**1. Introduction**

Research in historical ecology is cross-disciplinary, as the core objectives are to understand how interactions between societies and environments develop through time, and how these interactions have formed cultures and landscapes, e.g., [1–4]. Thus, historical ecology integrates topics from the humanities (e.g., history, archaeology, anthropology) and the natural sciences (e.g., ecology, vegetation science). These different academic disciplines have their own concepts and theories, as well as their own ways of understanding causation, i.e., why something happens, e.g., [5,6]. Accordingly, there is a need for conceptual frameworks with the ability to address questions and problems relevant for both the humanities and natural sciences, and also promote communication among researchers from these different disciplines.

Niche construction theory [7] is one framework that has been suggested as suitable for this purpose [8,9] (see Section 2 below). The overarching aim of this paper is to examine this suggestion, applied to the historical ecology of Scandinavian domesticated landscapes based on infield systems. Infield systems refer to a particular way of managing land and structuring land use, established during the early Iron Age, i.e., from the first centuries BC onwards [10–12]. Land was divided into infields (Swedish: *Inägor*) and outland (Swedish: *Utmark*). Infields were enclosed areas located near settlements incorporating semi-natural hay-meadows (i.e., manipulated, but comprising a native pool of species) used for production of livestock fodder, and permanent crop fields. The outland was located outside enclosures and was used mainly for livestock grazing, but also for collection of other

**Citation:** Eriksson, O.; Arnell, M.; Lindholm, K.-J. Historical Ecology of Scandinavian Infield Systems. *Sustainability* **2021**, *13*, 817. https:// doi.org/10.3390/su13020817

Received: 18 December 2020 Accepted: 12 January 2021 Published: 15 January 2021

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**Copyright:** © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

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resources. The outland may have been open land, but was probably mostly forest, or at least land with some cover of trees. Despite many later changes in organization and managemen<sup>t</sup> of land, for example concerning agricultural implements, crop rotation, land ownership, and land reforms, the key elements of infield systems were maintained until the modernization of agriculture and forestry initiated mainly during the 19th century. In present-day landscapes, there are plenty of legacies from historical infield systems, for example wood pastures [13] and semi-natural grasslands [14]. These remnant habitats are often species-rich, and are a concern for conservation biology. Forests today are mostly used for production of pulp and timber, and legacies of former land use are generally overlooked in forests as compared with the semi-natural grasslands, despite the fact that outland forests were an essential component of the historical infield systems [15].

Several previous studies have dealt with different aspects of the remains of old cultural landscapes in Scandinavia, for example the origin of infield systems, e.g., [16,17], the origin of meadow managemen<sup>t</sup> [18], land-use changes during the last century [19], and historical perspectives on species-pools and species richness in semi-natural grasslands, e.g., [14,20–26].

In our examination of the historical ecology of infield systems, we cover the whole c. 2000 years of these systems' existence, including remaining legacies of infield systems in today's landscapes. A brief introduction to niche construction theory is useful before we present the specific objectives and questions.

#### **2. Niche Construction as a Conceptual Framework for Historical Ecology**

Niche construction theory [7,27] is based on the idea that there is a continuously ongoing interaction between a niche-constructing agen<sup>t</sup> (typically a species) and its environment. Niche construction is defined broadly as a process by which a species alters its own ecological niche, or the niches of other species, and the feedback of these alterations to the niche-constructing species. There are two different aspects of niche construction, the alteration of the environment (the niche) by a species (which may affect many other species as well), and the response by the niche-constructing species to the altered environment [27]. The ecological niche refers to resources and requirements utilized by the niche-constructing species, or any other conditions affecting the species. Two key points in niche construction theory are that as species alter their environment, they not only respond to it, and that there is a reciprocal causation, generally meaning that the processes affecting change in the niche-constructing species and in the environment are mutually influencing each other [28]. Over time, along with changes in the niche-constructing species, there is an ecological inheritance (memory) of past environmental alterations.

Niche construction may apply to any species, but when focusing on humans, it has been termed cultural niche construction or human niche construction, e.g., [8,29,30]. In human niche construction, cultural changes are mediated by learning, memory, and knowledge transfer, i.e., components of cultural evolution, e.g., [31], or, in general terms, expressions of learned knowledge [27]. Since the dawn of the human species, people have been able to manipulate natural resources; agriculture was the big leap in such a manipulation, and the development of early agriculture and domestication of plants and animals has been considered as a prime example of human niche construction, e.g., [29,32,33]. In addition, human niche construction has, for example, been applied to a general understanding of the history of human societies, e.g., [34], and to impacts of the human society on other biota, e.g., [35].

Analogously to domesticated plants and animals, one may consider whole landscapes as domesticated, e.g., [36], thus incorporating also different ways of organizing and managing land, i.e., how land use is conducted and how it is spatially structured across landscapes. A starting-point for this paper is the notion that niche construction theory would be suitable for handling the processes underlying how landscapes are domesticated. A key question is thus whether there is a feed-back loop between the changing landscapes and how people conceive, utilize, and manage land.

There has been some disagreement about whether human niche construction necessarily reflects human intentionality. Hodder [37,38] criticized human niche construction theory for its presumed assumption of goal-directed behavior of humans to improve the resource base of societies. "If humans deliberately enhance their environments, it is not because they just decide to do that or because they have been forced to by unexplained increases in population or by climate change, but because they have become caught up in particular bio-socio-material entanglements that make specific intentions and adaptive responses possible" [37] p. 172. Indeed, one of the advocates for human niche construction clearly presumes goal directed intentions: "Humans utilize their capacity for goal-directed behavior to engineer environments in ways that enhance the productivity and predictability of economically important species" [33] p. 326. In a sense, the whole idea with niche construction theory is that a species (e.g., humans) modify its own niche by manipulating resources and environment. However, there is no reason why human niche construction necessarily reflects human intentions. Actions can be goal-directed and intentional, but they could as well be unintentional, with unexpected consequences.
