Mark S. Ashton

Restoration pathways for rain forest in southwest Sri Lanka: a review of concepts and models

Abstract In the last 10 years the Sri Lankan government has changed its policy regarding its remaining rain forest from one that promoted commercial exploitation to one of conservation. The growing importance of uplands as catchments for water production, biodiversity conservation and other downstream services has been recognized by the Sri Lankan government. It is therefore timely that we review 15 years of research investigating rain forest dynamics of southwest Sri Lanka with the objective of using this knowledge for forest restoration. We provide six common principles for understanding the integrity of rain forest dynamics in southwest Sri Lanka. The principles are: (i) disturbances provide the simultaneous initiation and/or release of a new forest stand; (ii) that disturbances are generally non-lethal to the groundstory vegetation; (iii) disturbances are variable in severity, type and extent across rain forest topography; (iv) guild diversity (habitat diversity) is dependent upon “advance regeneration”; (v) tree canopy stratification is based on both “static” and “dynamic” processes; and (vi) canopy dominant late-successional tree species are site specialists restricted to particular topographic positions of the rain forest. These principles are applied to determine effects of two rain forest degradation processes that have been characterized as chronic (continuous detrimental impacts) and acute (one-time detrimental impacts). Restoration pathways are suggested that range from: (i) the simple prevention of disturbance to promote release of rain forest succession; (ii) site-specific enrichment planting protocols for canopy trees; (iii) sequential amelioration of arrested fern and grasslands by use of plantation analogs of old field pine to facilitate secondary succession of rain forest, and plantings of late-seral rain forest tree species; and (iv) establishment and release of successionally compatible mixed-species plantations. We summarize with a synthesis of the restoration techniques proposed for reforestation using native vegetation on cleared conservation areas and parks, and for the stabilization of eroded upland watersheds. We conclude with a comparative analysis with restoration work done in other tropical forest regions.

Mapping tree density at a global scale

The global extent and distribution of forest trees is central to our understanding of the terrestrial biosphere. We provide the first spatially continuous map of forest tree density at a global scale. This map reveals that the global number of trees is approximately 3.04 trillion, an order of magnitude higher than the previous estimate. Of these trees, approximately 1.30 trillion exist in tropical and subtropical forests, with 0.74 trillion in boreal regions and 0.66 trillion in temperate regions. Biome-level trends in tree density demonstrate the importance of climate and topography in controlling local tree densities at finer scales, as well as the overwhelming effect of humans across most of the world. Based on our projected tree densities, we estimate that over 15 billion trees are cut down each year, and the global number of trees has fallen by approximately 46% since the start of human civilization.

Biomass estimations and carbon stock calculations in the oil palm plantations of African derived savannas using IKONOS data

This study developed biomass models to calculate carbon stock levels of the West African oil palms (Elaeis guineensis) using multi-date wet and dry season IKONOS images. Two benchmark areas of the derived savanna eco-regions of Africa were selected for analysis. Allometric equations related above-ground palm biomass to their stem heights. Empirical regression models based on field plot data were established to determine wet and dry biomass (kg m−2) of oil palm plantations in IKONOS images. The best models were exponential, involving bands 3, 3 and 1, or 3 and 4, and explaining between 63 and 72% of the variability in the data. Model evaluations with independent datasets showed there is 28-36% uncertainty in dry biomass predictions. At the landscape level, multi-date IKONOS data mapped oil palm plantations with an overall accuracy of 88-92%. However, the ability of IKONOS data to differentiate various age groups of oil palms was limited with a high degree of intermixing of classes. The best results were obtained when delineating agro-palm (palms mixed with agriculture and fallows), palm of 1-3 years, and palm of 4-5 years at an overall accuracy of 74.5% using all four IKONOS bands. The results indicate the need for additional spectral bands in the IKONOS sensor. The total carbon per unit area of oil palms was calculated across age groups for the two benchmark areas of West Africa and were 14.75 and 14.94 tonnes ha−1 (or Mg ha−1), respectively. The corresponding dry biomass (kg m−2) were 29.5 and 29.88 tonnes ha−1 (or Mg ha−1). The age of the oil palms were between 1 and 5 years across benchmark areas. The mean rate of accumulation of carbon was 2.95 t C ha−1 year−1 in benchmark area 1 and 2.99 t C ha−1 year−1 in benchmark area 2.

