Department of Applied Biological Sciences, Ghent University, 9000 Gent, BELGIUM.
After realizing the impact of its human/industrial system on nature and indirectly on itself, mankind became aware of its need for a sustainable relationship with nature. To obtain this sustainable relationship, assessments are required to unravel which managements of human/industrial and natural systems are best suited for that purpose. In our study, we have attempted to assess the environmental aspect of this sustainable relationship in a better manner, this exemplified for our relation with forest ecosystems. Latter ecosystem is of major importance as it covers 30% of the land surface and provides essential services to mankind (FAO, 2010). A challenge we wanted to overcome in order of revealing best practices, is to include the dynamic responses of natural systems, e.g. effect of thinning on forest growth and thus carbon dioxide uptake. Practically, methodological improvements were performed and the improved methods were applied to one specific forest, an intensively managed Scots pine stand in Belgium (Europe).
Firstly, a framework was developed with which the environmental impact and benefit of an integrated human/industrial-natural system can be assessed (chapter 2). We focus here on the life cycles of products, such systems are the collections of the various processes needed to produce, use and dispose a product. A case study was performed on the impact/benefit caused by the life cycle of 1 m3 sawn timber, encompassing wood growth in the Scots pine stand and industrial processing into sawn timber, usage of latter and burning of the wood. The results indicate that the (wood growth in the) forest was responsible for the larger share of the environmental impact/benefit. As the forest was intensively managed, this implied a biodiversity loss compared to a natural system. This loss, representing damage to ecosystem quality, was responsible for almost all of the diversity loss over the complete life cycle: 1.60E-04 species*yr m-3 sawn timber. Next to that, since the Scots pine stand is a plantation and managed intensively, the growth of natural vegetation was prevented, leading to the main loss of natural resources per amount of sawn timber, expressed in exergy (the amount of useful energy obtainable out of a resource, e.g. exergy content of biomass): 3.99E+02 GJex m-3. Regarding impact on human health over the life cycle, a total prevention of loss of 0.014 healthy life years m-3 sawn timber is obtained. This health remediating effect could be mainly attributed for 77% to the deposition of particulate matter < 2.5 μm (PM2.5) on the vegetative canopy of the Scots pine stand, and to CO2 uptake for the other share. This case study revealed the potential importance of considering impact of ecosystems in environmental sustainability assessment.
As PM removal appeared to be such a relevant provided forest service, we developed a model to calculate PM removal by a forest ecosystem (chapter 3). More specifically, we quantified the amount washed off via rainfall from the plant surface after net-deposition on it. For the Scots pine stand, this resulted in a removal of 7.38 kg PM2.5 ha-1 yr-1 in the year 2010. Integrating this model into a larger forest ecosystem growth model ANAFORE (Deckmyn et al., 2011, 2008), allowed us to calculate PM removal while the forest grows under different conditions. This model was run for different airborne PM2.5 concentration scenarios for the Scots pine stand during the period 2010-2030. Estimated avoided health costs due to PM2.5 removal of 915-1075 euro ha-1 yr-1 were obtained for these scenarios. Comparing these values with a rental price of 143.6 euro ha-1 yr-1 (based on the selling price for the Scots pine stand of 16000 euro ha-1, obtained from the current owner Agency of Nature and Forest, and on a local land buy to rent price ratio) possibly illustrates the for now underrating by society of this (ecosystem service delivered by the) forest.
Additionally, Ecological Network Analysis (ENA) was improved for application in environmental sustainability assessment (chapter 5). ENA is a methodology to study and characterize flux networks among defined ecosystem compartments over a certain period of time via indicators, e.g. cycling of nitrogen between different trophic levels of a forest ecosystem over a year. Main reasons for improvement and application of ENA are that a change in ENA-indicator can represent an impact on ecosystems, as an alternative for diversity loss, and ecosystem networks, studied via ENA, may be easily included in environmental sustainability assessment because of the same mathematical backbone. However, prior to application in environmental sustainability assessment the following matter should be addressed. There are no standards yet for the different choices in the ENA methodology, which can have an influence on the indicator values. Hence, defining such standards is a next important research step.
Finally, in light of the overall aim of the PhD, we performed an environmental impact assessment and monetary ecosystem service assessment of the Scots pine stand under different management and environmental change scenarios from the year 2010 up until 2090 (chapter 4). For the monetary valuation of ecosystem services, specific monetary values valid for Flanders were used, e.g. 150 euro kg-1 PM2.5 removed (Broekx et al., 2013; Liekens et al., 2013b). Disservices (e.g. NOx emission by the forest) are also considered and attributed negative economic values to them. An environmental impact assessment methodology was applied using our previous framework. In that particular framework the uptake of harmful compounds such as CO2 is considered (Schaubroeck et al., 2013), chapter 2, thus the benefit and the damage done by the Scots pine stand to mankind and nature was assessed. The addressed flows/ecosystem services in this analysis are: PM removal (PM2.5 and PM2.5-10), freshwater loss, CO2 sequestration, wood production, NOx emission, NH3 uptake and nitrogen pollution/removal. Note that is just a limited number of services/flow, e.g. freshwater loss due to evapotransipartion is considered a disservice while we did not consider the benifical effect of evapotranspiration: the counteracting of global warming by surface cooling (Bonan, 2008).
The management and environmental change scenarios represent the possible (indirect) influence we have on the forest. The ANAFORE model results of these scenarios therefore stand for the potential (indirect) effects which might occur through our actions on the forest, e.g. less wood growth by the forest induced by too much harvest. In latter model, the new PM removal submodel was integrated (chapter 3). In practice, three management and three environmental change scenarios were applied, resulting in nine overall scenarios.
Following main results were obtained. The monetary valuation results highlight the importance of services provided by the forest, with a total yearly average of 361-1242 euro ha-1 yr-1. PM2.5 removal is the key service with a value of 622-1172 euro ha-1 yr-1. This is a factor 2.5-8.6 higher than the earlier mentioned rental price. Concerning environmental impact assessment, with CO2 sequestration and thus the prevention of its damage as the most relevant contributor, a yearly average prevention in loss of healthy life years of 0.014 to 0.029 ha-1 yr-1 is calculated. There is however a yearly average biodiversity loss of -1.09E-06 to 7.3E-05 species*yr ha-1 yr-1, mostly through the intensive land use but counteracted by CO2 sequestration with 46-101%. The differences between climate scenario results are inferior to the discrepancies induced by the management scenarios. Regarding environmental change we can conclude that the less pollution of mainly PM2.5 through more stringent legislation, the less there can be pollution removal, an ecosystem service, and thus overall value provided. Concerning management scenarios, both approaches favor the use of the least intensive management scenario mainly since CO2 sequestration and PM removal are higher for these, latter induced by a higher needle surface area per ground area. Our framework has thus resulted in the clear selection of the best management scenario of the considered ones and this for the accounted ecosystem services/flows.
Overall, different methodological aspects were improved. Though, there are still a lot of methodological improvements needed. However during this study, it became clear that there was a more urgent issue, the lack in a clear consensus on which matters to prioritize in sustainability assessment. The most important question concering this topic is: ― ‘Which is more important to maintain: man or nature?’. A simple conceptual framework was proposed for sustainability assessment in which the total impact/benefit on human well-being was put central again, in correspondence with the original definition of sustainable development: ― ’the development that meets the needs of the present without compromising the ability of future generations to meet their own’ (WCED, 1987).