Spatializing willow productivity: more resolution and better estimates

Latest paper published:

MOLA-YUDEGO B. 2011. Predicting and mapping productivity of short rotation willow plantations in Sweden based on climatic data using a non-parametric method. Agricultural and Forest Meteorology. In Press.

Abstract
In this study, estimates for yield of short rotation plantations are provided based on climatic variables using the k nearest neighbour method. The calculations were based on climatic data and yield records from 1790 willow plantations in central and southern Sweden, divided into three categories based on local performance. The chosen neighbours were weighted proportionally to the inverse squared distance measured in the feature space defined by the climatic variables. The climatic variables included monthly averages of maximum, minimum and mean temperatures and precipitation. These were weighted using empirical constants after an optimisation process. The best accuracy was obtained with k = 4 for the group of high performance plantations, and k = 5 for the other groups. The relative RMSE values were 37.9%, 24.4% and 38.9% for the high, medium and low local performance, respectively, and the corresponding relative biases were 2.10%, −0.95% and −1.30%. The method was applied to interpolate the yield values in order to perform maps of potential productivity for the whole area. The results of this approach indicate that it can provide faster and more accurate predictions than previous modelling approaches, and can offer interesting approaches in the field of yield modelling.
Research highlights

► A k-NN method applied to climatic variables is effective for spatialising productivity. ► Relative RMSE were 37.9%, 24.4% and 38.9% for three levels of management performance. ► The method presented can serve to develop site index models for new areas.

Keywords: k-NN methods; Growth and yield models; Bioenergy; Wood fuels

About erosion and recreation...

This is our latest work published on erosion:

SELKIMÄKI M, MOLA-YUDEGO B. 2010. Estimating and modelling the resistance of nature to path erosion in Koli National Park, Finland. Boreal Environment Research 16. In Press.

Abstract

We studied the resistance of nature to trampling and path erosion using a case study of Koli National Park. The data are based on 201 field measurements made of paths together with digital datasets in order to identify the main factors affecting path erosion. Additionally, the resistance of different forest types to trampling was studied. Models for path erosion were constructed in order to predict the width and depth of a path. Slope of the path and the number of visitors were the two main factors explaining width and depth. The lowest resistance areas were identified in rocky site forest located on the hilltops, while the deepest paths were on moraine soils. Paths on meadows were highly resistant to trampling and the most resistance forest type was Oxalis myrtillus type. The results of this study can be applied in national park management and can be the basis for the design of measures to reduce path erosion. By mapping the most sensitive areas, the path network can be planned to be sustainable during the long term. Recreational pressure can be redirected to more resistant areas or structures such as duckboard and stairs can be built to protect the most sensitive areas. Developed models can be used for testing where to place new paths in order to minimize path erosion.

Keywords: erosion modeling, nature conservation, path erosion, tourism, vegetation resistance

Willow productivity grows!

There have been substantial increments in the productivity of short rotation willow plantations in Sweden, especially on those well tended and with good management. Find the details in this new publication:

MOLA-YUDEGO B, 2010. Trends and productivity improvements from commercial willow plantations in Sweden during the period 1986–2000. Biomass and Bioenergy. doi:10.1016/j.biombioe.2010.09.004

Abstract

The production trends of commercial willow plantations for bioenergy in Southern and Central Sweden were studied for the period 1986–2000 based on harvest records of the first cutting cycle after the establishment of 1512 plantations. The trends were modelled by using a mixed model in order to include the variability of management options by the growers, which were grouped into four classes according to their performance. The spatial variability of the productivity is included using an agro-climatic index based on the official estimates of oat yields. Results of the study show average yield increments of 2.06 odt ha−1 yr−1 per decade. Areas with high productivity have significantly increased the yields of willow during the period studied, from 1.3 to 5.4 odt ha−1 yr−1. Regarding management, the best growers group shows a national average increment of 2.75 odt ha−1 yr−1 per decade, and the latest plantings reach an average of 6 odt ha−1 yr−1. This group is formed by farmers with previous experience growing willow, who tend to have significantly higher yields. In addition, experienced farmers increased their yields an average of 0.34 odt ha−1 yr−1 regardless of the group they were classified in. It is expected that future improvements of the willow varieties will result in a significant increase in the mean yields in the near future.

Keywords: Salix; Growth and yield; Bioenergy; Mixed models; Management

In the case of the best areas (using oat productivity as a proxy variable) the productivity of willow has increased significantly (see figure 6), especially if the management and tending of the plantations have been good (including proper weeding, site location and fertilization). This has been mostly due to better varieties as well as improved practices, and it seems that this trend will keep on going, although possibly not linearly.

For citing the figure:  MOLA-YUDEGO B, 2010. Trends and productivity improvements from commercial willow plantations in Sweden during the period 1986–2000. Biomass and Bioenergy. doi:10.1016/j.biombioe.2010.09.004.