o you ever wonder if plants “communicate” with each other? If so, you're not alone. The research on this important and fascinating topic has increased dramatically in the last decade. My interest in it dates back decades to my graduate school thesis that involved how phenolic acids exuded by the roots of garden pea (Pisum sativum) accessions from around the world warded off weeds that would otherwise have crowded them out. This was an early form of biological weed control for sure! The seeds we studied were 20-30 years old and had been carefully stored and preserved in USDA facilities for research such as this.

 

They were all non-hybrids that had unadulterated natural genetic qualities. While I am in no way suggesting that plant breeding isn't overall a positive advancement, there are instances where something is lost when something is gained, and genes are certainly no exception! Sometimes breeding for an improvement in one facet (production per acre, nutrition, etc.) results in the loss of another genetically controlled factors that may be negative or positive.

At about the same time I was pursuing my research described above at University of Minnesota, University of Washington zoologist David Rhoades demonstrated how some plants defend themselves against insect attacks by changing the nutritional and/or taste of their foliage. In turn, insects that otherwise would chow down on the tasty leaves look elsewhere for their lunch. Since then, research identifying the multiple paths that plants use to exchange information with neighboring plants (largely within their own species) and ward off herbivores (organisms feeding mostly on plants), diseases, and weeds has nearly tripled. While a lot of this chemical information exchange relates to the release of volatile organic compounds in the root zone and through the air, electrical signaling among plants also occurs.

Below are a few recent examples:

-Lima beans attacked by insects signaled nearby lima bean plants who built up defenses to avoid damage

-Lodgepole pines attacked by a beetle signaled neighboring trees who had time to prepare for attack. 

While, traditionally, research identified these chemical warnings occurring only in neighboring plants of the same species, Cornell researchers discovered that  sagebrush (Artemisia tridentata)with insect damage can release chemical signals recognized by wild tobacco (Nicotiana attenuata). In turn, the tobacco plants pump up their arsenal of chemical defenses to avoid damage. (Interestingly, the tobacco plants don't waste precious nitrogen and carbon on defense mechanisms until they are actually attacked since these elements need to be conserved as much as possible for future seed production.)

Ted Farmer's team at University of Lausanne, attached leaves of thale cress (Arabidopsis thaliana) with microelectrodes prior to infesting them with Egyptian cotton leafworms. Almost immediately, voltage changes radiated outward from the damaged leaf tissue in the damaged plant and other neighboring plants resulting in accumulation of jasmonic acid which reduced further damage. Genes responsible for transmitting the electrical signal create membrane channels inside cell walls that provide a conduit for charged ions. The genes in some ways parallel receptors that animals rely on to relay sensory signals through their bodies.

And last but certainly not least, Kudos to UC Davis ecologist/entomologist Richard “Rick” Karban, who was named a fellow of the Ecological Society of America (ESA) for “his innovative contributions to community and evolutionary ecology, especially through providing conceptual advances and rigorous experimental work on plant-insect interactions." Want to learn a log more about this topic."  Still "hungry" for more information on this topic?   You're in luck! Dr. Karban wrote a 240-page book entitled: Plant Sensing and Communication (University of Chicago Press).

 

 

Did you ever wonder the origins of why people often choose to give red flowers to their significant others  for Valentine's Day?

The language of flowers became popular in the 17th and 18th centuries. Virtually every flower, even its color, had special significance during this period. Flowers even formed secret correspondence between men and women with bouquets being chosen carefully to convey sentiment.

Traditionally: 

- red roses: love

- pink roses: complete happiness

- daffodils: regard

- daisies: loyalty

- gardenia: clandestine or secret love.  

Flowers express traits of character, as well.

Here are some additional plants aptly named for feelings often accompanying  Valentine's Day sentiments: "Bleeding Heart" (Dicentra Spectabilis),"Love in Winter" (Chimaphila umbellata), "Kiss Me Over the Garden Gate" (Persicaria orientale), and "Love Lies Bleeding" (Amaranthus caudatus). Some, such as "Cupid Dart" (Catananche caerulea) were used in potions and other concoctions, in this case by ancient Greeks. And alas, the "All American Roses" of the year for 1980 were “Love”, “Honor” and “Cherish”. 

While you're reaching out to your significant others this Valentine's Day (or any day!) make memories last longer by adding the floral preservative that comes with most arrangements or can be purchased separately.

May your love be everlasting........

Janet 

Many previously “welcomed” urban tree species have outlived their stay, becoming invasive and crowding out other plants in our Southern California landscapes. You can help by avoiding planting these trees identified by various sources (including the California Invasive Plant Council) to be too aggressive and habitat/resource-depleting for further planting.

