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Stocking guidelines for the endemic Hawaiian hardwood, Acacia koa
Abstract and Figures
Stocking relationships are an important tool for foresters because they provide a means for evaluating how effectively the trees in a stand use available growing space. While stocking guidelines are not available for many tropical tree species, readily obtained measurements of stem and crown diameters can be used to develop preliminary stocking guidelines for most tree species. We demonstrate this approach for the endemic Hawaiian hardwood, Acacia koa, a species of major ecological and economic value in Hawaii. Using data from repeated censuses of multiple sites, we evaluated the influence of site quality and stand age on stocking guidelines for A. koa. Our results demonstrated that A. koa required less canopy space for a given dbh on moist windward sites than on drier leeward sites. In addition, we showed that on the windward sites A. koa required relatively less crown space with increasing tree size, whereas on the leeward site the opposite pattern was found. Size-density data from permanent inventory plots at the leeward study site showed excellent correspondence with the stocking guideline derived from the stem-crown diameter allometry. These stocking guidelines can be used to guide the establishment of new A. koa stands or to develop thinning regimes where information from spacing and thinning trials is not available and until better information is available.
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... More productive sites can support trees with proportionally smaller crowns, which results in a higher Gmax (Baker & Scowcroft 2005). Gmax is typically wellcorrelated with tree height at a standard base age (i.e. ...
... The pattern of increasing A. koa productivity with precipitation has been observed in previous studies across local precipitation gradients (Ares & Fownes 1999, Harrington et al. 1995. A separate study of A. koa populations distributed across the Island of Hawaii showed that trees in drier sites had larger crown growing space requirements, as well (Baker & Scowcroft 2005). Thus, productivity and Gmax are both lower in drier sites. ...
Precipitation and temperature are known to have important effects on forest productivity, but these effects may be strongly mediated through their influence on soil and leaf nutrients. We measured indicators of forest productivity and soil and leaf nutrients across independent gradients of precipitation and elevation/temperature in lower montane Hawaiian forests dominated by a single overstorey species, Acacia
koa, situated on 1500–3000-y-old soils that were mixtures of volcanic ash and basalt. Stand basal area was highest at the wettest site, 2000 mm mean annual precipitation (MAP), and leaf N and P were lowest at the driest site, 1000 mm MAP. Soil N availability and leaf N concentration declined across an 850-m elevation gradient, but this was not correlated with stand basal area or soil organic matter content. Across all stands, basal area was negatively correlated with the exchangeable soil P fraction. As well, the soil C:N ratio was negatively correlated with both soil P availability and the size of the primary mineral P fraction. Soil P availability and weathering appear to be important determinants of soil organic matter quantity and quality. Overall, precipitation is the major driving force for forest productivity, but P weathering and availability play important roles in limiting productivity in wetter sites and in controlling soil organic matter dynamics in these N-fixing forests.
... Advances in many aspects of forest restoration practices have helped to improve koa forest establishment in recent years. More specifically, techniques in breaking seed dormancy (Yoshinaga 1998), seedling outplanting (Scowcroft and Jeffrey 1999;Denslow et al. 2006), site preparation (Scowcroft and Adee 1991), and stocking guidelines (Baker and Scowcroft 2005;Scowcroft 2012) have been highlighted as evidenced by literature. Furthermore, improved nursery practices have demonstrated how seedling quality translates into better establishment and performance in the field Dumroese et al. 2009Dumroese et al. , 2011. ...
Restoring degraded mesic-montane forests represents a major challenge in maintaining functioning ecosystems throughout the tropics. A key example of this lies in Hawai‘i, where restoring native koa (Acacia koa, A. Gray) forests are a top conservation and forestry priority because of the critical habitat and high-value timber products that they provide. Efforts to restore koa forests, however, are directly impeded by extensive, non-native kikuyu grass (Pennisetum clandestinum Hochst. ex Chiov.) swards occupying deforested montane landscapes. In this study, we implemented a combination of grass suppression and selection of koa seedling stocktypes to measure outplanting performance in a naturalized site on the island of Maui. Seedlings were grown in a nursery in two root container sizes (111 and 207 cm3) and subsequently outplanted into grass-dominated plots that were either untreated or suppressed with a high-rate herbicide combination of imazapyr and glyphosate (1.7 kg a.i. ha−1, respectively), 30 days prior to planting. Across all treatments, seedling survival was high (>95 %). Thirty months after planting, trees from the larger stocktype had significantly greater growth in height and root-collar diameter. Initial grass suppression resulted in trees that were 34 % taller with 66 % larger root-collar diameters after 30 months. Herbicide treated plots also had significantly higher leaf area indices (2.6 vs. 1.8 m2 m−2), indicative of higher photosynthetic capacity and canopy closure. Grass suppression increased soil temperature along with soil moisture in the first year followed by a dramatic drop in moisture corresponding to large growth responses by koa seedlings after the first year. These results demonstrate how the combination of fundamental silvicultural practices in the nursery and on the outplanting site can accelerate tree growth to meet restoration goals in shorter time intervals. This is a first report of koa (a leguminous species) tolerance to a high-rate, pre-plant application of the herbicide active ingredient imazapyr. © 2015, Springer Science+Business Media Dordrecht (outside the USA).
