Forest structure and live aboveground biomass variation along an elevational gradient of tropical Atlantic moist forest (Brazil)

Live aboveground biomass (AGB) is an important source of uncertainty in the carbon balance from the tropical regions in part due scarcity of reliable estimates of live AGB and its variation across landscapes and forest types. Studies of forest structure and biomass stocks of Neotropical forests are biased toward Amazonian and Central American sites. In particular, standardized estimates of aboveground biomass stocks for the Brazilian Atlantic forest are rarely available. Notwithstanding the role of environmental variables that control the distribution and abundance of biomass in tropical lowland forests has been the subject of considerable research, the effect of short, steep elevational gradients on tropical forest structure and carbon dynamics is not well known. In order to evaluate forest structure and live AGB variation along an elevational gradient (0–1100 m a.s.l.) of coastal Atlantic Forest in SE Brazil, we carried out a standard census of woody stems ≥4.8 cm dbh in 13 1-ha permanent plots established on four different sites in 2006–2007. Live AGB ranged from 166.3 Mg ha⁻¹ (bootstrapped 95% CI: 144.4,187.0) to 283.2 Mg ha⁻¹ (bootstrapped 95% CI: 253.0,325.2) and increased with elevation. We found that local-scale topographic variation associated with elevation influences the distribution of trees >50 cm dbh and total live AGB. Across all elevations, we found more stems (64–75%) with limited crown illumination but the largest proportion of the live AGB (68–85%) was stored in stems with highly illuminated or fully exposed crowns. Topography, disturbance and associated changes in light and nutrient supply probably control biomass distribution along this short but representative elevational gradient. Our findings also showed that intact Atlantic forest sites stored substantial amounts of carbon aboveground. The live tree AGB of the stands was found to be lower than Central Amazonian forests, but within the range of Neotropical forests, in particular when compared to Central American forests. Our comparative data suggests that differences in live tree AGB among Neotropical forests are probably related to the heterogeneous distribution of large and medium-sized diameter trees within forests and how the live biomass is partitioned among those size classes, in accordance with general trends found by previous studies. In addition, the elevational variation in live AGB stocks suggests a large spatial variability over coastal Atlantic forests in Brazil, clearly indicating that it is important to consider regional differences in biomass stocks for evaluating the role of this threatened tropical biome in the global carbon cycle.     

A 3D approach to reconstruct continuous optical images using lidar and MODIS

Background: Monitoring forest health and biomass for changes over time in the global environment requires the provision of continuous satellite images. However, optical images of land surfaces are generally contaminated when clouds are present or rain occurs.Methods: To estimate the actual reflectance of land surfaces masked by clouds and potential rain, 3D simulations by the RAPID radiative transfer model were proposed and conducted on a forest farm dominated by birch and larch in Genhe City, Da Xing'An Ling Mountain in Inner Mongolia, China. The canopy height model(CHM) from lidar data were used to extract individual tree structures(location, height, crown width). Field measurements related tree height to diameter of breast height(DBH), lowest branch height and leaf area index(LAI). Series of Landsat images were used to classify tree species and land cover. MODIS LAI products were used to estimate the LAI of individual trees. Combining all these input variables to drive RAPID, high-resolution optical remote sensing images were simulated and validated with available satellite images.Results: Evaluations on spatial texture, spectral values and directional reflectance were conducted to show comparable results.Conclusions: The study provides a proof-of-concept approach to link lidar and MODIS data in the parameterization of RAPID models for high temporal and spatial resolutions of image reconstruction in forest dominated areas.     

