I'm just speculating about the economics here, and it kinda sounds like a high-school daydream solution, but I feel like you could artillery an area with some munitions filled with seeds and just rely on the natural rate of survival given a uniform-enough distribution of an airburst shell.

Some quick insomnia driven commentbox math

One 155mm shells has about ~11kg of payload capacity and a range of 25km. [0]

100 panderosa pine seeds is ~4g [1]

11kg means 275000 seeds / shell.

You'd plant pines at density of around 1000/acre [2]

The biggest question is seed survivor rates of being planted by artillery but let's consider a survivorship of 2%...

275000 * 0.02 = 5500 Surviving trees, or effective planting over 5.5 acres / shell.

A modern autoloading artillery can launch ~70 shells per hour. [3]

You'd have an effective planting rate of 385 acres / hour.
Or 1.54 km^2 / hour. 13400 km^2 / year.

With a single artillery that has a radius of 25km you get an area of 1900km^2.

Survivorship is a major bound here

Seed Survival Rate: 2%

9,504,000 trees / day

13400 km^2 covered / year

But at 1%

4,752,000 trees / day

6700 km^2 covered / year

In any case 100k/day seems quaint when you can plant nearly 10 million.

Assuming 2% survivorship, covering 1900km^2 at 1.54km^2/hour you can plant the entire effective area in ~55 days, as long as you keep loading the thing.

Comparing costs to this drone

An Archer artillery unit is ~$4,200,000 [4]
1 155mm shell is ~$500 [5]

It takes ~37 shells to plant 100k trees which means ~$19000 for munitions.

Using that $400 million dollar fund entirely for this idea

The fund intends to protect 5 million hectares, or 50000 km^2. [6]

Let's say we want to finish this endeavour within 2 years, and assume our effective time spent planting versus moving and getting the project off the ground is 50%, so we get 1 effective year of dedicated planting time.

One artillery piece can plant 13400km^2 / year.

50000km^2 total area / 13400km^2 coverage per year = ~4 pieces of artillery.

Let's buy 3x what we need so we can just flip them out when they break down and have some spares in case repairs/maintenance take a while.

12 pieces of artillery is ~$51,000,000

You need ~46 shells to cover 1km^2

50,000*46 = 2,300,000 shells

2,300,00 shells at $500 / shell = $115,000,000 for munitions

Artillery + munition cost is $166 million.

Throw $10mil each at R&D + Testing, Logistics, and Administration/Staff and you're at $196 million with more than half of the fund left over.

Hmmmmmmm......

I dunno it feels like it would be worth taking a couple million USD to borrow an Archer from Sweden and rig up a burst shell to see if it works at all.

It has some precedent: there have been some shotgun shells filled with seeds before that actually worked [7]

[0] https://en.wikipedia.org/wiki/M795
[1] https://www.fs.fed.us/pnw/olympia/kids/WASeeds.pdf
[2] https://www.nrcs.usda.gov/Internet/FSE_DOCUMENTS/nrcs141p2_0...
[3] https://en.wikipedia.org/wiki/Archer_Artillery_System
[4] http://www.army-guide.com/eng/product2819.html
[5] http://www.pmulcahy.com/ammunition/howitzer_rounds.html
[6] https://www.weforum.org/press/2017/01/400-million-fund-launc...
[7] http://www.businessinsider.com/flower-shell-shotgun-gardenin...