Aboveground Biomass Increment Research Articles

Phosphorus economics of tropical rainforest species and stands across soil contrasts in Queensland, Australia: understanding the effects of soil specialization and trait plasticity

Summary 1. Edaphic specialization among species may lead to greater productivity and resource use efficiency across heterogenous landscapes than could be achieved in the absence of specialization. Although this idea has been tested conceptually and in garden experiments, it has rarely been examined in undisturbed forests. 2. To address this gap in our knowledge, we measured aboveground net primary productivity (aboveground biomass increment plus litterfall; ANPP) and phosphorus use efficiency (ANPP/P uptake) for stands on infertile schist soil and fertile basalt soil on the Atherton Tablelands, Australia. We also measured aboveground biomass production and estimated P use efficiency (PUE) for 52 tree species within these stands. Soil P fractions and radiation use efficiency (ANPP/percent intercepted radiation) were also measured. 3. Phosphorus use efficiency was markedly variable (CV = 44%) among species across soil types. Phosphorus use efficiency of obligate specialists on infertile soil was twice as high as species common on both soil types. Plastic responses within species were also significant, with trees on infertile soil having 45% greater PUE than trees on fertile soil. At the ecosystem level, genotypic and phenotypic traits accounted for 49% and 29% of the total PUE variance. Phosphorus‐efficient trees (PUE >8 kg biomass g−1 P uptake) on schist soils contributed more to stand‐level species richness (schist = 73%, basalt = 20%), basal area (schist = 86%, basalt = 18%) and production (schist = 82%, basalt = 10%) than did P‐efficient species on basalt soils. 4. Forest on schist soils achieved higher PUE than forest on basalt soils by partitioning more P to leaves rather than wood and by retaining P for longer periods of time before losing it via tissue senescence. These PUE traits enabled forest on schist to achieve similar ANPP and radiation use efficiency (i.e. PUE was not traded for radiation use efficiency). It is possible that opportunity costs of high PUE may exist among other life‐history traits. 5. These results suggest that plasticity in traits that confer P conservation is significant, but limited, and that maximum P conservation at the landscape level must be achieved via genetic differences between species. Although this highlights the importance of genetic conservation in forests, it also demonstrates that high P conservation is possible with relatively few, but markedly plastic species.

Liana infestation impacts tree growth in a lowland tropical moist forest

Abstract. Ecosystem-level estimates of the effect of lianas on tree growth in mature tropical forests are needed to evaluate the functional impact of lianas and their potential to affect the ability of tropical forests to sequester carbon, but these are currently lacking. Using data collected on tree growth rates, local growing conditions and liana competition in five permanent sampling plots in Amazonian Peru, we present the first ecosystem-level estimates of the effect of lianas on above-ground productivity of trees. By first constructing a multi-level linear mixed effect model to predict individual-tree diameter growth model using individual-tree growth conditions, we were able to then estimate stand-level above-ground biomass (AGB) increment in the absence of lianas. We show that lianas, mainly by competing above-ground with trees, reduce tree annual above-ground stand-level biomass increment by ~10%, equivalent to 0.51 Mg dry weight ha−1 yr−1 or 0.25 Mg C ha−1 yr−1. AGB increment of lianas themselves was estimated to be 0.15 Mg dry weight ha−1 yr−1 or 0.07 Mg C ha−1 yr−1, thus only compensating ~29% of the liana-induced reduction in ecosystem AGB increment. Increasing liana pressure on tropical forests will therefore not only tend to reduce their carbon storage capacity, by indirectly promoting tree species with low-density wood, but also their rate of carbon uptake, with potential consequences for the rate of increase in atmospheric carbon dioxide.

Enhanced water use efficiency in a mixed Eucalyptus globulus and Acacia mearnsii plantation

