Watersheds and Trees Fall Together: An Analysis of Intact Forested Watersheds in Southern Patagonia (41–56° S)

Abstract

While intact forests have intrinsic value in terms of conserving biodiversity, they are also important for associated ecosystem services of soil and water conservation, in addition to the biodiversity, function and geomorphology of stream and river ecosystems. In this latter context, the perspective of watershed is more relevant than forest patch, however we are unaware of any landscape assessments of intact forested watersheds (IFWs). We mapped the coverage of forested watersheds with limited intervention for southern Patagonia (Chile, Argentina) using existing forest stand mapping and high resolution stream/watershed delineation (patch size ~ 0.4 km2). Validation and adjusted IFW boundaries was performed using high resolution satellite imagery for three major inland basins representing the north-south range of the study area. For both scales we evaluated size distribution, conservation status, forest type (deciduous vs. evergreen temperate forest) and bio-climatic zones (precipitation range 500 to >6000 mm/year). For the coarse regional analysis potential IFWs covered over 40% of land surface, and included nearly 60% of all forest cover. These figures were significantly reduced following basin scale validation to 6–21% for IFWs and 5–14% of forest contribution to IFW. IFWs identified in the regional analysis were lower elevation (0–100 m) due to abundant coastal drainages, whereas the basin analyses were higher elevation headwaters systems (1000+ m), the largest over 80 km2. Total IFW cover was estimated between 50,000–132,000 km2, the range a reflection of disparate results across these two scales, further highlighting the need for comprehensive revision and field validation. At the same time the difference in areas, defined mostly by minor levels of intervention, indicate the vast potential for management or restoration. Taken together they represent a nationally and globally significant contribution to of intact temperate forests and IFWs. Interactions between forest and stream ecosystems, and their implications for IFW conservation, are discussed in these contexts, based on examples from the region. Finally we used Getis-Ord Gi* statistics to identify hot and cold spots for different attributes, providing an example of a combined index for prioritizing IFW conservation.

Keywords

• intact watershed
• temperate forests
• Patagonia
• headwater streams
• old growth forests
• conservation