Chapter 6 Effects Of Global Household Proliferation On .

6 Effects of Global Household Proliferation on Ecosystem ServicesTable 6.1 (continued)Type of ecosystem serviceCrop pollinationPest and disease controlSupporting servicesNutrient cyclingSoilSeed dispersalPrimary production109Impact of household proliferation (examples)Reduces habitat for pollinators (Hansen et al. 2005); raiseshoney bees that can enhance pollination (Ogaba 2002)Reduces habitat for natural enemies, spreads pests anddiseases (e.g., by introducing garden plants) (Schölleret al. 1997), and creates habitat for pests and diseases;creates habitat for natural enemies and destroys habitatsfor pests and diseases (Altieri 1993)Disrupts nutrient cycling through land conversion (to housesand infrastructure such as roads and other buildings) andcreation of barriers (Kaye et al. 2006)Uses soil as household construction material, and affectschemical and physical properties of soils throughconstruction of associated infrastructure (e.g., roads,buildings) (Graf 1975)Prevents seed dispersal by forming impermeable surfaces(e.g., houses, roads) (Coffin 2007); facilitates seeddispersal through travel and shipping (Lodge et al. 2006)Damages and occupies areas for primary production throughland conversion (Liu et al. 2001)Cultural servicesCultural, aesthetic, intellectual and Destroys areas and remnants of cultural and spiritualspiritual inspirationsignificance through construction of housing andassociated infrastructure (Marsh 1992)Recreational experiencesDestroys through construction and occupies areas suitable(including ecotourism)for ecotourism (Anderson and Potts 1987)The impacts of household proliferation are different from those of population growth becausepatterns of household proliferation and population growth are not the same. For the sake ofsimplicity, the impacts are phrased in a linear manner, but the actual relationships are much morecomplex and are often nonlinear with thresholdsfor house construction and furniture (Liu et al. 2005), and more fuelwood forheating and cooking. As to fuelwood consumption, a decrease in household sizeincreases fuelwood consumption per capita (An et al. 2001) (Fig. 6.4). This isbecause houses with different numbers of people used similar amounts of fuelwoodfor heating. In terms of cooking, more fuelwood is consumed in a large householdbecause more food needs to be cooked for more people, but the efficiency percapita is still higher in a larger household if other conditions are similar (Liu et al.2005).On the other hand, households can be ecosystem service producers. Forexample, some households raise honey bees that are major pollinators (Ogaba2002), while some other households cultivate plants and flowers in their yards tofeed pollinators that can help enhance food production. Some households createhabitat for wildlife species and enhance biodiversity, which can generate a variety

110J. LiuFig. 6.4 Fuelwood consumption per capita under different household sizes (Liu et al. 2005)of ecosystem services. Some households also plant trees and protect forests thatsequester CO2, such as those who reduce greenhouse emissions from deforestationand forest degradation (REDD) (The United Nations Collaborative Programme onReducing Emissions from Deforestation and Forest Degradation in DevelopingCountries 2012), and who monitor forests from illegal harvesting, such as inChina’s National Forest Conservation Program (Liu et al. 2008). However, thesupply of ecosystem services from households is much less than the demand forecosystem services. As a result, ecosystem services continue to degrade rapidly(MA 2005).6.3.2 Impacts on Ecosystem ServicesHousehold impacts on ecosystem services are enormous (Table 6.1). In this section, two examples are given to illustrate the impacts.6.3.2.1 Impacts of Household Proliferation on Forestsand Panda HabitatHousehold proliferation is an important contributor to the significant changes inforests and panda habitat in Wolong Nature Reserve. From 1965 to 1997, forestcover and suitable panda habitat in Wolong was substantially reduced (Liu et al.2001) (Fig. 6.5) because people had used ecosystem services (e.g., fuelwood andtimber) in areas that pandas use. Both people and pandas prefer areas that are nottoo steep. The suitable panda habitat has been much fragmented by humanactivities (e.g., fuelwood collection, timber harvesting, road construction, andhome building). With increases in the total amount of fuelwood consumption and

