(Arboricultural-styled) 'Fact of the Day'

[Kveldssanger]

27/02/16. Fact #162.

 

Antitranspirants are products that, when applied to foliage, reduce the rate of foliar transpiration. Comprised of a wax, plastic, or resin, the application of an antitranspirant leaves a thin, protective film atop the leaf surface (Brent-Jones, 1966; Watson & Himelick, 1997; Watson & Himelick, 2013). The film may last for several weeks, though re-application is necessary if there is a desire to reduce transpiration rates for elongated periods of time. Furthermore, if leaves are still growing then the film will crack and its efficacy will be reduced as a result (Watson & Himelick, 2013), meaning application prior to the leaves being fully-grown is perhaps not wholly effective. In addition to this, as the spray dries to become invisible, there are no means to ascertaining how much has been applied or retained upon the leaf at any given time, and nor is there a way in which the extent of cracking can be ascertained (Brent-Jones, 1966).

 

When used improperly (applying too much and potentially also at overly-frequent intervals), application of an antitranspirant may be detrimental to plant health. Reductions in root and shoot growth may be observed, in such instances (Lee & Kozlowski, 1974; Watson & Himelick, 1997). However, when used properly, their application can increase growth rate and aid with plant establishment via the retention of more water (Davenport et al., 1972; Steinberg et al., 1990). There is also distinct variability in the efficacy of different products, though not only do the products themselves differ but differing environmental conditions, as well as different species, result in varying levels of efficacy across product ranges and also within the same product (Hipps & Nicoll, 1997; Watson & Himelick, 2013). For instance, on species including the pines (Pinus spp.), application can significantly reduce transpiration (by bolstering the already waxy leaf surface), though can also reduce the rate of photosynthesis very markedly; mainly due to reduced CO2 diffusion (Davenport et al., 1974; del Amor et al., 2010; Kozlowski & Davies, 1975; Watson & Himelick). When applied to some species, certain antitranspirants are also toxic.

 

Because application of an antitranspirant reduces transpiration, leaf surfaces may also potentially warm up considerably more during warmer periods. This can damage the leaf tissues, and result in dysfunction through injury (Watson & Himelick, 2013), leading to early senescence of leaves that have become damaged (Neumann, 1974). Root and shoot growth may therefore be impacted negatively, in response (Ranney et al., 1989; Wellburn et al., 1974).

 

Such products are nonetheless useful for regulating water loss post-transplanting (Berkowitz & Rabin, 1988), and may be particularly effective during the spring months (Harris & Bassuk, 1995). However, the reliance on such products should not replace good transplanting practice (Watson & Himelick, 1997), and care should be used when applying any type of antitranspirant. It is preferable to apply an antitranspirant only lightly, for an overall net benefit in response to an application (Watson & Himelick, 2013).

 

Granted, it should be noted however that once water availability within the soil reaches the lowest critical threshold, even the application of an antitranspirant is of no aid (Steinberg et al., 1990). It may therefore be wise to combine such application, in times of significant drought, with irrigation.

 

References

 

Berkowitz, G. & Rabin, J. (1988) Antitranspirant associated abscisic acid effects on the water relations and yield of transplanted bell peppers. Plant Physiology. 86 (2). p329-331.

 

Brent-Jones, E. (1966) Some aspects of moving semi-mature trees. Arboricultural Association Journal. 1 (3). p71-76.

 

Davenport, D., Fisher, M., & Hagan, R. (1972) Some counteractive effects of antitranspirants. Plant Physiology. 49 (5). p722-724.

 

del Amor, F., Cuadra-Crespo, P., Walker, D., Cámara, J., & Madrid, R. (2010) Effect of foliar application of antitranspirant on photosynthesis and water relations of pepper plants under different levels of CO 2 and water stress. Journal of Plant Physiology. 167 (15). p1232-1238.

 

Harris, J. & Bassuk, N. (1995) Effects of defoliation and antitranspirant treatment on transplant response of scarlett oak, green ash and Turkish hazelnut. Journal of Arboriculture. 21 (1). p33-33.