Germination and seedling growth of Quercus (section Erythrobalanus) across openings in a mixed-deciduous forest of southern New England, USA

Abstract In this study three species of the genus Quercus section Erythrobalanus (Quercus coccinea, Quercus rubra, Quercus velutina) were investigated. All occur together as canopy trees in forests of southern New England. Acorns of each Quercus species were planted in plots located in five zones that represent a range of forest gap/canopy conditions that can occur within a southern New England forest. These five zones were demarcated adjacent to and across large openings of two physiographic sites—valley and ridgetop. Experiments were designed to monitor germination and initial growth of seedlings for the first three growing seasons. During the start of the first growing season germination was monitored. At the end of the first growing season measurements of height and number of flushes were taken and destructive samples of seedlings made for dry mass of root, stem and leaves. At the end of the third growing season height was recorded for surviving seedlings. Comparisons were made of germination and growth of seedlings located in the different gap/canopy conditions. Results demonstrated clear differences in patterns of germination and early growth among species and among gap/canopy conditions of the sites. All species showed an increased lag in germination with reduced amounts of light. Highest growth and flushing rate were in the center conditions of the openings for all species during the first growing season. Quercus rubra had the greatest height growth the first growing season but a lower number of flushes than Q. velutina and Q. coccinea. In comparison with the other species, Q. rubra had the greatest total dry mass in most gap/canopy conditions after the first growing season. However, Q. velutina had the greatest total dry mass in the center of the ridgetop opening. In almost all gap/canopy conditions Q. velutina had greater proportions of dry mass allocated to roots compared with the other species. After 3 years, greatest height growth in any of the gap/canopy conditions was recorded for all three species in the center of the valley site. Under this condition Q. rubra had significantly greater growth than Q. velutina and Q. coccinea. Quercus rubra also had significantly greater height growth and survival beneath the canopy conditions of the valley site than the other species. On the ridgetop site regeneration failed to establish beneath canopy conditions that provided low amounts of light. Quercus velutina showed greatest height growth after three years in the center and edge conditions of the ridgetop opening compared with the other species. Environmental influences that determine species germination and growth performance are suggested.

Seedling growth of co-occurring Shorea species in the simulated light environments of a rain forest

Abstract Four tree species of Shorea section Doona ( Shorea megistophylla, Shorea trapezifolia, Shorea disticha, Shorea worthingtonii ) were investigated for differences in seedling growth among related species. These species occur together as canopy emergents in rain forest of southwest Sri Lanka. Seedlings of each species were grown in light treatments that simulated a range of light environments found in the groundstorey of the rain forest. Seedlings of S. megistophylla grew most in the full-sun treatment. The other species grew tallest in treatments that provided partial shade or lower amounts of direct sunlight. For two of these species, S. disticha and S. worthingtonii , greatest proportions of seedling dry mass allocated to roots were in either dark-understorey shade or long durations of direct sunlight. Seedlings of S. megistophylla allocated the greatest proportion of dry mass to roots in the full-sun treatment. In the dark-understorey shade seedlings of S. trapezifolia had the least proportion of dry mass allocated to roots compared with the other species. This might predispose S. trapezifolia to more stress during drought periods. Under treatments providing high amounts of light S. megistophylla increased leaf area by increasing the size of its leaves. For S. worthingtonii and S. trapezifolia , leaf area increased by the production of more leaves rather than by an increase in area of individual leaves. Leaf area increase by number was less marked for S. disticha . Findings suggest an explanation for the co-existence of these Shorea species in this rain forest. High light environments like that in the centre of a large canopy disturbance promotes growth of S. megistophylla seedlings. Smaller canopy openings that expose seedlings to some direct sunlight favour growth of S. trapezifolia and S. disticha . Light regimes of the forest understorey and gap edge favour seedling growth of the more shade-tolerant S. worthingtonii .

