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LIVE OAK – Above ground, planted pines stand in perfect geometric order, tufts of green needles balanced on lofty, fissured trunks. Underneath they are a jumbled, knotty mess of roots.
It’s this subterranean world, called the rhizosphere, that dictates the trees’ growth.
Water, microorganisms, roots and nutrients mingle here, sending chemical signals to the trees above. Pine needles sit atop all this action, preventing weeds from growing and sending natural fertilizers into the soil as they decompose.
These protective, restorative functions make pine straw an attractive mulch to landscapers. It is recommended by IFAS as “Florida Friendly”: a natural, sustainable choice for mulch.
But applying pine straw to residential flower beds means stripping it away from the forest floor.
The rhizosphere feels the loss.
A versatile mulch
In an older Florida, pine needles created a thick cushion over millions of acres of forest floor.
For most of its history, pine straw sat undisturbed: a meal for forest bacteria that funnel nitrogen and other nutrients into the ground as they feast.
Wildfires tore through corridors of forests frequently, their blazes releasing even more nutrients from the pine needles and taking out pines’ competition. Trees grew taller, sprouting new needles and dropping their dead ones, propelling the growth cycle forward.
Seminole and Calusa tribes used pine needles to weave baskets, longleaf’s namesake eight to twelve inch blades ideal for making smooth curves. In the 19th century, pine straw gained popularity as road cover, its soft needles cheap and malleable.
Early harvesters used pine straw sparingly. By one 1868 account, needles in a Suwannee forest were almost knee-high.
As the Florida pine straw industry emerged in the late 20th century, verdancy gave way to scarcity. Today, on a managed plantation, harvested yearly, pine straw beds are rarely thicker than a shoe’s sole.
“Any of your mulches, including pine straw, are going to help create an effective barrier against weeds, and they're going to help conserve moisture in the soil, and both of those things can help improve plant growth,” said Brooke Moffis, an IFAS extension agent in Lake County.
Pine straw breaks down and settles more quickly than other mulches, making it attractive in flower beds.
Since pine needles are already dead at the time of harvest, they’re considered more sustainable than cypress mulch, which once dominated Florida’s home and garden centers. In the early 2000s, cypress accounted for 60% of mulch sold at such centers, the remaining 40% split evenly between pine bark and other mulches.
Cypress mulch, as with most hardwood mulches, was initially produced as a byproduct of the timber industry. As demand for the mulch grew, foresters began to cut down young trees for the explicit purpose of making mulch, garnering widespread opposition from wildlife and water quality advocates.
The University of Florida advises against cypress and rubber mulches for their unsustainability, recommending grass clippings, invasive tree mulches and pine straw instead.
“Adding that pine straw mulch can help the landscape look like it belongs in Florida,” Moffis said, an ecological irony considering how development and logging have reduced longleaf pines to 5% of their original acreage throughout the Southeast.
Pre-raking
As bright green pines streaked past the pickup’s window, Suwannee County extension agent Raymond Balaguer Barbosa identified them in real time. The trick is in the branches, he explained. If their ends are thumb thick, the trees are longleaf pine. Pinky thick and they’re slash.
Both – and, occasionally, Loblolly – are grown for pine straw harvesting throughout the Southeast.
At a glance, Balaguer could tell not only what the trees were, but how they were doing.
“Someone’s serious about these longleafs,” he said, gesturing to a neatly manicured plot of young trees. “They’re mowing the in-betweens, they’re waiting for the second or third year to start really heavy on the herbicide.”
Weeds spring up in pine stands just as they do in any agricultural setting. Scrub oak, coral ardisia and torpedo grass are a land manager’s rivals. They compete with the growing trees for nutrients and sunlight. When neighboring roots get too close, they can stress the pines, making longleafs more susceptible to disease or insects.
Traditionally, foresters use prescribed fire to wipe out the weeds.
“Prescribed fire is really emulating what was a much more frequently occurring natural disturbance,” said Rachel McGuire, outreach and education coordinator for the Jones Center at Ichauway, which studies and conserves longleaf pine ecosystems. “We've just fragmented our landscape as humans so that we don't have those larger scale, frequent, low intensity fires.”
During a burn, flames trigger plants to release their seeds, regenerating a diverse understory that will house quail, gopher tortoises and grassland birds. The ash left behind sends nutrients into the ground, promoting longleaf growth and improving timber quality.
But most pine straw harvesters don’t burn.
To do so would be to set their profits aflame, golden needles turning black.
“If you could burn [weeds] off, that’s cheaper than mowing or spraying,” said Michael Lamb, who produces pine straw in Branford. He dismissed the thought with a laugh. “It’s too much liability for me.”
Plus, a pine operation’s goal is typically homogeneity, not diversity. “They’re at odds with each other,” McGuire said. “To be able to use mechanized pine straw equipment, you have to have the cleanest, most homogenous system possible to maximize production.”
Enter: herbicides.
