Abstract
In this paper stochastic dynamic programming is used to investigate land conversion decisions taken by a multitude of landholders under uncertainty about the value of environmental services and irreversible development. We study land conversion under competition on the market for agricultural products when voluntary and mandatory measures are combined by the Government to induce habitat conservation. We show that land conversion can be delayed by paying landholders for the provision of environmental services and by limiting the individual extent of developable land. It is found, instead, that the presence of ceilings on aggregate conversion may lead to runs which rapidly exhaust the targeted amount of land. We study the impact of uncertainty on the optimal conversion policy and discuss conversion dynamics under different policy scenarios on the basis of the relative long-run expected rate of deforestation. Interestingly, we show that uncertainty, even if it induces conversion postponement in the short-run, increases the average rate of deforestation and reduces expected time for total conversion in the long run. Finally, we illustrate our findings through some numerical simulations.
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Notes
On the economics of tropical deforestation and land use a theme issue can be found in Land Economics (Barbier and Burgess 2001).
The idea of a social planner implementing the social optimum by simply commanding the constitution of protected areas, is far from reality. Since the majority of remaining ecosystems are on land privately owned, the economic and political cost of such intervention makes the adoption of command mechanisms by Governments unlikely (Langpap and Wu 2004; Sierra and Russman 2006).
In Australia, the Productivity Commission reports evidence of pre-emptive clearing due to the introduction of clearing restrictions (Productivity Commission 2004). On unintended impacts of public policy see for instance Stavins and Jaffe (1990) showing that, despite an explicit federal conservation policy, 30 % of forested wetland conversion in the Mississippi Valley has been induced by federal flood-control projects. In this respect, see also Mæstad (2001) showing how timber trade restrictions may induce an increase in logging.
A similar effect has been firstly noted by Bartolini (1993). In this paper, the author studies decentralized investment decision in a market where a limit on aggregate investment is present.
In US the Conservation Reserve Program (CRP) is a voluntary program rewarding agricultural producers using environmentally sensitive land for the provision of conservation benefits (Farm Services Agency (FSA) 2012).
PES schemes have become increasingly common in both developed and developing countries. See e.g. Ferraro (2001), Ferraro and Kiss (2002), Ferraro and Simpson (2005) and Ferraro (2008). Following Wunder (2005, p. 3), a PES is “(1) a voluntary transaction where (2) a well-defined ES (or a land-use likely to secure that service) (3) is being “bought” by a (minimum one) ES buyer (4) from a (minimum one) ES provider (5) if and only if the ES provider secures ES provision (conditionality)”. See Pagiola (2008) on the PES program in Costa Rica and Wunder et al. (2008) for a comparative analysis of PES programs in developed and developing countries.
Note that in this case in line with Leahy (1993) the timing of conversion under competition would be equal to the timing of conversion set by a sole agent.
As in Bulte et al. (2002) \(A_{0}\) may represent the best land which has been already converted to agriculture.
For the sake of generality we simply refer to landholders. In our model in fact, as quite common in a developing country scenario, the appropriability of values attached to land is not conditional on the existence of a legal entitlement. See Gregersen et al. (2010).
The Brownian motion in (2) is a reasonable approximation for conservation benefits and we share this assumption with most of the existing literature. (Conrad (1997), p. 98) considers a geometric Brownian motion for the amenity value as a plausible assumption to capture uncertainty over individual preferences for amenity. Bulte et al. (2002, p.152) point out that “ parameter\(\alpha \) can be positive (e.g., reflecting an increasingly important carbon sink function as atmospheric CO\(_2\) concentration rises), but it may also be negative (say, due to improvements in combinatorial chemistry that lead to a reduced need for primary genetic material)”. However, this assumption neglects the direct feedback effect that conversion decisions may have on the stochastic process illustrating the dynamic of conservation benefits. See Leroux et al. (2009) for a model where such effect is accounted by letting conservation benefits follow a controlled diffusion process with both drift and volatility depending on the conversion path.
