Halifax Tree Project

 Nuisance Litter from Urban Trees

Hannah Machat & Zoe Coulter, Dalhousie University

2021-05-31

As the trees start to blossom and the signs of summer days become more prominent, many people emerge to enjoy their backyards and outdoor environments with great enthusiasm. Doubly, the most recent lockdown in Halifax has propelled citizens to embrace more fully their backyards and local parks. However, when people walk the streets of the city, they may become frustrated by the amount of nuisance litter created by many of the street trees. Nuisance litter includes debris like leaves (from deciduous trees in the fall), flowers in the spring, fruits & seeds, sap drip, and larger twigs & branches. 

Tree litter can be annoying for a range of reasons. Some are aesthetic: stinky fruits and flowers, untidy fallen twigs, nuts, and leaves, and sometimes sticky sap or fruit juices. Others may become more serious if left unattended too long. For example, enough fallen leaves on a sidewalk when it rains can become a slippery hazard. Large enough twigs and nuts can become tripping hazards or get caught in lawnmowers, and in the fall, leaves can get caught in and block eaves troughs and drains.

Often, the worst of these problems can be avoided altogether through species choices when planting trees in the city. All trees drop litter of some kind, but the amount and kind depend on what kind of tree it is. An oft-cited example is the female gingko tree, whose fruit has a strong and putrid scent, so cities tend to plant only male ginkgos. Another example is the Norway maple. This species is common on the streets of Halifax because it is fast-growing and hardy in the stressful urban environment, but Norway maples also drop a lot of leaves, seeds, and twigs. It is also not a particularly strong tree, so larger branches often come down in windstorms, which can pose a serious safety hazard. For these reasons, added to Norway maple’s tendency to become invasive in our woods, this species is no longer planted in the streets of Halifax. While the existing Norway maples require more maintenance due to their littering tendencies and potential structural weaknesses, the shade and other ecosystem services they provide make it worthwhile to keep them on our streets until they die or become hazardous.

Other trees can drop nuisance litter but are still desirable to plant in the city for a variety of reasons that make dealing with their litter worthwhile. Two examples are black walnut and horse chestnut, both of which drop large nuts. Those of the black walnut can stain the sidewalks, and those of horse chestnut are toxic if eaten raw. However, these two trees provide other benefits that often make their nuisance litter worthwhile. Horse chestnut trees have beautiful showy flowers in the spring and are good shade trees with spreading branches and dense foliage, while black walnuts are similarly good shade trees, with a beautiful large spreading form. Both trees grow well in cities and are present, even if in relatively small numbers, across Halifax. 

There’s no question about it - nuisance litter is a common issue throughout the urban forest in Halifax. No tree species planted streetside will not produce at least some amount of litter or debris that falls to the streetside ecosystem. A balance can be achieved to limit the nuisance of tree litter, while also ensuring that the positives outweigh the negatives. While we outline some common nuisances and headaches that tree litter gives, there are many benefits of keeping much of it nearby. Tree litter becomes an important factor in nutrient cycling and soil fertility, while also providing an important living environment for many organisms like earthworms and a multitude of decomposers like bacteria. If you have a backyard, you can help this process along by composting fallen leaves and other debris, and in a few years, they can be added to your yard or garden as rich soil. While the downsides of nuisance litter may outweigh the benefits for a few tree species, most trees are worth the hassle of tidying up after them. Regular maintenance of the streets and sidewalks to keep them clear of debris, and of the trees to keep them healthy, is the key to keeping tree litter at a safe and (mostly) tidy minimum.