... However, the selfthinning mortality does not reduce stand density sufficiently to maintain the early high growth rates of koa, and individual and stand-level basal area growth quickly stagnate (Pearson and Vitousek 2001). To avoid losing valuable years of growth to stagnation, forest managers must actively control stocking densities of koa (Baker and Scowcroft 2005). For most established second-growth koa stands, stocking control will involve thinning. ...
We examined the growth response of Acacia koa Gray (koa) in dense (10 000 trees/ha), ~25-year-old, second-growth stands on Hawai‘i to crown release (thinning) and grass control. Koa diameter increment increased within 2 months of thinning across the range of residual densities (200–900 trees/ha). After 3 years, diameter increment in the most intense thinning treatment was 180% greater than in the control treatment (1.4 vs. 0.5 cm/year); in the least intense thinning treatment diameter increment was 100% greater than the control (1.0 vs. 0.5 cm/year). Koa’s growth response was independent of all measures of tree size (diameter at breast height, height, and leaf area) across the range of tree sizes sampled. A grass control treatment to determine if reduced competition for soil water would improve koa growth showed no improvement in growth response. Koa phyllode δ13C values, which represent an integrated measure of tree water status, showed no evidence of tree water stress (mean δ13C = –28.3‰) and were not significantly different between the grass removal and control treatments. These results demonstrate that koa is capable of responding quickly and positively to crown release despite years of suppressed growth and suggest that landowners interested in managing koa forests may have considerable flexibility in the timing and application of thinning treatments to koa stands.
... -1 for all 29 plots in this mixed forest thirty years after harvesting compares well with basal areas of 10 to 40 m 2 .ha -1 in pure Acacia stands in other forests on leeward Hawai'i Island (Ares & Fownes 1999;Baker & Scowcroft 2005) and on Kaua'i (Harrington et al. 1995). Several small pure Acacia stands nearby, which probably regenerated after the same logging disturbances, vary from 26 to 48 m 2 .ha ...
Questions: Is the introduced timber species Fraxinus uhdei invasive in Hawai'i? Has logging disturbance facilitated the spread of Fraxinus and other alien species?
Location: Windward Mauna Kea, island of Hawai'i.
Methods: We surveyed 29 plots which were established before selective logging of the native tree Acacia koa in 1971 to determine if Fraxinus spread beyond the borders of an existing plantation and if other alien species increased. We created gaps in the canopy of the Fraxinus plantation and measured seed rain and regeneration, and we sampled foliar and soil nutrients inside and around the plantation.
Results: Basal area of Fraxinus increased from 0.7 m ² .ha ‐1 in 1971 to 10.8 m ² .ha ‐1 in 2000. Fraxinus was not found in plots that were located more than 500 m from those where it occurred in 1971 except along a road. Basal area of Acacia koa decreased after logging but subsequently recovered. Occurrence of the alien vine Passiflora tarminiana and alien grass Ehrharta stipoides decreased. Seedling regeneration of Fraxinus was prolific in gaps but did not occur under the canopy. Basal area of Fraxinus did not correlate with soil nutrient concentrations.
Conclusions: Fraxinus was able to regenerate following logging more rapidly than native tree species. Basal area growth of Fraxinus was great enough to offset a decline in native trees and cause an increase in forest productivity. If the Fraxinus plantation is harvested, managers should plan ways of favoring regeneration of the native Acacia which is more valuable both for timber and for conservation.