 

Hipps, N. & Nicoll, F. (1997) Preconditioning Trees to Improve Outplanting Performance. In Claridge, J. (ed.) Research for Amenity Trees No. 6: Arboricultural Practice – Present and Future. UK: HMSO.

 

Kozlowski, T. & Davies, W. (1975) Control of water balance in transplanting trees. Journal of Arboriculture. 1 (1). p1-10.

 

Lee, K. & Kozlowski, T. (1974) Effects of silicone antitranspirant on woody plants. Plant and Soil. 40 (3). p493-510.

 

Neumann, P. (1974) Senescence of attached bean leaves accelerated by sprays of silicone oil antitranspirants. Plant Physiology. 53 (4). p638-640.

 

Ranney, T., Bassuk, N., & Whitlow, T. (1989) Effect of Transplanting Practices on Growth and Water Relations of’ ‘Colt’ Cherry Trees During Reestablishment. Journal of Environmental Horticulture. 7 (1). p41-45.

 

Steinberg, S., McFarland, M., & Worthington, J. (1990) Antitranspirant reduces water use by peach trees following harvest. Journal of the American Society for Horticultural Science. 115 (1). p20-24.

 

Watson, G. & Himelick, E. (1997) Principles and Practice of Planting Trees and Shrubs. USA: International Society of Arboriculture.

 

Watson, G. & Himelick, E. (2013) The Practical Science of Planting Trees. USA: International Society of Arboriculture.

 

Wellburn, A., Ogunkanmi, A., Fenton, R., & Mansfield, T. (1974) All-trans-farnesol: a naturally occurring antitranspirant?. Planta. 120 (3). p255-263.

[sean]

Brilliant informative thread mate.

[Kveldssanger]

Cheers, Sean. Glad it's of use to people other than myself!

[Kveldssanger]

28/02/16. Fact #163.

 

Birds are without doubt the principal means of seed dispersal by animals, and trees that produce fleshy fruits are typically reliant upon such dispersal means to expand their geographical ranges. Ornamental trees that produce fleshy fruits grown within urban locations, which are not necessarily native to the area in which they grow, may therefore also benefit from such a dispersal mechanism and begin to succeed into the surrounding environment. Granted, frugivorous birds within urban environments may behave differently to birds within woodland stands (or other ‘natural’ setting), and not much is known about the foraging preferences of such birds in the urban setting. Despite this, it is considered that the colour of tree fruit is one driver influencing upon attracting birds, because of the good vision of birds (to make up for their poor sense of smell).

 

In this study, the authors investigate how the preference of birds to the fruits of Ilex aquifolium cultivars (and the standard Ilex aquifolium) growing within urban environments has impacted upon the dispersal of seed, and in turn enabled the species to advance into previously uncharted territory within northern Europe. Because the main dispersal mechanism of the species’ seed is via birds, understanding what fruit characteristics (colour, size, etc) influence avifaunal frugivory is important. By the same token, do birds preferentially select cultivated Ilex aquifolium, or instead opt to consume the fruits of the native non-cultivated species? Similarly, understanding what site qualities attract birds can help to improve understanding of the dissemination of Ilex aquifolium into the surrounding landscape.

 

Because the natural range of Ilex aquifolium reaches its north-eastern climax in Denmark, the study site was located around the current climax zone (within Greater Copenhagen). Within this area, six sites were selected, of which three were cemeteries and three botanic gardens – all within urban areas. Over the past few decades, this climax zone around had been relatively stable, until more recently (since the turn of the millennia) when it was observed to expand its range by a distance of 100-200km up into Greater Copenhagen. Such a shift, the authors remark, would be down to the more favourable climatic conditions, though would be facilitated by seed dispersal courtesy of frugivorous birds.

