Some very popular YouTubers got together over a year ago to raise money to plant 20 million trees. From what I could tell, people actually doing the planting where going out with shovels and seedlings.
My supposedly bright idea is to take the appropriate kinds of seeds and and throw them out of helicopters right before a rainstorm so that they tend to get buried and not just picked off by birds. This would seem to be much more cost-effective. Seeds aren’t naturally distributed to make trees at ideal distances anyway, and this would cover a lot more ground and get more trees planted in one season I would think.
The odds of any seed ending up as a full grown tree is extremely low and random spreading doesn’t help that. Seedlings have a better chance, largely because you can select the location for them, but then it takes more time and expense to plant them in those locations.
However, your idea is being done because seeds can be dropped by the millions. I believe they make a kind of module of seeds and nutrients to drop from planes in large numbers. I recall seedlings being dropped by planes in the past also where the seedling was attached to a little spike that would stick into the ground and hold up the seedling until it could take root.
ETA: Here’s an article on seedling drops. So far all the info I’ve seen is about seedlings, although often the devices dropped are called ‘seed bombs’.
I’m sure there are areas where seeds lying on the ground before an rainstorm tend to get buried, but that is definitely not how things are everywhere. In some the seed will still be lying on the surface after the storm, and in others it will be washed away and end up in a stream and then a river.
That said, if the goal is reforestation spreading seed could be cost effective if you have a cheap source of seeds. And I expect tree seeds are generally so expensive, growing seedlings in nurseries is the cost effective use of them.
Norwegian forestry, where cheap unskilled labor is harder and harder to come by, has moved towards leaving seed trees when cutting an area, allowing “natural” reforestation of the temporary clearings.
Direct seeding has/was done on a large scale in the U.S… It comes with a whole lot of problems. It’s a buffet for any animal in the area and some animals, like rodents, will reproduce in great numbers because of the temporary artificial food source. Damping-off fungi and pathogens can cause mortality of the seed in cool moist conditional.
The biggest issue though is that seed costs a lot of money. To properly collect seed you need to get cones at the right time of year, from the correct seed sources in the right seed zones. A lot of the cost of seedlings is in the seed collection and tracking.
To collect the cone you can climb the tree, cut down the tree, or shoot the cones off with shotguns. All the bags of cones have to be labeled and tracked. The cones have to be transported to heater/dryers and the seed has to be released, cleaned, and again labeled and tracked.
After everything, you have ten pounds of seed. You can sow a few pounds of it and get 100,000 seedlings to plant with a much higher survival. Also you can store the remaining seed in the freezer for the coming years. Many species have viable seed after 20 years of storage.
From a silvicultural perspective seedlings are great because you can gain a few years on the rotation (Planting a 2 year old seedling the spring after harvest). Less down time for shrubs, grasses and invasives. Less spraying or site prep. You can take advantage of post harvest microsites with partial shade, and exposed mineral soil.
I forget to add some of the typical reasons for planting.
You control the species mix, and the spacing. You can plant on a 10 ft by 10 ft spacing and the trees probably won’t compete until they are mature.
I recall seeing one scheme where the seeds dropped from the air would be embedded in a cardboard shape with hooks at each end, so when dropped they would “grab hold” of anything on the ground like roots or grasses, minimizing he chance of being washed away; and the seedling would be minorly protected from being eaten since it was hidden in a biodegradable package; The cardboard was shaped to form a minor dam if it ended up in a place with erosion, so that silt might build up against it and help bury the seed.
But I suppose for that amount of trouble, why not drop small seedlings instead? Or plant them manually? I think this was just some clever idea that never got used.
Plus, someone has to manually embed the seed(s) in your cardboard-hook-thingie, since I doubt that’s been automated by machines.
So you get labor costs either way.
Better and ultimately more effective (in terms of total trees living after a few years) to house the seeds in greenhouse environments, then hand-plant the seedlings.
Or outsource the planting labor to homeowners - provide free or low-cost tree seedlings to random citizens willing to select the site, dig the hole, provide followup care and watering: