Public Trust Doctrine
Vera Aguayo López
The Public Trust Doctrine originated in the US courts more than 100 years ago and remains in force today. It could be defined as a jurisprudential elaboration that limits the capacity of a public authority to dispose —that is, to sell, transfer or any other fashions of concessions— of public property, generally public owned, although there are some authors defending its application on private goods (Delgado Schneider & Hervé Espejo, 2022), contending there are certain assets that must be protected and conservated for a free use of the citizenship, whose interests would take precedence over any other.
This doctrine had been already applied on several occasions by the US courts, but it was not until a 1982 ruling by the US Supreme Court that it attained the necessary significance for its subsequent development in case law (De Armenteras, 2020). The litigious object of that case was a stretch of submerged land off the coast of Chicago, whose titularity had been granted in 1869 to the Illinois Central Railroad company and which had been, years later, revoked by the legislator. The court stablished the legislator had no competency to transfer the property rights over the land, as they were held in a public trust, and, consequently, the State of Illinois had the duty to preserve and protect it for the public, in its capacity as its trustee, that is to say, its legal custodian.
In the eyes of the US Supreme Court, the legal relationship at issue consisted of the prohibition to the trustee to alienate those assets—that is, allow them to leave its patrimony—as its duty of preservation remained in force; this constituted the negative dimension of the obligation, in essence, a “not to do” obligation. Furthermore, existed the duty of protection of the assets, which is usually understood as the positive dimension, a “doing” obligation. In short, the Court held that the public should be able to enjoy certain “common goods” without private interests obtruding them. According to Professor Joseph Sax’s influential article, this ruling marked the implementation of a mechanism of judicial sceptisim judicial, suitable for activation whenever a public administration sought to restrict the public uses of a resource available for free use, or to subject that resource to private interests (1970, p. 490).
The prohibition on alienation has not been maintained, as the Public Trust doctrine has gradually allowed diverse forms of public-private management, although a restrictive interpretation of transfers and other types of contracts remains in place. Even so, this permissibility will always exclude permits that imply an effective loss of the Administration’s capacity to govern the resource (Sax, 1970, p. 489). Thus, we can outline more precisely what is at stake: a real and substantial decimation of the public’s rights of use and access, in favour of private interests. This way, rights may be granted to a company over, for example, a lake, provided that the activity aimed at serving private interests is limited to a small portion of the resource and that the public authority can continue to monitor compliance with the conditions governing such access and use (as in the case of Lake Wingra in Massachussets, Sax, 1970). It is also possible for private-sector involvement to be directed towards serving public interests through a concession, in which case the public authority will retain a duty to control it. In other cases, however, the prohibition on disposal will be total.
Generally, the public trust notion presupposes a concept of the commons similar to that posited in ancient Rome by Aelius Marcianus, who defined the commons as those things which “in accordance with natural law, (…) are common goods for all”. Particularly, according to Aelius Marcianus, the air, running water, the sea and its coasts were to be understood as such. Subsequently, these common goods were used as a principle that would give rise to the right of public use and access to navigable waters and forest lands, as enshrined in the English Magna Carta and the Charter of the Forest, in 1215 and 1217 respectively (Domènech, 2018; Mattei, 2013). This principle was adopted and developed by the late-feudal peasant revolts in opposition to the enclosures and privatisations carried put by the nobility and the clergy, as was the case with the German Anabaptists, who firmly advocated the community of goods under the slogan omnia sunt communia, “all things are common”, popularised by the radical theologian Thoman Müntzer (Drummond, 2025).
Along the same lines, though from a less drastic position, Sax states that “(…) one does not own a property right in water in the same way he owns his watch or his shoes, but that he owns only an usufruct-an interest that incorporates the needs of others.” (1970, p. 485). This fractured and limited conception of property differs considerably from the model of absolute private property that eventually prevailed and gained ground in economic liberalism, as defined by the British jurist William Blackstone: “the sole and despotic dominion which a man claims and exercises over external things in the world, to the total exclusion of the right of any other individual in the universe” (1765–1769, p. 2). The Public Trust doctrine therefore facilitates the approaches advocated by other legal institutions, such as ecological property, which are at odds with the neoliberal vision championed by Blackstone (Takacs, 2008).
The interpretation of what constitutes a public trust has continued to broaden as the doctrine has become increasingly linked to the protection and conservation of nature. In the well-known 1983 Mono Lake case, the California Supreme Court ruled that, in addition to the traditional uses of navigation and fishing, ecology and recreation should be included within the scope of the doctrine (Delgado Schneider & Hervé Espejo, 2022). Furthermore, in 1989 Edith Brown Weiss published a manifesto in favour of a planetary trust. According to her, present generations are custodians of the natural and cultural heritage for future generations and have a fiduciary duty to conserve it (1984, p. 581). Twenty-five years later, Mary Christina Wood, who identified the trust as a “fundamental attribute of sovereignty”, advocated for an obligation that included the entire “ecological res”: “atmosphere, air, soils and forests” (p. 89). Her Nature’s Trust, and in particular of the Earth’s atmosphere, has been invoked in recent cases such as Juliana et al. v. United States (Ryan, 2025).
