Environmental Engineering Reference
In-Depth Information
(e.g., jack pine;
Pinus banksiana
) and advanced regeneration in the understory of
spruce (e.g.,
Picea spp.
) and balsam fir (
Abies balsamea
) stands that maintain
spruce budworm host availability over time [
31
] are evidence of this dynamic
feedback between disturbance and succession. The spatial patterns created through
forest management and their influences on forest succession in turn influence future
forest disturbances dynamics [
32
]. Spatial pattern analysis is important to better
understand the effects of human activities on natural disturbance dynamics.
Sources of Heterogeneity
Understanding the nature and consequences of spatial heterogeneity in ecosystems
requires an understanding of the processes that generate this heterogeneity. In this
section, different types of spatial heterogeneity and how different types of processes
may give rise to complex spatial patterns are described. The consequences and
potential challenges involved in indentifying the relative contributions of these
different and frequently interacting processes are discussed next [
6
].
Levels of Organization
Processes that generate spatial heterogeneity can be classified into a hierarchy of
spatial processes that operate at different levels of ecological organization: (1) indi-
vidual, (2) population, (3) community, and (4) landscape/ecosystem. Individual
processes include organism dispersal and habitat selection; population processes
can include demographic dynamics as well as immigration/emigration; community
level processes are highly relevant to natural disturbance dynamics and can include
successional changes and rates of species turnover. Examples of landscape/ecosys-
tem level processes include disturbance, climate change, and migration.
Processes within this organizational hierarchy are not necessarily independent
and can influence each other among levels. Such interactions can influence emer-
gent patterns due to potential cross-scale interactions and amplifications [
33
] and
can also further complicate efforts to identify clear cause-and-effect relationships.
A recent example of such cross-scale amplification in a forest ecosystem can be
found within the mountain pine beetle (
Dendroctonus ponderosae
) system of
Western Canada, where the recent outbreaks of the lodgepole pine infesting
beetle have affected an unprecedented millions of hectares [
34
]. Here, the local
dynamics of population control by host tree defenses were overcome when popula-
tion numbers increased dramatically due to persistent warmer temperatures in the
early 2000s. The interactions between these local- and landscape-level processes
are thought to have led to a positive feedback that allowed the outbreak to expand as
much as it did [
34
].
