V. Are We All Mutualists?
At the most general and theoretical level, Lockeanism and occupancy-and-use would seem at first glance to be poles apart in their requirements for maintaining ownership of a piece of land. Mutualists require ongoing occupancy and use as a criterion for ownership, whereas Lockeans consider a piece of land permanently appropriated by initial admixture of labor — regardless of whether occupancy is maintained — until the owner quits claim to it through death, gift or sale.
But in practice, any practical Lockean system in the real world will have to include standards for constructive abandonment, lest a major part of the world’s land wind up in a status analogous to “orphan works” under copyright law (that is, presumed to still be somebody’s private property, despite being vacant and unused for decades, because it was once somebody’s property and ownership was never formally transferred to someone else). Even if the owner explicitly declared their intent to return and resume possession at some indefinite future time, it would eventually be necessary after some duration for the community to assume that the owner had changed their mind, or perhaps died, without notifying anyone; otherwise appropriation would be irreversible and a growing share of vacant land whose owners had left it would fall under the dead hand of presumed ownership for all future time.
So — again — in practice, the fact that standards for constructive abandonment would be to a large extent a matter of local convention, with a wide range of possible thresholds for abandonment from the most liberal to the most stringent, means that Lockeanism and occupancy-and-use really differ only in degree rather than in kind. Or to put it another way, Lockeanism is occupancy-and-use, but with somewhat more lenient occupancy requirements for maintaining ownership than most explicit occupancy-and-use advocates call for.
Bill Orton, somewhat unusually for a self-described anarcho-capitalist, described it as differing degrees of “stickiness.”
In both systems [i.e., “sticky” (Lockean) and “non-sticky” (socialist/usufruct)], in practice there are well-known exceptions. Sticky property systems recognize abandonment and salvage; usufruct allows for people to be absent for some grace period without surrendering property, and of course allows trade. You might even see the two systems as a continuum from high to low threshold for determining what constitutes “abandonment.”
Lockean and mutualist property are “the same thing … with different parameters” for the length of time necessary to establish abandonment. 
And the wide range of possible stickiness standards in non-Proviso Lockeanism itself is evidenced in a striking manner by the fact that the non-Proviso Lockean majority of left-libertarians at ALL and C4SS tend to have significantly lower standards for constructive abandonment, and to give occupants of land left out of use for a considerable time a greater benefit of the doubt, than is typical of those on the libertarian-right.
It seems likely that land property regimes will be polycentric to the extent that majority mores vary from one locality to another, because absent a single legal regime enforced by a large territorial state, property claims will depend on the willingness of local communities to enforce them. And in a polycentric legal regime in which all enforcement is financed endogenously (by the beneficiaries, as opposed to externalizing the cost on society at large through exogenous funding from general revenues), the enforceability of one’s property claims will depend on whether the potential economic value of the property is sufficient to justify enforcement costs.
Non-state enforcement of property rights regimes is subject to the same prohibitive transaction costs that James Scott attributed to the enforcement of state governance in non-state spaces, in The Art of Not Being Governed. All forms of governance carry transaction costs. States (and state-protected economic ruling classes) differ mainly in their ability to shift those costs to third parties, and thereby make the enforcement of their authority and privileges artificially cost-effective.
So for example, a mutual defense association or an-cap private security firm in a Lockean community will probably have an exclusion clause against enforcing the collection of absentee landlord rent against an occupant in a mutualist community, or protecting landowners against collection of land rent in a Georgist community — or for that matter, restoring a dispossessed factory owner in a syndicalist or communist community. Likewise, mutual defense associations in occupancy-and-use communities will likely refuse to protect occupants of land in a Lockean community against rent collectors.
And occupancy-and-use is the likely default for most thinly populated rural areas simply because the likely economic potential of land in such places will be insufficient to justify the costs of enforcing absentee title against squatters.
I consider a system avowedly based on occupancy-and-use, in which a piece of land becomes open for homesteading after some reasonable period of vacancy, to be the most desirable because it explicitly takes occupancy-based ownership as its goal and facilitates it with a minimal amount of ajudication or other complications. Nevertheless, I believe that a principled Lockean system with even a relatively high time threshold and burden of proof for constructive abandonment, by opening up all vacant and unimproved land for immediate homesteading, would go a long way towards reducing the average rent of land and enable a significant share of the population to live free from rent altogether. The combined effect would increase the difficulty of acquiring large contiguous tracts of land, and greatly reduce the “compound interest” effect of land rent growing on itself. In so doing, even a strictly Lockean regime would make the engrossment of a majority of the land by absentee landlords much less likely than at present.
And that’s even more true of left-libertarian Lockeans, who from what I’ve seen, support relatively low thresholds of abandonment that favor the rights of occupants in cases like the South Central Farm in Los Angeles — not to mention placing high burdens of proof on ownership claims to things like vacant lots in urban areas.
So in practical terms, I see mutualists and principled Lockeans as united by more things than divide us.
1. Quoted material originally appeared on message boards at Anti-State.com. It’s quoted here from Chapter Five of my book Studies in Mutualist Political Economy (2007).