6 Effects of Global Household Proliferation on Ecosystem Services111Fig. 6.5 Change in theamount of panda habitat inWolong Nature Reservebefore and after the reservewas established in March1975. a Highly suitablehabitat, b suitable habitat, cmarginally suitable habitat,and d unsuitable habitat (Liuet al. 2001)exhaustion of forests near households, local residents went to areas far away fromtheir homes to collect more fuelwood. Consequently, the average distance betweenhomes and locations of fuelwood collection increased over time (He et al. 2009).Fuelwood collection in those remote areas is more damaging to pandas becausethey are the most suitable panda habitat (Fig. 6.6).The quantity of panda habitat is more sensitive to factors related to householdnumbers than to population sizes (An and Liu 2010). Simulations using an agent-

112J. LiuFig. 6.6 Percentages of fuelwood collection sites in three decades (1970s, 1980s, and 1990s)falling in four types of habitat (He et al. 2009)based model indicated that household numbers varied very differently than population sizes (An and Liu 2010). Fertility-related factors (e.g., fertility rate, spacingbetween births, and upper child-bearing age) caused almost instant changes inpopulation size. All the factors except age at the first marriage had time lags ofapproximately 20 years before they affected household numbers. Age at the firstmarriage changed household numbers most quickly. A reduction of age at the firstmarriage from 38 to 18 could lead to a difference of 90 households at year 5, 150households at year 10, and approximately 220 households at year 20. This islargely because of the household lifecycle: delayed marriage usually postpones theformation of new households and births of babies. It takes more time for otherfactors to take effect in changing household numbers. For example, increasingfertility rate increases the number of children, but the children still stay with theirparents until they establish their own households. This is why there is a time lag ofapproximately 20 years.Changing household numbers through age at the first marriage is the mosteffective and fastest way to lower panda habitat loss. Panda habitat is moreinfluenced by household numbers than population size. This is partly due to howfuelwood is consumed. A major proportion of fuelwood is used for heating, whichchanges little when an existing household has one more or one fewer person. Interms of cooking, adding or removing one person does not change fuelwood usemuch (An et al. 2001).6.3.2.2 Impacts of Household Proliferation on Food ProductionHousehold proliferation also has substantial impacts on other ecosystem services,such as food production (Table 6.1). Because household proliferation requiresmore areas for housing and associated infrastructures (e.g., roads and sewer services), much agricultural land has been converted into residential areas around theworld. Although there are no accurate statistics at the global level, there are

6 Effects of Global Household Proliferation on Ecosystem Services113numerous reports at the local level. Here are three examples from Africa, Asia, andSouth America. In Accra (Ghana, Africa), 2,600 ha of agricultural land per yearwere converted into residential areas (Maxwell 2000). From 1995 to 2005, Ho ChiMinh City of Vietnam lost more than 10,000-ha agricultural land to housing,roads, and other built-up areas (Van 2008). Similar patterns are common in Chinaand Indonesia (Verburg et al. 1999; Weng 2002). In the Pampas ecoregion ofArgentina, 39,187 ha of farm land have been converted to exurban use (Matteucciand Morello 2009). An immediate impact of housing expansion is the loss of periurban agriculture, which is usually significant in providing perishable food to theurban areas (Matuschke 2009). As a result, agricultural production may be forcedto shift to less productive areas and result in yield losses and increased cost oftransport.Food production is further compromised by the use of water by more households because more households require more water for daily consumption andreduce the retention of water because of the impervious surfaces. After the surfacewater and groundwater in the residential areas cannot meet household demand forwater, households have drawn water from far places. This creates cascading effectson distant ecosystem services (Liu et al. in press) and reduces the capacity of foodproduction in distant places (by lowering water table and increasing dry zones insoils), in addition to the agricultural areas that have been converted for residentialuse. All these affect food security and water security, and ultimately security of allecosystem services.Historical trends in household size suggest that there will be many morehouseholds even if human population declines. If average household size worldwide were the same as that of the United States (2.5 people per household) in2010, then the world would have over 40 % more households, or 800 millionadditional households in the 172 countries with available data (2.7 billionhouseholds rather than 1.9 billion households). If each household occupied a210 m2 house (the average U.S. house size in 2002), then 168,000 km2 extrahousing area would be required. Even assuming each house has two-stories, thenhousing needs 89,000 km2 of additional land area. T

agement Housing 6.1 Introduction Ecosystems and landscapes are coupled human and natural systems (Liu et al. 2007), in which humans interact with natural components. In the past, human population sizes and growth rates were usually used by ecologists in studying relationships between humans and natural systems. However, household numbers J. Liu (&)