THE SIMULATION OF ALLELOPATHY IN ECOSYSTEM-LEVEL
FOREST MODELS: A STUDY CASE IN THE PACIFIC NW*
Juan A. Blanco 1,2 , J.P. (Hamish) Kimmins 1
1 Dep.
Forest Sciences, Faculty of Forestry, The University of British Columbia, 3041-2424 Main Mall, V6T 1Z4, Vancouver, B.C.
2 Contact: [email protected]
* Poster presented at International Scientific Conference on “Forest Growth and Timber Quality”, hold in Portland, OR, in August 7-10 2007, and published in Blanco J.A., Kimmins J.P. 2009. The role of allelopathy in ecosystem-level forest models: a study case in the
Pacific NW. In: Dykstra D.P., Monserud R.A. (Eds.) Forest Growth and Timber Quality: Crown Models and Simulation Methods for Sustainable Forest Management. USDA Forest Service General Technical Report PNWGTR-791,Portland, USA. Pp 205-210.
The ideas presented in this poster are also developed in the paper Blanco, J.A. (2007) The representation of allelopathy in ecosystem-level forest models. Ecological Modelling, in press, doi:10.1016/j.ecolmodel.2007.06.014.
Allelopathy: An ecosystem-level process
Allelopathy is one of the factors that determine
interactions among plants. Despite the wide presence of this
phenomenon, forest models implementing allelopathy are
scarce or have been little developed, but its inclusion should
be carefully considered in forest models dealing with
environmental stress, introduction or invasion of exotic
species and ecological succession. In those situations, multiple
factors influence allelochemical production or toxicity such as
nutrient availability, soil moisture and texture, solar radiation,
and temperature, among others (Figure 1). Ecosystem-level
effects of allelopathy are changes in germination rates,
inhibition of seedling growth, mycorrhizal function, insect and
bacterial growth, inhibition of nitrification or litterfall
decomposition and dieback of mature trees (Figures 2).
WHY ALELOPATHY IN
ECOSYSTEM-LEVEL MODELS?
Levels of
biological
organization
Function of level
Ecosystem
Understanding and
Community
Understanding
Population
Understanding
Individual
Understanding and
Organ systems
Understanding
Organs, tissues
Understanding
Cell
Understanding and
Sub-cellular
Understanding
Levels of
biological
integration
Prediction
Ecosystem
Prediction
Individual
Prediction
Cell
ALLELOPATHY EFFECTS: CONCEPTUAL MODEL
Virtual experiment of allelopathy effects
on ecosystem dynamics
Allelopathy effects were simulated with the FORECAST
ecosystem-level forest model. Four different runs were carried
out, all of them with the same starting conditions: Site index 24
m at 50 years, 3000 stems ha-1 as initial density and initial
aboveground biomass of salal (Gualtheria shallon Pursh) of 35
kg ha-1. The rotation length was fixed at 100 years for all
simulations. The first run did not simulate any allelopathic
effect, and was considered a reference situation. For subsequent
runs, I selected the two effects most frequently described and
analyzed in the literature: A germination decrease of 15%
(Mallik and Pellissier 2000) and a reduction of decomposition
rates by 10% (Damman 1971). Finally, the fourth run simulated
both effects simultaneously. Results are showed in Figure 3.
RESULTS FROM A VIRTUAL
EXPERIMENT
Figure 1.
Tree-level influential
factors on
allelochemical
production (dotted
lines) and
physiological effects
of allelopathy (solid
lines)
Figure 2. Standlevel influential
factors on
allelochemical
toxicity (dotted
lines) and transport
paths of
allelochemicals
from donor to
target plant (solid
lines). Arrow
thickness in solid
lines is proportional
to empirical
evidence
FORECAST: Ecosystem-level Management Forest Model
Figure 3. Comparison of results from four different runs simulating the
same forest ecosystem without allelopathy effects vs. simulating allelopathy
as a reduction in decomposition rates, germination rates or both combined.
Hybrid model: It uses historical/field growth data to simulate
future growth & yield. This simulated growth is modified by
some biological processes: light competition and nutrient
availability (Kimmins et al. 1999).
CONCLUSIONS
Non-spatial stand-level model: It does not account for
individual stems and tree positions in the stand, but it does have
a tree list and tracks individual stem sizes
Ecosystem management model: It simulates interactions
between ecosystem component (trees, minor vegetation -shrubs,
herbs- and forest soil) and the influence of different
management practices and natural disturbances on them.
FORECAST user interface
My results showed different effects of allelopathy on several ecological
variables depending on the type of allelopathic influence simulated. In addition,
this experiment showed the suitability of ecosystem-level models to simulate, if not
directly allelopathic interactions, at least the ecological effects of allelopathy at the
ecosystem level. Overall, our work points out that forest managers and researches
should think carefully about the inclusion of allelopathy as a way of improving the
accuracy of forest models.
REFERENCES
Mallik, A.U., Pellissier, F., 2000. J. Chem. Ecol., 26:2197-2207. Damman, A.W.H., 1971. Ecol. Monogr. 41:253-270. Kimmins J.P., Mailly D., Seely B. 1999.. Ecol. Model. 122, 195-224.
Acknowledgements
Data for the virtual experiment were provided by Dr. B. Seely. The author was supported by a postdoctoral fellowship granted by the Spanish Ministry of Education