Diversity and structure of regenerating tropical dry forests in Costa Rica: Geographic patterns and environmental drivers

Much of the dry tropical forest biome has been converted to agricultural land uses over the past several centuries. However, in conservation areas such as those in the Guanacaste and Tempisque regions of Costa Rica, tropical dry forests are regenerating due to management practices including fire suppression. To better understand the patterns of secondary succession occurring in Costa Rican tropical dry forest, we established 60 20 × 50 m plots in mature and regenerating forests in the Sector Santa Rosa (formerly known as Parque Nacional Santa Rosa) and Palo Verde National Park. Plots were stratified into three plant communities: tropical dry oak forest (Quercus oleoides) (SROAK), Santa Rosa tropical dry forest (SRTDF), and Palo Verde tropical dry forest (PVTDF). In these plots we measured and identified and all individuals >10 cm DBH, measured but did not identify stems <10 cm but taller than 1.3 m, counted woody seedlings (<1.3 m height) and analyzed soil chemical and physical properties.     

Water use by Tabor and Kermes oaks growing in their respective habitats in the Lower Galilee region of Israel

We estimated water use by the two main oak species of the Lower Galilee region of Israel—Tabor (Quercus ithaburensis) and Kermes (Quercus calliprinos)—to develop management options for climate-change scenarios. The trees were studied in their typical phytosociological associations on different bedrock formations at two sites with the same climatic conditions. Using the heat-pulse method, sap flow velocity was measured in eight trunks (trees) of each species during a number of periods in 2001, 2002 and 2003. Hourly sap flux was integrated to daily transpiration per tree and up-scaled to transpiration at the forest canopy level. The annual courses of daytime transpiration rate were estimated using fitted functions, and annual totals were calculated. Sap flow velocity was higher in Tabor than in Kermes oak, and it was highest in the youngest xylem, declining with depth into the older xylem. Average daytime transpiration rate was 67.9 ± 4.9 l tree⁻¹ d⁻¹, or 0.95 ± 0.07 mm d⁻¹, for Tabor oak, and 22.0 ± 1.7 l tree⁻¹d⁻¹, or 0.73 ± 0.05 mm d⁻¹, for Kermes oak. Differences between the two oak species in their forest canopy transpiration rates occurred mainly between the end of April and the beginning of October. Annual daytime transpiration was estimated to be 244 mm year⁻¹ for Tabor oak and 213 mm year⁻¹ for Kermes oak. Adding nocturnal water fluxes, estimated to be 20% of the daytime transpiration, resulted in total annual transpiration of 293 and 256 mm year⁻¹ by Tabor and Kermes oaks, respectively. These amounts constituted 51% and 44%, respectively, of the 578 mm year⁻¹ average annual rainfall in the region. The two species differed in their root morphology. Tabor oak roots did not penetrate the bedrock but were concentrated along the soil–rock interface within soil pockets. In contrast, the root system of Kermes oak grew deeper via fissures and crevices in the bedrock system and achieved direct contact with the deeper bedrock layers. Despite differences between the two sites in soil–bedrock lithological properties, and differences in the woody structure, annual water use by the two forest types was fairly similar. Because stocking density of the Tabor oak forests is strongly related to bedrock characteristics, thinning as a management tool will not change partitioning of the rainfall between different soil pockets, and hence soil water availability to the trees. In contrast, thinning of Kermes oak forests is expected to raise water availability to the remaining trees.     

