Autumnal Sensations

When we think of autumn, a lot of things come to mind.  Chilly days, Halloween fun, pumpkin spice, the smell of autumn leaves and of course the magnificent visual display of the foliage.  Halloween and thanksgiving festivities aside, most of our autumnal associations are in some way, shape, or form, sensory.  There’s the visual display of reds, yellows, purples and oranges painted across the landscape.  There’s the tactile joy of stepping on that crunchy leaf (or the sorrow of discovering it only looked crunchy).  There’s the smell of walking through a forest in autumn, that earthy aroma which fills the nose and brings back memories of autumns past.  And of course the sound of rushing leaves, of the swish as we walk through them or as the wind whisks them along.  One more thing to notice too is that while most of our autumnal associations are sensory, those sensory experiences are almost entirely derived from one thing: Leaves.

This should come as no great surprise, we’ve all seen the art inspired by autumn displays.  Whether a photograph, painting, postcard, cinematography, or a family road trip to just take it all in, the colors of autumn inspire awe and give us something to look forward to as temperatures drop.  In the wild, this can mean mountainsides awash with colors; hues of red, orange, and yellow rolling across the hills or the horizon.  As designers, we can and do curate these experiences to achieve specific and striking visual effects.  At times it’s an allee of red maples, framing an entry drive and drawing inspiration from a New England farmstead, others it’s a grid of birch, the monochrome of yellow filling the courtyard, then falling to give a bright yellow carpet, accentuated by skeletal trunks rising from the painted ground.  Whether a monochromatic display or a mix of colors and textures, the landscape can go through dramatic changes come autumn.  The extent of the impact of these colors extends beyond visual, however.

Time for science class!  Of course photosynthesis requires chlorophyll, which is responsible for the green color of leaves.  Yellows and oranges are caused by carotenoids, which are always present in the leaf.  When temperatures drop and daylight hours get shorter, the production of chlorophyll slows and then halts.  Both the chlorophyll and also the carotenoids begin to degrade at this point and are reabsorbed by the tree, though the carotenoids do so more slowly.  Different leaves retain a different amount of carotenoids, with honey locust and gingko, for example, falling before the full breakdown and reabsorption of carotenoids, giving us the bright yellow we associate with them, while some species of oak lose their carotenoids quite quickly, giving the dry, brown leaves they are left with.  Anthocyanins are responsible for the red pigment in leaves and are not present in leaves before they begin to degrade.  The high concentration of sugars as chlorophyll and carotenoids break down kick starts the production of anthocyanins, and while their function is not fully understood, it is thought to serve as a photo-protector, protecting the compounds within the leaf from the sun and allowing the tree to more easily absorb them.  What all of this means is that the color of a tree’s leaves in autumn is dependent on what nutrients and chemicals it retains, and at what level.  

This retention of compounds and nutrients in the leaves is important for more than just visual effect, and shapes every sensory experience we have related to them.  Let's look at the tactile sense.  There is always a bit of childlike joy with stepping a leaf with high crunch potential, and either the satisfaction of the feel and sound as it crunches underfoot, or the crushing disappointment of being wrong and feeling it just squish.  When we picture these crunchy leaves though, we almost always picture a brown leaf.  Hard, an intense crunch, often a little curled up and standing lightly on the ground or other leaves.  Occasionally we’ll come across one which is lightly red, like from some species of maple, and which satisfies the other criteria of being dry and light, and so we give it a test and ar eat time rewarded with a very different, much lighter and crisper experience than the heavy crunch of a brown leaf.  What we don’t picture though, is a bright red or yellow leaf.  The retention of compounds and nutrients which give the leaves their color also leave them retaining moisture.  Through the process of senescence (aging) leaves lose their compounds and nutrients, and therefore their color and moisture.  So as a product of this process, the more colorful the leaf, the less crunchy.

This retention of compounds which leads to color, and also determines the tactile qualities of the leaf, then in turn have an impact on the auditory component of them.  Of course there is the auditory component to stepping on a leaf, either a crunch, a crisp, or a soft or silent squish.  The auditory experience of autumn is hard to pin down to just one, as it is so dependent on weather, surrounding infrastructure and other anthropogenic factors, and also, on the leaves.  One shift from summer to autumn is that sound travels further, and this is for a number of reasons.  The air loses humidity, which affects how sound waves travel.  The density of humid air means sound travels slightly faster, however, this humidity also leads to increased attenuation, meaning the sound wave loses energy and dissipates faster, dissipating into the heavier medium.  This increase in distance sound waves can travel gets paired with the loss of foliage which once acted as a barrier and a sound dampener, meaning that far distant sounds which were barely noticeable in July become much more acute in October.  

So, the leaves themselves shift from something which absorbs and dampens noise, to potential point sources of auditory stimuli.  The drier and less colorful the leaf, the more they will rustle and clatter together while still on the tree, giving that crisp, rushing sound as the wind passes through them, or whips them up on the ground.  As well, walking on them (or jumping in a pile of them) will create a distinct auditory impact which varies greatly based on the species of leaf and the corresponding retention of color and nutrients.  As well, the ephemeral quality of foliage creates auditory and visual barriers which are temporary, opening up views and spaces once separated by a wall of vegetation, allowing both sightlines and sound waves to pass more freely.  One way autumn can pose a specific challenge to those with sensory sensitivities is that this openness can create discomfort, in part due to how freely stimuli can now flow, creating a sense of exposure and sensory experiences which are less compartmentalized.  