Significant increases in aboveground biomass production have been observed when Eucalyptus is planted with a nitrogen-fixing species due to increased nutrient availability and more efficient use of light. Eucalyptus and Acacia are among the most popular globally planted genera with the area of Eucalyptus plantations alone expanding to over 19 Mha over the past two decades. Despite this, little is known about how nutrition and light availability in mixed-species tree plantations influence water use and water use efficiency (WUE). This study examined to what extent water use and WUE have been influenced by increased resource availability and growth in mixed-species plantations. Monocultures of Eucalyptus globulus Labill. and Acacia mearnsii de Wildeman and 1:1 mixtures of these species were planted. Growth and transpiration were measured between ages 14 and 15 years. Aboveground biomass increment (Mg ha −1) was significantly higher in mixtures ( E. globulus; 4.8 + A. mearnsii; 0.9) than E. globulus (3.3) or A. mearnsii monocultures (1.6). Annual transpiration (mm) measured using the heat pulse technique was also higher in mixtures ( E. globulus; 285 + A. mearnsii; 134) than in E. globulus (358) and A. mearnsii (217) monocultures. Mixtures exhibited higher WUE than monocultures due to significant increases in the WUE of E. globulus in mixtures (1.69 kg aboveground biomass per cubic metre water transpired) compared to monocultures (0.94). The differences in WUE appear to result from increases in canopy photosynthetic capacity and above- to belowground carbon allocation in mixtures compared to monocultures. Although further studies are required and operational issues need to be resolved, the results of this study suggest that mixed eucalypt–acacia plantations may be used in water-limited environments to produce a given amount of wood with less water than eucalypt monocultures. Alternatively, because mixtures can be more productive and use more water per unit land area (but use it more efficiently), they could be utilized in recharge zones where rising water tables and salinity result from the replacement of vegetation (fast growing trees) that uses higher quantities of water with vegetation (shallow rooted annual crops) that use lower quantities of water.

Transpiration along an age series of Eucalyptus globulus plantations in southeastern Australia

Many of the world's Eucalyptus plantations are grown on short rotations of 15 years or less, which often covers the most rapid phase of stand development and peaks in growth rates and leaf areas. Since transpiration is related to stand leaf area these short rotations that make use of rapid early growth rates, may also maximise plantation water use, which has implications for predicting their water requirements and impacts on catchment hydrology. This study examined the transpiration, leaf area and growth rates of Eucalyptus globulus Labill. plantations aged 2–8 years. Transpiration ( E), estimated using the heat pulse technique, increased from 0.4 mm day −1 at age 2 years to a peak of about 1.6–1.9 mm day −1 in stands aged 5–7 years. This was associated with similar trends for stand leaf area index (LAI) and periodic annual increments of aboveground biomass, which both peaked at about age 4–6 years resulting in a linear relationship between E and LAI. While stand sapwood areas were continuing to increase at age 8 years, E was already declining due to reductions in sap velocity, from 13.5 cm h −1 at age 2 years to 6.3 cm h −1 at age 8 years and reduced sapwood area growth rates. Trees compensated for this reduction in sap velocity with declines in the leaf area ( A L) to sapwood area ( A S) relationship ( A L :A S) with age. There was also a reduction in growth efficiency (aboveground biomass increment per LAI) with age. However, reductions in WUE were small after age 4 years, which explained the linear relationship between E and LAI. If E continues to decline successive short rotation lengths may not only make use of rapid early growth rates but could also increase plantation water use compared to longer rotations over the same period of time.

Contrasting patterns of diameter and biomass increment across tree functional groups in Amazonian forests

Species' functional traits may help determine rates of carbon gain, with physiological and morphological trade-offs relating to shade tolerance affecting photosynthetic capacity and carbon allocation strategies. However, few studies have examined these trade-offs from the perspective of whole-plant biomass gain of adult trees. We compared tree-level annual diameter increments and annual above-ground biomass (AGB) increments in eight long-term plots in hyper-diverse northwest Amazonia to wood density (rho; a proxy for shade tolerance), whilst also controlling for resource supply (light and soil fertility). rho and annual diameter increment were negatively related, confirming expected differences in allocation associated with shade tolerance, such that light-demanding species allocate a greater proportion of carbon to diameter gain at the expense of woody tissue density. However, contrary to expectations, we found a positive relationship between rho and annual AGB increment in more fertile sites, although AGB gain did not differ significantly with rho class on low-fertility sites. Whole-plant carbon gain may be greater in shade-tolerant species due to higher total leaf area, despite lower leaf-level carbon assimilation rates. Alternatively, rates of carbon loss may be higher in more light-demanding species: higher rates of litterfall, respiration or allocation to roots, are all plausible mechanisms. However, the relationships between rho and AGB and diameter increments were weak; resource availability always exerted a stronger influence on tree growth rates.

