Kevin Songer, Medicinal Power of Nature, Herbs & Art. : allelopathy

Showing posts with label allelopathy. Show all posts

Wednesday, September 4, 2013

Florida Green Roofs and Allelopathy

Allelopathy is the little referenced yet extremely important green roof secondary design principle of the bio-chemical influences certain plants and trees have on other plants and in this instance - on green roof plants. A recent Green Roof we completed had a planting area surrounded on three sides by tall trees. Some of these trees are deciduous and loose their leaves during the winter, others like the laurel oaks keep leaf cover most of the year.

An alleopathic tree usually exerts negative influence on adjacent vegetation via a number of different processes including;

Fog & dew drip
Leaf litter
Volatilization
Sap drip
Pollen
Other biological processes

Trees impacting the recent green roof include;

Triadica sebifera, Chinese tallow - western border of green roof
Quercus laurifolia, Laurel Oak - northwestern corner and eastern side of green roof
Platanus occidentalis, American sycamore - southeastern and southwestern corners of green roof

According to the University of Georgia, School of Forestry Resources , there are a number of significant allelopathic trees requiring attention when planting other plants nearby. They include;

Strong Potential for Allelopathic Impacts
Acacia spp
Acer saccharum
Ailanthus altissima
Celtis laevigata
Celtis occidentalis
Eucalyptus camaldulensis
Eucalyptus globulus
Eucalyptus spp
Juglans cinerea
Juglans nigra
Leucaena spp
Myrica cerifera
Picea engelmannii
Platanus occidentalis
Populus deltoides
Prosopis juliflora
Prunus cornuta
Prunus serotina leaf
Quercus falcata leaf
Quercus marilandica
Quercus rubra
Quercus stellata
Robinia pseudoacacia
Sassafras albidum
Ulmus americana

Moderate Potential for Allelopathic Impacts
Abies amabilis
Abies balsamea
Abies grandis
Acer circinatum
Acer negundo
Acer platanoides
Acer pseudoplatanus
Acer saccharinum
Aesculus glabra
Aesculus hippocastanum
Aesculus octandra
Arbutus menziesii
Carya illinoensis
Carya ovate
Corylus spp
Crataegus spp
Fraxinus excelsior
Ginkgo biloba
Gleditsia triacanthos
Juniperus monosperma
Juniperus scopulorum
Kalmia spp
Picea spp
Pinus banksiana
Pinus contorta
Pinus densiflora
Pinus edulis
Pinus elliotii
Pinus monophylla
Pinus ponderosa
Pinus sylvestris
Prunus pumila
Quercus alba
Quercus borealis
Quercus douglasii
Quercus gambelii
Quercus michauxii
Quercus shumardii
Rhododendron maximum
Rhus copallina
Sorbus sitchensis
Tsuga canadensi

Slight Potential for Allelopathic Impacts
Abies concolor
Aesculus spp
Betula pendula
Carpinus spp
Casuarina spp
Cupressus macrocarpa
Fagus spp
Fraxinus spp
Larix decidua
Picea excelso
Pinus palustris
Pinus spp
Populus spp
Pseudotsuga menziesii
Quercus petraea
Quercus robur
Quercus rubra
Salix pellita
Sambucus racemosa
Sequoia sempervirens
Taxus brevifolia
Thuja plicata
Tilia americana
Tilia cordata
Tilia planifolia
Ulmus laevis
Ulmus parvifolia
Umbellularia californica

As mentioned, a recently completed Green Roof will be adjacent Chinese tallow trees, Laurel Oaks and American Sycamores.

Quercus laurifolia, Laurel oak - although literature suggests laurel oak does not possess allelopathic qualities, care should be given to potential impacts of pollen and flower litter. The laurel oak adjacent the northwest corner of the green roof has stained the white TPO and covered the roofing material with a layer of leaf and pollen litter. Though laurel oak may not exhibit direct allelopathic influence on the green roof plants, potential for covering the plants with litter exists. Continued site inspection will be required to confirm any impacts on the green roof plantings.