EU-wide maps of growing stock and above-ground biomass in forests based on remote sensing and field measurements

The overall objective of this study was to combine national forest inventory data and remotely sensed data to produce pan-European maps on growing stock and above-ground woody biomass for the two species groups “broadleaves” and “conifers”. An automatic up-scaling approach making use of satellite remote sensing data and field measurement data was applied for EU-wide mapping of growing stock and above-ground biomass in forests. The approach is based on sampling and allows the direct combination of data with different measurement units such as forest inventory plot data and satellite remote sensing data. For the classification, data from the Moderate Resolution Imaging Spectroradiometer (MODIS) were used. Comprehensive field measurement data from national forest inventories for 98,979 locations from 16 countries were used for which tree species and growing stock estimates were available. The classification results were evaluated by comparison with regional estimates derived independently from the classification from national forest inventories. The validation at the regional level shows a high correlation between the classification results and the field based estimates with correlation coefficient r = 0.96 for coniferous, r = 0.94 for broadleaved and r = 0.97 for total growing stock per hectare. The mean absolute error of the estimations is 25 m³/ha for coniferous, 20 m³/ha for broadleaved and 25 m³/ha for total growing stock per hectare. Biomass conversion and expansion factors were applied to convert the growing stock classification results to carbon stock in above-ground biomass. As results of the classification, coniferous and broadleaved growing stock as well as carbon stock of the above-ground biomass is mapped on a wall-to-wall basis with a spatial resolution of 500 m × 500 m per grid cell. The mapped area is 5 million km², of which 2 million km² are forests, and covers the whole European Union, the EFTA countries, the Balkans, Belarus, the Ukraine, Moldova, Armenia, Azerbaijan, Georgia and Turkey.     

Intensive tree planting facilitates tropical forest biodiversity and biomass accumulation in Kibale National Park, Uganda

The extensive area of degraded tropical land and the calls to conserve forest biodiversity and sequester carbon to offset climate change demonstrate the need to restore forest in the tropics. Deforested land is sometimes replanted with fast-growing trees; however, the consequences of intensive replanting on biomass accumulation or plant and animal diversity are poorly understood. The purpose of this study was to determine how intensive replanting affected tropical forest regeneration and biomass accumulation over ten years. We studied reforested sites in Kibale National Park, Uganda, that were degraded in the 1970s and replanted with five native tree species in 1995. We identified and measured the size of planted versus naturally regenerating trees, and felled and weighed matched trees outside the park to calculate region-specific allometric equations for above-ground tree biomass. The role of shrubs and grasses in facilitating or hindering the establishment of trees was evaluated by correlating observed estimates of percent cover to tree biomass. We found 39 tree species naturally regenerating in the restored area in addition to the five originally planted species. Biomass was much higher for planted (15,675 kg/ha) than naturally regenerated trees (4560 kg/ha), but naturally regenerating tree regrowth was an important element of the landscape. The establishment of tree seedlings initially appeared to be facilitated by shrubs, primarily Acanthus pubescens and the invasive Lantana camara; however, both are expected to hinder tree recruitment in the long-term. Large and small-seeded tree species were found in the replanted area, indicating that bird and mammal dispersers contributed to natural forest restoration. These results demonstrate that intensive replanting can accelerate the natural accumulation of biomass and biodiversity and facilitate the restoration of tropical forest communities. However, the long-term financial costs and ecological benefits of planting and maintaining reforested areas need to be weighed against other potential restoration strategies.     

Crown area allometries for estimation of aboveground tree biomass in agricultural landscapes of western Kenya

Classical allometries determine biomass from measurements of diameter at breast height or volume. Neither of these measurements is currently possible to be derived directly from remote sensing. As biomass estimates at larger scales require remotely sensed data, new allometric relations are required using crown area and/or tree height as predictor of biomass, which can both be derived from remote sensing. Allometric equations were developed from 72 trees semi-randomly selected for destructive sampling in three 100?km² sentry sites in western Kenya. The equations developed fit the data well with about 85?% of the observed variation in aboveground biomass explained by crown area. Addition of height and wood density as second predictor variables improved model fit by 6 and 2?% and lowered the relative error by 7 and 2?%, respectively. The equation with crown area in combination with height and wood density estimated representative aboveground biomass carbon to be about 20.8?±?0.02?t?C?ha^?1; which is about 19?% more than the amount estimated using an allometry with diameter at breast height as predictor. These results form the basis for a new generation of allometries using crown area as a predictor of aboveground biomass in agricultural landscapes. Biomass predictions using crown area should be supported by height and wood density and the application of crown area equations for remote sensing based up-scaling should consider crown interactions with competing or coexisting neighboring trees.     

