Summary

This paper introduces human appropriation of net primary productivity (HANPP), a metric which tracks the percentage of global net primary production that humans use for their own purposes such as food, livestock production, fuel extraction and use, as well as the loss of potential NPP as a result of land use by humans. Analysing the results of HANPP data allows us to understand where humanity has the largest impact in terrestrial environments. We can use HANPP to understand the effect of human activities on ecosystems and how this impacts the quality of life of wild animals. This paper summarises available evidence on HANPP with the goal of defining opportunities for further research.

Introduction

One of the obstacles in understanding how humanity impacts wild animals is in measuring the impact of human activities on resources for wild animals. One promising metric is that of human appropriation of net primary productivity (HANPP). HANPP tracks the percentage of global net primary production that humans use for their own purposes such as for food, livestock production, fuel extraction and use, as well as the loss of potential NPP as a result of human use. It is promising because, by focusing on NPP in the biosphere, we circumvent the complexity involved in aggregating short- and long-term effects of human activities directly on wild animal populations and indirectly on their environments.

Section 3 briefly introduces NPP and how it is measured along with some data on levels of NPP over three decades. Section 4 is an introduction into HANPP. I explain what HANPP measures, how it is defined and calculated, some of the main issues with the methodology and share some results based on various definitions of HANPP across a century of data collection. Section 5 provides a snapshot of one HANPP study which disaggregates results by land use category. Section 6 looks at one HANPP study which examines trends over the 20th century. Section 7 considers HANPP by geographic region and looks at regional trends over time. Lastly, Section 8 explores directions for further research. It considers how we can use HANPP to understand humanity’s impact on wild-animal suffering.

Net primary production

What is net primary production?

Primary production is the formation of chemical energy in organic compounds by living biological organisms (“Terrestrial Primary Production: Fuel for Life | Learn Science at Scitable,” n.d.). An example is the process of photosynthesis whereby energy sourced from sunlight is used to transform the inorganic compounds, carbon dioxide and water, into simple organic molecules, such as glucose. The newly created organic molecules may then undergo further transformations to synthesize more complex organic molecules such as complex carbohydrates, or they may be respired (“Terrestrial Primary Production: Fuel for Life | Learn Science at Scitable,” n.d.). In other words, respired organic molecules are used to maintain the life of the biological organism which synthesized it. The organic molecules that are not respired by the primary producer are either eventually consumed by other organisms or may be deliberately or accidentally destroyed, for example, by fire. Primary producers in terrestrial ecosystems are predominantly vascular plants with only a small percentage of primary production performed by algae.

Gross primary productivity (GPP) is the rate of chemical energy creation in organic compounds by primary producers in a given length of time (Haberl, Erb, & Krausmann, 2014, p. 365). Net primary productivity (NPP) is GPP minus the chemical energy respired to perform work by primary producers. Therefore, NPP is the rate of “net useful chemical energy” creation (Haberl et al., 2014, p. 365) by primary producers in a given length of time.

How is net primary production measured?

In terrestrial ecosystems, NPP is measured as “mass of carbon per unit area per year” and measurement is conducted primarily through field measurements of biomass changes over time (Scurlock, Johnson, & Olson, 2002). This measurement method is limited because of logistical difficulties in measuring elements such as below ground productivity, litterfall, and herbivory, among others. In addition, different landscapes require different measurement techniques which complicates NPP accounting.

Human appropriation of net primary productivity

What is human appropriation of net primary productivity?

HANPP was first developed as a measure for the impact of human activities on the biosphere in 1986 (Vitousek, Ehrlich, Ehrlich, & Matson, 1986). NPP, in the form of biomass, is the source of life and development for all heterotrophic species, including humans. However, humans appropriate a large share of NPP, with one of the first global calculations putting HANPP at nearly 40% of terrestrial NPP (Vitousek et al., 1986, p. 372). The amount of NPP appropriated by humans is significant because NPP flow is limited (once appropriated it cannot be used again) and must support all heterotrophic life.

