Abstract
The forest ecology literature is rife with debate about how to: (i) define a ‘forest’ and distinguish it from similar systems, such as woodlands, savannas, parklands or plantations; (ii) identify transitions from ‘forested’ to ‘non-forested’ states and, most challengingly; (iii) quantify intensities of degradation. Here we argue that past attempts to define forests and forest degradation, focusing on attributes of living trees (e.g., height, canopy cover), combined with regenerating processes such as recruitment and succession, whilst useful, are ecologically incomplete. These approaches do not adequately represent processes that, operating over long time scales, determine whether a forest system is structurally healthy (as opposed to degraded), functional and persistent. We support our case using a conceptual model to illustrate how deeper-time processes, as well as instantaneous or chronic disturbances that cause degradation, might be revealed through analysis of the patterns of size structure and density of the fallen wood, in relation to the living trees and standing dead. We propose practical ways in which researchers can incorporate dynamic, long-term processes into definitions of forests and forest degradation, using measurements of dead and fallen trees. Doing so will improve our ability to manage and monitor forest health under global change.
Highlights
The forest biome provides vital global ecosystem services like nutrient cycling and carbon storage, and is the habitat for an immense diversity of terrestrial species (Gentry 1992)
Many studies focussing on the impact and sustainability of activities associated with human development on forest biomes, and their interaction with the agents of global change have been done over the last two decades (e.g. Clark et al 2011; Lindenmayer and Franklin 2002; Noss 1999)
These studies typically use plot-based surveys as ‘snap shots’ of standing pattern, time series of marked individuals, and remotesensed imagery. Such information can be used to characterise the ecological status of the forest, and to categorise and quantify both forest health and forest degradation over space and time
Summary
The forest biome provides vital global ecosystem services like nutrient cycling and carbon storage, and is the habitat for an immense diversity of terrestrial species (Gentry 1992). Clark et al 2011; Lindenmayer and Franklin 2002; Noss 1999) These studies typically use plot-based surveys as ‘snap shots’ of standing pattern, time series of marked individuals, and remotesensed imagery. Assessing the extent of degradation or loss of forest cover, and measuring the success of actions that seek to protect existing forests or ameliorate past damage, remains a fundamental challenge This is, in part, because the definition of ‘forest’ and ‘forest degradation’ is still elusive (Putz and Redford 2010). The forest biome is often sub-categorized according to variation in the structure and dynamics—covering a wide span of climatic and latitudinal gradients These cross-continental differences make it quixotic to define a generic ‘forest’ (Chazdon et al 2016).
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