The pattern of tree seedling establishment relative to staghorn sumac cover in Michigan old fields

摘要: Trees invading 10-year and 16-year-old abandoned fields in Michigan were aged to determine year of establishment. Vegetation cover was mapped develop correlates between tree establishment patterns vegetation type. Few trees established the 1st 5 years after from cropping. Most (74%) 947 individual 2 age. The density seedlings all significantly higher under a canopy shrub, staghorn sumac (Rhus typhina), compared areas without canopy. It is argued that while "promotes" seedling success, effect indirect, mainly by reducing amount type ground-level which inhibits seedlings, secondly increasing seed arrival via animal activity. INTRODUCTION mechanisms how late successional species appear sere have been discussion for some time (see reviews McCormick, 1968; Drury Nisbet, 1973; Horn, 1974; Connell Slatyer, 1977; McIntosh, 1980). There are three general views: first earlier colonists "prepare way" (called "reaction" Clements, 1916, or "facilitation" 1977) later modifying environment so it more suited species. This view perhaps most common presented textbooks popular literature, but has questioned repeatedly ecologists, notably Egler (1954) further McCormick (1968), Niering (Niering Egler, 1955; Goodwin, 1974), Nisbet (1973) others. likely describes mechanism operates primary succession, not very important secondary succession. second inhibit invasion arrivals replaced only when they die naturally; there much evidence support this claim (1968) (1973). third sequence determined solely life history characteristics organisms, late-appearing those arrived grew slowly larger sizes, eventually dominating community. To what degree do early inhibit, tolerate facilitate (terminology arriving species? Experimental studies would be required test various models proposed. Some experiments conducted communities show rapid change (e.g., estuarine fouling invertebrates, Dean Hurd, 1980), with results showing inhibitory interactions prevalent than facilitation interactions. Experiments terrestrial rare, because require such long impractical; an analysis pattern existing may still among best regard problem. In field study reported here, agricultural practice 16 10 whether had part "initial floristic composition" (Egler, 1954) 1Present address: B. P. 817; Yaounde, Cameroon, Africa.