Oak Regeneration Across Central and Northern Wisconsin

Abstract

CHAPTER 1- STUMP SPROUT HEIGHT GROWTH SUCCESS RATE OF NORTHERN PIN OAK AND LONG-TERM EFFICACY OF COPPICE HARVEST IN CENTRAL WISCONSIN Abstract: Coppice with 2-3 reserve trees per acre is the Generally Accepted Practice (GAP) for managing oak stands on nutrient poor sandy sites (colloquially called "scrub oak sites") in Wisconsin. The future stocking of the stand is therefore dependent predominantly on stump sprouts with varying levels of contribution from advanced regeneration. Two groups of sites ( 4 cut in 1998 and 4 cut in 2006) were measured to examine the success of the stump sprouts. For the sites harvested in 2006 over 85 percent of stumps had sprouted during the first year after harvest (Mujuri and Demchik 2009). By 2010, 74 percent of the sprouts from stumps that had sprouted had been successful in reaching a height of at least 6 feet ( dete1mined to be beyond the height of heavy deer browsing of the terminal buds). For the sites harvested in 1998, transects were run to measure 25 stump sprouts and an additional 20, 11735th acre regeneration plots were measured to determine the success of seedling regeneration. Ninety percent of regeneration plots sampled had at least one desirable timber species with 85 percent of the plots containing at least one viable oak seedling/sapling and 41 percent of these plots contained an oak at least 10 feet tall. The average sprout height measured across all sites was 24 feet. While there was some variability seen between sites that likely resulted from varying site history, the GAP of coppice with reserve trees does seem to be effective at regenerating scrub oak sites. CHAPTER 2 -THE EFFECT OF RESERVE TREES ON OAK REGENERATION ON SCRUB OAK SITES IN CENTRAL WISCONSIN Anecdotally, higher retention levels after harvest are believed to have a negative impact on oak regeneration accumulation. For this study, harvests with four retention levels of 0%, 15%, 30% and 45% were established to determine the impact of overstory retention on success of oak regeneration after harvest. Previous research has shown that an increase in reserve trees can increase the accumulation of the intermediate shade tolerant oak as well as other intermediate and shade tolerant species while reducing the abundance of more intolerant species such as aspen. Five sites were selected and three replicates of each treatment were established. Four of the sites were harvested in the winter of 2007 and one in the winter of 2008. Due to the time difference and variation, the site harvested in 2008 was eliminated from the statistical analysis. The regeneration levels in all plots met the requirements for adequate stocking based upon DNR set standards. There were no significant differences between retention levels. Tallest seedlings per plot were also analyzed to see if one retention level had taller seedlings more likely to recruit into the overstory, but there were no significant differences. While there were no significant differences between retention levels, there was an increasing trend for height of desirable species other than oak, total arboreal seedlings, and both the number and height of oak seedlings. At this stage of regeneration, it appears that oak can persist under higher retention levels, but fu1iher study will be necessary to determine recruitment into the canopy. CHAPTER 3 - OAK ADVANCEDREGENERATION POTENTIAL ACROSS A SITE QUALITY GRADIENT IN CENTRAL AND NORTHERN WISCONSIN Abstract: The purpose of this study was to determine if habitat type (Kotar and Burger, 2002) can be used as an accurate predictor of oak advanced regeneration accumulation and if so, to classify habitat types into three categories: "intrinsic accumulators", "ambivalent accumulators" and "recalcitrant accumulators" (Johnson et al. 2002). Forest managers across the state were asked which habitat types currently supported at least 40- 50% oak in the overstory. Based upon responses, the 9 most dominant (representing the greatest number and coverage of counties) were selected to be included in the study. Due to the mosaic nature of two sets of these habitat types, they were combined for replication. For each habitat type/category 10 sites were selected including 5 replicates of both high and low density to determine if canopy cover could also be used as a predictor of oak regeneration. The main factors examined at each site were: stand density (basal area), canopy cover, site index, and regeneration. Data analysis was done with a multifactorial ANCOV A with deer browse intensity used as a covariate. Initial sampling and research has shown that oaks regenerate more predictably on lower quality sites where they have a higher competitive advantage and regenerate poorly on high quality sites where they are often outcompeted by faster growing species. Only one habitat type surveyed, AAt, was not fully stocked with oak regeneration. All other habitat types/categories had sufficient oak regeneration (WIDNR 2006a), with some variability between habitat types. According to the guidelines of Steiner et al. (2008), ArDe and AQVb-Gr/ATiFrCi are the only habitat types fully stocked with oak when examining aggregate height, without taking post-harvest stump sproti'ts into consideration. While not significantly different, habitat types in central Wisconsin (Wood, Portage, Waupaca, Juneau, Adams, Waushara, Marquette, and Green Lake counties) did tend to have higher accumulation of oak seedlings, but in general, it appears that most of the habitat types in this study are regeneration accumulators (with the exception of AAt). The lack of successful regeneration of high quality oak sites, at least for the habitat types surveyed, does not appear to be an advance regeneration barrier. There are a number of other possible barriers, as well as the interaction of these barriers.