One of the most powerful associations with autumn is the olfactory experience.  The humidity dies down, holding on to fewer compounds in the air, and with the retreat of foliage and the passing of flowers, there are simply fewer things in the air to smell, heightening and making more clear those smells we so strongly associate with autumn. While the visuals of the rainbow foliage are striking, our sense of smell is tied heavily to memory, and has the power to take us back to our childhood, bringing out a sense of nostalgia with just one whiff.  Sometimes this happens strongly; walking through the woods on a dry autumn day, the scent of sun baked leaves will take me back to hayrides and apple cider as a kid.  Other times, the impact isn’t as immediate or intense, the smell just isn’t triggering the same emotions and memories.  While mood and setting can play a big part, it also at times is simply because the leaves smell different.  

On those dry, sunny days, we can expect to be greeted by the warm smell of sun baked leaves, crisping up and releasing a hay-like smell.  On a cooler day, perhaps right after a rainfall, the smell will be heavier, damp, and sweet.  The wet leaves begin to decay, releasing a different set of organic compounds as they decompose.  Yet even within these two situations there is plenty of variation.  Once again, the color forming compounds and nutrients in leaves, as well as others which are retained, contribute heavily to the scent they emit once they fall from the tree.  Oak leaves, having lost most of their organic compounds to the trees' winter storage efforts, have little to define their scent and so give off a heavy, earthy smell in damp decay, and a hay like aroma when warmed in the sun. The leaves of the katsura release maltol into the air as they break down, giving off an aroma of sugar or vanilla, leading to names like the cake tree or caramel tree.  The color of leaves is dependent on the nutrients and compounds they retain.  This then affects moisture content and texture.  Finally, as they senesce, they release these compounds for our noses to pick up.  Just how the more nutrients and compounds are retained, the more colorful a leaf will be, so too will this cause a more dynamic smell, with colorful reds like a maple leaning towards sweeter smells than the earthy pungence of a rain soaked oak forest in autumn.  

Our sense of taste is heavily tied to smell, with coffees and wines having a certain “aroma” based on origin and preparation techniques.  These aroma flavors are not triggered by our taste buds, but by our nose.  There is a certain experience I love when the smell of the autumn leaves is heavy enough, especially when they are wet. I've experienced a slight taste to go with it, in some ways similar to an earthier tea.  So even if we aren’t eating the foliage, an essence of gustatory sensation can still creep into our landscapes if the aromas are strong enough.

It’s incredible to me how something as simple as the color variance in leaves can create such drastic impacts across the senses.  Our world is full of such interconnections, often with one main association which can hint at deeper intricacies.  As designers of the public realm, we not only lay out spaces, but curate and author experiences.  Having a deeper understanding of the specific sensory impacts of the plants around us across seasons allows for a much more honed execution of our designs and curation of the spaces and experiences we wish to bring out from a space.   Autumn color provides us a palette to paint with, and can also serve as a cue to what other kinds of experiences can be expected from a space.  An oak grove creates a space to run and play, to jump into a pile of leaves and engage with that light, crunchy, and very nostalgic experience.   Grove of honey locust, meanwhile, would leave the ground covered in a mat of yellow, with the small leaflets gently floating down with the slightest breeze, creating almost a snowstorm of yellow across the landscape.  Here the ground wouldn’t crunch, and can even get a little slick after a rain.  It would have a different smell, different sound, and much different visual impact.  Perhaps one of these is the goal, and a deeper dive into the sensory implications of the trees we choose can help us accentuate and celebrate their specific impacts and create a more nuanced experience.  Or, perhaps we want to try and incorporate a mix of species, attempting to blend and capture our favorite experiences across each sense, giving a taste of it all rather than diving full into one.

Whatever our design goals, this sensory exploration of autumn through something simple, like leaves, opens up doors for creativity and nuance in our designs.  I’ve spoken a lot about the sensory experiences here, and not as much on the other aspects of my research into it, which is on neurodiversity, sensory sensitivities, and accessibility.  I would like for sensory design to become a deeper part of our everyday design process, and our design process for every person.  We all think to some degree about the sensory as we design, we consider what a space will feel like to stand in, to walk through, to play in, etc.  To dive more deeply into the sensory experience of a place is to dive more deeply into the human experience of a place.

Of course I will always advocate for increased accessibility for every user, that we should consider beyond physical accessibility and design for neuro-inclusion as well.  The basis for this next step, for diving into sensory design and neuro-inclusion, is to understand and explore sensory experiences in a more intentional way.  Every single person has their own experience of the world as they move through it, one defined and driven by their senses.  To design a sensory experience with clarity and intent helps define the space for everyone who uses it, and the process of doing this analysis opens the door for us to ask deeper questions about accessibility.  The more we understand and get into the habit of considering questions of sensory experience, the more we can address concerns of sensory sensitivities and accessibility.  As with all aspects of design, designing accessible spaces has positive impacts which reach beyond the intended group which the accommodations exist for.  

And so my exploration here has been focused on the senses themselves, on smells, textures, sounds, visuals; on the ways we engage with them and on how they can be another tool in our design kits.  I hope this discussion has sparked an idea, or an excitement for the next project.  I would invite everyone reading this to take an extra moment to think and analyze their plant selection the next time they get to that point.  How will it smell, and not just the flowers?  How will it feel?  Sound?  Are these sensory impacts advancing your idea and design intent?  How might someone with a sensitivity to one of these senses react to it?  And as always, this way of thinking extends beyond the autumn season, and this analysis can have the same impact across seasons and regions.  I want to end by reiterating…

To dive more deeply into the sensory experience of a place is to dive more deeply into the human experience of a place.