Reproductive ecophysiology of Rubus occidentalis in southeastern Michigan I. A survey of tolerance ranges

Research on Rubus occidentalis (black raspberry or blackcap) has recently intensified due to the health benefits of its fruits, its potential as a crop, and its aggressive growth in certain sensitive environments. However, the conditions in the wild in which stands of the species best persist and fruit are currently unknown. I measured light, soil pH, soil organic matter, soil fine particle fraction, and soil nitrogen in 49 R. occidentalis stands in southeastern Michigan and, using generalized linear and general mixed-effects models, examined whether these environmental factors were correlated with measures of reproductive success. Rubus occidentalis stands generally grew in moderate to low incident light and in neutral to mildly acidic (pH ∼5-7.5), coarsely textured soils with average to low levels of organic matter and inorganic nitrogen. Stands had a significantly higher proportion of successfully fruiting canes as light and soil pH increased and as organic matter decreased. Stands also had significantly more fruit receptacles and fruits per cane as light, ammonium, and pH increased. Significantly greater premature cane dieback during the fruiting season was observed as organic matter, nitrate, and soil pH increased and as soil texture became finer. Wild R. occidentalis appears to persist well in low-light environments with coarse, neutral, organic matter-poor soils, but it may achieve higher fruiting success in higher light environments with finer and more ammonium-rich soils. This study is the first to quantitatively assess the degree to which environmental context influences stand persistence and reproductive success for R. occidentalis in the wild.