Ingrid Burke Ash vs Non Ash Nitrogen Moisture May 08 2006 Ash and Non Ash Nitrogen and Moisture Levels in Whitaker s Forest Canopy Gaps Ingrid Burke Abstract Creation of canopy gaps is an innovative forest management technique that provides space and light for new growth while maintaining the ecology and biodiversity of the forest A current study on the canopy gap regeneration of giant sequoia Sequoiadendron giganteum in Whitaker s Forest southern Sierra Nevada Mountains California shows a marked difference in the size and vigor of seedlings growing in ash beds which resulted from burning logging debris compared with those growing in bare mineral soil To investigate this difference I collected soil and foliar samples as well as soil moisture measurements from both ash and non ash areas of four 1 acre gaps The soil and foliage samples were analyzed using extractable nitrate and ammonium tests Soil sample nitrogen levels range from 0 1 ppm to 64 5 ppm foliage samples range from 5 ppm to 650 ppm and soil moisture readings range from 0 044 to 0 36 none of the three shows statistically significant difference between ash and non ash Levels of soil nitrogen don t appear to be related to those of foliar nitrogen and nitrogen levels do not appear to be related to soil moisture Neither ash nor non ash areas in large gaps show the expected high moisture levels near gap center This pilot study outlines the high variability in nitrogen and moisture levels in the system and also illuminates the spatial scale at which the variability occurs Future work can use these baselines to continue the examination of potential influences of ash on conifer regeneration p 1 Ingrid Burke Ash vs Non Ash Nitrogen Moisture May 08 2006 Introduction If current even aged forest management is to be converted into more ecologically beneficial uneven aged management we must thoroughly understand the factors influencing seedling growth within canopy gaps Gagnon et al 2004 Seedlings within gaps can grow in ash beds and bare mineral soil To quantify the differences in growing conditions provided by these two substrates I measured their soil nitrogen and moisture content I also measured the foliar nitrogen content of seedlings grown in ash and soil The influence of ash on regeneration in gaps is an important consideration because it has the potential to enable increased growth yet further study is necessary to determine whether this occurs Regeneration of the giant sequoia Sequoiadendron giganteum within canopy gaps is currently being studied at Whitaker s Forest in the southern Sierra Nevada Twenty canopy gaps were created in 2003 by small group selection harvests Differences between gaps and surrounding forest have been shown to persist for a minimum of two years from gap formation Ritter et al 2005a so these areas can still be expected to have exhibited gap characteristics when the data for this study was collected in 2005 Within each canopy gap logging debris was piled in a north south strip called a windrow and burned Seedlings and seeds were planted in the resulting ash beds and in the adjacent bare mineral soil Seedlings planted in ash have exhibited higher growth rates when compared to those in bare mineral soil but in the context of York s study this difference was less powerful than the effect of gap size on growth R York 2006 manuscript in progress However when considered independently growth differentials between ash and non ash hold interesting implications and I seek to explore these differences in this study Seedling growth is regulated by the availability of three basic variables sunlight moisture and nutrients These three variables are all closely intertwined for example rates of soil nutrient cycling are determined by soil temperature and moisture Prescott 2002 and soil nitrogen levels are determined partially by soil moisture Kennedy and Pitman 2004 It is impossible to gain a clear understanding of the seedling responses at Whitaker s Forest without examining all of these factors Gaps in the forest canopy allow greater amounts of sunlight to reach the ground which may cause interactions with soil moisture Despite the increased evaporation implied in gap scenarios conditions of reduced competition result in higher soil moisture within canopy gaps when p 2 Ingrid Burke Ash vs Non Ash Nitrogen Moisture May 08 2006 compared with surrounding forests of both beech and Douglas fir In fact moisture levels are often at capacity within gaps while being as low as 50 of capacity outside Gray et al 2002 Ritter et al 2005a Ritter et al 2005b Conditions of high water and high sunlight are beneficial to seedling growth but the color and texture of an ash substrate may react in a different way from soil and provide very different growing conditions Nutrient availability is the final essential factor in seedling growth and nitrogen has been found to be the only nutrient that promotes forest growth when administered individually to conifers Nohrstedt 2001 For centuries the availability of nutrients such as nitrogen has been thought to be augmented by the introduction of ash to the soil This can easily be done in managed forests by the on site burning of logging debris The comparison of ash and soil is particularly interesting in my study because the windrow technique of debris burning used has been found to have dramatic and lasting effects on soil development in the southeastern United States Johnston and Crossley 2002 yet its effects on regeneration have not been investigated There is some disagreement regarding the effects that wood ash has on seedling growth One study showed that ash did not affect foliar nutrients growth or biomass production in a willow plantation Park et al 2005 Another study showed an overall increase in biomass after burning in a pine forest but attributed this partially to an increase in light availability Skre et al 1998 A third study found that ash results in minor conifer growth stimulation in nitrogen rich sites while it decreases growth in nitrogen poor sites Nohrstedt 2001 Some canopy gaps even those as small as 0 1 hectare have exhibited increased soil nitrogen availability Prescott 2002 which supports the idea that gaps are excellent places to examine the effects of ash It has been shown that a fire event can exert great influence over vegetation patterns through increased moisture retention by burned conifer forest litter versus unburned litter Whitney 1979 and through variations in
View Full Document
Unlocking...