Lianas and self-supporting plants during tropical forest succession

Lianas (woody vines) are an important component of tropical forests, with a strong impact on forest dynamics, but their responses during forest succession have received relatively little attention. Here, we present an analysis of the changes in stem density, biomass, and species richness of lianas and self-supporting plants during tropical forest succession. We surveyed lianas ≥0.5 cm diameter at breast height (dbh) and self-supporting plants ≥2.5 cm dbh in 0.1 ha inventory plots in a chronosequence of 30 sites in northeastern Costa Rica, 23 sites on abandoned pastures 10–44 years of age, and seven sites in old-growth forest. Stem density of self-supporting plants showed no predictable chronosequence trend, but liana stem density declined significantly with forest age. Aboveground biomass of self-supporting vegetation increased rapidly during succession, with forests 31–44 years exhibiting higher levels of biomass than old-growth forests. Liana biomass accumulated more slowly, with the highest levels in old-growth sites. Species richness of self-supporting vegetation increased significantly during succession, but species richness of lianas showed no change or a slight decline with forest age, depending on the method of assessment. The differences between tree and liana responses during succession stem from the unique physiology and life history traits of lianas.     

Estimation of aboveground biomass in mangrove forests using high-resolution satellite data

Mangroves play important roles in providing a range of ecosystem services, mitigation of strong waves, protection of coastlines against erosion, maintenance of water quality, and carbon sink in the context of global warming. For trees in mangrove forests in southern Ranong Province, Thailand, we investigated the allometric relationship between crown area derived from high-resolution satellite data and stem diameter and used the resulting model to estimate aboveground biomass. We used QuickBird panchromatic and multispectral data acquired for the study area on 15 October 2006 as the high-resolution satellite data. Individual tree crowns were extracted from the satellite image of panchromatic data by using the watershed method, and the species were identified by using the maximum-likelihood method for the multispectral data. Overall classification accuracy for species identification was 88.5 %. The biomass derived from our field survey was plotted against aboveground biomass in the sample plots, estimated from the QuickBird data. The regression line through the origin between the satellite-estimated biomass and biomass based on the field data had a slope of 1.26 (R ² = 0.65). Stand aboveground biomass estimated from the high-resolution satellite data was underestimated because of a lack of data on the biomass of suppressed trees and inappropriate segmentation of crowns of large trees into two or more trees.     

Impacts of selective logging on above-ground forest biomass in the Monts de Cristal in Gabon

Selective logging is an important socio-economic activity in the Congo Basin but one with associated environmental costs, some of which are avoidable through the use of reduced-impact logging (RIL) practices. With increased global concerns about biodiversity losses and emissions of carbon from forest in the region, more information is needed about the effects of logging on forest structure, composition, and carbon balance. We assessed the consequences of low-intensity RIL on above-ground biomass and tree species richness in a 50 ha area in northwestern Gabon. We assessed logging impacts principally in 10 randomly located 1-ha plots in which all trees ?10 cm dbh were measured, identified to species, marked, and tagged prior to harvesting. After logging, damage to these trees was recorded as being due to felling or skidding (i.e., log yarding) and skid trails were mapped in the entire 50-ha study area. Allometric equations based on tree diameter and wood density were used to transform tree diameter into biomass.Logging was light with only 0.82 trees (8.11 m³) per hectare extracted. For each tree felled, an average of 11 trees ?10 cm dbh suffered crown, bole, or root damage. Skid trails covered 2.8% of the soil surface and skidding logs to the roadside caused damage to an average of 15.6 trees ?10 cm dbh per hectare. No effect of logging was observed on tree species richness and pre-logging above-ground forest biomass (420.4 Mg ha⁻¹) declined by only 8.1% (34.2 Mg ha⁻¹). We conclude from these data that with harvest planning, worker training in RIL techniques, and low logging intensities, substantial carbon stocks and tree species richness were retained in this selectively logged forest in Gabon.     

