Kudzu vs. Honeysuckle: Functional differences and their impacts

Many of us can remember those hot summer days and the sweet scent of the honeysuckle in the backyard. Similarly, we can remember driving along the highway and seeing the haunting figures of dead trees covered in thick vines of kudzu. While these are a shared experience of many people, details of these invasive impacts are unknown to most.

Most people can name at least a few invasive plants. Some of the most common to come to people’s minds are kudzu or honeysuckle. We are used to seeing these plants here and there everyday places. However, they are likely more common than we may believe.  Once a population of an invasive species is established it can spread from there to new habitats that are suitable for its survival. The ecological response to invasive species introduction varies. In this post I will cover the differences and similarities between kudzu and honeysuckle in terms of the functional differences of the two invasives.

Kudzu & Honeysuckle as model invasives

Invasive plants can be introduced for many different reasons, or sometimes for no reason at all. One example of an intentional introduction is how honeysuckle was introduced for the purpose of horticulture (Schierenbeck 2004) due to their appealing flowers (Figure 3) and heartiness in less than ideal environments. Since introduction, honeysuckle has spread to cover almost all of the eastern US as well as isolated parts of the western US (Figure 1). Unlike honeysuckle which grows as a shrub, kudzu is a vine and grows at an alarming rate per year (14-18 meters!) (Forseth 1987) (Figure 4). This invasive vine can grow happily in either shaded or sunny areas, although high levels of sunlight are preferred. Kudzu is able to grow up along the trunks of establish trees, and break through the canopy layer of the trees. Once through this barrier (and with more sunlight available) they quickly take up and suffocate everything under and around them (Forseth 1987). In 2004, it was estimated that kudzu completely covered approximately three million hectares in the Southeastern US alone (Forseth 2004). That’s 12,000 square miles, which is the size of the state of Maryland! See Figure 2 for distribution map of where kudzu if found in the US. This plant has continued to spread since 2004 and with the impacts of climate change affecting the range of both plants and animals alike, we can expect to see a northward expansion of this invasive vine.

Figure 1: Map of where Japanese Honeysuckle is found (EDDMaps.org)

Figure 2: Map of where kudzu is found (EDDMaps.org)

Figure 3: image of honeysuckle blooming (AnnekeDeBlok/iStock/GettyImages)

Figure 4: image of kudzu near Atlanta, GA (Wikipedia)

Now, one may ask, why should we worry about invasic vines? It’s just a vine, what’s the big deal? In the same Foresth (2004) study, it was estimated that kudzu alone has caused somewhere between $100 and $500 million dollars in lost productivity of forests in the US. Therefore, understanding how invasive vines function may provide insight into how to manage, and mitigate their effects. If we know what type of habitat they prefer, maybe we can take preventative measures to halt its spread.

Do invasives function differently than native plants?

Many factors impact plant fitness, including nutrient and water availability and water use efficiency, and the plant’s morphology. Understanding these factors for invasive vines is critical for their management. The relationship between the invasive plants’ uses and the native plants’ uses of resources varies depending on resource availability. Some examples of this shift in resource allocation are a difference in the effect of limiting factors (Heberling et al. 2013; Matzek 2011), and the difference in above/below ground biomass and growth (van Kleunen et al. 2011).

Greater plasticity in invasives is another functional attribute that contribute to their success. Plasticity is defined as an individual or populations ability to shift its function in order to better survive and thrive. For instance, invasive honeysuckle has been shown to more readily make use of climbing supports and therefore increase its fitness over native plants in the same situation (Schweitzer & Larson 1999).

Additionally, invasive honeysuckle is proven to be a successful competitor in terms of its ability to take over both above ground (shading out the understory and decreasing the success of other saplings) and below ground (taking up nutrients and water and therefore decreasing the success of surrounding plants) (Schierenbeck 2004). These techniques of out-competing other species for necessary resources has resulted in a decrease in native plant fitness and consequently overall plant biodiversity in the invaded areas (Hartman & McCarthy, 2008).

As I briefly addressed earlier, climate change is expected to force plants to higher latitudes which were previously inaccessible to them. These opportunistic species are known to have a wide tolerance for unsuitable habitats, so if given the chance invasive plants will continue to utilize this shift in temperature regimes and expand their ranges. Additionally, these invasive plants are able to take necessary resources away from the native plants of a region. Because of this, these previously mentioned threats to the biodiversity of forests and overall health of an ecosystem will spread into newly invaded areas.

Conclusions & Take-aways

Some invasive species can be thought of in a positive light, like honeysuckle and its beauty. Some others are commonly known as pest species, like kuzdu. We know these species have thoroughly invaded many regions of the US, and in the face of continued spreading, its easy to give up hope in truly controlling these plants. However, there can be hope for a shift in tide of this continued invasion. Knowledge and education of the risks and impacts of these plants are some of the key factors to slow this spread. The general public must know of the threats and only then can we help combat the spread of these species. For instance, rather an allowing honeysuckle to spread (or god forbid planting it purposefully) because of the aesthetically pleasing, sweet tasting flowers, we can do our part to inhibit its growth and spread. With kudzu, although it is more commonly known as a pest-plant, one can try to not allow it to take hold in their area, and therefore hopefully stem the spread. With these steps, along with general awareness of the issues at hand, we may be able to avoid the spread of invasive species like honeysuckle and kudzu.

Citations:

Forseth, I.N., Teramura, A.H. “Field photosynthesis, microclimate and water relations of an exotic termperate liana, Pueraria lobata, kudzu” Oecologia, 71, 262-267. (1987)

Forseth, I.N., Innish, A.F. “Kudzu (Pueraria montana): history, physiology, and ecology combine to make a major ecosystem threat.” Critical Reviews in Plant Sciences, 23(5), 401-413. (2004)

Hartman, K.M., McCarthy, B.C. “Changes in forest structure and species composition following invasion by a non-indigenous shrub, Amur honeysuckle (Lonicera maackii)” Journal of the Torrey Botanical Society, 135(2), 245-259. (2008)

Heberling, J.M., and Fridley, J.D. “Resource-Use Strategies of Native and Invasive Plants in Eastern North American Forests.” The new phytologist. 200(2), 523–533. (2013)

Matzek, V. “Superior performance and nutrient-use efficiency of invasive plants over non-invasive congeners in a resource-limited environment.” Biological Invasions, 13, 3005-3014. (2011)

Schierenbeck, K.A. “Japanese Honeysuckle (Lonicera japonica) as an invasive species; history, ecology, and context.” Critical Reviews in Plant Sciences, 23(5), 391-400. (2004)

Schweitzer, J.A., Larson, K.C. “Greater Morphological Plasticity of Exotic Honeysuckle Species may make them better invaders than native species.” Torrey Botanical Society, 126(1), 15-23. (1999)

van Kleunen, M., Schlaepfer, D.R., Glaettli, M., Fischer, M. “Preadapted for invasiveness: do species traits or their plastic response to shading differ between invasive and non-invasive plant species in their native range?” Journal of Biogeography. 38 (7), 1294-1304. (2011)