 

To investigate if birds had different preferences with regards to fruit from different cultivars, the following cultivars were used within the study: ‘Bacciflava’ (strong yellow fruits, in clusters of 3-5, and 8mm in diameter), ‘Crinkle Green’ (vividly red fruits, in clusters of 1-3, and of 7-9mm in diameter), and ‘Pyramidalis’ (vividly red fruits, in clusters of 1-4 and of 8-10mm in diameter). The standard Ilex aquifolium fruits also featured, in order to compare cultivars to the standard (and native) holly species. To understand the fruit properties of all four hollies used, samples were taken from the individuals from which branches were sourced for the study, and the maximum diameter of the fruits, the fresh mass of the fruits (pulp:seed ratio), and water content were measured.

 

Ilex aquifolium ‘Bacciflava’. Source: University of Richmond.

 

From the three cultivars and the native species, branches containing fruits were sourced (within Denmark) and placed at the six locations (from December to February). All branches had similar qualities, possessing 10-20 leaves and fruits, and were fixed to identical wooden boards atop a 1.6m wooden stick to expose the fruits to birds exclusively. Five of these boards were set up in open areas at least 5m away from trees over 3m in height, and five were set up under trees and tall shrubs over 3m in height. Over the course of the survey period, the branches were all checked 15 times, and records gathered as to how many of the fruits had been taken from each sample.

 

Once the survey was completed, it was found that birds (blackbirds and robins) had eaten 2,655 of the 3,404 (78%) fruits across all four branch types. However, the rate at which the fruits were removed varied between branches, with ‘Crinkle Green’ having its fruits removed most abundantly. In terms of the total number of fruits removed from each branch type, the cultivar ‘Bacciflava’ massively reduced the average by having only 35% of its fruits removed. ‘Crinkle Green’ had 94% of its fruits removed, ‘Pyramidalis’ 92%, and the native holly 91%. Therefore, it is evident that birds had a strong preference for red-coloured fruits (fruit of ‘Bacciflava’ was a green-yellow in colour), though there is little evidence to suggest there is any preference as to what fruits were eaten beyond mere red colouration. There was also a marked difference in the rate at which fruit was removed from the different feeding station locations, with branches under trees having their fruit removed at a much higher rate than those in exposed settings.

 

Ilex aquifolium ‘Pyramidalis’. Source: Helmers.

 

In light of the results, it can first be noted that birds did eat the fruits from all four branch types and across both feeding station locations (exposed and sheltered). Therefore, there is potential for many Ilex aquifolium cultivars to enable for seed dispersal and the associated expansion in the native range of the species. Granted, red fruits were eaten far more readily, and this suggests that cultivars with red fruits (and the red fruits of the standard Ilex aquifolium) are far more appealing to birds. It must of course be noted that other fruit colours, such as white and orange (which some Ilex aquifolium cultivars have), were not used within this study, and therefore all that can be ascertained is that red fruits are more desirable to birds than green-yellow fruits.

 

Looking beyond fruit colour, it can be said that smaller fruits are removed more readily by birds. This is because ‘Crinkle Green’, which had 94% of its fruits removed, possessed the smallest fruits. Such a finding does however conflict with the understanding of larger fruits being more desirable to birds (up to a point, when fruits become too large to fit within a bird’s beak), and particularly earlier in the fruiting season of Ilex aquifolium. The pulp:seed ratio was however shown not to be an influencing factor, as ‘Crinkle Green’ in fact had the lowest pulp:seed ratio, whilst the second highest branch type from ‘Pyramidalis’ had the highest ratio. Building upon this, because the nutritional profile of fruits was not measured, it is difficult to make the assertion that the amount of flesh on a fruit is significant in determining bird frugivory. It may very well be that birds seek nutritional fruits, and these fruits may very well have varying pulp:seed ratios.

 

A robin perched upon the branch of an Ilex aquifolium. Source: Warren Photographic.

 

In terms of the amount of fruit per branch, because the number of fruits was relatively similar across all branches (10-20 fruits on each branch), there was little data to support claims that the abundance of fruits influences upon bird frugivory. Of course, if entire specimens were studied, then it may very likely be found that fruit abundance does influence upon frugivorous birds. In fact, other research has shown exactly this, and the authors remark that Ilex aquifolium cultivars that produce more fruits will hasten the species’ expanding range by attracting birds more readily.

