Phillip E. Reynolds

Biophysical and Ecological Interactions in a Temperate Tree-Based Intercropping System

SUMMARY Tree-based intercropping is considered an excellent farming system and can contribute much to our understanding of sustainable agriculture practices. Our current research goals are to address and quantify the numerous biophysical interactions that occur at the tree-crop interface in order to enhance our understanding of the ecology of tree-based intercropping (a form of agroforestry). In 1987, the University of Guelph established a large field experiment on 30 ha of prime agricultural land in Wellington county southern Ontario, Canada to investigate various aspects of intercropping trees with agricultural crops. A variety of spacing, crop compatibility and tree growth, and survival experiments were initiated at that time, utilizing 10 tree species within the genera Picea, Thuja, Pinus, Juglans, Quercus, Fraxinus, Acer, and Populus. Two between row-spacings (12.5 m or 15 m) and two within row-spacings (3 m, or 6 m) were utilized in conjunction with all possible combinations of three agricultural crops (soybean, corn, and either winter wheat or barley). Investigations over the last decade have documented several complementary biophysical interactions. Nitrogen (N) transfer from fall-shed leaves to adjacent crops with enhanced soil nitrification as the proposed mechanism was estimated to be 5 kg N ha−1. Soil organic carbon (C) adjacent to tree rows has increased by over 1%, largely as a result of tree litterfall inputs and fine root turnover. It is estimated that intercropping has reduced nitrate loading to adjacent waterways by 50%, a hypothesized function of deep percolate interception by tree roots. We have also noticed increased bird diversity and usage within the intercropped area as compared to mono-cropped adjacent agricultural areas, and have recorded increases in small mammal populations. Earthworm distribution and abundance was also found to be higher closer to the tree rows when compared to earthworm numbers in the crop alleys. We speculate that these are indicative of major changes in the flow of energy within the trophic structure identified with intercropping systems. In light of climate change mitigation processes, C sequestration and NO2 reduction potentials in tree-based intercropping systems were studied and compared to conventional agricultural systems. The results suggest that sequestration of C was 5 times more in the former system than in the latter. Competitive interactions between trees and crops for nutrients, moisture and light were also studied. The tangible benefits that are derived from properly designed and managed tree-based intercropping systems place this land management option above conventional agriculture in terms of long-term productivity and sustainability.

Growth response of Picea mariana seedlings to competition for radiation.

The growth response of 4-year-old black spruce seedlings (Picea mariana (Mill.) B.S.P.) to reduced radiation availability (DIFN) caused by herbaceous and woody competitors was investigated on a clay and on a loam site on a research plot in Ontario, Canada. Variability in black spruce growth was less explicable by reduced radiation availability caused by woody competitors than growth variability caused by herbaceous competitors. On the clay site, competition from fireweed (Epilobium angustifolium L.), Canada bluejoint grass (Calamagrostis canadensis (Michx.) Nutt.) and red raspberry (Rubus idaeus L. var. strigosus (Michx.) Maxim.) decreased black spruce diameter by more than 40% compared to seedlings without competition. Canada bluejoint grass and fireweed also distinctly reduced black spruce diameter performance on loam (>30%). These results are discussed in relation to the need of vegetation control.