Spatial distribution pattern of coarse woody debris in two typical forest types in Tianbaoyan national nature reserve#
 

Abstract: The spatial distribution pattern of coarse woody debris of two typical forest ecosystems was
conducted with Taylor’s power law，Iwao’s distribution function，and seven aggregation indexes in
Tianbaoyan National Nature Reserve．The results showed that：1）the spatial distribution pattern of
CWD were aggregated ，and the aggregation intensity declined with the scale increased；2）Compared
with natural disturbance，the aggregation intensity of logs and snags were increased by human
disturbance；3）It was tested by Blackith’s method，the spatial distribution pattern of CWD tend to be
susceptible by the external environment condition in small-scale．The spatial distribution pattern of
CWD was formed by long-term interaction between natural environment and external disturbance．To
some extent，based on these results，we will directly acquaint ourselves with the forest death patterns in
the population development， then reveal how the external disturbance，environmental heterogeneity
and individual biological features influence the population dynamics，thus provide theoretical basis for
predicting population dynamics.
 

Keywords: coarse woody debris (CWD); typical forest ecosystems; spatial distribution pattern

0 Introduction
The spatial and temporal distribution of plant population dynamics and its influencing factors
are important parts in studying population ecology，while analysis of population spatial patterns is
the major approach in studying population characteristics，population interactions and the
relationship between the population and the environment [1]．Different spatial distribution patterns
reflect the population’s status of use of natural resources．This is helpful not only in disclosing the
spatial and structural features of the population distribution，but also of far-reaching significance
in predicting the population dynamics and clarifying its succession laws， ecological features and
renewal strategy ．

In the study of population structures and patterns， most of the current research focuses on
the living trees[1~5]，while the dead wood is rarely involved [6~8]．As an important component of the
forest ecosystem [9]，the dead wood’s spatial distribution patterns play a key role in revealing the
forest population dynamics．External interference and the coarse woody debris (CWD) left behind
by dead trees， widely exist in the forest ecosystem， and participate in the forest material
circulation and energy flow [10~11]．Current research on the CWD centers around such areas like its
quantitative features[12]，decomposition[13]，respiration[14]，nutrient dynamics[15~17]，ecological
functions[18~21]，the spatial patterns is seldom referred [6~8]．However，this paper attempts to
introduce the aggregation index method，and selects the Tsuga Longibracteata forest type which
was less affected by interference，and Crytomeria fortunei forest type which was seriously cutting at the Tianbaoyan National Nature Reserve， as the study object． By employing the aggregation index， the interaction law between the CWD’s spatial distribution features and the environment
under the influence of different disturbance was analysed，thus it entails a better understanding of
the forest population dynamics with a view to provide a theoretical framework 45 for the protection
and management of the forest ecosystem．

4 Conclusion
The formation of the populations’ distribution patterns is the result of long-term mutual
adaptation and interaction between the species and the environment．On the one hand，it depends
on the species’ ecological and biological characteristics and the ecological completion processes
between species．On the other hand，it is closely related to the species’ environment and
interference [26~27]．The CWD’s aggregation decreases with the expansion of the research scale，the
CWD is inclined to aggregated distribution under the samller research scale，but inclined to
random distribution when the research scale is larger than a critical scale [8]．The CWD under the
spatial scale in our study is aggregated distributed， which shows that there are still limitations in
our traditional research method of the spatial pattern compared with the point p attern．It is difficult
to visually reflect the changes of the CWD’s distribution patterns under different research scales，
especially for the defining of the critical scale．Nevertheless，in the absence of individual
coordinates，using the aggregation indicators can serve as a better and more convenient method for
analyzing the populations’ spatial distribution．In this spatial distribution analysis，we add
Blackith’s population aggregation mean λ to investigate the reasons of aggregation．The outcome
shows not only that it is somehow feasible to adopt the indicators to analyze the CWD’s reason of
aggregated distribution，but also that it will remedy the defects of such methods，therefore
provides valid information for inferring its impact factors [28]，and also provides theoretical basis
for formulating effective forest management and protection strategies．

This study reveals that the small-scale study is more susceptible to reflect the influence of the
external environmental heterogeneity to the CWD’s spatial distribution patterns．It also reveals
that compared with the natural disturbance，human disturbance will increase the aggregation of the
logs and snags at the forests．The research results will help people understand the CWD’s spatial
distribution patterns and its interaction with the external interference，and provide reliable
theoretical basis for predicting the tendency of population development．The death of the forest
trees is the natural result of forest development，the dead wood is a typical feature of the forest
ecosystem dynamics (Luo et al，2004)．This study，takeing the CWD as the object，and directly
revealing the occurrence law of wood death during the population development process， will help
disclosing the impact of the external interference，the environmental heterogeneity，and individual
biological features on the population dynamics change．It is also of great significance in clarifying
the population’s succession law，ecological features，and its renewal strategy．

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