What State, County and City is the property located? What was the purchase price of the property? Who is the open space easement in favor of? How does the affected the assessed property value?
Here in California, San Mateo County to be exact, we have two Open Space groups that obtain open space easements to preserve the either wild, or agricultural use of the land. One is a voter created, tax funded group, which is exempt from most taxes, and the other is a private nonprofit, which while exempt from some taxes, is not exempt from all.
An open space easement can greatly reduce the market value, therefore sales price of a property. Here in CA, property taxes are based on a percentage of the value of the property, which is based on the last sales price. Thanks to Prop. 13, the property is not reassessed until it is sold again.
Open space easements are often given in exchange of “consideration” (payment) – and taxes may be due on the easement estate.
Again, here in CA – if the open space agreement is in favor of a tax funded nonprofit, the easement itself is exempt from taxes.
Little hint, many counties (or parishes or whatever they are called in your state) have property tax statements available online. They can usually be looked up based on property address, but you may need to research to find the Assessor’s parcel number for the property.
As appsolute says, most open space tax exemptions or tax reductions are based on state or local law, so you would need to know the law in your area. Typically, the laws allow for the owner of a property to pay their property taxes at a reduced rate because they have agreed to keep the property undeveloped. In some cases, the property can be developed, if the developer is willing to pay substantial penalties. In Connecticut, some of those open space provisions are for a limited number of years and must be renewed.
There are often lower tax rates assessed on agricultural land, and an equine facility may or may not qualify as agricultural.
I know in my area, properties with open space easements are usually less valuable on the open market because the easements are generally "permanent" and prevent subdivision and land development (lowering future value). In many cases, the easements are held by a nonprofit open space group, who can restrict the use of the property.
For example, if a person buys a 100 acre property with a house on it and wishes to turn it into a boarding facility, they will have to work with the nonprofit who holds the easement to plan out the location of any future buildings, rings, pastures, trails, etc., usually to ensure that any natural resources are adequately protected. Another aspect of these easements, is that the property owners who have granted the easement, in exchange for tax breaks, often have to make some or all of the property accessible to the public, which also lowers the value of the property.
Another type of open space preservation/tax break in our area, is the reduction of property taxes for properties over a certain size. Should the property owner decide to sell the property to a developer to subdivide and develop, the property owner (or the developer) is required to pay the savings realized from the tax break for a pre-established number of years. This is a little less permanent and allows farm/land owners to pay less in taxes, but also allows them an out, should they decide that they need to sell the land at its highest value.
The special exception permit from the county probably has nothing to do with the easement. The special exception is basically a use that is permitted under the zoning laws, but there are special conditions that must be met in order to allow the use. For example, the owner may have needed to plant a property line buffer to reduce the noise and visual impact of the farm/ competitions on its neighbors.
For land under conservation easement in Virginia, the land will automatically qualify for land use valuation for property tax purposes, negating the need to apply for that valuation every year.
Easements are not just designed to prevent subdivision. Their purpose (if they're written to be consistent with state and federal law) is to protect conservation values. In my part of Virginia, that means protecting water quality, farming soils, and scenic viewsheds (among other things). Prohibiting subdivision, limiting where buildings can be constructed, and limiting the commercial and industrial use of properties are all things that help protect those conservation values.
Likely, the former owner of the property who placed the land in easement received federal, and possibly state, tax incentives for donating the easement. They took a hit on the value of the property, and were partially compensated through those benefits. The income tax benefits would not transfer to the new owner, but as I said, in Virginia, the new owner would automatically qualify for land use valuation.
Feel free to PM me if you're in Virginia and have other questions. I work for a large land trust in Virginia and would be happy to answer questions.
The person putting the restrictions on the land will get a federal tax benefit, so that applies to all states. Then, the law varies within the states. In NY there is now a tax credit up to $5,000 for land with conservation easements on it.
Any restriction will be filed with the land's deed, so if you want to know the details you can get them that way. As Hinderella says, in Connecticut the restriction can be limited to a period of years, while in NY it is permanent. Look at the easement itself to see what it says.
If you need more info then asking your local land trust would be a good place to start.
(I placed conservation easements on my farm, and sit on the Board of our County's land trust).