PART IX — TERRESTRIAL ECOSYSTEMS 



The original goals of the Hubbard 

 Brook Ecosystem Study were to un- 

 derstand the energy and biogeochem- 

 ical relationships of northern-hard- 

 wood forest watershed ecosystems as 

 completely as possible in order to 

 propose sound land management pro- 

 cedures. A small-watershed ecosys- 

 tem approach was used to study 

 hydrologic cycle-nutrient cycle inter- 

 action in forest-stream-lake ecosys- 

 tems. This concept provided an 

 opportunity to deal with the complex 

 problems of the ecosystem on an 

 experimental basis. 



Integrated ecological studies of 

 these small, watertight, replicated for- 

 ested watersheds were begun in 1963 

 by Likens and Bormann in coop- 

 eration with the U.S. Forest Service. 

 The study has involved some 32 

 senior scientists from ten universities, 

 one national laboratory, and three 

 government agencies. The specific 

 work ranges from studies of complete 

 nutrient budgets, including measure- 

 ments of inputs of cations and anions 

 in precipitation and losses of cations 

 and anions in dissolved and particu- 

 late matter exiting the system, to 

 studies of nutrient cycle-hydrologic 

 cycle interactions, weathering rates, 

 soils, litter accumulation and degrada- 

 tion, biomass measurements, produc- 

 tivity, nutrient turnover within the 

 biota, phenology, energy pathways 

 and relationships, and experimental 

 manipulation (deforestation) of an 

 entire watershed ecosystem. Figure 

 IX-9 illustrates the results of one 

 such study. In addition, a biogeo- 

 chemical study of a small lake within 

 the general drainage area of Hubbard 

 Brook is under way. Computer simu- 

 lation and systems-analysis proce- 

 dures are being developed to facilitate 

 understanding of the complex inter- 

 relationship of these ecosystems. 



The results of the study to date 

 have been described in numerous 

 publications. The project has been 

 endorsed by the U.S. National Com- 

 mittee for the International Biological 

 Program (IBP), and the study has 

 been accepted as a part of the U.S. 



Figure IX-9 — ECOLOGICAL EFFECTS OF DEFORESTATION 



TRANSPIRATION 

 REDUCED 100% 



EVAPOTRANSPIRA- 

 TION 0.3X 



COMPLETE CUTTING 



AND HERBICIDE 



REPRESSION OF 



NEW GROWTH 



VELOCITY OF 



STREAM DISCHARGE 



UP, VISCOSITY OF 



STREAMWATER 

 DOWN IN SUMMER 



RELEASE FROM INHIBITION 



BY VEGETATION? 



MICROCLIMATE 



WARMER, SOIL 



MOISTURE HIGHER 



IN SUMMER 



BIOTIC REGULATION 



OF EROSION AND 



TRANSPORTATION 



REDUCED 



OUTPUT OF STREAM- 

 WATER 1.4X 

 MOSTLY IN SUMMER 



ORGANIC MATTER 

 TURNOVER ACCELERATED 



NITRIFICATION 

 INCREASED 2.5X->100X 



ACIDIFICATION OF 



CATION EXCHANGE 



SITES 



CATIONS 



CATIONS 

 ANIONS 



CONCENTRATION OF 



DISSOLVED INORGANIC 



SUBSTANCES IN 



STREAMWATER 4 IX 



OUTPUT OF 



PARTICULATE 



MATTER 



ca. 4.0X 



I 



NET OUTPUT— DISSOLVED 



INORGANIC SUBSTANCES 14.6X 



pH OF STREAMWATER 



5.1 DOWN TO 4.3 



TO DOWNSTREAM ECOSYSTEM 



The diagram summarizes some of the ecological effects of the deforestation of 

 Watershed 2 in the Hubbard Brook Experimental Forest. The rates at which the 

 processes are taking place are based on data obtained during 1966-68, and are 

 expessed in terms of increases above those observed before the watershed was 

 deforested. High nutrient concentrations, coupled with the increased amount of 

 solar radiation, have resulted in significant eutrophication. This study is an example 

 of how a known change in one component of an ecosystem can change the structure 

 and function in another section of the same or related ecosystem in an unexpected 

 way. 



program for the IBP and the Inter- 

 national Hydrological Decade. 



The Value of the Small-Watershed 

 Approach 



The small-watershed approach has 

 already shown its power to draw 

 together aspects of the fields of mete- 

 orology, limnology, geology, soils, 

 hydrology, biology, and ecology into 

 one coherent study on the structure 

 and function of an ecosystem. This 

 type of approach is basic to advance- 

 ment of knowledge of how landscapes 

 really work. In turn, good land-use 

 planning is dependent on knowledge 



of the structure and function of 

 ecological systems. 



Although the hydrologic aspects 

 of many types of watersheds, forested 

 and otherwise, are under study, there 

 are relatively few watersheds where 

 comprehensive biogeochemical stud- 

 ies are under way. This is a serious 

 deficiency and should be remedied. 

 Comparative small-watershed studies, 

 where the watersheds are well de- 

 fined, should be initiated in all major 

 biomes where they are presently not 

 part of IBP planning. Twenty to 

 thirty of these studies scattered 

 throughout the North American con- 

 tinent in various biomes and involv- 



294 



