Financial performance of diverse levels of early competition suppression and pre-commercial thinning on loblolly pine stand development     

Tanger  S. M.  Blazier  M. A.  Holley  A. G.  McConnell  T. E.  Vanderschaaf  C.  Clason  T. R.  KC  Dipesh 《New Forests》2021,52(2):217-235

New Forests - Competition suppression within loblolly pine plantations (Pinus taeda L.) is typically carried out within the first 2 years of a plantation, but competition control for longer...  相似文献   

Determining productivity gains from herbaceous vegetation management with 'age-shift' calculations     

South  David B.; Miller  James H.; Kimberley  Mark O.; Vanderschaaf  Curtis L. 《Forestry》2006,79(1):43-56

Gains in stand volume that result from competition control andfertilization are sometimes reported as ‘percentage gains’.Because percentage gains arithmetically decline over time asstand volume increases, plantation managers have difficultyin using percentage gains to project growth and revenues. The‘age-shift’ method quantifies the year advancementsin stand growth due to silvicultural treatments and, for herbaceousvegetation management, it has been proposed that this metricis less likely to change after the juvenile growth phase. Totest the sensitivity of the ‘age-shift’ method totime and hardwood competition, we used 20-year volume data from11 loblolly pine (Pinus taeda L.) studies that had early completeherbaceous and woody competition control. Volume growth gainswere expressed in terms of percentages and ‘age-shifts’.On all sites with no woody competition, percentage gains declinedfrom age 8 years to age 20 years. In contrast, age-shift estimateson these plots either remained constant or increased over time.However, in four cases where woody basal areas were greaterthan 4 m² ha^–1 at age 15 years, age-shift gains due toherbaceous control decreased and eventually resulted in volumelosses. When evaluating the response to early herbaceous competitioncontrol, age-shift calculations have promise as a useful predictivetool on sites with low levels of hardwood competition. Fivemethods for calculating age-shift are presented.  相似文献   

Assessing the impacts of species composition, top height and density on individual tree height prediction of quaking aspen in boreal mixedwoods     

Shongming Huang  Douglas P. Wiens  Yuqing Yang  Shawn X. Meng  Curtis L. Vanderschaaf 《Forest Ecology and Management》2009,258(7):1235-1247

In this study we developed an individual tree height prediction model for quaking aspen (Populus tremuloides Michx.) grown in boreal mixedwood forests in Alberta using the nonlinear mixed model (NLMM) approach. We examined the impacts of density, species composition, and top height on aspen height predictions. Statistically significant stand level variables were incorporated into the base height–diameter model to increase the predictive ability and accuracy of the model at both the population and subject-specific levels. Our analyses showed that top height and density impacted height growth, but species composition did not. More importantly, we found that the inclusion of additional variables into the base model, despite improving model fitting statistics on the modelling data, did not improve the model's predictive ability and accuracy when cross-validated and when tested on an independent testing data set. Under the NLMM framework the base model performed as well as or better than the expanded models that contained other stand level variables. This has important theoretical and practical implications because, other than for biological reasons, more accurate local tree height predictions for aspen can be achieved simply by using the base height–diameter model fitted with the NLMM approach without the inclusion of other variables.  相似文献   

Accounting for serial correlation and its impact on forecasting ability of a fixed- and mixed-effects basal area model: a case study     

Shawn X. Meng  Shongming Huang  Curtis L. Vanderschaaf  Yuqing Yang  Guillermo Trincado 《European Journal of Forest Research》2012,131(3):541-552

Successfully accounting for serial correlations has always been a vital part of growth and yield modeling when using repeated measurement data. In this case study, 16 alternative functions addressing the serial correlations of errors from a basal area model of black spruce (Picea mariana (Mill.) B.S.P.) were examined and compared. Results from this study showed that functions incorporated into the fixed and mixed models to account for the serial correlations improved model fit. The serial correlation of the residuals from the fixed model with directly modeled error structure was significantly lower than that from the fixed model without a modeled error structure. For the mixed model, modeling error structure resulted in only a moderate reduction in serial correlation of residuals. The comparison of the fixed and mixed models with and without directly modeling the error structure showed that for fixed model, a substantial improvement in forecasting ability was achieved when the error structure was directly modeled to account for serial correlation, and when the forecasts were adjusted based on the estimated correlation. But for the mixed model, further modeling of the error structure to account for more serial correlation resulted in worsened or comparative forecasting ability of the fitted model.  相似文献