Tree-cavity occurrence, cavity occupation and reproductive performance of secondary cavity-nesting birds in oak forests: The role of traditional management practices

Secondary cavity-nesting birds (SCN), which cannot create their own breeding cavities, are expected to be influenced by habitat alteration caused by forest management practices, but the mechanisms underlying the distribution pattern of SCN subjected to different management systems are poorly known. To improve our knowledge on these mechanisms, we examine cavity abundance, cavity occupation and reproductive performance of SCN in Pyrenean oak (Quercus pyrenaica) forests subjected to two management systems: (i) dense “young forests”, maintained at such stage by clear-cuttings and burns, and (ii) “old forest”, subjected to extensive traditional grazing and scarce firewood extraction by selective cutting. Young forests had considerably lower density of cavities (1.29 ± 0.71 vs 15.09 ± 2.00 cavities ha⁻¹), SCN species (0.18 ± 0.11 vs 0.61 ± 0.07 species ha⁻¹) and nests (0.40 ± 0.27 vs 2.67 ± 0.25 nests of all SCN ha⁻¹) than old forests, indicating that a low availability of cavities may limit SCN assemblages in young oak forests. However, reproductive parameters of great (Parus major) and blue (Cyanistes caeruleus) tits associated with the availability of food (laying date, clutch size, nestling number and weight, adult weight) did not differ between both forest types, suggesting that food supply was not reduced in young forests, at least for tits during the breeding season. Large diameter (up to 170 cm dbh) decayed trees were the most likely to hold cavities, but birds preferred smaller living cavity-trees for nesting (90% of nests in 21-65 cm dbh trees). The preservation of cavity-trees within traditionally managed old oak forests is crucial in providing nesting opportunities to SCN. Besides, the protection of these traditionally managed forests would also benefit to other forest organisms that depend on old and open oak forests.     

Tree biomass estimation in regenerating areas of tropical dry vegetation in northeast Brazil

Allometric equations have been developed for various different vegetation types but have rarely been validated in the field and never for dry tropical forest such as caatinga. In three areas of semi-arid Brazil, with regenerating caatinga vegetation, we measured and weighed twelve hundred individuals of four tree species and used the data to validate equations previously determined in mature caatinga. They and several other equations developed for tropical vegetations overestimate the biomass (B) of trees from the regeneration areas by more than 20%, possibly because these trees have reduced crowns, with lower branch masses. We then determined new allometric equations for them, validating equations for one site against data of the others and pooling the data if they were cross-validated. The best equations were power ones, based on diameter at breast height (D), with little improvement by including height, crown area and/or wood density (Caesalpinia pyramidalis, B = 0.3129D^1.8838; Croton sonderianus, B = 0.4171D^1.5601; Mimosa ophthalmocentra, B = 0.4369D^1.8493; and Mimosa tenuiflora, B = 0.3344D^1.9648 and 0.4138D^1.7718).     

Distribution and population patterns of the threatened palm Brahea aculeata in a tropical dry forest in Sonora, Mexico

The use of non-timber forest products (NTFPs) has great potential for the conservation of natural resources and rural development. Palms are important NTFPs, providing numerous products, including leaves. The harvest of palm leaves rarely results in the immediate death of individuals and can be considered one example of the sustainable use of forest resources. However, in most cases basic ecological information, such as distribution and abundance of the species is unknown, as is information on the ecological implications of human impacts, such as leaf harvest and livestock grazing. In the tropical dry forests of northwest Mexico, leaves from the threatened palm Brahea aculeata are harvested for roofing material and represent an important NTFP. In this study, we assessed the distribution and abundance patterns of this species across 52 plots in the tropical dry forest of Sierra de Álamos-Rio Cuchujaqui Reserve (SARCR) in Sonora, Mexico. We also evaluated patterns of leaf harvest and cattle browse intensity on palm populations. We found that B. aculeata density is highly variable across the landscape with a mean (±SE) of 121.7 ± 36.3 ha⁻¹. Results indicate that B. aculeata is primarily distributed near to arroyos and rivers. The highest densities were found in sites with low incidence radiation (<0.06 MJ cm⁻²) and narrow stream width of arroyos/rivers (<9.5 m). Palm abundance also varied within the plots, and B. aculeata attained its highest densities near to the arroyo edge (first 20 m from the edge), perhaps indicating a microhabitat effect on palm demography. Overall, fewer than 6% of the stems were seedlings. Leaf harvesting and browsing appear to affect demographic vital rates of the species; specifically we found a significant effect of harvesting and browsing activity on the proportion of reproductive active adults. Thus, low levels of seedlings in the populations may be the result of reduced fruit production by adults and higher mortality rates of seedlings due to livestock herbivory. Result from interviews with land owners also indicated that past land use, especially along arroyos might also have important impacts on the observed distribution, low densities and absence of recruitment in some areas. We believe current distribution and abundance of NTFP, such as B. aculeata at SARCR may be a result of combined effects of environmental factors and human impacts. Results from this study will be used to develop appropriate conservation, management and restoration plans of B. aculeata in the area.     

