Our street trees are Chinese evergreen elms. They form a shady canopy over the two blocks of our neighborhood and are the envy of folks on the next street west, who have no uniform street trees.
Evergreens, I have learned, are also everbrown. They never lose all their leaves, but are always losing some of their leaves as well as patches of bark. Chinese evergreen elms have a growth spurt in the early spring, when they're susceptible to wind and so will dump great quantities of light-green leaves. What this means is that we're always sweeping up tiny leaves and disk-like seeds.
Since we started our current regimen of suburban permaculture gardening, we have viewed the year-round supply of elm leaves as a major asset. They form a clean, attractive layer of mulch and, being small, break down quickly to enrich the soil.
Ramona, our permaculture maven, has instructed us to lay down a thick layer of corrugated cardboard and top it with three or more inches of light mulch, for which the Chinese evergreen elm leaves and seeds are ideal. A layer of compost under the cardboard gives a head start to decomposition, and soaking the cardboard is another optional boost.
Just before Christmas, we topped the mulch with a thickish layer of shredded white paper. Let it SNOW! Now the 'snow' is getting a topping of pulled-up green weeds, which will get another topping of brown elm leaves. Our worms and legless lizards are fat and sassy, and I am attuned to the aesthetics of fallow.