Land Use, Freshwater Flows and Ecosystem Services in an Era of Global Change

The purpose of this thesis is to analyse interactions between freshwater flows, terrestrial ecosystems and human well-being. Freshwater management and policy has mainly focused on the liquid water part (surface and ground water run off) of the hydrological cycle including aquatic ecosystems. Although of great significance, this thesis shows that such a focus will not be sufficient for coping with freshwater related social-ecological vulnerability. The thesis illustrates that the terrestrial component of the hydrological cycle, reflected in vapour flows (or evapotranspiration), serves multiple functions in the human life-support system. A broader understanding of the interactions between terrestrial systems and freshwater flows is particularly important in light of present widespread land cover change in terrestrial ecosystems. The water vapour flows from continental ecosystems were quantified at a global scale in Paper I of the thesis. It was estimated that in order to sustain the majority of global terrestrial ecosystem services on which humanity depends, an annual water vapour flow of 63 000 km3/yr is needed, including 6800 km3/yr for crop production. In comparison, the annual human withdrawal of liquid water amounts to roughly 4000 km3/yr. A potential conflict between freshwater for future food production and for terrestrial ecosystem services was identified. Human redistribution of water vapour flows as a consequence of long-term land cover change was addressed at both continental (Australia) (Paper II) and global scales (Paper III). It was estimated that the annual vapour flow had decreased by 10% in Australia during the last 200 years. This is due to a decrease in woody vegetation for agricultural production. The reduction in vapour flows has caused severe problems with salinity of soils and rivers. The human-induced alteration of vapour flows was estimated at more than 15 times the volume of human-induced change in liquid water (Paper II).

Marine Seaweed Invasions : the Ecology of Introduced Fucus evanescens

Biological invasions are an important issue of global change and an increased understanding of invasion processes is of crucial importance for both conservation managers and international trade. In this thesis, I have studied the invasion of the brown seaweed Fucus evanescens, to investigate the fate and effect of a perennial, habitat-forming seaweed introduced to a coastal ecosystem. A long-term study of the spread of F. evanescens in Öresund (southern Sweden) showed that the species was able to expand its range quickly during the first 20 years after the introduction, but that the expansion has been slow during the subsequent 30 years. Both in Öresund and in Skagerrak, the species is largely restricted to sites where native fucoids are scarce. Laboratory experiments showed that the restricted spread of F. evanescens cannot be explained by the investigated abiotic factors (wave exposure and salinity), although salinity restricts the species from spreading into the Baltic Sea. Neither did I find evidence for that herbivores or epibiota provide biotic resistance to the invader. On the contrary, F. evanescens was less consumed by native herbivores, both compared to the native fucoids and to F. evanescens populations in its native range, and little overgrown by epiphytes. Instead, the restricted spread may be due to competition from native seaweeds, probably by pre-occupation of space, and the establishment has probably been facilitated by disturbance. The studies provided little support for a general enemy release in introduced seaweeds. The low herbivore consumption of F. evanescens in Sweden could not be explained by release from specialist herbivores. Instead, high levels of chemical anti-herbivore defence metabolites (phlorotannins) could explain the pattern of herbivore preference for different fucoids. Likewise, the low epibiotic colonisation of F. evanescens plants could be explained by high resistance to epibiotic survival. This shows that colonisation of invading seaweeds by native herbivores and epibionts depends on properties of the invading species. The large differences between fucoid species in their quality as food and habitat for epibionts and herbivores imply that invasions of such habitat-forming species may have a considerable effect on a number of other species in shallow coastal areas. However, since F. evanescens did not exclude other fucoids in its new range, its effect on the recipient biota is probably small.

Global trade, food production and ecosystem support : Making the interactions visible

Modern food production is a complex, globalized system in which what we eat and how it is produced are increasingly disconnected. This thesis examines some of the ways in which global trade has changed the mix of inputs to food and feed, and how this affects food security and our perceptions of sustainability. One useful indicator of the ecological impact of trade in food and feed products is the Appropriated Ecosystem Areas (ArEAs), which estimates the terrestrial and aquatic areas needed to produce all the inputs to particular products. The method is introduced in Paper I and used to calculate and track changes in imported subsidies to Swedish agriculture over the period 1962-1994. In 1994, Swedish consumers needed agricultural areas outside their national borders to satisfy more than a third of their food consumption needs. The method is then applied to Swedish meat production in Paper II to show that the term “Made in Sweden” is often a misnomer. In 1999, almost 80% of manufactured feed for Swedish pigs, cattle and chickens was dependent on imported inputs, mainly from Europe, Southeast Asia and South America. Paper III examines ecosystem subsidies to intensive aquaculture in two nations: shrimp production in Thailand and salmon production in Norway. In both countries, aquaculture was shown to rely increasingly on imported subsidies. The rapid expansion of aquaculture turned these countries from fishmeal net exporters to fishmeal net importers, increasingly using inputs from the Southeastern Pacific Ocean. As the examined agricultural and aquacultural production systems became globalized, levels of dependence on other nations’ ecosystems, the number of external supply sources, and the distance to these sources steadily increased. Dependence on other nations is not problematic, as long as we are able to acknowledge these links and sustainably manage resources both at home and abroad. However, ecosystem subsidies are seldom recognized or made explicit in national policy or economic accounts. Economic systems are generally not designed to receive feedbacks when the status of remote ecosystems changes, much less to respond in an ecologically sensitive manner. Papers IV and V discuss the problem of “masking” of the true environmental costs of production for trade. One of our conclusions is that, while the ArEAs approach is a useful tool for illuminating environmentally-based subsidies in the policy arena, it does not reflect all of the costs. Current agricultural and aquacultural production methods have generated substantial increases in production levels, but if policy continues to support the focus on yield and production increases alone, taking the work of ecosystems for granted, vulnerability can result. Thus, a challenge is to develop a set of complementary tools that can be used in economic accounting at national and international scales that address ecosystem support and performance. We conclude that future resilience in food production systems will require more explicit links between consumers and the work of supporting ecosystems, locally and in other regions of the world, and that food security planning will require active management of the capacity of all involved ecosystems to sustain food production.