Triadica sebifera, Chinese tallow - one medium height tree exists adjacent the western border of the BGC green roof. Chinese tallow has been the subject of numerous allelopathic studies and research. Interestingly, research exists to support the theory of Chinese tallow leaf litter and fog drip may actually support germination and shoot growth on adjacent plants. In fact, Chinese tallow was shown to actually improve germination and growth rates in Little Bluestem, Schizachyrium

Importantly, the American Sycamores, Platanus occidentalis located in the southeastern and southwestern corners of the green roof have the potential to exert significant negative influence over the green roof plants. As indicated in the above list, American sycamore produces strong allelopathic effects. Data exists showing the active ingredients, scopoletin and chlorogenic acid found in the sycamore leaf may interfere with the ability of stomata on certain plant's leaves to malfunction, interrupting the vital processes of photosynthesis and either stunting plant growth or killing the plant. Close observation will be required on the effects of the American sycamore on the entire green roof planting area and in particular, the southeast and southwest corner plantings. Pruning of sycamore limbs away from the green roof may be necessary.

Finally, good green roof design incorporates the effects of adjacent trees and other vegetation and allelopathic effect possibilities. Recognizing and dealing with a potential allelopathic problem is much easier and more cost-effective up front. Know the basics of adjacent tree and plant allelopathism and how your green roof design integrates into a site with pre-existing trees.

One of the related positive issues of anti-allelopathism and green roof adjacent trees is a benefit derived from leaf micro-nutrient content.

Friday, November 25, 2011

Green Roof and Leaves, Cation Exchange and Anti-Allelopathy Issues for Design Consideration

I had a couple of comments yesterday about my post on Allelopathy and Green Roof design. As we focused on the potential negative impacts adjacent trees and their sap drip, leaves, seeds and shade can have on green roof plants we should also remember certain trees can bring distinct advantages to a green roof or nearby permaculture garden.

Leaves on the Green Roof can exert both Allelopathic and/or anti-Allelopathic influences

One comment suggested we should take into account the addition of organic matter from leaves, replacing lost or broken down compost.

Trees or adjacent shrubs that stimulate growth through their presence, leaf or sap drop or other factors are commonly referred to as possessing 'Anti-Allelopathic' properties. An anti-allelopath encourages nearby plant growth. Actually this is a big complicated name describing a common simple practice - composting.

Chinese tallow tree, Triadica sebifera, a terribly invasive species here in Florida and across tropical areas is rated as one of the best anti-Allelopaths, her leaves and sap encouraging adjacent plants to grow as though fertilizer has just been aded to their base.

Leaves can be very useful on the rooftop garden, green roof or in the ground level permaculture garden! Leaves cool the soil, promote soil moisture content, provide organic matter (good for bacterial breakdown of pollutants) and supply micronutrients, can adjust pH and cation exchange potential.

No leaves? May not be too glamorous yet very practical ( remember Louis Sullivan and functionalist architecture) collecting your neighbor's bagged up yard leaves can benefit your green roof or permaculture garden and benefit your wallet.

As mentioned, cation exchange capacity and pH are two important variables of a green roof. Additionally, leaf compost can add valuable trace minerals needed by the rooftop plants. Some trees, including certain maples containing high sugar content in their sap and leaves possess an extremely low pH, in the range of approximately 4.5 to 5.5. Other leaves such as white ash and popular may have quite high pH's, approaching 8.0 or above.

American sycamore leaves shown here can exert Allelopathic influences

Leaf compost typically contains twice the amount of trace minerals by weight as does horse manure.

Interestingly, leaves from different species of trees offer varying characteristics. While ash leaves are relative neutral in pH, some maple species leaves are documented to possess a pH of around 4.5.

Research also shows use of properly composted leaves greatly increases the cation exchange capacity of soils. One of the important functions needed in green roof soil media is cation exchange capacity.

