Changes in Hawaii’s agricultural landscape can occur the way plants grow: slowly.

A few major decisions affecting large-scale farming operations took place this year — notably state approvals to urbanize 2,300 acres of Oahu farmland so developers can build 16,750 homes.

The approvals in June by the state Land Use Commission allow developers to seek City Council zoning approval for two projects, Ho‘opili by D.R. Horton with 11,750 homes in Ewa, and Koa Ridge by Castle & Cooke with 5,000 homes in Central Oahu.

But opponents of the controversial plans have vowed to fight the two commission decisions in state court, which could stop or at least delay construction, which the developers hope to begin next year.

If Ho‘opili and Koa Ridge do move forward next year, it still would be a slow transition from row crops to residential communities, as the developers anticipate displacing farming on the land gradually over 20 years.

Aloun Farms and Larry Jefts Farms (Sugarland Farms) are the biggest tenants on the two project sites. Aloun and Larry Jefts have said they are shifting production to other land in Central Oahu and in the Wahiawa area to continue farming, though some changes in certain crops will be necessary.

Other agriculture operations that will be displaced also include Fat Law’s Farm, some seed corn production and cattle ranching.

In the short term, agriculture in Hawaii is expected to remain fairly stable, with one sugar plantation, one big pineapple producer, lots of diversified crop farming and a leveling off of seed corn, which has been the state’s highest-value crop since 2006.

Promising endeavors are under way to try to rebuild a shrunken local milk supply and expand locally raised beef by improving grazing methods for milk cows and cattle.

Last month, Parker Ranch announced a trial project with local social investment firm Ulupono Initiative to improve grass pasture management as a way to reduce the cost of raising cattle on the Hawaii island ranch, which annually ships about 5,000 head of cattle to mainland feedlots, where it’s cheaper to fatten the animals for slaughter.

Also in the works is a plan by a company from New Zealand to share grazing practices from that country’s thriving dairy industry to rebuild Hawaii’s local milk supply, which was severely diminished in recent years due to high feed costs.

An affiliate of Dairy Solutionz (NZ) Ltd. announced in December that it had formed a venture with Ulupono and a dairy consultant to establish an initial 1,000-cow farm by 2013 and assist others in starting similar-size farms in an effort to increase local milk production that is presently at about 10 percent.

It remains to be seen whether those two ambitious plans for dairy cows and cattle will be realized.

The biggest crop in Hawaii by “value” is seeds, dominated by seed corn, at $247 million in 2010, according to the most recent assessment by the National Agricultural Statistics Service.

Because seed companies don’t sell what they grow in Hawaii (they grow the seeds for research and mass propagation outside the state), the Agricultural Statistics Service measures the industry’s value by the cost of production, which for any profitable crop is lower than sales.

A couple of crops more recognized as Hawaii products — macadamia nuts and coffee — continue to be stable parts of local agriculture, with the number of farms and acreage unchanged over the past five years.

There were 570 mac nut farms on 17,000 acres in the 2011-12 season, the same as the previous four seasons, a recent Agricultural Statistics Service report said. Coffee farm numbers also held steady at 830 on 8,000 acres over the same period, the agency reported.

Sugar cane, once Hawaii’s top crop, is still rooted on Maui at the Hawaiian Commercial & Sugar Co. Plantation owner Alexander & Baldwin Inc. has been studying potential alternative crops for renewable energy production for several years, but strong sugar prices in the past few years have helped sustain HC&S.

Hawaii’s other one-time top crop, pineapple, is still in production and dominated by Dole Food Co., which produces the fruit on about 2,000 acres on Oahu. A few other smaller companies, including Maui Gold Pineapple Co. and Hawaii Pineapple Co. LLC, also got into the business in recent years after shutdowns of Maui Pineapple Co. and Del Monte Fresh Produce.

One major pressure that Hawaii food farming may face in the years ahead is the push for renewable energy production, especially growing crops to produce fuel and installing photovoltaic solar panels, often referred to as solar farms, on farmland.