The propagation of Ramón (Brosimum alicastrum Sw.; Moraceae) in Mayan homegardens of the Yucatan peninsula of Mexico

In the Yucatan peninsula of Mexico, Maya natives have been propagating important species for centuries. However, little documentation exists of these methods, and traditional knowledge is fading as younger generations seek work in urban centers. With growing interest in using some of these species for plantation-scale production, this knowledge should be captured to aid in propagation and cultural methods of selected species. One such species, Ramón (Brosimum alicastrum Sw.), is grown in Mayan homegardens primarily as a source of dry season forage. We conducted a survey of Mayan families in several municipalities to determine basic propagation habits and procedures for cultivating Ramón, and used this information to conduct some controlled-environment studies of reproductive ecology of the species. Our survey showed that all or most Maya grow the Ramón tree in homegardens for forage and that the tree is both cultivated from wild seedlings as well as planted on a small scale. Propagation is by seed and young seedlings are irrigated until they are established. We examined the effects of temperature on seed germination and found that maximum germination occurred between 27° and 38 °C, with best germination and growth of healthy seedlings at 33 °C. No germination occurred below 21° or above 44 °C. Simulated Maya irrigation gave a four-fold increase in growth rate of seedlings, aiding early establishment. Watering gave seedlings of greater biomass, greater stem and root length, and greater numbers and size of leaves. This magnitude of response may provide an economic return for plantation culture of Ramón for forage production.     

Reimplementation of the Biome-BGC model to simulate successional change

Biogeochemical process models are increasingly employed to simulate current and future forest dynamics, but most simulate only a single canopy type. This limitation means that mixed stands, canopy succession and understory dynamics cannot be modeled, severe handicaps in many forests. The goals of this study were to develop a version of Biome-BGC that supported multiple, interacting vegetation types, and to assess its performance and limitations by comparing modeled results to published data from a 150-year boreal black spruce (Picea mariana (Mill.) BSP) chronosequence in northern Manitoba, Canada. Model data structures and logic were modified to support an arbitrary number of interacting vegetation types; an explicit height calculation was necessary to prioritize radiation and precipitation interception. Two vegetation types, evergreen needle-leaf and deciduous broadleaf, were modeled based on site-specific meteorological and physiological data. The new version of Biome-BGC reliably simulated observed changes in leaf area, net primary production and carbon stocks, and should be useful for modeling the dynamics of mixed-species stands and ecological succession. We discuss the strengths and limitations of Biome-BGC for this application, and note areas in which further work is necessary for reliable simulation of boreal biogeochemical cycling at a landscape scale.     

Defining competition vectors in a temperate alley cropping system in the midwestern USA: 2. Competition for water

A study was carried out in an alley cropping system in the Eastern Maize Belt of the United States with the objective of quantifying the competition for water between trees (black walnut (Juglans nigra L.) and red oak (Quercus rubra L.) and maize (Zea mays L.). Spatial and temporal variation in soil moisture, tree and maize rooting patterns, tree and maize water uptake, and maize leaf area expansion were determined in three treatments; barrier (polyethylene root barriers separating maize and tree roots), trench (trenching without a polyethylene barrier), and no barrier (control). Significant temporal variation in soil moisture was observed in both black walnut and red oak alley cropping systems. The barrier and trench treatments resulted in higher soil moisture in the maize alley and lower soil moisture in the tree row than the no barrier treatment. Uptake of water by maize was higher in the barrier than the no barrier treatment. However, tree water uptake was higher in the no barrier treatment than in the barrier treatment because tree roots utilized water from the maize alley. Maize leaf area was negatively impacted by water stress in the no barrier treatment. Quantification of rooting patterns revealed that maize and tree roots were concentrated in the top 30 cm soil layer where water fluctuations were greatest. The barrier and trench treatments successfully eliminated the belowground root competition between trees and maize and resulted in greater leaf area and higher grain yields than the no barrier treatment. Thus, competition for water rather than competition for light seems to be critical in defining the productivity and sustainability of this alley cropping system.This revised version was published online in November 2005 with corrections to the Cover Date.     

Branch mortality and potential litterfall from Douglas-fir trees in stands of varying density

Forest floor characteristics influence nutrient cycling and energy flow properties of forest ecosystems, and determine quality of habitat for many forest plants and animals. Differential crown recession and crown development among stands of differing density suggest that an opportunity may exist to control the input of fine woody litter into the system by manipulating stand density. The objective was to measure the rate of branch mortality among stands of differing density and to estimate the range in total per hectare necromass inputs. Although litter traps are reliable for estimating per hectare rates of litterfall, branch mortality dating on sectioned stems uniquely allows assessment of several other litterfall components: (1) individual tree contributions to total litterfall; (2) the amount of branch material released by mortality, regardless of whether the branches are shed to the forest floor; (3) the distribution of basal diameters characterizing the litterfall from a given tree and stand. Twenty-four trees were felled and sectioned on permanent plots that were part of a silvicultural study of stand density regimes in Douglas-fir (Pseudotsuga menziesii (Mirbel) Franco.). Whorl branches were dissected out of bole sections to determine the dates of mortality, and a branch biomass equation was applied to estimate potential rate of litterfall. Periodic annual rates were expressed in four ways: (1) number of branches per tree; (2) mass of branches per tree; (3) mass of branches per unit of crown projection area; (4) mass of branches per hectare. For the growth periods investigated, larger trees and trees growing on denser plots tended to release a greater necromass through branch mortality. Average branch basal diameter generally decreased with increasing stand density. Annual branch mortality ranged from 33 to 430 g m⁻² crown projection area for individual trees, and from 236 to 1035 kg ha⁻¹ for individual plots. These rates approached the low end of the range of previously published fine litterfall rates for Douglas-fir. Rates on these plots were relatively low owing to the temporary delay in crown recession imposed by artificial thinning. A conceptual model of branch litter dynamics is presented to depict consistencies with crown development among stands managed under different density regimes.     