Around the world, forest regions vary according to their level of plant, animal, insect, and fungal species diversity; their soil and topographic complexity; and their developmental history. The fundamental practices for managing forests and natural resources can be applied anywhere on the globe, but differences in forest character may require modifications to these practices to best meet the needs and demands of each location. Having an understanding of forested regions around the globe allows us to develop a broader perspective on forestry and natural resource management and understand how current management practices and policies may vary from one continent (or subcontinental region) to the next. Understanding the developmental history of forests and natural resources of a country will also help us to understand the opportunities and challenges posed for foresters and natural resource managers in these areas. This knowledge may also allow us to speculate on how the developmental situation in another country may have evolved had the initial endowment of resources and developmental circumstances been different. In summary, developing a broad understanding of forests and natural resources in parts of the world other than our own may broaden our perspectives and facilitate greater opportunities for employment as our careers develop.
An 8-year-old dense monotypic stand of naturally regenerated koa (Acacia koa A. Gray) on the Island of Hawaii was selected to determine the effects of precommercial release thinning, phosphorous (P) fertilization and herbaceous weed control on growth of potential crop trees over approximately 30 months. Thinning consisted of cutting down all stems within a 4.5-m radius of the crop tree. Phosphorus was added at a rate of 300 kg ha⁻¹ over two years. Herbaceous weeds were sprayed once with imazapyr, a broad-spectrum herbicide. Thinning alone or in combination with P fertilization significantly increased stem diameter increment and allometric estimates of the growth of leaf area and aboveground biomass. There was no significant increase in stem diameter, leaf area or biomass in the absence of thinning. Within the thinned treatment, P fertilization resulted in significant increases in tree height over time. Herbaceous weed control had no effect on tree growth. The atmospherically resistant vegetation index (ARVI), which was derived from spectral analyses of high-resolution satellite imagery (GeoEye1), was significantly higher for thinned than unthinned trees 25 months after study initiation, suggesting greater light absorbance and a possible explanation for overall greater growth of thinned trees. When considered with results from previous studies, these findings indicated that crop tree selection and precommercial release thinning in dense, even-aged koa stands should be done early in stand development to prevent loss of crown vigor and growth potential. Additional interventions like P fertilization or herbaceous weed control may not be necessary until trees are older or site conditions suggest important soil resource limitations.
Introduction to Forestry and Natural Resources presents a broad overview of the profession of forestry. The book details several key fields within forestry, including forest health, economics, policy, utilization, and forestry careers. Chapters deal specifically with forest products and harvesting, recreation, wildlife habitats, tree anatomy and physiology, and ethics. These topics are ideal for undergraduate introductory courses and include numerous examples (mainly graphical) and questions for students to ponder. Unlike other introductory forestry texts, which focus largely on forest ecology rather than practical forestry concepts, Introduction to Forestry and Natural Resources encompasses economic, ecological, and social aspects providing a uniquely balanced text. The wide range of experience of the contributing authors equips them especially well to identify missing content from other texts in the area and address topics currently covered in corresponding college courses.
We present management tools for growing four valuable broadleaved tree species, indigenous to subtropical southern China. Crown diameter (CD) of the species studied can be predicted very well by using a model that is solely a linear function of diameter at breast height (DBH). The addition of tree age (AGE) and yield class (YC) to this model did not significantly improve its predictive capacity. We used species-specific crown diameter models to calculate the amount of growing space and subsequently stand density that each species needs to achieve desired stem radial growth rates. Furthermore we used this information to calculate a “distance factor”, a rule of thumb that roughly estimates the distance between two neighboring trees needed to achieve a desired future target diameter. These tools facilitate the planning of thinning regimes by using crown diameter models combined with annual radial growth rates to calculate the number of crop trees per hectare required to reach a desired target stem diameter.
Increasingly private landholders in Hawaii are considering native forest restoration for their lands, and some public agencies have already started such work. Initial efforts have focused on reestablishing Acacia koa to recover alien-grass-dominated sites. This study was done in Hakalau Forest National Wildlife Refuge, Island of Hawaii, to determine the efficacy of disk plowing to stimulate natural regeneration of koa from buried seeds. Sites with four different koa parent tree configurations were treated–single live overhead koa canopy, multiple live canopies, downed snags, and no parent koa tree. Tree growth and survival were assessed periodically over 21 years. Average initial stand densities ranged from 100 to 1,500 trees ha−1 of scarified land, although some open areas had as few as 20 trees ha−1. The distributions of seedlings with increasing distance from plot center were variable within and between parent tree configurations. Initial seedling density was significantly greater for the multiple-live-parent than for the no-parent configuration. Densities for the single-live and dead configurations differed from the no-parent configuration only when densities were based on the entire scarified area of each plot. Stand densities declined 10–67 % during the next 20 years. Survival was a negative, non-linear function of initial stand density. Initial stand density exerted strong control over stem diameter and crown size at age 21-years, but had little effect on the proportion of trees with single-stems. The relationships between stand basal area and density at 21 years conformed to the existing koa stocking guidelines. While moderate to high densities of natural regeneration can be expected from scarifying around live and dead koa trees, single trees or low density stands are likely in open areas.
