The payoff of conservation investments in tropical countryside

Abstract

The future of biodiversity and ecosystem services hinges on harmonizing agricultural production and conservation, yet there is no planning algorithm for predicting the efficacy of conservation investments in farmland. We present a conservation planning framework for countryside (working agricultural landscapes) that calculates the production and conservation benefits to the current baseline of incremental investments. Our framework is analogous to the use of reserve design algorithms. Unlike much countryside modeling, our framework is designed for application in data-limited contexts, which are prevalent. We apply our framework to quantify the payoff for Costa Rican birds of changing farm plot and border vegetation. We show that installing windbreaks of native vegetation enhances both bird diversity and farm income, especially when complementing certain crop types. We make predictions that differ from those of approaches currently applied to agri-environment planning,: e.g., although habitat with trees has lower local species richness than farm plot habitats (1-44% lower), replacing any plot habitat with trees should boost regional richness considerably. Our planning framework reveals the small, targeted changes on farms that can make big differences for biodiversity.

Fig. 1.

A hypothetical illustration of the methodology for predicting the impacts on a biodiversity metric (species richness, S) of adding marginal amounts of a given habitat element (tree-tangle border habitat adjacent to coffee plots). In this example, there is a baseline (dotted line) of 100 quanta (observation minutes) of tree-tangle border and a corresponding 141 species observed in the entire study area (rightmost diamond). Diamonds to the left represent the number of species observed in the study area given simulated removal (jackknifing) of 20, 40, and 60 quanta of habitat (and correspondingly, observation time). These diamonds from jackknifing runs (1,000 in actual analyses) are then used in a regression to predict impacts of addition of habitat, represented by the dashed regression line.

Fig. 2.

The incremental impact on abundance (N) of adding different border types to coffee plots (A) and to pasture (B). Impacts are presented per 1% change in the landscape border habitat, relative to a whole-landscape baseline of 4,987 observed birds (N); missing bars are projected zero impacts. Only coffee and pasture results are shown because these habitats were the most prevalent in the study area, and other plot types had more variable results. Border types are ordered by roughly increasing vertical complexity of vegetation. Error bars represent 95% confidence intervals about the mean.

Fig. 3.

The predicted incremental impact associated with the conversion of plot habitat to residential land. Change in species richness (S) is from a baseline of 141 species. The results for “trees” are conservative, because they only include the impacts of converting plot habitat on the adjacent borders, not the changes in the plots themselves (plots of trees were not sampled).

Fig. 4.

The predicted marginal impacts on the bird community in borders of replacing each of the major plot types with strips of trees (riparian strips and second growth forest). (A and B) The units are percentage of change in number of species (A) and landscape H′ (B) per percentage of change in the landscape borders. (C) For comparison also shown are the predictions of change in local richness based on site species densities derived from rarefaction curves, a standard measure of the conservation value of habitat (by which strips of trees are relatively species poor). This is nonmarginal logic, because it is solely based on local richness, unlike A and B, which are based on each habitat's contribution to landscape richness.

Fig. 5.

The impact of replacing habitat with strips of trees on species richness (S) of 18 forest specialist species relative to the impact on 96 nonforest specialists (expressed as a percentage of these 2 species communities). Results are conservative, because they include only the impacts of converting plot habitat on the adjacent borders and not the changes in the plots themselves (plots of trees were not sampled).

Fig. 6.

The predicted incremental impacts on richness (A), abundance (B), and diversity (C) of changes to border habitat beside coffee plantations or active pasture: either installing windbreaks (dense border vegetation that cuts the wind; as exotic shrubs or complex native vegetation) or living fences (rows of small pruned trees, whose trunks serve as fence posts). Impacts are presented per 1% change in landscape border habitat, relative to landscape baselines of 141 species (S), 4,987 observed birds (N), and Shannon–Wiener diversity of 5.74 (H′) Both forms of windbreaks are likely to be profitable to farmers within 3 years (46), whereas living fences are costly to install (C. Harvey, personal communication). Missing bars are projected zero impacts.