Ecosystem Properties and Forest Decline in Contrasting Long-Term Chronosequences

Abstract

During succession, ecosystem development occurs; but in the long-term absence of catastrophic disturbance, a decline phase eventually follows. We studied six long-term chronosequences, in Australia, Sweden, Alaska, Hawaii, and New Zealand; for each, the decline phase was associated with a reduction in tree basal area and an increase in the substrate nitrogen-to-phosphorus ratio, indicating increasing phosphorus limitation over time. These changes were often associated with reductions in litter decomposition rates, phosphorus release from litter, and biomass and activity of decomposer microbes. Our findings suggest that the maximal biomass phase reached during succession cannot be maintained in the long-term absence of major disturbance, and that similar patterns of decline occur in forested ecosystems spanning the tropical, temperate, and boreal zones.

How does pedogenesis drive plant diversity?

“…[29]. In that system, smaller islands are less frequently burnt and, therefore, have a thicker humus layer, which is associated with slower cycling of nutrients and, thus, lower productivity [30]. Surprisingly, spatial heterogeneity in soil properties was lower on smaller islands (i.e., those with older, nutrient-poor soils), which supported the highest plant species richness [29].…”

“…Increases in plant species density with soil age (represented by the ranked variable 'chronosequence stage') for four representative soil chronosequences from contrasting climates. All of these soil chronosequences include retrogressive stages [9,30]. Data are from [5], except data from the Jurien Bay chronosequence [10], which are unpublished (Graham Zemunik).…”

Forest ecosystem responses to environmental changes: the key regulatory role of biogeochemical cycling

“…These forests not only provide timber and nontimber forest products, but more importantly, ecological services such as biodiversity and protection of watershed and soil resources and sequestration of C (Dixon et al 1994;Chen et al 2004a;Lamb et al 2005;Purves and Pacala 2008). The N, P, and C interact in their biogeochemical cycles in ecosystems, and the stoichiometric balance is essential for maintaining forest ecosystem diversity, functioning, and stability (Wardle et al 2004;Chen et al 2005;Davidson et al 2007). Environmental changes such as elevated atmospheric CO 2 and temperature, atmospheric N deposition, land-use change, and forest fires, have transformed much of the land surface on the earth in the past century (e.g., Wardle et al 2004;Pan et al 2008Pan et al , 2009.…”

“…The N, P, and C interact in their biogeochemical cycles in ecosystems, and the stoichiometric balance is essential for maintaining forest ecosystem diversity, functioning, and stability (Wardle et al 2004;Chen et al 2005;Davidson et al 2007). Environmental changes such as elevated atmospheric CO 2 and temperature, atmospheric N deposition, land-use change, and forest fires, have transformed much of the land surface on the earth in the past century (e.g., Wardle et al 2004;Pan et al 2008Pan et al , 2009. It is essential to understand the ecosystem responses to these changes and the underlying processes regulating the responses (Dahlgren 2006).…”

Influence of Fuel Load Dynamics on Carbon Emission by Wildfires in the Clay Belt Boreal Landscape

“…In contrast, BS-NS forests showed the slowest increase due to the thick residual organic layers left after fire which favor unproductive open BS self-replacement [34,48,[52][53][54]. Following the growth influx, a decrease in tree loads [34,73] was predicted at 80, 110, and 200 years for TA, JP, and BS forests, respectively. Over time, tree mortality starts, gaps are created, and shade-tolerant species appear in the canopy [74,75].…”