Measuring HANPP

Land use/land cover classification

Land use and land cover classification systems are not universally defined. However there are some key categories that can be found in national and multinational agricultural statistics. The categories most applicable to HANPP measurements are defined below.

Agricultural land

Agricultural land is land that is primarily appropriated by humans and devoted to the production of crops and rearing of livestock (Anderson, Hardy, Roach, & Witmer, n.d., p. 23). It includes “arable land, land under permanent crops and land under permanent meadows and pastures” (Directorate, n.d.)

Arable land. “Land under temporary crops (double-cropped areas are counted only once), temporary meadows for mowing or pasture, land under market and kitchen gardens and land temporarily fallow (less than five years)” (FAO Production Yearbook, n.d.)

Land under permanent crops. “Land cultivated with crops that occupy the land for long periods and need not be replanted after each harvest, such as cocoa, coffee and rubber; this category includes land under flowering shrubs, fruit trees, nut trees and vines, but excludes land under trees grown for wood or timber” (FAO Production Yearbook, n.d.)

Permanent pastures. “Land used permanently (five years or more) for herbaceous forage crops, either cultivated or growing wild (wild prairie or grazing land)” (FAO Production Yearbook, n.d.).

Forests

“Forest includes natural forests and forest plantations. It is used to refer to land with a tree canopy cover of more than 10 percent and area of more than 0.5 ha. Forests are determined both by the presence of trees and the absence of other predominant land uses. The trees should be able to reach a minimum height of 5m…The term includes forests used for purposes of production, protection, multiple-use or conservation (i.e. forest in national parks, nature reserves and other protected areas), as well as forest stands on agricultural lands, and rubberwood plantations and cork oak stands. The term specifically excludes stands of trees established primarily for agricultural production, for example fruit tree plantations. It also excludes trees planted in agroforestry systems” (Food and Agriculture Organization of the United Nations, n.d.).

Other natural ecosystems

For the purposes of this paper, all forms of natural ecosystems not discussed above that are not appropriated by humans fall under this category. This includes “savanna, shrubland and chaparral, temperate grasslands, tundra and alpine, and desert” (Garí, 1996, p. 5).

Urban or built-up land

“Urban or built-up land is defined as areas characterized by buildings, asphalt, concrete, suburban gardens, and a systematic street pattern. Classes of urban development include residential, commercial, industrial, transportation, communications, utilities, and mixed urban. Political boundaries, such as city limits, were not used to define urban limits. Undeveloped land completely surrounded by developed areas, such as cemeteries, golf courses, and urban parks is recognized within urban areas” (“Land Cover Institute (LCI),” n.d.).

How do humans appropriate NPP?

The land use/land cover classifications defined above constitute the global terrestrial ecosystem. Agricultural and urban or built-up land are ecosystems that are primarily appropriated by humans (Garí, 1996, pp. 4–5). In forest ecosystems, humans appropriate NPP in two ways. Firstly, through managed forests where humans source wood (Garí, 1996, p. 5). Secondly, through deforestation (Garí, 1996, p. 5). In addition to these, it is important to include the loss of potential NPP as a result of human use (Garí, 1996, p. 6). For example, urbanising natural ecosystems will result in lower NPP over the affected area.

Defining HANPP

Total NPP is the amount of “net useful chemical energy” in the form of plant biomass produced in each of the land use/land cover categories mentioned above. HANPP is the amount of this plant biomass that is diverted to humans (Garí, 1996, p. 7). Consistency in HANPP results is hampered by varying definitions of what constitutes human appropriation of NPP. Human Appropriation of the Products of Photosynthesis (Vitousek et al., 1986) is the seminal paper on global calculations of HANPP. It divided human use of NPP into three categories :

Low estimate: this is “the amount of NPP people use directly-as food, fuel, fiber, or timber.” (Vitousek et al., 1986, p. 368)

Intermediate estimate: this is “all the productivity of lands devoted entirely to human activities (such as the NPP of croplands, as opposed to the portion of crops actually eaten)…[it also includes] the energy human activity consumes, such as in setting fires to clear land” (Vitousek et al., 1986, p. 368).

