Tree seedling survivorship, growth, and allocation in the Cross Timbers ecotone of Oklahoma, USA

Abstract

In order to better understand tree dynamics and maintenance of the ecotone between eastern deciduous forest and tallgrass prairie, I planted seedlings of five different species into a Cross Timbers area in North West Oklahoma for one-year. The seedlings were planted in four different patchtypes under two different herbivore treatments. I found that (1) out of the original 200 seedlings, 58 survived after one-year with lacebark elm (Ulmus parrifolia), osage orange (Maclura pomifera), and eastern redbud (Cercis canadensis) surviving the most and protection from herbivores increasing survivorship by more than an order of magnitude, (2) elm (Ulmus parrifolia) showed the slowest stem growth but protection from herbivory increased stem growth rate by approximately 50%, leaf area ratio was largest for elm (Ulmus parrifolia) but seedlings growing in sumac (Rhus copallina) patches had the smallest values, specific leaf area was the largest for orange (Maclura pomifera) seedlings with tree seedlings growing in grass patches showing greater values than those grown in other patches, and (3) leaf mass ratio was largest for elm (Ulmus parrifolia) with seedlings grown in sumac (Rhus copallina) patches showing the smallest values and rough-leaf dogwood (Cornus drummondii) had the most root biomass relative to shoot biomass compared to all other species. Results suggest tree invasion and establishment across this ecotone is influenced both by species identity and by the variation in resources associated with the distribution and patch dynamics of vegetation from both eastern deciduous forest and tallgrass prairie.

Fire dynamics distinguish grasslands, shrublands and woodlands as alternative attractors in theCentralGreatPlains ofNorthAmerica

“…J. virginiana suppresses grass growth with dense canopies that intercept the majority of sunlight (Hoch, Briggs & Johnson ; McKinley et al . ; Myster ; Limb et al . ; Van Els et al .…”

The role of seed predation in the maintenance of the Cross Timbers ecotone of Oklahoma, USA

“…After germination, those tree seedlings that can escape herbivory have a major advantage. Oak seedlings growing under trees have a low mortality, but high mortality if growing under shrubs and in grass patches, perhaps due to intense below-ground competition for water (Myster 2009b). Taken together then the slow oak invasion, and ecotonal change, that has been observed for decades may be due, in part, to poor oak dispersal and the lack of patches which have high survivorship and growth for both oak seeds and oak seedlings.…”

“…Past studies in the Cross Timbers and other forestgrassland ecotones have focused on the seedling and sapling stage of the tree life cycle and investigated controlling mechanisms such as water availability in the form of rainfall, below-ground competition, burning regime, patch-type, and wind-disturbance (Petranka & McPherson 1979;Hoffmann et al 2004;Myster 2009aMyster , 2009bMyster & Malahy 2010). The seed stage, however, is also a critical part of the regeneration niche (Grubb 1977) in the Cross Timbers and needs investigation (see California ecotone studies by Kennedy 2005;Kennedy & Diaz 2005) for a complete understanding of the mechanisms maintaining this ecotone.…”

“…The asexual habit of these shrubs helps their ramets establish in grass mats and many of the oaks in the Cross Timbers also send up root suckers (Myster, personal observation) to take advantage of this strategy and, perhaps, increase the probability of oak establishment. Once established, oak seedlings grow more under shrubs (as indicated by leaf chlorophyll content) and elm seedlings survive best and grow more under sumac (as indicated by leaf area ratio and leaf mass ratio : Myster 2009a: Myster , 2009b.…”

“…Whereas seed mechanisms (e.g. dispersal, predation, and germination) may not be barriers to tree advancement, seedling mechanisms, and tolerances to, for example, temperature and soil moisture could be key in controlling this ecotone (Myster 2009a(Myster , 2009b) by determining how, or if, individual trees replace the resident grasses (Myster 2007(Myster , 2012a.…”