Here is a word problem for netters: There are three islands in the ocean that are identical. Each is 12 hectares in size and each is covered with 10 hectares of woods (the beach covers about 1 hectare and there is 1 hectare of high ground). Each island is inhabited initially by a couple who can obtain all the food they need from the ocean. However, they need wood for cooking. Firewood is consumed at a rate of 1 cubic meter/person/year. The woods produce about 24 cubic meters (CM) of wood/yr and this wood can be collected on a sustainable basis without reducing the growing stock. However, the trees are very small and therefore the standing volume of the forest never exceeds 2.4 cubic meters/ha. To clarify, the 10 hectare forest has 24 CM of wood on January 1st and during the year, 24 CM of firewood (dead branches etc) can be collected. On December 31, the standing volume of the forest is still 24 CM. If the firewood is not collected, the branches fall off the trees and either decay or are occasionally washed off the island. However, firewood can be collected and stored indefinitely (in a dry place) without wood decay. If harvesting reduces the standing volume to less than 24 CM, the firewood production will only equal the standing volume on January 1st (for ease of calculation). The couples all have the same major objectives. To keep cooking food and to keep at least half of the woods in a natural state. Although firewood can be collected from the natural woods, the objective is to not reduce the standing volume on the 5 hectare preserve. For years, everything goes well until one tragic day when they learn that the population is going to increase by 2 persons/year (apparently, the population on nearby developed islands did not practice population control and has exceeded their carrying capacity). Starting on January 1st in all future years, 2 additional people will inhabit each island. The three couples have 1 year to prepare for the invasion. However, they decide to manage their woods in different ways. The couple on island A, decides to collect all the firewood from the woods (24 CM ) and stores the extra firewood for future needs. On January 1st (year 1), the couple has 22 CM of firewood in storage. The couple on island B, decides to cut down 5 hectares of wood and stores this firewood. However, they establish a 5 hectare willow plantation. This willow plantation is harvested each year and will produce 10 cubic meters of firewood/ha/yr. On January 1st (year 1), the couple on island B has 72 CM of firewood in storage (50 from the plantation, 12 from cutting down 5 hectares of wood, and 12 from collecting firewood from the preserve; -2 CM from cooking food). They plan on continuing to establish 5 hectares of willow plantation each year (and adding kelp for fertilizer to maintain production level at 10 CM/ha/yr). The couple on island C does the same as the couple on island B. On January 1st, (year 1) they also have 72 CM of stored firewood. However, they place a requirement on each new couple. Each new couple must conduct research to increase the volume production from the willow plantation. By determining how to increase volume production, they help become part of the solution instead of part of the problem. Amazingly, each new couple figures out a way to increase willow production by 0.2 CM/ha/yr. For example, the first willow crop was 50 CM, the second was 51 CM, the third was 52 CM, etc. None of the islands can sustain a population growth of 2 persons/year. Therefore, the real problem for all three islands is population growth. Limited resources can not sustain unlimited population growth. With a 5 ha preserve, Island A can only sustain a population of 24 people; Island B can sustain 62 people; Island C can sustain about 122 people. However, the management regimes have vastly different effects on protecting the 5 ha "reserve." By storing firewood collected from the natural wood, the wood supply runs out during year 24. On Jan 1, year 25, there are 52 people on the island and the entire preserve is harvested for wood. By growing willow in a plantation, the firewood production is increased on Island B. When combined with storage, the wood supply lasts for 61 years before the supply runs out. The "reserve" was protected for more than 3 decades longer than island A. By investing time and effort in research, the people of island C were able to find new ways to increase volume production per hectare. As a result, the "reserve" was protected for 244 years. --------------------------------- Comment. The purpose of this word problem is to illustrate the "yin-yang" aspects associated with tree monocultures and native woodlands. A few people believe that a dualistic philosophy is superior to the "all or none" philosophies touted by others. The question I think is important is: how much land do we want to devote to each of the major cover types (wilderness, tree farms, cities, farm crops, pasture land, wetlands, native forests, roads, etc.)? To me, this seems more relevant than debating the pros and cons of individual management regimes. --------------------------------- Although the three islands are fictitious, real islands (countries) exist to illustrate each management type. David South School of Forestry Auburn University, AL 36849-5418 dsouth@forestry.auburn.edu 205-844-1022 205-844-1084 (FAX)
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