Aboveground biomass dynamics of subalpine old-growth forest in the upper reach of the Minjiang River

Biomass estimation of old-growth forests in the upper Minjiang River (UMR) is important in quantifying carbon (C) sequestration and C sink size because majority of the natural forests in UMR are mature or over-mature. Based on the forest resource data from 27 fixed sampling plots that have been surveyed consecutively, the dynamics of the aboveground biomass density (AGBD) were characterized by the allometric relationships, and the space-time variations of the C sink size in the sub-alpine old-growth forests of UMR were explored. Our results showed that 1) the net increase in AGBD was (27.311 ± 15.580) Mg·hm −2 and the mean annual growth rate and mean annual death rate were (1.930 ± 1.091) and (2.271 ± 1.424) Mg·hm −2·a −1 during 1988–2002, respectively. 2) The aboveground biomass (AGB) largely depended on the growth and death rates of the trees with different diameters at the breast height (DBH) classes and the recruitment rate from one DBH class to another as well. The largest increment component of AGB came from the DBH class of 20 to 40 cm, whereas the minimum increment component of AGB was above 80 cm in DBH. The net negative increment of AGB occurred at DBH classes of 40–60 and 60–80 cm. 3) There were space-time variations of AGB in the alpine old-growth forests, indicated by AGB changing over time in the same sampling plot and varying among the locations or plots during the same sampling period. These variations were not only reflected in numerical value but also in positive or negative biomass increment.

Temporal variation and efficiency of leaf area index in young mountain Norway spruce stand

Temporal variation of leaf area index (LAI) in two young Norway spruce stands with different densities was monitored during eight consecutive growing seasons (1998–2005). We focused on: (1) LAI dynamics and above-ground mass production of both spruce stands and their comparison, (2) leaf area duration (LADU), crop production index (CPI) and leaf area efficiency (LAE) evaluation, and (3) thinning impact on the above-mentioned parameters. Also, we tried to deduce the most effective LAI value for the Norway spruce forest investigated. The LAI values of both spruce stands showed a typical seasonal course. To describe the LAI dynamics of the stand, we recommend taking LAI measurements within short time intervals at the time of budding and needle expansion growth (i.e., in early spring) and close to the LAI peak, when the twig growth has been completed. The reason was that after reaching the seasonal maximum, no significant differences between subsequently obtained values were found in the following 2 months. Therefore, we recommend this period for the estimation of seasonally representative LAI values, enabling the comparison of various spruce stands. The maximum hemi-surface LAI value reached 12.4. Based on our results, the most effective LAI values for maximum above-ground biomass production were within the range of 10–11. We found an LAI over these values to be less effective for additional production of above-ground biomass. In forest practice, thinning intensity is mostly described by percentage of stocking reduction. We want to show that not only thinning intensity, but also the type of thinning is important information. The type of thinning significantly affected the stand above-ground biomass increment, canopy openness, stand LAI and LAI efficiency. The stimulating effect of high-type thinning was observed; the LAE as well as the CPI increased. Low-type thinning had no such effects on LAE increments compared to the high-type thinning with similar intensity.

No simple relationship between above-ground tree growth and fine-litter production in tropical forests

An important deficiency of the tropical forest data set on above-ground net primary productivity (ANPP) is the paucity of studies where requisite components of forest productivity have been measured at the same location. Missing data on above-ground biomass increment (ABI, which refers to the incremental growth of trees) and fine-litter production (leaves, fruit, flowers, small twigs, but excluding coarse woody debris) is particularly problematic as these are the two major components of ANPP. The fragmentary nature of the data is reflected by the fact that only 13 of 39 (33%) plots reviewed by Clark et al. (2001) and 8 of 104 (8%) plots reviewed by Malhi et al. (2004) had data on both major components of productivity. In an attempt to retain the geographic coverage and replication of data in analyses, researchers have proposed ways to infer missing data. Typically ratios or (more recently) fitted relationships between ABI and litter production have been used for this purpose (Bray & Gorham 1964, Clark et al. 2001, Murphy 1975).

