Non-sustainable vegetation management – modern horticultural practice – an industry-driven tree killer?
My apologies to AA readers for holding back on Part 2 of ‘Conservation Arboriculture in Action’. Part 2 is based on a recent Treepeeps PTY LTD advanced tree – tree planting project. At the time of drafting Part 1 (last edition), I had expected for us to have completed the job soon enough to write the Part 2 article. Not so, in the meantime I am sharing this article on tree decline based on non-sustainable land management.
This article is founded on a report I drafted for a S.E. Queensland council. As a professional arborist I have worked contractually and as a consultant all over the world, Australia, PNG, Vanuatu, America, Canada, Germany, Portugal and the United Kingdom. As a traveller I have also explored much of Europe.
All round the world I have seen the same standard of a collective lack of tree care, with most amenity trees seldom living beyond the first 1/3 of their lifespans.
This is because of environmentally non sustainable land management practices – largely driven by horticulture, with nonsustainable development, agriculture and arboriculture driving home the final coffin nails. Few of us have the awareness or the gumption to speak out, let alone the fortitude to make change.
Even in our profession we have enabled industry to direct our cultural practises to do more damage to trees than benefit them, our limited education (i.e. a lack of biology) is also a reflection of an industry drive.
To achieve sustainability enterprise must balance the environment with economy, there can be no shortcut. The model that is current to land based industry around the world is failing.
The following report is a reflection of the kind of horticulture that kills trees Australia wide.
Project – Mossman Park, Stevens Oval and D’Aguilar Highway, Dalby and Jondaryan S.E. QLD.
Following a request from the VACC Parks and Gardens Coordinator – to assess three treed avenues at Mossman Park, Stevens Oval (Dalby) and D’Aguilar Highway (Jondaryan) – I carried out site/ tree assessments on 18/12/18. The scope of the assessment was to ascertain stress factors (on top of drought stress) likely to be causing tree decline and death. With the three sites in mind approximately ¼ of the Pine trees are dead with more dying.
The first site assessed was the avenue of trees on Domingo road adjacent to Mossman Park. The trees are a mix of Pinus spp (Pinus radiata or possibly Pinus taeda), Hoop pines (Araucaria cunninghamiana) and Kauri pines (Agathis robusta), though largely Pinus (as requested this report is concerned with the Pinus spp). Though there has been a recent history of drought there had been rainfall before my arrival on site and the soil was well hydrated.
The Pines stand at (on average) 15m tall with an approximate crown spread of 3-5m. The stem diameters (at chest height) average 40cm and the trunk flare diameters (at ground level) are around 60cm. These trees are largely made up of a single main stems, have symmetrical crowns (trunk, branches and canopy) and are approximately aged 30+ years. The Mossman park avenue is made up of approximately 50 trees.
A question has been raised in relation to the trees condition with the long term in mind, the symptoms that bought these trees into consideration involve scattered dieback in the internal foliage of the trees, leading to complete folial/canopy/upper crown death. Study of the Hoop pines and Kauri pines shows that these trees are also showing stress symptoms.
Evidence of Genus, Species and Health
The Pines – (P. radiata or P. taeda) have fair/poor vitality to none – this is evidenced by stunted foliage, leaf size and leaf colour, leading to death evidenced by scattered dieback in the internal foliage of the trees, leading to complete folial/canopy/upper crown death.
Evidence of Crown Structure (relating to biomechanical assessment)
The crown structure of these young trees is fairly standard for the Genera (Pinus, Araucaria and Kauri) which is generally stable even when stressed in my experience of S.E. QLD. Though the focus of this report relates to tree health.
Observations/Discussion – Site Limitations/Herbicide Concerns
The first study site is where I spent the bulk of my time (my observations of that site form the backbone of this report), study of the second two tree avenue sites validated my observations of the Domingo road avenue. Study of the trees in general revealed that the Pine trees are the most sensitive of the avenue trees to the environmental conditions. Though the other tree Genera reveal symptoms that support the decline in the Pines.
The three avenue sites (ref: Fig. 4. and opening image on page 32, Mossman Park, Fig. 6. Stevens Oval, Fig. 7. D’Aguilar Highway) share identical features/symptoms.
- The trees are roadside with the bulk of their root systems being in adjacent gullies
- The growing environments are regularly mown lawns
- All trees have recent evidence of herbicide application within their structural root zones
- The avenue trees are surrounded by old agricultural land • The soils are heavily compacted (years of transport vehicle, mower and people access)
- Crown dieback largely in the Pine trees (ref. Figs 2-7.), but also noted in the Hoop pines (ref. Figs 16-21)
- Most of the trees have mower damaged exposed roots (ref. selection of Figs 8-12)
- Large swathes of dead lawn was noted, mostly in gully areas between/adjacent to trees (ref. Figs 13-15).
