Ecosystems and Spatial Patterns - Ecological Systems - page 103

and represent future challenges to forest and land managers. Uncertainty regarding
future disturbance dynamics, in particular fire and insects outbreaks, in the context of
global climate change makes investigations into disturbance interactions and
potential long-terms consequences for ecosystem spatial structure and functioning
particularly relevant.
Forest Ecosystems
In North American forests, disturbance processes generally include landscape level
fires, insect outbreaks, forest management (i.e., logging), and fine-scale local
disturbances such as windthrow and fungal diseases. The patterns created through
the interactions among disturbances can have important economic and ecological
consequences. For example, Stadler et al. [ 20 ] demonstrated that hemlock wolly
adelgid ( Adelges tsugae ) infestations in New England can affect both fast and slow
ecosystem dynamics, nutrient cycling dynamics in the short term, and landscape-
scale patterns of forest composition in the long term. Similarly, compounded
disturbances (e.g., fire and logging) in the eastern boreal forest can result in alternate
forest states [ 21 ], which can have consequences for biodiversity conservation. Eco-
nomically, it has been clearly demonstrated that forests under risk of disturbance,
either through fire or insect outbreaks, required longer rotation periods to accommo-
date for the losses [ 22 ].
Logging, fire, and insect outbreaks represent disturbance processes that revert
forest stands to early seral stages. Succession describes processes of forest recov-
ery, regeneration, and change that vary in response to different disturbances.
Although multiple processes generate forest spatial heterogeneity, not all influence
it in the same way. Spatial disturbance legacies vary in terms of shape, size,
intensity, boundary characteristics, influence on forest succession, and effects on
forest age structure [ 18 , 23 - 25 ]. The interactions among processes, or more prop-
erly, interactions among current disturbance and existing spatial legacies, create
and maintain heterogeneous forest landscapes. This cascade of effects and
constraints creates mutual dynamic feedbacks among patterns (spatial legacies)
and spatial processes (disturbances) [ 26 , 27 ] with important consequences for
ecosystem dynamics.
Different forest disturbances create different forms of spatial structure. Indeed,
each disturbance imposes its own unique “spatial signature” on the landscape that
also has different temporal characteristics contingent on a disturbance's interaction
with succession ( Fig. 7.2 ). Fires, for example, tend to produce relatively discrete
patches that occur over a short time frame and vary in terms of the residual forest
structure that is left behind [ 28 ]. Logging is somewhat similar to fires in that the
patches created are discrete and occur over short time frames and forest managers
have control over the scale and amount of residual structure. Insect disturbances,
such as outbreaks of spruce budworm ( Choristoneura fumiferana ), forest tent
caterpillar ( Malacasoma disstri ), and the mountain pine beetle ( Dendroctonus