I have developed a specific selection criteria on why these three types of trees have been singled out by this dissertation as potential sources of local timber. These criteria are not a linear checklist but rather important variables for tree selection that should be met if architectural timber harvesting were to occur. They are culture, weed assessment, environment, population and properties.
The criteria is:
CULTURE- Does the tree have any cultural value or significance? Would using it be offensive or beneficial for the Hawaiian way of life?
For example, timber like koa is aesthetically beautiful and mechanically makes great timber for building. However, this native trees is a precious plant in Hawaii and it is generally frowned upon to cut a healthy koa down for the purpose of building a home. Most koa used for furniture or building today is deadfall and because it is relatively rare the wood is very expensive. On the other hand, ironwood is a major weed species and has little cultural value. If other criteria were met this tree could be a potential timber resource. Cultural importance may vary from person to person but generally there are certain species of trees that due to their history in the Hawaiian way of life, their
Figure 8.12: Hawaiʻi Timber Selection Criteria
Source: Own work
population or their intrinsic value are significant enough that there use for a new type of residential architecture would simply not make sense.
WEED ASSESSMENT – How invasive is the tree species? Does it spread too rapidly, cause harm to the environment, economy and/or human health?
The Hawaiʻi Invasive Species Council, a State interdepartmental collaboration funds the Hawaiʻi Pacific Weed Risk Assessment System (HPWRA) which ranks plant species in Hawaiʻi for their potential as weeds. While this system is not the be all, end all
resource that determines if a tree should qualify as a weed it is said to be 95%
accurate at catching would be invasive plants. The HPWRA uses 49 questions regarding a plants biological, ecological and invasive properties which botanists
and researchers can then answer to give an initial score of low, medium or high risk. After this, another screening is done and a predictive weed assessment score is assigned. The higher the more of a risk the plant is, currently, the highest rank is lantana camara at 32 and the lowest is thuja
“Green Giant” at negative (-)14. all of the species of timber that I chose for this project are very high risk on the HPWRA.
Figure 8.13: Hawaiʻi Pacific Weed Risk Assessment System
Source: Own work
ENVIRONMENT – Would harvesting the tree harm the environment / ecosystem that it is growing in?
Would it benefit the environment if it was removed and/or turned into a new crop?
Trees play an important part in ecosystems that they are part of. They provide homes for animals and insects and their presence in the soil can either be beneficial or detrimental. Certain trees fix nitrogen in the soil, others steal it, some release chemicals which make it hard for other plants to grow, some reduce soil pH and some shade out other plants from their canopy or droppings.
When a tree species has been selected for harvesting attention should be made to how removing that tree will affect the ecosystem it is part of. Further, after the tree(s) are removed will they be replanted, cycled with other tree species or will the land be left to
whatever plant takes over?
Deforestation, clear cutting and
improper forest management are serious issues and can leave ecosystems scarred for long periods of time200 as well as attributing to climate change.201 In Hawai‘i, deforestation not only affects plants, animals and insects but also influences our watersheds, and has serious cultural, social and economic implications.202 Studying the variables related to the harvesting or planting of tree species should be carefully studied before choosing a tree species for timber production.
200 D.H. Grossman, “Early recovery of a Hawaiian lowland rainforest following clearcutting at Kalapana on the Island of Hawaii” (PhD diss, University of Hawaii, 1992).
201 “Clearcutting and Climate Change,” Center for Biological Diversity, accessed December 2, 2016.
202 G. Timmons and Sam Gon III, Last Stand: The Vanishing Hawaiian Forest (Honolulu, HI: The Nature Conservancy of Hawaii, 2003).
Figure 8.14 Alan L, Native Hawaiian Hawk
Source: Alan L
Figure 8.15: Maile Lei, Picked from Hawaii Island Forest
Source: Own work
POPULATION – How many of the tree species exist? Is it a large enough population that a consistent timber supply could be achieved?
This criterion is probably the most straightforward and requires less investigation and explanation than the others. Simply, if a tree is exceedingly rare it would not make a good candidate for multiple residential projects. If large numbers exist and the other criteria are met, then that species would probably be more desirable for future timber production.
Figure 8.16: Eucalyptus Forest near Honokaa
Source: Own work
Population is highly correlated with environmental factors and the inherit properties of each species.
In other words, some trees grow quickly in a variety of soils like ironwood and others which may be even better suited for timber but grow slowly or require special environmental conditions.
PROPERTIES –What are the inherit mechanical properties of the timber? Is it strong or weak, does it check, crack or warp? What are the physical properties, does it have natural resistance to insects, will it hold up in the climate?
There are many mechanical and inherit properties of trees which are correlated to the other search criteria for a good local timber species. For instance, the growth rate and density of each species of tree is directly related to their environmental impact, weed assessment, growth rate and tree density. In other words, if a tree can multiply rapidly and in great numbers they may have a greater effect on the soil chemistry, ecosystem diversity and economic viability.
Properties such as their specific gravity, strength characteristics, timber defects (cracking, splitting, warping) and termite resistance are also important variables in timber selection. A tree which grows fast and in large numbers but is relatively weak or susceptible to disease or termites would need intervention to make it usable. For instance, Joseph Valenti of University Of Hawai‘i at Mānoa School of Architecture, in his doctorate dissertation chose to use one of the highest risk invasive species of albizia for use in Hawaiian architecture. However, Valenti notes that the inherit mechanical and physical properties of albizia, are like ponderosa pine and would benefit from engineered wood techniques like cross lamination or interlocking cross lamination to give them more structural capability, adaptability and economic viability.203 Valenti, like this dissertation aims to take advantage of a local invasive species to create a new type of Hawaiian architecture.
203 Valenti, Joseph J. “[Re]Scaling Urbanism: Fostering Low-Tech, Digitally Fabricated, and Transient Structures Through Innovation in Local Renewable Material,” doctorate diss., University of Hawaii, 2016, ProQuest (AAT 1095969).
Timber can be acquired from a vast variety of tree species, regardless of this checklist.
Even tree species which are proven like typical Douglas fir or American pine do not fulfil all of the search criteria but the ability to adapt these species with engineered techniques, chemical treatment and proper forest management makes them incredibly viable as building materials. It is not the purpose of this dissertation to challenge the fact that a Douglas fir glue-lam beam or 2” x 4” pine board are viable building products, because they have been proven for years with millions of houses and buildings. Rather, like Valenti I would challenge that a local timber supply would make more sense environmentally, economically and culturally than an imported source.
The main issues with my selections are regarding their environmental impact and inherit properties, as will be explained in the following section. However, it is important to remember a few things before moving forward. First, any monocrop will cause harm to the environment, eventually, if it is not properly managed, rotated or planted with symbiotic partner plants. Second, many
technologies, engineering systems and design mitigations are available to adapt issues with inherit properties or external forces (termites, climate). Finally, all timbers have positives and negatives for their use in architecture. It is not solely the purpose of this project to say one species of wood is the answer to Hawaiian residential architectures problems. Rather it is the summation of the research and the designed kit of parts that could adapted to various types of building materials.