In the following, “landholder” refers to an agent conserving land and “farmer” to an agent cultivating it.
Note in fact that with the simultaneous inclusion of two stochastic variables, the problem has no closed form solution and must be solved numerically. However, this characterization would not impact significantly on our main results.
In Brazil, for instance, according to the legal reserve regulation a private owner must keep the 20 % (80 % in the Amazon) of the surface in the property covered by forest or its native vegetation (Alston and Mueller 2007). The choice of \(\lambda \) may account for considerations related to habitat fragmentation, critical ecological thresholds, enforcement and transaction costs for the program implementation, etc. Finally, note that our analysis is general enough to include also the case where \(\lambda \) is not imposed but is endogenously set by each landholder. In fact, due for instance to financial constraints limiting the extent of the development project, the landholders may find optimal not to convert the entire plot (Pattanayak et al. 2010).
A lower payment rate can be justified on the basis of a less valuable ES provision due to the disturbance, implicitly produced by developing the plot, to the previously intact natural habitat. For instance, one may assume that an unique payment rate \(\eta \) is fixed but that once the plot is developed the per-unit ES value, \(B(t),\) is lowered by some \(k\in [0,1)\). It is straightforward to see that by simply setting \(\eta _{2}=k\eta _{1}\) our results would still hold.
As pointed out by Engel et al. (2008), by internalizing external non-market values from conservation, PES schemes have attracted increasing interest as mechanisms to induce the provision of ES. Consistently, the payment rates, \(\eta _{1}\) and \(\eta _{2}\), may be interpreted as the levels of appropriability that the society is willing to guarantee on the value generated by conserving, i.e. \(B(t)\) and \(\lambda B(t)\) respectively. Finally, note that as \(\eta _{1}\) and \(\eta _{2}\) are constant then payments also follow a geometric Brownian motion [easily derivable from (2)]. However, this is different from the way payments are modelled in Isik and Yang (2004) where they also depend on the fluctuations in the conservation cost opportunity (profit from agriculture, changes in environmental policy, etc.).
On ecosystem resilience, threshold effects and conservation policies see Perrings and Pearce (1994). Note that the quality of our results would not change if one characterized \(\bar{A}\) as the expected surface at which the Government will impede further land conversion.
To consider infinitesimally small agents is a standard assumption in infinite horizon models investigating dynamic industry equilibrium under competition. See for instance Jovanovic (1982), Dixit (1989), Hopenhayn (1992), Lambson (1992), Dixit and Pindyck (1994, chp. 8), Bartolini (1993), Caballero and Pindyck (1992), Dosi and Moretto (1997) and Moretto (2008).
Note that we may use either \(N(t)\) or \(A(t)\) when evaluating the individual decision process.
Note that the expected value must be taken accounting for \(A(t)\) increasing over time as land is cleared. See Harrison (1985, p. 44).
Bulte et al. (2002, p. 152) define \(c\) as “the marginal land conversion cost”. It “may be negative if there is a positive one-time net benefit from logging the site that exceeds the costs of preparing the harvested site for crop production”. We also assume, without loss of generality, that the conversion cost is proportional to the surface cleared.
Note that, as shown in Di Corato et al. (2011), the problem can be equivalently solved considering a landholder evaluating the option to develop.
In the following we will drop the time subscript for notational convenience.
In our setting the (competitive) equilibrium bounding the profit process for each farmer can be constructed as a symmetric Nash equilibrium in entry strategies. By the infinite divisibility of \(F\), the equilibrium can be determined by simply looking at the single landholder clearing policy which is defined ignoring the competitors’ entry decisions (see Leahy 1993).
See Appendix A.1.
This means the \(A^{+}th\) is the last landholder for whom \( V_{B}(A^{+},B^{*}(A^{+});\bar{A})=0.\)
In Bartolini (1993) a similar result is obtained. Under linear adjustment costs and stochastic returns, investment cost is constant up to the investment limit where it becomes infinite. As a reaction to this external effect, recurrent runs may occur under competition as aggregate investment approaches the ceiling. See also Moretto (2008).
