Post fire Regeneration of Riparian Vegetation in the Duncan Creek Watershed Sara Hanna Abstract Wildfires are an important factor in forested ecosystems as they have the potential to alter the composition and structure of the forest Most of the studies conducted thus far in the Sierra Nevada have focused on how fire affects the mixed conifer forest failing to address what impact the fire has on riparian vegetation The objectives of this study were to determine how wildfires effects on riparian vegetation and regeneration are related to the distribution of vegetation along a gradient up from the water table with particular attention to the sprouting responses of various hardwood species Ceanothus ssp and Quercus ssp showed the greatest regeneration potential followed by Salix ssp Cornus ssp and Alnus ssp By measuring vegetation along various terraces and slopes observations were made as to the relationship between regeneration and proximity to the stream and water table Plants that were closer to the water table had more shoot resprouting than those further away There was no correlation between the fire severity in an area and the percentage of plants that were resprouting However hardwoods growing in areas of higher fire severity showed more reproductive success in the form of shoot sprouting The information obtained from this study can be useful in determining whether or not fire should be excluded from riparian zones Management decisions concerning riparian zones are exceedingly important as they have an impact on stream water quality Introduction California s mixed conifer forests contain heavy fuel loads and an unhealthy forest composition resulting from the first establishment of national parks in the Sierra Nevada in 1890 which encouraged fire exclusion from forested lands Parsons and van Wagtendonk 1996 A policy of fire suppression was due in part to the public opinion that all wildland fires were harmful Biswell 1989 Almost one century later the negative view towards fires shifted as resource management professionals started to understand how fires play an integral role in forest composition Leopold et al 1963 This shift in opinion has resulted in a new era of prescribed burning in national parks and forests to simulate natural fire processes that have been excluded from these areas for years Although research has been conducted on how fires affect mixedconifer forests there have been very few studies on how fires affect riparian vegetation One study conducted by W H Russell 2001 found that a fire s importance as a determining factor on forest composition reduces as it approaches the riparian region L M Ellis 2001 observed that although fire frequency and severity have increased in riparian vegetation in the southwestern United States in the past few years the role fire plays in riparian ecosystems is not clearly understood Forested water catchment areas are extremely important as they are the headwaters for the river systems from which we get our water Therefore understanding how riparian zones function is vital including how they respond to disturbances such as fire Previous studies have shown that aquatic ecosystems are at risk of damage after a large fire event USFS 2002 When riparian forests burn the result is increased solar radiation which elevates stream temperatures Additionally there is an increase in surface erosion and gullies during heavy storm events for the following few years due to the existence of fire induced water repellency DeBano 1981 All of these aforementioned changes resulting from fire have an effect on the quality of the water Despite the several studies based on stream ecosystem responses to fire Rinne 1996 Minshall et al 1997 Gerla et al 1998 Minshall et al 2001 there are very few studies focusing specifically on how fires affect riparian vegetation When studying post fire effects on riparian vegetation it is important to ascertain how vegetative composition changed in response to the fire including which plants had greater mortality after burning and which plants had greater regeneration Different species of plants have different post fire reproductive strategies For example hardwoods sprout after they are burned either from the stem or from the root with reproductive success varying from species to species Gom 1999 Vegetative responses also vary with fire severity and intensity The amount of organic debris present before the fire effects the fire severity indicating that heavy pre fire fuel loads result in fires of higher severity Ellis 2001 Often fires will burn in patches as they approach riparian areas This patchy effect is characterized by areas with high intensity canopy fires less intense surface fires and unburned areas and results from differing vegetative cover slope soil and other factors Minshall et al 1989 It is therefore important to look at the system as a whole including various plant species vegetation density slopes of riparian zones fire severity and location of the species in relation to surface water Study Site This study took place in a section of the Duncan Creek watershed in the Tahoe National Forest Data was collected on the creek and three of its tributaries The study site was located next to French Meadows Reservoir approximately 20 miles northeast of Foresthill CA The average elevation of the creeks studied was 5 300 feet The vegetation type surrounding the study site is mixed conifer forest characterized by several defining species including Abies concolor white fir Calocedrus decurrens incensecedar Pseudotsuga menziesii Douglas fir Pinus jeffreyi Jeffrey pine Pinus lambertiana sugar pine Pinus ponderosa ponderosa pine and Quercus kelloggii black oak while the riparian species bordering the creek and its tributaries was comprised mostly of Alnus incana mountain allder Alnus rhombifolia white alder Arctostaphylos ssp manzanita Ceanothus ssp California lilac Cornus nuttallii mountain dogwood Cornus sericea red osier Populus balsamifera black cottonwood Quercus ssp oaks and Salix ssp willows The Star Fire originated on August 25 2001 and was contained on September 13 2001 This fire burned almost 17 500 acres in the Tahoe and El Dorado National Forests Riparian areas that burned include the Middle Fork American River and its tributaries including Duncan Canyon Creek Within the above mentioned 17 500 acres 4 309 acres are within the Duncan Canyon Inventoried Roadless Area The burned areas contained old growth forest
View Full Document
Unlocking...