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Scenarios analysis
Starting from an interior solution for population and forests, there are two locally stable steady states (ss3 and ss4), as demonstrated above. Thereby, by increasing the slope of the extinction line, E(Bt) (higher ecological footprint), ss4 collapses to ss3 (Figure 3.2).
Applying the population-forest-biodiversity model to Easter Island Parameter choice
This paper exploring the evolution of species stock, the dynamics of the system can be investigated in a paradigm similar to Brander and Taylor (1998), Dalton and Coats (2000) and Bologna and Flores (2010), among others. The Easter Island economic literature use the following values for carrying capacity of forest F , intrinsic regeneration rate g, net birth rate b − d, labour harvesting productivity q, preference for the harvest good γ and the fertility parameter α: F = 12000, g = 0.04, b − d = −0.10, q = 0.00001, α = 4 and γ = 0.4. The latter parameter, γ, implies that consumers prefer the manufactured good to the resource-based one.
Equation (16) includes the carrying capacity of biodiversity (B) and ecological footprint parameters δ1 and δ2 . Values for these parameters can be identified using the same intuition as the Schaefer’s production function. Similar to the harvest function, where an effort LH is used to a harvest H = qLH F , lost of forests γqNtFt and increase of population (b− d+ αγqFt)Nt cause biological species lost respectively given by δ1 (γqNtFt)Bt and δ2 (b − d + αγqFt)NtBt. Therefore, values given to the parameters q, δ1 and δ2 are to be of comparable ranges. Moreover, δ1 and δ2 should take values lower than the intrinsic regeneration rate g, to allow an assessment of the role of preferences, fertility and other parameters in species loss.
Regarding B, similar to F where researchers consider the starting value of forest resources as being equal to the carrying capacity, we argue that B = B0 and choose a value for biodiversity carrying capacity in the range of forest stock: B = 10000.
Impact of intensive harvest, preference and fertility
Impact of population growth and intensive harvest. The evolution of the couple population-forest being largely discussed in existing study, we focus here on their interaction with species stock, given the amplitude of forest clearing and population growth. Thereby, we start from a perspective where there is no ecological footprint with regard to biodiversity, which remains equal to its carrying capacity or starting value (Figure 3.3 (Panel A)).
Firstly, with a significant ecological footprint or impact of human activities ({δ1 , δ2 } = 0), species stock diverges from its carrying capacity to converge to a new steady state below B (ss4). Secondly, since both population growth and forest clear-ing enhance biodiversity loss, relatively rapid decline in species stock is observed. It is also noticeable in every scenarios assessed that species stock reaches its minimum for the whole period, when human population reaches its peak. The system leading to two locally stable steady states with positive human population, Figure 3.3 helps notice that for relatively high ecological footprint, ss4 becomes ss3, as species stock reaches zero.
Applying the population-forest-biodiversity model to Easter-Island reveals two interesting teachings. Foremost, the combined impact of population growth and deforestation overwhelms natural regeneration of biological species, even when the rates of species loss due to population and deforestation {δ1 , δ2 } = 0 are quite inconsequential compared to the intrinsic regeneration rate g. Hence, as far as economic activities exploit forest or natural resources and there are conflicts over habitats between human and biological species, ecological destruction (deviations from B and F ) will increase until a societal collapse occurs. After a population collapse, forest and species stocks regeneration overcomes the ecological impact of human activities and stocks finally converge oscillatory to a long-run steady state. Nevertheless, when high ecological footprint lead to extinction, a significant species stock regeneration becomes impossible (ss3), supporting the so-called empty forest hypothesis.
Impact of changes in the preference for the resource-based good. The bench-mark model and parameter choice as specified above assume that individuals prefer the manufactured goods to resource-based ones, since γ = 0.4. Starting from the case where the couple {δ1 , δ2 } allows for an interior steady state with relatively low ecological impact oh human activities (Figure 3.3), we investigate how changes in preferences affect the long-run behaviour of the system. It is then obvious that an equal preference for both goods or a higher preference for the harvest good will amplify human ecological impact, leading to rapid forest clearing and species loss. Thereby however, it is to observe that the rapid resource depletion occurs, the sooner population collapses (Figure 3.2 (Panel B)). Reciprocally, disfavouring resource-based goods delays (and even dampens) the occurrence of the population overshoot (Figure 3.4 (Panel A)).