High estimate: this is “productive capacity lost as a result of converting open land to cities and forests to pastures or because of desertification or overuse (overgrazing, excessive erosion).” (Vitousek et al., 1986, p. 368)

In 1990, Wright (Wright, 1990) introduced a new way to define HANPP by focusing on the difference between potential and actual biomass in the ecosystem, but this definition was restricted to “biomass actually lost as input to food webs” (Haberl et al., 2014, p. 366). Wright’s suggestion to compare potential and actual biomass was adopted in 1997 when Haberl (1997) defined NPP appropriation as “the difference between the NPP of the potential natural vegetation…i.e. the vegetation that would prevail if human interference were absent) and the amount of biomass currently available in ecological cycles…” (Haberl, 1997, p. 143). This definition was then used in a recalculation of all three of Vitousek’s categories in 2007 (Haberl et al., 2007).

Calculating HANPP

For the rest of this paper, I rely on the broadest definition of HANPP as it is likely to offer the most data. This definition was first outlined by Haberl in 1997 (Haberl, 1997) and explained in detail in (Haberl et al., 2014, p. 366):

“HANPP is defined as the difference between the NPP of the natural vegetation thought to exist in the absence of land use (NPPpot) and the fraction of NPP remaining in the ecosystem after harvest under current conditions (NPPeco)… NPPeco is calculated by subtracting harvested NPP (HANPPharv) from NPPact, i.e., the NPP of the currently prevailing vegetation. Changes in NPP resulting from land conversion and land use—i.e., the difference between NPPpot and NPPact—are denoted as HANPPluc.” (Haberl et al., 2014, p. 366)

For the purpose of this paper, when calculating NPPeco, HANPPharv comprises crop harvest, wood harvest, human-induced fires, and by-flows. Therefore:

HANPP = NPPpot – NPPeco where NPPeco = NPPact – HANPPharv.

Or

HANPP = HANPPluc + HANPPharv where HANPPluc = NPPpot – NPPact

This breakdown is demonstrated in Figure 1. (Haberl et al., 2014, p. 368)

Figure 1: Definition of HANPP explained using global estimates for the year 2000

HANPP by land use

A study published in 2007 calculated global HANPP, disaggregating by land use categories, using data collected in 2000. The results are displayed in Table 1 (Haberl et al., 2007, p. 12943) and Table 2 (Haberl et al., 2007, p. 12944)

Table 1: Global carbon flows related to the human appropriation of net primary production (HANPP) around the year 2000

Table 2: Breakdown of global HANPP (excluding human-induced fires) in the year 2000 to land-use classes

The results are analysed as follows:

“We find significant alterations in NPP resulting from human induced land changes. As shown in Table [2], land use has resulted in an aggregate reduction of global NPP by 9.6%… Cropland and infrastructure areas are used most intensively, resulting in global average HANPP values on these areas of 83% and 73% (Table [3]). HANPP is much lower on grazing land (19%) and in forestry (7%). In the global average, areas currently under forestry are most productive, followed by areas used today as cropland and infrastructure. The potential productivity of grazing land is lower than that of cropland, reflecting the fact that fertile areas are used for cropping rather than for grazing, but its current productivity is slightly higher. This stems from a substantial reduction of productivity on croplands that can be explained on the one hand by the prevalence of low-yield agriculture in developing countries and on the other hand by the low belowground productivity of crops. Table [3] also reveals the low productivity of most of earth’s remaining wilderness areas. Harvest per unit area and year is by far largest on cropland (296 g C/m2/yr), which helps to explain why cropping alone accounts for 50% of global HANPP (Table [3]), despite its limited spatial extent (12% of earth’s terrestrial surface, excluding Antarctica and Greenland). In total, agriculture (cropping and grazing) is responsible for 78% of global HANPP, the remaining 22% being caused by forestry, infrastructure, and human induced fires.” (Haberl et al., 2007, pp. 12943 – 12944)