Synthesis and Conclusions

This chapter provides an overview of the role of tropical forests in the international efforts to negotiate a new global climate treaty. Under the existing treaty, the Kyoto Protocol and its “flexible mechanisms” – particularly the Clean Development Mechanism (CDM) – have succeeded in building a billion dollar market for emission reduction projects in developing countries. Since the decision to include efforts to reduce emissions from tropical deforestation and forest degradation (REDD) in the 2007 Bali Action Plan, considerable attention has focused on designing a REDD and REDD+ program for inclusion in the next global climate agreement. The positions taken by different countries on REDD are driven by their circumstances – from those with large areas of standing forest to those with few remaining forests, from those facing rapid rates of deforestation to those engaged in reforestation. The overarching issues to be decided in developing the framework of a REDD mechanism include: the scope of the forestry activities to be covered; the scale of accounting for forestry activities and the baseline for measuring reference emissions levels; the type of financing to be provided for REDD activities; how to address fundamental issues of capacity and governance; and the consideration of co-benefits. There is some convergence around the scope of a REDD mechanism, the need to ultimately undertake activities at a national scale, the likelihood that financing will be both fund and market based, and the potential to implement REDD in phases. However, many contentious issues remain, including how to set baselines and accounting rules for REDD/REDD+ and how to incorporate governance concerns.

Big-leaf mahogany (Swietenia macrophylla) seedling survival and growth across a topographic gradient in southeast Para ´, Brazil

Abstract Adult populations of big-leaf mahogany (Swietenia macrophylla) occur in aggregations along seasonal streams in transitional evergreen forests of southeast Para, Brazil. To test whether variable seedling survival and growth across topography may underlie this observed distribution pattern, we planted nursery-grown seedlings in the forest understory and in artificial gaps at opposite ends of a slope gradient where mahogany occurs (low-ground hydromorphic soils) and does not occur (high-ground dystrophic soils). At both positions seedling survival and growth were significantly greater through 42 months in gaps than in adjacent forest understories, though mean understory survival exceeded that in gaps through the first growing season. Mean seedling growth in gaps on low ground was significantly greater than growth in gaps on high ground. Under nursery conditions (well watered, 70% full sun light), growth of seedlings planted in soils from low ground was significantly higher than that of seedlings planted in soils from high ground, indicating that differences in soil nutrient status, particularly Ca and Mg, may account for results in the outplanting experiment. Ca+Mg nutrient supplement accelerated growth rates of nursery seedlings planted in high-ground soils relative to growth rates of seedlings planted in low-ground soils, nullifying significant differences between controls. Soil differentiation across topographic relief with consequent gradients in soil nutrient status complements canopy disturbance regimes (increased light levels) in shaping adult distribution patterns and population structures. This implies that recruitment success under natural and artificial regeneration management practices may vary as a function of both gap size and soil fertility.

Detecting floristic structure and pattern across topographic and moisture gradients in a mixed species Central African forest using IKONOS and Landsat-7 ETM+ images

