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Spatiotemporal trends of black walnut forest stocking under Climate Change.
Aziz Ebrahimi, Akane O. Abbasi, Jingjing Liang and
Douglass F. Jacobs*
Department of Forestry and Natural Resources, Purdue University, West Lafayette, IN, United States
Basal area is a key measure of forest stocking and an important proxy of forest
productivity in the face of climate change. Black walnut (Juglans nigra) is
one of the most valuable timber species in North America. However, little is
known about how the stocking of black walnut would change with differed
bioclimatic conditions under climate change. In this study, we projected the
current and future basal area of black walnut. We trained different machine
learning models using more than 1.4 million tree records from 10,162 Forest
Inventory and Analysis (FIA) sample plots and 42 spatially explicit bioclimate
and other environmental attributes. We selected random forests (RF) as the
final model to estimate the basal area of black walnut under climate change
because RF had a higher coefficient of determination (R2), lower root mean
square error (RMSE), and lower mean absolute error (MAE) than the other
two models (XGBoost and linear regression). The most important variables
to predict basal area were the mean annual temperature and precipitation,
potential evapotranspiration, topology, and human footprint. Under two
emission scenarios (Representative Concentration Pathway 4.5 and 8.5), the
RF model projected that black walnut stocking would increase in the northern
part of the current range in the USA by 2080, with a potential shift of
species distribution range although uncertainty still exists due to unpredictable
events, including extreme abiotic (heat, drought) and biotic (pests, disease)
occurrences. Our models can be adapted to other hardwood tree species to
predict tree changes in basal area based on future climate scenarios.
Saunders Looks at Impacts of Prescribed Fire
on Quality, Economic Value
Prescribed fire is one technique utilized for forest management and tree stand improvement, but what effects does it have on resulting lumber in the treated area and, in turn, what economic impacts could that have long term.
Mike Saunders, associate professor of ecology and natural resources, is the principal investigator on a project with the U.S. Forest Service that aims to answer those questions by determining the effects of prescribed fire on tree and stand quality, resulting potential lumber grade recovery and projected economic value.
The research, which is funded by the Join Fire Science program, also counts Jan Wiedenbeck, Dan Dey and Thomas Schuler of the Forest Service as co-PIs.
The group aims to quantify the relationship between average tree quality and time since inception of a prescribed fire application in a mature stand, to describe the relationship between lumber value recovery and visual fire damage characteristics on standing trees, and then apply those findings from tree-level to stand-level to determine lumber value recovery related to fire history in the oak-dominated stands.
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