In a 10-season study, pine stands mowed and treated with chemical herbicides had higher survival rates and grew trees twice as large as their untreated counterparts.
“I used to be more wary of talking about herbicides,” Balaguer said. “But there's no running away from it. You need it.”
On a pine stand, he explained, many weeds are stubborn enough to warrant spraying, making the “last resort” the only option.
One of the most common herbicides used to prepare a pine site is glyphosate, more commonly known as Roundup. It is non-selective, meaning that it finds and binds to a specific growth enzyme, be it in plant or bacteria, native or invasive.
It’s so potent, in fact, the Environmental Protection Agency found in 2020 that the chemical’s allowable (labeled) uses were “likely to adversely affect” 93% of species listed under the Endangered Species Act.
Florida’s manatees are among the affected. A 2021 study of manatees in Crystal River and various waterways in South Florida found glyphosate in 55.8% of blood samples, spiking before and during sugar cane harvest, in which glyphosate is used as a ripener.
According to data from the U.S. Geological Survey, glyphosate use in Suwannee County is low, 6.62 pounds per square mile in 2019 compared to an average of 29.1 pounds per square mile in Martin, Glades and Lee counties, where manatees were studied.
“Herbicide has a place. It’s not like it’s a bad thing, nor do I think pine straw operations are a bad thing.” Rachel McGuire
Still, the increasing scrutiny on glyphosate has led some land managers, including Melissa Snodgrass, to explore more selective herbicides.
“There's been a lot of advancements in chemical products that are weed specific,” she said. “If you have a Bahia problem, there's a certain chemical that you use for that. If you have this type of weed, you use this. So that's improved over the years.”
Some land managers have turned to drones for more targeted herbicide applications, used in Japan since 1985. Often, drones use cameras to scan crops, differentiating between weeds and seedlings to determine where to spray. The practice is relatively new in the U.S., with the Federal Aviation Administration first allowing it in 2015.
Since longleaf pines live for decades or hundreds of years, McGuire explained, one option for land managers is to harvest pine straw early on to make a few years of profit before thinning the plantation and incorporating prescribed fire. The older trees benefit from regular burns and native plant diversity tucked in the underground seed bank may reemerge.
“I would rather more people plant longleaf and have it in a pine straw operation with the plans of eventually converting it to a more open, natural stand that's managed with fire,” she said, “than to not plant longleaf.”
Post-raking
After raking, the pine forest floor looks like a lunar landscape. Grey dirt, hidden under a year of pine needles, is suddenly exposed to the elements.
A single straw harvest removes between five and 60 pounds of nitrogen per acre and between 0.5 and five pounds of phosphorus per acre. Compounded year after year, nutrient losses from pine straw harvesting are more than those from timber harvesting.
Pat Minogue is a forestry professor at UF and extension specialist in pine straw. His studies show nutrient deficiencies emerge after five to 10 years of harvesting. Pine roots and the microbes intertwined with them struggle to find phosphorus and nitrogen, causing tree growth rates to slow.
While multiple studies have looked at how nutrient deficiencies affect longleaf pines, almost none have explored how deficiencies affect the tiny, microbial powerhouses underground.
When nutrients are abundant, fungi transport nutrients including phosphorus and nitrogen to pine roots, store heavy metals and produce defense molecules against invading species. Pines in symbiosis with fungi have higher tolerance to temperature changes, higher carbon dioxide levels and drought, according to a 2024 study,
Scientists don’t yet know what long-term effects pine straw harvesting has on these nutrient cycles, according to Duke University mycologist Rytas Vilgalys.
They do know that raking up pine needles strips off nutrients, so “you have to put back what you take,” said Minogue, the forestry professor. “We might fertilize every five or 10 years, depending, but it’s all about monitoring what the tree needs.”
Minogue and his colleagues collect needle samples from multiple trees throughout the stand and analyze their chemical composition. They mix up a blend of nitrogen, copper, magnesium and potassium that addresses any nutrient deficiencies and apply it in the spring.
If pine straw is a microbial meal, fertilizer is a nutrient smoothie, supplying them faster but at a greater risk of runoff.
Get the timing right and “all those nutrients and the nitrogen will go into the tree, not into the water,” Minogue said.
A 2020 study in North Florida pine forests found fertilizing trees according to best management practices kept streams clean. Even when the authors applied four years worth of fertilizer in a single growing season, nutrient levels in the watershed didn’t increase.
Yet, come storm cell or high water, it’s still possible for fertilizers to wash into streams that feed an already-contaminated springshed.
Almost a million acres of longleaf pines are in private ownership in Florida, more than in state conservation lands. Only a fraction of these acres are harvested for timber or pine straw, making forestry’s ecological footprint seem small compared to the 9.7 million of acres in agriculture in the state.
It’s a footprint nonetheless.
“When we're raking, that's a disturbance. We're taking stuff away,” Minogue said, noting wildfires, floods and other natural phenomena do the same, but with one important difference.
“Nature's gonna take 150 years and we're gonna do it in 10 days.”
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