Mixed litter decomposition in a managed Missouri Ozark forest ecosystem

We monitored the decomposition of mixed leaf litter (Quercus spp., Carya spp., and Pinusechinata) in a Missouri Ozark forest eight years after experimental harvest. Leaf litter mass losses and changes in carbon chemistry (extractive, acid soluble, and acid insoluble fractions) were measured over 32 months in field incubations to determine the effects of litter composition and stand manipulation on decomposition and nitrogen (N) concentration in the remaining litter. The decay (k) rate over this period ranged between 0.39 (±0.010) and 0.51 (±0.002) year⁻¹ for oak, oak–hickory, and oak–pine litter. There were significant main effects of stand manipulation (p = 0.03) and litter type (p < 0.01) on decay. Mass losses of oak and oak–hickory litter were 7% (p = 0.02) and 4% (p = 0.04) higher on harvested stands than controls, respectively. Mass loss of oak–hickory litter was 3% faster than oak–pine (p = 0.03) and 6% faster than oak (p = 0.02) litter on control stands, whereas the oak–hickory litter mass loss was 5% higher than oak litter on harvested stands (p = 0.01). The decay (k) rate had a linear relationship with initial leaf litter nitrogen content and lignin-to-N ratio. The nitrogen concentration in remaining litter had a nonlinear relationship to cumulative mass loss suggesting an exogenous source of N. In summary, this study demonstrated significant effects of timber harvest and litter mixtures on decomposition and N dynamics in a managed Missouri Ozark forest.     

Ectomycorrhizal fungal communities of rehabilitated bauxite mines and adjacent,natural jarrah forest in Western Australia

Species richness and species composition of ectomycorrhizal (EM) fungi were compared among rehabilitated mine sites and unmined jarrah forest in southwest Western Australia. Species richness, measured in 50 m × 50 m plots, was high. In the wetter, western region, mean species richness per plot in 16-year-old rehabilitated mine sites (63.7 ± 2.5, n = 3) was similar to that of unmined jarrah forest (63.6 ± 9.6, n = 9). In the drier, eastern region, species richness in 12-year-old rehabilitated mine sites (40.3 ± 2.1, n = 3) approached that of nearby forest (52.4 ± 9.3, n = 9). Species composition was analysed by detrended correspondence analysis. Rehabilitated sites of similar age clustered together in the analysis and species composition was closer to the native jarrah forest in the older rehabilitated plots. In unmined forest, species composition of fungal communities in the wetter, western region was different from communities in the drier, eastern region.     

Reduced soil respiration in gaps in logged lowland dipterocarp forests

We studied the effects of forest composition and structure, and related biotic and abiotic factors on soil respiration rates in a tropical logged forest in Malaysian Borneo. Forest stands were classified into gap, pioneer, non-pioneer and mixed (pioneer, non-pioneer and unclassified trees) based on the species composition of trees >10 cm diameter breast height. Soil respiration rates did not differ significantly between non-gap sites (1290 ± 210 mg CO₂ m⁻² h⁻¹) but were double those in gap sites (640 ± 130 mg CO₂ m⁻² h⁻¹). Post hoc analyses found that an increase in soil temperature and a decrease in litterfall and fine root biomass explained 72% of the difference between gap and non-gap sites. The significant decrease of soil respiration rates in gaps, irrespective of day or night time, suggests that autotrophic respiration may be an important contributor to total soil respiration in logged forests. We conclude that biosphere-atmosphere carbon exchange models in tropical systems should incorporate gap frequency and that future research in tropical forest should emphasize the contribution of autotrophic respiration to total soil respiration.     

