J. Doland Nichols

Intercropping legume trees with native timber trees rapidly restores cover to eroded tropical pasture without fertilization

As tropical deforestation progresses, increasing areas of land are being degraded through erosion, overgrazing and other processes, leading subsequently to soil infertility and loss of agricultural productivity. Reforestation is a potential way to rehabilitate some of these lands. We planted a commercially valuable native timber species on a degraded pasture in southwestern Costa Rica to test methods of forest establishment that would enhance tree growth without inorganic fertilizer and provide diverse economic and ecological benefits. In addition to an unmanipulated control and fertilized plots, we mixed the timber tree (Terminalia amazonia) with two species of nitrogen-fixing trees, with cover crops, or with edible beans. In the beans treatment, height growth of T. amazonia at the end of 4 years was significantly lower than in any of the other treatments, and bean production was poor. In the first year fertilized trees grew significantly faster than in all the other treatments. At 2 years, fertilized trees were still significantly taller than in six of seven other treatments. The cover crops did not establish and one of the two legume trees suffered high mortality. Fastest height growth occurred when T. amazonia was interplanted with legume trees, especially Inga edulis. Plots with I. edulis interplanted with T. amazonia closed canopy first, saved effort in hand-weeding, and provided large amounts of litter biomass as well as edible fruit pods. Block effects were large and were probably related to unmanipulated factors with which growth in plots correlated, in particular, degree of erosion and plot topography. Our results showed that fertilizer is wasted investment on this site because T. amazonia grows well with minimal input even on eroded land. Importantly, timber trees in species-diverse plantations can perform at least as well as in monocultures. The more diverse systems provide ecological benefits including nitrogen fixation and multiple products for humans.

Survival, growth and gall formation by Phytolyma lata on Milicia excelsa established in mixed-species tropical plantations in Ghana

1 Milicia excelsa (Moraceae) is an important timber tree in much of Africa and when grown in monocultural plantations has been subject to nearly complete destruction by gall‐forming psyllids in the genus Phytolyma.

Patterns of seedling survival in the tropical African tree Milicia excelsa

The spatial patterns of canopy tree and seedling life stages in the African Tropical Tree Milicia excelsa were examined to test the Janzen-Connell hypothesis (escape hypothesis). The Janzen-Connell hypothesis states that the mortality of seeds and seedlings is highest near the adult tree and declines with distance away from the adult tree of the same species. This hypothesis argues that this effect is partially responsible for maintaining the high tree species diversity of tropical forests. Solar radiation and fruit dispersal were investigated as possible explanations of observed patterns in seedling distribution. Milicia excelsa trees ≥ 30 cm DBH were found to be randomly dispersed and occurred at a density of ≤ 1 ha. Milicia exceisa seedlings were located in small clumps between parent trees and up to 150 m from parents at a mean density of 65 seedlings ha -1 . Fruits were in abundance (> 9000 on the ground) beneath female trees. Light levels at locations of natural seedlings ranged from 2-29% of full irradiance. Planted seedlings did not suffer greater mortality closer to adult conspecifics, and survived at light levels between 2-37% of full irradiance. Phytolyma spp., gall-forming psyllids which cause high mortality in Milicia seedlings in large openings and plantations, were not observed on any natural or planted seedlings, although galls were present in the crowns of dominant trees.

Performance of Eight Eucalypt Species and Interspecific Hybrid Combinations at Three Sites in Northern New South Wales, Australia