 

The fact that birds also more routinely ate fruits from branches sheltered by the canopy of trees and tall shrubs is also telling. From an evolutionary and habitual perspective, this is not surprising, because birds will utilise the cover to reduce the risk of predation whilst they are foraging for food. An open environment leaves the bird exposed, and therefore if fruits can be obtained in sheltered settings then that is much preferred. Such a preference is actually quite beneficial for Ilex aquifolium, the authors allege, because it is a shade-tolerant species that can readily exist beneath tree canopies. By this token, the habit of birds eating fruits from sheltered hollies in urban areas may enable the species to expand its range by using urban woodland sites (and other sheltered locations) as vectors.

 

Therefore, it can be said that, if an Ilex aquifolium is to be planted within an urban setting then it is to be located in an exposed area, and should not have red fruits. Granted, this is assuming that its northward spread is not to be desired. Furthermore, because the survey sites were only in botanic gardens and cemeteries, there is a failure in recognising how small to medium-sized gardens within the urban and sub-urban setting may impact upon bird frugivory and the subsequent dispersal rate of Ilex aquifolium. Nonetheless, the results are interesting, and there is certainly scope for considering what types of cultivar to plant within an urban environment if succession of the species is of concern. This applies not only to Ilex aquifolium, but across the entire botanical spectrum.

 

Source: Møller, L., Skou, A., & Kollmann, J. (2012) Dispersal limitation at the expanding range margin of an evergreen tree in urban habitats?. Urban Forestry & Urban Greening. 11 (1). p59-64.

[Kveldssanger]

01/03/16. Fact #164.

 

The utilisation of a device that creates a wound means that the locally-exposed surface can be readily colonised by a pathogen, thereby meaning decay propagation around the wound area and then further beyond is possible – particularly if the tree cannot compartmentalise the wound effectively. If the tree is already weak, which may likely be the reason for such an investigative practice (to determine extent of decay), decay has an even higher probability of either setting in or further propagating. Furthermore, the deeper the wound, the more potentially significant the wound becomes in terms of decay onset and facilitating succession into surrounding areas – small, shallow holes that span no further in than two growth rings are the lowest risk, followed by narrow holes that delve deeper into the wood (Johnstone et al., 2010; van Wessenaer & Richardson, 2009; Watson, 2006; Weber & Mattheck, 2006). Species-specific traits in relation to CODIT do of course dictate how decay may develop (Shigo, 1986; Shigo, 1991), though artificial drilling (or the removal of bark plates) is never beneficial from an energy perspective as the discolouration of wood local to the wound means less wood is available for the tree to store energy, in addition to the potential onset of decay and the consequences incurred thereafter.

 

It is important to recognise that decay organisms can travel down a bore hole and propagate further within the tree as a result, albeit on a local scale initially. Over-frequent boring can therefore exacerbate instances of decay – particularly as it breaks the natural barriers formed by the tree to stop further decay from occurring (reaction and barrier zones) that may have been laid down in response to pre-existing decay (Lonsdale, 1999; Schubert, 2007; Weber & Mattheck, 2006). Further, the larger the bore hole the greater the risk, on average, of decay onset or propagation (Kersten & Schwarze, 2005). Species that lack true heartwood may be more susceptible to the adverse effects of drilling, because their ‘heartwood’ does not have the extractives that react with oxygen as a mode of defence against pathogenic invasion (Shigo, 1991).