We studied changes in stand structure, productivity, canopy development, growth efficiency, and intrinsic water use efficiency
(WUE=photosynthesis/stomatal conductance) of the native tree koa (Acacia koa) across a gradient of decreasing rainfall (2600–700 mm) with increasing elevation (700–2000 m) on the island of Hawaii. The
stands were located on organic soils on either smooth (pahoehoe) or rough (aa) lava flows. In the greenhouse, we also examined
growth and WUE responses to different water regimes of koa seedlings grown from seeds collected in the study area. We tested
the hypotheses that (1) stand basal area, aboveground net primary productivity (ANPP), leaf area index (LAI), and growth per
unit leaf area decreased with decreasing rainfall, (2) WUE increased with decreasing rainfall or water supply, and (3) WUE
responses were caused by stomatal limitation rather than by nutrient limitations to photosynthesis. The carbon isotope composition
of phyllode tissues (δ13C) was examined as an integrated measure of WUE. Basal area and LAI of koa stands on both pahoehoe and aa lava flows, and
ANPP on aa lava flows decreased with elevation. Basal area, LAI, and ANPP of koa in mixed stands with the exotic tropical
ash (Fraxinus udhei) were lower compared to single-species koa stands at similar elevations. Along the gradient, phyllode δ13C (and therefore WUE) increased with elevation from –30.2 to –26.8‰. Koa in mixed stands exhibited higher (less negative)
δ13C than in single-species stands suggesting that koa and tropical ash competed for water. In the greenhouse, we observed the
same trend observed in the field, as phyllode δ13C increased from –27.7 to –24‰ as water supply decreased. Instantaneous gas exchange measurements in the greenhouse showed
an inverse correlation of both maximum (morning) photosynthesis (A) and conductance (g) with δ13C values and, also, a good agreement between instantaneous (A/g) and integrated measures of WUE. Phyllode δ13C was not correlated with foliar concentrations of N or other nutrients in either the field or the greenhouse, indicating
that differences in δ13C were caused by stomatal limitation rather than by nutrient-related changes in photosynthetic capacity. This study provided
evidence that long-term structural and growth adjustments as well as changes in WUE are important mechanisms of koa response
to water limitation.
Four species of different successional status (Albizia falcataria = Paraserianthes falcataria, Alstonia macrophylla, Michelia champaca and Swietenia macrophylla) were surveyed to construct spacing and thinning guidelines for their establishment in plantations in C and SW Sri Lanka. Data of diameter breast height and crown width were used to construct spacing and thinning guidelines that were compared among species. -from Authors
Stocking and density standards are presented for upland hardwood stands (chiefly oak-hickory and mixed species) in the central states. Utilizing the open grown and forest grown tree-area requirements, limits of stocking and density for full site utilization are established. The standards presented are not influenced by site quality, stand age, or stand structure. The wide distribution of diameters in even-aged upland hardwood stands is due in part to differential species growth. Coefficients of variation, skewness, and kurtosis are given for a range of stand conditions. Under most stand conditions of even-aged upland hardwoods, stand structure can be ignored in the appraisal of stocking. Evidence is also presented to show that stand structure has very little effect on volume growth.