Tree growth, mortality, and above-ground biomass accumulation in a holm oak forest under a five-year experimental field drought

A holm oak forest was exposed to an experimental drought during 5 years to elucidate the growth responses of the dominant species Quercus ilex, Arbutus unedo and Phillyrea latifolia. Soil water availability was partially reduced, about 15% as predicted for this area for the next decades by GCM and ecophysiological models, by plastic strips intercepting rainfall and by ditch exclusion of water runoff. The stem diameter increment was highly correlated with annual rainfall in all species, and drought treatment strongly reduced the diameter increment of Q. ilex (41%) and specially of A. unedo (63%), the species showing higher growth rates. Stem mortality rates were highly correlated with previous stem density, but drought treatment increased mortality rates in all species. Q. ilex showed the highest mortality rates (9% and 18% in control and drought plots, respectively), and P. latifolia experienced the lowest mortality rates (1% and 3% in control and drought plots, respectively). Drought strongly reduced the increment of live aboveground biomass during these 5 years (83%). A. unedo and Q. ilex experienced a high reduction in biomass increment by drought, whereas P. latifolia biomass increment was insensitive to drought. The different sensitivity to drought of the dominant species of the holm oak forest may be very important determining their future development and distribution in a drier environment as expected in Mediterranean areas for the next decades. These drier conditions could thus have strong effects on structure (species composition) and functioning (carbon uptake and biomass accumulation) of these Mediterranean forests.

Soil Carbon Cycling and Soil CO2Efflux in a Red Pine (Pinus densiflora) Stand

This study was conducted to evaluate forest carbon cycling and soil <TEX>$CO_2$</TEX> efflux rates in a 42-year-old pine (Pinus densiflora) stand located in Hamyang-gun, Korea. Aboveground and soil organic carbon storage, litterfall, litter decomposition, and soil <TEX>$CO_2$</TEX> efflux rates were measured for one year. Estimated aboveground biomass carbon storage and increment in this stand were <TEX>$3,250gC/m^2\;and\;156gC\;m^{-2}yr^{-1}$</TEX>, respectively. Soil organic carbon storage at the depth of 30 cm was <TEX>$10,260gC/m^2$</TEX> Mean organic carbon inputs by needle and total litterfall were <TEX>$176gC\;m^{-2}yr^{-1}\;and\;235gC\;m^{-2}yr^{-1}$</TEX>, respectively. Litter decomposition rates were faster in nne roots less than 2 mm diameter size (<TEX>$<220\;g\;kg^{-1}yr^{-1}$</TEX>) than in needle litter (<TEX>$<120\;g\;kg^{-1}yr^{-1}$</TEX>). Annual mean and total soil respiration rates were <TEX>$0.37g\;CO_2m^{-2}h^{-1}$</TEX> and <TEX>$2,732g\;CO_2m^{-2}yr^{-1}$</TEX> during the study period. A strong positive relationship existed between soil <TEX>$CO_2$</TEX> efflux and soil temperature (r=0.8149), while soil <TEX>$CO_2$</TEX> efflux responded negatively to soil pH (r=-0.3582).

Carbon storage, litterfall and soil CO2efflux of a larch(Larix leptolepis)stand

Abstract This study was carried out to evaluate soil carbon cycling of a 36‐year‐old larch (Larix leptolepis) stand in Korea. The aboveground and soil organic carbon storage, litterfall, and soil respiration rates were measured over two‐year periods. The estimated aboveground biomass carbon storage and increment were 4220 gC m-2 and 150 gC m−2 yr-1, respectively. Mean organic carbon inputs by needle and total litterfall were 118 gC m-2 yr-1 and 168 gC m-2 yr-1, respectively. The aboveground carbon increment of the stand was similar to the annual input of carbon from total litterfall. The soil respiration rates correlated exponentially with the soil temperature at a depth of 20 cm (R2 = 0.86). In addition, the exponential regression equation indicated a relatively strong positive relationship between the soil respiration rates and soil temperature, while there was no significant relationship between the soil respiration rates and the soil moisture content. The annual mean and total soil respiration rates were 0.40 g CO2 m-2 h-1 and 3010 g CO2 m-2 yr-1 over the two‐year study period, respectively.