Currently, the public trust doctrine focuses on the protection of the so-called “diffuse interests” (De Armenteras, 2020; Sax, 1970); that is to say, interests around which it can be difficult to organise a movement, for several reasons: they are shared by a majority of citizens, they are intergenerational in nature and, finally, they commonly clash with the extractivist and commodifying view of nature (see Capitalism and the ecological crisis and Extractivism in contrast to private, specific and immediate interests, which typically have greater influence in the legislative and administrative process, as well as more financial resources. Thus, the judicial approach on which this doctrine was based helps torelieve the power imbalance between interests and contributes to democratising the access to tools of territorial sovereignty. Furthermore, it has transcended the third power of the State and is now enshrined in several State constitutions, such as that of Pennsylvania (1971) and Hawaii (1978) (Delgado Schneider & Hervé Espejo, 2022).
However, the influence of this doctrine is not limited to the United States. In their comparative study, Callies and Smith show that it has not only been invoked by the highest courts in Canada, Kenya, Tanzania and Pakistan, but has also been explicitly included in the constitutions of South Africa, Uganda, Ecuador and Brazil. The example with the most implementation and effectiveness is found in India, where case law routinely applies it, drawing on the legacy of English common law, the Illinois Central Railroad and Mono Lake rulings, as well as on the right to life deemed in its constitution (2020). In 2022, Article 134 of Chile’s Constitutional Convention included a model of public stewardship of nature over “natural common goods”, inspired by the notion of the public trust. Delgado Schneider and Hervé Espejo argue that this model sought to reconcile ecocentric and anthropocentric perspectives, as it would oblige the state both to maintain the contributions of ecosystems to society (see Ecosystem services) and to guarantee their integrity (2022).
Under Spanish law, given that the role of judges is considerably more limited than in common law, the application of the Public Trust doctrine can only be achieved through legislation. Currently, Article 132 of the Spanish Constitution establishes a special legal regime for certain goods which, apart from the possibility of the law to designate them, are constitutionally stipulated and correspond to those typically covered by the doctrine in other countries: “the maritime-terrestrial zone, beaches, territorial waters and the natural resources of the economic zone and the continental shelf”. These are referred to as public State-owned assets, and the law defines them as inalienable, imprescriptible and unseizable.
The legal framework governing this category of assets was subsequently developed by the 33/2003 Law on Public Administration Assets, which, in its 29th Article, establishes the Administration’s duty of stewardship in respect to them. This article must be analysed in along with the guiding principle contained in Article 45 of the Constitution, which obliges public authorities to ensure the “rational use of all natural resources, with the aim of protecting and improving the quality of life and defending and restoring the environment…”. In this way, one can indeed discern a form of protection similar to a public trust. However, it has some significant limitations: i) the weak effectiveness of Article 45, as it is a guiding principle that does not entail the same transcendence as fundamental rights; ii) the fact that these public State-owned assets are viewed primarily from the anthropocentric perspective of ecosystem services; and iii) the State’s absolute dominance in the identification, regulation and management of these assets, at the expense of more democratic forms of management.
The latter does not necessarily imply that the public interest is taken into account. Proof of this can be found in the privatisation of public services, which is affecting dozens of states worldwide. On this point, authors such as Mattei (2013) and Lloredo (2023) argue that, in a neoliberal context, the state becomes an actor serving the interests of the market, which is economically more powerful. Ortiz García’s reasonable critique of public management models, in which the administration unilaterally decides what should be done, is therefore relevant here. The author advocates for the implementation of public-community governance models, where the questions of who decides and how decisions are made take on particular significance (2024, p. 86). These are models shared between the state, civil society and the market, which would allow for a management of the commons that is relocalised and grounded in the real needs of the territory, ecosystems and people, thus moving away from the much-criticised state-market duality (Ortiz García, 2024; De Armenteras, 2020; Lloredo, 2023; Mattei, 2013). An inspiring example can be found in the Rodotà Commission, a team of legal experts that sought to develop the legal framework for the commons in Italy, establishing them as the essential and necessary basis for the exercise of fundamental rights and, at the same time, creating a fiduciary duty incumbent upon the State (García López, 2021).
The creation of this type of legal institutions, alongside others such as land stewardship, could represent the future and legacy of the Public Trust doctrine, which has often focused excessively on the issue of public or private ownership rather than on how to encourage a qualitatively better relationship with the resources in question. Given the limitations of current legal systems, based on some exclusive and exclusionary property rights that facilitate accelerated ecosystem degradation in the service of capital accumulation (Mattei, 2013), it would be appropriate to include the dimension of collective management or use, which could make communities the true custodians of public assets.
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