Summary Eight eucalypt taxa, represented by six seedlots and nine clones (two seedlots of Corymbia citriodora subsp. variegata (CCV), one seedlot each of Eucalyptus cloeziana, E. dunnii and E. pilularis, one seedlot and two clones of E. grandis, one clone of E. saligna, three clones of the interspecific hybrid E. grandis × E. camaldulensis and five clones of the hybrid E. urophylla × E. grandis) were tested in taxa trials on three sites in northern New South Wales, Australia. Significant differences between sites and between taxa in survival, growth, stem form and attack by stem-boring insect larvae were demonstrated. All taxa grew best on the Convery site that had the highest mean annual rainfall, 1400 mm, on a Red Ferrosol soil derived from volcanic parent material; E. dunnii and E. pilularis grew to a mean dominant height of 17 m in 6 y, E. cloeziana to 15 m, C. citriodora subsp. variegata and E. saligna to 14 m. Fewer than 2% of trees of all taxa at this site were attacked by insects. The other two sites had Brown Dermosol soils and were drier, the Muller site receiving 1200 mm y−1 and the Ironbolt site 1100 mm y−1. Height and diameter growth of all taxa was slower at these sites, with E. pilularis and E. cloeziana showing the greatest reduction in growth while E. grandis × E. camaldulensis showed the least reduction. Overall survival at age 6 y was acceptable at all three sites, being highest at Convery site (86%) followed by Muller (77%) and Ironbolt (74%). While C. citriodora subsp. variegata and E. cloeziana had minimal damage at Mueller and Ironbolt, the other taxa had from 9% to 100% of stems affected by borers, with E. grandis, the E. saligna clone and E. urophylla × E. grandis proving particularly susceptible on these sites.

A method for assessing arbuscular mycorrhizal fungi group distribution in tree roots by intergenic transcribed sequence variation

We identified five taxonomic groups of arbuscular mycorrhizal fungi (AMF) inside roots of young trees of six species of legumes and six species of non-legumes from a field site in southern Costa Rica using an AMF group-specific PCR assay of the intergenic transcribed sequence and 18S rRNA gene fragment. Assay specificity was verified by cloning and sequencing representatives from four of the five AMF groups. We found no difference in overall AMF diversity levels between legumes and non-legumes or between plant species. Some groups of AMF may associate more frequently with legumes than others, as Glomus Group A (Glomus mosseae/intradices group) representatives were detected more frequently in legumes than non-legumes relative to Glomus Group B (Glomus etunicatum/claroideum) representatives.

Estimating above-ground biomass by fusion of LiDAR and multispectral data in subtropical woody plant communities in topographically complex terrain in North-eastern Australia

We investigated a strategy to improve predicting capacity of plot-scale above-ground biomass (AGB) by fusion of LiDAR and Landsat5 TM derived biophysical variables for subtropical rainforest and eucalypts dominated forest in topographically complex landscapes in North-eastern Australia. Investigation was carried out in two study areas separately and in combination. From each plot of both study areas, LiDAR derived structural parameters of vegetation and reflectance of all Landsat bands, vegetation indices were employed. The regression analysis was carried out separately for LiDAR and Landsat derived variables individually and in combination. Strong relationships were found with LiDAR alone for eucalypts dominated forest and combined sites compared to the accuracy of AGB estimates by Landsat data. Fusing LiDAR with Landsat5 TM derived variables increased overall performance for the eucalypt forest and combined sites data by describing extra variation (3% for eucalypt forest and 2% combined sites) of field estimated plot-scale above-ground biomass. In contrast, separate LiDAR and imagery data, and fusion of LiDAR and Landsat data performed poorly across structurally complex closed canopy subtropical rainforest. These findings reinforced that obtaining accurate estimates of above ground biomass using remotely sensed data is a function of the complexity of horizontal and vertical structural diversity of vegetation.