This result is in line with Ferraro (2001, p. 997) where the author states that conservation practitioners “may also find that they do not need to make payments for an entire targeted ecosystem to achieve their objectives. They need to include only “just enough” of the ecosystem to make it unlikely, given current economic conditions, infrastructure, and enforcement levels, that anyone would convert the remaining area to other uses”.
Although most of the PES programs in developing countries were introduced as quid pro quo for legal restrictions on land clearing, there are no specific contract conditions preventing the landholder from clearing the area enrolled under the program ((Pagiola 2008, p. 717)). In principle, sanctions may apply. For instance, in the PSA (Pagos por Servicios Ambientales) program in Costa Rica, payments received plus interest should be returned by the landholders exiting the scheme (FONAFIFO 2007). However, in a developing country context, economic and political costs may reduce the enforcement of such sanction.
On compensation and land taking see Adler (2008).
See also Di Corato et al. (2012) for an application concerning the derivation of the long-run average growth rate of capital.
Note in fact that in general we may have long periods of inaction when \(\xi <\hat{\xi }\) followed by short periods of rapid bursts of land conversion whenever \(\xi \) reaches \(\hat{\xi }\). In the first case, no entries in the market occur and the average rate of deforestation is null. In contrast, in the second case, since entry in the market is instantaneous then the rate of deforestation is infinite (see Harrison 1985; Dixit 1993).
We show in Appendix A.4 that to a higher \(\sigma \) corresponds a higher probability of hitting \(\hat{\xi }\) and thus a higher long run average deforestation rate.
Further details are available at http://www.acto.go.cr/general_info.php and http://www.sinac.go.cr/areassilvestres.php.
The total forested area includes 100,000 ha under protection and 48,000 ha without.
We simply subtract from 355,375 ha the surface of 148,000 ha that, up to Calvo (2009, p. 11), is still forested.
See Bulte et al. (2002, pp. 154–155).
To model the decreasing marginal benefits of deforestation Bulte et al. (2002, pp. 153–154) adopts a linear programming model. The model allows for three types of land quality, nine crop and five pasture activities, and several different farm management practices.
Our findings seem in contrast with the calibration used in Leroux et al. (2009) where the authors assume a deforestation rate equal to 2.5 with \( \alpha =0.05\) and \(\sigma =0.1\). In fact, we show that for those values the deforestation rate should be null. A \(2.5~\%\) deforestation rate would be justified only for lower \(\alpha \) and higher \(\sigma .\)
Numerical results under other scenarios are available upon request.
Tables illustrating scenarios with land conversion run for \(\widetilde{B} =200 \) and without land conversion run (\(\bar{A}\ge \hat{A}\)) are available in the Appendix.
Note that having assumed \(\eta _{1}\ge \eta _{2}\), we have \(\eta _{1}>\lambda \eta _{2}.\) This implies that only a fall in \(B\) can induce conversion. Di Corato et al. (2010) show that by relaxing such assumption also an increase in \(B\) may induce land conversion.
The total surface cultivated, \(A\), is constant over the time interval \(dt\) and the farmer can be seen as holding an asset (his plot) paying \(\Delta \pi (A,B;\bar{A})~dt\) as cash flow and \(E[dV(A,B;\bar{A})]\) as capital gain.
The solution for the homogeneous part of (15) is \(V(A,B;\bar{A})= Z_{1}(A)B^{^{\beta _{1}}}+Z_{2}(A)B^{^{\beta _{2}}}\) where \(\beta _{1}>1\) and \(\beta _{2}<0\) are the roots of \(Q(\beta )=0\) and \(Z_{1}(A)\) and \( Z_{2}(A)\) are two constants to be determined. However, as \(B\) increases, the value of the option to develop land should vanish, i.e., \(\lim _{B\rightarrow \infty }\) \(V(A,B;\bar{A})=0\). Hence, we must drop the first term by setting \( Z_{1}(A)=0\).