As well as the major symptoms listed above this report details my other observations and reasoning as to why the VACC Pine trees are in decline.
The avenue sites are by their nature problematic as growing conditions for any tree. The soil compaction and lack of nutrient cycling through the soil profile is known to have a significant impact on tree longevity in itself.
But the sustained use of herbicide application and mower damage on structural roots must be considered, mower injuries are similar (on the impact to trees) as perennial cankers in that as soon as tissue is generated by the tree to close the wound it is damaged on the next round of mowing (the same pattern occurs with canker infection or bird damage).
The wound wood being generated by the tree starts of as cambial tissue which may absorb a measure of the herbicide itself, though it is understood that this usually only occurs with the presence of chlorophyll in plant tissue (perhaps not always present in cambial tissue in stems or roots).
Based on my studies and the evolution of Plant Health Care science (ref: Soil Food Web principles – Dr. Elaine Ingham) the key issue that sustained herbicide use has on soils relates to excess salt.
Bituminous road surfaces are know to leach chemical salts (pollutant runoff is also a factor) that impact on soil health. Trees as woody plants need oxygen and microbial association in soils for sustained nutrient exchange, prolonged lawn environments are known to lead to depletion in essential soil microbiology for woody trees. Though the build up of salts and heavy metals are also a key issue with tree health. Figs. 13-15 are indicative of issues below ground with impacts on turf as well as the trees.
Further to my observations of the trees I make reference to observations of the Hoop Pines (ref. Figs. 16 to 21). Study of the Hoop Pines in all three sites revealed symptoms/perceived stressors that need to be discussed. These involved dieback in shooting epicormic growth (mostly shoots generated following lower branch removal ref: Fig. 16) as well as internal dieback (similar to that of the Pines ref: Fig. 18), comparison to other local Hoop pines in surrounding areas showed me trees without these symptoms. I suspect that this is another indicator of site issues below ground, though I believe that management need to carefully consider herbicide application as being a direct impact.
Discussion with fellow consulting Arborists via the Facebook Australian Arborists Network AAN – Brands such as Roundup, Grazon, Conquest, and chemicals Glyphosate, Picloram, Triclopyr, Metsulfuron-methyl, Dicamba have all been cited as having a direct influence on tree poisoning and death.
It has also been discussed within my circles that Hoop pine deaths are attributed to herbicide application.
Pine nematode Another possible factor in the trees decline which requires consideration and elimination is Pine nematode – Bursaphelenchus vallesianus. Outbreaks of Pine Nematode have been recorded in the Sydney region (2016) and are discussed in this document (since publication the nematode has spread north and is now reputed to be in northern NSW State Forest). Check out: https://www.dpi.nsw.gov.au/biosecurity/ plant/insect-pests-and-plant-diseases/ pine-nematodes? fbclid=IwAR1N6O8TK RIS5S3DjaX-ZgDjyhsANxZQO3E6cRUfkpsRJDPB0k1DGEshDk
Study of the above does provide similarities to the dieback symptoms discussed in this report. The nematode impacts on the trees vascular system by forming air pockets which causes death.
The Pine nematode has been discussed as being present on the following Pines:
- Aleppo pine (Pinus halepensis)
- Austrian pine (Pinus nigra)
- Common spruce (Picea abies)
- Maritime pine (Pinus pinaster)
- Ponderosa pine (Pinus ponderosa)
- Radiata pine (Pinus radiata)
- Stone pine (Pinus pinea)
- Scots pine (Pinus sylvestris)
- Turkish pine (Pinus brutia)
The contacts concerning this matter I made where via the Department Of Primary Industries – DPI NSW and the Department of Agriculture and Fisheries – QLD who I have alerted to the possible issue of a Pine nematode outbreak, at the time of my completion of this report DAF staff where due to make contact.
For a useful conclusion to be reached there is the need for further investigation, I recommend analysis of the soils for salt and heavy metal levels, I also recommend that Council compile a list of all products that are currently being used for herbicide application (as well as frequency of application) as a means to assess/ eliminate the contributing cause of the tree decline/death. Bearing in mind that the herbicide companies downplay the side effects of the products they sell I am more inclined to pay attention to field experience than the ‘literature’ on this topic.