Does tree species composition control soil organic carbon pools in Mediterranean mountain forests?

We compared soil organic carbon (SOC) stocks and stability under two widely distributed tree species in the Mediterranean region: Scots pine (Pinus sylvestris L.) and Pyrenean oak (Quercus pyrenaica Willd.) at their ecotone. We hypothesised that soils under Scots pine store more SOC and that tree species composition controls the amount and biochemical composition of organic matter inputs, but does not influence physico-chemical stabilization of SOC. At three locations in Central Spain, we assessed SOC stocks in the forest floor and down to 50 cm in the mineral in pure and mixed stands of Pyrenean oak and Scots pine, as well as litterfall inputs over approximately 3 years at two sites. The relative SOC stability in the topsoil (0-10 cm) was determined through size-fractionation (53 μm) into mineral-associated and particulate organic matter and through KMnO₄-reactive C and soil C:N ratio.Scots pine soils stored 95-140 Mg ha⁻¹ of C (forest floor plus 50 cm mineral soil), roughly the double than Pyrenean oak soils (40-80 Mg ha⁻¹ of C), with stocks closely correlated to litterfall rates. Differences were most pronounced in the forest floor and uppermost 10 cm of the mineral soil, but remained evident in the deeper layers. Biochemical indicators of soil organic matter suggested that biochemical recalcitrance of soil organic matter was higher under pine than under oak, contributing as well to a greater SOC storage under pine. Differences in SOC stocks between tree species were mainly due to the particulate organic matter (not associated to mineral particles). Forest conversion from Pyrenean oak to Scots pine may contribute to enhance soil C sequestration, but only in form of mineral-unprotected soil organic matter.     

Coppice forests and genetic diversity: A case study in Quercus pyrenaica Willd. from Central Spain

The amount of standing genetic diversity found in oak coppice forests has been subjected to intense debate amongst forest ecologists and managers. In this study, the level of vegetative propagation and the genetic diversity found in a coppice forest of rebollo oak (Quercus pyrenaica) was examined. The current range of rebollo oak in the Iberian Peninsula reveals its adaptation to sub-Mediterranean mountain ecosystems. High sprouting capability, mainly by root suckers, has favoured traditional exploitation of rebollo oak in coppice forests. Using nine microsatellite loci, we have detected 14 clone assemblies compounded by 2–4 stems (7.9 ± 1.3 ramets per genet, considering stand density) and covering an average surface of 11.4 m² per genet. The levels of genetic diversity and the amount of unique genotypes were high (D = 0.9972, G/N = 0.86) and similar to the clonality levels found in a nearby open oak woodland. Despite numerous clear-cutting rotations, known at least since 1750, and the heavy root sprouting observed after a thinning event, low clonal propagation (∼27%) was detected. This fact pointed towards the long-term persistence of several small clonal assemblies in this coppice. Our findings suggest that intense thinning practices are unadvisable in the conversion of Q. pyrenaica coppice into high forest due to the significant losses of genetic diversity when removing unique genotypes.     

