Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Exploring the tug of war between positive and negative interactions
  among savanna trees: Competition, dispersal, and protection from fire   Savannas are characterized by a discontinuous tree layer superimposed on a
continuous layer of grass. Identifying the mechanisms that facilitate this
tree-grass coexistence has remained a persistent challenge in ecology and is
known as the "savanna problem". In this work, we propose a model that combines
a previous savanna model (Calabrese et al., 2010), which includes competitive
interactions among trees and dispersal, with the Drossel-Schwabl forest fire
model, therefore representing fire in a spatially explicit manner. The model is
used to explore how the pattern of fire-spread, coupled with an explicit,
fire-vulnerable tree life stage, affects tree density and spatial pattern. Tree
density depends strongly on both fire frequency and tree-tree competition
although the fire frequency, which induces indirect interactions between trees
and between trees and grass, appears to be the crucial factor controlling the
tree-extinction transition in which the savanna becomes grassland. Depending on
parameters, adult trees may arrange in different regular or clumped patterns,
the later of two different types (compact or open). Cluster-size distributions
have fat tails but clean power-law behavior is only attained in specific cases.

29
The categories of this paper are: funct-an
28
The categories of this paper are: alg-geom
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The categories of this paper are: bayes-an
20
The categories of this paper are: acc-phys
5
The categories of this paper are: gr-qc
19
The categories of this paper are: eess
15
The categories of this paper are: nucl-ex
0
The categories of this paper are: hep-ph
36
The categories of this paper are: cmp-lg
22
The categories of this paper are: chao-dyn
35
The categories of this paper are: mtrl-th
6
The categories of this paper are: astro-ph
33
The categories of this paper are: plasm-ph
21
The categories of this paper are: adap-org
18
The categories of this paper are: econ
37
The categories of this paper are: supr-con