For Analytical services we recommend Southern Cross University Lismore to assess the sites soils for heavy metals and salts www.scu.edu.au/environmentalanalysis-laboratory—eal/
Concerning the possible outbreak of Pine nematode for the record – all pests and diseases are side effects of site issues that impact on tree health, in the case of trees – site issues impact soils which impact tree vitality (principally a lack of soil oxygen, humus for nutrient cycling and allied micro-organisms that compartmentalise disease causing organisms in the soil). Study of the linked Pine nematode document validates this by stating “Control of pine nematode is limited to prevention”. If the Pine nematode is present this will have to be accounted for but not at the expense of treating the site constraints and the factors that have lead to the cause of the most current problem (note – contact with DPI NSW Biosecurity validated my observation that the Pine nematode is an issue only on stressed trees).
Road side avenues of trees are probably the most sensitive and vulnerable to health limitations, tree death is almost always a result of multiple imposition, good management involves removing or reducing stress factors that impact on trees. Non-sustainable horticultural practices are in my opinion the key constraint that require management input.
As a matter of short term and long term soil/tree health I recommend improving on the avenue trees growing environments by establishing Nutrient Beds (comprised of cold processed composted mulch). To help keep people off the Nutrient Bed and accelerate the assimilation of nutrients (activate the soil root-interface) I also recommend the establishment of a Plant System (plant component of an ecosystem), to help proof the nutrient bed and keep vehicles out (exclusion zone). In the course of establishing a plant system I also recommend vertical inoculation of the trees root zone with Soil Food Web grade cold processed compost – humus (this can be done at the time of planting tube stock vegetation).
Trees which have died are best replaced by Hoop pines which are considerably more tolerant of the site constraints.
The use of herbicide in the trees root zones is a practise that needs to be replaced by a more sustainable means.
Likewise to enable wound wood generation and compartmentalisation of exposed sapwood from root damage and likely inoculation by herbicide – lawn mowers need to be kept out of the tree root zones.
If it is not feasible to establish nutrient beds and plant systems I recommend the planting of rings of sturdy vegetation – such as Lomandra hystrix around the structural root zones of trees (as a minimum) to keep mowers/spray crews out. Grass can be cut to the edge of these plants which even deflect brush cutters. The solution to non-sustainable horticulture is sustainable horticulture, practised by old school horticulturists around the world.
In conclusion with thanks to VACC senior management being responsive to recent rapid tree decline this report is a reflection of symptoms presented by the site and the resident avenue trees.
Following rapid death of Pine trees located within three avenue treed sites in the Grand-Border region at Dalby (*2 sites) and Jondaryan (*1), on behalf of VACC I was commissioned to assess the trees with a view to determining reasons for decline in association with drought.
Modern Arboriculture recognises that tree decline/death is generally caused by multiple factors working against the tree as one.
My 18/12/18 assessment has validated this understanding, the combination of soil compaction, lack of nutrition, drought, mower damage, excess herbicide use, the build-up of salt (in the soil profile) and heavy metals, has lead to excessive stress loading on the Pine trees which are the most sensitive to these site limitations. Arboricultural experience supports the symptoms of rapid tree death to herbicide use (this report has recommended that VACC do an audit on brands/types of herbicide used, as well as frequency of application). Likewise the study of information residual to the symptoms presented by the trees has revealed that there is a recent outbreak of Pine nematode extending North from Sydney, out of responsibility I notified DAF of the issue and an investigation by the department is now underway (advice relating to the management of Pine nematode is available within the document linked on page 36, Observations/ discussion/Pine nematode).
With prevention of such declines I have recommended the review of horticultural practises, as well as cultural improvement of the sites soils, this is with a view to protecting the Hoop pine population which are more resistant to the issues behind the Pine trees decline and death, I have also recommended replacing the dying Pines with Hoop Pines for this reason. If the sites in question do prove to be infected with Pine nematode a protocol has been established by the DPI for its management, this will need to be considered in relation to advise from DAF.
Post-report conclusion For the sake of this technical feature, I have altered names locations and dates in the report, the photographs and content of the report remain true.
Following the drafting of this report DAF made contact with me to confirm that there was no Pine nematode – Bursaphelenchus vallesianus present in any of the soil profiles they sampled concerning the 3 sites (this report I passed on to the client along with my contacts). When we consider the long term economic and environmental costs of managing trees non-sustainably verses via sustainable systems (post establishment) the benefits are multifaceted. The problem is getting tree and people managers to start. To create the precedent for conservation arboriculture we need good local government support, a challenge when we live in a society that makes an economy from being non-sustainable, such as via repetitious herbicide use.
With sustainable tree management in mind Conservation Arboriculture is the solution, though this will save money as opposed to make money – perhaps an anathema to industry, but a great boon to land/vegetation managers. The enterprise of such management and CA will get arborists out of trees and into the soil…
Long live the rhizosphere.