Instant trees: Using giant vegetative stakes in tropical forest restoration

Remnant trees have been widely reported to facilitate tropical forest recovery, however, few restoration strategies can mimic the role such trees play in their absence. This study evaluated the establishment success and growth of planting oversized vegetative ‘stakes’ (>4 m tall) of three species: Ficus pertusa (Moraceae), Bursera simaruba (Burseraceae), and Erythrina poeppigiana (Fabaceae) at three different sites in southern Costa Rica. I found high establishment rates for all species (range 67–100%) with no mortality for Erythrina. This result was coupled with a rapid development of canopy area over 1 yr for Erythrina (7.69 ± 0.86 m²) and Bursera (1.82 ± 0.86 m²), but not Ficus (0.23 ± 0.04 m²). Similar results are reported for height. The study presents an important new addition to the growing body of literature on the use of stakes in tropical restoration, where, oversized stakes may be planted as solitary individuals in restoration sites to mimic the role played by remnant trees in forest recovery.     

Size, species, and fire behavior predict tree and liana mortality from experimental burns in the Brazilian Amazon

Anthropogenic understory fires have affected large areas of tropical forest in recent decades, particularly during severe droughts. Yet, the mechanisms that control fire-induced mortality of tropical trees and lianas remain ambiguous due to the challenges associated with documenting mortality given variation in fire behavior and forest heterogeneity. In a seasonally dry Amazon forest, we conducted a burn experiment to quantify how increasing understory fires alter patterns of stem mortality. From 2004 to 2007, tree and liana mortality was measured in adjacent 50-ha plots that were intact (B0 - control), burned once (B1), and burned annually for 3 years (B3). After 3 years, cumulative tree and liana mortality (≥1 cm dbh) in the B1 (5.8% yr⁻¹) and B3 (7.0% yr⁻¹) plots significantly exceeded mortality in the control (3.2% yr⁻¹). However, these fire-induced mortality rates are substantially lower than those reported from more humid Amazonian forests. Small stems were highly vulnerable to fire-induced death, contrasting with drought-induced mortality (measured in other studies) that increases with tree size. For example, one low-intensity burn killed >50% of stems <10 cm within a year. Independent of stem size, species-specific mortality rates varied substantially from 0% to 17% yr⁻¹ in the control, 0% to 26% yr⁻¹ in B1, and 1% to 23% yr⁻¹ in B3, with several species displaying high variation in their vulnerability to fire-induced mortality. Protium guianense (Burseraceae) exhibited the highest fire-induced mortality rates in B1 and B3, which were 10- and 9-fold greater than the baseline rate. In contrast, Aspidosperma excelsum (Apocynaceae), appeared relatively unaffected by fire (0.3% to 1.0% mortality yr⁻¹ across plots), which may be explained by fenestration that protects the inner concave trunk portions from fire. For stems ≥10 cm, both char height (approximating fire intensity) and number of successive burns were significant predictors of fire-induced mortality, whereas only the number of consecutive annual burns was a strong predictor for stems <10 cm. Three years after the initial burn, 62 ± 26 Mg ha⁻¹ (s.e.) of live biomass, predominantly stems <30 cm, was transferred to the dead biomass pool, compared with 8 ± 3 Mg ha⁻¹ in the control. This biomass loss from fire represents ∼30% of this forest's aboveground live biomass (192 (±3) Mg ha⁻¹; >1 cm DBH). Although forest transition to savanna has been predicted based on future climate scenarios, our results indicate that wildfires from agricultural expansion pose a more immediate threat to the current carbon stocks in Amazonian forests.     