Estimation of aboveground biomass and net biomass increment in a cool temperate forest on a landscape scale

AbstractI clarified aboveground biomass (AGB), net biomass increment (NBI) and its spatial heterogeneity in a cool temperate forest on a landscape scale (&gt;2,200 ha). The relationships among AGB, NBI, and the size frequency distribution of trees of each stand were examined by combining an analysis of vegetation using aerial photographs, and data from 146 inventory plots (28.8 ha in total). This area included natural broad‐leaved stands, harvested broad‐leaved stands, and artificial conifer plantations. A −3/2 power distribution density function was applied to the individual mass frequency distribution of each plot. Estimated AGB in carbon (C) equivalent was 480–5,615 g C m−2 (3,130 g C m−2 on average), and NBI was −98 to 436 g C m−2 year−1 (83.0 g C m−2 year−1 on average). NBI had a single significant relationship with the reciprocal of theoretical maximum individual mass, while NBI was not significantly related to AGB. My results showed that, on a landscape scale, AGB and NBI strongly depend on the size structure of forest stands.

Above‐ground space sequestration determines competitive success in juvenile beech and spruce trees

A 2-yr phytotron study was conducted to investigate the intra- and inter-specific competitive behaviour of juvenile beech (Fagus sylvatica) and spruce (Picea abies). Competitiveness was analysed by quantifying the resource budgets that occur along structures and within occupied space of relevance for competitive interaction. Ambient and elevated CO(2) and ozone (O(3)) regimes were applied throughout two growing seasons as stressors for provoking changes in resource budgets, growth and allocation to facilitate the competition analysis. The hypothesis tested was that the ability to sequester space at low structural cost will determine the competitive success. Spruce was a stronger competitor than beech, as displayed by its higher above-ground biomass increments in mixed culture compared with monoculture. A crucial factor in the competitive success of spruce was its ability to enlarge crown volume at low structural costs, supporting the hypothesis. Interspecific competition with spruce resulted in a size-independent readjustment of above-ground allocation in beech (reduced leaf : shoot biomass ratio). The efficient use of resources for above-ground space sequestration proved to be a parameter that quantitatively reflects competitiveness.

BIOMASS ACCUMULATION AFTER 10–200 YEARS OF SHIFTING CULTIVATION IN BORNEAN RAIN FOREST

I examined the effect of repeated long-fallow shifting cultivation on biomass accumulation in a rain-forest landscape occupied for over 200 years in West Kalimantan, Indonesia. The diameters of stems >5 cm dbh were measured in nine secondary forests using a stratified random design of nested plots (3000 m2 per site). The stands were 9–12 years old and had experienced from 1 to 10 or more cycles of shifting cultivation. Accounting for differences in soil fertility, analysis of covariance (ANCOVA) demonstrated that aboveground live biomass increment (ABI, in megagrams per hectare per year) was significantly greater after four cycles than after six or more cycles. ABI was lowest after two cycles, highest after one or four cycles and intermediate after 6–10 cycles. Differences were driven by the density and biomass of trees >10 cm dbh, which followed a similar pattern. Although the diameter increment and contribution to total biomass of trees >10 cm dbh increased significantly with inherent soil fertility, va...

DEVELOPMENTAL PATTERNS AND NUTRITION IMPACT RADIATION USE EFFICIENCY COMPONENTS IN SOUTHERN PINE STANDS

A number of contemporary forest productivity models use some variation of a growth efficiency (ε) approach. Typically, these models predict production (aboveground net primary production, ANPP, in units of dry mass biomass per unit of area per unit of time) as the product of two terms: radiation use efficiency (ε, in units of dry mass biomass per megajoule of photosynthetically active radiation [PAR] intercepted or absorbed by the plant canopy) and the sum of PAR intercepted or absorbed by the canopy (Φpar, in units of megajoules per unit of radiation area per unit of time). Predicting productivity in a biologically realistic manner requires an understanding of how model components are affected by natural and anthropogenic environmental factors, as well as other influences such as aging or stand development. We measured or calculated all components of the ε model (aboveground woody biomass increment, IWB; foliage biomass increment, IFB; aboveground net primary production, ANPP; leaf area index, LAI; Φpar; and aboveground radiation use efficiency, εA) from ages 4 to 18 yr in loblolly and slash pine stands in north-central Florida grown under replicated fertilizer and understory vegetation control treatments that induced a large gradient in soil nutrient availability. Treatments impacted all measured components, which in turn led to strong responses in aboveground radiation use efficiency. Age 6–9 yr εA, averaged across species, ranged from 0.78 g/MJ to 0.83 g/MJ in treatments receiving fertilizer or vegetation control vs. 0.53 g/MJ in untreated plots. Stand developmental processes modified these responses, however, with εA declining by over 40% in treated plots from age 6–9 yr to age 15–16 yr. Variation in εA in both species was linked to development of stand basal area (BA), with a positive, linear relationship between εA and BA for values of BA < 18 m2/ha and a declining, linear relationship for values of BA > 18 m2/ha. Loblolly pine εA was positively correlated with foliar nitrogen concentration, [N]. These data highlight the dynamic nature of εA and suggest that both stand developmental and nutritional processes drive changes in ANPP and εA in southern pines.

