Laundry washing increases dispersal efficiency of cloth-dispersed propagules - our new paper in NeoBiota

 

In our recently published paper, we study an interesting ecological phenomenon in our everyday life, namely the fate of propagules attached to our clothing after laundry washing.

The paper has been published in the journal NeoBiota and can be freely downloaded by clicking here.

Valkó, O., Lukács, K., Deák, B., Kiss, R., Miglécz, T., Tóth, K., Tóth, Á., Godó, L., Radócz, Sz., Sonkoly, J., Kelemen, A., Tóthmérész, B. (2020): Laundry washing increases dispersal efficiency of cloth-dispersed propagules. NeoBiota 60: 1-16.

During fieldwork, excursions or outdoor sports we often notice a large number of seeds or other propagules attached on our clothing and footwear. Several species developed adaptations that support the attachment of their propagules on mammals fur, such as hooks, awns, spikes or glabrous surface. The propagules of these species can travel long distances via epizoochory, and are often attached also on our clothing.

After a field trip, we can find many propagules on our clothing and footwear.

 

Epianthropochory, i.e. dispersal of propagules on human clothing is a special case of epizoochory. We people are unique dispersal vectors as we can connect distant habitats which would not have any biological connections otherwise, for example we move between big cities and natural ecosystems, we can move between distant biogeographical regions or even between continents. Due to the increased global population and mobility, people became very abundant long-distance dispersal vectors for plant propagules.

There are many open questions regarding the fate of human-dispersed propagules, especially regarding their establishment prospects. It is still a question how the mechanical and chemical effects to which propagules are exposed during human-mediated dispersal, affect their germination potential and establishment prospects. One of the most drastic events that can happen to a clothing-dispersed propagule is laundry washing. Everyday observations of field biologists, hikers and people participating in outdoor sports show that propagules attached to clothing often end up in washing machine. In our study we asked the following questions: Do clothing-dispersed propagules remain germinable after laundry washing? What are the effects of washing intensity and washing medium on the germination? Are there differences in the germination dynamics in the washed and unwashed (control) seeds?

 

We selected 18 model species, all of them are widespread in Central-Europe and have some morphological adaptations for epizoochory. During the germination experiments, we applied six combinations of washing intensity (30 °C or 60 °C) and washing medium (water, soap nuts or detergent) and an unwashed (control) treatment. We had five replicates of 25 propagules per species and treatment.

We put the propagules into these fabric sacks. We sewed the sacks and appended them with a string to prevent the propagules escaping. We washed the sacks subjected to the six washing treatments in six separate laundry cycles.

Propagules of Arctium lappa that have already started to germinate during the intensive washing treatment.

There were a lot of germinated seedlings one month after the start of the experiment.

This group photo showes the germinated seedlings of Bromus sterilis. Each column contains pots with the same treatment. From the left to the right: column 1 is the control, columns 2-4 are the gentle washing and columns 5-7 are the intensive washing treatments.

Similar group photo of Physocaulis nodosus seedlings. You can see that after washing at 60 C, no seeds could germinate.

Our results showed that gentle washing at 30 C did not decrease the germination potential of any of the studied species compared to the unwashed control! Intensive washing at 60 C decreased the germination potential of the half of the studied species, but for the other half, it was neutral. Our results suggest that, in general, the new trend for using lower washing temperatures to reduce energy consumption probably increases the ratio of viable propagules that leave the laundry cycle.

We showed that intensive washing desynchronised the germination of eight species. Compared to the classical case of epizoochory on mammal’s fur, here the dispersal process itself has direct effects on germination dynamics. These effects of laundry washing on germination dynamics have important consequences for establishment: elongated and desynchronised germination is especially advantageous in unstable environments characterised by frequent and unpredictable disturbances, although it is disadvantageous for establishment in stable or harsh environments. If germination is desynchronised, there is a higher chance that at least some seeds will germinate under the most suitable conditions in a new environment.

We also studied the retention potential of dry propagules and also of propagules after washing and drying. We found that a considerable amount of propagules has the potential to enter the laundry cycle, especially in the case of cotton and fleece clothing. We found that washed propagules had even higher retention rates compared to dry ones; thus, laundry washing increases potential dispersal distances for a fraction of the propagules that remain attached even after washing. The retention rates of dry and washed propagules were influenced by species identity, being the longest for species with the most developed appendages.

 On the fruits of Agrimonia eupatoria, hairs and hooks support attachment on fur, or in our case, clothing.

The involucrum of Arctium lappa has many hooks which can attach very strongly to fur or fabrics.

Propagules of Daucus carota attached on cotton socks.

What is the final destination of the washed propagules? Our results suggest that there are two main directions of post-washing dispersal. Propagules that are detached during drying of the clothes probably get into rural or urban environments or some of them do not get outside of the houses. As urban habitats often provide suitable conditions for the establishment of alien species, it is possible that some of the seeds will germinate and establish in urban habitats and it is also possible that some might become urban invaders. Urban habitats are often considered as invasion hotspots, from where invasive alien species can arrive in periurban areas and later in natural habitats.

Those propagules that remain attached on clothes after drying have the potential for post-laundry long-distance dispersal. We showed that, after laundry washing and drying, there is a fraction of the washed propagules that attach better to the clothes than the dry ones. The transport of washed propagules on the clothes to natural ecosystems is a realistic threat if we consider that we wear outdoor clothes primarily during outdoor activities and therefore propagules have a high chance to be dispersed outdoors.

Globally, the largest mass invasion events are connected with transport by vehicles, construction of roads and buildings, international trade and agriculture; all these processes move a considerable amount of soil, plants and animals over large distances and contain a large number of viable propagules. Clothing-dispersal can also transport a large number of propagules from native ranges to new areas, if we consider the increasing size and mobility of the human population. However, the most important feature of clothing-dispersal is that it can also affect the relatively undisturbed nature reserves which are not exposed to the above-mentioned mass invasions caused by vehicles, construction works, trade or agriculture. Long-distance dispersal after laundry washing might be a major source of plant invasions in such reserves, hiking areas and other remote locations having a unique flora.

In such isolated ares, like this isolated mountain peak on an oceanic island, the most probable way of the arrival of propagules of non-native species is clothing-dispersal.

Mountains and islands harbour a considerable amount of biodiversity worldwide, but they are also under an increasing pressure by tourism. Geographical isolation and the harsh environmental conditions were able to prevent the spread of invasive alien species in these areas in the past, but due to the increased human pressure and climatic changes, these areas have recently become increasingly threatened by plant invasions. The dispersal mode described in our study can further aggravate this process and increase the vulnerability of these ecosystems to invasions: washing of clothing-dispersed propagules might increase the dispersal distances and also affect their germination dynamics. In this way, laundry washing can support invasive alien species in a new environment to overcome both propagule and establishment limitations, those factors that controlled their establishment in the past.

To decrease the chances for dispersing propagules on our clothing, we suggest a few simple precautional measures. When visiting nautre reserves, we recommend wearing of closed and waterproof clothing, made of fabrics with low retention potential. Also, it is important not picking and leaving the attached propagules on natural sites.