Profound impoverishment of the large-tree stand in a hyper-fragmented landscape of the Atlantic forest

Large tree species have a disproportional influence on the structure and functioning of tropical forests, but the forces affecting their long-term persistence in human-dominated landscapes remain poorly understood. Here we test the hypothesis that aging forest edges and small fragments (3.4–295.7 ha) are greatly impoverished in terms of species richness and abundance of large trees in comparison to core areas of forest interior. The study was conducted in a hyper-fragmented landscape of the Atlantic forest, northeast Brazil. Large tree species were quantified by recording all trees (DBH ≥ 10 cm) within fifty-eight 0.1-ha plots distributed in three forest habitats: small forest fragments (n = 28), forest edges (n = 10), and primary forest interior areas within an exceptional large forest remnant (n = 20). Large tree species and their stems ≥10 cm DBH were reduced by half in forest edges and fragments. Moreover, these edge-affected habitats almost lacked large-stemmed trees altogether (0.24 ± 0.27% of all stems sampled), and very tall trees were completely absent from forest edges. In contrast, large trees contributed to over 1.5% of the whole stand in forest interior plots (2.9 ± 2.8%). Habitats also differed in terms of tree architecture: relative to their DBH trees were on average 30% shorter in small fragments and forest edges. Finally, an indicator species analysis yielded an ecological group of 12 large tree species that were significantly associated with forest interior plots, but were completely missing from edge-affected habitats. Our results suggest a persistent and substantial impoverishment of the large-tree stand, including the structural collapse of forest emergent layer, in aging, hyper-fragmented landscapes.     

What factors influence the collapse of trees retained on logged sites?: A case-control study

Living trees (green trees) are intentionally retained on logged sites for many purposes such as wildlife conservation, future wood potential and aesthetics. Minimizing the risk that these trees collapse in the short-term will improve the chances that green-tree retention meets its objectives. In a retrospective case-control study, we identified factors significantly associated with the collapse of living trees retained on logged and slash-burnt sites in south-eastern Australia within 8 years of harvesting. Trees with incomplete crowns or trees with at least one visible cavity were, on average, at three times greater risk of collapse relative to trees with complete crowns or no visible cavities, respectively. Trees with fire-scarring, trees retained greater than 50 m from intact forest or trees retained in isolation were, on average, around twice the risk of collapse relative to trees without fire-scarring, trees retained within 50 m of intact forest or trees retained among other trees, respectively. When considered jointly, the significant factors in a model predicting the collapse of retained trees – tree height, tree diameter, crown form – were all associated with the health of trees. Choosing the healthiest trees possible for fulfilling their function, protecting trees from damage (e.g. fire) and retaining trees near, or among, other trees are likely to reduce the risk of collapse among retained trees and thus contribute to the effectiveness of green-tree retention in logged eucalypt forests.     

面向对象的退耕还林造林效果遥感特征提取技术研究

以河北省张家口市2002年的退耕还林地为研究对象,以高空间分辨率(以下简称高分辨率)遥感(Quick-bird-快鸟,分辨率0.6m)为信息载体。运用严格的传感器物理模型对快鸟预正射影像进行正射处理,采用Median滤波、Gaussian滤波和均值滤波三种滤波技术对图像进行增强处理。采用面向对象的图像信息提取技术,提取退耕还林地树冠特征值,进而计算退耕还林造林保存率。研究结果表明:由遥感数据自动提取的树冠尺寸(直径)在1.2m以上,平均保存率为85.11%,精度达到了89.837%。     

基于遥感图像的林况因子提取研究进展

随着遥感技术的不断发展,部分林况因子调查逐渐从传统的人工地面调查转向遥感调查,虽然提高了工作效率和精度,但也存在一些尚未解决的问题。文中系统总结了基于遥感图像的树种、树高、树冠、胸径、位置、郁闭度、年龄、株数、蓄积量、生物量等林况因子目视判读和计算机提取研究的现状及存在的问题,并对今后发展提出了建议。     

