North Cascade glaciers. Since 1993, the National Park Service has conducted rigorous studies on four park glaciers: Noisy Creek, Silver, North Klawatti and Sandalee Glaciers. The National Park Service research indicated that these four glaciers experienced rapid decrease in volumes between 1993 and 2011. In 1998, a National Park Service and Portland State University aerial photographic inventory showed a 13 percent loss in park-wide glacial volume since Austin Post's inventory in 1971. The NPS stated that in the last 150 years since the end of the Little Ice Age, a period of several centuries in which the earth experienced a cooling phase, glacial ice volumes in the North Cascades have been reduced by 40 percent. This loss of glacial ice has contributed to decreased melt in the summer. In a paper published in 2016, it was reported that since 1959 the Skagit River watershed has seen a 25 percent reduction in the summertime streamflow. Map Geographical features in the area can be found in this clickable map: Ecology Eight distinctive life zones support thousands of different plant and animal species in the North Cascades National Park ecosystem. With an elevation gain of nearly , the park has one of the largest ranges of biodiversity found in any US national park. Flora The flora in North Cascades National Park is influenced by the great vertical relief, the amount of moisture an area receives, the slope and soil types as well as the fire ecology. This wide array of ecological niches has allowed a great biodiversity to evolve. Few other North American national parks have recorded as many vascular plant species as have been documented in North Cascades National Park. With 1,630 species documented, experts estimate adding non-vascular plants and fungi could more than double the number of known plant species. The park contains an estimated of old-growth forests. As little of the park was previously logged, significant stands of old growth forest can be found in the valleys and lower slopes up to the timberline at . From the lowest valley floors to about , virgin stands of western hemlock, red cedar and Douglas fir are common. These species are heavily dependent on deep soils, and red cedars 1,000 years old and over tall can be found on Big Beaver Creek. These lowest elevation forests can be accessed by trails, such as the Happy Creek Forest Walk off State Route 20,