Evaluation of Different Topographic Corrections for Landsat TM Data by Prediction of Foliage Projective Cover (FPC) in Topographically Complex Landscapes

The reflected radiance in topographically complex areas is severely affected by variations in topography; thus, topographic correction is considered a necessary pre-processing step when retrieving biophysical variables from these images. We assessed the performance of five topographic corrections: (i) C correction (C), (ii) Minnaert, (iii) Sun Canopy Sensor (SCS), (iv) SCS + C and (v) the Processing Scheme for Standardised Surface Reflectance (PSSSR) on the Landsat-5 Thematic Mapper (TM) reflectance in the context of prediction of Foliage Projective Cover (FPC) in hilly landscapes in north-eastern Australia. The performance of topographic corrections on the TM reflectance was assessed by (i) visual comparison and (ii) statistically comparing TM predicted FPC with ground measured FPC and LiDAR (Light Detection and Ranging)-derived FPC estimates. In the majority of cases, the PSSSR method performed best in terms of eliminating topographic effects, providing the best relationship and lowest residual error when comparing ground measured FPC and LiDAR FPC with TM predicted FPC. The Minnaert, C and SCS + C showed the poorest performance. Finally, the use of TM surface reflectance, which includes atmospheric correction and broad Bidirectional Reflectance Distribution Function (BRDF) effects, seemed to account for most topographic variation when predicting biophysical variables, such as FPC.

Biology of Creiis lituratus Froggatt: (Hemiptera: Psyllidae), Pest on Eucalyptus dunnii Maiden in Plantations: Morphology, Life Cycle and Parasitism

Summary The psyllid Creiis lituratus Froggatt is the most significant defoliating pest of young Eucalyptus dunnii Maiden plantations growing in north-eastern New South Wales. This paper describes aspects of the life history of C. lituratus, information required to monitor psyllid populations and develop management strategies. The psyllid has five nymphal instars. Feeding by these nymphs causes considerable damage to the foliage of host trees. The different nymphal instars are distinguishable on the basis of body and lerp dimensions, colouration and wing bud morphology. Mean fecundity in captive populations was 95 eggs per female (observed range 130–148). Egg and juvenile development had threshold temperatures of 3°C and 10°C respectively, and the relationship between development rate and temperature was determined for both stages. Adult longevity was reduced at high temperatures, which affected fecundity and may account for the low psyllid population densities observed in plantations over summer. Parasitism of the nymphal instars by two species of Psyllaephagus wasps was observed. While parasitism may exceed 90% in field surveys it is uncertain what role it plays in regulating populations. No specialised parasitism or predation of eggs or adults was observed.

Site Index Prediction of 'Eucalyptus dunnii' Maiden Plantations with Soil and Site Parameters in Sub-tropical Eastern Australia

Summary The Eucalyptus dunnii Maiden plantation estate in north-eastern NSW and south-eastern Queensland is significantly expanding on ex-grazing land. Thirty-one growth plots (average age 5.2 y) covering a latitudinal range of about 3.2° (370 km) and at altitudes from 8 m to 740 m asi in NSW were used to evaluate the correlation of site, soil and climatic variables with growth of E. dunnii. Using height at an age of 10 y as a standard, site indices for E. dunnii across the 31 sites averaged about 16 m, ranging from around 5 m to 26 m. The factors available-water storage capacity of the soil, rainfall and altitude accounted for 62% of the variation in site index. Inclusion of measures of fertility did not improve the predictive capacity of the model, possibly because of the limited size of the data set with soil chemical analyses. The predictive model, based on simple, easily assessable site factors, has the capacity to improve the quantitative evaluation of the productivity of sites for E. dunnii plantations. The need for a simple field assessment procedure for selection of suitable sites was highlighted by the wide range of productivity exhibited across the plots.

Agroecology and Sustainable Rural Livelihoods: A Conceptual Framework to Guide Development Projects in the Pacific Islands

This article reviews rural development literature in the areas of sustainable livelihoods and agroecology. Combining agroecological and sustainable livelihoods approaches enables interdisciplinary research that incorporates principles from sociology, economics, agronomy and ecology. The outcome of this literature analysis alongside participatory research in Vanuatu and Fiji in 2013–2014 was the development of the integrated Agroecology and Sustainable Rural Livelihoods Framework (ASRLF). The Pacific Island nations have a well-developed traditional economy, but appropriate rural economic development has been problematic. The ASRLF seeks to function in the local Pacific Island context while also having relevance to sustainable rural development projects elsewhere.