 

Polyporus squamosus, for example, was found on half of the specimens subjected to increment bore holes during one study. As a fungal species that has a strategy that involves entry via stem wounds, such bore holes may provide conditions for germination of its fungal spores (Kersten & Schwarze, 2005). Such an observation can act as a proxy indicator for similar fungal strategists, that too employ such a tactic for entry. Curiously, the study suggests that certain fungal species might be adversely impacted by the presence of bore holes, given the conditions created as a result of such boring. In this study, Inonotus hispidus was found to have limited radial outgrowth around areas of boring damage sustained by an increment borer (that creates larger holes up to 10mm), whilst not having limited radial outward growth from damage via the IML-Resistograph (that creates much smaller holes). This may be to do with Inonotus hispidus having a preference for low-oxygen, high-carbon dioxide conditions, which other decaying fungi are also adapted to – these conditions are not present when bore holes are larger.

 

In this longitudinal cross-section of ash (Fraxinus excelsior), we can observe how the tunnel created by the increment borer has led to discolouration around the wounded region. The hole itself, though only within the reaction zone region, has also been filled by a mycelial plug of the shaggy bracket fungus (Inonotus hispidus). Such a mycelial plug keeps conditions right for fungal decay, which would have been temporarily altered (adversely) by the creation of the tunnel courtesy of the removal of a wood core. Source: Kersten & Schwarze (2005).

 

With regards to micro-drills in particular, and for other devices that bore into the wood, shavings created from the drill’s passage through the wood can sometimes be displaced along the bore tunnel, thereby directly aiding with internal propagation and the spread of decay organisms (Axmon et al., 2004; Johnstone et al., 2010; Kersten & Schwarze, 2005). Research has nonetheless concluded that such decay onset from micro-drills is typically short term (8-10 years), after which point compartmentalisation had fully completed. In trees that were tested that had no evidence of decay there was no onset of decay post-drilling (Kersten & Schwarze, 2005; Shigo, 1986). Concerns should however manifest when boring into trees with existing decay, as drilling can, as established, facilitate fungal progression into sound areas of wood.

 

How drilling with a resistograph enabled the decay from honey fungus (Armillaria sp.) on black poplar (Populus nigra) to propagate outwards along the boring tunnel. Source: Weber & Mattheck (2006).

 

One must also note that vascular tissue will be damaged during the boring process, which can impact upon hydraulic conductivity and efficiency of the tree’s vascular system by default, in addition to the fact aeration of the xylem and subsequent risk of xylem dysfunction (and subsequent decay onset) will potentially manifest. This is particularly an issue where dulled drill-bits are used – if drilling is necessary, very sharp drill-bits must be utilised. Caution must also be exercised so that, when preparing for drilling, no pulling or twisting movements to remove bark are undertaken, in addition to not drilling when bark is loose in the spring and autumn, and not plugging or dressing the drill holes (Johnstone et al., 2010; Kersten & Schwarze, 2005; Shigo, 1991). Such aforementioned practices can facilitate in the creation of more expansive decay regions, either by providing entry or making site conditions preferable for rapid succession. In addition, bore hole presence can provide conditions for cracks to propagate laterally out from the hole (Shigo, 1986). This can bring about a situation where future failure or weakness can establish and / or cracks can propagate under mechanical stress, caused initially by the presence of the bore hole (Weber & Mattheck, 2003). Ultimately, unless the invasive increment leaves a spindle-shaped hole, the force-flow of the wood grain locally will be interrupted in a manner that detracts from equal stress distribution (Mattheck & Kubler, 1997). The presence of a bore hole (which cannot possibly leave a spindle-shaped tunnel) might therefore impact upon the structural integrity of the tree, given acute stress build-up.

 

Invasive techniques also require human operation for large portions of the process, and thus the process is open to human error more so than in computerised techniques – i.e. a radial core sample may not be a true radial core sample and thus a second sample may need to be taken, and if a sample is being taken and assessed for decay via feel, smell, etc, then it is open to more subjectivity and prognosis might be incorrect. Computerisation brings about objectivity and improved accuracy, which is critical when looking to determine internal wood decay (Nicolotti & Miglietta, 1998). Human error can simply lead to unnecessary (further) wounding, which will have adverse impacts upon the health of the tree that, given the reasons behind invasive tests, will likely already be under stress. Shigo (1986) even suggests that, if boring is necessary, the operative should practice on a fallen log first.

