Browsing by Author "Kaarto, Elli-Nora"

Agroforestry is a collective name for agricultural land-use practices where combinations of woody perennials such as trees and shrubs are intentionally managed with crops and/or livestock in same land units for various environmental and economic benefits. As a sustainable farming practice, agroforestry is used to increase food production without adding harmful impacts of agriculture on natural environment. Agroforestry is a common farming practice in Taita Hills, Kenya, where it is motivated by Kenyan policies supporting tree planting in the fields. This study aims to find out how canopy height and canopy cover have changed during the last ten years in the croplands of Taita Hills to get more knowledge on the state and trends of agroforestry in the study area. Changes in canopy height and canopy cover in croplands are approached by multitemporal airborne laser scanning (ALS) data. ALS is an active remote sensing method used to acquire three-dimensional point cloud data of a target landscape. Canopy height models (CHM), 99th percentile canopy height and canopy cover data were derived from two ALS data sets from 2014/2015 and 2022 and used for the change detection of canopy height and canopy cover during the study period. Field data from 2013 and 2022 containing tree measurements from 28 field plots were used in the validation of ALS-based analyses. The results indicate that there has been a slight increase in canopy height and canopy cover during the study period. It is acknowledged that the study period is quite short to detect changes in tree growth. Hence, only slight positive changes in canopy height and canopy cover were expected. Based on CHM changes, almost 20% of the area outside forests had ≥ 2 m increase in the canopy height. Furthermore, 7% of the area outside forests had ≤ -5 m decrease in the canopy height, which corresponds to tree loss. Results for CHM based canopy height were supported by 99th percentile canopy height changes. The area outside forest with ≥ 10% canopy cover increased from 67.4% to 68.0%. Even though canopy height and canopy cover had a slight increase in the croplands, forest cover was detected to be increasing during the study period. ALS and field measurements matched well with each other. In the tree height measurements, there were more variance with taller trees, probably caused by difficulties in measuring taller trees in the field. Moreover, ALS data was found to underestimate tree height changes. The average absolute deviation for tree height changes was 1.3 m shorter for ALS-measured tree heights than field measurements. Number of trees in field plots has mainly decreased during 20132022. ALS-based mean canopy height and canopy cover changes in the plots explain the actual changes well if large number of trees have been cut down during the study period. The thesis provides valuable information on the state and trends of agroforestry in Taita Hills. However, more exact land cover classification could have enhanced the accuracy of the results even more. All in all, the results were mainly positive, indicating that there has been an increasing trend in canopy height and canopy cover in the croplands in Taita Hills.