An indicator of tree migration in forests of the eastern United States

Changes in tree species distributions are a potential impact of climate change on forest ecosystems. The examination of tree species shifts in forests of the eastern United States largely has been limited to simulation activities due to a lack of consistent, long-term forest inventory datasets. The goal of this study was to compare current geographic distributions of tree seedlings (trees with a diameter at breast height ≤2.5 cm) with biomass (trees with a diameter at breast height > 2.5 cm) for sets of northern, southern, and general tree species in the eastern United States using a spatially balanced, region-wide forest inventory. Compared to mean latitude of tree biomass, mean latitude of seedlings was significantly farther north (>20 km) for the northern study species, while southern species had no shift, and general species demonstrated southern expansion. Density of seedlings relative to tree biomass of northern tree species was nearly 10 times higher in northern latitudes compared to southern latitudes. For forest inventory plots between 44° and 47° north latitude where southern tree species were identified, their biomass averaged 0.46 tonnes/ha while their seedling counts averaged 2600 ha⁻¹. It is hypothesized that as northern and southern tree species together move northward due to greater regeneration success at higher latitudes, general species may fill their vacated niches in southern locations. The results of this study suggest that the process of northward tree migration in the eastern United States is currently underway with rates approaching 100 km/century for many species.     

高空间分辨率遥感森林参数提取探讨

介绍了高空间分辨率遥感在森林参数提取方面的研究和应用情况,并结合国内外学者在此方面所做出的研究成果,对不同森林参数的提取分别做了阐述,包括单木树冠轮廓信息、胸径、森林生物量、树种识别和分类、叶面积指数、森林郁闭度、木材结构和性质。最后分析了高空间分辨率遥感在森林参数提取方面存在的问题,并对该领域的应用前景作了展望。     

Oak mortality associated with crown dieback and oak borer attack in the Ozark Highlands

Oak decline and related mortality have periodically plagued upland oak–hickory forests, particularly oak species in the red oak group, across the Ozark Highlands of Missouri, Arkansas and Oklahoma since the late 1970s. Advanced tree age and periodic drought, as well as Armillaria root fungi and oak borer attack are believed to contribute to oak decline and mortality. Declining trees first show foliage wilt and browning, followed by progressive branch dieback in the middle and/or upper crown. Many trees eventually die if severe crown dieback continues. In 2002, more than 4000 living oak trees ≥11 cm dbh in the relatively undisturbed mature oak forests of the Missouri Ozark Forest Ecosystem Project (MOFEP) were randomly selected and inventoried for tree species, dbh, crown class, crown width, crown dieback condition (healthy: <5% crown dieback, slight: >5–33%, moderate: 33–66%, and severe: >66%) and number of emergence holes created by oak borers on the lower 2.4 m of the tree bole. The same trees were remeasured in 2006 to determine their status (live or dead). In 2002, about 10% of the red oak trees showed moderate or severe crown dieback; this was twice the percentage observed for white oak species. Over 70% of trees in the red oak group had evidence of oak borer damage compared to 35% of trees in the white oak group. There was significant positive correlation between crown dieback and the number of borer emergence holes (p < 0.01). Logistic regression showed oak mortality was mainly related to crown width and dieback, and failed to detect any significant link with the number of oak borer emergence holes. Declining red oak group trees had higher mortality (3 or 4 times) than white oaks. The odds ratios of mortality of slightly, moderately, and severely declining trees versus healthy trees were, respectively, 2.0, 6.5, and 29.7 for black oak; 1.8, 3.8, and 8.3 for scarlet oak; and 2.6, 6.5 and 7.1 for white oaks.     

基于多源数据协同作业的森林信息提取研究进展

传统森林调查手段正逐渐被激光雷达、光学遥感及卫星遥感等新兴的遥感技术所代替。随着研究的不断深入,单一遥感数据源往往难以满足高精度的森林信息提取需求。因此,文中以激光雷达为研究主体,综述摄影测量、高光谱遥感及卫星遥感等多种遥感技术在森林信息提取中不同遥感技术协同作业的研究进展。相较于单一数据源,多源数据协同作业在森林结构参数提取、生物量估测以及树种识别等领域均有明显优势。结合目前的研究工作,从数据获取成本、获取方式、多源数据融合、配套软件及系统构建等方面展望了多源数据协同作业方式的发展趋势。     