Carbon density and accumulation in woody species of tropical dry forest in India

We studied the carbon density and accumulation in trees at five sites in a tropical dry forest (TDF) to address the questions: how is the TDF structured in terms of tree and carbon density in different DBH (diameter at breast height) classes? What are the levels of carbon density and accumulation in the woody species of TDF? Is the vegetation carbon density evenly distributed across the forest? Does carbon stored in the soil reflect the pattern of aboveground vegetation carbon density? Which species in the forest have a high potential for carbon accumulation? The WSG among species ranged from 0.39 to 0.78 g cm⁻³. Our study indicated that most of the carbon resides in the old-growth (high DBH) trees; 88-97% carbon occurred in individuals ?19.1 cm DBH, and therefore extra care is required to protect such trees in the dry forest. Acacia catechu, Buchanania lanzan, Hardwickia binata, Shorea robusta and Terminalia tomentosa accounted for more than 10 t ha⁻¹ carbon density, warranting extra efforts for their protection. Species also differed in their capacity to accumulate carbon indicating variable suitability for afforestation. Annually, the forest accumulated 5.3 t-C ha⁻¹ yr⁻¹ on the most productive, wettest Hathinala site to 0.05 t-C ha⁻¹ yr⁻¹ on the least productive, driest Kotwa site. This study indicated a marked patchy distribution of carbon density (151 t-C ha⁻¹ on the Hathinala site to 15.6 t-C ha⁻¹ on the Kotwa site); the maximum value was more than nine times the minimum value. These findings suggest that there is a substantial scope to increase the carbon density and accumulation in this forest through management strategies focused on the protection, from deforestation and fire, of the high carbon density sites and the old-growth trees, and increasing the stocking density of the forest by planting species with high potential for carbon accumulation.     

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.     

Estimations of total ecosystem carbon pools distribution and carbon biomass current annual increment of a moist tropical forest

With increasing CO₂ in the atmosphere, there is an urgent need of reliable estimates of biomass and carbon pools in tropical forests, most especially in Africa where there is a serious lack of data. Information on current annual increment (CAI) of carbon biomass resulting from direct field measurements is crucial in this context, to know how forest ecosystems will affect the carbon cycle and also to validate eddy covariance flux measurements. Biomass data were collected from 25 plots of 13 ha spread over the different vegetation types and land uses of a moist evergreen forest of 772,066 ha in Cameroon. With site-specific allometric equations, we estimated biomass and aboveground and belowground carbon pools. We used GIS technology to develop a carbon biomass map of our study area. The CAI was estimated using the growth rates obtained from tree rings analysis. The carbon biomass was on average 264 ± 48 Mg ha⁻¹. This estimate includes aboveground carbon, root carbon and soil organic carbon down to 30 cm depth. This value varied from 231 ± 45 Mg ha⁻¹ of carbon in Agro-Forests to 283 ± 51 Mg ha⁻¹ of carbon in Managed Forests and to 278 ± 56 Mg ha⁻¹ of carbon in National Park. The carbon CAI varied from 2.54 ± 0.65 Mg ha⁻¹ year⁻¹ in Agro-Forests to 2.79 ± 0.72 Mg ha⁻¹ year⁻¹ in Managed Forests and to 2.85 ± 0.72 Mg ha⁻¹ year⁻¹ in National Park. This study provides estimates of biomass, carbon pools and CAI of carbon biomass from a forest landscape in Cameroon as well as an appropriate methodology to estimate these components and the related uncertainty.     

Early seedling establishment of two tropical montane cloud forest tree species: The role of native and exotic grasses

Tropical montane cloud forest has been undergoing a drastic reduction because of its widespread conversion to pastures. Once these forests have been cleared exotic grasses are deliberately introduced for forage production. Exotic grass species commonly form monodominant stands and produce more biomass than native grass species, resulting in the inhibition of secondary succession and tree regeneration. The purpose of this study was to assess the effect of native vs. exotic grass species on the early establishment of two native tree seedlings (Mexican alder, Alnus acuminata and Jalapa oak, Quercus xalapensis) on an abandoned farm in central Veracruz, Mexico. Seedling survival and growth were monitored (over 46 weeks) in relation to grass cover and height, and available photosynthetic active radiation (PAR). More seedlings survived in the presence of the native grass Panicum glutinosum than those growing with the exotic grass Cynodon plectostachyus (92% vs. 48%). The causes of seedling mortality varied between species; Q. xalapensis was affected by herbivory by voles but mainly in the exotic grass-dominated stands, whereas A. acuminata seedlings died due to competition with the exotic grass. A. acuminata seedlings increased more in height in the exotic grass-dominated stands (102 ± 7.8 cm) compared to native grass-dominated stands (51 ± 4.7 cm). Grass layer height, cover and available PAR were correlated (Pearson; p < 0.05). In the exotic grass dominated plots, grass layer height was correlated with the relative height growth rates of Q. xalapensis (Pearson; p < 0.05). These results indicate that the exotic grass may be affecting tree regeneration directly (grass competition) and indirectly (higher herbivory). Passive restoration may occur once P. glutinosum dominated pastures are abandoned. However, when C. plectostachyus dominates, introduction of early and mid successional tree seedlings protected against vole damage is needed.     

