Building the Forest Floor

by Birgitt Evans

Think about the last time you walked in a forest. There was a carpet of leaves, the newly fallen lying atop decomposing layers of leaf litter, the smell of dampness, perhaps some mushrooms poking up ready to send their spores out into the woods. And if you lifted the layers of leaves forming a rich mulch for those lucky trees, you would find an entire ecosystem. From fungal hyphae and bacteria breaking down the leaves and helping release nutrients back into the soil to worms, millipedes, sowbugs, beetles, spiders, and slugs living amidst the layers of leaves to the birds, amphibians, reptiles and mammals supported by these smaller creatures. An entire world arising from that leaf litter.

Sorrel and Ferns with Redwood Leaf litter

Now return to our own world of houses and streets where, the minute the leaves drop, you hear the sound of leaf blowers and see people hired especially to rake them up and haul them away, leaving a barren wasteland where no creature can live. And moreover, where nutrients no longer filter down through their own leaves to feed the trees. Instead, the people bring in bark or rocks to cover the land and make it look neat and tidy, attractive in a controlled manner. The irony of bark is that it is the one layer of the tree designed to resist decay; to not break down to feed the plant.

While large amounts of un-decayed plant material, including sticks and other kindling could possibly create a fire hazard, a living ecosystem with some moisture to assist the organisms of decay during drought years will create a living mulch that will feed trees and other plantings with little effort or expense and create homes for everything from soil microorganisms to amphibians and birds.

In addition, the litter from two of Alameda’s native trees, the Coast Live Oak (Quercus agrifolia) and the Redwood (Sequoia sempervirens) will help stabilize the soil and will form a sponge that will absorb water and allow it to percolate into the ground, slowing runoff.

While the redwood doesn’t have a lot of understory plants, its leaf litter will support the sword fern (Polystichum munitum); the lovely pink flowered redwood sorrel (Oxalis oregana) – not to be confused with the aggressive Oxalis pes-capre with its yellow flowers; rhododendrons; huckleberry (Vaccinium spp.); salal (Gaultheria shallon); and common snowberry (Symphoricarpos albus).

The coast live oak, on the other hand, is adapted to a variety of habitats from forest to chaparral. Their understory plants vary accordingly – from trees such as the California bay, toyon and tanbark oak in forest settings to manzanita, gooseberries, currants (Ribes spp), ceanothus, monkeyflower (Diplacus) and black sage in more open settings, such as you would find with a single tree in your backyard.

Surrounded by their natural leaf litter and underplanted with native species, these trees can create a haven for both animals and people, cooling the land and air during our increasingly regular ‘heat events’ and softening pounding rains during atmospheric rivers.

And you can do the same thing with most any tree you already have growing; no need to wait decades for a tree to grow up!

When creating your mini-forest paradise, make sure you remove large twigs and branches that could become fire hazards and check to make sure that leaves and leaflets are breaking down and not piling up in thick, dry mats. Add water (to all but oaks) if you are not seeing decomposition and remove excess build up of plant materials. And, while Alameda is designated ‘urban unzoned’ in the County of Alameda’s Local Hazard Mitigation Plan, it is still a good idea to follow Calfire’s guidance and leave a 5′ buffer around your house that is free of flammable items and which features non-flammable plants and mulch.

More mini-forests dispersed throughout Alameda will help both people and wildlife to live comfortably in the years to come. So plant more trees and maintain the ones you already have in a manner that supports their growth so that we can all thrive.