Epiphyte diversity and biomass loads of canopy emergent trees in Chilean temperate rain forests: A neglected functional component

We document for the first time the epiphytic composition and biomass of canopy emergent trees from temperate, old-growth coastal rainforests of Chile (42°30′S). Through tree-climbing techniques, we accessed the crown of two large (c. 1 m trunk diameter, 25–30 m tall) individuals of Eucryphia cordifolia (Cunoniaceae) and one large Aextoxicon punctatum (Aextoxicaceae) to sample all epiphytes from the base to the treetop. Epiphytes, with the exception of the hemi-epiphytic tree Raukaua laetevirens (Araliaceae), were removed, weighed and subsamples dried to estimate total dry mass. We recorded 22 species of vascular epiphytes, and 22 genera of cryptogams, with at least 30 species of bryophytes, liverworts and lichens. The dominant vascular epiphytes were Fascicularia bicolor (Bromeliaceae), Raukaua laetevirens, Sarmienta repens (Gesneriaceae), and filmy ferns (Hymenophyllaceae). Epiphyte loads per tree ranged between 134 and 144 kg dry mass, with 60–70% water. The hemi-epiphytic tree R. laetevirens added between 1 and 2.6 t of dry mass to each host tree. A main component of epiphyte biomass, making 70% of the weight, was detritus and roots, while leaves, stems, and fronds made up the remaining 30%. Emergent trees hold a high proportion of the regional diversity of epiphytes: 33% of all flowering epiphytes, and 50% of all filmy ferns described for Chilean temperate forests. Dry epiphyte biomass associated only with the emergent E. cordifolia trees in coastal forests was estimated in 10 t/ha. Epiphyte biomass may store up to 300 l of water in each emergent tree, and add 40–150% of photosynthetic biomass to the tree crowns. Based on this evidence, epiphytes may play key but generally neglected roles in ecosystem carbon uptake, water storage, and nutrient cycling. Moreover, emergent trees represent nuclei of biodiversity and ecosystem functions distributed throughout mature forests. Forest management should recognize large trees as significant management units for the preservation of biodiversity and ecological functions.     

Estimates of forest biomass in the Brazilian Amazon: New allometric equations and adjustments to biomass from wood-volume inventories

Uncertainties in biomass estimates in Amazonian forests result in a broad range of possible magnitude for the emissions of carbon from deforestation and other land-use changes. This paper presents biomass equations developed from trees directly weighed in open forest on fertile soils in the southern Amazon (SA) and allometric equations for bole-volume estimates of trees in both dense and open forests. The equations were used to improve the commonly used biomass models based on large-scale wood-volume inventories carried out in Amazonian forest. The biomass estimates from the SA allometric equation indicate that equations developed in forests on infertile soils in central Amazonia (CA) result in overestimates if applied to trees in the open forests of SA. All aboveground components of 267 trees in open forests of SA were cut and weighed, and the proportion of the biomass stored in the crowns of trees in open forest was found to be higher than in dense forest. In the case of inventoried wood volume, corrections were applied for indentations and hollow trunks and it was determined that no adjustment is needed for the form factor used in the RadamBrasil volume formula. New values are suggested for use in models to convert wood volume to biomass estimates. A biomass map for Brazilian Amazonia was produced from 2702 plots inventoried by the RadamBrasil Project incorporating all corrections for wood density and wood volume and in factors used to add the bole volume of small trees and the crown biomass. Considering all adjustments, the biomass map indicates total biomass of 123.1 Gt (1 Gt = 1 billion tons) dry weight (aboveground + belowground) for originally forested areas in 1976 in the Brazilian Legal Amazon as a whole (102.3 Gt for aboveground only) at the time of the RadamBrasil inventories, which were carried out before intensive deforestation had occurred in the region. Excluded from this estimate are 529,000 km² of forest lacking sufficient RadamBrasil inventory data. After forest losses of 676,000 km² by 2006 – not counting 175,000 km² of this deforested area lacking RadamBrasil data – the estimated dry biomass stock was reduced to 105.4 and 87.6 Gt (aboveground + belowground and only above-ground). Thus, in 2006 the carbon storage in forested areas in Brazilian Amazonia as a whole will be around 51.1 Gt (assuming 1 Mg dry biomass = 0.485 Mg C). Biomass estimates by forest type (aggregated into 12 vegetation classes) are provided for each state in the Brazilian Legal Amazon.     

