Vegetation development in a hardwood-forest chronosequence in Nova Scotia

Abstract

Vegetation and aboveground biomass and nutrient capital (N, P, K, Ca, and Mg) were examined in a 22-stand, 75-year chronosequence within an angiosperm-dominated forest in Nova Scotia. Stands 20 years old and younger originated with clear-cutting, whereas older stands originated with wildfire. Early successional, ruderal species of vascular plants were prominent for ca. 5 years after clear-cutting, but they occurred as a part of a diverse, species-rich community dominated by more-tolerant species, many of which survived the disturbance of clear-cutting. The rate of accumulation of aboveground biomass averaged 2.2 t•ha−1•year−1 during the first 11 years after clear-cutting, 4.7 t•ha−1•year−1 between 11 and 30 years, and then decreased to 1.5 t•ha−1•year−1 between 30 and 75 years. Foliage biomass recovered to a quantity typical of mature stands within only 3–5 years of disturbance, as a result of the vigorous growth of both ground vegetation and stump sprouts of certain tree species. The patterns of accumulation of N, P, K, and Mg were similar to that of biomass, except that initially their relative rates of accumulation were faster because of the large proportion of nutrient-rich foliage in young stands. The accumulation of Ca was relatively slower, because of its large concentration in tree bark, a tissue whose proportion in the aboveground biomass reached a maximum much later than did foliage.

Comparison of the Ground Vegetation in Spruce Plantations and Natural Forest in the Greater Fundy Ecosystem, New Brunswick

“…Other studies have reported relatively high richness and diversity of ground vegetation during the initial stages of succession after timber harvesting, followed by a large decline as more shaded conditions develop (Shafi and Yarranton 1973;Bormann and Likens 1979;Hibbs 1983;Schoonmaker and McKee 1988;Burton 1989;Reiners 1992;Crowell and Freedman 1994;Gilliam et al 1995;Qi and Scarratt 1998;Roberts and Methven 1998). It has been suggested that the highest diversity of trees occurs in intermediate regenerative conditions, as this transitional period contains both early-and later-successional species (Loucks 1970;Auclair and Goff 1971;Pickett 1976;Connell 1978).…”

“…The higher species richness and diversity in young plantations is due to their relatively open conditions and the spatial heterogeneity of environmental factors and vegetation (Shafi and Yarranton 1973;Crowell and Freedman 1994). Other studies have reported relatively high richness and diversity of ground vegetation during the initial stages of succession after timber harvesting, followed by a large decline as more shaded conditions develop (Shafi and Yarranton 1973;Bormann and Likens 1979;Hibbs 1983;Schoonmaker and McKee 1988;Burton 1989;Reiners 1992;Crowell and Freedman 1994;Gilliam et al 1995;Qi and Scarratt 1998;Roberts and Methven 1998).…”

“…The total cover in reference stands (average 68%; range 40-98%) was lower than in most plantations. Studies of natural regeneration after the clear-cutting of temperate hardwood or mixedwood forest have shown that an approximately complete foliar canopy of herbaceous and shrubsized plants can re-establish within only 4-6 years of disturbance, casting substantial shade over the forest floor (Bormann and Likens 1979;Burton 1989;Crowell and Freedman 1994). As the over-topping canopy of shrubs and trees further develops, there is a substantial decline in lower-growing plants of the ground vegetation.…”

“…117 The overall successional pattern of species composition in plantations is one of increasing tolerance of the stressful conditions occurring beneath the developing overstorey (see Sparling 1967;Crowell and Freedman 1994;Freedman 1995). Species with the greatest prominence in younger plantations (up to 8 years old) varied in their ability to tolerate shading, as these stands included both ruderal invaders (such as Agrostis scabra, Epilobium angustifolium, Polytrichum commune, and Solidago graminifolia) and more tolerant ones that survived the disturbance event (e.g., Cornus canadensis, Maianthemum canadense, Picea mariana, and Pleurozium schreberi).…”

“…Important effects include: reduction of biomass and nutrient capital (with potential damage to site quality and decreased carbon storage), increased erosion, altered hydrology, and changes in biodiversity at the levels of species, community, and landscape (Anonymous 1986;Freedman et al 1994;Freedman 1995;Kohm and Franklin 1997;Mallik et al 1997;Hunter 1999;Lindenmayer and Franklin 2002;Kimmins 2003). The changes in composition and diversity of plant communities after clear-cutting and associated management practices, such as those involving plantation establishment, are influenced by biotic and abiotic qualities of the site and by the colonizing and competitive abilities of particular species (Grime 1979;Smith 1980;Crowell and Freedman 1994;Freedman 1995).…”