Sustainable Resource Management

Renewable and nonrenewable resources

An oil well runs dry after a few decades of pumping. A pine forest in the Cordillera Central, if well managed, can provide timber for generations. But if we cut all of it down in a few months, it will take centuries to recover, or it may never recover. What determines whether we can use a resource indefinitely?

Overexploitation and maximum sustainable yield

Renewal is not the same for every population size. With very few individuals, almost no new young are born. With the population at the maximum the environment can support, there is so much competition for food and space that it does not grow either. Renewal is highest at intermediate sizes.

Where the catch line is below the curve, the population renews more than is removed and grows. Where it is above, more is removed than is replaced and the population declines. The two crossing points are equilibrium points (renewal = catch), but only the one on the right is stable.

This calculation is a simplified model. There are at least two uncertainties that make it unreliable:

• The actual size of the stock is estimated by sampling and always has error. If it is overestimated, the calculated quota is too high.

• The renewal rate is not fixed: it changes with sea temperature, available food, predators, and habitat quality (healthy reefs and mangroves). A bad breeding season suddenly lowers recruitment.

Why setting the quota at the maximum is dangerous

The previous graph looks a lot like the logistic growth curve. A population with growth rate $r$ and carrying capacity $K$ grows each year by approximately $rN\left(1-\frac{N}{K}\right)$, where $N$ is its size. That growth is maximum when $N = K/2$, and equals $rK/4$.

Suppose $K = 100{,}000\ \text{t}$ and $r = 0.4$. The renewal at each size is:

If a constant quota of $10{,}000\ \text{t}$ is set (the theoretical maximum), there is exact equilibrium only at $N = 50{,}000$. What happens if, because of an estimation error or a bad season, the stock ends up at $45{,}000$?

Fisheries management tools

What rules allow many boats and fishers to share a fishing ground without depleting it? Let's look at the three basic tools.

To set a responsible quota, the manager needs reliable data: the stock size (estimated through scientific surveys and landing data), the age at first reproduction (to decide the minimum size), and the annual recruitment (how many young fish join the population). If the quota is calculated with outdated data, it may be too high for the real stock, and the fishery slips into overexploitation without anyone noticing in time.

Recovering a fishing ground and certifying fish

When a fishing ground has already collapsed, it must be recovered. A good plan combines several measures, each with its biological reason:

For a short-lived species with highly variable recruitment (such as anchovy), the closed season can be shorter and the monitoring more frequent than for a long-lived species.

Certifications. Sustainable fishing labels, such as the MSC, promise that consumers can "vote with their wallets." They guarantee that the fishery was evaluated by an independent body: that the stock remains healthy, that damage to the ecosystem is minimized, and that an effective management system exists. Their limits: the cost of certification is hard for small-scale fishers to pay, control on the high seas is complicated, and the variety of labels confuses the consumer.

Forests: forest management and deforestation

A forest produces timber, but it also regulates water, protects soil, and shelters biodiversity. How can we use it without destroying it?

Deforestation sets off a chain of effects:

1. When trees are cut or burned, the CO₂ stored in the wood goes into the atmosphere, and the forest that absorbed it is lost: atmospheric CO₂ rises.

2. Without trees, evapotranspiration and shade decrease: the local climate becomes drier and hotter.

3. The soil is left bare: rain erodes it, washes it into rivers, and fills dams and reefs with sediment.

4. Without roots to hold the water, upper watersheds lose streamflow in droughts and floods get worse.

5. The habitat of endemic species is lost, and with it biodiversity.

This is the loss of ecosystem services: regulation of climate and water, soil protection, habitat, recreation, and supply of timber and food.

What should be replanted? Compare a plantation of fast-growing, short-rotation exotic species (for example, eucalyptus for paper pulp) with a mixed native forest:

New reforestation should be guided by ecological criteria and not just yield: native species adapted to the area (for example, the Hispaniolan pine and broadleaf trees of the Cordillera Central), a mix of species, protection of watersheds and slopes, and participation of local communities.

Sustainable agriculture and agroforestry systems

Soil and crops are also resources. Modern agriculture can be very productive, but sometimes at the expense of the soil, water, and natural cycles.