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We wish to thank Guido Candela, Yishay Maoz and Peter Kort for helpful comments. We are also grateful for comments and suggestions to participants at the 12th International BIOECON conference; the 51st SIE conference; the 18th Annual EAERE Conference; the 8th workshop of the International Society of Dynamic Games; the 16th Real Options Conference; and to seminar participants at FEEM and IEFE, Bocconi University, University of Stirling, CERE, Umeå University, University of Brescia. The usual disclaimer applies.
Appendix
Appendix
1.1 A.1 Proof of Proposition 1
Let \(V(A,B;\bar{A})\) be twice-differentiable in \(B\) and consider a short interval \(dt\) where no conversion takes place.Footnote 50 So, by applying a standard dynamic programming approach, the farmer’s value function in (5) can be rewritten as follows:Footnote 51
Expanding \(dV(A,B;\bar{A})\) using Ito’s Lemma, the solution to (14) must solve the following differential equation:
Using standard arguments the solution of (15) is (see Dixit and Pindyck 1994):Footnote 52
where \(\beta \) is the negative root of the characteristic equation \(Q(\beta )=\frac{1}{2}\sigma ^{2}\beta (\beta -1)+\alpha \beta -r=0\) and \(Z(A)\) is a constant to be determined.
To determine \(Z(A)\) and \(B^{*}(A)\) some suitable boundary conditions on (16) are required. First, further land development, by increasing the number of competing farmers in the market, keeps the value of being an active farmer below \((1-\lambda )c\) (value-matching condition). Formally, this is equivalent to impose:
Second, by differentiating the value-matching condition (17a) totally with respect to \(A\), we obtain
Now, let’s recall that marginal rents for an active farmer must be null at \(B^{*}(A)\) (see e.g. Proposition 1 in Bartolini (1993) and Grenadier (2002, p. 699) i.e.:
Substituting (17c) into (17b) yields the following condition (extended smooth-pasting condition):
where \(V_{B}(A,B^{*}(A);\bar{A})=\beta Z\left( A\right) B^{*}(A)^{\beta -1}+\frac{\lambda \eta _{2}-\eta _{1}}{r-\alpha }\).
Third, considering the limit on conversion, \(\bar{A}\), imposed by the Government, the last boundary condition to be considered is:
Note that condition (17d) plays the same role of a complementary-slackness condition in standard programming. That is, it must hold whenever control takes place.
Assume for the moment that (17d) holds over the interval \([A_{0},\bar{A}]\) with \(\frac{{\small dB}^{*}{\small (A)}}{dA}\ne 0\). This implies that \(V_{B}(A,B^{*}(A);\bar{A})=\beta Z(A)B^{*}(A)^{^{\beta -1}}+\frac{ \lambda \eta _{2}-\eta _{1}}{r-\alpha }=0\). Note that since \(\frac{\lambda \eta _{2}-\eta _{1}}{r-\alpha }<0\), then, as conjectured, \(Z(A)<0\). Hence, each landholder exercises the option to convert at the level of \(B^{*}(A) \) where the value, \(V(A,B^{*}(A);\bar{A})\) is tangent to the conversion cost, \(\left( 1-\lambda \right) c\). This critical threshold is given by the solution of the system including equations (17a) and \( V_{B}(A,B^{*}(A);\bar{A})=0\). Solving it, we obtain
which, as one can easily verify, is a continuous decreasing function of \(A\).
