Dogs in tree care: Exploring the use of hounds to detect decay

REFERENCE sources tell us how a dog’s sense of smell is the most powerful weapon in this species’ armoury. The olfactory system of canines is, of course, much more complex and developed than that of we mere human beings.

Man’s best friends boast roughly 40 times more smell-sensitive receptors than you or I, ranging from about 125 million up to nearly 300 million in some breeds, such as bloodhounds. 

These receptors are spread over an area about the size of a pocket handkerchief (compared to five million over an area the size of a postage stamp for Homo sapiens). An added plus is that the dog has mobile nostrils that help it determine the direction of the scent too.

And man continues to turn this canine olfactory prowess to good use. 

What is a detection dog?

Sniffer dogs are commonly used by the police throughout the world. Could they soon be a more regular sight next to arborists? (Image: Getty)

A detection or sniffer dog is one trained to use its senses to detect substances such as explosives, illegal drugs, wildlife droppings or scat, currency, blood, smuggled plants and animals, and contraband electronics.

They come in many breeds, shapes and sizes, as well as temperaments. 

Hunting dogs, which search for or pursue game, and search and rescue ones are generally not classed as “detection dogs”, but instead come under their own categories. There is, of course, some overlap, as in the case of so-called cadaver dogs, trained to search for human remains.

A police sniffer dog is essentially a detection one used as a resource in law enforcement for specific scenarios such as conducting drug raids, finding missing criminals, or locating stashed currency. 

Frequently, detection pooches are thought to be used only for law enforcement purposes, but that is far from the case. 

They are also useful as a valuable research tool for wildlife biologists and in environmental work to do with forestry, arboriculture and tree health.

A few examples

Everyone is familiar with dogs being used to detect rogue items. (Image: Getty)

These canine champions are trained to sniff out a wide and expanding range of targets – from bedbugs to COVID and cancers to illegal trafficked goods and SIM cards.

Here are just a sample of some skills related to land-use disciplines. 

•  In tree health. Sniffer dogs are ever more frequently used in detecting pests and diseases in valuable trees.

In California, specially-coached mutts are in action to hone in on low incidences of insect pests that the human eye might overlook. Each species of insect has a unique odour which the canine olfactory system can detect and differentiate from other invertebrate pests.

Also in the Sunshine State, proficient specialist canines pick up on bacterial infections of commercial citrus crops both speedily and accurately, even before visible clinical symptoms show.  

My saying so on here may raise hackles but there is certainly at least one decay detection dog doing the rounds in the tree world in the UK – a female border collie called “Sika” (like the deer, not the misspelt spruce) – nosing out a selection of decay fungi in arboricultural surveys, often in terrain challenging to human tree folk and before ‘tell-tail’ symptoms surface and become visible to the human eye. She made a star appearance at the 2023 ARB Show. So, the expression “barking up the wrong (or right) tree” takes on a whole new meaning!

• Invasive and rare species.  Sniffer dogs can be schooled to locate low-level infestations of invasive and non-native species. In California, such animals are even trained to discover quagga mussels on the keels of boats hauling out at public boat ramps because these molluscs are exotic and harmful for the local marine environment.

Dogs have been used to locate noxious weeds such as Japanese knotweed that a person might miss. Across the planet, canine sleuths have been taught to sniff out rare plants in the field too.

Once trained using dogs in survey work for discovering target species, these motivated, four-legged specialists can cover far more ground than we two-legged ones, producing accurate data whilst saving time and money.

•  Gourmet fungi. Famed and treasured truffle hounds hunt out these highly-prized underground fungi in France and Italy and are easier to manage than ravenous single-minded pigs on a similar mission. Attempts are underway to inoculate trees such as hazel with truffle spores to plant out on promising sites dubbed “trufflearia” in southern Britain. Might sniffer dogs soon be at a premium in the UK? 

•  Endangered wildlife. You may have suffered the indignity of a prying cold wet nose probing your person when waiting for your luggage in airports and ferry arrival halls. Dogs are not only used in finding smuggled dead and live wildlife products, but also in surveying sites for listed wildlife in the UK. 

Detection dogs have been used here for checking if endangered vertebrates – such as harvest mice, red squirrels, great crested newts and pine marten – are around in the wild before major environmental works such as afforestation schemes are approved or underway. 

READ OUR CASE STUDY ABOUT SIKA

A word of warning though. Using specialist dogs to find endangered animals in Britain may require the green light from the relevant national conservation authorities. 

•  Scat. Whether you call them droppings, fewmets, faeces, poo or my preferred term of ‘scat’, there’s a lot of information to be gleaned from what wildlife leaves behind. 
Detection dogs can specialise in finding and collecting the faeces of a diverse array of species. This process is politely dubbed wildlife scat detection.

And sniffer dogs are an agile way of covering a lot of ground in the search for these signs to determine which species is around, an idea of abundance and diet, sex or health; scat is the stuff to fall back on for valuable information. 

Wildlife scat detection represents a fairly non-invasive method of study for many species where live or dead capture was once the order of the day. Compared with other methods, these descendants of wolves are able to cover and survey larger tracts of land in less time at decreased costs and with increased accuracy.   

Excremental dumping

More controversially in recent times, sniffer dogs are used as part of countryside hunts. (Image: Getty)

All dogs can have a detrimental impact on our natural environment – leaving aside the vexed issues of fouling, poo bags adorning trees, dogs worrying livestock or wildlife, legal situations, dangerous breeds and Alabama rot.

Keep Britain Tidy estimates there are over eight million dogs of all types in the UK, voiding around 1,000 tonnes of excrement between them each and every day of the year. 

New research suggests significant amounts of phosphorous and nitrogen found in dog faeces and urine left behind in nature reserves or popular recreational forests can result in over-enrichment of the soil. This can impact sensitive varieties of plant and animal life and interactions between species for the worse.

Some sources have voiced concern that soil-borne tree diseases might spread on paws and parasites in droppings be passed on to people. As an antidote, Forestry England’s Wyre Forest in the Midlands even boasts a paid, DIY ‘dog wash’ for dousing down after walks.    

Training

Sniffer dogs are being used to find Japanese knotweed at sites across the UK. (Image: National Highways)

The discipline of detection dogs is expanding.

Training an animal – and its handler – may take anything up to two years of daily routine reinforcement learning for both the dog and the person. 
Sniffer dogs are normally trained for just one specific target.

If you want to hone up on this expanding speciality, there is a Facebook page at ‘Ecology Detection Dogs in Britain and Ireland’ – with almost a thousand members.

And an outfit called ‘UK Sniffer dogs’ offers online training courses.