距離與自然資源願付價值之關係－－對評估資源邊際價值及總價值的啟示

The Relationship between Distance and Willingness to Pay for the Protection of Natural Resource: Implication for the Evaluation of Marginal Value and Total Value of Natural Resource

民眾對於自然資源呈現出高低不同的願付價值（willingness to pay, WTP），然不同的WTP分量區間下，各解釋變數的邊際影響將可能有所不同，又考量到調查樣本常呈現資料受限的特徵，本文以受限分量迴歸模型估計維護彰化海岸未定濕地之自然資源總價值，並依據估計結果，估算在不同分量下距離變動對WTP的影響，以期能夠更細緻的詮釋距離與WTP之間的關係。結果顯示受訪者與資源所在地之距離與WTP不僅存在負向的關係，同時也有正向關係存在的可能性。正向關係的發生，可能是鄰近濕地的居民因保護區的劃設，土地及相關經濟活動受到限制而導致呈現出較低的WTP，而隨著距離越遠反而有較高的WTP；反之，負向關係出現時是因比較重視保護國家特有景觀、生物多樣性與生態系統的受訪者，有相對高的WTP，因而離濕地越近其WTP也將越大。整體而言，距離與WTP的關係，是當地居民與／或外來一般民眾，願意支付高低不同金額間拉扯下的結果。此外，距離彈性值之估計結果顯示，WTP較高者之距離彈性較WTP較低者為大。因距離隨著WTP增加而上升，以各分量戶數權重乘上各分量平均WTP得到之各分量總價值，加總後的總價值為每年83億元，此明顯高於以Tobit模型所估計的每年38億元。因此，若未使用適當模型，資源的總價值大為低估。 While people state different levels of willingness to pay (WTP) for the conservation of natural resources, distance away from the resource site and other important factors that influences WTP have different impacts for different levels of WTP. With accounting for protest sample, the relationship between distance and WTP cannot be appropriately portrayed by a single function. As such, this study employs censored quantile regression model to estimate the relationship between distance and WTP delicately for the protection of Changhua Coast Undetermined Wetland. Moreover, estimation from traditional used Tobit model is conducted to compare the difference between those from censored quantile regression model. Finally, the total value of Changhua Coast Undetermined Wetland is computed according to the weight WTP under each quantile and its corresponding numbers of households. The estimation results show that it not only exist negative relation between distance and WTP under certain level of quantile but also potentially exist positive relation for other levels of quantiles. Local residents state low WTP due to restriction of their land development and economic activities from the conservation of certain natural resource. However, high WTP is also possibly stated for local residents if they concern more about conservation of natural resources and environment than development of land. Existence value may highly be stated by other general residents who live farther away from the resource site. As a result, the trade off and balance between the values stated by local residents and general residents determine the final relationship between distance and WTP. In addition, distance elasticities are higher for those WTP in high quntiles than those in low quantiles. From the estimation results of censored quantile regression model, a weighted total value of Changhua Coast Undetermined Wetland is estimated by multiplying the average WTP per household each year with the numbers of households under each quantile. The weighted total value estimated from censored quantile regression model is 8.3 billions NT dollars and the result from Tobit model is 3.8 billion NT dollars annually. It is clearly demonstrated that without the use of proper estimation model the total value of the natural resource will be underestimated.

While people state different levels of willingness to pay (WTP) for the conservation of natural resources, distance away from the resource site and other important factors that influences WTP have different impacts for different levels of WTP. With accounting for protest sample, the relationship between distance and WTP cannot be appropriately portrayed by a single function. As such, this study employs censored quantile regression model to estimate the relationship between distance and WTP delicately for the protection of Changhua Coast Undetermined Wetland. Moreover, estimation from traditional used Tobit model is conducted to compare the difference between those from censored quantile regression model. Finally, the total value of Changhua Coast Undetermined Wetland is computed according to the weight WTP under each quantile and its corresponding numbers of households. The estimation results show that it not only exist negative relation between distance and WTP under certain level of quantile but also potentially exist positive relation for other levels of quantiles. Local residents state low WTP due to restriction of their land development and economic activities from the conservation of certain natural resource. However, high WTP is also possibly stated for local residents if they concern more about conservation of natural resources and environment than development of land. Existence value may highly be stated by other general residents who live farther away from the resource site. As a result, the trade off and balance between the values stated by local residents and general residents determine the final relationship between distance and WTP. In addition, distance elasticities are higher for those WTP in high quntiles than those in low quantiles. From the estimation results of censored quantile regression model, a weighted total value of Changhua Coast Undetermined Wetland is estimated by multiplying the average WTP per household each year with the numbers of households under each quantile. The weighted total value estimated from censored quantile regression model is 8.3 billions NT dollars and the result from Tobit model is 3.8 billion NT dollars annually. It is clearly demonstrated that without the use of proper estimation model the total value of the natural resource will be underestimated.