Let's compare an intensive farm with an organic farm in the same area:

External costs are damages that do not appear in the price of the product and are paid by society. Those of intensive agriculture are environmental; those of organic agriculture are mainly the higher price for the consumer and the need for more land.

Agroforestry and silvopastoral systems. They combine trees, crops, and livestock on the same land. In our country the best-known examples are shade-grown coffee and cacao plantations, where the trees protect the crop and shelter birds and other wildlife, and pastures with scattered trees that shade the cattle. The typical conflict in these systems is between economy (more livestock, more hunting, more harvest) and conservation (habitat for sensitive species and threatened birds). A compatible model: limit the stocking rate so as not to degrade the soil and pasture, regulate hunting with limits and seasons, maintain and renew the tree cover, and pay landowners for the services they provide.

These systems sustain ecosystem services such as soil and water retention, carbon capture, biodiversity, and the production of several products (meat, milk, fruit, timber, honey).

Aquaculture and protein sources

That is why it is not the definitive solution to overfishing: it depends on external resources and creates its own impacts. It is one piece of the puzzle, not the whole puzzle.

Trophic efficiency. Remember the 10% rule: at each step of the chain, about 90% of the energy is lost. Let's see how much energy reaches the consumer at different levels:

• Legumes (beans, pigeon peas): eaten directly from the producer level. Very efficient, with a low footprint.

• Extractive fishing of carnivorous fish: secondary or tertiary consumer level; little energy per unit of primary production, and it depends on the fishing ground not being overexploited.

• Aquaculture: depends on the species. Tilapia, which eats plant-based feed, is more efficient than a carnivore fed with fishmeal.

A sustainable combination for the Dominican diet: more legumes (which are already part of the bandera dominicana), small-scale fishing under quotas and closed seasons for local species, and aquaculture of herbivorous or omnivorous species with balanced feed of plant origin. This means eating more variety, less carnivorous fish, and more local products.

Water management

There are two philosophies for dealing with scarcity:

Both strategies are complementary, but demand must be controlled first: there is no point bringing in more water if it is lost through broken pipes.

Chain of decisions and effects: an export crop is prioritized → rivers are diverted → the lake level drops and its salinity rises → fish die and fishing disappears → the exposed lakebed turns into a salt desert → the lake's climate regulation is lost → the population's health worsens.

Lesson for Dominican rivers: watersheds such as those of the Yaque del Norte or the Yuna support irrigation, human consumption, hydroelectric plants, and ecosystems all at once. It is necessary to set ecological flows (water that must remain in the river), measure what is extracted, and evaluate every new canal or dam for its effects downstream, at the river mouth, and in wetlands.

Case of an aquifer being depleted. Imagine an agricultural region whose work depends on intensive irrigation from an aquifer that drops every year. There is a conflict between current employment and future sustainability; if the aquifer is depleted (or coastal wells become salinized by seawater intrusion), everyone's jobs disappear. An orderly transition could be:

1. Modernize irrigation (drip, nighttime irrigation, repair of canals).

2. Change crops toward those that use less water or to adapted varieties.

3. Reuse treated water for irrigation.

4. Progressive water pricing: cheap for basic use and more expensive for excessive consumption.

5. Reduce extraction in stages, with metering and licenses for wells.

Who should pay? A reasonable split: large users and the companies that extract the most (the more you use and benefit, the more you pay), with state aid for small farmers, because the aquifer is a public good and because the transition protects everyone's jobs and food security.

Energy: the energy transition

The electricity that turns on the fan or charges the cell phone also comes from resources. Many are nonrenewable: oil, natural gas, and coal are imported and emit CO₂ when burned.

Three technical obstacles:

• Intermittency: sun and wind are not always available. When they are not, another backup source is needed.

• Power grid: it must be reinforced and modernized to receive energy from new points and reduce losses.

• Storage: batteries or reservoirs that keep the surplus to use at night or when there is little wind; it is still expensive.

Savings and efficiency are sometimes called "the first source of energy": the cheapest and cleanest energy is the energy that is not used. An LED bulb, an efficient refrigerator, or a properly sized air conditioner, plus reducing losses in the grid, make it possible to meet the same need with less generation.

Summary