BIOLOGICAL BENEFITS

Several studies have been completed and others are underway by a variety of researchers aimed at helping us to understand the long-term effects of forest management. These include our own ongoing research on forest composition and production as well as other work looking at a wide variety of forest organisms from the canopy to the forest floor.

The Forest (Tree Species) Composition and Structure Through Time

Our own research on single-tree selection harvests in the Missouri Ozarks has been underway since 1952. At that time we designed a comprehensive forest inventory to provide a representative sampling of the forest as a whole, as well as its various overstory and understory components under an uneven-aged management system using single-tree selection harvests. This continuously updated dataset, now nearly 50 years old, provides one of the most interesting long-term records on the dynamics of growth and development for a forested landscape in the Ozarks.

Our data shows forest-wide increases in volume per acre since 1952. These increases have been while harvests have been ongoing throughout the forest. This indicates that managing a forest in this manner can be successful over long periods of time. In other words, both the number and size of the trees making up the forest will continue to increase.

Much of the earlier research on Ozark forests claimed that uneven-aged management was not easily applied and furthermore that oak seedlings required complete sunlight in order to successfully grow. A University of Missouri study completed in 1996 examined our dataset and found that the diameter distributions on the forest conformed to a scale of 0.6 of an acre. In other words, the application of uneven-aged management across an extensive landscape, under a wide variety of individual markers, and through a relatively long period of time can be very consistent. The best measure of the successful application of uneven-aged management is that recruitment and regeneration of the forest continues through time. Problems with regeneration within a forest would be expressed in the smaller diameters first; in fact basal area measurements for trees in every diameter class below 16 inches in diameter have nearly doubled since 1957.

Other interesting questions which are beginning to be answered are whether the species composition of a forest will change and how does the distribution of various diameters on the forested landscape change under management. Our data collection continuously examines seven species or major groups of species: red oak (collectively black oak, scarlet oak, and northern red oak), shortleaf pine, white oak, hickory, post oak, black gum, and all other species as a separate group. From this we have learned that six of these seven species or species groups have maintained their relative proportion of the forest mix. Even after 45 years of harvesting trees the original mix of forest species has not changed. Furthermore, from the standpoint of structure and character within the forest we are seeing all diameters from 5 inches to 18 inches either increase or maintain their presence. We also measure and monitor tree diameters larger than 18 inches and for the 45-year period these have fluctuated around the initial measurement figure.

Birds

During the early 1990’s a two-year study examined migrant songbird response to managed forest treatments in southern Missouri. Sample sites from Pioneer Forest represented the single-tree selection portion of the study. While there are many different bird species found in Missouri, we have known for some time that Ozark forests provide a unique opportunity for certain species. For example, we learned from this study that hooded warblers and northern parula warblers were more abundant in the single-tree selection cuts than from clearcuts, shelterwoods, or even unharvested mature sites which were studied. Bird species such as the red-eyed vireo, worm-eating warbler, and acadian flycatcher, all species commonly found in mature forest, were also abundant in the Pioneer Forest sample.

Why are these birds more commonly found here? The reasons vary, but in each case the preferences of these birds for specific forest characteristics continues to be found on these forested lands, even after they are cut. Acadian flycatchers prefer large trees, a dense understory, and a closed canopy. Red-eyed vireos prefer a closed canopy. Ovenbirds prefer a closed canopy and short regeneration height. Hooded warblers prefer a high density of smaller trees, relatively low density of large diameter trees, high shrub stem counts, and high canopy closure. Each of these last four variables fairly describes the uneven-aged forest character resulting from single-tree selection harvests.

The conclusions are that these birds in particular are likely selecting a combination of forest characteristics; the most important here were canopy closure and basal area. From a forest management perspective, management is best for migrant songbirds when it maintains a variety of forest characteristics, retains the forest on the land, and prevents its fragmentation or removal.

Salamanders

Salamanders are the most abundant vertebrate animals. Their annual production of biomass exceeds that of birds or small animals. While birds are more mobile, salamanders are not, therefore more directly reflecting the quality of the immediate site. In the late 1990’s a portion of a study investigating salamander response to various forest management practices showed that salamander populations were reduced to very low numbers when mature forests had been intensively harvested. Estimated mean densities per hectare were 1422 for mature forests and less than 15 for clearcuts. Removal of the forest canopy decreases moisture and increases ground temperature. Complete or nearly complete removal of the forest canopy (clearcutting/even-aged management) shortens forest development to a period of 75-120 years and prevents development of the structure associated with older forests (uneven-aged management) such as larger trees, accumulation of down wood, and the development of high density foliage layering.

Insects, Spiders and Other Leaf Litter Arthropods

A study is currently underway comparing arthropod communities from three different forest management treatments: one where all the trees were cut and removed nearly forty years ago, with vast canopy openings; a forest management site on Pioneer Forest where single tree selection harvests preserve continuous canopy coverage; and a third site, also on Pioneer Forest, where no trees have been cut or removed. The study is attempting to determine how different forest management regimes influence forest structure and arthropod community composition at varying levels of spatial scale.

Preliminary results indicate that arthropod species richness and abundance are significantly higher in the selection harvest sites on Pioneer Forest as compared to the clearcut being sampled elsewhere. These results suggest that select harvest may be a management regime more similar to the historical disturbance regime in the region. In addition, spatial variation in abiotic parameters like temperature and humidity are higher in the clearcut site and in the preservation site, as compared to the select logging site.