Invasive Trees to Avoid Planting

Athel (Tamarix aphylla)

Black Locust (Robinia pseudoacacia)

Blackwood Acacia (Acacia melanoxylon)

Brazilian Pepper (Schinus terebinthifolius)

Chinaberry (Melia azedarach)

Chinese Tallow Tree (Triadica sebifera)

English Hawthorn (Crataegus monogyna)

Peruvian Pepper Tree (Schinus molle)

Red Gum (Eucalyptus camaldulensis)

Russian Olive (Elaeagnus angustifolia)

Saltcedar (Tamarix ramosissima, T. gallica, T. chinensis)

Silver Wattle (Acacia dealbata)

Smallflower Tamarisk (Tamarix parviflora)

Tasmanian Bluegum (Eucalyptus globulus)

Plant These Instead

They are drought/heat resistant, low maintenance, and have no known significant pest or disease problems and are not currently overplanted). Find other suggestions here: https://www.cal-ipc.org/solutions/prevention/landscaping/dpp/?region=socal

African Fern Pine (Afrocarpus falcatus) (formerly Podocarpus elatior)

Cascolote (Caesalpinia cacalaco Smoothie®)

Desert Willow ‘Bubba' (Chilopsis linearis)

Fringe Tree (Chionanthus virginicus)

Island Oak (Quercus tomentella)

‘Maverick' Mesquite (Prosopis glandulosa)

Mulga (Acacia aneura)

Netleaf Hackberry (Celtis reticulata)

Pink Chitalpa (x Chitalpa tashkentensis 'Pink Dawn')

‘Red Push' Pistache (Pistacia x ‘Red Push')

Thornless South American Mesquite (Prosopis x Phoenix)

Benefits of Plants to People, Communities and Urban Ecosystems:  Part 1:

The link between horticulture and health and well-being and to urban ecosystems has been scientifically documented for centuries. In 1812, psychiatrist, professor, and Declaration of Independence signer Dr. Benjamin Rush reported in his book “Medical Inquiries and Observations, Upon the Diseases of the Mind” (Rush 1812) that patients “digging in the dirt”

fared better than their non-gardener counterparts. Since then, hundreds of scientific studies have been published documenting benefits of active (e.g. gardening/landscaping) and passive (e.g. viewing nature through a window, taking a walk in a park) interactions between people and plants and the value of plants in urban ecosystems.

Benefits related to cognitive functioning, societal and community health, and mental health are summarized below. Ecosystem and physical health benefits from interacting with nature will be discussed in next month's blog.

Improved Cognitive Functioning

Several studies link participation in gardening activities to enhanced cognitive functioning (Bratman et al. 2012; Dadvand et al. 2015; Kuo et al. 2021; Ohly et al. 2016; Park et al. 2019; Stevenson et al. 2018; Wells 2000. Research conducted by Kuo and Sullivan (2001) and Mayer et al. (2009) found that exposure to nature in urban settings can enhance attention span, working memory, and concentration. Both youth and adults who participate in greening and gardening projects were also found to have higher cognitive functioning in the areas of short and long term memory, focus and concentration (Dadvand et al. 2015; Markevych et al. 2019; Matsuoka 2010; Meuwese et al. 2021; Park et al. 2019; Stevenson et al. 2018) and reduced symptoms of ADHD (Faber Taylor and Kuo (2011).

Other studies summarized in a literature review (Williams and Dixon 2013) found that kindergarten and middle school students who participated in school gardening activities linked to classroom learning in biology, nutrition, mathematics, and other subjects earned higher grades and attained greater academic achievement than non-participants. A recent study linked high tree canopy coverage on school grounds with higher achievement scores in math and reading in middle school students across a wide range of socioeconomic and ethnic backgrounds (Kuo et al. 2021). The experiential (hands-on) learning elements of school gardens can also bridge the gap between traditional and non-traditional learners due to its multi-sensory nature (Kolb and Kolb 2005). School gardens play an especially important academic role among elementary-aged youth from low-wealth inner city communities exposed to outdoor experiential learning that was previously lacking (Dyg et al. 2020; Kuo et al. 2021; Ray et al. 2016; Williams et al. 2013). However, Hoover et al. (2021) found that successful, sustainable school gardens require strong administrative and district support in addition to enthusiasm and support from parents and teachers.

