Remote sensing and tree-ring study of forest condition in Northeastern Kansas.

Abstract

Vegetation changes related to climatic events were studied using remotely-sensed datasets combined with climatic data and tree-ring core samples. The study site was a deciduous forest at Fort Leavenworth in northeastern Kansas. My study correlated tree-ring width with forest growth and climatic events. Monthly data for temperature, precipitation, and drought indices were obtained from the National Climatic Data Center(NCDC). Oak trees (Quercus spp.) on an undisturbed forested ridge were sampled using an incremental borer. Ring widths were measured for the period from 1967 to 1996, crossdated, and standardized to remove the age-related trend. The growth of tree-rings was synchronized with the year-to-year variation of climatic pattern. The narrowest rings were found in 1977, 1980 and 1988 with the negative drought (-0.98, -1.02 and -2.06) Palmer Drought Severity Index values. The mid-1980s were favorable years for the forest in the Fort Leavenworth area. Ring widths were significantly correlated with overall climatic events and highly correlated with positive values for PDSI. Temperature did not influence ring-growth of oak species in the study area. Tree-ring data were compared to Normalized Difference Vegetation Index values (NDVI) from the remotely-sensed Landsat TM images. Changes in NDVI values were not in phase with the climatic patterns and ring width patterns. Narrow ring growth occurred in the drought year of 1988 when NDVI values were high. However, greater ring growth occurred in a normal year (1990) when the NDVI value decreased. Results showed that ring widths responded immediately to the climate change, but tree-leaf growth responses apparently lagged by one to two years.