EFFECTS OF TREE DENSITY AND STAND AGE ON CARBON ALLOCATION PATTERNS IN POSTFIRE LODGEPOLE PINE

Validating the components of the carbon (C) budget in forest ecosystems is essential for developing allocation rules that allow accurate predictions of C pools and fluxes. In addition, a better understanding of the effects of natural disturbances on C cycling is critical, particularly in light of alterations to disturbance regimes that may occur with global climate change. However, quantitative data about how postfire differences in ecosystem structure affect C allocation patterns are lacking. For this study, we examined how above‐ and belowground C pools, fluxes, and allocation patterns varied with fire‐initiated differences in tree density and stand age in lodgepole pine stands in Yellowstone National Park of four forest types: low (&lt;1000 trees/ha), moderate (7000–40 000 trees/ha), and high tree densities (&gt;50 000 trees/ha) in 13‐year‐old stands, and in ∼110‐year‐old mature stands. C pools in live biomass and detritus were estimated with allometric equations and direct sampling. Aboveground net primary productivity (ANPP) was estimated as aboveground biomass increment plus fine litterfall, and total belowground carbon allocation (TBCA) was estimated using a C balance approach. Our results indicate that the magnitude of C pools and fluxes varies greatly with fire‐initiated differences in tree density and stand age. Coarse woody debris and mineral soil carbon accounted for the majority of total ecosystem C in young stands (91–99%), in contrast to mature stands where the largest amount of C was found in live biomass (64%). ANPP and TBCA increased with tree density (mean ANPP was 59, 122, and 156 g C·m−2·yr−1, and TBCA was 68, 237, and 306 g C·m−2·yr−1 for low‐, moderate‐, and high‐density young stands, respectively), and with stand age (ANPP was 218 g C·m−2·yr−1 and TBCA was 382 g C·m−2·yr−1 for 110‐year‐old stands). ANPP and TBCA were positively correlated, and both variables were well correlated with leaf area index. Notably, the ratio of TBCA to (TBCA + ANPP) remained remarkably constant (0.63–0.66) across extreme gradients of tree density and stand age, differing only slightly for the low‐density young stands (0.54). These results suggest that C allocation patterns in a postfire lodgepole pine ecosystem are independent of tree density and stand age.

Spatial and temporal variation of biomass in a tropical forest: results from a large census plot in Panama

SummaryWe estimated the dry, living, above‐ground biomass (AGB) standing stock and its turnover in a 50‐hectare forest plot located in moist tropical forest on Barro Colorado Island, Panama. The estimates were obtained using inventory data collected every 5 years from 1985 to 2000, including measurements of all trees ≥ 1 cm diameter.Four different allometric regressions relating trunk diameter and height with AGB were compared. Based on the most consistent method, we estimated that the Barro Colorado forest holds 281 ± 20 Mg ha−1(1 Mg = 103kg) of AGB, lianas included. A third of the AGB is stored in trees larger than 70 cm in diameter.Stand‐level AGB increment (growth plus recruitment) was highest in the period 1985–90 (7.05 ± 0.32 Mg ha−1 year−1, mean ± 95% confidence limits based on samples of multiple hectares) and smallest in the period 1990–95 (5.25 ± 0.26 Mg ha−1 year−1), while AGB losses were similar during the three intervals (mean 5.43 ± 0.72 Mg ha−1year−1). This resulted in significant differences in AGB change (defined as increment minus loss) among census intervals; including branchfalls, the AGB of Barro Colorado Island increased in 1985–90 (+0.82 ± 0.84 Mg ha−1 year−1), decreased in 1990–95 (−0.69 ± 0.82 Mg ha−1 year−1), and increased again in 1995–2000 (+0.45 ± 0.70 Mg ha−1year−1). The 15‐year average was +0.20 Mg ha−1 year−1, but with a confidence interval that spanned zero (−0.68 to 0.63 Mg ha−1 year−1).Branchfalls and partial breakage of stems had a significant influence on the AGB changes. They contributed an average of 0.46 Mg ha−1 year−1to the AGB loss. About 5% of AGB increment was due to trees less than 10 cm in diameter.To test whether the AGB of tropical forests is increasing due to climate change, we propose that in each forest type, at least 10 hectares of forest be inventoried, and that measurements of the small classes (&lt; 10 cm diameter) as well as large size classes be included. Biomass loss due to crown damage should also be estimated.

