Investments in Bronx and northern Manhattan parks were tied to a drop in crime between 2003 and 2016, a study released Tuesday argues.

The New York Restoration Project, a nonprofit parks conservancy that operates in low-income communities, funded a study of its own investments in Inwood, Washington Heights and East Harlem in Manhattan and Highbridge and Hunts Point in the Bronx. Crime rates in those neighborhoods before and after 2003 were compared with rates in three demographically similar neighborhoods where it did not invest: Kingsbridge Heights and Soundview in the Bronx and central Harlem.

Non-major felony crime dropped more in the areas where the nonprofit either helped to maintain city-owned parks or owned and maintained smaller community parks and gardens.

"The point of the study is to try and develop some data behind what we know to be true: Investing in quality open space and providing people with access to nature reduces crime and improves public health, among other things," said Deborah Marton, executive director of the restoration project.

In particular, the study found that areas with heavy green investment saw 3.8 fewer non-major felonies per 1,000 residents in the years after the restoration project became active. Even in neighborhoods that received only modest investments, the non-major felony rate fell by 1.5.

The study from data company Glass Frog Solution was not peer reviewed by other experts in the field, which is a way to ensure academic studies are more accurate. But the results align with the conclusions of several other reports.

An analysis released earlier this year, for example, found that cleaning up vacant lots in Philadelphia was associated with lower rates of gun violence. And other studies have found rates of narcotics possession fell near Philadelphia stormwater plots that were improved with green infrastructure, and crime dropped around public lots that were maintained in Youngstown, Ohio. A correlation was even seen between decreased crime and well-manicured private lawns in Baltimore.

Marton called for a more robust study of the issue in New York City and argued that pumping money into green spaces could be more cost-effective than other approaches being used to achieve the de Blasio administration's goals of promoting equity between high- and low-income areas.

"If you grow up without any access to nature and are surrounded by trash, your outcomes are going to be less favorable than if you have these types of green amenities in your community," she said.