Increasing wood production through old age in tall trees

How long forest trees can sustain wood production with increasing age remains an open question, primarily because whole-crown structure and growth cannot be readily measured from the ground or on felled trees. We climbed and directly measured crown structures and growth rates of 43 un-suppressed individuals (site trees) of the two tallest species – Eucalyptus regnans and Sequoia sempervirens – representing a wide range of tree sizes and ages. In both species, ground-level measurements of annual growth, including height, ring width, and basal area increment, exhibited the oft-reported trend of decreasing growth (or no change in growth) with age, yet wood production of the entire main trunk and whole crown both increased with size and age up to and including the largest and oldest trees we measured. The balance between structural metrics of whole-crown respiratory demands (cambium area, inner bark volume, sapwood volume, and heartwood deposition area) and photosynthetic capacity (leaf area and green bark area) was statistically independent of size but not age. After accounting for the effect of size, trees with lower potential respiratory demands grew more than trees with higher potential respiratory demands per unit photosynthetic area. The strongest determinant of tree energy balance was the ratio of aboveground cambium area to leaf area. Among the site trees we examined, over 85% of the variation in annual wood production was explained by variation in size, and the proportion of total aboveground wood production in appendages (branches, limbs, and reiterated trunks) increased linearly with size. With increasing age in both species, the proportion of annual wood production converted to heartwood increased in main trunks and appendages. The oldest tree we measured produced more heartwood in its main trunk over 651 years (351 m³) than contained in any tree we measured <1500 years old. The two tallest tree species achieve similar stature despite divergent growth dynamics and ecologies. At one extreme, E. regnans attains great size quickly but dies relatively young because trees are susceptible to fire and fungi. At the other extreme, S. sempervirens attains great size more slowly but has a long lifespan because trees resist fire and prioritize investment in decay-resistant heartwood. Increasing wood production as trees age is a mechanism underlying the maintenance of biomass accumulation during forest development and the carbon-sink capacity of old-growth forests.     

Relationship between annual rainfall and tree mortality in a tropical dry forest: Results of a 19-year study at Mudumalai,southern India

Variability in rainfall is known to be a major influence on the dynamics of tropical forests, especially rates and patterns of tree mortality. In tropical dry forests a number of contributing factors to tree mortality, including dry season fire and herbivory by large herbivorous mammals, could be related to rainfall patterns, while loss of water potential in trees during the dry season or a wet season drought could also result in enhanced rates of death. While tree mortality as influenced by severe drought has been examined in tropical wet forests there is insufficient understanding of this process in tropical dry forests. We examined these causal factors in relation to inter-annual differences in rainfall in causing tree mortality within a 50-ha Forest Dynamics Plot located in the tropical dry deciduous forests of Mudumalai, southern India, that has been monitored annually since 1988. Over a 19-year period (1988–2007) mean annual mortality rate of all stems >1 cm dbh was 6.9 ± 4.6% (range = 1.5–17.5%); mortality rates broadly declined from the smaller to the larger size classes with the rates in stems >30 cm dbh being among the lowest recorded in tropical forest globally. Fire was the main agent of mortality in stems 1–5 cm dbh, elephant-herbivory in stems 5–10 cm dbh, and other natural causes in stems >10 cm dbh. Elephant-related mortality did not show any relationship to rainfall. On the other hand, fire-related mortality was significantly negatively correlated to quantity of rainfall during the preceding year. Mortality due to other causes in the larger stem sizes was significantly negatively correlated to rainfall with a 2–3-year lag, suggesting that water deficit from mild or prolonged drought enhanced the risk of death but only with a time lag that was greater than similar lags in tree mortality observed in other forest types. In this respect, tropical dry forests growing in regions of high rainfall variability may have evolved greater resistance to rainfall deficit as compared to tropical moist or temperate forests but are still vulnerable to drought-related mortality.