NET PRIMARY PRODUCTION IN TROPICAL FORESTS: AN EVALUATION AND SYNTHESIS OF EXISTING FIELD DATA

Information on net primary production in tropical forests is needed for the development of realistic global carbon budgets, for projecting how these ecosystems will be affected by climatic and atmospheric changes, and for evaluating eddy covariance mea- surements of tropical forest carbon flux. However, a review of the database commonly used to address these issues shows that it has serious flaws. In this paper we synthesize the data in the primary literature on NPP in old-growth tropical forests to produce a consistent data set on NPP for these forests. Studies in this biome have addressed only a few NPP com- ponents, all aboveground. Given the limited scope of the direct field measurements, we sought relationships in the existing data that allow estimation of unmeasured aspects of production from those that are more easily assessed. We found a predictive relationship between annual litterfall and aboveground biomass increment. For 39 diverse tropical forest sites, we then developed consistent, documented estimates of the upper and lower bounds around total NPP to serve as benchmarks for calibrating and validating biogeochemical models with respect to this biome. We developed these estimates based on existing field measurements, current understanding of aboveground consumption and biogenic volatile organic carbon emissions, and our judgment that belowground production is bounded by the range 0.2-1.2 3 ANPP (aboveground NPP). Across this broad spectrum of tropical forests (dry to wet, lowland to montane, nutrient-rich to nutrient-poor soils), our estimates of lower and upper bounds on total NPP range from 1.7 to 11.8 Mg C·ha 21 ·yr 21 (lower bounds) and from 3.1 to 21.7 Mg C·ha 21 ·yr 21 (upper bounds). We also showed that two relationships that have been used for estimating NPP (the Bray-Gorham relationship based on leaf litterfall and the Miami model based on temperature or precipitation) are not valid for the tropical forest biome.

Poplar breeding and testing strategies in the north-central U.S.: Demonstration of potential yield and consideration of future research needs

We present results from a Populus Regional Testing Program that has been conducted in Minnesota, Iowa, Wisconsin, and Michigan over the past six years. Our objectives have been to: 1) identify highly productive, disease resistant intra- and inter-specific clonal selections and 2) understand patterns of genotype × environment interactions within the region that would, logically, govern commercial deployment of new clones. Clones were developed by breeding and selection programs at the University of Illinois, Iowa State University, University of Minnesota, and the USDA Forest Service for experiments established in 1995. We report results of analyses of variance and principal component analyses of tree diameters and estimated above-ground biomass that demonstrate significant genotype main effects and significant genotype × environment interactions. Maximum mean annual above-ground biomass increments have surpassed 16 Mg ha−1 y−1, exceeding previously reported yields of poplars grown under similar conditions in the north-central U.S. We also discuss the breeding and selection of poplars in general with specific attention to regional research needs. Key words: Populus, biomass, multi-trait selection, genotype, genotype × environment interaction

Preliminary estimates of biomass growth in the Tamaulipan thornscrub in north-eastern Mexico

The objective of this research was to estimate the biomass growth of 10 typical species of the Tamaulipan thornscrub in north-eastern Mexico. In total, eight biomass growth models of three parameters were tested. Parameter fitting was conducted by least square techniques in non-linear regression. The best model for each shrub species generated growth and increment of above-ground dry biomass. The results showed that the Logistic and Weibull models consistently fitted better the observed biomass growth for 60% of the studied shrub species. Models predict that Diospyros texana, Acacia berlandieri and Cordia boissieri have the largest growth rates of standing biomass in contrast to Helietta parvifolia, Acacia rigidula and Pithecellobium pallens. At the spatial scale, the Tamaulipan thornscrub produces a peak periodic biomass increment of 4·11 Mg ha−1year−1. However, this biome currently produces a periodic biomass increment of 1·67 Mg ha−1year−1. This report highlights the need to establish permanents sampling plots to observe and better model biomass growth at the stand level.