Though varying opinions of organic compost value to green roofs exist throughout the industry, many believe organic material in the soil media is highly beneficial to green roof plants.

Massachusetts' state DEP has published an informative paper on the value of leaves for compost, including discussing issues and benefits, nitrogen to carbon ratios, composting processes and more. This information is helpful to those just starting composting or those interested in studying potential allelopathic or anti-allelopathic effects on their green roof, living wall or ground level permaculture bed.

Fossa alterna technology also relies heavily on leaf use and in turn has produced informative leaf nutrient information.

Remember, green roofs are individual ecosystems, intricate webs of life with complex interactions.

Flat roofs with poor drainage may or may not require lower organic content to prevent water saturation and facilitate drainage.

Sloped roofs may function appropriately with high organic content.

Again, if you lack adjacent anti-allelopathic trees then go out about the cityand find leaf waste destined for the landfill. Collecting heavy duty garbage bags filled with fresh raked leaves (we avoid those lawns heavily treated with fertilizers and herbicides/pesticides - those lawns are easy to spot here in the US due to the small advertising signs the lawn companies stick in the lawn after a fertilizer application - and speaking of lawns and fertilizers - a short must-see video of the history of the American Lawn will have you rolling in your chair and scratching your head at the same time can be viewed here) is a positive step for the environment.

Other benefits include;

Free highly effective cation exchange capacity supplements from the leaf compost
Free organic matter from the leaf compost
Free trace minerals from the leaf compost
Free pH adjustment material from the leaf compost (this is especially important when using higher pH soil media or media high in calcium)
Free garbage bags
And a lesson to your children riding with you to scavenge that recycling is more important than pride. :)

Wednesday, November 23, 2011

Green Roof Plant Design - Useful and Harmful Effects of Allelopathy

Plant matter such as bark, leaves, twigs, nuts and pollen can act as a herbicide, interfering with other plant's cell division, nutrient uptake, photosynthesis, et al. Some plants have strong effects on other plants, preventing growth in some and encouraging growth in others.

American Sycamore leaves are known for allelopathic properties (maybe they will surpress the Bidens alba!)

The University of Florida defines allelopathy as, "beneficial or harmful effects of one plant on another plant, both crop and weed species, by the release of chemicals from plant parts by leaching, root exudation, volatilization, residue decomposition and other processes in both natural and agricultural systems."

Plant matter such as bark, leaves, twigs, nuts and pollen can act as a herbicide, interfering with other plant's cell division, nutrient uptake, photosynthesis, et al.

An allelopathic tree usually exerts negative influence on adjacent vegetaion via a number of different processes, including;

Fog & dew drip
Leaf litter
Volatilization
Sap drip
Pollen
Other biological processes

Understanding allelopathy is especially important for green roofs and rooftop gardens with surrounding, adjacent taller trees. Allelopathy can greatly surpress rooftop food production.

According to the University of Georgia, School of Forestry Resources , there are a number of significant allelopathic trees requiring attention when planting other plants nearby. They include;

Adjacent to the Breaking Ground Green Roof (see photo above) there are American Sycamores, Platanus occidentalis located in the southeastern and southwestern corners of the living roof. The American Sycamore can produce significant allelopathic influence on adjacent green roof plants. Data exists showing the active ingredients, scopoletin and chlorogenic acid found in the Sycamore leaf may interfere with the ability of stomata on certain plant's leaves to function.

Interestingly, according to the University of Florida's IFAS publication referenced above, allelopathic properties can also be used strategically to control certain weeds, i.e. dried mango leaves surpress nutsedge tubers from sprouting.

Finally, good green roof design incorporates into design the potential and foreseeable effects of adjacent trees and other vegetation. Recognizing and dealing with a potential allelopathic problems during design can save months or years of not knowing why a green roof is barely surviving.

Know the basics of plant allelopathy is you intend to work in green roof design!