Gardening in the Sky: High Line Habitat

Each March hundreds of volunteers join our horticulture team to complete the massive task of cutting back all the perennials in the park by hand. Though many gardens cut back their plants in fall, we leave our displays of dried leaves, stalks and seedheads up through the winter for their beauty and for the habitat they provide for birds and other animals. When we remove this material in the spring, we compost it onsite and return it to the gardens. As we learn more about how our horticultural practices, like Spring Cutback, affect the many lifeforms that use the park, we are taking new steps to better manage soil health and to protect the habitats of bees and other invertebrates.

High Line staff and volunteers cut back perennial plants in March. Photo by Liz Ligon.

In 2017 we partnered with entomologists from the American Museum of Natural History to learn more about the different kinds of wild bees that nest and feed in the park. The scientists collected samples throughout the summer and catalogued over twenty species of wild bees. They found small carpenter bees ( Ceratina calcarata), which are native to New York State. Only about a quarter of an inch long, they nest in plant stems. Corey Smith of the AMNH says, "Interestingly, these small, metallic-green bees are considered to be sub-social, meaning that they care for their young from egg to adulthood, and in some cases, can make the leap to weak eusociality." On one end of the sociality spectrum are solitary bees, which nest and forage alone. Colonies of eusocial bees, like honeybees (Apis sp.) and bumblebees (Bombus sp.), are considered to be more evolved. The colonies function almost as a single organism, with different individuals performing different roles such as reproduction, defense, or food gathering, on behalf of the larger whole.

This leaf-cutter bee is one of several types of solitary bees found on the High Line. Photo by Steven Severinghaus.

On the High Line, Smith and his colleague, Sarah Kornbluth, also found five of the fifteen Hylaeus bee species that live in New York State. These solitary bees build nests by sealing pollen along with their eggs into plant stems. One of most surprising things we learned is that some of these bees are so tiny they nest in plant stems no wider than a plastic coffee stirrer! As an experiment, we are not cutting down four different plant species with slender stems. We'll see if these dried stems increase nesting opportunities for wild bees in the park. While, the dried stalks of astilbe (Astilbe chinensis 'Visions in Pink') and hedgenettle (Stachys officinalis 'Hummelo') might look a little out of place amongst the fresh new growth of spring, we believe this is a small price to pay in order to preserve more bee habitat.

The slender stems of astilbe (Astilbe chinensis) may be used as nesting sites by tiny, wild bees. Photo by Timothy Schenck.

This year we are also leaving more leaf litter in the gardens as habitat for beneficial invertebrates, like spiders and insects. These critters overwinter in leaf litter and do not become active until spring temperatures rise. By leaving this layer of habitat, we can ensure that we have more spiders, pirate bugs, lacewings, and ladybugs in the garden to eat our pests. Dead leaves also form a protective cover over the soil, helping to reduce compaction and erosion. Furthermore, this material contains important nutrients that feed plants and soil organisms.

We will also continue to apply organic matter in the form of compost to feed our plants and soil organisms. For several years, we have been composting onsite the plant material removed from our gardens. We chip the dry, dead debris from winter to reduce its bulk, then store and eventually compost it. The dry or "brown" material from winter is rich in carbon, but low in nitrogen. To kick-start the composting process, we need to mix in fresh green material from the gardens or coffee grounds from neighboring businesses. Both of these are rich sources of nitrogen. By composting our own plant material, we avoid wasting fuel on transportation and generate a wonderful product that nourishes our gardens.

One of the many joys of gardening is the constant opportunity to learn. Our horticulture team strives to keep abreast of new information and apply it to our management plans. We'll keep you posted as we learn more about how to support the many life forms that share the High Line.


Our horticultural team counts on members and friends like you to help keep the High Line beautiful and thriving. Join our community of supporters who play an essential role in the High Line's most important gardening projects.


SUPPORT

TD Bank is the Presenting Green Sponsor of the High Line.

The High Line Volunteer Program is supported, in part, by REI.

The Volunteer Program is also supported, in part, by public funds from the New York City Council.

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