Now, consider a landholder following the smooth-pasting policy in (19) and suppose he is the last able to convert his plot. By using (16) and (18) it follows that
where \(V(\bar{A},B^{*}(\bar{A});\bar{A})=(1-\lambda )\frac{\delta \bar{A} ^{-\gamma }}{r}+(\lambda \eta _{2}-\eta _{1})\frac{B^{*}(\bar{A})}{ r-\alpha }\)
Note that the inequality (20) holds due the presence of the term, \(Z(A)B^{\beta }\), accounting for future market entries. The upward jump in value in (20) contradicts the optimality of \(B^{*}(A)\) by violating the smooth-pasting condition \(V_{B}(A,B^{*}(A);\bar{A})=0\). Note in fact that in this case \(V_{B}(\bar{A},B^{*}(\bar{A});\bar{A})=\frac{\lambda \eta _{2}-\eta _{1}}{r-\alpha }<0\). Hence, by using (17a), at \(A=\bar{A}\) the optimal conversion threshold is given by
Furthermore, as all landholders are equal, all expect such upward jump in value occurring at \(B=B^{*}(\bar{A})\). Therefore, as \(B^{*}(A)\) is decreasing in \(A,\) by starting at \(\bar{A}\) each landholder would maximizes the value of his conversion option by pre-empting the entry of others. By playing backward, pre-emption is then a (perfect) Nash equilibrium strategy up to a certain \(A=A^{+}\) where \(V(A^{+},B^{*}(A^{+});\bar{A})-\lim _{B\rightarrow B^{*}(A^{+})}V(A,B;\bar{A})=0\). Note that this implies that: (a) the candidate policy in the interval \([A^{+}, \bar{A}]\) is to impose \(\frac{dB^{*}(A)}{dA}=0\); (b) the optimal conversion threshold for all the discrete amount of conversion in the interval \([A^{+},\bar{A}]\) is the value-maximizer \(B^{*}(\bar{A})\); (c) at \(A^{+}\) the necessary condition for optimality, \(V_{B}(A,B^{*}(A); \bar{A})=0,\) holds again.
Finally, to determine \(A^{+}\) consider that \(A^{+}\) splits the interval \( [A_{0},\bar{A}]\) into an interval where landholders rush and a run takes place and an interval where landholders follows a “smooth-pasting” conversion policy. This means that \(A^{+}\) must satisfy both (19) and (21), i.e., \(B^{*}(A^{+})=B^{*}(\bar{A})\).
Substituting and solving for \(A^{+}\), we obtain
Finally, let’s consider the following two scenarios: \(\hat{A}\le \bar{A}\) and \(\hat{A}>\bar{A}\). From (22a) it follows that:
Studying (22b) we can state that since \(\frac{\beta }{\beta -1}>0\):
-
if \(\hat{A}\le \bar{A}\) then it must be \(\bar{A}\le A^{+}\). This implies that there is no run taking place. Land will be converted smoothly according to (19) up to \(\hat{A}\) since \(\frac{\delta }{r} A^{-\gamma }\le c\) for \(A\ge \hat{A}\);
-
if \(\hat{A}>\bar{A}\) then it must be \(A^{+}<\bar{A}\). In this case, land is converted smoothly up to \(A^{+}\) where landholders start a run to convert land up to \(\bar{A}\).
1.2 A.2 Long-run distributions
Let \(h\) be a linear Brownian motion with parameters \(\mu \) and \(\sigma \) that evolves according to \(dh=\mu dt+\sigma dw\). Following Harrison (1985, pp. 90–91); see also Dixit (1993, pp. 58–68)] the long-run density function for \(h\) fluctuating between a lower reflecting barrier, \(a\in (-\infty ,\infty )\), and an upper reflecting barrier, \(b\in (-\infty ,\infty )\), is represented by the following truncated exponential distribution:
We are interested to the limit case where \(a\rightarrow -\infty .\) In this case, from (23) a limiting argument gives:
Hence, the long-run average of \(h\) can be evaluated as \(E\left[ h\right] =\int _{\Phi }hf\left( h\right) ~dh\), where \(\Phi \) depends on the distribution assumed. In the steady-state this yields:
1.3 A.3 Proof of Proposition 3
Taking the logarithm of (11) we get:
where \(J\mathbf = \frac{\beta }{\beta -1}\left( r-\alpha \right) \Psi \frac{ P_{A}\left( A\right) }{r},\,\Psi =\frac{1-\lambda }{\eta _{1}-\lambda \eta _{2}}\) and \(J>B\). Rewriting \(\ln \left[ J-B\right] \) as \(\ln \left[ e^{\ln J}-e^{\ln B}\right] \) and expanding it by Taylor’s theorem around the point ( \(\widetilde{\ln J},\widetilde{\ln B}\)) yields:
where
By substituting the approximation into (26) it follows that:
Now, by Ito’s lemma and the considerations discussed in the paper on the competitive equilibrium, \(\ln \xi \) evolves according to \(d\ln \xi =v_{2}d\ln B=v_{2}[(\alpha -\frac{1}{2}\sigma ^{2})~dt+\sigma dw]\) with \(\ln \hat{\xi }\) as upper reflecting barrier. Setting \(h=\ln \xi \), the random variable \(\ln \xi \) follows a linear Brownian motion with parameter \(\mu =v_{2}(\alpha -\frac{1}{2}\sigma ^{2})>0\) and has a long-run distribution with (24) as density function.