HANPP over time

(Krausmann et al., 2013) compiled a global time series of HANPP covering 1910 – 2005 to measure changes in HANPP over time and relative to population and economic growth. Some results can be seen in Figure 2. (Krausmann et al., n.d., p. 16)

Figure 2: Development of NPP components and HANPP by land use type from 1910 to 2005 in gigatonnes of carbon per year (GtC/y).

The results are analysed as follows:

“During the last century, total human appropriation of plant growth has almost doubled. Global HANPP measured in GtC/y grew by 116% and by 2005 reached 14.8 GtC/y. As a percentage of the potential plant growth of native vegetation (NPPpot), HANPP grew from 13% in 1910 to 25% in 2005…During the same period, [the] population grew by 274% and gross domestic product (GDP) (in constant 1990 dollars) grew by 1,655%. HANPP per capita has therefore declined…Although efficiency gains contributed to the decline of HANPP per dollar, the lion’s share of that reduction was due to a decreasing reliance on food and timber harvest for total economic production. In general, [increasing land use efficiency] has occurred overwhelmingly because of the rise in crop yields. In the vast majority of the world’s lands, converting forest and grassland to cropland reduces NPP. Although irrigation and heavy use of fertilizer have increased NPP in specific regions such as the Nile delta or The Netherlands even above NPPpot, most croplands have lower NPP due to the shorter growing period of crops and to the inability of one or a few crops to use the total solar radiation and other productive resources as fully as a mix of native species. However, by increasing yields over the last 50 [years], farmers brought cropland closer to replicating the productivity of native vegetation, which meant that HANPPluc decreased…In fact, HANPPluc was slightly lower in 2005 even than 1910 despite almost a doubling of cropped area from 7 million km^2 to 13 million km^2. As a consequence, HANPPluc on cropland as a percentage of NPPpot declined from 49 to 21%. That also meant that the share of harvest in total HANPP grew from 55% in 1910 to 70% in 2005. Unlike rising crop yields, increasing harvest from forest land and the expansion of land occupied by infrastructure, buildings, and associated land have contributed to increasing HANPP. However, they have played a relatively small role because agriculture dominates HANPP globally, representing 84–86% of total appropriation of plant growth over the entire period, with 42–46% on cropland and 29–33% on grazing land.” (Krausmann et al., 2013, pp. 10325 – 10326)

HANPP by geographic region

Data on HANPP by geographic region is analysed by both studies discussed above. Haberl et al. provide a regional breakdown based on data collected in 2000. The results can be found in Table 3. (Haberl et al., 2007, p. 12944)

Table 3: Regional breakdown of global HANPP (excluding human-induced fires) in the year 2000

The results are analysed as follows:

“A regional breakdown of global HANPP (Table [3]) reveals considerably different patterns in various world regions. Aggregate HANPP may be as low as 11-12% in Central Asia, the Russian Federation, and Oceania (including Australia), whereas land is used much more intensively in other regions. For example, Southern Asia has an overall HANPP value of 63%, and land-use intensity is also high in Eastern and Southeastern Europe (52%). Land-use-induced reductions in productivity (NPPluc) vary from 5% in Eastern Asia to 27% in Eastern and Southeastern Europe.” (Haberl et al., 2007, p. 12944)

Krausmann et al. breakdown the regional trends in HANPP over the last century. Data on per capita factors relevant to regional trends can be found in Table 4. (Krausmann et al., n.d., p. 18)

Table 4: Factors influencing HANPP per capita

The data is analysed as follows:

“[S]pecific patterns of HANPP differ substantially. Asia, Africa, and Latin America experienced very high growth rates in HANPP; as a percentage, HANPP doubled or even tripled in these regions during the last century. With the expansion of agriculture, these regions caught up with or even surpassed the initially high HANPP percentage levels in the Western Industrialized region and the former Soviet Union and Eastern Europe (FSU-EE). In contrast, in the Western Industrialized region, HANPP grew only modestly. It rose from 18% to 23% of NPPpot in the 1980s and has stabilized since then. The development of HANPP in FSU-EE mostly tracked that in the Western Industrial region until 1990, but after the collapse of the Communist system and the disintegration of its agricultural production system, HANPP rapidly declined from 22% to 16% of NPPpot. HANPP as a percentage of NPPpot has converged globally and falls into a relatively narrow range in all regions except Asia (ranging from 16% to 23% in 2005), but per capita HANPP varies greatly. HANPP per capita reflects three key factors: one, the amount and mix of biomass products consumed per capita, which generally increases with income and consumption of more HANPP-intensive products such as meat and milk; two, the efficiency of biomass production relative to NPPpot; and three, net biomass imports or exports. Latin America has the highest HANPP per capita (5.8 tC/cap per [year]) because it has a relatively high level of biomass consumption, has only moderate yields compared with Asia, Europe, and North America, is a major world exporter, and produces a great deal of beef through relatively unproductive pasture from former forests, which entails a large HANPPluc. Asia has the lowest HANPP per capita (1.3 tC/cap per y[ear]). This low figure results from an intensive and high-yielding production system, a low role for livestock products in diets, a lower-than-average level of wood consumption, and a heavy reliance on imports. Africa is not only the region with the steepest increase in total HANPP, it also experienced a fast decline in HANPP per capita from 5.8 to 2.6 tC/cap per y[ear]. This decline is not comforting. The growth in HANPPluc is one measure of inefficiency of land use, and HANPPluc has been growing at faster rates in Africa than in any other region. HANPPharv has also increased, but the growth rate has still been much smaller than that of Africa’s rapidly growing population for a number of reasons: the number of livestock per capita declined considerably, yields have remained low, and the region has increased its reliance on imports of food. In the Western Industrial region, a very high level of biomass consumption, high exports, and a considerable density of livestock are counterbalanced by a highly efficient production system and a resulting large decline of HANPPluc over time. HANPP per capita amounted to 3.5 tC/cap per y[ear] in 2005. It declined only moderately in the 20th century and remained more or less stable after 1980. Together with Asia, the Western Industrial region has the most HANPP-efficient biomass production system. The ratio of total HANPP to harvest in this region is 30% below the global average because of the lowest HANPPluc.” (Krausmann et al., 2013, pp. 10326 – 10327)

Directions for further research

The amount of NPP humans appropriate and the biomes most affected have important implications for the manner in which humans affect wild-animal welfare. Unfortunately, there are no studies exploring the effects of HANPP on wild-animal welfare beyond looking at species health. This section defines a few key directions for further research.

Who are the primary consumers?

Primary consumers are the second trophic level in the food chain, otherwise known as secondary producers (McNaughton, Oesterheld, Frank, & Williams, 1991). They consume primary producers for sustenance. At first glance there might not be a simple answer to this question. Primary consumers might be more commonly classified as herbivores which fall across many classes. For example, there are herbivorous insects, mammals, birds, and reptiles. There are also herbivorous fungi and bacteria. Importantly, reductions in NPP reduce the food supply of primary consumers who then face an increase in resource competition. The experience of competing for resources is already a source of suffering. Increasing this may mean we increase suffering experiences in the wild.

Is an increase in resource competition necessarily bad?