Riparian forest and instream large wood characteristics,West Branch Sheepscot River,Maine, USA

This study examined riparian forest and instream large wood characteristics in a 2.7 km reach of the West Branch of the Sheepscot River in Maine in order to increase our basic knowledge of these components in a system that is known to have undergone multiple land conversion. The West Branch is approximately 40 km long, drains a 132 km² watershed and is vitally important to the remnant population of Atlantic salmon (Salmo salar) and other native species. The riparian forest is comprised of relatively small trees with a mean DBH of 21 cm (SD ± 10.92) with 56% of the trees having a DBH <20 cm. Balsam fir (Abies balsamea) and red maple (Acer rubrum) are the most common species (54%), and 75% of all trees are short-lived, small diameter species. These data suggest the riparian forest in the West Branch Sheepscot River is dominated by young forest stands, a legacy of land use. During a survey conducted in 2005, 210 pieces of large woody debris (LWD) were identified in the study reach; an average of 78 pieces km⁻¹. The total volume of pieces was 8.5 m³ or 3.2 m³ km⁻¹ (LWD in this study is defined as pieces ≥10 cm in diameter and >2 m in length). The mean diameter of LWD was 17 cm with 75% of all pieces having a diameter <20 cm. Most pieces were oriented parallel or nearly parallel to the channel and did not appear to influence channel morphology. In contrast, larger pieces were more often in perpendicular or nearly perpendicular orientations, and were more likely to have a pool-forming function. Overall, the reach has low levels of stable large wood, which do not have a major influence on stream habitats.     

Carbon accumulation in the biomass and soil of different aged secondary forests in the humid tropics of Costa Rica

Efforts are needed in order to increase confidence for carbon accounts in the land use sector, especially in tropical forest ecosystems that often need to turn to default values given the lack of precise and reliable site specific data to quantify their carbon sequestration and storage capacity. The aim of this study was then to estimate biomass and carbon accumulation in young secondary forests, from 4 and up to 20 years of age, as well as its distribution among the different pools (tree including roots, herbaceous understory, dead wood, litter and soil), in humid tropical forests of Costa Rica. Carbon fraction for the different pools and tree components (stem, branches, leaves and roots) was estimated and varies between 37.3% (±3.3) and 50.3% (±2.9). Average carbon content in the soil was 4.1% (±2.1). Average forest plant biomass was 82.2 (±47.9) Mg ha⁻¹ and the mean annual increment for carbon in the biomass was 4.2 Mg ha⁻¹ yr⁻¹. Approximately 65.2% of total biomass was found in the aboveground tree components, while 14.2% was found in structural roots and the rest in the herbaceous vegetation and necromass. Carbon in the soil increased by 1.1 Mg ha⁻¹ yr⁻¹. Total stored carbon in the forest was 180.4 Mg ha⁻¹ at the age of 20 years. In these forests, most of the carbon (51-83%) was stored in the soil. Models selected to estimate biomass and carbon in trees as predicted by basal area had R² adjustments above 95%. Results from this study were then compared with those obtained for a variety of secondary and primary forests in different Latin-American tropical ecosystems and in tree plantations in the same study area.     

