Herbage yield in agroforestry systems as a function of easily measured attributes of the tree canopy

• Published in: Forest ecology and management Vol. 65; no. 2; pp. 195 - 200
• Main Authors: Sibbald, A.R., Griffiths, J.H., Elston, D.A.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.06.1994; Elsevier
• Subjects: Agricultural and farming systems; AGROFORESTERIA; AGROFORESTERIE; AGROFORESTRY; Agroforestry system; Agronomy. Soil science and plant productions; Biological and medical sciences; CANOPY; COUVERT; CROP YIELD; CUBIERTA DE COPAS; CULTIVOS DE PASTO; Fundamental and applied biological sciences. Psychology; General agroecology. Agricultural and farming systems. Agricultural development. Rural area planning. Landscaping; General agronomy. Plant production; Generalities. Agricultural and farming systems. Agricultural development; HERBAGE CROPS; Herbage yield; PINUS RADIATA; PLANTE POUR HERBAGE; RENDEMENT DES CULTURES; RENDIMIENTO DE CULTIVOS; Tree canopy; New Zealand; Oceania; Herbage yield; Agroforestry system; Tree canopy; Canopy; Monocotyledones; Multilocal experiment; Cropping system; Picea sitchensis; Fodder; Microclimate; Grassland management; Gramineae; Angiospermae; Softwood forest tree; Gymnospermae; Tree crown; Temperate climate; Coniferales; Spermatophyta; Yield; Fodder crop; Lolium perenne; Vegetation structure; Agroforestry; Canopy(vegetation); Field study
• ISSN: 0378-1127; 1872-7042
• DOI: 10.1016/0378-1127(94)90170-8

Data from an experiment that measured rates of herbage yield below different tree canopies have been used to investigate the relationship between annual herbage growth and readily estimated parameters of the canopy structure of evergreen conifers. Canopy structure data were collected by destructive sampling of trees removed from the experimental area immediately prior to its establishment, and from subsequent measurements on growing trees during the following 2 years. In New Zealand, it was found that relative pasture yield (the ratio of growth below a canopy to open pasture growth) was linearly related to green crown length in the case of Pinus radiata canopies. More recently, a family of relationships between relative pasture yield and green crown length, indexed by the mean height of trees forming the canopy has been derived. For our data, the regression of annual herbage yield on green crown length is good ( R 2 = 92.5%) but shows systematic variation in the residuals. Hence, other related explanatory variables were investigated to see if any gave a more satisfactory fit to the data. By assuming that individual trees have a canopy in the shape of a regular cone, the areas of the projections of the tree canopies at different inclinations to the vertical were calculated. If it is further assumed that the canopies are of even density, the projections can be used to estimate the proportion of direct light which is incident on the herbage under the trees as a function of the angle of the sun above the horizon. A regression using both vertical and horizontal projections in varying proportions indicated that the best fit to the data was obtained using the horizontal projection alone ( R 2 = 94.0%). These results indicate: first, that the horizontal projection of the crown gives a good, simple prediction of annual herbage yield; and secondly, that the horizontal component of incident light is most important for herbage growth at Scottish latitudes.