Spatial relationships between Forest Canopies and Microclimate and Heat flows in a Patchy Mixed-conifer Forest

_{As a part of multi-discipline forest ecosystem research in a Mediterranean climate in the Sierra Nevada mixed conifer forest, the study is developed to detect the spatial variances of physical variables and forest structure in a heterogeneous mixed-conifer forest ecosystem and determine the microclimatic characteristics of this typical Mediterranean climatic environment. We investigated air temperature (Ta), air relative humidity (h%), surface temperature (Tsf), photosynthesis active radiation (PAR), soil heat flux (G), and wind velocity (v) through 18 automatic microclimate stations from August 1998 to August 1999 at the Teakettle Experimental Forest (TEF), CA. Based on dominant patch types defined by cluster analysis of vegetation and litter depth measurements, mobile microclimate stations were also installed in the 3 patch types: open area (I), canopy cover (II), and open area with ceanothus understory cover on the ground (III). We found that the spatial variation of microclimatic variables significantly exists (p<0.001) but depends on the patch types and canopy coverage, variable features though the greatest variations generally happen in type II. The means of spatial differences of Ta are 0.4°C, 1.7°C, and 1.3°C , respectively, in three patch types, but the largest differences of Tsf (2.3°C) occurs in type III, instead of Type II (1.1°C). The differences of PAR and Tsf exhibited obvious obviously seasonal patterns, but those of Ta, h%, and G are patch-type dependent. The mechanisms behind this pattern were explained by heat-structure interactions, i.e., canopy cover, litter depth, and understory vegetation directly control amount of energy flow through the ecosystem. In contrast, the simultaneous existence of hot-spot and cold-pocket within the patchy forest ecosystem is one of the determining factors causing the formation and dynamics of patch types. The regression relationships among G, PAR, Tsf, and spatial patch types are developed. They regulate the ecological processes in the system. We also conclude that horizontal heat exchange between sink and source patches is the key in understanding energy balance of the heterogeneous nature of the ecosystem.}