Wood density in forests of Brazil's ‘arc of deforestation’: Implications for biomass and flux of carbon from land-use change in Amazonia

Wood density is an important variable in estimates of forest biomass and greenhouse-gas emissions from land-use change. The mean wood density used in estimates of forest biomass in the Brazilian Amazon has heretofore been based on samples from outside the “arc of deforestation”, where most of the carbon flux from land-use change takes place. This paper presents new wood density estimates for the southern and southwest Brazilian Amazon (SSWA) portions of the arc of deforestation, using locally collected species weighted by their volume in large local inventories. Mean wood density was computed for the entire bole, including the bark, and taking into account radial and longitudinal variation. A total of 403 trees were sampled at 6 sites. In the southern Brazilian Amazon (SBA), 225 trees (119 species or morpho-species) were sampled at 4 sites. In eastern Acre state 178 trees (128 species or morpho-species) were sampled at breast height in 2 forest types. Mean basic density in the SBA sites was 0.593 ± 0.113 (mean ± 1 S.D.; n = 225; range 0.265–0.825). For the trees sampled in Acre the mean wood density at breast height was 0.540 ± 0.149 (n = 87) in open bamboo-dominated forest and 0.619 ± 0.149 (n = 91) in dense bamboo-free forest. Mean wood density in the SBA sites was significantly higher than in the bamboo dominated forest but not the dense forest at the Acre site. From commercial wood inventories by the RadamBrasil Project in the SSWA portion of the arc of deforestation, the wood volume and wood density of each species or genus were used to estimate average wood density of all wood volume in each vegetation unit. These units were defined by the intersection of mapped forest types and states. The area of each unit was then used to compute a mean wood density of 0.583 g cm⁻³ for all wood volume in the SSWA. This is 13.6% lower than the value applied to this region in previous estimates of mean wood density. When combined with the new estimates for the SSWA, this gave an average wood density of 0.642 g cm⁻³ for all the wood volume in the entire Brazilian Amazon, which is 7% less than a prior estimate of 0.69 g cm⁻³. These results suggest that current estimates of carbon emissions from land-use change in the Brazilian Amazon are too high. The impact on biomass estimates and carbon emissions is substantial because the downward adjustment is greater in forest types undergoing the most deforestation. For 1990, with 13.8 × 10³ km² of deforestation, emissions for the Brazilian Amazon would be reduced by 23.4–24.4 × 10⁶ Mg CO₂-equivalent C/year (for high- and low-trace gas scenarios), or 9.4–9.5% of the gross emission and 10.7% of the net committed emission, both excluding soils.     

An assessment of Hawaiian dry forest condition with fine resolution remote sensing

Remote sensing offers the potential to spatially map forest cover quickly and reliably for inventory purposes. We developed a new image analysis approach using an integrated methodology of “object-based” image classification techniques and field-based measurements to quantify forest cover in a degraded dry forest ecosystem on the leeward side of the Island of Hawaii. This new approach explicitly recognized the transitional areas between tree crowns and tree shades (tree shadows) as a unique class and fully utilized them for the quantification of canopy cover. Object-oriented classification of Ikonos-2 satellite images allowed delineation of tree shades and crowns and the transitional areas between them from objects with similar reflectance and size that were surrounding the trees. These included patches of fountain (Pennisetum setaceum) and kikuyu (Pennisetum clandestinum) grass, lava outcrops and lava–grass mixtures. Crown-shade transitions were clearly differentiated in spite of their wide range of spectral values and reflectance similarities with areas of lava–grass mixture. Segments representing tree shades and dark lava outcrops were also classified into their respective classes even if they were contiguous. The image estimates of canopy cover using the tree shade plus transition classes were linearly related with field estimates of canopy cover (R² = 0.86 and slope = 0.976). Based on this relationship, dry forest cover throughout the 2627-ha area was estimated at 7.7 ± 1.9%. An immediate application of this new approach is to select and delineate areas with higher canopy cover in order to concentrate ecological restoration and conservation efforts.