Solving (27) with respect to \(\ln A\) we obtain the long-run optimal stock of deforested land, i.e.:
From (28) by some manipulations we can show that at \(\xi (\tilde{ B},\tilde{A})=\hat{\xi }\)
and
Note that since \(\tilde{A}<\hat{A}\) then \(-\frac{1}{\gamma }[ 1-(\frac{ \tilde{A}}{\hat{A}})^{\gamma }] <0\).
Taking the expected value on both sides of (28) leads to:
Since by (25) \(E(h)\) is independent on \(t\), differentiating with respect to \(t\), we obtain the expected long-run rate of deforestation:
By the monotonicity property of the logarithm, \(\widetilde{B} \)must exists such that \(\ln \widetilde{B}=\widetilde{\ln B}\). Furthermore, by plugging \(\widetilde{B}\) into (7), we can always find a surface \(\tilde{A}\) and \( \widetilde{J}=\frac{\beta }{\beta -1}\left( r-\alpha \right) \Psi \frac{ P_{A}( \tilde{A}) }{r}\) such that a linearization along (\(\widetilde{\ln B},\widetilde{\ln J}\)) is equivalent to a linearization along (\(\ln \widetilde{B},\ln \widetilde{J}\)), where \(\widetilde{\ln J}=\ln \widetilde{J}\). This implies that by setting \((\widetilde{B},\tilde{A})\), the long-run average rate of deforestation can be written as:
where \(\frac{P_{A}(\tilde{A}) }{r}=\frac{\widetilde{B} }{\frac{\beta }{\beta -1} ( r-\alpha ) \Psi }+c\) and \(\tilde{A}< \hat{A}\).
1.4 A.4 The impact of uncertainty on the distribution of \(\xi \)
Rearranging (27) yields
where \(U_{\xi }=\ln \frac{\eta _{1}-\lambda \eta _{2}}{r-\alpha } +v_{0}+v_{1}\ln J.\)
By some manipulations:
Using Ito’s lemma
Calculating first, second moment and variance for \(\xi \) we obtain:
Note that since \(\alpha +\frac{1}{2}(v_{2}-1)\sigma ^{2}<0\) and \(v_{2}<0\) then \(E(\xi )\) is increasing in \(t\). Finally, by deriving \(Var(\xi )\) with respect to \(\sigma \) it is easy to check that
That is, as \(\sigma \) soars \(Var(\xi )\) increases and so does the probability of hitting \(\hat{\xi }\) which in turn implies an increase in the long run average deforestation rate.
1.5 A.5 Additional tables
With land conversion run (Table 7).
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Di Corato, L., Moretto, M. & Vergalli, S. Land conversion pace under uncertainty and irreversibility: too fast or too slow?. J Econ 110, 45–82 (2013). https://doi.org/10.1007/s00712-013-0348-2
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DOI: https://doi.org/10.1007/s00712-013-0348-2