The answer turns on the quality of life of individual wild animals. Key researchers and advocates have written on the various experiences that cause wild animals to suffer. (Horta – Rel.: Beyond Anthropocentrism & 2015, 2015; Ng, 1995; Tomasik, 2015). Many of them conclude that when surveying the range of experiences and the reproductive strategies of the most numerous animals, the majority of them experience more or more intense negative than positive events. For animals that would otherwise have lived to adulthood and had many pleasurable experiences, increasing resource competition beyond what they would have naturally experienced will probably decrease their welfare. For animals that are highly susceptible to unstable or unpredictable environments, sustained increased resource competition might mean a reduced population growth rate and smaller numbers of offspring who would have died prematurely. It is also the case that there are many more animals in the latter category than the former.

In addition to an existing demand to determine the intensity and numerosity of negative and positive experiences of wild animals, further research could explore the breakdown of primary consumers on a regional or global level and assess which are most affected by HANPP in the short- and long-term.

How would the NPP we appropriate be otherwise used?

The extent to which HANPP affects the welfare of wild animals depends on how NPP would have been consumed but for human interference. For example, if the NPP we appropriate is consumed by primary consumers that are extremely unlikely to have the capacity to feel pain, then at the second trophic level we need not be concerned about animal welfare implications. Depending on our view of the net sign of HANPP on wild-animal welfare we might favour increasing HANPP in some biomes and decreasing it in others.

However, this considers only the effects on primary consumers. A thorough research project would need to also explore the flow-through effects to the third, fourth, fifth, etc. trophic levels. Reduced NPP at the second trophic level will likely translate to some degree of resource competition at higher levels as well. The degree to which this affects wild-animal welfare depends on the same considerations noted in the previous section.

Further research could explore:

The form NPPpot takes on a global scale. This could be categorised by region and used to develop a model for how that NPP would have been consumed.

The form NPPact takes on a global scale. This could be used to identify biomes or regions with high amounts of wild-animal suffering.

Whether it is net-positive to increase HANPP.

Does the way we appropriate NPP matter?

An important consideration in understanding the effect of HANPP on wild-animal welfare is the way we appropriate NPP. Humans appropriate NPP in a variety of ways, for example, land conversion into: urban or built-up land, agricultural land, and managed forests. Other effects include human-induced fires, desertification, and large scale ecosystem degradation. Land conversion has consistently led to lower levels of actual NPP than potential NPP in the absence of human interference. However the extent to which levels of NPP are reduced depends on the way in which we use the land. For example, agricultural land creates a larger discrepancy between NPPpot and NPPact than managed forestries. The form of HANPP that reduces wild-animal suffering depends on a number of considerations including:

The primary consumers who would have consumed that NPP;

Whether we believe we should reduce the abundance of populous species who give birth to many short-lived offspring (Brennan, 2017);

The reversibility of different types of HANPP; and

The efficiency of different types of HANPP.

Further research could explore these considerations in more detail.

Are there effects other than resource competition?

Resource competition is the immediate and direct effect of HANPP on wild animals. However, there are a likely to be a number of indirect and flow-through effects that also impact the welfare of wild animals. For example, land conversion results in habitat loss for many species. In addition to a reduction of available resources, this also likely to lead to a short-term increase in mortality due to exposure. Converting natural vegetation to agriculture is usually accompanied by population control measures against herbivorous animals (Eskander, 2017a, 2017b). It may also lead to more chronic welfare conditions such as an increase in parasitism or disease due to higher wild animal population densities (Ray, 2017), or an increase intraspecific aggression and conflict (Gilad, 2008). Whilst in the short term some populations face a reduction in welfare, it is plausibly the case that in the long-term, reduced NPP leads to a lower ceiling of suffering on an aggregate level (Brian Tomasik, 2013).

Large scale land conversion may also effect environmental resilience in ways that are difficult to predict and the impacts of which are difficult to assess (Melillo et al., 1993). This is an extremely complex issue, and research into this area is quite likely beyond the scope of the Wild-Animal Suffering Research project. It is, however, both extremely important and neglected. The sooner we can encourage experts to explore this field, the sooner we will understand how we can better advocate for wild animal welfare.

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