 

The financial cost is generally relatively acceptable for many invasive devices, though particular devices may cost tens of thousands of pounds. However, the modest cost does not make up for the need for operators to be properly trained and knowledgeable in the interpretation of the results from the device. If operators are not skilled in the device they are using, not only may the tree be falsely-diagnosed but, as previously mentioned, additional invasive tests may need to be undertaken to obtain the required readings. Additionally, notably for drills, the only decay that will be detected is along the bore tunnel – decay pockets could be missed by a fraction of an inch and thereby avoid detection (Nicolotti & Miglietta, 1998). A skilled operator will be more likely to successfully bore into the correct areas after fewer attempts.

 

Weighing up the cost versus the benefits really doesn’t paint such invasive techniques as ultimately good for health of the tree, in light of the aforementioned points. However, the ease of use of many invasive methods, when compared alongside accuracy (critical for the safety levels of trees in urban areas, in particular), cost, and reduced implications to tree health with their appropriate (not excessive) use, can justify their utilisation without significant concern (Johnstone et al., 2010). Of course, for specimen trees or trees that are otherwise deemed critically important, non-invasive (or minimally-invasive – the PICUS Sonic Tomograph) means of decay-detection might be preferable – thermal imaging may be the chosen option in such a scenario (Catena & Catena, 2008).

 

References

 

Axmon, J., Hansson, M., & Sörnmo, L. (2004) Experimental study on the possibility of detecting internal decay in standing Picea abies by blind impact response analysis. Forestry. 77 (3). p179-192.

 

Catena, A. & Catena, G. (2008) Overview of Thermal Imaging for Tree Assessment. Arboricultural Journal. 30 (4). p259-270.

 

Johnstone, D., Moore, G., Tausz, M., & Nokolas, M. (2010) The Measurement of Wood Decay in Landscape Trees. Arboriculture & Urban Forestry. 36 (3). p121-127.

 

Kersten, W. & Schwarze, F. (2005) Development of Decay in the Sapwood of Trees Wounded by the Use of Decay-Detecting Devices. Arboricultural Journal. 28 (3). p165-181.

 

Lonsdale, D. (1999) Principles of Tree Hazard Assessment and Management (Research for Amenity Trees 7). London: HMSO.

 

Mattheck, C. & Kubler, H. (1997) Wood – The Internal Optimization of Trees. USA: Springer.

 

Nicolotti, G. & Miglietta, P. (1998) Using High-Technology Instruments to Assess Defects in Trees. Journal of Arboriculture. 24 (6). p297-302.

 

Schubert, S. (2007) Acousto-Ultrasound Assessment of Inner Wood-Decay in Standing Trees: Possibilities and Limitations. PhD Dissertation (Diss. ETH Nr. 17126). Swiss Federal Institute of Technology, Zürich.

 

Shigo, A. (1986) A New Tree Biology. USA: Shigo and Trees Associates.

 

Shigo, A. (1991) Modern Arboriculture. USA: Shigo and Trees Associates.

 

van Wessenaer, P. & Richardson, M. (2009) A Review of Tree Risk Assessment Using Minimally Invasive Technologies and Two Case Studies. Arboricultural Journal. 32 (4). p275-292.

 

Watson, B. (2006) Trees: their use, management, cultivation, and biology. India: The Crowood Press.

 

Weber, K. & Mattheck, C. (2003) Manual of Wood Decays in Trees. UK: The Arboricultural Association.

[David Humphries]

Is there nothing in the Codit Principal relating to this subject Chris?

 

 

 

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[Kveldssanger]

I shall check!

[Kveldssanger]

It seems there is. Pages 97-101. Some really good pictures, and some good accompanying text. By no means extensive, though there are probably a few bits I could have added to my coursework / subsequent blog post. Not sure why I didn't consult it when writing it, to be honest.

[David Humphries]

Slacker

 

 

.

[Kveldssanger]

Somtimes I do wonder how I ever live with myself!