Factors controlling spatial variation of tree species abundance in a forested landscape

Spatial patterns of tree species in forested landscapes are regulated by a variety of environmental and disturbance factors. Biological factors such as disturbance and competition that operate within a local neighborhood (neighborhood factors) might also influence these patterns. We sought empirical evidence for the role of neighborhood factors in determining spatial patterns of abundance of dominant tree species in the 3160-ha Hubbard Brook Experimental Forest (HBEF), a second growth, northern hardwood-conifer forest in New Hampshire, USA. We measured tree abundance patterns and a suite of environmental and disturbance factors expected to regulate these patterns in 0.05-ha plots distributed throughout the Hubbard Brook Valley. Environmental and disturbance effects were modeled using linear regression with spatially correlated errors described by semivariograms. These models explained 26-62% of the variation in abundance among the seven tree species that comprise 90% of the total basal area in the HBEF Semivariograms described residual spatial autocorrelation of the abundance of each tree species after accounting for environmental and disturbance effects. One species, Betula alleghaniensis, did not exhibit significant residual spatial autocorrelation in its spatial pattern of abundance. The other six species exhibited abundance patterns with highly significant residual spatial autocorrelation, suggesting that factors other than environment and disturbance are needed to adequately explain their spatial patterns, of abundance. The range and normalized sill semivariogram values from the residual spatial autocorrelation of the different species were consistent with a role of seed dispersal distance and root sprouting in regulating patterns of abundance of several. tree species in the HBEF We argue that neighborhood factors significantly influence patterns of tree species in forested landscapes.