We tested whether variation in growth of native koa (Acacia koa) forest along a rainfall gradient was attributable to differences in leaf area index (LAI) or to differences in physiological performance per unit of leaf area. Koa stands were studied on western Kauai prior to Hurricane Iniki, and ranged from 500 to 1130 m elevation and from 850 to 1800 mm annual precipitation. Koa stands along the gradient had basal area ranging from 8 to 42 m2/ha, LAI ranging from 1.4 to 5.4, and wood increment ranging from 0.7 to 7.1 tonnes/ha/year. N, P, and K contents by weight of sun leaves (phyllodes) were negatively correlated with specific leaf mass (SLM, g m-2) across sites; on a leaf area basis, N increased whereas P and K decreased with SLM. LAI, aboveground woody biomass increment, and production per unit leaf area (E) increased as phyllode 13C became more negative. The 13C data suggested that intrinsic water-use efficiency (ratio of assimilation to conductance) increased as water availability decreased. In five of the six sites, phyllode P contents increased as LAI increased, but biomass increment and E were not correlated with phyllode nutrient contents, suggesting that productivity was limited more by water than by nutrient availability. Because vapor pressure deficits increased with decreasing elevation, actual water-use efficiency (ratio of assimilation to transpiration) was lower at drier, low-elevation sites. There was a trade-off between intrinsic water-use efficiency and production per unit of canopy N or P across the gradient. In summary, koa responds to water limitation both by reducing stand LAI and by adjusting gas exchange, which results in increased intrinsic water-use efficiency but decreased E.
This paper presents a review and critique of statistical null hypothesis testing in ecological studies in general, and wildlife studies in particular, and describes an alternative. Our review of Ecology and the journal of Wildlife Management found the use of null hypothesis testing to be pervasive. The estimated number of P-values appearing within articles of Ecology exceeded 8,000 in 1991 and has exceeded 3,000 in each year since 1984, whereas the estimated number of P-values in the Journal of Wildlife Management exceeded 8,000 in 1997 and has exceeded 3,000 in each year since 1991. We estimated that 47% (SE = 3.9%) of the P-values in the Journal of Wildlife;fe Management lacked estimates of means or effect sizes or even the sign of the difference in means or other parameters. We find that null hypothesis testing is uninformative when no estimates of means or effect size and their precision are given. Contrary to common dogma, tests of statistical null hypotheses have relatively little utility in science and are not a fundamental aspect of the scientific method. We recommend their use be reduced in favor of more informative approaches. Towards this objective, we describe a relatively new paradigm of data analysis based on Kullback-Leibler information. This paradigm is an extension of likelihood theory and, when used correctly, avoids many of the fundamental limitations and common misuses of null hypothesis testing. Information-theoretic methods focus on providing a strength of evidence for an a priori set of alternative hypotheses, rather than a statistical test of a null hypothesis. This paradigm allows the following types of evidence for the alternative hypotheses: the rank of each hypothesis, expressed as a model; an estimate of the formal likelihood of each model, given the data; a measure of precision that incorporates model selection uncertainty; and simple methods to allow the use of the set of alternative models in making formal inference. We provide an example of the information-theoretic approach using data on the effect of lead on survival in spectacled elder ducks (Somateria fischeri). Regardless of the analysis paradigm used, we strongly recommend inferences based on a priori considerations be clearly separated from those resulting from some form of data dredging.
The strong environmental gradients and natural experimental design of Mauna Loa volcano, Hawaii, provide an outstanding opportunity to study controls on ecosystem development. We measured above-ground vascular plant biomass and species composition on 42 sites on which precipitation, temperature, substrate texture, and substrate age varied substantially and largely independently. Biomass and species richness of live plants were strongly correlated with precipitation and lava flow age, but not with temperature or lava flow texture. Species composition, as measured by correspondence analysis, was likewise correlated with precipitation and flow age, but composition was also strongly influenced by temperature. Lava texture had a complex effect on vegetation, with 'a'a lava favoring vegetation development on wet sites and pahoehoe favoring development on dry sites. Many locations remain virtually free of invasion by alien species; aliens appear where disturbance has facilitated invasion, either from stand-level dieback in rainforest or a grass-fire cycle on the dry, leeward side of the mountain. All four of the environmental factors studied here (precipitation, temperature, substrate texture, and substrate age) exert significant and independent control over vegetation biomass and/or species composition on Mauna Loa.
Shape of a teak tree
- S Rajkhowa
RAJKHOWA, S. 1970. Shape of a teak tree. Indian Forester 96: 719-731.
Thinning and spacing guidelines for blue mahoe (Hibiscus elatus Sw.)
- P M S Ashton
- J S Lowe
- B C Larson
ASHTON, P. M. S., LOWE, J. S. & LARSON, B. C. 1989. Thinning and spacing guidelines for blue mahoe
(Hibiscus elatus Sw.). Journal of Tropical Forest Science 2: 37-47.