Abstract The strengths and limitations of high spatial resolution broadband IKONOS data and Landsat-7 ETM+ data are compared with respect to, distinguishing floristic structure (basal area, stem density) and pattern (diversity indices, species associations) across a topography that exhibits subtle variations in surface hydrology and elevation. Three site types can be described in relation to the topography and hydrology of the study area: (1) seasonally drought stressed; (2) valley streams; and (3) well-drained bottomlands. Non-metric Multidimensional Scaling (NMS) emphasized the importance of seasonal moisture stress in determining floristic structure and species associations in this forest. Forest structure and species data gathered across the three sites of the topographic/hydrologic gradient are related to spectral values and indices gathered from IKONOS and ETM+. Statistical tests of significance at 95% confidence level or higher showed that the IKONOS wavebands and vegetation indices were most sensitive to changes in floristic structure and species composition for images taken during the dry season (October–March) as compared to those for the wet season (April–September). Within the IKONOS data, the near-infrared (NIR) waveband (band 4) was most sensitive to changes in forest structure and species composition across the three site types (seasonally drought stressed; valley streams; and well-drained bottomlands). However, the IKONOS spectral relationships with biotic variables did not exceed an R2 value of 0.34, with an overwhelming number of best regression models having any two waveband combinations; typically combinations of band 1 and 2, or 1 and 3, or 2 and 3. The best relationships were obtained when ETM+ mid-infrared (MIR) band 5 or 7 were involved with R2 values of 0.52 and 0.54 for basal area and stem density respectively, explaining about 20% greater variability compared to IKONOS data. Thereby, the most interesting aspect of the paper was the degree to which the MIR band of the ETM+ added to the strength of regressions used to explain variation in stem density and basal area of rainforests.

Floristics of bamboo-dominated stands in lowland terra-firma forests of southwestern Amazonia1

Abstract We investigated distinctive aspects of the floristic communities associated with bamboo dominance (Guadua sarcocarpa and Guadua weberbaueri) in terra-firma forests of the Tambopata River watershed, southeastern Peru. Data were collected at five sets of paired plots (five bamboo-dominated, five tree-dominated) in which no evidence of prior human disturbance was identified. Three components of the plant community were analyzed: (1) trees (≥ 5 cm diam), (2) tree saplings (< 5 cm diam), and (3) large understory plants (shrubs and herbs ≥ 1.5 meters). We used three statistical techniques (DCA, TWINSPAN, and ANOVA) to identify distinct assemblages of genera associated with the presence/absence of bamboo, and/or other factors (e.g., soil drainage, geographic location). All three statistical techniques produced similar results: the presence of bamboo is associated with a distinctive floristic community of trees and understory plants, but the tree sapling component of the plant communities was not distinct. Species richness in bamboo-dominated stands, as compared with tree-dominated stands, was 60% lower for trees and 36% lower for understory plants, but not significantly different for tree saplings. Bamboo-associated canopy trees and understory plants were characterized by fast growth rates, tolerance of poorly drained soils, and capacity for vegetative re-sprouting in response to physical damage to stems. These results suggest that differences in both soil and disturbance regimes drive floristic differences between bamboo-dominated stands and adjacent stands without bamboo.

Effects of light and fertilization on arbuscular mycorrhizal colonization and growth of tropical rain-forest Syzygium tree seedlings

This study investigated the effects of light and soil fertility, on arbuscular mycorrhizal fungi (AMF) colonization, and the growth responses (height and dry mass) of Syzygium seedlings. Seedlings of four Syzygium spp. were grown for 2 y in six different light treatments at the research station of the Sinharaja Forest, Sri Lanka. The light treatments exposed seedlings to: (1) 3%; (2) 16%; (3) 50%; (4) 100% of full sun (control); (5) short periods (2 h d−1) of direct sunlight; and (6) long periods (6 h d−1) of direct sunlight. In the 16% of full sun treatment five sets of fertilizer applications supplied: (1) magnesium; (2) potassium; (3) phosphorus; (4) all three nutrients combined; and (5) no fertilizer (control). The Syzygium species had the greatest mycorrhizal colonization in brighter treatments that provided direct light. Comparison across species revealed S. firmum to have moderate mycorrhizal colonization but high total dry mass. Syzygium operculatum had high percentages of mycorrhizal colonization while S. rubicundum had low percentages of mycorrhizal colonization especially in deep shade. Syzygium makul showed moderate levels of mycorrhizal colonization and dry mass, but low height growth. Among fertilizer applications, phosphorus enhanced seedling growth and mycorrhizal colonization for all species. However, species showed decreased growth with high amounts of potassium and combined fertilizer applications. Results suggest that AMF colonization will be highest, and Syzygium spp. growth greatest, beneath canopy openings large enough to receive direct sun in phosphorus-rich soils.