Enhancement of Societal and Community Health

Urban greening projects that remediate vacant land, landscape streets and neighborhoods, create community gardens, and improve the health of wetlands and undeveloped natural environments can build community cohesiveness, neighborhood bonding, and mutual community pride (Diamant and Waterhouse 2010; Draper 2010; Glover et al. 2005; Hartwig and Mason 2016; Kuo and Sullivan 2001; Moyer et al. 2019; Neo and Chua 2017; Saldivar-Tanaka and Krasny 2004). With blighted uncared-for vacant lots comprising nearly 15% of total land area of U.S. cities (Branas et al. 2018) these opportunities are substantial. Results also indicate that gardening and urban greening projects unite people from different cultural and ethnic backgrounds who enjoy growing and sharing produce from their native regions (Agustina and Beilin 2012; Baker 2004; Cruz-Piedrahita et al. 2020; Dyg et al. 2016; Hartwig and Mason 2016; Teig 2009). Building a sense of community through social engagement, celebrations, and communal meals has also been found to benefit both gardeners and non-gardener participants (Ober et al. 2008).

Well-designed and maintained urban green spaces not only bring people together, but can reduce crime, gun violence and enhance the safety and cohesiveness of urban neighborhoods, as summarized in several literature reviews (Bogar and Byer 2016: Mancus and Campbell 2018; Shepley et al. 2019). Some of the strongest links reported in the literature involve crime reduction in vegetated and well maintained urban neighborhoods and walkways (Branas et al. 2018; Demotto 2006; Garvin et al. 2013; Locke et al. 2017) and a reduction in gun violence in neighborhoods with green spaces including trees (Branas et al. 2018; Kondo 2017; Schertz et al. 2021; Wolfe et al. 2012). One study found that community-based greening projects that vegetated vacant lots was an effective strategy to improve neighborhood safety, resulting in a nearly 40% decrease in violent crime (Heinze et al. 2018). It should be noted that other researchers (Groff and McCord 2012) found a higher incidence of opportunistic crime in high tree canopy covered areas, perhaps due to concealed illegal activities. Another study found that actively participating in community greening projects from design through implementation and maintenance can result in a sense of accomplishment and satisfaction (Murphy-Dunning 2009). Neighbors caring for urban green spaces together also tend to spend more time conversing and building important social relationships than do non-participants (Peters et al. 2010).

Improved Mental Health 

Multiple literature reviews link interactions with nature to improved mental health in both youth and adults (Bowler et al. 2010; Clatworthy et al. 2013; Coventry et al. 2021; Cruz-Piedrahita et. al. 2020; De Vries et al. 2003; Tillmann et al. 2018) in studies conducted in parks, gardens, urban green spaces, and even shopping malls. The restorative impact of simply viewing plants has also been widely studied. Walking through a park and even viewing a natural scene through a window can lead to a sense of well-being, restfulness, reflection, and reduced mental fatigue (Shanahan et al. 2019). More recently, Dzhambov et al. (2020) found lower rates of depression in students homebound for long periods of time during the COVID-19 pandemic with views of plants (indoors and out) compared to students who lacked plant interactions. Bowler's (2010) literature review also highlighted strong associations for self-reported positive emotions and lower levels of anger and sadness in natural settings compared to non-natural settings. Interactions with nature can also reduce symptoms of depression and anxiety (Beyer et al. 2014; Gonzalez et al. 2010; Lee and Maheswaran 2011; Van den Berg and Custers 2011; Wilson and Christensen (2011).

Thompson Coon et al. (2011) reported that exercising outdoors in natural settings led to greater feelings of positivity and revitalization, less tension, anger, and depression compared to the same amount of exercise indoors. Other studies link gardening to feelings of peace and contentment (Meuwese et al. 2021; Shanahan et al. 2015; Shanahan et al. 2019). MacKerron and Mourato (2013) reported that individuals who interact with nature are often happier than those lacking this interaction and Ambrose et al. (2020) reported that home gardeners growing food crops experienced particularly high levels of happiness and meaningfulness. Bakolis et al. (2018) linked two elements of mental well-being (optimism and energy) to interactions with nature while Van den Berg and Clusters (2011) and Wood et al. (2016) found a link between engagement with nature and a reduction in stress. While White et al. (2019) determined that these benefits are maximized when individuals spend 120 minutes a week or more interacting with nature, shorter periods of exposure are also beneficial (Shanahan et al. 2016; Shanahan et al. 2019; White et al. 2019).

Other studies reported a link between growing food and a deepened sense of purpose (Tzoulas 2007; Wiesinger 2006). Digging in the soil can be a welcome distraction from busy lives laden with deadlines, traffic jams, and other everyday stressors. Focusing on the needs of plants, whether it be watering, fertilizing, harvesting or other tasks, can prove pleasantly distracting, providing time for reflection and even problem resolution (Capaldi et al. 2015; Meuwese et al. 2021; Stevenson et al. 2018). Several research papers report important positive roles that plants play related to mental health as impacts of climate change increase (Cryder et al. 2006; Dillman-Hasso et al. 2021; Doherty 2018; Fernandez et al. 2015) related to posttraumatic stress disorder (PTSD), major depressive disorder, stress, anxiety and others.

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