Impact of changes in fertility α. Besides the preference for manufactured and resource-based good, individual decisions over fertility affect demands, thus re-sources harvest and population dynamics. Compared to the starting model, where the fertility parameter α = 4 (Figure 3.3 (Panel B)), we simulate two scenarios considering α = 3 and α = 5, in order to assess how changes in fertility impact the long-run equilibrium. Using the parametrization of the benchmark model (Figure 3.3 (Panel B)) and changing the fertility parameter produces results comparable to change in individual’s preference.
Reducing the fertility parameter by 25% slows population growth (which reaches a peak of 4000 after 1400 year) and mitigate societal collapse, as a very smooth de-crease in population is observed after its peak. Thereby, a very slow environmental depletion (deforestation and species loss) is noticeable. Respectively, a 25% increase in α leads to rapid population growth producing a collapse after 60 decades associ-ated with rapid resource depletion and a relatively low steady state values for forest and species stocks.
Population-forest-biodiversity in a developing resource-intensive economy
Developing economies, mostly characterized by relatively high population growth, intensive resource harvest, represent a group a countries the scenarios discussed above can be associated with. A feasible parametrization for resource-intensive economies should concurrently consider higher net birth rate or fertility parameter α, preference for the harvest good and human impact {δ1 , δ2 }. Thereby, compared to Figure 3.3 (Panel A), we increase α, γ, and {δ1 , δ2 }, combining the different experiments conducted above.
Our simulations (3.3 (A)) indicate a rapid growth in population, which reaches a size higher than those observed in previous scenarios. Reciprocally, a sudden drop in forest and species stocks is noticeable following human population growth. The latter falls dramatically after 40 decades of flourishment, allowing forest and species stocks to smoothly recover. A second case, increasing values of parameters, displays a more rapid increase in population (of about 35000) after 25 decades, associated with rapid decline in forest and species stock, which converge to zero. As expected, the collapse of population also occurs sooner.
Table of contents :
1 Chapitre introductif
1.1 Motivation
1.2 Aperçu et contribution
Introductory Chapter
2 Is there a peaceful cohabitation between human and natural habi-tats?
2.1 Introduction
2.2 Related literature
2.3 Data and descriptive statistics
2.3.1 The data
2.3.2 Data on threatened species
2.4 Econometric specification
2.4.1 The count model
2.4.2 Endogeneity
2.5 Estimation results
2.5.1 Tests for overdispersion
2.5.2 Determinants of biodiversity loss
2.5.3 Regional heterogeneities
2.6 Discussion: Beyond the peaceful cohabitation
2.7 Concluding remarks
3 A simple Ricardo-Malthusian model of population, forest and bio- diversity
3.1 Introduction
3.2 A brief literature review
3.3 The basic structure of the model
3.3.1 Firms’ behaviour
3.3.2 Preference and budget constraints
3.3.3 Competitive equilibrium and market clearing
3.4 Dynamics of population, forest and species
3.4.1 Population dynamics
3.4.2 Forest dynamics
3.4.3 Dynamics of species stock
3.5 Steady state and linear stability analysis
3.5.1 Steady state
3.5.2 Linear stability analysis
3.5.3 Population, forest cover and species stock interactions
3.6 Scenarios analysis
3.6.1 Applying the population-forest-biodiversity model to Easter Island
3.6.2 Population-forest-biodiversity in a developing resource-intensive economy
3.7 Discussion and concluding remarks
3.7.1 Brander and Taylor, HANDY and the Population-Forest-Biodiversity model
3.7.2 Concluding remarks
4 Do Species-poor forests fool conservation policies?
4.1 Introduction
4.2 Related literature
4.3 The data
4.3.1 Descriptive statistics
4.3.2 An Insight into the data on forest and PAs cover
4.4 The PAs-income, forest and species richness
4.5 Econometric model
4.6 Estimation results
4.6.1 Some tests: Evidence of spatial dependence in PAs
4.6.2 Estimating spatial lag models of PAs
4.7 Robustness and heterogeneity analysis
4.7.1 Robustness check
4.7.2 Regional analysis
4.8 Concluding Remarks
5 Institutions and geography: A « two sides of the same coin » story of primary energy use
5.1 Introduction
5.2 Related literature
5.3 Data and descriptive statistics
5.4 Econometric model
5.5 Results and discussion
5.5.1 Modelling primary energy use: Preliminary tests
5.5.2 Results of estimating spatial FE models for primary energy use
5.6 Robustness, role of geographical location and functional forms
5.6.1 Robustness check
5.6.2 Does location matter to primary energy use?
5.6.3 The primary energy use, income and urbanization nexus
5.7 Concluding remark
