The Point Reyes National Seashore is investigating reported habitat destruction by rancher Gino Lucchesi Jr. on the historic ranch he leases near Drakes Estero. 

Park officials said Mr. Lucchesi cleared brush and bulldozed along the banks of a sensitive unnamed creek on the Home Ranch. “The activity at Home Ranch took place without park knowledge or authorization and is not permitted under the terms of the Home Ranch agricultural lease,” said Melanie Gunn, a park spokeswoman. She added: “The rancher understands these actions were not authorized and is committed to fully implementing all corrective actions.” 

Ms. Gunn said Mr. Lucchesi bulldozed a 165-foot stretch of vegetation along the creek, bulldozed another 360-foot section near the access gate where the ranch road crosses the creek, and lightly graded a 515-foot stretch of uplands parallel to the road. 

Mr. Lucchesi and his wife, Kathy, who did not respond to the Light’s calls or emails, graze cattle on the Home Ranch, the oldest ranch in the seashore, and the neighboring N Ranch. But parkland comes with many restrictions. The Lucchesis’ lease bars them from bulldozing or removing timber without first obtaining authorization. 

Park superintendent Craig Kenkel met with the couple at the ranch last week to review the habitat disturbance and discuss corrective measures they must take. According to Ms. Gunn, Mr. Lucchesi agreed to restore the creek by removing the sediment pushed into the bed and installing biodegradable erosion matting along the bank to protect from further erosion. 

It was concerned citizens, not park officials, who discovered the bulldozing. On Aug. 12, birders hiking on the Estero Trail noticed a bulldozer operating in the riparian area upstream from Drakes Estero, according to a letter sent to the park by Chance Cutrano, director of programs at the nonprofit Resource Renewal Institute. 

Mr. Cutrano wrote that the clearing and grading along the stream could have a significant negative environmental impact. Sediment deposits caused by bulldozing could threaten the central California coast steelhead that have been spotted in the creek, and the removal of brush was also a concern. 

“Many of the animals that live in this riparian zone—especially fish and amphibians— require cool water to survive,” Mr. Cutrano wrote. “The overhanging foliage shades the waters that pool and flow in this perennial stream, keeping the water cool.” 

The birders reported the bulldozer to the park the next day, and park staff visited the site, confirming that Mr. Lucchesi had cleared willows and other vegetation and conducted light grading to more easily access areas along the creek. Mr. Lucchesi’s bulldozer became mired in the soil but was later removed, according to a letter Mr. Kenkel sent to the Lucchesis. 

Ms. Gunn said an ongoing investigation by the park will result in “long-term corrective actions.” 

In 2016, the Lucchesis were among the ranching families who intervened in a lawsuit filed by the Resource Renewal Institute and other environmental groups against the National Park Service. The resulting settlement agreement prompted the park to amend its general management plan, proposing longer grazing leases to ranching families. 

Ms. Lucchesi’s family, the McDonalds, have deep ranching roots in West Marin. Her father, Merv McDonald, grazed cattle at Pierce Ranch before being evicted in 1978 when the land was turned into a tule elk preserve.