Browse yield and nutritive value of two Salix species and Dorycnium rectum in New Zealand

The willows Salix matsudana x alba and S. kinuyanagi, and the leguminous shrub Dorycnium rectum, are used for soil conservation in New Zealand and have potential value as browse plants. Two experiments were conducted in the lower North Island to ascertain the effect of selected establishment and cutting practices on their browse yield and nutritive value. A hill site experiment determined the effect of rooted and unrooted stem cuttings on establishment and initial production of the Salix species. A flat site experiment determined the effect of cutting height (0.10–0.30 m, 0.80 m, and 1.20 m above ground) and cutting frequency (once or twice per year) on yield of the Salix species and D. rectum. The establishment and dry matter (DM) yields of the Salix species were unaffected by the type of stem cutting. S. matsudana x alba (1.2 kg DM/tree) plants yielded more edible DM than S. kinuyanagi (0.9 kg DM/tree) and D. rectum (0.4 kg DM/tree). Cutting height had no effect on edible DM yield but affected total DM yield of the Salix species. Nitrogen concentration in edible DM, of all species, was 18–22 g/kg DM. In vitro organic matter digestibility of S. matsudana x alba (648–691 g/kg DM) and D. rectum (664–666 g/kg DM) was greater than S. kinuyanagi (611–615 g/kg DM). The condensed tannin concentration in edible DM of S. kinuyanagi was four-fold higher than in S. matsudana x alba (255 vs. 59 g/kg DM). It was concluded that S. matsudana x alba had the greatest potential as a browse species and D. rectum the least.This revised version was published online in November 2005 with corrections to the Cover Date.     

Carbon, water and nutrient flux in Maya homegardens in the Yucatán peninsula of México

The Yucatán Peninsula of México has shallow soils and receives low amounts of precipitation, and has therefore low agricultural potential. Lacking large-scale irrigation from rivers and adequate rainfall, the indigenous Maya groups maintain agricultural productivity by adapting a variety of practices. Multistrata homegardens, one of their agricultural systems, have provided goods for trade, sale and personal consumption for many centuries. Nevertheless, an understanding of the controlling biological factors and interactions within these systems can lead to yield improvements. Photosynthetic rates, water use and litter production for a variety of species have been studied in these gardens to determine how Maya management impacts resource flow, productivity and diversity. When irrigated, diurnal photosynthetic rates nearly doubled for Manilkara zapota and water use increased two fold for M. zapota and Cordia dodecandra. Total litter production in traditional homegardens varied from 1,000 to 4,000 kg ha⁻¹ yr⁻¹ and ten arboreal species were found to contribute more than 33% of total litterfall biomass. Nutrient concentrations in the leaves of the predominant species were analyzed; Meliococcusbijugatus and Spondias purpurea were found to contribute the largest quantities of N, P and C. Our research indicates that species and structural diversity are critical to sustainability of homegardens, allowing efficient use and transfer of carbon, nutrients and water. This revised version was published online in June 2006 with corrections to the Cover Date.     

The structure of four home gardens in the Petén,Guatemala

Forest-covered home gardens around the tropical world vary in their structure, but serve to supply food and other products for direct family consumption or marketing. Little quantitative data exist defining home garden structure. Thus, this study was undertaken to examine the variation in home garden structures in response to market or household needs and the subsequent variation in light interception and productivity.Four home gardens were studied in the Department of the Petén, in northern Guatemala. Areal extent and height of canopies were mapped in transects through four gardens representing a range of site water regimes and market orientation. Light intensities incident on the ground were measured along each transect to assess light use. Results showed structural complexity, with full canopy closure in the one or more layers within the canopy for most gardens. The garden architectures made efficient use of light and space, with intersive management for food and fuel production. Farmers grew the crops for both cash and family subsistence. One home garden on a comparatively dry site with shallow soil seemed less structured, with only a single broken canopy layer, but with diverse species of plants.The results indicate that development of gardens in this area utilized existing trees, thinning them to leave the most useful, and inserting other desirable trees and shrubs in the understory and in open spaces. This strategy seemed to maximize light use, regardless of market orientation.This look at the structure and composition of four home gardens, in a forested area of current immigration, demonstrated (1) variety of organization and plant components, (2) different architecture for different soil/site conditions and market orientations, and (3) efficient use of available light through the arrangement of plants.     

Mechanisms and management of acaricide resistance for Tetranychus urticae in agroecosystems

Journal of Pest Science - The two-spotted spider mite, Tetranychus urticae Koch, is a constant threat to sustainable production of numerous economically important crops globally. Management of T....