory canopy closes. These relationships provide opportunity for sericea lespedeza to exert long-term effects on plant communities. Modifying these relationships may increase the rate of change from dominance by sericea lespedeza to woodlands or divert the trajectory of succession away from a developing dominance by sericea lespedeza. During decades of use in pastures and hay fields, defoliation practices served as effective disturbance mechanisms to control dense populations. Fertilization practices enhanced competitive ability of other pasture plants frequently resulting in depletion of sericea lespedeza stands. Thus, particular opportunity may exist for use of strategic disturbance to allow woody species to establish in appropriate environments. In grassland ecosystems, nutrient enrichment rather than woody plant establishment may be a key component to combine with strategic disturbance to suppress sericea lespedeza. Timing and cost of disturbance events must be appropriate for the problem presented. Fire and grazing, with appropriate timing and frequency, perhaps provide the most cost-effective means of disturbance for established populations. Appropriately timed mowing and herbicide application may also be effectively used [Altom et al., 1992; Jordan et al., 2002; Koger et al., 2002; Cummings et al., 2007].

Sericea lespedeza has undoubtedly become a difficult-to-suppress, unwanted plant in some situations. It has also been a difficult-to-obtain, highly desired plant in other situations. Some currently undesired populations of this plant were deliberately planted. Others, as with previously mentioned Conservation Reserve Program plantings in Kansas [Kilgore et al., undated], were planted but inadvertently. As also previously mentioned, sericea lespedeza has the ability to volunteer or grow where not previously planted. Even with this potential, Munger [2004] noted that it most often occurs on or near sites where it was planted previously. Munger [2004] further noted that there is lack of a documented long-distance seed dispersal mechanism for this legume with inadequate information about seed dispersal not related to anthropogenic activities. Along with potential spread through hay contaminated with the seed, it has been stated that seed is spread by animals [Vermeire et al., 1998]. Ohlenbusch et al. [2001] noted that quail consume the seed and deer browse the plant in winter when seed can be present. Cattle consume the plant primarily early in the growing season long before plant reproductive development and presence of seed. Considerable progress in understanding aspects of potential invasiveness could be made with some rather simple evaluations of feces samples from various animals with access to sericea lespedeza populations following seed maturation. If substantial passage of viable seed through the digestive tract of domestic livestock readily occurs, grazing of pastures during times of seed availablilty could be managed appropriately. Certainly under such conditions, cattle should not be moved at this time from a pasture with this plant to pastures without it (if spread of the plant is not desired).

Due to widespread planting over several decades and general lack of documentation of such plantings, it is difficult to unequivocally determine that discovery of sericea lespedeza at a particular site is due to non-anthropogenic dispersal. Even recent familiarity with the plant community does not preclude long-term presence as a component of a soil seedbank. Nonetheless, controlled experiments have been used to evaluate population dynamics of sericea lespedeza and propose that sericea lespedeza is invading rangelands of the southern

Great Plains at a rate of almost 2% per year [Cummings et al., 2007]. Treatments including herbicides or burning and grazing reduced only the rate of spread of sericea lespedeza. In contrast, small plots of sericea lespedeza in Louisiana allowed to grow undisturbed and maintain a dense canopy during a 7-year period recruited new plants only within the plot area and around the immediate edges of original plants despite substantial seed production [Pitman, 2006]. No evidence of spread or potential dispersal was detected despite presence of adjacent recently disturbed sites. Such a contrast suggests that grazing livestock, which were not present on the Louisiana site, could be a key aspect of the increase on Oklahoma rangelands. Alternatively, initial dispersal by anthropogenic means may have produced a widespread but sparse population which is now increasing from seed produced on site.

Both the potential seed dispersal mechanisms and the ecosystems vulnerable to invasion need further clarification. Since many current forests in the Southeast developed on retired farmlands, soil seedbanks may include sericea lespedeza seed from previous plantings which were shaded out as forest canopies closed. Greater knowledge of soil seedbanks is needed to determine if such long-term seed survival of this species occurs. Perhaps most of the unwanted sericea lespedeza now present in the Southeast was actually planted. Whether this is the case or not, tremendous quantities of seed are now available in some locations for further distribution by either unintended human activity or natural biotic or abiotic dispersal. Undoubtedly some seed on the soil surface is moved by runoff following high-rainfall events. Some transfer of seed likely occurs within vulnerable ecosystems in association with livestock and wildlife activity. If these are only secondary or minor sources of seed dispersal to new areas and human activity is the major factor, approaches to control the spread can be focused on human activities. Populations resulting from planting seed on prepared seedbeds on Appalachian minespoil or Great Plains rangelands hardly substantiate invasiveness of even an unwanted and difficult-to-remove dominant species. Approaches appropriate and resources justified for public investment in control of sericea lespedeza may need further assessment in at least some instances. Some populations which appear to present problems may be only temporary in forest ecosystems where closure of overstory canopies can suppress and perhaps even eliminate sericea lespedeza populations. Differences in invasiveness and persistence among varieties, which differ substantially in such characteristics as tannin concentration, leafiness, nutritive value, and palatability, have apparently not been assessed. Effective strategies for sustainable control of existing sericea lespedeza populations and approaches to restrict additional unwanted spread appear to require further research for adequate efficacy of recommendations in many instances.

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  • klaus
    When to mow sericea lespedeza?
    9 years ago
  • Yonas
    How has the sericea lespedeza impacted native species?
    9 years ago

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